linked States
Environmental Protection
Agency
. Office Of Water
(WH-547)
EPA832-F-93-013
September 1993
&EPA
Municipal Wastewater
Management Fact Sheets
Storm Water
Best Management Practices
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MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS
STORM WATER BEST MANAGEMENT PRACTICES
EPA-832-F-93-013
Prepared by the Municipal Technology Branch
United States Environmental protection Agency
Office of Water, Washington, B.C.
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INTRODUCTION.
Storm water runoff is part of a natural hydrologic process.
However, human activities, particularly urbanization, can alter
drainage patterns and add pollution to the rain water and snow
melt that runs off the earth's surface and enters our Nation's
rivers, streams, lakes, and coastal waters. A number of recent
studies have shown that storm water runoff is a .major source of
water pollution as indicated by a decline in fish population and
diversity, beach closings or restrictions on swimming and other
water sports, bans on consumption of .fish and shellfish and other
public health concerns. These conditions limit our ability to
enjoy many of the benefits that our Nation's waters provide.
In response to this problem, the States and many municipalities
have been taking the initiative to manage storm water more
effectively. In acknowledgement of these storm water management
concerns, the U.S. Environmental Protection Agency (EPA) has
undertaken a wide variety of activities, including providing
technical assistance to States and municipalities to help them
'improve their storm water management programs.
This document contains fact sheets on storm water best management
practices (BMPs). These fact sheets represent two types of BMPs:
pollution prevention and treatment. Pollution prevention BMPs
include both source controls and administrative practices.
However, many are not stand alone BMPs, but are most effective
when combined with other BMPs in a comprehensive storm water
management plan. These BMPs are suitable for both municipal and
industrial applications and can be used to supplement other EPA
guidance documents such as Storm Water Management for Industrial
Activities; Developing Pollution Prevention Plans and Best
Management Practices (EPA 832-R-92-006) and Storm Water
Management for Construction Activities; Developing Pollution
Prevention Plans and Best Management Practices (EPA 832-R-92-005)
as well as other State or local guidance. .
i - , " •
In order to better serve our customers and identify additional
information needs, a short questionnaire Is included at the end
of this document. Please take a few minutes to tell us if this
document was helpful g.n meeting your needs and what other needs
you have concerning storm water management. Responses can be
mailed to the-Municipal Technology Branch (4204), US EPA, 401 M
Street, SW, Washington, DC, 20460 ,or faxed to (202) 260-0116.
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TABLE OF CONTENTS
Introduction
Fact Sheet—Storm Water Best Management Practice
1. Catch Bask Cleaning
2. Coverings .
3. Dost Control
y
4. Employee Training
5. Flow Diversion
6. Infiltration Drainfields
7. Internal Reporting
8. Materials Inventory .
9. Non-Storm Water Discharges
10. Porous Pavement
11. Preventive Maintenance
12. Record Keeping
13. Spill Prevention . •
14. Stormwater Contaminatkm Assessments
15. Vegetative Covers
16. Vegetative Swales
17. 'Visual Inspections
Customer Questionnaire
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PREFACE
This document is part of a series of municipal wastewater
management fact sheets. These fact sheets are intended to serve
a wide audience including: the consulting engineer who is looking
for basic technical information on technologies; the municipal
engineer who must understand these technologies well, enough tp
evaluate the assets and limitations; the municipal official who
must sell the technologies as part of a comprehensive pollution
prevention program; the state regulator who must approve the
technologies used to meet permit requirements;'and ultimately the
citizen who must understand the importance of preventing
pollution of the Nation's waters.
The material presented is guidance for general information only.
This info'rmation should not be used without first obtaining .
competent advice with respect to its suitability to any general
or specific application. References made in this document to any
specific method, product or process does not constitute or imply
an endorsement, recommendation or warranty by the' U.S.
Environmental Protection Agency.
Municipal Wastewater Management .Fact Sheets are divided into
several sets: Wet Weather Flow Management Practices; Innovative
and Alternative Technologies; Bipsolids Technologies and
Practices; Wet Weather Technologies; Water Conservation, etc.
Each set is published separately starting with Storm Water Best
Management Practices, September, 1993. Updates to this .set of
fact sheets and development of additional sets is dependent upon
continued resources being available.
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STORM WATER BMP:
CATCH BASIN CUNNING
Office of Wastewater Enforcement & Cemptance9
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
Catch basins are chambers or sumps, usually built at the curb line, which allow surface water
runoff to enter the storm water conveyance system. Many catch basins have a low area below
the invert of the outlet pipe intended to retain sediment. By trapping coarse sediment, the catch
basin prevents solids from clogging die storm sewer and being washed into receiving waters.
Catch basins must be cleaned out periodically to maintain their sediment trapping ability. The
removal of sediment, decaying debris, and highly polluted water from catch basins has aesthetic
and water quality benefits, including reducing foul odors, reducing suspended solids, and
reducing the load of oxygen-demanding substances that reach surface water.
CURRENT STATUS . ;
Catch basin cleaning is an easily implemented but often overlooked Best Management Practice.
Frequently, the cleaning procedures deal with removal of debris from grate openings but do not
extend down into the catch basin itself. . . •
APPLICATIONS ,
Catch basin cleaning is applicable to any facility that has an on-site storm sewer system which
includes catch basins and manholes. • ..
LIMITATIONS , ,
Limitations associated with cleaning catch basins include:
Catch basin debris usually contains appreciable amounts of water and offensive organic
material which must be properly disposed of.
Catch basins may be difficult to clean in areas with poor accessibility and in areas with -
traffic congestion and parking problems.
Cleaning is difficult during the winter when snow and ice are present.
PERFORMANCE
It is not possible, based on current data, to quantify the water quality benefits to receiving
-waters of catch basin cleaning. The rate at which catch basins fill with debris, as well as the
total amount of material which can be removed by different frequencies of cleaning, are highly
variable and cannot be readily predicted. Past studies have estimated that typical catch basins
retain up to 57 percent of coarse solids and 17 percent of equivalent biological oxygen demand
(BOD). •' . . ' ' ' . • -f
MAINTENANCE " . '
A catch basin should be cleaned if the depth of deposits are equal to or greater than one-third
the depth from the basin bottom to the invert of the lowest pipe or opening into' or out of the
basin. Catch basins should be, at a minimum, inspected annually. If a catch basin is found
during the annual inspection to significantly exceed the one-third depth standard, it should be
inspected and cleaned on a more frequent basis. If woody debris or trash is likely to accumulate
in a catch basin,'it should, at a minimum, be inspected and cleaned, if necessary, on a monthly
basis. ' . '...--
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In addition, data collected as part of a Nationwide Urban Runoff Program CNURP) project .in
Castro Valley Creek, California indicated that a typical catch basin, which were cleaned once per
year or once every other year contained approximately 60 pounds of material each.
Catch basins can be cleaned either manually or by specially designed equipment. These include.
bucket loaders and vacuum pumps. Material removed from catch basins is usually disposed of in
landfills.
COSTS
Catch basin cleaning costs will vary depending upon the method used, required cleaning
frequency, amount of debris removed, and debris disposal costs. Cleaning costs for catch basins
were estimated in three NURP program studies (Midwest Research Institute, 1982). These
estimates are summarized in Table 1 below. , .
TABLE 1. CLEANING COST PER CATCH BASIN .
LOCATION
METHOD
COST
Castro Valley, CA.-
Sall Lake County, UT,-
Winston-Salem, NC~~
SOURCE: Rcftnin U
. Vacuum attached to street sweeper-— $7.70
-Vacuum attached to street sweeper- $10.30
—Vacuum attached to street sweeper- ~—$6.30
In communities equipped with vacuum street sweepers, a cleaning cost of $8 per basinCleaned
is recommended for budgetary purposes . (Southeastern Wisconsin, Regional Planning
Commission, 1991). Cleaning catch basins manually costs approximately ™»J™*£
cleaning the basins with a vacuum attached to a sweeper. Therefore a cost estjnute .of$16^per
catch basin cleaned may be used for manual cleaning. It should be noted that costs vary
depending on local market conditions.
ENVIRONMENTAL IMPACTS
Sediment and debris removed from catch basins must be disposed of in a proper manner to
avoid negative environmental impacts.
REFERENCES
1. Midwest Research Institute, ^nllerrion of Economic Data from< Nationwide Urban Runoff
Program Proiects-Final Report. Report to U.S. Environmental Protection Agency, March,
1982. ' ' ' ,
2. Minnesota Pollution Control Agency, Prorectine Water Quality in Urban Areas. 1989.
3. Southeastern Wisconsin Regional Planning Commission, Cost of TTfhan Nonpoint Source
Water Pollution Control Measures. Technical Report No. 31, June, 1991.
4. U.S. EPA, Results of the Nationwide Urban Runoff Program. December, 1983.
5. U.S. EPA, Catch Basin Technology Overview and Assessment. May, 1977.
6- Washington State Department of Ecology, Srnrm Water Management Manual for Puget
Sound. February, 1992.
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IMTB
STORM WATER BMP:
COVERINGS
Offta of Wastewaw Erforoeiner
MUNICIPAL TECHNOLOGY
DESCRIPTION . ,
A simple yet effective Best Management Practice (BMP) is covering. Covering is the partial or total
enclosure of raw materials, byproducts, finished products, containers, equipment, process operations, and
material storage areas which, when exposed to rain and/or runoff, could contaminate stormwater.
Tarpaulins, plastic sheeting, roofs, buildings, and other enclosures are examples of .temporary or
permanent covering that are effective in preventing stormwater contamination; The most prominent
advantage of covering is that it is inexpensive in comparison to other BMPs.
CURRENT STATUS
A review of numerous NPDES group applications indicates that covering is a commonly implemented
BMP. As more facilities identify potential sources of stormwater contamination, the use of coverings will
increase significantly due to its effectiveness from a performance arid cost perspective.
APPLICATIONS'
Covering is appropriate for loading/unloading areas, raw material, byproduct and final product outdoor
storage areas, fueling and vehicle maintenance areas, and other high risk areas.
LIMITATIONS
Limitations associated with covering as a BMP include:
Temporary methods such as plastic sheeting can become torn or ripped, .
1 exposing the contaminant to precipitation and/or stormwater runoff.
Costs may prohibit the building of complete enclosures.
May pose health or safety problems for enclosures built over certain
materials or activities.
Requires frequent inspection.
A structure with only a roof may not keep out all precipitation.
PERFORMANCE
It is difficult, based on data currently available, to quantify the mitigation of runoff contamination when
covering is used. However, significant runoff water quality benefits are expected by simply reducing the
contact between potential contaminants and precipitation or stormwater runoff. One source has
estimated that 80 percent of the environmental damage from de-icing chemicals is caused by inadequate
storage facilities. ,
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DESIGN CRITERIA ' , .
Evaluate the integrity and durability of the covering, as well as its compatibility with the material or'
SSrbSi^Sd. • When desiring an enclosure, one should consider materials access handling
ShwX? Materials that pose environmental and/or safety dangers because they. are radioactive,
Sc flammaWe, explosive, or reactive require special ventilation and temperature considerations.
Covering alone may, not protect exposed materials from stormwater contact. Placing material on an
de3imp^n?able surface or building curbing around the outside of the materials may be required to
prevent contact with stormwater runoff from adjacent areas.
Practicing proper materials management within an enclosure or underneath a covered area^is essential.
pS«Sle floor drainage within an enclosure should be properly designed and connected to a sanitary
leweTSe' local pu?Sdy owned treatment works should be consulted to determine if there are any
P^Satrient requirements, restrictions, or compatibility problems pnor to discharge.
*
MAINTENANCE . ' .
Maintenance involves frequent inspection of the covering for rips, holes, and general wear. Inspecting
coverings should be part of an overall preventive maintenance program.
COSTS.
for the longest period.
ENVIRONMENTAL IMPACTS • .
The impact from a covered area depends on the degree of complexity in the covering design. A simple
Sasti^shee^can possibly have a stormwater diversion, and allow for disposal of unconaminated
then need to be connected to some suitable containment area for later disposal. . ; .
REFERENCES ' • • ,
1. Minnesota Pollution Control Agency, Prorating the Water Quality in Urban Areas, 1989.
2 US T?PA, smrmwater Management for Industrial Activities; Developing Pollution Prevention
Plans and Best Management Practices. Pre-print, July 1992.
3. Washington State Department of Ecology, Srormwater Manager Manual for Puget Sound,
February 1992.
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JMTB
STORM WATER BMP;
DUST CONTROL
Office of Wagewater BifmtucX t. (
MUNICIPAL TECHNOLOOr BRANCH
.DESCRIPTION
Dust controls are methods that prevent pollutants from entering stormwater discharges by reducing the
surface and air transport of dust caused by industrial or construction activities. .Control measures can
prevent dust from spreading into areas of a facility where runoff may eventually transport the material to
a storm sewer collection system or directly to a receiving waterbody.
Dust control for industrial activities normally involves mechanical systems designed to reduce dust
emissions from in-plant, processing activities, and/or materials handling. These may include hoods,
cyclone collectors, bag-type collectors, filters, negative pressure systems, or mechanical sweepers.
Dust control measures for construction activities include windbreaks, minimization of soil, spray^on
adhesives, tillage, chemical treatment, and water spraying.
COMMON MODIFICATIONS
There are a number of temporary alternatives for dust control. However, another consideration is to
eliminate the need for temporary dust control completely by permanent modification of the site. This
could include such measures as covering exposed areas with vegetation, stone, or concrete. .
APPLICATIONS , ,
•
Dust control measures may be applied to any site where dust generation can cause damage to. the site or
adjacent properties. However, application of dust controls is especially critical in arid areas where
reduced rainfall levels expose soil, particles for transport by air and runoff into water bodies. Dust
control measures should also be applied to, any industrial activity Where dust poses a threat of
contamination to water bodies. . ' .
LIMITATIONS . ,
Primary limitations of dust control include :
Some temporary dust controls must be reapplied or replenished on a regular basis.
Some controls are expensive (e.g., chemical treatment) and may be ineffective under
certain conditions. .
Some controls may cause an increase in the amount of mud being tracked off-site.
Typical windbreaks are not as effective as chemical treatment or mulching and
seeding,, and may require land space that might not be,available at all locations.
Industrial dust control is typically labor and equipment intensive and may not be
effective for all sources of pollution (e.g. street sweepers)..
More elaborate industrial dust control systems require'trained personnel to operate
them, an require-the implementation of alpreventive maintenance and repair program
to ensure operational readiness^ ' . ' •• . .
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PERFORMANCE
The decision on which dust control measures to implement must take into consideration .the
performance objectives required for a particular site. Some examples, of performance objectives include:
Prevent wind and water-based erosion of disturbed areas
A reduction of employee respiratory problems.
Rapid implementation at low cost and effort.
Little or no impact on the environment.
Permanent control of the dust problem. - .
Based on the objectives simply sweeping the impervious areas for larger particles on a routine basis may
provide an efficient and reliable method of dust control that can be quickly implemented. Other controls
might include vegetative windbreaks which would provide a much more permanent and environmentally
safe alternative to chemical use. •
DESIGN CRITERIA ' •
The main goals of the dust.control project design is to limit dust generation and reduce the amount .of
soil or dust participate exposed. However this must also take into consideration the performance
objectives established for the particular project. Additionally, some project sites may require solutions to
both industrial and dust control problems. Realistically it may not be practical or possible to develop a
design that meets all of the project goals and objectives at one time. Therefore it may be more
appropriate to develop a phased design approach that' utilizes a combination of temporary, permanent, or
mechanical measures for dust control. •
TEMPORARY MEASURERS
Vegetative Coverings: Temporary seeding and mulching may be applied to
cover bare soil and prevent wind erosion.
Adhesives: Use spray-on adhesives according to Table 1 below. It is
recommended using these adhesives only if other methods cannot be used
as many of them are difficult to work with and form fairly impenetrable
surfaces.
Wetting: This is generally done as an emergency treatment. The site is
sprinkled with water until the surface is wet and repeated as necessary. If
this method is to be employed, it is recommended that a temporary gravel
rock entrance be created to prevent carry-out of mud onto local streets.
Tillage: This practice roughens the soil and,brings clods to the surface. It is
an emergency measure that should be used before wind erosion starts.
Plowing should begin on the windward side of the site using chisel-type
plows spaced about 12 inches apart, spring-tooth harrows, or similar plows.
Barriers: Solid board fences, snow fences, burlap fences, crate walls,
bales of hay, and similar material can be used to control air currents and
soil blowing. Barriers placed at right angles to prevailing currents, at
intervals of about 15 times the barrier height are effective in controlling
wind erosion.
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Calcium Chloride: This material, is applied'at a'rate that will keep the surface.
moist. Pretreatment may be necessary due to varying site and climatic conditions.
TABLE l; DESIGN OF ADHESIVE MEASURERS
Type of Emulsion
Anionic Asphalt
Latex
Resin and Water
SOURCE: Sffamet L
Water Dilution
7 to 1.
12.5 to 1
4 to 1
Nozzle Type
Coarse
Fine
Fine
Application Rate
(gallons per acre)
1,200
235
300
PERMANENT MEASURERS
Permanent Vegetation: Seeding and sodding should.be done to
permanently stabilize exposed areas against wind erosion. It is
recommended that existing trees and large shrubs remain in place
to the greatest extent possible during site grading processes.
Stone: The purpose of this method is to place coarse gravel or crushed
stone over highly erodible soils. ; .
Topsoiling: This method is recommended when permanent vegetation
cannot be established on a site. Topsoiling is a process in which less
erosive soil material is placed on top of highly erodible soils.
Cyclone Collectors. Cyclone collectors separate dry dust and paniculate
pollutants in the air by centrifugal force;
Bag Collectors/Fabric Filters. Bag collectors or fabric filters remove dust
by filtration. Storage of collected dust should be carefully considered so
that it does not become a source of fugitive dust. . ,
Negative Pressure Systems. These-systems minimize the release of dust
from an operation by maintaining a small negative pressure or suction to
confine the dust to a particular operation.
Water Spraying. This temporary mechanical method confines and settles
the dust from the air by dust and water particle adhesion. Water is
sprayed through nozzles over the problem area.
Street Sweepers. Two kinds of street sweepers are common in mechanical
dust collection systems. The brush system has proven to be,an efficient
method at an industrial facility generating dust on a daily basis. It has
proven to be extremely dependable and picks up the majority of the dust.
Vacuum sweepers are presumed to be more efficient because .the
pollutants typically associated with contaminating stormwater are the
smaller particles which may be left behind by a brush street sweeper. .
-However, no performance data are as yet available to verify that
vacuum sweepers are more efficient than brush sweepers.
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MAINTENANCE ..
Typically all dust control measures require periodic and diligent maintenance. For example, mechanical
equipment should be operated according to the manufacturers recommendations and inspected regularly
as part of an industrial site's preventive maintenance program. Temporary dust control measures, such
as chemical spraying, watering, etc. require periodic renewal. Permanent solutions such as vegetation,
wind barriers, impervious services also require upkeep and maintenance in order to remain effective.
COSTS , .
The costs associated with dust control measures are generally lower for vegetative and barrier methods,
and increases significantly for chemical and mechanical treatments. For example, an industrial facility
purchased a mechanical brush sweeper for approximately $35,000. .. .
ENVIRONMENTAL IMPACTS .
there are several negative environment impacts which are related to the dust control BMPs; These
include :
•If over-application of a chemical treatment to control dust occurs, excess
chemicals could be exposed to both wind and rain erosion with potential, for
both surface and groundwater contamination.
Oil should never be used to control dust because of the high potential for
polluting stormwater discharges.
When using mechanical measures such as street sweepers, disposal is a major
problem and could involve parameter testing of dust particulate. RCRA
regulations may be applicable to this situation.
REFERENCES . '
1. r,\ry nf P;i5arij Minnesota, Erosion Control Manual. 1984 -
2. Hennepin County, Minnesota, Erosion and Sediment Control Manual, 1989.
3. Minncrotn Board of ™r— —* «»* *~™™*- Minnesota Construction Site Erosion and Sediment
Control Planning Handbook. November 1987.
4. TT.fi. F.PA. NPDES Best Management Practices Guidance Document. December 1979.
5. TT g EPA, Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. September 1992. ' •
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MTB
STORM WATER BMP:
EMPLOYEE TRAINING
Offto of .Wasawator
MUNICIPAL TECHNOLOQr
DESCRIPTION
In-house training programs are designed and implemented to teach employees about stormwater
management, potential sources of contaminants, and. Best Management Practices (BMPs). Employee
training programs should instill all personnel with a thorough understanding of their Stormwater
Pollution Prevention Plan (SWPPP). This includes identification of BMP's, processes and materials they
are working with, safety hazards, practices for preventing discharges, and procedures for responding
quickly and properly to toxic and hazardous material incidents. .
CURRENT STATUS
Typically, most industrial facilities have an employee training program: Usually these address such
areas as health and safety training, or fire protection. The effort required to modify these programs to
include discussion of stormwater management and BMP implementations should be reasonable.
APPLICATIONS
Employee training program implementation can be achieved through posters and bulletin boards
designed to raise awareness of stormwater management, potential contaminant sources, and prevention
of surface water runoff contamination. Field training programs where employees are shown areas of
potential stormwater contamination and associated pollutants, followed by a discussion of site-specific
BMPs by trained personnel, would also be beneficial for implementing the program.
LIMITATIONS . -..''.
Limitations of .an employee training program include:
Lack of employee motivation
Lack of incentive to become involved in BMP implementation
Lack of commitment from senior management
PERFORMANCE
' ' '" s^
Quantitative performance will vary between facilities because. performance is dependent on employee
participation and commitment from senior management to reduce point and nonpoint sources of
pollution. Employee training programs that teach identification of. potential sources of contaminants, are
highly recommended for implementation at all facilities. Support of these programs should given the
highest priority, by senior management.
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DESIGN CRITERIA .
Specific design criteria for implementing an employee training program include:
Meetings should be held at intervals frequent enough to ensure adequate understanding
of SWPPP goals and objectives.
A strong commitment by, and periodic input from, senior management
Transmission of knowledge from past spill causes and solutions to prevent future spills.
Making employees aware of internal reporting procedures relative to BMP monitoring and
spill reporting procedures.
Operating manuals and standard procedures;
Implementation of spill drills to minimize potential contamination of stormwater runoff
from toxic pollutants.
MAINTENANCE .
An employee training program should be an 6n-going yearly process, There should be at a minimum,
SnS meeting to discuss SWPPPs.. These meetings could be held in conjunction with other traimng
programs. Figure 1 below illustrates a sample employee training tracking worksheet.
EMPLOYEE TRAINING
WorkshMt
Comptoud by:
Tltta: •-
Date
Tralnlnf T«otc«
Spa Piivwttion end RMCXXIM
Good HouukMping
Uiwul Man«>*< Trak^nf
to (*.g.. I
eouna)
Sdwdute «0f Training
'
Arand««
FIGURE 1: SAMPLE WORKSHEET IFOR TRACKING EMPLOYEE TRAINING
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COSTS ,
• • • ' • ' '.'.'•
Costs for implementing an employee training program are highly variable. It is anticipated that most
stormwater training..program costs will.be directly related to labor and associated overhead costs.
however, the example shown in Table 1 below can be used to estimate what the annual costs might be
for an in-house training program at your facility. Figure 2 can be used as a worksheet to calculate the
estimated cost for an employee training programs •..
TABLE!:: EXAMPLE OF ANNUAL EMPLOYEE TRAINING COSTS
Estimated
Yearly
Avg. , Hours '' fist
Hourly Overhead* onSW Annual
Tide Quantity Rate ($) Multiplier Training Cost($)
Stormwater Engineer 1 x 15 x 2.0 x 20
Plant Management 5 ,x 20 x 2.0 x 10
Plant Employees 100 x 10 x 2.0 x 5
TOTAL ESTIMATED ANNUAL COST
Note: Defined as a multiplier (typically ranging between 1 and 3) that
those costs associated with, payroll expenses, building expenses, etc.
SOURCE: EPA
600
= 2,000
= 10.000
$12,600
takes into account.
Estimated
Yearly
Avg. Hours
Hourly Overhead onSW
Tide Quantity Rate ($) Multiplier Training
. x '- x x .„ =
X X . X =
• ' x x • x . , ='
X X X
' TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOURCE: RefaatccZ "
Est.
Annual
Cost ($)
(A5
(B)
• CO
(D)
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REFERENCES
1. U.S. EPA, NPDES BMP Guidance Document. December, 1979.
2. TT.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September, 1992. .
, US EPA. «lM *M SW. Wuto^-v DC W60.
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IMTB
STORM WATER BMP:
FLOW DIVERSION
Ctfce.ci Wastewattr EWorcement & (
MUNICIPAL TECHNOLOGY
DESCRIPTION , ;...-;
Structures which collect and divert runoff (such as gutters, drains, sewers, dikes, berms, swales, and
graded pavement), are used in two ways to prevent the contamination of storm water and receiving
water bodies. First, flow diversion structures may be used to channel storm water,away from industrial
areas so that storm water does not mix with on site pollutants. Second, they may also be used to carry
contaminated runoff directly to a treatment facility. •
Storm water conveyance systems can be constructed from many different materials,'-including concrete,
clay tiles, asphalt, plastics, inetals, rip-rap, and compacted soils covered with vegetation. The type of
material used depends upon the design criteria used for conveyance of storm water runoff. These
conveyances can be temporary or permanent.
Some advantages of storm water conveyance systems used for flow diversion purposes are:
Direct storm water flows around industrial sites.
. . Prevent temporary flooding of industrial site. . .
Require low maintenance. •
Provide erosion-resistant conveyance of storm water runoff.
Can typically be installed at any time. •
Provide long-term control of storm water flows. .
COMMON MODIFICATIONS .
Flow diversion structures can be modified by incorporating them with other pollution control best
management practices. For example, diverted flow can be fed into an infiltration drain field system,
diverted to an infiltration basin, diverted to a constructed wetland treatment facility, qr diverted to an
onsite 'treatment facility for discharge under the NPDES program. Another common modification is to
construct a temporary flow diversion to determine its effectiveness. If the diversion structure is proven
effective, it could then be converted to a permanent structure. .
APPLICATIONS
Storm water diversions work well at most industrial sites. Storm water can be directed away from
industrial areas by collecting it in a channel or drain-system., Diversions can be used to collect storm
water "from the site and direct it down slope where it can be kept separate ,from runoff that has not been
in contact with those areas. .When potentially contaminated storm water is collected in a conveyance
system, it can be directed to a treatment facility. , •
A good example of the .utilization of a diversion structure is The Isle La Plume Wastewater Treatment
Plant in La Crpsse, WI The -area immediately surrounding, the facility has been regraded so that storm
water runoff can be directed into the process tanks where it is treated right along with other waste"water..
Figure 1 below illustrates this storm water runoff control method.
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PERFORMANCE •
Properly designed storm water diversion systems are very effective in preventing storm water from being
contaminated or in routing contaminated flows to' a: proper treatment facility. For example, at the
Denver Stapleton International Airport, flow diversion techniques intercept 99 percent of the glycol used
and prevent its introduction to Sand Creek, the local-receiving waterbody. At the La Crosse WI
Waste-water Treatment Plant, it is estimated that approximately one-third of the storm water runoff from
the facility is diverted into their treatment process.
DESIGN CRITERIA .
Planning for flow diversion structures should consider the typical volume and rate of storm water runoff
present Also, the patterns of storm water drainage should be considered so that the channels may be
located to efficiency collect and divert the flow. When deciding on .the type of material for the
conveyance structure, consider the resistance of the material to erosion, its durability and compatibility
with any pollutants it may carry. • .
Diversion systems are most easily installed during facility construction. Existing grades should be used
to limit CO-S. Positive grades should be provided to allow for contmued movement rf*?™**"**
the conveyance system. (Note: care must be exercised to limit velocities which could potentially
increase erosion.) A typical diversion swale is shown in Figure 2 Below.
Dyke
Dyke Top Width
Channel
Existing Grade
aocmcti
FIGURE 2: TYPICAL DIVERSION SWALE DETAILS
MAINTENANCE
A maintenance program should be established to ensure proper funcnaaing of the system Storm water
diversion systems should be inspected to remove debris within 24 hours after iL significant ramfall event
sSeav^storms may clog or damage them. Flow diversion structure, should also be inspected on an
annual basis to ensure that.they meet their hydraulic design requirements for proper performance.
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.^. Secondary Clarifier wall
Secondary Clarifier Wall
FIGURE 1: STORM WATER RUNOFF CONTROL MEASURERS
At the Denver Stapleton International Airport, the terminal area, aprons, and support facility areas (O.5
square miles), where activities resulting in storm water contamination, are concentrated, are served by
four individual large diameter storm .sewers which collect storm water, snow melt, fuel spills, de-icing
agents, and wash down flows. These storm sewers have hydraulic diversion structures in place which,
convey storm water flows to a 9 mgd detention basin. The basin contents are pumped to a sanitary
sewer interceptor where it is then transferred to a local treatment facility. •
Another concept being adapted into the new regional airport in Denver is based on centralized de-icing
areas for use by all airlines. All de-icing area flows will be diverted to an on-site glycol recovery system
or diverted to detention basins for discharge to the local treatment facility.
LIMITATIONS . '
Storm water flow diversion structure limitations include:
Once flows are concentrated, they must be routed through stabilized structures, or
treatment facilities in order to minimize erosion prior to discharging to receiving waters.
. May increase flow rates. ,
May be impractical if there are space limitations.
. . May not be economical especially for small facilities or after a site has been constructed.
', ' May require maintenance after heavy rains.
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COSTS . . ' . .
Costs vary depending on the type of flow diversion structure used. For example, if vegetated swales- are
to be used for flow diversions, the Southeastern Wisconsin Regional Panning Commission (SEWRPC)
reported that, in 1991, costs may vary between $8.50 to $50 per lineal foot, depending upon swale depth
in feet and bottom width. Capital costs for the Stapleton International Airport flow diversion system,
including basins, diversion structures in each of the four main .storm sewers, ..and additional flow
diversion modifications made by airport staff were $6 million in 1988.. Clearly the cost will be
determined by the scope of the project and design requirements. •
*
ENVIRONMENTAL IMPACTS '
Environmental impacts include: •
Erosion problems due to concentrated flows. .
Potential groundwater contamination if conveyance channels have high infiltration
capacities. -
Undersized water treatment facilities may result in discharges that have not been
adequately treated. •
REFERENCES ' ' ; : . ' .
1. James M. Montgomery. Consulting Engineers, Inc., Site Visit Data, September 1992.
2. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas, 1989.
3. Southeastern Wisconsin Regional Planning Commission, Costs of Urban Nonpoint Source
Water Pollution Control Measures, technical Report No. 31, June 1991.
4. U.S. EPA, NPDES BMP Guidance Document. June 1981.
5. TT.5S. EPA. Storm water Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September, 1992. , . •
6. Wirhingt-m gnr-
February 1992.
Storm water Management Manual for Puget Sound.
n* BHPfta jfetr ~~
Uauapal Tidndcv Smd, (4W). VS EPA. 401 MSa^.SW.Wahmfai, DC,, 20460.
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iMTB
STORM WATER BMP:
INFILTRATION DRAINFEELDS
Offin of Watfcwater Enforcement 6 < .
MUNICIPAL TECHNOLOGY •RANCH
DESCRIPTION
Infiltration drainfield structures are constructed to aid in stormwater runoff collection and are designed
to allow stormwater to infiltrate into the subsoils. Runoff is diverted into a storm sewer system which
passes through a pretreatment structure such as an oil and grit separator. • The oil and grit chamber
effectively removes coarse sediment, oils, and grease. Stormwater runoff continues through a manifold
system into the infiltration drainfield. The manifold system consists of perforated-pipe which distributes
the runoff evenly throughout the infiltration drainfield. The runoff then percolates through the
aggregate sand filter, the filter fabric arid into the subsoils: A schematic of a typical system is illustrated
in Figure 1 below. .
Perforated Pipe Manifold
Observation Well
Top Soil
Washed Stone Reservoir
6",-12" Sand Filter
SOURCE: Reference I.
FIGURE 1: TYPICAL INFILTRATION DRAINFIELD SCHEMATIC
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COMMON MODIFICATIONS . • . . . '
Common design modifications include the installation of porous pavement surrounded by a grass filter
strip over the infiltration drairifield or insertion of an emergency overflow -pipe in the oil and grit
pretreatment chamber. The overflow pipe allows, runoff volumes exceeding design capacities to
discharge directly to a trunk storm sewer system. Infiltration draihfields are very similar to infiltration
trenches and basins. .
CURRENT STATUS .
Currently there is litde information on infiltration drainfields. However, in general the same principals •
that apply to infiltration basins and infiltration trenches will apply to design of infiltration drainfields.
The Environmental Protection Agency is currently evaluating the following issues related to the design
and operation of infiltration drainfields: -
Is the oil and grit separator the most effective pretreatment system to protect infiltration
capacity? .
What is the pollutant removal capacity of infiltration drainfields with various pretreatment
systems? .
Is the performance of infiltration drainfields better than infiltration basins and trenches
during subfreezing weather and snow melt runoff conditions?
What level of maintenance is required to ensure proper performance?
APPLICATIONS '
Infiltration drainfields are most applicable on sites with a relatively small drainage area (less than 15
'acres) They can be used to control runoff from parking lots, rooftops, impervious storage areas, or
other land uses. Infiltration drainfields should not be used in locations that receive a large sedunent
load that could clog a pretreatment system, which in turn, would plug the infiltration dramfield and
reduce its effectiveness. , . . .
Soils should have field-verified permeability rates of greater than 0.5 inches per hour and there should
be a 4-foot minimum clearance between the bottom of the system and bedrock or the water table.
LIMITATIONS
The use of infiltration drainfields may be restricted in'regions with colder climates, arid regions,' regions
with high wind erosion rates (increased windblown sediment loads), and areas where sole source
potable aquifers could be contaminated. Some specific limitations of infiltration dramfields include:
High maintenance when sediment loads to the drainfield are heavy.
High costs of excavation, fill material, engineering design, and
pretreatment systems. , . .
Short life span if not well maintained.
Not suitable for use in regions with clay or silty soils.
Not suitable for use in regions where groundwater is used locally for human consumption.
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Systems require sufficient time between storm events to allow the soil to dry out, or
anaerobic conditions may develop in underlying soils which could clog the soil and
reduce the capacity and performance of the system. .
PERFORMANCE
The effectiveness of infiltration drainfields depends upon their design. When-runoff enters the
drainfield, many of the pollutants are prevented from entering surface water. However, any water that
bypasses the pretreatment system and drainfield will not be treated. Pollutant removal mechanisms
include absorption, straining, microbial decomposition in the soil below the drainfield, and trapping of
sediment, grit, and oil in the pretreatment chamber. '
Currently there is little monitoring data on the performance of infiltration drainfields. However, some
monitoring data is available on porous pavements which incorporate many similar design criteria as
infiltration drainfields. An estimate of porous pavement pollutant removal efficiencies range between 82'
and 95 percent for sediment, 65 percent for total phosphorus, and .80 to 85 percent for total nitrogen.
Some key factors that increase performance and pollutant removal efficiencies include:
Good housekeeping practices in the tributary drainage area. .
Sufficient drying time (24 hours) between storm events.
Highly permeable soils and subsoils. - -
Pretreatment "system incorporated.
, . Sufficient organic matter in subsoils.
. . ' Proper maintenance. •
Use of a sand layer on top of a filter fabric at the bottom of the drainfield.
DESIGN CRITERIA
Infiltration drainfields, along.with most other infiltration BMPs (infiltration basins, trenches, etc.) have
demonstrated relatively short life spans in the past. Failures have generally been attributed to poor
design, poor construction techniques, subsoils with low permeability and lack of adequate preventive
maintenance. .Some design factors which can significantly increase the performance and. reduce the risk
of failure of infiltration drainfields and other infiltration processes '-are shown in Table 1 below.
MAINTENANCE
•
Routine maintenance of infiltration drainfields is extremely important. The pretreatment grit chamber
should be checked at least four times per year and after major storm events. Sediment should be
cleaned out when the sediment depletes more than 10 percent of the available capacity. This can be
done manually or by vacuum pump. Inlet a'nd outlet pipes should also be inspected at this, time. '
The infiltration drainfield should contain an observation well. The purpose of the monitoring well is to
provide information on how well this system is operating. It is recommended that the observation well
be monitored daily after runoff-producing storm events. If the infiltration drainfield does not drain after
three days, it usually means that the drainfield is clogged. Once the performance characteristics of the
structure have been verified, the monitoring schedule can be reduced to a monthly or quarterly basis.'
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TABLE 1: INFILTRATION DRAINFIELD DESIGN CRITERIA
Design Criteria ..
Guidelines
Site Evaluation
Design Storm Storage Volume
Dralnage.Time for Design Storm
Construction
Pretreatment
Dispersion Manifold
• TaKe soil borings to a depth of at least 4 feet '•.
. be'.ow bottom of stone reservoir to check for
so;) permeability, porosity, depth to seasonally
hlgtv water table, and depth to bedrock.
• Not recommended on slopes greater than 5
percent and best when slopes are as flat as
possible.
• Minimum Infiltration rate 3 feet below bottom
of stone reservoir: 0.5 Inches per hour.
• Minimum depth to bedrock and seasonally high
water table: 4 feet.
• Minimum setback from water supply wells:
100 feet.
• Minimum setback from building-foundations:
10 feet downgradlent, 100 feet upgradient.
• Drainage area should be less than 15 acres.
• Literature values-suggest this parameter Is
highly variable and dependent upon regulatory
requirements. One typically recommended
storage volume Is the stormwater runoff
volume produced In the tributary watershed by
the 6-month, 24-hour duration storm event.
• Minimum: 12 hours.
•. Maximum: 72 hours.
• Recommended: 24 hours.
• Excavate and grade with light equipment with
tracks or oversized tires to prevent soil
compactloa'
• As needed, divert stormwater runoff away from
site before and during construction.
,-• A typical infiltration cross-section consists of
the following: 1) a stone reservoir consisting of
coarse 1.5 to 3-Inch diameter stone (washed);
2) 6 to 12r1nch sand filter at the bottom of the
dralnfleld; and 3) filter fabric.
• Pretreatment Is recommended to treat runoff
-. from all contributing areas.
• A dispersion manifold should be placed 1n the
upper portions of the infiltration dralnfleld.
The purpose of this manifold 1s to evenly
distribute stormwater runoff over the largest
possible area.' Two to four manifold extension
pipes are recommended for most typical
' infiltration dralnfleld applications.
SOURCE: Ar/cxnccZ
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COSTS
There is little information on the cost of infiltration drainfields. However, the construction costs for
installing an infiltration drainfield that is 100 feet long, 50 feet wide, 8 feet deep and with 4 feet of
cover can be estimated using the general information in Table 2 below.
TABLE 2: ESTIMATED COST FOR INSTALLING AN INFILTRATION DRAINFIELDS
Excavation Costs:
Stone Fill
Sand Fill
Filter Fabric
Perforated Manifold
and Inlet Pipe
Observation Well
;Pretreatment Chamber
(2,220 cy) ($5.00/cy)
(1,296cy)($2o!o0/cy)
(185cy)($10.00/cy)
sn.roo.
25,920
1,850
4,550
Top and Bottom - 10,000 sf
Sides = 1,600 * 800 »= 2,400 sf
Total = 12.400 Sf * 10% = 13,640 Sf
(13,6,40 sf) (1 sy/9 sf) ($3.00/sy-)
75' + 4(40') - 235'
40'
(275)($10.00/ft)
1 at $500 ea
1 at $10,000
Miscellaneous ...
'(Backfilling, overflow pipe, sodding, etc.)
2,750
. .500
10,000
1,000
$57,670.
..'..-. , . SUBTOTAL
Contingencies (Engineering, administration, permits, etc.) * 25%_14.420
. • TOTAL • $72,090
Note: Unit prices will vary greatly depending upon local market conditions.
SOURCE:
ENVIRONMENTAL IMPACTS;
One potential negative impact of infiltration drainfields is the risk of groundwater contamination.
Studies.; to date do not indicate that this is a major risk. However, migration of nitrates and. chlorides
has been documented. . . .
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REFERENCES '"
1. Metropolitan Washington Council of Governments, Controlling Urban Runoff: A Practical Manual
• for Planning and Designing Urbari BMPs. 1987.
2. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas. 1989.
3. Southeastern Wisconsin Regional Planning Commission, Costs of Urban Npnpoint Source Water
Pollution Control Measures. Technical Report No. 31, June 1991. •
4. TT.fi. F.PA, Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices, Pre-print. July 1992. , ;
5. Worhinston 3ntr P-i"""""1' »f B^"py- -^nrmwater Management Manual for the Puget Sound
Basin. February 1992.
, US EPA. 401 VS«* SW, WaMnfon. DC, 20460.
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IMTB
STORM WATER BMP:
INTERNAL REPORTING
Office of Wasewater Erforoemert&< ,
MUNICIPAL TECHNOLOGY •IANCH
DESCRIPTION ' .'.-.' x •• .
Internal reporting provides a framework for "chain-of-command" reporting of stormwater management
issues. Typically, a facility develops- a Stormwater Pollution Prevention Team (SWPPT) concept for
implementing, maintaining, and revising the facility's Stormwater Pollution Prevention Plan (SWPPP).
The purpose of identifying a SWPPT is to clarify the chain of responsibility for stormwater pollution
prevention issues and provide a point of contact for personnel outside the facility who need to discuss
the SWPPP.,
CURRENT STATUS
The U.S. EPA first identified internal reporting as a Best Management Practice (BMP) in the late 1970s.
Currently, internal reporting has evolved into development of an SWPPT for facilities implementing an
SWPPP as part of their NPDES stormwater discharge permit. This SWPPT concept is a new arid
innovative part of the SWPPP. . • , . - ' < '
IMPLEMENTATION
The key to implementing internal reporting as a BMP is to establish a qualified SWPPT. Where setting
up an SWPPP is appropriate, it is important to identify key people on-site who are most familiar with die
facility and its operations, and to provide adequate structure and direction to the facility's entire
stormwater management program. Limitations involved in developing an internal reporting system are
the potential lack of. corporate commitment in designating appropriate funds, inadequate staff hours
available for proper implementation/arid a potential lack of motivation from SWPPT members that could
inhibit the transfer of key stormwater pollution information. •
PERFORMANCE •
The performance and effectiveness of an internal reporting system is highly variable and dependent upon
several factors. Key factors include: . •
/ ' •
Commitment of senior management.
Sufficient time and financial resources. .
Quality of implementation.
Background and experience of the SWPPT members.
DESIGN CRITERIA
When establishing an internal reporting structure, it is important to select appropriate personnel to serve
on the team. Both team and individual responsibilities should be-designated with clear goals defined for
proper stormwater management. Internal reporting should be tied to other baseline BMPs such as
employee training, individual inspections, and record keeping to. ensure proper implementation. Figure 1
below, illustrates an example SWPPT organization chart. - . , . ' ,
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*
Senior
Plant
Management
•
':
| 1 1 . 1 "t
• Research 5
Engineering I and | Production
$ ' Development \ M|
1 Waste Material^ Maintenance |
| Handling | $ . •
i iz:_ i
§ Material
Manufacturing | storage
• Shipping and
I Receiving
SOURCE; Refamxi
1 FIGURE 1: EXAMPLE SWPPT ORGANIZATION CHART
MAINTENANCE
To ensure that an internal reporting system remains effective, the person or team responsible for
'maintaining the SWPPP must.be aware of any changes in plant operations or key team members to
determine if modifications must be made in the overall execution of the SWPPP.
t '.
COSTS
Costs associated with implementing an internal reporting system are those associated with additional
staff hours-and related overhead costs.' Annual costs can be estimated using die example shown m
Table 1 below. Figure 2 can be used as a worksheet to calculate the estimated costs for an internal
record keeping program.
TABLE 1: EXAMPLE OF ANNUAL INTERNAL REPORTING COSTS
Tide
Stormwater Engineer
Plant Management
Plant Employees
SOURCE: EPA
Note: Defined as a
those costs associated
Estimated
Yearly
Avg. * Hours Est
Hourly Overhead* onSW Annual
Quantity Rate ($) Multiplier Training Cost ($)
1 x 15 x 2.0 x
5 x 20 x 2.0 x
100 x 10 x 2.0 x
TOTAL ESTIMATED ANNUAL
multiplier (typically ranging between 1 and 3) diat
with payroll expenses,' building expenses, etc.
,20 -= 600
10 = 2,000
5 = 10.000
COST $12,600
takes into account
-------
Estimated
Teariy
/ Avg. Hours
Hourly Overhead on SW
Tide , Quantity Rate ($) Multiplier Training
X X X =
' , X X X • =
X X X =
X X X =
EsL
Annual -
Cost ($)
fAI
fB)
fCV
(Dl
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOURCE: Rlfatncti
HGURE 2: SAMPLE ANNUAL INTERNAL REPORTING COST WORKSHEET
REFERENCES
1. U.S. EPA, NPDES BMP Guidance Document. June 1981,
2. U.S. EPA, Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. September, 1992. .
7K, BMP /~ ***
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-------
MTB
STORM WATER BMP;
MATERIALS INVENTORY
Offca of Wstfewata- Erftrcemert & <
MUNICIPAL TECHNOLOGY a'iANCH*'
DESCRIPTION
A materials inventory system involves the identification of all sources and quantities of materials that
may be exposed to direct precipitation or storm water runoff at a particular site. Significant materials
are substances related to industrial activities such as process chemicals, raw materials, fuels, pesticides,
and fertilizers. When these substances'are exposed to direct precipitation or storm water runoff, they
may be carried to a receiving waterbody. Therefore, identification of these substances and other
materials helps to determine sources of potential contamination and is the first step in pollution control.
CURRENT STATUS .
Most facilities already have in place a materials inventory system. However, the inventory of significant
materials is not generally performed from a storm water contamination viewpoint. Modification of the
existing materials inventory program to include storm water considerations should be minimal. The
inventory should be incorporated into the Storm Water Pollution Prevention Plan (SWPPP).
APPLICATIONS
A materials inventory system is applicable to most industrial facilities. Inventory of exposed materials
should be part of a baseline administrative program and is directly related to both record keeping and
visual inspection Best Management Practices (BMP)»' . •
LIMITATIONS . '
Limitation of materials inventory system BMP include:
It is an on-going process that continually needs updating. r
. . ' Qualified personnel are required to perform the materials inventory from a storm
water perspective. >. .
. Materials inventory records should be readily accessible.
PERFORMANCE
It is not possible to-quantify water quality benefits to receiving waters of a materials inventory program
since the program is intended to prevent .pollution before it occurs. However, it is anticipated that an
effective materials inventory program -will result in improved storm water discharge quality.
DESIGN CRITERIA .
Keeping an up-to-date inventory of all materials (hazardous and non-hazardous) on the site will help to
•limit material costs caused by overstocking, track how materials are stored and handled on site, and
identify which materials and activities pose the greatest risk to the environment. The following basic
steps should be used in completing a materials inventory:
-------
Identify all chemical substances present in the work place. Walk through the facility and
review the purchase orders for the previous year. List all chemical substances .used in the
work place and then obtain the material safety data sheets (MSDS) for each.
Label all containers to show the name and type of substance', stock number, expiration
•date health hazards, suggestions for handling, and first aid information. This
information can usually be found "on the MSDS. Unlabeled chemicals and chemicals with
deteriorated labels are often disposed of improperly or unnecessarily.
Clearly mark on the inventory hazardous materials that require specific handling, storage,
use, and disposal considerations. .
material-inventory tracking system.
Based on your materials inventory, describe Hie. significant materials that were exposed to storm water
during the past three years and/or are currently exposed. Other BMPs should then be evdu*ted and
SeLnted or constructed to eliminate exposure of theses materials tp storm water or that provide
appropriate treatment before discharge to receiving waters. Figure 2 below illustrates a sample
worksheet for evaluating exposed materials.
MATEMAL INVENTORY
Imcuetlon*: Un * iraurtata uwd. now*« produetd ant**.
norm wttv njnoff.
WorfcthMt
CompiMwJby:
TMta:
O«M:
Aims* and •rakuM th«t» mwtriito tar (Mr ponntW to eonrtbut* pofcttntt «o
SOURCE: RtfamxZ.
FIGURE 1: SAMPLE MATERIAL INVENTORY
-------
DESCRIPTION (
>mnjction<: Bu*d 01
, and/or •
•MHimmmilil
SOURCE; Reference
IF EXPOSE
lyourmmrli
• cwrantfy*
Z
osiowFic
it Invmtorv,
xpoMd.
0 Mill
!»•••<
MM
.ANT MATERIAL
tacrib* Uw ilgnifieint nu
, tu.lfc.
to> MtoRX B» •»••
OWl
• -
1
IworfcihMt
Computed by:
THta:
D*M:
MffMlB ffl*t WM HlHpOUd 1
.,(.-!-. >*i. Ml. Mkl
1
> •tofin wfltor ounfiQ ttM ptst DWM VMTS
.
-.
FIGURE 2: EXPOSED MATERIAL WORICSHEET
MAINTENANCE . .
The key to a proper materials inventory system is continual updating of records. Maintaining''an up-to-
date materials inventory is an efficient way to identify what materials are handled on-site that may
contribute to storm water contamination problems. .
COSTS . .
The major cost of implementing a materials inventory system is the time required to implement a
program that places emphasis on storm water quality. Typically, this is a small incremental increase if a
materials inventory program already exists at the facility. Keeping an up-to-date inventory of; all
materials present on your site will help to keep material costs down by identifying waste and
overstocking.
REFERENCE
1. U.S. EPA, NPDES Best Management Practices Guidance Document. December. 1979.
2. U.S. EPA, Storm water Management for Industrial Activities: Developing Pollution Prevention
Plans, and Best Management Practices. September. 1992.
Thii BMP faa Aea wan pnpaed by Ac Munidfol Tedutaloy Branch <<204), US EPA. W M Street, SW, Wajiinfon, DC, 20460.
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-------
JMTB
STORM WATER BMP:
NON-STORM WATER DISCHARGES
OffioofWa
aterEnfa
rtt
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
Identifying and eliminating non-storm water discharges is an important and very cost-effective Best
Management Practice (BMP)., Examples of non-storm water discharges include process water, leaks from
portable water tanks or pipes, excess landscape watering, vehicle wash water, and sanitary wastes. Non-
storm water discharges are typically the result of unauthorized connections of sanitary or process
wastewater drains that discharge to the storm sewer rather than to the sanitary sewer. Connections of
non-storm water discharges to a storm water collection system are .common, yet often go undetected.
Another form of non-storm water discharge is wash water discharge to a storm drain. Typically these
discharges are significant sources of pollutants, and unless regulated by.an NPDES permit, are illegal.
CURRENT STATUS
Identifying and eliminating non-storm water discharges as a BMP have rarely been used at industrial
facilities. Part of the problem is educational. Many facility operators are unaware of what constitutes a
non-storm water discharge, and the potential impact. The new NPDES permit requirements for the
presence of non-storm water discharges will greatly improve the implementation of this BMP.
APPLICATIONS
Identification of potential non-storm water discharges is applicable to almost every industrial facility that
has not been tested or evaluated for the presence of such non-storm water discharges. Generally, a non-
storm discharge evaluation includes:
Identification of potential non-storm water discharges locations.
. Results of a physical site evaluatipn for the presence of non-storm water discharges.
The evaluation criteria or test method used. .
. . The date of testing and/or evaluation. * • .
. The on-site drainage points 'that were directly observed during the test and/or evaluation.
LIMITATIONS
> * .
Possible problems in identifying non-storm water discharges include: . ;
The possibility that a non-storm water discharge may not occur on the date of
the test or evaluation.
The method used to test or evaluate the discharge may not be applicable to. the
situation. • '...,.•
Identifying an illicit connection may prove difficult due to the lack of available data on
the location of storm drains and sanitary sewers, especially in older industrial facilities.
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PERFORMANCE .
The question of whether or not the elimination of non-storm water discharges, is an effective BMP is
answered by evaluating the environmental impact of these .discharges. If a significant loading of
•pollutants is common from these discharges, then their elimination will be an effective BMP.
Several studies exist on the contents of non-storm water discharges. Pitt and Shawley (1982) reported
that non-storm water discharges were found to contribute substantial quantities of many pollutants even
though the concentrations were not high. The long duration of- the base flows offset the lower
concentration leading to a substantial loading of pollutant?. Gartner, Lee and Associates Ltd (1983)
conducted an extensive survey of non-storm water discharges in the Humber River watershed CToronto)
Out of 625 outfalls, about 10 percent were -considered significant pollutant sources. Further
investigations identified many industrial and sanitary non-storm water discharges into _ the storm
drainage system For example, problems found in industrial areas included liquid dripping from. animal
S s'torS rtanSry yards'and washdowns of storage yards at meat packing facilities Therefore, it is
anticipated that elimination of non-storm water discharges will be a highly effective BMP.
DESIGN CRITERIA
Key program criteria includes the identification and location of .non-storm water entries into storm
drLage>Sems. It is important to note that for any effective investigation of pollution within a ^tonn
water sysSm, all pollutant sources must be included. For many pollutants storm water may conmbute
Ae smaller portion of the total pollutant mass discharged from a storm drainage system. Significant
pollutant sources may include dry-weather entries occurring during bo* warm and "Unurtte art
Lwinelt runoff, in addition to conventional storm water associated with rainfall, 'onsequend y, much
less pollution reduction benefit will occur if only storm water is considered in a control ptan i for
controlling storm drainage discharges. The investigations may also idenufy illicit point source outfalls
Sat do not carry storm water. Obviously, these outfalls also need to be controlled and permitted.
Figure 1 below can be used as a sample worksheet to report non-storm water discharges.
NON-STORM WATER DISCHARGE
D*i»of
Taster
Evaluation
Outfall DiractJy
Obiamd During tha
Tt« M»'«*i m intiinj »•
,
MathodUaadto
TMt or Evaluate
•
Worksheet
Data: : — i
Daacriba Raaufts from Tan for
ttw Pru«nc« of Non-Storm
Waur Diachva*
tdwitify PoMntW'
Significant SburoM
.
NMM of Penan 'Wmo
Conducud ftM T*n or
• Evaluation
SOURCE. Reference*.
FIGURE 1: SAMPLE WORKSHEET FOR RECORDING NON-STORM WATER DISCHARGES
-------
There are four primary methods for investigating non-storm water discharges. These methods include:
. Sanitary and Storm Sewer Map Review. A review of a plant schematic Is a simple way to
determine if there are any unauthorized connections to the storm water collection system.
A sanitary or storm sewer map, or plant schematic is a map of pipes and drainage
systems used to carry process wastewatier, non-contact cooling water, and sanitary wastes.
These maps (especially as-built plans or record drawings of the facility) should be
. . reviewed to verify that there are no unauthorized connections. A common problem is
that sites often do not have accurate or current schematics or plans. .
. Visual Inspection. The most simple method for detecting non-storm water connections in
the storm water collection1 system is to observe all discharge points during periods of dry
weather. Key parameters to look for are the presence of stains, smudges, odors, and other
; abnormal conditions. -
. Sampling and Chemical Analysis. Sewer mapping and visual inspection are also helpful in
identifying locations for sampling. Chemical tests are needed to .supplement the visual or
physical inspections. Chemical tests can help quantify the approximate components of
the mixture at the outfall or discharge point. Samples should be collected, stored, and
analyzed in accordance with standard quality control and quality assurance (QA\QC)
, procedures. Statistical analysis of the chemical test results can be used to estimate the
relative magnitude of the various flow sources. In most cases, non-storm water
discharges are made up of may separate sources of flow (such as leaking domestic water
systems, sanitary, discharges, ground water infiltration, automobile washwater, etc.). Key
parameters that can be helpful in identifying the source of the no -storm water flows
include, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total
organic carbon (TOC), specific conductivity, temperature, fluoride, hardness, ammonia
ammonium, potassium, surfactant fluorescence, pH, total available chlorine, and toxicity
screening. It may be possible to identify the source of the non-storm water discharge by
. ' examining the flow for specific chemicals.
Just as high levels of pathogenic bacteria are usually associated with a discharge from a
sanitary, waste water sources, the presence of certain chemicals are generally associated
with specific industries. Table 1 below includes a listing of various chemicals that may
• be associated with a variety of different activities. . , .
. Dye Testing. .Another method for detecting improper connections to the .storm water .
collection system is dye testing. A dye test can be performed by simply releasing a dye
(either pellet or powder) into either the sanitary or process wastewater system.
Discharge points from the storm water collection system are them examined for color
change. • ' '
MAINTENANCE
A maintenance program consists of annual inspections for non-storm water discharges, even if previous
tests have been negative. New processes, building additions, and other plant changes, if they are'not
carefully reviewed during design, may result in future unauthorized connections to the storm water
conveyance system.
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TABLE 1: CHEMICALS COMMONELY FOUND INDUSTRIAL DISCHARGES
Chemical;
Acetic add
Alkalies
Ammonia •
Arsenic
Chlorine .
Chromium
Cadmium
Citric acid
Copper
Cyanides
Fats, oils
Fluorides
Formalin
Hydrocarbons
Hydrogen peroxide
Lead
Mercaptans
Mineral adds
Nickel
Nitro compounds
Organic adds
Phenols
Silver
Starch
Sugars
Sulfldes
Sulfltes
Tannic acid
Tartaric acid
Zinc
Industry;
Acetate rayon, pickle and beetroot manufacture
Cotton and straw kiering, cotton manufacture, mercerizing, wool
scouring, laundries
Gas and coke manufacture, chemical manufacture
Sheep-dipping, felt mongering
Laundries, paper mills, textile bleaching
Plating, chrome tanning, aluminum anodizing
Plating
Soft drinks and citrus fruit processing
Plating, pickling, rayon manufacture v
Plating, metal cleaning, case-hardening, gas manufacture
Wool scouring, laundries, textiles, oil refineries
Gas and coke manufacture, chemical manufacture, fertilizer plants,
transistor manufacture, metal refining, ceramic plants, glass etching
Manufacture of synthetic resins and penicillin
Petrochemical and rubber factories
Textile bleaching, rocket motor testing „
Battery manufacture, lead mining, paint manufacture, gasoline
manufacture -
Oil refining, pulp mills
Chemical manufacture, mines, Fe and Cu pickling, brewing, textiles,
photoengraving, battery manufacture
Plating
Explosives, and chemical works
' Distilleries and fermentation plants
Gas and coke manufacture, synthetic resin manufacture, textiles,
tanneries, tar, chemical, and dye manufacture, sheep-dipping
Plating, photography
Food, textile, wallpaper manufacture
Dairies, foods, sugar refining, preserves, wood process
Textiles, tanneries, gas manufacture, rayon manufacture
' Wood process, viscose manufacture, bleaching
Tanning, sawmills
Dyeing, wine, leather, and chemical manufacture
Galvanizing, plating, viscose manufacture, rubber process
SOURCE.- Reft
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COSTS
The above methods are mostly time-intensive and their cost are dependent on the amount of effort and
level of expertise employed. Visual inspections are the least expensive of the three. Dye testing may be
.more cost effective for buildings that do not have current schematics of their sanitary and storm sewer
systems. The cost of disconnecting illicit discharges from the storm water system will vary depending on
the type and location of the connection and the type of corrective action needed.
The Full use of all of the applicable procedures is most likely necessary to successfully identify pollutant
sources. Attempting to reduce costs, for example, by only examining a certain class of outfalls, or using
inappropriate testing procedures, will significantly reduce the utility of the testing program and result in
inaccurate conditions.
ENVIRONMENTAL IMPACTS <
Eliminating non-storm water discharges can have significant impacts on improving water quality in the
receiving waters.
REFERENCES
1. Pitt, Robert, and Field, Richard, Non-Storm water Discharges into Storm Drainage Systems.
NTIS Report No. PB92-158559, 1992. '
•> - ' - "^
2. Pitt, R. and Shawley, G., A Demonstration of Non-Point Pollution Management on Castro Valley
Creek. Alameda County Flood Control District (Hayward, California) -and,U.S. EPA,
Washington, DC, June 1982. . *
3. Gartner, Lee and Associates, Ltd., Toronto Area Watershed Management Strategy Study.
Technical Report No. 1. Humber River and Tributary Drv Weather Outfall Study. Ontario Ministry
of the Environment, Toronto, Ontario, November 1983.
4. U.S. EPA, Storm water Management For Industrial Activities: Developing Pollution Prevention
Plans and Best Manaeement Practice^ September 1992.
5. Washington State. Department of Ecology. Storm water Management Manual for the Puget •
Sound Basin. February 1992.
fi California F.nvironmental Protection Agency. Staff Proposal for Modification to Water Quality.
Order No. 91-13 DWO Waste Discharge Requirements for Discharges of Storm water Associated •
with Industrial Activities. Draft, August 1992. -
7. Pitt, Robert, Barbe, Donald; Adrian, Donald, and Field, Richard, Investigation of Inappropriate
Pollution Entries Into Storm Drainage Systems - A Users Guide. US EPA, Edison, New Jersey, 1992.
US EPA 401 USota. SW, WoMiifen. DC..20460.
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IMTB
STORM WATER BMP:
POROUS PAVEMENT
Offics of Wstmvaler Biaiaiat & (
MUNICIPAL TECHNOLOGY BtANCtT
DESCRIPTION
Porous pavement is a specially designed and constructed pavement which allows stormwater to pass
through it. The purpose of porous pavement is to reduce the speed and amount of runoff from a site,
and to filter potential pollutants from the stormwater. There are two principal types of porous
pavement: porous asphalt pavement, and pervious concrete pavement. Porous asphalt pavement
consists of an open graded coarse aggregate bound together by asphalt with sufficient interconnected
voids to provide a high rate of water percolation. Pervious concrete consists of specially formulated
mixtures of Portland cement,,uniform open graded coarse aggregate, and water. When properly handled
and installed, pervious concrete has a high percentage of void space which allows rapid percolation of
liquids through the pavement. • \ • ', .
The porous pavement surface is typically placed over a highly permeable layer of open graded gravel and
crushed stone. ; The Void spaces in the aggregate layers provide a storage reservoir for runoff. A filter
fabric is placed beneath the gravel and stone layers to prevent the movement of fine soil particles into
these layers.. Figure 1 below illustrates a common porous asphalt pavement installation.
Berm Keeps Off-site
Runoff and Sediment Out.
Provides Temporary
Storage
Asphalt is Vacuum Swept.
Followed by Jet Hosing to
Keep Pores Free
Site Posted to Prevent
Resurfacing and Use of
Abrasives, and to Restrict
Truck Parking
Reverse Perforated Pipe Only
Discharges When 2 Year
Storage Volume Exceeded
Stone Reservoir Drans in 48*72 Hours or Less
Overflow Pipe
Filter Fabric Lines
Sides of Reservoir
to Prevent
Sediment Entry
Observation Well
Gravel Course or
6 Inch Sand-Layer
Undisturbed Soils with an Ic > 0.27 inches/Hour
Preferably 0.50 Inches/Hour or More
SOURCE:
FIGURE 1: TYPICAL POROUS PAVEMENT INSTALLATION
Porous pavement offers a number of advantages including:
Provides water quality improvement by removing pollutants. '
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Reduces the need for curbing and storm sewer installation.
Improves road safety by-increasing skid resistance. (Tests have shown that there
is up to 15 percent less hydro-planing and skidding on porous pavement surfaces.)
Provides recharge to local aquifers.
COMMON MODIFICATIONS .
A common modification for porous pavement design systems .consists of varying the amount of storage to
be provided in the stone reservoir located directly beneath the pavement, and adding perforated pipes
near the top of the reservoir to discharge stormwater runoff after the reservoir has been filled to design
capacity. Stone reservoirs may be designed to accept the first flush of stormwater runoff or. provide
enough storage to accommodate runoff from a chosen design storm for infiltration through the-
underlying subsoil. Pretreatment of off-site runoff is highly recommended. Another variation of pervious
concrete is the use of a concrete block or brick system with individual blocks separated by a pervious
material.'
CURRENT STATUS . . ' .
Currently there is little information on porous pavement. However, in general information about
infiltration trenches and basins also applies to porous'pavement. The following concerns are
currently being evaluated by the EPA. . •
Can pavement porosity be maintained over the long term,
particularly with resurfacing needs and snow removal?
• What is the pollutant removal capability of porous pavement
during subfreezing weather and snow removal conditions?
What are the optimal relationships between porous pavement,
groundwater, sandy soils, and high water table conditions?
What are the costs of maintenance and rehabilitation options
for restoration of porosity?
APPLICATIONS ' . ; /
Porous pavement is applicable as a substitute for conventional pavement'on parking areas and low traffic
volume roads provided that the grades, subsoils, drainage characteristics, and groundwater table
conditions are suitable. Slopes should be very., gentle to flat. Soils should have field-verified
permeability rates of greater than 0.5 inches per hour, and there should be a 4-foot minimum clearance
from the bottom of the system to bedrock or the water table. Additional areas for use of porous
pavement include fringe overflow parking areas and taxiway and runway shoulders at airports.
LIMITATIONS
The use of porous pavement may be restricted in regions with extremely cold climates, arid regions or
regions with high wind erosion rates (increased windblown sediment loads) and areas where sole source
potable aquifers could be contaminated. The .e of porous pavement is highly constrained, requiring
Seep permeable soils, restricted traffic; and accent land uses. Some specific disadvantages of porous
pavement include:.
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The -lack of experience with this technology with most pavement
engineers and contractors. .
Porous pavement has a tendency to become clogged if improperly
. installed or maintained.
The high failure rate of porous pavement sharply limits the
ability to meet watershed stormwater quality and quantity goals.
Slight to moderate risk of groundwater contamination depending
on soil conditions and aquifer susceptibility.
Possible transport of hydrocarbons from vehicles and leaching
of toxic chemicals from asphalt and/or binder surface.
Some building codes may not allow for the installation of porous
pavement. '
The possibility exists that anaerobic conditions may develop in
underlying soils if the soils,,are unable to dry out between storm
events.
PERFORMANCE .
Traditionally, porous pavement sites have had a high failure rate (75 percent). Failure has been
attributed to poor design, inadequate construction techniques, low permeability soils, heavy
vehicular traffic, and resurfacing with nonporous pavement materials. •
Porous pavement pollutant removal mechanisms include absorption, straining, and microbiological
decomposition in the soil underlying the aggregate chamber and trapping of particulate matter
within the chamber. An estimate of porous pavement pollutant removal efficiency is provided by .
two long-term monitoring studies. These studies indicate long-term removal efficiencies of
between 82 and 95 percent for sediment, 65 percent for total phosphorus, and 80-85 percent 'of
total nitrogen. They also indicated high removal rates for zinc, lead, and chemical oxygen,
demand. 'Some key factors to increase pollutant removal and prevent failure include:
Routine vacuum sweeping and high pressure washing.
Maximum recommended drainage time of 24 hours.
. Highly permeable soils.
Pretteatment of off-site runoff.
Inspection and enforcement of specifications during construction;
Organic matter in subsoils. ,
Clean-washed aggregate.
Use only in low-intensity parking areas.
Restrictions on use by heavy vehicles. .
Limiting use.of de-icing chemicals and sand. •
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DESIGN CRITERIA ' '
Porous pavement, along with other infiltration BMPs (infiltration basins, trenches, etc.) have
demonstrated relatively short life spans in the past. Failures have general been attributed to poor
design poor construction techniques, subsoils with low permeability, and lack of adequate preventive
maintenance. Key design factors that can significantly increase the-performance and reduce the risk of
failure of porous pavements and other infiltration BMPs' is shown in Table 1 below.
TABLE 1: DESIGN CRITERIA FOR POROUS PAVEMENT.
Design Criteria
Guidelines
Site Evaluation
Traffic Conditions
Take soil borings to depth of at least 4 feet
below bottom of stone reservoir to check for
soil permeability, porosity, depth to seasonally
high water table, and depth to bedrock.
Not recommended on slopes greater than 5
percent and best with slopes as flat as possible.
Minimum infiltration rate 3 feet below bottom of
stone reservoir: 0.5 inches per hour.
Minimum depth to bedrock and seasonally high.
water table: 4 feet.
Minimum setback from water supply wells: 100
feet
Minimum setback from building foundations: 10
feet downgradient, 100 feet upgradient.
Not recommended in areas where wind erosion
supplies significant amounts of windblown
sediment. '
Drainage area should be less than IS acres.
Use for low volume automobile parking areas
and lightly used access roads.
Avoid moderate to high traffic areas and
significant truck traffic.
SOURCE. Rtf>
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TAB^E 1: DESIGN CRITERIA FOR POROUS PAVEMENTS.
(CONTINUED)
Design Criteria
Guidelines
Design Storm Storage Volume
Drainage Time for Design Storm
Construction
While the standard porous pavement design is
believed to withstand freeze/thaw conditions
normally encountered in most regions of the
country, the porous pavement system is sensitive to
clogging during snow removal operations. Therefore,
the area should be posted with signs to restrict the
use of sand, salt, and other deicing chemicals
typically associated with snow cleaning activities.
Literature values suggest this parameter is highly
variable and dependent upon regulatory
requirements. One typically recommended
storage volume is the stormwater runoff volume
produced in the tributary watershed by the
produced in the tributary watershed by the
6-month, 24-hour duration storm event
Minimum: 12 hours.
Maximum: 72 hours.
Recommended: 24 hours.
Excavate and grade with light equipment with
tracks or oversized tires to prevent soil
compaction.
As needed, divert stormwater runoff away from
planned pavement area to keep runoff and
sediment away from site before and
during construction.
A typical porous pavement cross-section consists
of the following layers: 1) porous asphalt course,
2-4 inches thick; 2) filter aggregate course; 3)
reservoir coarse of 1.5-3-inch diameter stone; and
4) filter fabric.
Porous Pavement Placement
Pavement temperature: 240-260' F.
Minimum air temperature: 50* F.
Compact.with one or two passes of a 10-ton
roller.
Prevent any vehicular traffic on pavement for at
least two days.
SOURCE: Riff
Pretreatment'Pretreatment is recommended to
treat runoff from all off-site areas. An example
would be a 25-foot wide vegetative filter strip
placed around the perimeter of the porous
pavement where drainage flows onto the
pavement surface.
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MAINTENANCE
Routine maintenance of porous pavements is extremely, important. Maintenance should include vacuum
JSX^SJfour times per year, followed by high-pressure hosing to limit sediment cloggmg in the
^res of the top layer. Potholes and cracks can be filled with typical patching mixes unless more than
iSpercent o?the surface area needs repair. Spot-clogging may be fixed by. drilling, half-inch holes
through the porous pavement layer every few feet.
The lavement should be inspected several times during the first few months following installation and
thSeafter. Inspections after large storms are necessary to check for poo Is of water. These
g. The condition of adjacent pretreatment facilities should also be mspected.
COSTS ,
The costs of developing a porous pavement system 100 feet by 50 feet and with a 4 foot deep storage
area can be estimated using the example in table 2 below.
Estimated costs for an average annual maintenance program of a porous pavement parking lot are
acre "per year. This cost assumes four inspections, vacuum sweeping and jet
hosing treatments per year.
TABLE 2: ESTIMATED COSTS FOR A POROUS PAVEMENT SYSTEM
1. Excavation Costs:
2. Filter Aggregate/Stone Fill
3. Filter Fabric
4. Porous Pavement
5. Overflow Pipes
6. Observation Well
7. Grass Buffer
8. Erosion Control
740 cy x S5.00/cy
740 cy x $20.00/cy
760 sy x S3.00/sy
556syxS13.00/sy
200 ft x $12.00/ft
1 at $200 ea
833 sy x $1.50/sy
Sl.OOO/lump sum
SUBTOTAL
9. Contingencies (Engineering, Administration, etc.) = 25%
TOTAL*
S 3,700
14,800
2,280
7,228
2,400
200
1,250
_1.000
532,858
8.215
$41,073
SOURCE
..s any storm sewers, curb and gutter should be
juui ™ — the difference in total cost for implementing a
i Unit costs will vary according to local market conditions.
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ENVIRONMENTAL IMPACTS
One potential negative impact of porous pavement is the risk of groundwater contamination. Pollutants
(such as nitrates and chlorides) not. easily trapped, absorbed, or reduced may continue to move through
the soil profile and into groundwater. This is not a desirable • condition, as it could lead to
contamination of drinking water supplies. Therefore, until more scientific data is available, it is
advisable not to site porous pavement near groundwater drinking supplies.
REFERENCES
1. A Current Assessment of Best Management Practices; Technidues for Reducing Nonooint Source
Pollution in a Coastal Zone. December 1991. .
2. Field. Richard et al.. An Overview of Porous Pavement Research. Water Resources Bulletin. Volume
18, No. 2, pp. 265-267, 1982.
- r ' ' ' . • 9 . • • - , ' •
3. Metropolitan Washington Council of Governments. Controlling Urban Runoff: A Practical Manual for.
Planning and Designing Urban BMPs. 1987.
4. Southeastern Wisconsin Regional Planning Commission, Costs of Urban Nonpoint Source Water
Pollution Control Measures. Technical Report No. 31, June 1991. "' .
5. U.S. EPA, Best Management Practices Implementation Manual. April 1981.
6. US. EPA, Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
' and Best Management Practices. September 1992. .
7. Washington State Department of Ecology. Stormwater Manaeement Manual for the Puget Sound
Basin. February 1992.
, WaHnfon. DC. X460.
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STORM WATER BMP:
PREVENTIVE, MAINTENANCE
MTB
.
MUNICIPAL TECHNOLOGY IRANCH
DESCRIPTION
Preventive maintenance involves the regular inspection and testing of. plant equipment and operational
systems. These inspections should uncover conditions such as cracks or slow leaks which could cause
breakdowns or failures that result in discharges of chemicals to surface waters either by direct overland
flow or through storm' drainage .systems. The purpose of the preventive maintenance program should be
to prevent breakdowns and failures by adjustment, repair, or replacement of equipment before a major
breakdown or failure can occur. '
Preventive maintenance has been practiced predominantly in those industries where excessive down time
is extremely costly. As a storm water best management practice BMP, preventive maintenance should be
used selectively to eliminate or minimize the spill of contaminants to receiving waters. For many
facilities this would simply be an extension of the current plant preventive maintenance program to
include items to prevent storm water runoff contamination.
, • - x
For sites that have storm drainage facilities, proper maintenance is necessary to ensure that they serve
their intended function. Without adequate maintenance, sediment and, other debris can quickly clog
facilities and render them useless. Typically, a preventive maintenance program should include
inspections of catch basins, storm water detention areas, and water quality treatment systems.
CURRENT STATUS
Most plants already have preventive maintenance programs that provide some degree of environmental
protection. This program could be expanded to include stormwater considerations, especially the upkeep
and maintenance of storage tanks, valves, pumps, pipes, and storm water management devices.
APPLICATIONS ,
Preventive maintenance procedures and activities are applicable to almost every industrial facility.
Preventive maintenance should be part of a general good housekeeping program designed to maintain a
clean and orderly work environment. Often the most effective first step towards preventing storm water
pollution from industrial sites simply involves good common sense to improve the facility preventive
maintenance and general good hbusekeeping methods.
LIMITATIONS
•I"'-' v
Primary limitations of implementing a preventive maintenance program include:
. Additional costs. . <
Availability of trained preventive maintenance staff technicians.'
. Management direction and staff motivation in expanding the preventive
maintenance program to include storm water considerations.
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PERFORMANCE
Quantitative data is not available on the effectiveness of preventive maintenance as a best management
pS However' it is clear that an effective" preventive maintenance program can result in improved
storm water discharge quality.
DESIGN CRITERIA
Elements of a good preventive maintenance program should include:
Identification of equipment or systems which may malfunction and cause spills.leaks, or
other situations that could lead to contamination of storm water runoff. Typical
equlpS to inspect include pipes, pumps, storage tanks and bins, pressure vessels,
pressure release valves, process and material handling equipment, and storm water
• • management devices. . •
Once equipment and areas to be inspected have been identified at the facility, establish
schedules and procedures for routine inspections.,
' Periodic testing of plant equipment for structural soundness is a key element in a
preventive maintenance program.
Promptly repair or replace defective equipment found during inspection and testing.
Keep spare parts for equipment that need frequent repair.
It is important to include a record keeping system for scheduling tests and documenting
inspections in the preventive maintenance program.
• • ' '' Record test results and follow up with corrective action taken. Make sure records are
' compfeSiS defatted. These records should be kept with other visual inspection records.
MAINTENANCE RECORDS ' . .
The kev to properly tracking a preventive maintenance program is through the continual updating of
Se preventiveSitenance procedures and tasking should be implemented as necessary.
COSTS
The major cost of implementing a preventive *~«^^^
quality is the staff time required to implement the program. Typically ""^
increase if a preventive for training and maintenance program already exists at the facility.
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REFERENCES ','.-.
1. tLS. EPA, NPDES-best management practice Guidance Document. June 1981. • '•
2. U.S. EPA, Storm water Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. September, 1992.
3. Washington State Department of Ecology, Storm water Management Manual for Puget Sound.
February 1992. . .
Thii BMPfaa*at wupirpaKd by *e Muue^l TttAnaloy Bmdt (1204), US EPA. 401MSato. SW. WaUi^Of. DC,-20460.
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IMTB
STORM WATER BMP:
RECORD KEEPING
Offta of Waaewatar Brforcemat & < ,
MUNICIPAL TECHNOLOQT IRANCH
DESCRIPTION
A record keeping system should be implemented for documenting spills, leaks, and other discharges such
as hazardous substances. Keeping record* and reporting events that occur on-site are effective ways of
tracking the progress of pollution prevention efforts and waste minimization. Analyzing records of past
spills can provide useful information for developing improved Best Management Practices (BMPs) to
prevent future spills. Record keeping represents a good operating practice because it can increase the
efficiency of a facility by reducing down, lime and increase the effectiveness of other prevention and
treatment BMPs. Typical record keeping items include reported incidents and follo'w-up on results of
inspections, and reported spills, leaks, or other discharges.
IMPLEMENTATION - ' ' ' " .
Record keeping as a BMP should be; an integral part of a BMP implementation program and should be
incorporated into Stormwater Pollution Prevention Plans (SWPPP).If a separate record keeping system for
tracking BMPs, monitoring results, etc., is not currently in place at, a 'facility, existing record keeping
structures could be easily adapted to incorporate this data. An ideal tool for implementation is the
record-keeping procedures laid out in an SWPPP. In many cases the record keeping system can be
maintained on a personal or desk top computer using standard spreadsheet or data base management
software.
LIMITATIONS '
Limitations associated with a record keeping system are:
It is an on-going process that continually needs updating.
Qualified personnel required to complete the record keeping forms.
Accessible of records.
Security of Confidential information. ! • '
PERFORMANCE
Record keeping .performance as a BMP is highly variable. It depends on the time and commitment
dedicated to implementing an effective system. The benefit of an effective record keeping system being
incorporated into an overall SWPPP is improved stormwater discharge leaving facility grounds. The
effectiveness of the record keeping system is often dependent on the following:
. The commitment of senior management to implementing and maintaining an effective
record keeping system.
. ' The quality of the record keeping program.
The background and experience of the assigned record keeping team.
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DESIGN CRITERIA '
Record keeping 'and reporting procedures for spills, leaks, inspections, maintenance, and monitoring
activities should include the following, a sample worksheet for keeping records of spills and leaks is
shown in Figures 1 below.
The date, location, and time of material, inventories, site inspections, sampling
observations, etc.
The indiyidual(s) who performed site inspections, sampling observations, etc.
The dateCs) analyses were performed,and the-time(s) analyses were initiated, the
individual or individual(s) who performed the analyses, analytical techniques or methods
used, and results of such analysis. , .
Quality assurance/quality control results. •
The date, time, exact location.and complete characterization of significant spills or leaks.
Visual observation and sample collection exception records.
All calibration and maintenance records of instruments used in stormwater monitoring.
All original strip -chart recordings for continuous monitoring equipment.
UST OF SIGNIFICANT SPILLS AND LEAKS
WorinhMt
Comptoud by:
THto:
Dine***: R»cc«!b«low«l«JQnHici«it
SOURCE;
FIGURE 1: SAMPLE WORKSHEET FOR TRACKING SPILLS AND LEAKS
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MAINTENANCE . ,
The key to a proper maintenance program for record keeping is continual updating. Records should be
updated with the correct name and address of the facility, name and location of receiving waters,
number and location of discharge points, principal product and significant changes in raw material
storage outside, and reports of monitoring results and .spills at the site. It is recommended that all
reports be maintained for a period of at least five years from the date of sample observation,
measurement, or spill report. Some simple techniques used to accurately document and report results
include:
Field notebooks
. , Timed and dated photographs ' .; :
Videotapes ;
'-..' Drawings and maps .
Computer spreadsheet and database programs
COSTS .
Costs associated with implementing a record keeping system are thbse associated with additional staff
hours to initially develop the system and to keep records up to date, along with related overhead costs.
Annual costs can be estimated using the example shown in Table 1 below. Figure 4 can be used as a
worksheet to calculate the estimated annual cost for a record keeping system.
TABLE 1: EXAMPLE OF ANNUAL RECORD KEEPING COSTS
Tide Quantity
Stormwater Engineer 1
Plant Management 5
Plant Employees 100
Avg.
Hourly .
Rate($)
x 15 x
x 20 x .
x 10 x
Overhead* '•
Multiplier
2.0 x
2.0 x
2.0 x
Estimated
Yearly
Hours
onSW
Training
20 =
10 «=
5 . «
TOTAL ESTIMATED ANNUAL COST
Note: Defined as a multiplier (typically ranging between 1 and
those costs associated with payroll expenses, building expenses, etc
SOURCE: EPA ,
Est. .
Annual
Cost($)
600 -
2,000
10.000
$12,600
3) that takes into account
-------
Tide
Avg.
Hourly
Quantity Rate ($)
x
X
X
X
Overhead
Multiplier
x
X
X
X
Estimated
Yearly
Hours
onSW
-Training
EsL
Annual
Cost($)
x
X
X
X
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B4-C+D)
SOURCE) Rtfi
FIGURE 2: SAMPLE ANNUAL RECORD KEEPING COST WORKSHEET
(A)
C3),
(C)
CD)
REFERENCES , • ' '• '
1 California Environmental Protection Agency, Stuff Proposal for Modification to Water Quality
Order No 91-13 DWO Waste Discharge Requirements for Dischargers of Stormwater .
Associated with Industrial Activities. Draft Wording. Monitoring Program and Reporting
Requirements. August 17, }992. .
2. U.S. EPA, NPDES BMP Guidance Document. June, 1981.
3. U.S. EPA,
• M
t for Industrial Activities:
Pollution Prevention
Plans and Best Management PracticesJ September, 1992.
. US EPA. 401 MS^ SW. Wat***. DC, 20460.
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iMTB
STORM WATER BMP:
SPILL PREVENTION PLANING
OtttoofWa
'Erfa
ntt
MUNICIPAL TECHNOLOGY IIANCH
DESCRIPTION
A Spill Prevention Plan identifies areas where spills can occur on site, specifies materials handling
procedures, storage requirements, and identifies spill clean-up procedures. The purpose of this plan is to
establish standard operating procedures, and the necessary employee training to minimize the likelihood
of accidental releases of pollutants that can contaminate stormwater runoff. Spill Prevention is prudent
from both an economic as well as environmental standpoint because spills increase operating costs and
lower productive
Storm water contamination assessment, flow division, record keeping, internal reporting, employee
training, and preventive maintenance are associated BMPs that should be incorporate into a
comprehensive Spill Prevention Plan. ,
CURRENT STATUS
Typically most businesses and public agencies that generate hazardous waste and/or produce, transport,.
or store petroleum products. are required by state and federal law to prepare spill control and cleanup
plans. Therefore, a Spill Prevention and Response Plan may have already been developed in response to
other environmental regulatory requirements. Existing, plans should be re-evaluated and- revised if
necessary to address stormwater management issues. i
APPLICATIONS
A Spill Prevention Plan is applicable to facilities that transport, transfer, and store hazardous materials,
petroleum 'products, and fertilizers that can contaminate stormwater runoff. An important factor of an
effective spill prevention plan is quick notification of the appropriate emergency response teams. In
some plants each area or process may have a separate team leader and team of experts. Figure 1 beloy
illustrates a sample spill prevention team roster for quick identification of team leaders and their
responsibilities.
LIMITATIONS
Spill Prevention Planing can be limited by the following:
Lack of employee motivation to implement plan.
Lack of commitment from senior management
. Key individuals identified in the Spill Prevention Plan may not be properly
trained in the areas of spill prevention, response, and cleanup. .
PERFORMANCE ,
Past experience has shown that the single most important obstacle to an effective Spill Prevention Plan is
its implementation. Qualitatively, implementation of a well prepared Spill Prevention Plan should
significantly decrease contamination of stormwater runoff.
-------
POLLUTION PREVENTION TEAM
Worksheet
Completed by:
Title:
Date:
SOURCE: Rtfamxl.
FIGURE 1: SAMPLE SPILL PREVENTION TEAM ROSTER
DESIGN CRITERIA . .
General guidelines for the preparation of a Spill Prevention Plan include: . •.
The first part of the plan should contain a description of the facility including ihe owner's
' namHnd address, the nature of the facility activity, and the general types of chemicals
used in the facility. , '
' The plan should contain a site plan showing the location of storage areas for chemicals,
' location of the storm drains, tributary drainage *™ ™* f™^,™™^£*af
location and description of any devices to stop spills from leavmg the site such as
collection basins. .
The plan should describe notification procedures to be used n the event of a.spill such as
' phone numbers of key personnel, and appropriate regulatory agencies such as local
Pollution Control Agencies and the local Sewer Authority.
The plan should provide specific instructions regarding cleanup procedures.
-------
The ovvner, through an uiternal reporting procedure, should have a designated person.
•"..-. . with, overall responsibility for spill response. Through an employee training- program, key
personnel should be trained in the use of this plan. All employees should have basic
knowledge of spill control procedures.
A summary of the plan should be written and posted at appropriate points in the building
(i.e., lunch rooms, cafeteria, and areas with a high spill potential), identifying the spill
cleanup coordinators, location of cleanup kits, and phone numbers of regulatory
agencies to be contacted in the event of a spill. • • " ;
Cleanup of spills should begin immediately. No emulsifier or dispersant should be used.
In fueling areas, absorbent should be packaged in small bags for easy use and small
drums should be available for storage of absorbent and/or used absorbent Absorbent '
materials shall not be washed down die floor drain or into the storm sewer.
Emergency spill containment and cleanup kits should be located at the facility site. The
contents of the kit should be appropriate to the type and quantities of chemical or goods
stored at the facility.
Some structural methods to consider when developing a Spill Prevention Plan include:
Containment diking- Containment dikes are temporary or permanent earth or concrete
berms or retaining walls that are designed to hold spills. Diking can be used at any
industrial facility, but is most common for controlling large spills or releases from liquid
storage and transfer areas. Diking can provide one of the best protective measures against
, the contamination of stormwater because it surrounds the. area of concern and-holds the
spill, keeping spill materials separated from the stormwater outside of the diked area.
Curbing- Like containment diking, curbing is a barrier that surrounds an area of concern.
Because curbing is usually small-scale, it cannot contain large spills like diking can.
However, curbing is common at many facilities and small areas where liquids are handled
and transferred.
Collection basins. Collection basins are permanent structures where large spills or
contaminated stormwater are contained and stored before, cleanup or treatment.
. Collection basins are designed to receive spills, leaks, etc., that may occur, and prevent
these materials from being released to the environment. Unlike containment dikes,
collection basins can receive and contain materials from many locations across a facility.
* • '
Once a hazardous material spill occurs and is contained, the material has to be cleaned up and disposed
of to protect plant personnel from potential health and fire hazards, and to prevent the release of the
substance to surface waters. Methods of cleanup, recovery, treatment, or disposal include:
Physical. Physical methods for cleanup of dry chemicals include the use of brooms,
shovels, sweepers, or plows. , '
Mechanical. Mechanical methods for cleanup include the use of vacuum cleaning systems
and pumps. , , , .
^ • ' •
Chemical. Chemical cleanup of material can be accomplished with the use of sorbents,
gels, and foams. Sorbents are compounds that immobilize materials by surface
absorption or adsorption in the sorbent bulk. Gelling agents interact with the spilled
chemical (s) by concentrating and congealing to form a rigid or viscous material more
conducive to mechanical cleanup. Foams are mixtures of air and aqueous solutions of
proteins and surfactant-based foaming agents. "The primary purpose.bf foams is to reduce
the vapor concentration above the spill surface thereby controlling the rate of
evaporation. . • . .
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MAINTENANCE . . ' .
A facility Spill Prevention Plan should be reviewed at least annually and following any spills to evaluate
Sie SpUl Prevention Plan's level of success and how it can be improved. Other times for significant
review of the plan should be when a new material is introduced to the plant as a result of a processing
modification, or when a change has occurred in a materials handling procedure.
COSTS
If a facility already has a SpOl Control and Cleanup Plan in^place, modifications, to address stormwater
related parameters. Costs for structural containment deuces will also need to be- identified, for each
facility. . , • .
ENVIRONMENTAL IMPACTS
Preventing or containing spills, especially toxic or hazardous materials, is important in reducing storm
water contamination and in maintaining the water quality of the receiving water.
REFERENCES • . '
1. u.S. EPA, srormwater Man?~ment for Industrial Activities: Developing Pollution Prevention Plans.
and Best Management Practices. September 1992.
2. Washington State Department of Ecology, Stormwater Management Manual for Puget Sound,
February 1992. - • .'...-,
WaMnfoH. DC, XM60.
-------
Create a map of the facility site to locate pollutant sources and determine
stormwater management opportunities. This site map should include all
surface waterbodies on or next to the site, and should also identify, if any
that are in place. Tributary drainage areas with identification of flow direction
should also bed identified during this mapping phase. Table 1 contains a list of
features that should be indicated on the site map.
Conduct a material inventory throughout the facility.
Evaluate past spills and leaks.
Identify non-stormwater discharges and non-approved connections to
stormwater facilities. '. • '.'.'-.-
Collect and evaluate stormwater quality data.
Summarize the findings of this assessment.
TABLE 1: CRITERIA FOR DEVELOPING A SITE MAP
DEVELOPING A SITE MAP
Worksheet
Completed by:
Title: ^
Date: -
Instructions: Draw a map of your site including a footprint of all buildings, structures, paved areas, and
parking lout. The information below describes additional elements
• All outfalls and storm water discharges
• Drainage areas of each storm water outfall
• Structural storm water pollution control measures, such as:
- Flow diversion structures
- Retention/detention ponds
- Vegetative swales . ' '",'".•
- Sediment trapit .
• Name of receiving waters (or if through a Municipal Separate Storm Sewer System)
• Locations of exposed significant materials
• Locations of past spills and leaks
• Locations of high-risk, waste-generating areas and activities common on industrial sites such as:
Fueling stations
Vehicle/equipment washing and maintenance areas v
Area for unloading/loading materials
- Above-ground tanks for liquid storage
- Industrial waste management areas (landfills, waste piles, treatment plants, disposal areas)
- Outside storage areas for raw materials, by-products, and finished products
Outside manufacturing areas ' •
- Other areas of concern (specify:_ )
SOURCE: Reft
-------
IMTB
STORM WATER BMP:
CONTAMINATION ASSESSMENT
DESCRIPTION
A Stormier Contain A—t
v , •
, i Mi»+a,r m • nrVim- BMP's such as materials inventory, non-stormwater
^^ * effective these, and oth* BMP, should be
incorporated into a comprehensive pollution preventum program. -
APPLICATIONS
purposes is being performed.
^IMITATIONS .
Limitations associated with a contamination assessment program include:
Assessments need to be performed by qualified personnel.
A corporate commitment must exist to reduce the contamination '
sources once discovered.
Assessments need to be periodically updated. •
PERFORMANCE .
pollutant capabilities will result in positive water quality benefits.
DESIGN CRITERIA
A SWCA program should include the following key activities:
Assess potential pollutant sources and associated high risk Activities such
as loading and unloading operations, outdoor storage activities, °"tdo°r
manufacturing or processing activities, significant dust or parnculate-generatmg
'•' activities, and on-site waste disposal practices.
-------
Once you have completed the above steps in your pollutant source assessment, you have enough
information to .determine which areas, activities, or materials are a risk towards contributing pollutants
to stormwater runoff from your site. An important benefit is that by using this information, you can
effectively select other cost-effective BMPs to prevent or control pollutants.
IMPLEMENTATION
In addition to identifying problems within the storm sewer system, it is even more important to prevent
problems from developing at all, and to provide an environment in which future problems can be
avoided, thus, an effective stormwater assessment program should include implementation activities to
insure success and follow-up activities to measure results. Keys to a successful implementation program
should include:
Public education, on organized systematic program of disconnecting commercial and
industrial stonmwater entries into the storm drainage system.
Tackling the problem of widespread septic system failure.
Disconnecting direct sanitary sewerage connections.
Rehabilitating storm or sanitary sewers to abate contaminated
, . water infiltration.
. Developing zoning and other ordinances. -
In extreme cases, it may be that while it was thought that a community had a separate sanitary sewer
system and a separate storm sewer system, in reality the storm sewer system is acting as a combined
sewer system. In these cases, consideration should be given to .the economic and practical advantages of
designating the storm sewer system a combined sewer and applying end-of-pipe treatment to the entire
system. : •
A SWCA program needs to be periodically updated. Updating is especially important upon the
introduction of new raw materials or changes in processes at the site.
It is also important to establish parameters for measuring the success of the correction program. If
results do not meet expectation, then reassessment and appropriate changes to the correction program
should be made. ' ~ •••'
COSTS
Costs for the initial assessment may be high. However, by pinpointing high potential areas or activities a
SWCA program may reduce overall costs associated with a complete BMP implementation program. The
costs associated with an assessment program for stormwater.are small when compared to or a part of a
larger overall hazardous waste site assessment. ,
ENVIRONMENTAL IMPACT
A comprehensive SWCA program can eliminate pollution sources that can significantly impair receiving
water quality. •. •••'.•
-------
REFERENCES ' , ' , . . .". . .
1. TI-S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans'.
and Best Management Practices. September 1992. •
2. U.S. EPA, NPDES Best Management Practices Guidance Document. June 1981.
3 Pitt Robert, Barbe, Donald; Adrian, Donald, arid Field, Richard, Investigation of Inappropriate
Pollutant Entries into Storm Drainage System - A User's Guide. U.S. EPA, Edison, New Jersey, 1992.
US EPA. 401MS**,.SW. W
-------
IMTB
STORM WATER BMPs
VEGETATIVE COVERS
Ofto of Watewator Bfcrcawrt 6 «"
MUNICIPAL TECHNOLOGY ICANCH
DESCRIPTION
This Best Management Practice (BMP) involves preserving existing vegetation or revegetating disturbed
son as soon as possible after land disturbance activities in order to control erosion and dust. Vegetative
covers include sod, temporary and permanent seeding and other vegetative covers, as well 'as
preservation of existing vegetation. Sod is a strip of permanent grass cover placed over disturbed areas
to provide an immediate and permanent turf that both stabilizes the soil surface, and-eliminates sediment
due to erosion, mud, and dust. Temporary vegetative cover involves planting grass seed immediately
after rough grading to provide protection until establishment of final cover.. Permanent vegetative cover
is the establishment of perennial vegetation in disturbed areas. Preservation of natural vegetation
(existing trees, vines, bushes, and grasses) provides a natural buffer zone during land disturbance
activities. . , ,
Vegetative covers provide dust control and a reduction in erosion potential by increasing infiltration,
trapping sediment, stabilizing the soil, and dissipating the energy of hard rain. Application of mulch
may be required for seeded areas. Mulch is the application of plant residues or other suitable materials
to the soil surface to protect the soil surface from rain impact and the velocity of stormwater runoff.
APPLICATIONS
Vegetative covers are applicable to all land uses. Soils, topography, and climate wffl be determinants^ in
the selection of appropriate tree, shrub, and ground cover species. Local climatic conditions determine
the appropriate time of year for planting. Temporary seeding should be performed on areas disturbed by
construction left exposed for several weeks or more. Permanent seeding and planting is appropriate for
any graded or cleared area where long-lived plant cover is desired. Some areas where permanent
seeding is especially important are filter strips, buffer areas, vegetated swales, steep slopes,.and stream
banks. Design criteria for vegetative Covers is included in Table 1 below. ••.-,.
LIMITATIONS . .
Limitations of vegetative covers as a BMP include:
The establishment of vegetative covering must be coordinated with climatic
conditions for proper establishment. For example, cold climate areas have
limited growing seasons and arid regions require careful selection of species.
The key to proper performance is implementation of a maintenance program to
ensure healthy vegetative covering.
PERFORMANCE
Qualitatively, vegetative covers are clearly effective in controlling dust and erosion when properly
implemented, the amount of runoff generated from vegetated areas is considerably reduced and is of
better quality than from unvegetated areas. However, it is not possible, based on data currently
available, to quantify the water quality benefits of the vegetative .coverings as a BMP. '^
-------
-------
TABLE!; DESIGN CRITERIA FOR VEGETATIVE COVERS
Measure
Temporary
Seeding
'
Permanent
Seeding,
.
iOt/RCE: Refe
Extent and
Material
Place topsoil as
needed to
enhance . plant
growth. A loamy
soil with an
organic content
of 1.5 percent or
greater is
preferred. Use
rapid-growing
annual , grasses,
small grains, or
legumes. Apply
seeds using a
cyclone seeder,
drill, cultipacker
seeder, or
hydro seeder.
Place topsoil as
needed to
enhance plant
growth. A loamy
soil, with an
. organic content
. of 1.5 percent or
greater is
preferred.
Where possible,
use low
maintenance
local plant
species. Apply
seeds using a
cyclone seeder,
drill, cultipacker
seeder, or
hydroseeder.
mctl.
Dimensions
Place topsoil,
where needed,
to a minimum
compacted
depth of 2
inches, on 3:1
slopes or
steeper; and of
4 inches on
flatter slopes.
Apply mulch to
slopes 4:1 or •
steeper, if soil is
sandy or clayey
or if weather is
excessively hot
or dry. Place
topsoil where
needed.
, .
Hydraulic
Divert .
channelized flow
away from
temporarily
seeded areas to
prevent erosion
and scouring.
Divert
channelized flow
away from
seeded areas to
prevent erosion
and scouring.
' -
Avoid
Heavy clay .or
organic soils as
topsoil. . Hand-
broadcasting of
seeds (not
uniform), except
in .very small
. areas. Mowing
temporary
vegetation.
High-traffic
areas.
"• .
Heavy clay or
organic soils as
, topsoil. Hand-
broadcasting of
seeds (not
uniform), except
in very small
.areas. High
traffic areas.
. . '
Miscellaneous
Use where
vegetative cover
is needed for less
than 1 year. Use
'chisel plow or .
tiller to loosen
compacted soils.
As needed, apply
water, fertilizer,-..
lime, and mulch.
Incorporate lime
and fertilizer
into top 4-6
inches of soil.
Plant small
grains,' 1 inch
deep. Plant
grasses and
legumes 1/2-inch
deep.
Use chisel plow
or tiller to loosen
compacted soils.
As needed, apply
water, fertilizer,
lie, and mulch.
Incorporate lime
and fertilizer
into top 4-6
inches of soil.
Plant small
grains 1 inch
deep. . Plant
grasses and
legumes 1/2-inch
deep.
-------
TABLE 1: DESIGN CRITERIA FOR VEGETATIVE COVERS
(Continued)
Measure
Extent and
Material
Dimensions, Hydraulic
Avoid
Miscellaneous
Mulching
Prefer Organic
mulches such as
straw (from
wheat or oats),
wood chips, and
shredded bark.
Commercial
mats and fabrics
may also be very
effective.
Chemical soil
stabilizers or
binders are less
effective, but
may be used to
tack wood fiber
mulches.
Application,
rates (per acre):
straw, one to
two tons; wood
chips, five to six
tons; wood
fiber, 0.5 to one
ton; bark, 35
cubic yards;
asphalt (spray),
0.10 gallon pel-
square yard.
After spreading
much, less than
25 percent • of
the ground
surface should*
be visible.
Mulch may be
. applied by
machine or by
hand. Chemical
mulches .and
wood fiber
mulches, when
used alone, often
do not provide
adequate soil
protection. Use
'nets or mats in
areas subject to
water flow.
Anchor mulch by
• punching into
soil, or by
applying
chemical agents,
..nets, or mats.
?Secure nets and
mats with 6
inches or longer.
No. 8 gauge or
heavier, wire
staples placed at
3-foot intervals
SOURCE. Rtfacncxl.
-------
TABLE 1: DESIGN CRITERIA FOR VEGETATIVE COVERS
(Continued)
Measure
Extent and
Mateirial
Dimensions Hydraulic
Avoid
Miscellaneous
Sodding
Sod should be
machine-DUt at a
uniform
thickness of 1/2
to 2 inches.
In waterways,
select plant
types able to
withstand design
flow velocity.
Gravel or nonsoil
surfaces.
Unusually wet or
dry weather.
Frozen soils.
Mowing for at
least two to three
Preservation
Natural
Vegetation
of
Careful planning Wherever
is required prior ' possible, .
to start of maintain
construction. existing
contours.
Maintain
existing
hydraulic
characteristics.
Activities within
the drop line of
trees.
Concentrating
flows at new
locations.
be
and
Prior to laying
sod, clear soil
surface of debris,
roots, branches,
and stones
bigger than 2
inches in
diameter. Sod
should
harvested,
delivered,
installed within
36 hours. Lay
sod with
staggered joints
along the
contour. Lightly
irrigate soils'
before sod
placement
during dry or hot
periods. After
placement, roll
sod and wet soil
to a depth of 4 ,
inches. On
slopes steeper
than 3:1, secure
sod with stakes.
In waterways,
lay • . sod
perpendicular to
water flow.
Secure sod with
stakes, wire, or
netting.
Preservation of
vegetation
should be
planned before
any site
disturbance
begins. Proper
maintenance is
vitally
important.
Clearly mark
areas to be
preserved.
SOURCE; Rife
-------
MAINTENANCE , .'._'•'
Areas should be checked following each rain to ensure that seed sod, and mulch have not 'been
displaced Staking the sod or netting for seeded areas may be required.
staking, or improper placement of sod pieces.
before repeating seed bed preparation and seeding procedures.
one. . ve^v. cover h.
small and damaged areas.
COSTS
^^
very depending on local conditions.
TABLE 2: INSTALLATION COSTS
Description
Level
>400 square yards
100 square yards
50 square yards
Slopes
400 square yards
Mechanical Seeding .
Pine Grade/Seed
Push Spreader
Grass Seed
Limestone
Fertilizer
Level Areas
Sloped Areas
Hay
Unit
Square yard
Square yard
Square yard
Square yard
Acre
Square yard
Square yard
1.000 square
feet
1.000 square
fut;t
1.000 square
feet
Acre
Acre
Acre
Square yard
Material
$0.98
•1.36
1.95
1.03
$410.00
0.08
0.15
$8.60
2.05
5.40
578.21
578.21
$255.76
Labor
$0.85
1.07
1.14
1.19
$435.00
0.09
0.85
$0.67
0.67
0.67
149.30
238.88
$74.65
Equip-
ment
$0.17
0.22
0.23
''. 0,24
$165.00
• 0.03
0.17
S&.26
0.26
0.26.
• 80.63
129.00
$40.31
Indirect
, Cost
$0.56
0.70
0.80
0.72
$290.00
0.06
0.48
$1.22
0.58
0.92
251.00
328.75
$118.50
NOTE: Total cost includes operation and maintenance, taxes, insurance and
Total
Cost
$2.56
3.35
. 4.12
3.18
$1.300.00
0.26
1.65
$10.75
3.56
7.25
1,059.14
1,274.84
$489.22
0.58
0.25rl.OO
Year of
Cost
January
1989
January
1989
January
1989
Mid- 1988
Mid- 1988
1983,
Comment*.
^.^•.••.^•M^^
1
Includes
fertilizer
and lime
..
.--
Average
Typical
range
other contingencies.
900*3: ModiBed from Rzfertnce 4. • • ^ ^^
-------
ENVIRONMENTAL IMPACTS
None for proper installation of vegetative covers. However, care must be taken to avoid contamination
of run off and ground water from over use of fertilizers, weed control herbicides and other hazardous
chemicals.
REFERENCES
1. Hennepin Conservation District, Minnesota, Erosion and Sediment Control Manual. 1989.
2. Metropolitan Washington Council of Governments, Controlling Urban Runoff: A Practical
Manual for Planning and Designing Urban BMPs. 1987.
3. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas. 1989.
4. Southeastern Wisconsin Regional Planning Commission, Costs of Urban Nonpoinf Source
Water Pollution Control Measures. Technical Report No. 31, June 1991. .
5. U.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution
Prevention Plans and Best Management Practices. September,1992. ,
6. Washington State Department "of Ecology, Stormwater Management Manual for the Puget
Sound Basin. February 1992. - . • • .
TKi BMP fact +** vaspKpatd by Ac ttuiiapal Toduuicy Bmdi (4204), VS EPA. 401 MSeeo. SW, WaMnfon. DC, 20460.
-------
MTB
Offce of Watowatar Erforcwnent & < ,
JlUNIC JFAtTiCHNO LOST l'«ANCHv
STORM WATER BMP:
VEGETATED SWALES
DESCRIPTION
Vegetated swales are natural or man made, broad, shallow channels with a dense stand of vegetation
covering the side slopes and main channel. Vegetated swales trap participate pollutants (total suspended
solids and trace metals), promote infiltration, and reduce the flow velocities of stormwater runoff.
Figure 1 below illustrates an example of a vegetated swale. •
Vegetated swales can serve as an integral part of an area's minor stormwater drainage system by
replacing curbs and gutters and storm sewer systems in low-density residential, industrial, and
commercial areas. The swale's advantages over a storm sewer system generally include reduced peak
flows increased pollutant removal, and lower capital costs. However, vegetated swales typically have a
limited capacity to accept runoff from large storm, since high velocity flows can cause erosion of the
swale or damage the vegetated cover.
3.1 or Lam
SwXcSlap*
RaOrandlte
Cluck Own to
IneniM taf ikration
Hoto
SOURCE: Reference 1.
Stonae Praw>m
Dowmtrawn Scour
FIGURE 1: EXAMPLE OF A VEGETATED SWALE.
COMMON MODIFICATIONS ,
The effectiveness of vegetated swales can be enhanced by adding check dams approximately every 50
feet to increase storage, decrease flow velocities, and promote paniculate settling. Structures to skim ott
floating debris may also be added. Incorporating vegetated filter strips parallel to the top of the channel
banks can also help to treat sheet flows entering the swale.
CURRENT STATUS
Vegetated swales are relatively easy to design and incorporate into a site drainage plan. While -swales
are not generally used as a stand alone Stormwater Best Management Practice (BMP),; they are very
effective when used in conjunction with other BMP's such as wet ponds, infiltration strips, wetlands, etc.
-------
APPLTCATTONS .
Vegetated swales can, be used in all regions of the country where climate and soils permit the
establishment and maintenance of a dense vegetative cover. The suitability of a vegetated swale at a
particular site depends on the area, slope, and imperviousness of the contributing water shed, as well as
the dimensions, slope, and vegetative covering employed in the swale system.
GENERAL LIMITATIONS x
The limitations of vegetated swales include: ,
Vegetated swales are generally impractical in areas with very flat grades, steep
topography, or wet or poorly drained soils. .
Swales provide minimal water quantity and quality benefits when flow volumes and/or
velocities are high.
Swales may pose a potential drowning hazards, create mosquito breeding areas, and cause
odor problems. .
. The use of vegetated swales may be limited by the availability of land.
Many local municipalities prohibit the use of vegetated swales if peak discharges exceed
five cubic feet per second (cfs) or flow velocities'are greater .than three feet per second
. Cfps). .
t ' ' • ' , • ' '' ' ' , -
Vegetative swales are generally impractical in areas with erosive'soils or where a dense
vegetative cover is difficult to maintain.
Certain quantitative aspects of vegetated swales are not known at this time. These
include whether pollutant removal rates of swales decline with age, the effect of slope on
the filtration capacity of vegetation, the .benefit of check dams, and the degree to which
design factors can enhance the effectiveness of pollutant removal.
PERFORMANCE
Conventional vegetated swale designs have achieved mixed results in removing particutate pollutants,
such as suspended solids and trace metals. For example, three grass swales in the Washington, DC, area
were monitored by the Nationwide Urban Runoff. Program (NURP). NURP found no significant
improvement in urban runoff quality for the pollutants analyzed., However, the weak performance of
these swales was attributed to the high flow velocities in the swales, soil compaction, steep slopes, and
short grass height. A Durham, NC, project monitored the performance of a carefully designed artificial
swale that received runoff from a commercial parking lot. The project monitored 11 storm and
concluded that particufate concentrations of heavy metals (Cu,Pb,Zn, and Cd) were reduced by
approximately 50 percent. However, the swale proved largely ineffective for removing soluble nutrients.
A conservative estimate is that properly designed vegetated swales may achieve a 25 to 50 percent
reduction in particulate pollutants, including sediment and sediment-attached phosphorus, metals, and
bacteria. Lower removal rates Qess than 10 percent) can be expected for dissolved pollutants, such as
soluble phosphorus, nitrate, and chloride.- .. ;.
The literature suggest that vegetated swales represent a practical and potentially effective technique for
control of urban runoff quality. While limited quantitative performance data exists for vegetated swales,
some known positive factors for pollutant removal are check dams, flatter slopes, permeable soils, dense
grass cover, longer contact time, and smaller storm events. Negative factors include compacted soils/
short runoff contact time, larger storm events, frozen ground, short grass heights, steep slopes, and high
runoff velocities and discharge rates. . • .. . . '
-------
The useful life of a vegetated swale system is directly proportional to the effectiveness and frequency of
maintenance. If properly designed and regularly maintained, vegetated swales can last an indefinite
period of time.
DESIGN CRITERIA
Although specific quantitative performance data for vegetated swales is limited, design criteria have been
established for implementation of the vegetated swales'and is presented below.
Location. Vegetated swales are typically located along property boundaries, although they
can be used effectively wherever the site provides adequate space. Swales can be used in
place of curbs and gutters along parking lots. .
Soil Requirements. Gravelly and coarse sandy soils that cannot easily support dense
vegetation should be avoided. If available, alkaline soils and subsoils should be used to
promote the removal and retention of .metals, Soil infiltration rates should be greater .
than one-half inch per hour, therefore, care must be taken to avoid compacting the soil
• during construction.
Vegetation. Fine, close-growing, water-resistant grass should be selected for use in
vegetated swales. Dense vegetation maximizes water contact, improving the effectiveness
of the swale system. The vegetation should be selected on the basis of pollution control
' objectives and the ability to thrive in the conditions present in the conditions present at
the site. Some examples of vegetation appropriate for swales include reed canary grass,
grass-legume mixtures, and red fescue.
General Channel Configuration. It is recommended that a parabolic or trapezoidal
cross-section with side slopes no steeper than 3:1 be used, maximizing the wetted,
channel perimeter. Recommendations for longitudinal channel slopes vary within the
existing literature. For example, Shuler (1987) recommends a vegetated swale slope as
close to zero as drainage permits. The Minnesota Pollution Control Agency (19893
• recommends that the channel slope be less than 2 percent. The Stormwater Management
Manual for the Puget Sound Basis (1992) specifies channel slopes between 2 and 4
percent; slopes of less than 2 percent can be used if drain tile is incorporated into the
design, and slop.es greater than 4 percent can be used if check dams are placed in the
channel to reduce flow velocity. .
Drainage Area. The maximum flow rate' (Q) to the swale can "be calculated using the
Rational Formula, depending on the size of the drainage area (A), the percentage of the
drainage area that is impervious (C) and the rainfall intensity (I) for the design storm.
Q = CiA
A typical design storm used for sizing swales is a six-month frequency, 24- hour storm
event. The exact intensity must be calculated for your location and is generally available
from the US Geological Survey (USGS). Swales are generally not used where the
maximum flow rate exceeds 5 cfs.
• Sizing Procedures. The width of the swale can be calculated using various forms of the
Sing equation. However, this methodology can be simplified to the following rule of
thumb: the total surface area of the swale should be 500 square feet for each acre that
drains to the swale.
Unless a bypass is provided, the swale must be sized as both a treatment device and to
pass the peak hydraulic flows. But to be most effective as a treatment device, the depth
of the stormwater should-not exceed the height of the grass in the swale.
-------
Design Parameters. Based on limited research, swales can generally be designed using the
following parameters: v . .
1. Minimum grass height of finches (Figure 2).
2. Maximum depth of stormwater during, the design storm of 4 inches
(Figure 2).
3. Maximum flow in the swale of 5 cfs.
4. Maximum velocity in the swale of 3 fps.
5. Channel slope between 2 and 5 percent. ...
- Slopes of less than 2 % can be used if the-swale is drained to
prevent ponding (Figure 2). ••••.,'
- Slopes of more than 5 % can be used if check dams are placed
in lie swale to maintain channel velocity below 3 fps
(Figure 2). • .
6. To provide maximum long term treatment effectiveness, the swale width
/should be calculated using a design, flow of 0.2 cfs per acre of area
- draining into the swale. However, the minimum width is 18 inches.
7. If a by-pass is not provided, the channel width and/or height should be
increased, if needed, to pass peak hydraulic flows.
8. In order to provide adequate treatment, the swale should have a
minimum length of 200 feet.. If a shorter length must be used, the
width should be .increased proportionally to maintain a treatment
surface area of at least 500 square feet; as discussed above.
However, the minimum length is 25 feet.
tar«-Mffft
SOURCE: Reference 3.
ft.. j?%..
•T- • -«i^rs
r
I—
(iniuttnm
> NMCft
3*w. •'
! t-OMCt
^••BnM ' *•»•
FIGURE 2: DESIGN PARAMETERS
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Construction. The subsurface of the swale should be carefully constructed to avoid
compaction of the soil. Compacted soil -reduces the infiltration and inhibits growth of the
grass. Damaged a;., -as should be restored immediately to ensure that the desired level of
treatment is maintained and to prevent further damage due to erosion of exposed soil.
Check Dams. Check dams can be installed in swales to promote additional infiltration,
increase storage, and reduce velocities. The check dam may be a railroad tie embedded
into the swale with riprap placed on the downstream side of the tie to prevent a scour
hole' from forming. Earthen check dams are not recommended because of their potential
to erode. Check dams should be installed every 50 feet if longitudinal slope exceeds 4
percent. '
MAINTENANCE . ...... '• ,
The primary swale maintenance objectives are to maintain the hydraulic efficiency of the
maintain a dense, healthy grass cover. Maintenance activities should include periodic mowing (wm
^S^vi cuf shorter ttaf*. design flow depth),,Weed control, watering during .drought condmons
Ceding bare areas, and clearing of debris and blockages. Cuttings, should be removed from the
channel and disposed in a local composting facility. Accumulated sediment should be removed
periodically. Application of fertilizers and pesticides should be minimal, if required.
Research has not yet identified proper mowing strategies. However, mowings during the spring a*d
summer should keep the grass at the 6" design height. In some commercial applications where £ may
cause an aesthetic problem the grass can be cut to 4" but the last mowing of the season should not be
bdowT". MowSgPencourag.s gSwth thereby improving the removal of soluble pollutants. The .find
mowing should occur near the end of the growth season. Failure to remove the growth before the
dormant season will cause a loss of pollutants back to the stormwater.
Any damage to the channel such as rutting must be repaired with suitable soil, properly tamped and
seeded. The grass cover should be thick; if it is not reseeding as necessary.
Any standing water removed during the maintenance operation must be disposed to a sanitary sewer at
an approved discharge location. Residuals (ie, silt, grass cuttings, etc.) must be disposed ,of m
accordance with local or state requirements.
COSTS
Veeetated swales typically cost less to construct than curbs and gutters or underground storm, sewers
ShSS OSS ) reputed Lt costs may yary from $4.90 to $9.00 per lineal foot for a 15-foot wide
channel (top width).
The Southeastern Wisconsin Regional Planning -Commission (SEWRPC) reported that _cosK .may v*ry
from $8.50 to $50.00 per lineal foot depending upon swale depth and bottom widtfi (1991). The
SEWRPC cost estimates are higher than other published estimates because ^ *clu*'±*
acrivSes such as clearing, grubbing, leveling, Ming, and sodding, which may not be included m
of the reported costs. Construction costs depend on specific site considerations and local costs for labor
and materials. The Table 1 below shows estimates capital cost of a vegetated swale. .
Annual costs associated with maintaining vegetated swales are approximately $0.58 per -lineal [
Soot deep channel, according to SEWRPC (1991). Estimated average annual operatmg and
maintenance costs of vegetated swales can be estimated using Table 2 below. , , .
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TABLE 1: ESTIMATED CAPITAL COSTS
r
2 to
1
SOURCE: Reference 4,
a j • «
SWA1E DEPTH IN FEET
TABLE 2: ESTIMATED O & M COSTS
I .' 3
SWALE DEPTH IN FEET
SOURCE: Reference 4,
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ENVIRONMENTAL IMPACTS .
Negative environmental "impacts of vegetated swales may include:
Leaching from culverts and fertilized iawns may increase the presence of trace
metals and nutrients in the runoff.
.Infiltration through the swale may affect local groundwater quality.,
Standing water in vegetated swales can result in potential safety, odor, and
mosquito problems.
REFERENCES . .
1. U.S. EPA, A Current Assessment of Best Management Practices; Torhniques for Reducing Nonpoint
Source Pollution in the Coastal Zone, December 1991.
2. Minnesota Pollution Control Agency. Protecting Water Quality in Urban Areas, 1991.
3. Shuler. Thomas R., Controlling Urban Runoff. A Practical Manual for Planning and
' Designing Urban BMPs. Julv 1987. ,
4. Southeastern Wisconsin Regional Planning Commission, Post nM Irhar, Nonpoint Source
Water Pollution Control Measures, Technical Report No. 31. 1991.
5. U.S. EPA, Stormwater Management for Industrial Activities: TWriopinff Pollution Prevention
Plans and Best Management Practices. September 1992. , •
6. U.S. EPA, Results of the Nationwide Urban Runoff Program December 1983.
7. Washington State Department of Ecology, Stnmwater Mana^nr Manual for the Puget Sound
, Februaru 1992. '
.pnp** by* M»uc^/ T^dogf BmnA (W). US EPA. «1 M S~« SW. Wo****. DC X»*
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iMTB
STORM WATER BMP:
VISUAL INSPECTIONS
Offae of WastavngtBT B luvans 14« ,
MUNICIPAL TECHNOLOGY iSANCH
DESCRIPTION
Visual inspection is the process by which'members of a Stormwater Pollution Prevention Team (SWPPT)
visually inspects stormwater discharge from material storage and outdoor processing areas to identify
contaminated stormwater and its possible sources. ,
An example of a visual inspection is examination within the first hour of a.storm event that produces
significant stormwater runoff for the presence of floating and suspended materials, oil and grease,
discolorations, turbidity, odor, or foam. Another example would be to examine a raw materials storage
area where materials are stored in 55-gallon drums and look for leaks, discolorations, or other
abnormalities that may cause a pollutant to contaminate stormwater runoff.
CURRENT STATUS .
The U.S. EPA has recognized visual inspections as a baseline Best Management Practice (BMP) for over
10 years. Its implementation across the country, however, has been sporadic. Stormwater Pollution
Prevention Plan (SWPPP) development will increase implementation of visual inspections in the future as
facility management recognizes it to be an effective BMP from a water quality and cost savings
perspective. .
LIMITATIONS
Limitations associated with visual inspections include: .
Inspections are limited to those areas clearly visible to the human eye .
. . Visual inspections need to be performed by qualified personnel
Lack of a corporate commitment to actively implement inspections on a
routine basis - .
Inspectors need to be properly motivated to perform a thorough visual . .
inspection.
PERFORMANCE
The performance of visual inspections'as an effective tool in reducing stormwater runoff contamination
is highly variable and dependent upon site-specific parameters such as industrial activity occurring at the
facility, maintenance procedures, and employees. Currently there is no quantitative data regarding the
effectiveness of visual inspections as a BMP.
DESIGN CRITERIA
Visual inspections should be performed routinely for the presence of non-stormwater discharges. Flows
during a dry period should be observed to determine the presence of any dry weather flows, stains,
sludges, odors, and other abnormal conditions. ...
-------
Visual inspections should be made of all stormwater discharge outlet locations during the first hour of a
storm event that produces a significant amount of stormwater runoff. In geographic locations with a
high frequency of-storm events, inspections should be performed at least once per month. Inspection for
the presence of floating and suspended materials, oil and grease, discolorations, turbidity, foam, and
odor should be performed. . . .
The inspection frequency interval is a key design criterion in a visual inspection program. To determine
the inspection frequency, experienced personnel should evaluate the causes of previous incidents and
assess the probable risks for occurrence in the future. Conditions in the stormwater discharge permit
may also dictate inspection frequency. ,
Another key design criterion is proper record keeping of an inspection. .Record keeping should include
the date of the inspection, the names of the personnel who performed the inspection, and the
observations made during the inspection. Records should be forwarded to appropriate personnel
through an internal reporting system. Remedial modifications to a facility can then be. implemented
based on documented inspections. '",•...
Visual inspections of a facility should focus on the following key areas:
Storage facilities ' 1, '
Transfer pipelines , •
Loading and unloading areas
Pipes, pumps, valves, and fittings
Internal and external inspection for tank corrosion
Wind blowing of dry chemicals .
Tank support or foundation deterioration
Deterioration of primary or secondary containment facilities
Damage to shipping containers .
Wind blowing of dry chemicals and dust particles
Integrity of stormwater collection system
v*
Leaks, seepage, and overflows from sludge and waste disposal sites -
IMPLEMENTATION
A visual inspection BMP program should be incorporated within the facility's record keeping and internal
reporting BMP structure. Estimates of outfall flow rates, and noting the presence of oil sheens
floatables, coarse solids, color, odors, etc. will probably be the most useful indicators of potential
problems. Specific parameters to look for in completing a visual inspection include:
Odor--The odor of a discharge can vary widely and sometimes directly reflects the source
of contamination. Industrial discharges will often cause the flow to smell like a
particular spoiled product, oil, gasoline, specific chemical, or solvent. As an
example, for many industries, the decomposition of organic wastes in the discharge
will release sulfide compounds into the air above the, flow in the sewer, creating an
intense smell of rotten eggs. In particular, industries involved in the production of
meats, dairy products, and the preservation of vegetables or fruits, are commonly
found to discharge organic materials into storm drains. As these organic materials
-------
sp6il and decay, the sulfide production creates this highly apparent and
unpleasant smell. Significant sanitary wastewater contributions will also cause
pronounced and distinctive odors. • .
Color-Color is another important indicator of inappropriate discharges, especially from
industrial sources. Industrial discharges may be of any .color. Dark colors, such as
brown, gray, or black, are most common. For instance, the color contributed by
meat processing industries is usually a deep reddish-brown. Paper mill wastes are
.also brown. In contrast, textile wastes are varied. Other intense colors, such as
plating-mill wastes, are often yellow. Washing of work areas in cement and stone
working plants can s\cause cloudy discharges. Potential sources causing various
colored contaminated waters from industrial areas can include process waters (slug
or continuous discharges), equipment and work area cleaning water discharged to
floor drains, spills during loading operations (and subsequent washing of the ,
material into the storm drains). ,
Turbidity-Turbidity of water is often affected by the degree of gross contamination.
Industrial flows with moderate turbidity can be.cloudy, while highly turbid flows can be
opaque. High turbidity is often a characteristic of undiluted industrial discharges, such as
those coming from some continual flow sources, or some intermittent spills. Sanitary
wastewater is also often cloudy in nature.
Floatable matter--A contaminated flow may also contain floatables (floating solids or
liquids). Evaluation of floatables often leads to the identity of the source of industrial or
sanitary wastewater pollution, since these substances are usually direct products or
byproducts of the manufacturing process, or distinctive of sanitary wastewater. Floatables
of industrial origin may include substances such as animal fats, spoiled food products,
oils, plant parts,, solvents, sawdust, foams, packing materials, or fuel, as examples.
Deposits and Stains-Deposits and stains (residue) refer to any type of coating which
remains after a non-stormwater discharge has :ceased. They will cover the area
surrounding the stormwater discharge and are usually of a dark color. Deposits and
stains often will contain fragments of floatable substances and, at times, take the form of
a crystalline or amorphous powder. These situations are illustrated by the grayish-black
deposits that contain fragments of animal flesh and hair which often are produced by
leather tanneries, or the white crystalline powder which commonly coats sewer outfalls
due to nitrogenous fertilizer wastes. ,
Vegetation-Vegetation surrounding a stormwater discharge may show the effects of the
wastewater. Industrial pollutants will often cause a substantial alteration in the chemical
composition and Ph of the discharge water. This alteration will affect plant growthj even
when the source of contamination is intermittent. For example, decaying organic
materials coming from various food product wastes would cause an increase in plant life.
In contract, the discharge of chemical dyes and inorganic pigments from textile mills
could noticeably decrease vegetation, as these discharges often have a very acidic Ph. m
either case, even when the cause of industrial pollution is gone, the vegetation
surrounding she discharge will continue to show the effects of the contamination.
In order to accurately judge if the vegetation surrounding a discharge is normal, the
observer must take into account the current weather conditions, as well as the time of
year in the area. Thus, flourishing or inhibited plant growth, as well as dead and
decaying plant like, are all signs of pollution or scouring flows when the condition of the
vegetation just beyond the discharge disagrees with the plant conditions near the. •
discharge. It is important not to confuse .the adverse effects of high stormwater flows on
vegetation with highly toxic flows. Poor plant growth could be associated with scouring .
flows occurring during storms. -,-.'>.
-------
Structural Damage-Structural damage is another readily visible indication of industrial
discharge contamination. Cracking, deterioration, and spalling of concrete or peeling of
surface paint, occurring at an outfall are usually caused by severely contaminated
discharge's^ usually of industrial origin. These contaminants are usually very acidic or
basic in nature. For instance, primary metal industries have a strong potential for .
causing structural damage because their batch dumps are highly acidic. Poof.
construction, hydraulic scour,"and old age may also adversely affect the condition of
structures. •
Implementation of visual inspections should be assigned to qualified staff such as maintenance personnel
oTSonmental engineers. Figure 1 provides a-sample visual evaluation worksheet which can be used
to record the results of the inspections. ,
Outfall #.
Location:
Photograph*.
Date:
Weather: air temp.: "C rain: Y N sunny cloudy
Outfall flow rate estimate: L/sec
Known industrial or commercial uses in drainage area?. Y* N
describe: . . : •
PHYSICAL OBSERVATIONS:
Odor: none sewage sulfide . oil gas rancid-sour other:_
Color: none yellow .brown green red gray other: .
Turbidity: none cloudy opaque
Floatables: none petroleum sheen sewage other: (collect sample)
Deposits/stains: none sediment oily describe:___ (collect sample)
Vegetation conditions: normal excessive growth inhibited growth
extent: '-.
Damage to outfall structures: .
identify structure:
damage: none / concrete cracking / concrete spalling / peeling paint /
corrosion
other damage: : ;—:
extent: ' ; . —: •——
SOURCE: Reference 4.
FIGURE 1: VISUAL INSPECTION WORKSHEET
MAINTENANCE
Maintenance involved with visual inspections as a BMP include developing a schedule for perfonning
visual inspections and follow-up to make sure the inspections are performed on schedule. Conunual
record updates need to be performed with each inspection, and properly routed through the internal
reporting structure of a SWPPT. • .
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COSTS
Costs are those .associated with direct labor and overhead costs for staff: hours. Annual costs can- be
estimated using the example in Table 1 below. Figure 2 can be used as a worksheet to calculate the
estimated annual cost for implementing a visual inspection program. . . ' '
TABLE 1: EXAMPLE OF ANNUAL VISUAL INSPECTION PROGRAM COSTS
Tide Quantity
Stormwater Engineer 1
Plant Management 5
Plant Employees 100
Avg.
Hourly
Rate ($)
x 15
x 20
x 10
x
X .
X
Overhead*
Multiplier
2.0
2.0
2.0
Estimated
Yearly
Hours
onSW
Training
x 20
x 10
x 5
TOTAL ESTIMATED ANNUAL COST
Est.
Annual
Cost($)
. 600
2,000
10.000
$12,600
Note: Defined as a multiplier, (typically ranging between 1. and 3) that takes into account
those costs associated with payroll expenses, building expenses, etc.
SOURCE.-EPA
[( . • ......
Estimated
. Yearly
Avg. Hours
, Hourly Overhead ' • on SW
Tide Quantity Rate ($) Multiplier Training
XX X =
X X ~3t =
• '- .' ' x x -1 -. . x- •=
X X X =
TOTAL ESTIMATED ANNUAL COSt
Est
Annual
Cost($)
(AV
(Bl
fCl
fD)
u (Sum of A+B+C+D)
SOURCE: Reference 3. ' ' - • , . ' ' •
FIGURE 2: SAMPILE ANNUAL VISUAL INSPECTION PROGRAM COST WORKSHEET.
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ENVIRONMENTAL IMPACTS . . '•
Visual inspections is an effective way to identify a variety of problems. Correcting these problems can
have a significant impact on improving water quality in the receiving water.
REFERENCES ' , ;.
Prnrrfti— A-"T gfaff Proposal for Modification to Water Quality
™.«» Dis^e P 1^*™** for Dfachmw of Sformwater Associated.
, Manuring Promm and Reporting Requirements,
August 17. 1992.
2. TT.p. EPA. NPDES BMP Guidance Document.. June 1981.
^ ' TT c -PDA gtnrrmMtEr ManageiP^ for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September 1992.
4 Pitt
4' pS
1992.
Robert- Barbe Donald; Adrian, Donald, and Field, Richard, Investigation of Inappropriate
nr K^s in" «^i nr.in^e Sv*™ - A users euide. U. S. EPA, Edison, New Jersey,
. US EPA. 401 MSma, SW, WiMxfcn. DC. 20460.
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In order for the Municipal Technology Branch to be effective in'meeting your
needs, we need to understand what your needs are and how effectively we are
meeting them. Please take a few-minutes to tell us if this document-was helpful in
meeting your needs, and what other needs you have concerning wastewater
treatment, water use efficiency, or reuse.
Indicate how you are best described:
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Name and Phone No. (optional) •
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We thank you for helping us serve you better. To return this questionnaire,
tear it out, fold it, staple it, put a stamp on it and mail it.' Otherwise, it may be
faxed to 202-260-0116 ,
MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS:
STORM WATER BEST MANAGEMENT
Office of Wastewatar-ErfarBigit & Camptsix^^i^C WA.mrvfi
MUNJCIPAL TECHNOLOGY BRANCH^-" - riU\V*llV^o
-------
STAPLE HERE
FOLD HERE
Municipal Technology Branch (4204)
United States Environmental Protection Agency
401 M Street, SW
Washington, DC, 20460
- FOLD HERE
-------
ADDENDUM TO
MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS
STORM WATER BEST MANAGEMENT PRACTICES
EPA-832-F-93-013
September, 1994
Prepared by the Municipal Technology Branch
United States Environmental protection Agency
Office of Water, Washington, D.C.
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PREFACE
This document is part of a series of municipal wastewater
management fact sheets. These fact sheets are intended to. serve
a wide audience including: the consulting engineer who is looking
for basic technical information on technologies; the municipal
engineer who must understand these technologies well enough to
evaluate! the assets and limitations; the municipal official who
must sell the, technologies as part of a comprehensive pollution
prevention program; the state regulator who must approve the
technologies used to meet permit requirements; and ultimately the
citizen who must understand the importance of preventing ,
pollution of the Nation's waters.
The material presented is .guidance for general information only.
This information should not be used without first obtaining
competent advice with respect to its suitability to any general
or .specific application. References made in this document to any
specific method, product or process does not constitute or imply
an endorsement, recommendation or warranty by the U.S.
Environmental Protection Agency.
Municipal Wastewater Management Fact Sheets are divided into
several sets: Wet Weather Flow Management Practices; Innovative
and Alternative Technologies; Biosolids Technologies and
Practices; Wet Weather Technologies; Water1 Conservation, etc.
Each set is published separately starting with Storm Water Best
Management Practices, September, 1993 (EPA 832-F-93-013).
Updates to this set of fact sheets and development of additional
sets is dependent upon continued -resources, being available.
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ADDENDUM
TABLE OF CONTENTS
Introduction
Fact Sheets—Storm Water Best Management Practice
1. Airplane Deicing Moid Recovery Systems
2. Infiltration Trenches
3. Sand Filters
4. Vortex Solid Separators
5. Water Quality Inlets
6. Wet Detention Ponds
Customer Questionnaire
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INTRODUCTION
Storm water runoff is part of a natural hydrologic process.
However, human activities, particularly urbanization, can alter
drainage patterns and add pollution to the rain water and snow
melt that runs off the earth'a s surface and enters our Nation's
rivers, streams, lakes, and coastal waters. A number of recent
studies have shown that storm water runoff is.a major source of
water pollution as indicated by a decline in fish population and
diversity, beach closings or restrictions on swimming and other
water sports, bans on consumption of fish and shellfish and other
public health .concerns. These conditions limit our ability to
enjoy many of the benefits that our Nation's waters provide.
In response to this problem, the States and many municipalities
have been taking the initiative to manage storm water more .
effectively. In acknowledgement of these storm, water management
concerns, the U.S. Environmental Protection Agency (EPA) has .
undertaken a wide variety of activities, including providing
technical assistance to States and municipalities to help them
improve their storm water management programs.
This addendum contains fact sheets on storm water best management
practices (BMPs).. However, many are not stand alone BMPs, but
are most effective when combined with other BMPs in a
comprehensive storm water management plan. These BMPs are
suitable for both municipal and industrial applications and can
be used to supplement other EPA guidance documents such as Storm
Water Management for Industrial Activities; Developing Pollution
Prevention Plans and Best Management Practices (EPA 832-R-92-006)
and Storm Water Management for Construction Activities;
Developing Pollution Prevention Plans and Best Management
Practices (EPA 632-R-92-005) as well as other State or local
guidance. , • •
In order to better serve our customers and identify additional
information needs, a short questionnaire is included at the end
of this document. Please take a-few minutes to tell us if the
information in this addendum was helpful in meeting your needs
and what other needs you have concerning storm water management.
Responses can-be mailed to the.Municipal Technology Branch
(4204), US EPA, 401 M Street, SW, Washington, DC,.20460 or faxed
to (202) 260-0116.
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STORM WATER BMP:
AIRPLANE DEICING FLUID
RECOVERY SYSTEMS
Office of Wastewater Management "
MUNICIPAL TECHNOLOGY BRANCH
DESCRIFOON
Ethylene or prppylene glycol recovery is accomplished by a three-stage process typically consisting
of primary filtration, contaminant removal via ion exchange or nanofiltration, and distillation as shown in
Figure 1 below. The process technologies involved in glycol recovery have been proven in other industries
and are now being applied to spent airplane deicing fluid (ADD.
I9N CXCMMMK
0EMWAL OF DISSOLVED tOUWJ
WASTEVMTEM
CWIMDOE RUCK
Mint
.C004CtKTIUTtD
OWCOL
SOURCE: Rdf
FIGURE 1: TYPICAL AMP3LANE DEICING FLUID RECOVERY SYSTEM
The purpose of the primary filtration step is to remove entrained suspended solids from contact with
the aircraft and pavement ifrom the used ADF. The suspended solids must be removed to avoid plugging of
downstream equipment anil heat exchangers. Primary filtration is defined, as the removal of solids greater
than 10 micron in size. Primary filters employed by ADF systems may be polypropylene cartridge or bag
filters. Ion exchange may be employed to remove dissolved solids such as chlorides and sulfates. Ion
exchange removes ions from an aqueous solution by passing the wastewater through a solid material (called
ion exchange resin) which accepts the unwanted ions, while giving back an equivalent number of desirable
ions from the resin. Nanofiltration may be employed to remove polymeric additives. Nanofiltration systems
are pressure-driven membrane operations that use porous membranes for the removal of colloidal material.
-------
Colloidal material and polymeric molecules with molecular weights in excess of 500 are normally removed by
nanofllters. The requirement to remove polymer additives is dictated by the specifications of the end user
of the recovered ADF product.
The key process step in the overall ADF recycling system is distillation. Distillation is defined as the
separation of more volatile materials (in this case, water) from less volatile materials (glycol) by a process of
vaporization and condensation. Distillation is capable of recovering volaffles with little degradation,which
Is an important advantage in this application where the recovered product can be sold or recycled. Product
nurity ofany desired Jevel can theoretically be obtained by distillation, however in some cases the processing
costs may be prohibitive. In most ADF applications, the separation of water from cither.a water-ethylette
Elvcol or a water-propylene glycol mixture of ADF, employs a two stages of distillation process. This ^11
typically, remove enough water to produce a recovered ADF with a minimum of a 50% glycol content. The
requirement glycol concentration is dictated by the specifications of the end user of the recovered ADF
product. • .
COMMON MODIFICATIONS
The details of the distillation process that each vendor employs are proprietary. Design variables
include temperature; distillation column design (number of stages, type of packing, size) and reflux ratio.
Batch distillation systems are generally employed due to the variation in the composition of the influent and
the irregular supply of the feed. Secondary filtration and ion-exchange stages vary with the quality of the
influent feed and the specifications of the end-user. The temperature of distillation also varies between
ethylene glycol and propylene glycol recovery applications.
CURRENT STATUS
This fact sheet contains general information only, and should not be used as the basis for designing
an airplane deicing fluid recovery system. While the basic technologies used to recycle ethylene and propylene
elycol are well established, actual operating experience in recycling airplane deicing fluids is limited. To
date, there is only 6ne on-site application of ADF recovery operating in the United States. This is a Pilot^
operation conducted for Continental Airlines at the Denver Stapleton Airport. Another P>lot-scale ADF
operation fa currently being conducted in Canada at the L.B. Pearson Airport in Toronto. While, recovery
systems are proposed for the St. Louis, Missouri Airport and the Indianapolis, Indiana airport, these systems
are not in operation. There are also three ADF recovery systems in operation at airports in Europe: Lulea,
Sweden; Oslo, Norway; and Munich, Germany.
There are currently three vendors actively designing, testing or marketing ADF recovery systems for
use on-site at airports in North America: Deicing Systems (DIS), Glycol Specialists, Inc. (GSI), an* Canad™
Chemical Reclaiming (CCR). There are also a number of chemical waste service companies that wfllprovide
off-site processing for spent glycol for other industries. The technology and process applications of ADF are
evoTving Spidly The equipment manufacturers and the airport operators should be contacted for the currerat
state of the art information. '
APPLICATIONS
* Ethylene or propylene glycol recovery systems are generally applicable at any airport that collects
ADF with a minimum concentration of approximately 15% glycol. Spent ADF mixtures with lower glycol
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content are generally unpractical to recover via distillation, without expensive preconcentration steps such as
reverse osmosis. Dilute streams are typically discharged to municipal wastewater treatment plants, if
permitted, treated by oxidation to destroy the organics prior to direct discharge, or hauled away be a
chemical waste contractor. A number of other BMPs such as water quality inlets and oil\water separators
are being tested to demonstrate then- ability and reliability to concentrate dilute streams.
LIMITATIONS
In order for the ADF to be recovered or regenerated, it must first be collected at the airport. The
implementation of ADF collection must respond to the unique requirements of each airport. The feasibility
of glycpl recovery is dependent on the ability of the collection system to contain a relatively concentrated waste
stream without significant contamination by other storm water components. Since distillation is an energy
intensive process, it is generally not cost effective to distill and recycle waste glycol solutions at low
concentrations (< 15%). However, individual airports may have to collect and recover lower concentrations
of waste glycol solutions to satisfy requirements of their storm water NPDES permit. Remote or centralized
deicing with the containment and collection of used glycol is one method for collecting a more concentrated
used glycol. However, centralized deicing systems may be impractical for all but the largest airport
operations due to their cost and physical size. For established airports, a switch to centralized deicing systems
would present a number of operational and logistical problems. In lieu of a centralized facility, used glycol
can be collected via vacuum trucks and fluid collections containers that siphon glycol from runway aprons.
Roller sponge devices have been employed at the Toronto Airport with mixed results due to uneven surfaces.
Mixtures of ethylene and propylene glycols cannot be recovered effectively in a single batch process
because the technology currently available cannot cost effectively separate the two glycols. While there is a
market for either recovered ethylene glycpl or propylene glycol, there is little demand for a recovered blend
of both glycols by end users. 'In order to recover either ethylene or propylene glycol from spent ADF, an
airport must use one or the other, or isolate application and runoff areas. Treated separately, each type of
water-glycol mixture can then be recovered effectively via the distillation process.
DESIGN CRITERIA
There area number of important criteria that must be determined in order to properly design an ADF
system. Table 1 below list some of the key criteria. Storage and handling of process chemicals, energy
requirements, and disposal of spent chemicals and residuals generated in the recovery process must also be
carefully considered. Other factors such as site drainage, weather patterns, water quality requirements, state
and local restrictions, marketability of the recovered product, etc., will also influence the final design of the
system. .
Sodium hydroxide (NaOH) and hydrochloric acid (HCL) are required for regeneration of the ion
exchange process unit. As ii part of the recertification process, wetting agent and a corrosion inhibitor must
be added to the recovered product prior to reuse as airplane deicing fluid. While recertification and reuse
od recovered airplane deicing fluids is practiced in Europe, the Federal Aviation Administration (FAA)
currently has no recertification guideline for reuse of recovered ADF in the United States. Care should be
taken when handling these chemicals to avoid contact with skin. Eye protection should also be worn.
For the most part, energy requirements are dependent on the waste stream glycol concentration of
the fluid to be recycled and the purity required by the end user. Recovery by distillation is energy-intensive,
with nominal energy requirements being about 5.81x10* to 2.79x10* J/kg of feed (250 to 1200 BTU/lb of feed).
As the technology is refined and as operating experience grows, these costs should decrease.Flush and spent
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TABLE 1: KEY CRITERIA FOR DESIGNING AN AIRPLANE DEICING FLUID RECOVERY
SYSTEM :
• Deicing Fluid Data
- Type
- Concentration
- Total consumption per season
- Total consumption per peak-day
- Average consumption per aircraft
• Airport Operations Data
- Flights per day
- Peak Traffic Periods
• Length of deicing season
- Number of deicing days per season
• Future traffic extension plans
• Spent Fluid Data
- Volume generated
- Glycol concentration
- Contaminants
• Reuse Specifications
- Glycol concentration
- Acceptable impurities
SOURCE: References 10 and 11
wastewater are generated by recovery processes which employ ion-exchange systems. These fluids may be
disposed of, after neutralization by addition of acids or bases, to the sanitary sewer. Spent filter cartridges
maybe generated in some systems and may be disposed of to landfills. Distillation condensate, with less than
1.5% glycol, is also generated and may be reused or disposed. Currently discharges to the sanitary sewer
system may require permitting under local pretreatment programs.
PERFORMANCE
Three ADF recovery systems were evaluated using data provided by three vendors. In each ADF
recovery system investigated, the quality of the fluid recovered was dictated by the specification objective.
The data provided for the ethylene glycol recovery system at the Toronto Airport shows that the process
reliably produced an effluent with a glycol content over 80%. The data from the ADF recovery system iin
Denver showed that high purity (98.5% glycol) can be reliably produced. The process at the Munich Airport
reliably produced an effluent with a glycol content over 50%, which meets the lower end-user requirements
in Europe.
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COSTS
Since there are no full-scale ADF systems currently operation in the U.S., it is difficult to determine
the actual construction costs. However, based on pilot study at the Denver Stapletbn Airport, the total capital
cost for the complete project, including deicing and anti-icing application equipment, collection piping, storage
facilities, and glycol recovery system has been estimated to be between $6 and $7 million dollars. The
construction costs for the ADF collection system, storage and handling facilities, piping, and recovery system
has been estimated at approximately $600,000 (GSI, 1993).
The total capital cost for the new Denver International Airport, including deicing and anti-icing
application pads and equipment, drainage and collection piping, storage and handling facilities, and complete
glycol recovery system is currently estimated at between $20 and $25 million dollars. These costs are based.
on a complete package including planning, engineering design, equipment, construction and installation, start-
up services and other contingencies. The construction costs for the ADF collection system, storage and
handling facilities, piping, controls and instrumentation, and complete recovery system is currently estimated
at approximately $5 million dollars.
The major operating expense for all ADF systems is cost of energy used in the distillation process.
Other maintenance costs include flushing of filters and ion-exchange units, disposal of spent filter cartridges,
process and neutralization chemical, lubrication of pumping equipment, arid inspection and repairs to the
distillation equipment and heat exchanger. The collection system sand storage facilities will also require
periodic cleaning and maintenance. Based on vary limited operating data from the pilot study at the
Stapleton Airport, the cost for processing ADF with a 28 percent glycol concentration, is approximately 35
cents per gallon treated. However, this cost will vary depending on the volume treated and concentration of
glycol in the waste stream. As the technology is refined and as operating experience grows, these costs
should decrease. , .
ENVIRONMENTAL IMPACT
While the potential for volatile-organic emissions to the air is considered small, the discharges of air
emissions from the distillation process through losses from condenser vents, accumulator tank vents, and
storage tank vents must be considered. Ion-exchange flush and spent wastewater are generated by recovery
processes may generally be discharged to the sanitary sewer. These spent byproducts may require
neutralization by addition of acids or bases before discharge. Currently discharges to the sanitary sewer
system may require permitting under local pretreatment programs. Spent filter cartridges may be generated
hi some systems. In most cases these can be disposed of in the local landfill.
Distillation condensate, with less than 1.5% glycol, is also generated and may be reused or disposed.
However, release of more than i pound of ethylene glycol to the environment must be reported under the
Comprehensive Environmemtal Response, Compensation and Liability Act (CERCLA) requirements. The
EPA currently has under review a proposal to raise the disposal limit to 5000 pounds. This proposal is
expected to be promulgated as a rule in calendar year 1995. A spill prevention control and countermeasure
(SPCC) plan should be developed for all ADF systems to address the handling, storage and accidental release
of chemicals, regenerated products and waste byproducts.
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REFERENCES '••'-..
1. American Association of Airport Executives. Conference on Aircraft Deicing, August, 1993.
Washington, D.C.
2. Comstock, C., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Pflrm f" Ai^p^r* stnrm w«if,.r P.mnff". in Chemical Deicers in the Environment, ed. frank M. D'ltri.
Lews Publishers, Inc., Chelsea, MI.
3. ENSR Consulting and Engineering, 1993. Evaluation of the Biiotic Communities arid Chemistry of the
Water and Sediments in Sand Creek near Staoleton International Airport. Prepared for Stapleton
International Airport. Document Number. 6321-002,
4. Freeman, H.M., 1989. Standard Handbook of Hazardous Waste Treatment and Disposal. McGraw-Hill,
New York, N.Y.
5. Federal Aviation Administration, 1991. Advisory Circular (150/5320-15): Management of Airport
Industrial Waste. U.S. Department of Transportation, Washington, D.C.
6. Federal Register Notice, Vol. 55, No. 222, page 48062, November 16, 1990. EPA Administered Permit
Programs; the National Pollutant Discharge Elimination System.
7. Federal Register Notice, Vol. 58, No. 222, page 491587, November 19, 1993. Fact Sheet for the Multi-
Sector Storm Water General Permit (Proposed). .
8. Hartwell, S.I., D.M. Jordan!, E.B., May. 1993. Toxicitv of Aircraft Deicer and Anti-icer Solutions
to Aquatic Organisms. Chesapeake Bay Research and Monitoring Division, Annapolis, Maryland.
Document Number CBRM-TX-93-1.
9. Health Advisory, 1987. Ethvlene Glvcol. Office of Drinking Water, U.S. Environmental Protection
Agency. Document Number PB87-235578.
10. Kaldeway, J., Director of Airport Operations, 1993. L.B. Pearson International Airport, Toronto,
Canada. Personal communications with Lauren Fillmore, Engineering-Science, Inc. ,
11. Legarreta, G.,Civil Engineer, 1993. Design and Operations Criteria Division, Federal Aviation
Administration. Personal communication with Lauren Fillmore, Engineering-Science,Inc.
12. Lubbers L., 1993. Laboratory and Field Studies of the Toxicitv of Aircraft Deicing Fluids. Presentation
to the SAE Aircraft Ground Deicing Conference, Salt Lake City, Utah, June 15-17, 1993.
13. McGreevey, T., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Deicers in Airport Storm Water Runoff', in Chemical Deicers in the Environment, ed. Frank M. D'ltri.
"" Lewis Publishers, Inc., Chelsea, MI.
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14 Morse, C., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of Deicers
in Airport Storm Water Runoff", in Chemical Deicers in the Environment, ed. Frank M. D Kn. Lewis
Publishers, Inc., Chelsea, ML .
-15. NIOSHHC1" Search Results - Ethylene Glycol, Propylene Glycol
16. Roberts, D., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Deicers in Airport Storm Water Runoff1, in Chemical Deters in the Environment, ed. Frank M. D Itn.
Lewis Publishers, Inc., Chelsea, MI..
17. SAE International, May 17,1993. Unconfirmed Minutes of Meeting No. 37 of AMS Committee, Rome,
Italy. • ' .
18 Sills. R.D. and Blakeslee, P.A., 1992*. "The Environmental Impact of Deicers in Airport Storm Water
ffiJ^ ™-mi~i nP,U in the Envimnn,Pnt. «1. Frank M. D'ltri. Lewis Publishers, Inc., Chelsea,
MI.
19 Transport Canada. 1985. Stet«Mif-the-Art ttenort of Aircraft Dacing/Anti-icine. Professional and
' Technical Services, Airports and Construction, Airport Facilities Branch, Facilities and Environment
Management. Document Number AK-75-09-129. (Type I Fluid Only)
20. Verschueren, K., 1983. Handbook of Environmental Data on Organic Chemicals. 2nd Edition, Van
Nostrand Reinhold Co., New York, N.Y.
TO, BMP fact *«t ™ pnptttd bT te Monfc^U TKhaotoBy Bnmch (4204), US EPA, 401 M Slrert, SW. W^togton, DC. 20460
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MTB
STORM WATER BMPs
INFILTRATION TRENCH
Office of WattewaterManagoment °^*f
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
.Infiltration trenches are used to remove suspended solids, participate pollutants, coliform bacteria,
organics and some soluble forms of metals and nutrients from storm water runoff. An infiltration trench,
as shown in Figure 1 below, is an excavated trench* 3 to 12 feet deep, backfilled with stone aggregate. A
small portion of the runoff, usually the first flush, is diverted to the infiltration trench, which is located either
underground or at grade. The captured runoff exits the trench by infiltrating into the surrounding soils.
Filtration through the soil is the primary pollutant removal mechanism. Infiltration trenches also provide
ground water recharge and preserve base-flow in nearby streams.
trr.-
UOSTUWED MR.
MMMJM MFH.TMLTION RATE'
OF OJW MCM PEK HOUR
;. .' f \^
9 MCH «6u*K£ STCEL FOOT PLATE
SOURCE: Reference*
1HGPRE1: TCTICALINFILTRATICW TRENCH
Infiltration trenches capture and treat small amounts of runoff, but do not control peak hydraulic
flows. Infiltration trenches may be used in conjunction with another best management practice (BMP), such
as a detention pond, to provide both water quality control and peak flow control (Schueler, 1992, Harrington,
1989). Runoff that contain:; high levels of sediments or hydrocarbons (oil and grease) that may clog the
trench are often pretreated with other BMPs, Examples of pretreatment BMPs include grit chambers, water
quality inlets, sediment trap:;, swales and vegetated filter strips (SEWRPC,'l991, Harrington, 1989).
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COMMON MODIFICATIONS • ;
The innitration trench can be modified by substituting pea gravel for stone aggregate in the top 1 foot
of the trench. The pea gravel improves sediment filtering and maximizes the pollutant removal in the top
of the trench. When the modified trenches become clogged, they can generally be restored to fulll
performance by removing and replacing only of the pea gravel layer with out replacing theilower stone
aggregate layers. Infiltration trenches can also be modified by adding a layer of organic material (peat) or
loamito the trench subsoil. This modification appears to enhance the removal of metals and nutnent through
adsorption. , .
CURRENT STATUS ;
Infiltration trenches are often used in place of other BMPs where limited land is available.
Infiltration trenches are most widely used in warmer, less arid regions of the U.S. However, recent studies
conducted in Maryland and New Jersey on trench performance and operation and maintenance, have
demonstrated the applicability of infiltration trenches fa colder climates (Lfadsey, et al, 1991).
LIMITATIONS
The use of infiltration trenches may be limited by a number of factors, Including type of soils,
climate, and location of groundwater tables. Site characteristics, such as the slope of the drainage area, soil
tvoe and location of the water table and bedrock, may preclude the use of infiltration trenches. The
surrounding area slope should be such that the runoff is evenly distributed fa sheet flow as it enters the
trench. Generally, infiltration trenches are not suitable for areas with relatively impermeable soils such as
clayey and silty soils or in areas with fill. The trench should be located above the water table so that the
runoff can filter through the trench and into the surrounding soils and eventually into the groundwater. In
addition, the drainage area should not convey heavy levels of sediments or hydrocarbons to the trench. For
this reason, trenches serving parking lots should be preceded by appropriate pretreatment. Generally,
trenches that are constructed under parking lots are also difficult to access for maintenance.
As with any infiltration BMP, the potential of groundwater contamination must be carefully
considered, especially if the groundwater is used for human consumption or agricultural purposes. . In some
cases the infiltration trench may not be suitable for sites that use or store chemicals or hazardous materiaHs.
In these areas other BMPs that do not interact with the groundwater should be considered. If mfUtratiffln
trenches are selected, hazardous and toxic materials must be prevented from entering the trench. The
potential for spills can be minimized by aggressive pollution prevention measures. Manymumc palitiesand
industries have developed comprehensive spill prevention control and countermeasure (SPCC) plans. These
plans should be modified to include the infiltration trench and the contributing drainage area. For example,
diversion structures can be used to prevent spills from entering the infiltration trench.
An additional limitation is the climate. In cold climates, trench surface may freeze, thereby
preventing the runoff from entering the trench and allowing the untreated runoff to enter surface water.
The surrounding soils may also freeze reducing infiltration into the soils and groundwater. However, recent
studies indicate if properly designed and maintained infiltration trenches can operate effectively in colder
climates. By keeping the trench surface free of compacted snow and ice and by ensuring the part of the
trench is constructed below the frost line, will greatly improve the performance of the infiltration trench
during cold weather.
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PERFORMANCE
Infiltration trenches function similarly to rapid infiltration systems that are used in wastewater
treatment. Estimated pollutant removal efficiencies from wastewater treatment performance and modeling
studies are shown in Table 1 below. Based on this data, infiltration trenches can be expected to remove up
to 90 percent of sediments, metals, coliform bacteria and organic matter, and up to 60 percent of phosphorus
and nitrogen in the runoff (Schueler, 1987,1992). Biochemical oxygen demand (BOD) removal is {estimated
to be between 70 to 80 percent. Lower removal rates for nitrate, chlorides and soluble metals should be
expected especially in sandy soils (Schueler, 1992).
TABLE 1: TYPICAL POLLUTANT REMOVAL EFFICIENCY
PoDotant
Sediment
Total Phosphorus
Total Nitrogen
Metals
Bacteria
Organics
Biochemical Oxygen Demand
SOURCE: References 4 and 5
Typical Percent Removal Rates
90%
60%
60%
90%
90%
90%
70 - 80%
Pollutant removal efficiencies may be unproved by using washed aggregate and adding organic matter
and loam to the subsoil. The stone aggregate should be washed to remove dirt and fines before placement
in the trench. The addition of organic material and loam to the trench subsoil will enhance metals and
nutrient removal through adsorption. . .
LONGEVITY
There have been a number of concerns raised about the long term effectiveness of infiltration trench
systems. In the past, infiltration trenches have demonstrated a relatively short life span with over 50 percent
of the systems checked, having partially or completely failed after 5 years. A recent study of infiltration
trenches in Maryland (Lindsey et al., 1991) found that 53 percent were not operating as designed, 36 percent
were partially or totally clogged, and another 22 percent exhibited slow filtration. Longevity can be increased
by careful geotechnical evaluation prior to construction. Soil infiltration rates and the water table depth
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should be evaluated to ensure that conditions are satisfactory for proper operation of an infiltration trench.
Prefreatment structures, such as a vegetated buffer strip or water quality inlet, can increase longevity by
***»*• *-**""*•*** J _ , - «_ .*•__.*. _IA» Ai.A 4*«MMnl« 1>Amiloi* vnainTAnsitlP(^
,
nsemens, hydrocarbons and other materials that may clog the trench.
taduding the replacement of dogged aggregate, will also increase the effectiveness and Me of the trench.
DESIGN CRITERIA
Prior to trench construction, a review of the design plans may be required by rtate and local
govenmS The design plans should indude a geotechnical evaluation that determhies flu L^Oity of
ShST infiltration traS at the site. Soils should have a low silt and clay content and have **"*»»*•
STthan 0.5 inches per hour. Acceptable soil texture classes mdude sand, loamy sand, sandy loam and
E ThSe soils are within the A or B hydrologic group. Soils tathe C «r D hydrologic groups ; shouWbe
wrtded. Soil survey reports published by the Soil Conservation Service can be used to identify soil types and
mfi uSonrates. However, suffident soil borings should always be taken to verify sit^conditions. Feasible
SSouldta ve a minimum of 4 feet to bedrock in order reduce excavation costs. There should also^be a
1^4 fWt bdJwth"trench to the water table to prevent potential ground water problems. Trenches should
akobe U^tedTt iSstWO feet up gradient from water supply wells and 100 feet from building foundations.
Sd av^abOityln; depth tobedrodc and the depth to the water table will determine Defter «be
infiHration trench is located underground or at grade. Underground trenches receive runoff though pipes
or channels, whereas surface trenches collect sheet flow from the drainage area.
In general taffltration trenches are suitable for drainage areas up to 10 acres (SEWRPC, 19911,
becareM
n ge
Harrington, 989). However, when the drainage area exce«l 5 acre, other Bm* should be.careMy
ctSeVed (Schueler, 1989 and 1992). The drainage area must be fully developed and stabihzed with
v^[o7bSore coveting an infiltration trench. High sediment loads from^stabilized a^U quick [,
dog the infiltration trench. Runoff from unstabiKzed areas should be diverted away from the trench until
vegetation is established.
The drainage area slope determines the vdocity of the runoff and also influences the amount of
pollutants entrained in the runoff. Infiltration trenches work best when the up gradient drainage areaslope
btasta iMKrcent (SEWRPC, 1991). The down gradient slope shouldbe no greater than 20 percent to
minimize slope failure and seepage.
The trench surface may consist of stone or vegetation with inlets to evenly distribute the runoff
entering the trench (SEWRPC, 1991, Harrington, 1989). Runoff can be captured by depressing thetrench
^rfacTor by placing a benn at the down gradient side of the trench. Underground trenches are covered with
an impermeable geotextile membrane overlain with topsoil and grass.
A vegetated buffer strip (20 to 25 foot wide) should be established adjaceni to the infiltration trench
to capture S sediment particles in the runoff. The buffer strip should be installed immediately after
£Tch ^SoTSng sKstead of bydrose^ding (Schueler, 1987) The buffer strip should be
wto a slope between 0.5 and 15 percent so that runoff enters the trench as sheet flow If runoff^
channeled to the trench, a levd spreader can be installed to create sheet flow (Harnngton, 1989).
During excavation and trench construction, only light equipment such as backhoes or wheel and
ladder type trLhers should be used to minimize compaction of the surrounding soik. Fitter fabric ^should
placSaround the walls and bottom of the trench and 1 foot below the trench surface. The filter fabric
Sd overlap each side of the trench in order to cover the top of the stone aggregate layer (see Rgure 1).
e filter fabric prevents sediment in the runoff and soil particles from the sides of the trench from clogging
eaBgregate Rlter fabric that is placed 1 foot below the trench surface will maximize pollutant removal
within the top layer of the trench and decrease the pollutant loading to the trench bottom.
or
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The required trench volume can be determined by several! methods. One method calculates the
volume based on capture of the first flush, which is defined as the first 0.5 inches of runoff from the
contributing drainage area (SEWRPC, 1991). The State of Maryland (MD., 1986) also recommends sizing
the trench based on the first flush, but defines first flush as the first 0.5 inches from the contributing
impervious area. The Metropolitan Washington Council of Governments (MWCOG) suggests that the trench
volume be based on the first 0.5 inches per impervious acre or the runoff produced from a 1 inch storm. In
Washington D.C., the capture of 0.5 inches per impervious acre accounts for 40 to 50 percent of the annual
storm runoff volume. The runoff not captured by the infiltration trench should be bypassed to another BMP
(Harrington, 1989) if treatment of the entire runoff from the site is desired.
Trench depths are usually between 3 and 12 feet (SEWRPC, 1991, Harrington, 1989). However, a
depth of 8 feet is most commonly used (Schueler, 1987). A site specific trench depth can be calculated based
on the soil infiltration rate, aggregate void space, and the trench storage tune (Harrington, 1989). The stone
aggregate used in the trench is normally 1 to 3 inches hi diameter, which provides a void space of 40 percent
(SEWRPC, 1991, Harrington, 1989, Schueler, 1987). '
A minimum drainage time of 6 hours should be provided, to ensure satisfactory pollutant removal
in the infiltration trench (Schueler, 1987, SEWRPC, 1991). Although trenches may be designed to provide
temporary storage of storm water, the trench should drain prior to «he next storm event. The drainage tune
will vary by precipitation zone. In the Washington, B.C. area, infiltration trenches are designed to drain
within 72 hours. •
An observation well is recommended to monitor water levels in the trench. The well can be a 4 to
6 inch diameter PVC pipe, which is anchored vertically to a foot plate at the bottom of the trench as shown
hi Figure 1 above. Inadequate drainage may indicate the need ffbr maintenance.
MAINTENANCE
Maintenance should be performed as needed. The principal maintenance objective is to prevent
clogging, which may lead to trench failure. Infiltration trenches and any pretreatment BMPs should be
inspected after large storm events and any accumulated debris or material removed. A more through
inspection of the trench should be conducted at least annually. Annual inspection should include monitoring
of the^ observation well to confirm that the trench is draining within the specified tune. Trenches with filter
fabric should be inspected for sediment deposits by removing a small section of the top layer. If inspection
indicates that the trench is partially or completely clogged, it should be restored to its design condition.
*•• ' -..-•' -
When vegetated buffer strips are used, they should be inspected for erosion or other damage after
each major storm event. The vegetated buffer strip should have healthy grass that is routinely mowed.
Trash, grass clippings and other debris should be removed from the trench perimeter. Trees and other large
vegetation adjacent to the trench should also be removed to prevent damage to the trench.
COSTS .
Construction costs include clearing, excavation, placement of the filter fabric and stone, installation
of the monitoring well, and establishment of a vegetated buffer strip. Additional costs include planning,
geotechnical evaluation, engineering and^ permitting. The Southeastern Wisconsin Regional Planning
Commission (SEWRPC, 1991) has developed cost curves and tables for infiltration trenches based on 1989
dollars. The 1993 construction cost for a relatively large infiltration trench (i.e., 6 feet deep and 4 feet wide
with a 2,400, cubic foot volume) ranges from $8,000 to $19,000. A smaller infiltration trench (i.e., 3 feet deep
and 4 feet wide with a 1,200 cubic foot volume) is estimated to cost from $3,000 to $8,500 (1993).
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pewent of the original capital cost (SEWRPC, 1991).
ENVIRONMENTAL IMPACTS ,
- Infiltration trenches provide efficient removal of suspended solids, particulate
the surrounding soils and increases
recharge and base-flow in nearby streams.
Negative impacts include the potential for groundwater contamination. Fortunagj
Ksasras^
gZndTater. fa the future, federal or state agencies may require a groundwater injection permit for
infiltration trench sites (Schueler, 1992).
REFERENCES
1. Harrington, B.W., 1989. "~ V »n* Construction of Infiltration Tirnrhes in l^JPn of Urban Runoff
Quality Control. American Society of Civil Engineers.
2. Lindsey, G.. Roberts. L.t and Page. W.. 1991. Stnrm W.tor ™«™?™™* Infiltration Maryland
of the Environment. Sediment and Storm Water Administration.
Division.
TR 1987 rnntrolling Urfrm Runoff: A Practical Manu«l for Planning and Designing Urban
nt Practices. Metropolitan Washington Council of Governments.
5. Schueler, T.R. 1992. A *"•"-"•"* A~minit of Urban Rest Management Practices., Metropolitan
Washington Council of Governments.
6 Southeastern Wisconsin Regional Planning Commission (SEWRPC), 1991. Costs of Urban Nonpoint
Snnrce Water Pollution Control Measures. Technical Report No. 31.
7. United States Environmental Protection Agency (USEPA), 1991. TMention and Retention Effects on .
Groundwater, Region V.
8. Washington, State of, 1992. stnm, Water Manapement Manual for the Fnpet Sound Basin CThe
Technical Manual), Department of Ecology.
TO. bet *«• «~ P«P««
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SMTB
STORM WATER BMP:
SAND FILTERS
Office of Waaewater Mar
%*IKJC « wiaiiinuuj maunancnt . .V'N-T
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
Sand filters are most often designed for storm water quality control and generally provide limited
storm water quantity management. A typical sand filter system consists of at least two chambers or basins
with one designed for sedimentation and one for filtration. The first chamber, the sedimentation chamber,
removes floatables and heavy sediments. The second chamber, the filtration chamber, removes additional
pollutants by filtering the runoff through a sand bed. The treated filtrate normally is discharged through
an underdrain system to a storm drainage system or directly to surface waters. Sand filters can achieve high
removal efficiencies for sediment, biochemical oxygen demand (BOD) and fecal conform bacteria. However,
total metals removal is moderate and nutrient removal is often low. •
There are three main sand filter designs currently in common use: the Austin sand filtration system
(Figure la), the Washington, D.C. sand filter (Figure Ib) and the Delaware sand filter (Figure Ic). The
primary differences in these designs are location (i.e., underground or surface and on-line or off-line),
drainage area served, filter surface areas, land requirements, and quantity of runoff treated.
To Stormwater
Detention Basin
Energy Dissipators
L
A
nk.^rfnn &««M
rtUmtan HUM)
Sedimentation
Basin
StoimwaJer Channel
Drop Intel
i* • i*
»• V
Hi Ji
'
T:
Filtered Outflow
Stone
ftp Rap
W«r To Achieve
Uniterm Discharge
Channel Sloped to
Facilitate Sediment
Transport into
Sedroemabon Basin
SOURCE: Reference 2
Perforated Riser
vth Trash Rack
A • A
" -" - °- j^
t
Unctadrain Piping Syttm
FIGURE la: TYPICAL AUSTIN SAND FILTER DESIGN
COMMON MODDJICATIONS
• '. ' ;V •
Modifications that may improve sand filter . design and performance are being tested. One
modification is the addition of a peat layer in the filtration chamber. The properties and characteristics of
the peat may increase the microbial growth within the sand filter and improve pollutant (e^g., metals and
nutrients) removal rates. Another design variation, which is included in the Washington, D.C. ,sand filter
design, includes an underdrain that is extended above the sand filter layer. This allows for backwashing of
the filter when it becomes clogged. .
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50" MANHOLE
FRAME ft* COVER
Stf-MANHOLE
aCWER
FRAME » COVER
INFLOW
PIPE
WASHED |"
AGGREGATE
6"PVC
DE WATERING
DRAIN WITH
PVCGATE
VALVE.
OUTFLOW
PIPE
CLEAN OUT
PIPE WITH CAP
•FILTER
FABRIC
SOURCE: Reference 3
FIGURE Ib: TYPICAL WASHINGTON, DC SAND FILTER DESIGN
GHATEOCOVER SOLID COVER
FLOW
GRATlfFABWC WRAPPED
OVER ENTIRE CRATE OPENING)
SOURCE: Reference 1
FIGURE lc: TYPICAL DELAWARE SAND FILTER DESIGN
CURRENT STATUS
Sand filters are currently in use in the State of Delaware; and the Cities of Austin, Texas; Alexandria,
Virginia: and Washington, B.C. Studies on the pollutant removal efficiencies are currently being performed
for the Washington, B.C. and the Austin sand filters. However, additional evaluations need to be conducted
in other locations and on alternative designs and media.
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APPLICATIONS
In general, sand filters are preferred over infiltration practices, such as infiltration trenches, when
groundwater contamination is of concern due to high ground water tobies or in areas where underlying soils
- are unsuitable. In most cases, sand filters can be constructed with impermeable basin or chamber bottoms
to collect, treat, and discharge runoff to a storm drainage system or directly to surface water without the
contaminated runoff coming into contact with the groundwater.
The selection of the type, of sand filter depends largely on the drainage area characteristics. For
example, the Washington, D.C. and Delaware sand filter systems are well suited for highly impervious areas
where land availability for structural controls is limited. Both the Washington, D.C. and Delaware sand filter
designs are intended for underground installation. These sand filters are often used to treat runoff from
parking lots, driveways, loading docks, service stations, garages, airport runways/taxiways, and storage yards.
The Austin sand filtration system is more suited for larger drainage areas with both impervious and pervious
surfaces. This system is located at grade and is often used at transportation facilities, large parking areas
and commercial developments.
All three types of sand filters can generally be used as alternatives for water quality inlets, which are
more frequently used to treat oil and grease contaminated runoff from drainage areas with heavy vehicle
usage. In climatic zones where evaporation exceeds rainfall, the Austin sand filtration systems can also be
used as an alternative to wet ponds for treatment of contaminated storm water runoff. In high evaporation
zones, wet ponds will not likely be able to maintain the required permanent pool unless there is adequate
baseflowfrom the groundwater. '
LIMITATIONS
The size and characteristics of the drainage area as well as the pollutant loading will greatly influence
the effectiveness of the sand filter system. In some cases other best management practices (BMPs), such as
wet ponds, may be less costly for sites with large drainage areas and should also be considered if removal of
nutrients and metals is required. Drainage areas with heavy sediment loads may result in frequent clogging
of the filter. The lack of maintenance to the clogged- filters will limit the performance. Certain climatic
conditions may also limit'the performance of the filters. For example, it is not known how well sand filters
will operate in colder climates where sustained freezing conditions are encountered.
PERFORMANCE
Participates are removed by both sedimentation in the sedimentation chamber and by filtration in
the filtration chamber. The City of Austin has estimated pollutant removal efficiencies (Austin, 1988) based
oh preliminary findings of the City's storm water monitoring program. The estimates shown in Table 1
below, are average values for various sand filters serving several different size drainage areas.
As. shown hi Table 1, no removal of nitrate was observed in the preliminary findings. The removal
of other dissolved pollutant; was not monitored. Additional monitoring is currently being performed by the
City of Austin to supplement the preliminary estimates.
LONGEVITY
There have been a number of concerns raised about the long term effectiveness of sand filter systems.
Proper design and maintenance are critical factors in maintaining the useful life of any filter system. The
life of the filter media may be increased by a number of methods including: stabilizing the drainage area so
that sediments loadings in the runoff are minimized; placing a sedimentation chamber that removes sediments
prior to the filtration chamber; providing adequate detention times for sedimentation and filtration to occur;
and frequently inspecting and maintaining the sand filter to ensure proper operation. In some cases,
replacement of the filter media may be' required every 3 to 5 years. The useful life of the media will depend
on the pollutant loading to the filter and the design and maintenance of the system.
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TABLE 1: TYPICAL, POLLUTANT REMOVAL. EFFICIENCY
Pollutant
Fecal Coliform
Biochemical Oxygen Demand (BOD)
Total Suspended Solids (TSS)
Total Organic Carbon (TOC)
Total Nitrogen (TN)
Total Kjeldahl Nitrogen (TEN)
Nitrate as Nitrogen (NO3-N)
Total Phosphorus (TP)
Iron (Fe)
Lead (Pb)
Zinc (Zn)
SOURCE: Reference 4
Typical Percent Removal
76
70
70
48
21
46
0
33
45
45
45
DESIGN CRITERIA
Typically the Austin sand filter system is designed to handle runoff from drainage areas up to SO
acres. The collected runoff is first diverted to the sedimentation basin, where heavy sediments and floatable;
are removed. There are two designs for the sedimentation basin: the full sedimentation system, as shown in
Figure la, and a partial sedimentation system, where only the initial flow is diverted. Both systems arc
located off-line and are designed to collect and treat the first 0.5 inch of runoff. The partial system has the
capacity to hold only a portion (at least 20%) of the first flush volume in the sedimentation basin, whereas
the full system captures and holds the entire flow volume. Equations that are used to determine the
sedimentation basin surface areas (AJ in acres are shown in Table 2 below.
TABLE 2: SURFACE AREA EQUATION FOR
THE AUSTIN SAND FILTER SYSTEM
Partial Sedimentation
A, =
Af -
- 1/10)
Full Sedimentation
A, = (A^tfQ/lO
' A, = (A,>)(H)/18
Note:
D, (feet) = depth of the sedimentation basin;
H (feet) = depth of rainfall, 0.042 ft (0.5 inches); and
AD (acres) = impervious and pervious areas that provide
contributing drainage.
SOURCE: Reference 4
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Flow is conveyed from the sedimentation basin either through a perforated riser, gabion wall, or
benn to the flltration basin.. The filtration basin consists of an 18-inch layer of sand 0.02 to 0.04 inch hi
diameter that may be underlain with a gravel layer. Equations that are used to determine the filtration basin
surface areas (A,) in acres are also shown in Table 2. The filtrate is discharged from the filtration basin
through underdrain piping 4 to 6 inches in diameter with 3/8-inch perforations. Filter fabric is placed around
the underdrain piping to prevent sand and other particulates from being discharged.
Typically the Washington, D.C. sand filter system is designed to handle runoff from completely
impervious drainage areas of 1 acre or less. The system, as shown un Figure Ib, consists of three chambers:
a sedimentation chamber, a filtration chamber, and a discharge chamber. The reinforced concrete chambers
are located underground. The sand filter system is designed to accept the first 0.5 inch of runoff. Coarse
sediments and floatables are removed from the runoff within the sedimentation chamber. Runoff is
discharged from the sedimentation chamber through a submerged wen-, where it then enters the filtration
chamber. The filtration chamber consists of a combination of sand and grave layers totaling 3 feet hi depth
with an underdrain system wrapped in filter fabric. The underdram system collects the filtered water and
discharges if to the third chamber, where the water is collected and discharged to a storm water channel or
sewer system. An overflow weir is located between the second and third chambers to bypass excess flow.
The Washington, D.C. sand filter is often constructed on-line, but can be constructed off-line. When the
system is off-line the overflow between the second and third chambers is not included.
The Delaware sand filter, as shown in Figure Ic, is similar to the Washington, D.C. sand filter; both
utilizing underground concrete vaults. However, the Delaware sand filter has two chambers: a sedimentation
chamber and a filtration chamber.' A 1-iiidi design storm was selected for the sizing of the sedimentation
basin because it is representative of most frequent storm events. In Delaware, 92% of all storms are less than
1 inch in depth. Runoff enters the sedimentation chamber through a grated cover and then overflows into
the filtration chamber, which contains a sand layer 18 inches in depth. Gravel is not normally used in the
filtration chamber, although the filter can be modified to include gravel. Typical systems are designed to
handle runoff from drainage areas of 5 acres or less. A major advantage of the Delaware sand filter is its
shallow structure depth of only 30 inches, thereby reducing excavation requirements.
MAINTENANCE
All filter system designs must provide adequate access to the filter to perform the required inspection
and maintenance. The sand filters should be inspected after all storm events to verify that they are working
as designed. Since the D.C. and Austin sand filter systems can be relatively deep, they may be designated
as confined spaces, therefore, require compliance with confined space entry safety procedures. .
Typically, sand filters begin to experience clogging problems within 3 to 5 years (NVPDC, 1992).
Accumulated trash, paper and debris should be removed from the sand filters every 6 months or as necessary
to keep the filter clean. A record should be kept of the dewatering tunes for all sand filters to determine if
maintenance is necessary. Corrective maintenance of the filtration chamber includes removal and
replacement of the top layers of sand, gravel and/or filter fabric that have become clogged. The removed
media may usually be disposed of in a landfill. The City of Austin has tests their waste media before disposal.
Results thus far indicate that the waste media is not toxic and can be safely landfilled (Schueler, 1992). Sand
filter systems may also require the periodic removal of vegetative growth.
COSTS
The construction cost for an Austin sand filtration system is approximately $17,750 (1993 dollars)
for a 1-acre drainage area. The cost per acre decreases with increasing drainage area. For example the cost
for a 15-acre site is approximately $3,300 (1993 dollars) per acre for a total of $49,500 (Austin, 1990b). The
cost for precast Washington, D.C. sand filters with drainage areas of less than 1 acre ranges between $6,300
and $10,500. This is considerably less than the cost for the same size cast-in-place system of approximately
$26,400 (D.C., 1992). Costs for the Delaware sand filter are similar to that of the D.C. system, except the
excavation costs are generally lower, because of the filters shallower depth.
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Annual costs for maintaining sand filter systems averages about 5 percent of the initial construction
cost (Schueler, 1992). Media replacement is performed as needed. Currently the sand is being replaced in
the B.C. filter systems about every 2 years. The cost to replace the gravel layer, filter fabric and top portion
of the sand for D.C. sand filters is approximately $1,600 (D.C. 1992). The City hopes that improved
maintenance procedures will extend the life of the filter media and reduce the overall maintenance costs.
ENVIRONMENTAL IMPACTS
The three types of sand filters achieve high removal efficiencies for sediment, BOD and fecal coliform
bacteria and generally require less land than other BMPs, such as ponds or wetlands. SandI fitters
constructed with impermeable basin liners limit the potential for groundwater contamination, Sand litters
generally do not provide storm water quantity control and, therefore, do not prevent downstream stream
bank and channel erosion. Sand filters may also be of limited value in some applications because of their
traditionally low nutrient removal and metals removal capabilities. Waste.media from the fitters does not
appear to be toxic and is environmentally safe for landfill disposal.
REFERENCES
1. Shaver, Earl, 1991. Sand Filter Design for Water Quality Treatment. Delaware Department of Naturall
Resources and Environmental.Control. .
2. Schueler, T.R. 1992. A Current Assessment of Urban Best Management Practices. Metropolitan
Washington Council of Governments.
3. Troung,H. 1989. The Sand Filter Water Quality Structure. District of Columbia.
4. City of Austin, Texas, 1988. Design Guidelines for Water Quality Control Basins. Environmental Criteria
Manual. . • '.'.,••
5. City of Austin, Texas, 1990. Removal Efficiencies of Storm Water Control Structures.' Environmental
Resource Division, Environmental and Conservation Services Department.
6. City of Austin, Texas, 1990b. Memo from Leslie Tull, Water Quality Management Section (June 20,1990).
7. Northern Virginia Planning District Commission (NVPDC), 1992. Northern Virginia BMP Handbook,
8. Washington, D.C. (DC), 1992. Personal Communication.
ters:
_^ __ _ A Proposed Storm Water Management Practice for Urbanized
Areas, Metropolitan Washington Council of Governments.
9. Galli, John, 1990. P
TO. BMP bd «b«t w* pr«p««d by the Munldpd Techi**^ Bra* (4204). US EPA, 401 M S*^ SW, W«*fa*oo, DC, 20460
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MTB
STORM WATER BMP:
VORTEX SOLIDS SEPARATOR
Office of Wastewater Management' »*
MUNICIPAL .TECHNOLOGY BRANCH
DESCRIPTION '"•'.'.'
A vortex solids separator Is a wastewater treatment technology with no moving parts which uses
velocities imparted from vortex swirling to assist the settling and removal of concentrated solids. During a
storm event, flow enters the cylindrical unit tangentially and induces, a swirling vortex which concentrates
solids in the underflow and reduces their concentration in the clarified liquid. A general view of the vortex
solid separator and liquid flow paths is shown in Figure 1 below.
Floatable Solids
Outer Vessel Wall
SetUcable Solid!
SOURCE: Reference 19
FIGURE Is GENERAL VIEW OF THE VORTEX SOLED SEPARATOR
Vortex units are moist often applied to combined sewer overflow (CSOs), but can also be used to treat
storm water runoff. In CSO treatment applications, the concentrated solids are removed from the bottom
of the unit and conveyed via the sanitary sewer to a Wastewater treatment plant (WWTP). In separate storm
water applications, the concentrated underflow would likely go to a holding tank or pond. Effluent exits the
top of the unit and is discharged to the receiving water. Vortex units may be used on-line or off-line, and
in combination with other Best Management Practices (BMPs) such as storage tanks or detention ponds.
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CURRENT STATUS .
This fact sheet contains general information only, and should not be used as the basis for designing
a vortex solit eparators for storm water applications . While the basic vortex separator technologies used
for CSO applications are well established, actual operating experience for storm water applications is limited.
The three types of vortex solids separators currently being actively marketed in the United States are listed
below While all three types use the same basic principal, this fact sheet will discuss some of the differences
in design and performance of the different units. The technology for storm water applications is evolving
rapidly. The equipment manufacturers and the municipal operators should be contacted for the current state
of the art information. •
• The EPA Swirl Concentrator.
• The Fluidsep.
• The Storm King. •
The design specifications for the EPA Swirl Concentrator were developed by the U.S. Environmental
Protection Agency (EPA) in the early 1970s. Currently, there are 20 full-scale EPA Swirl Concentrator units
in the U.S. and four in Japan (EPA, 1977). All of these units were designed for CSO treatment. However,
the EPA Swirl Concentrator design was extensively tested during a study for separated storm water treatment
in West Roxbury, Massachusetts in the early 1980s (EPA, 1982,1984).
. Fluidsep is a patented design that is licensed by a German firm, but is available in the U.S. There
are 13 full-scale Fluidsep units operating in the U.S. and Europe, with additional units planned for
construction. Fluidsep has been consistently used for CSO applications and has not been tested on separated
storm-sewer systems.
Storm King, a patented unit, is available in the U.S. from H.I.L. Technology, Inc. There are no full-
scale Storm King units in operation in the U.S. at this time. However, there are more than 100 Storm King
treatment units in operation in Europe and Canada, almost exclusively on CSOs. Full-scale Storm King units
have been selected by the City of Columbus to treat CSOs. Storm water treatment by the Storm King, has
been limited to a pilot study in Bradenton, Florida and a full-scale unit in Surrey Heath, England.
APPLICABILITY
Vortex separators are most effective where the separation of gritty materials, heavy particulates or
floatables from wet-weather runoff is required. The technology is particularly well suited to locations where
there is limited land availability which may preclude the use of other BMPs such as settling basins or
detention ponds. Vortex separators can also be applied as satellite units to treat smaller subareas of the
collection system, minimizing the high cost of conveyance systems needed for centralized treatment facilities.
Units can be designed to remove solids and capture floatables. However, solids with poor settleabihty are not
effectively removed in vortex solids separators.
LIMITATIONS
The use of vortex solids separators as a wet-weather treatment option may be limited by the poor net
solids removal (10-34 percent). In some cases this level of solids removal may not meet the treatment
objectives for a potential location. There is even less information on the ability of vortex solids separators
to remove pollutants other than solids. Pollutants such as nutrients and metals that adhere to fine particulates
or are dissolved will not be significantly removed by the vortex separator.
-------
Site constraints, including the lability of suitable land, appropriate soil depth and stability -to
DESIGN
Regardless of the type of vortex separator selected, the type an
anticipated in the influent are the basis of the design of all umt types.
The oerformance of each unit is based on the vortex separation mechanism. Each unit type has its
SKSir3E£!l5te Fluidsep design is based on modeling of particulate settleabihty detennmed
during site-specific studies, including flow gauging and rainfall measurements.
PERFORMANCE
Vortex separators designed primarily for removing grittier material, may have difficulty removing
test in West Roxbury, Massachusetts. Average performance characterist,cs for the three
of separators in shown in Table 1 below. This data is for CSO applicatums only.
Solids are removed in the underflow by flow splitting even if there is no concentration of particulates
and is not included in Table 1.
MAINTENANCE ' ' ;
Vortex separators do not have any moving parts, and are therefore not
However wash dels are required following every CSO event to prevent odors. To accomphsh
, some
-------
TABLE 1: AVERAGE VORTEX PERFORMANCE CHARACTERISTICS
FOR CSO APPLICATIONS
total Net
Unit Type Location Effluent Hydraulic Solids Solids Treatment
Flow (MGD) Reduction Removal Removal Factor
Swirl Washington, DC 10
Fluidsep Tengen, Germany 11
Storm King James Bridge, UK 7.5
Storm King Columbus, GA 4.3
*-• .
SOURCE: References 10,11,20, and 21
24
47
39
23
38
54
53
61
12
7
14
34
1.7
1.2
1.7
2.6
units have been designed to be self-cleansing. This may not be necessary for storm water treatment
applications. Pretreatment
BMPs such as bar screens or street sweeping can be used to decrease the quantity of wastes reaching the
vortex separators, but.it is not required. Maintenance would be required for pretreatment and pumping
equipment. •
COSTS
The capital cost for vortex solids separator treatment facilities are dependant on site-specific
characteristics. Commonly, vortex solids separators are used with other treatment technologies such as
automatic bar screens, and disinfection. The capital cost for vortex solids separator treatment facilities in
the U.S. varies between $3,000 and $5,250 per acre of drainage basin (1993 dollars). Typically the capital
cost for installed vortex solids separator units without pretreatment is approximately $4,900 per million
gallons of flow treated (1993 dollars).
Total costs of vortex units often include predesign costs, capital costs and operation and maintenance
(O&M) costs. Foe example, predesign study costs for the Storm King are typically $20,000 (1993 dollars).
Predesign costs for the Fluidsep, range between $25,000 and $100,000 (1993 dollars). There are no predesign
study costs associated with the EPA Swirl Concentrator, because published settleability curves are used for
the basis of design.
-------
Vortex solids separator units do not generally require significant-energy expenditures unless pumping
is required. Operating expenses primarily include labor for wash down or energy costs for automatic wash
down or bar screens. However some installations such as the Storm King unit in Surry Heath, England, do
hot have a sanitary or foul sewer line for disposing of collected solids. These facilities must collect its
residuals in a collection zone or holding tank. The frequency for pumping out the collected residuals will be
dependent on the amount of material collected per storm, the number of storm events and the size of the
holding zone or tank. The Surry Heath facility is estimating the holding zone will require pump out every
2-3 years. The cost for periodic emptying and disposal of the collected residuals is estimated to be between
$300-450 per cleaning (1993 dollars).
ENVIRONMENTAL IMPACTS
Improvements can often be observer in water quality or in the health of the ecosystem. For. example,
the Washington, D.C. CSO Abatement Program, which includes EPA Swirl Concentrators and upstream
storage, has resulted in decreased oxygen demands in the receiving water. Fish have returned to the once
oxygen-depleted water. Much of the improved receiving water quality is attributable due to a combination
of the upstream storage, and the bar screens, disinfection, and operation of the vortex units.
For CSO applications the vortex solid separators must be washed down after each storm events to
prevent objectionable odors. Odor control for some storm water applications and for residual storage
facilities may. also be required. Collected residuals from storm water applications have not evaluated.
However, collected residuals should be evaluated for toxicity and metals content before disposal.
REFERENCES
1. American Public Works Association, 19781 The Swirl Concentrator as a CSO Regulator Facility. U.S.
EPA Report Number EPA-43079-78-006.
2. Boner, M., 1993. Personal communication.
3. Brombach, H., 1992. Solids Removal from CSOs with Vortex Separators. Novatech 92, Lyon, France,
pp 447-459.
4. Drysdale, 1993. Personal communication.
5. Engineering-Science, Inc. and Trojan Technologies, Inc., 1993. Modified Vortex Separator and UV
Disinfection for CSO Treatment. Prepared for the Water Environment Research Foundation,
Alexandria, VA. . '
6. Engineering-Science, Inc., 1993. Trip Report for Work Assignment 1-09 EPA Contract No. 68-C2-0102.
7. Hedges^ P.D., Lockley, P.E., and Martin, J.R., 1992. A Field Study of an Hvdrodvnamic Separator
CSO. Novatech 92. Lvon. France.
8. H.I.L. Technology, 1993. Informative brochures and memos.
9. NKK Corporation, 1987. Solid-Liquid Separation by Swirl Concentration. Brochure.
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10. O'Brien and Gere, 1992. CSO Abatement Program Segment 1; Performance Evaluation. Prepared for
the Water and Sewer Utility Administration, Washington, D.C..
11. Fisano, William C., 1992. Survey of High Rate Storage and Vortex Separation Treatment for CSO
Control. For the Daly Road High Rate Treatment Facility Demonstration Project, Cincinnati, Ohio.
12. Pisano, WHIiam C., 1993a. Summary: The Fluidsep Vortex Solids Separator Technology. WK Inc.
Marketing Brief, Belmont, MA.
13. Pisano, William C., 1993b. Personal communication.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Purcell Associates, 1975. Pollution Abatement Plan. Newark. New Jersey. Prepared for 4he City of
Newark, Department of Public Works.
Randall, Clifford W., Ellis, Kathy, Grizzard, Thomas J., and Knocke, William R., 1983. "Urban
Runoff Pollutant Removal by Sedimentation." Proceedings of the Conference on Storm Water Detention
Facilities. American Society of Civil Engineers. New York, NY.
Smith and Gillespie Engineers, Inc., 1990. Engineer's Study for Storm Water Management
Demonstration Project No. 2 for Evaluation of Methodologies for Collection. Retention. Treatment and
Reuse of Existing Urban Storm water; S&.G Project Number 7109-133-01.
Sullivan, R.H., et al., 1974. The Swirl Concentrator as a Grit Separator Device. EPA Report Number
EPA-670/2-74-026.
Sullivan, R.H., et al., 1974. Relationship Between Diameter and Height for the Design of a Swirl
Concentrator as a CSO Regulator. EPA Report Number EPA-670/2-74-026.
US EPA, 1977. Swirl Device for Regulating and Treating CSOs. EPA Technology Transfer Capsule
Report. EPA Report Number EPA-625/2-77-012.
US EPA, 1982. Swirl and Helical Bend Pollution Control Devices. EPA Report Number
EPA-600/8-82-013.
US EPA, 1984. Swirl and Helical Bend Regulator/Concentrator for Storm and CSO Control. EPA
Report Number EPA-600/2-84-151.
Water Environment Federation, Manual of Practice, MOP FD-20, 1992. Design and Construction of
Urban Storm Water Management Systems. Water Environment Federation, Alexandria, VA; American
Society of Civil Engineers, New York, NY!
Washington, D.C., undated. CSQ abatement program.
Washington, D.C., July 22, 1993. Site visit to the D.C. Swirl Concentrator.
Whipple, W., and Hunter, J.V., 1981. "Settleability of Urban Runoff Pollution." Journal of the Water
Pollution Control Federation. Vol. 53. No. 12. Water Environment Federation, Alexandria, VA.
Tills BMP fact shttt was prepared by the Municipal Technology Branch (4204), US EPA, 401 M Street, SW, Washington, DC, 20460
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STORM WATER BMP;
WATER QUALITY INLETS
IMTB
Office of Wastewatar Msagement <*=*
MUNICIPAL TECHNOLOGY IRANCH
DESCRHTION
s . ' '
Water quality inlets (WQIs) consist of a series of chambers that allow sedimentation of coarse
materials, screening of larger or floating debris, and separation olF free oil (as opposed to emulsified or
dissolved oil) from storm waiter. They capture only the first portion olF runoff for treatment and are generally
used for pretreatment before discharging to other best management practices (BMPs). A typical WQI, as
shown in figure 1 below, consists of a sediment chamber, an oil separation chamber and a discharge
chamber. WQIs are also commonly called oil/grit separators or oil/water separators. WQIs can be purchased
as a pre-manufactured unit or can be constructed' on site.
•bmwattr •** ***
SOURCE: References
FIGURE 1: PROFILE OF A TYPICAL WATER QUALITY INLET
COMMON MODIFICATIONS
The design of WQIs can be modified to improve their performance. Possible modifications include
(1) an additional orifice and chamber that replace the inverted pipe elbow, (2) the extension of the second
chamber wall up to the top of the structure, or (3) the addition of a diffusion device at the inlet. The
diffusion device is intended to dissipate the velocity head and turbulence and distribute the flow more evenly
over the entire cross-sectional area (API, 1990). Suppliers of pre-manufactured units (i.e., Highland Tank
& Mfg., Jay R. Smith Mfg., etc.) can also provide modifications of the typical design for special conditions.
CURRENT STATUS , .
WQIs are widely used in the U.S.; however, recent studies indicate that the lack of regular
maintenance adversely affect their performance. There is also some concern that, because the collected
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residuals contain hydrocarbon by-products, the residuals may be considered too toxic for conventional landfill
disposal. Maintenance requirements and residual disposal, should be carefully evaluated in selecting a WQL
Possible alternatives to the WQI include sand filters, oil absorbent materials, and other innovative BMPs (i.e.,
Stormceptor System);, ,
APPLICATIONS
WQIs are often used where land requirements and cost prohibit the use of larger BMP devices, such
as ponds or wetlands. WQIs are also used to treat runoff prior to discharge to other BMPs. WQIs can be
adapted to all regions of the country (Schueler, 1992), and are typically located in small, highly impervious
areas, such as gas stations, loading areas or parking areas. Sites with high automotive related uses can be
expected to have higher hydrocarbon concentrations than other land uses (MWCOG, 1993). Increased
maintenance and residual disposal, due to these higher hydrocarbon concentrations from these areas, must
be carefully evaluated before selecting a WQI for these applications.
LIMITATIONS
Two major constraints limit the effectiveness of WQIs. Theses constraints are (1) the size of the
drainage area and (2) the activity within the drainage area. WQIs are generally recommendedfor•drainage
areas of 1 acre or less (Berg, 1991, NVPDC, 1992). Construction costs often become prohibitive for larger
drainage areas. High sediment loads interfere with the ability of the WQI to effectively separate oil and
grease from the runoff. Therefore, WQIs should not accept runoff from disturbed areas unless the runoff
has been pretreated to reduce the sediment loads to acceptable levels.
WQIs are also limited by maintenance requirements and pollutant removal capabilities. Maintenance
of underground WQIs can be easily neglected because the WQI is often "out of sight and out of mind."
Regular maintenance is essential to ensuring effective pollutant removal. Lack of maintenance will often
result in resuspension of settled pollutants. WQIs are most effective in removing heavy sediments and floating
oil and grease. WQIs have demonstrated limited ability to separate dissolved or emulsified oil from runoff.
WQIs are also not very effective at removing pollutants such as nutrients or metals, except where the metals
are directly related to sediment removal.
PERFORMANCE
More than 95 percent of all WQIs operate as designed during their first 5 years. Very few
structural or clogging problems or problems with the separation of the pollutants and water are experienced
during that period. However, WQIs have a very poor record of pollutant removal due to a lack of regular
clouts and the resuspension of the sediments (Schueler, 1992). The efficiency of oil and water separation
in a WQI is inversely proportional to the ratio of the discharge rate to the unit's surface area (API, 1990).
Due to the small capacity of the WQI, the discharge rate is typically very high and the detention time is very
short, which can result in minimal pollutant settling. The average detention tune in a WQI is less than 0.5
hour (MWCOG, 1993).
The WQI achieves slight, if any, removal of nutrients, metals and organic pollutants other than free
petroleum products (Schueler, 1992). Grit and sediments are partially removed by gravity settling within the
first two chambers. A WQI with a detention time of 1 hour may expect to have 20 to 40 percent removal of
sediments.
The Metropolitan Washington Council of Governments (MWCOG) performed a long-term study to
determine WQI performance and effectiveness. Monitoring of more than 100 WQIs indicated that less than
2 inches of sediments (mostly coarse-grained grit and organic matter) were trapped ini the WQis.
Hydrocarbon and total organic carbon (TOC) concentrations of the sediments averaged 8,150 and 53,SKH>
mc/ke, respectively. The mean hydrocarbon concentration in the WQI water column was 10 mg/L. Ihe
studfalso indicated that sediment accumulation did not increase over time, suggesting that the sediments
becdLe re-suspended during storm events (MWCOG, 1993). Although the design of the WQI effectively
separates oil and grease from water, re-suspension of the settled matter appears to limit removal efficiencies.
Actual removal occurs when the residuals are removed from the WQI (Schueler 1992).
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DESIGN CRITERIA
Prior to WQI design, the site should be evaluated to determine if another BMP would be more cost-
effective in removing the pollutants of concern. WQIs should be used where no other BMP is feasible. The
site should be near a storm drain network so that flow can be easily diverted to the WQI for treatment
(NVPDC, 1992). Construction activities within the drainage area should be completed and the drainage area
should be revegetated so that the sediment loading to the WQI is minimized. Upstream sediment control
measures should be installed to decrease the sediment loading.
WQIs are most effective for small drainage areas. Drainage areas of 1 acre or less are often
recommended. WQIs are typically used in aia off-line configuration (i.e., portions of runoff are diverted to
WQI),. but they can be used as an on-line unit (i.e., receive all runoff). Generally off-line units are designed
' to handle the first 0.5 inches of runoff from the drainage ares. Upstream isolation/diversion structures can
be used to divert the water to the off-line structure (Schueler, 1992). On-line units receive higher flows that
will likely cause increased turbulence and resuspension of settled material; thereby reducing WQI
performance.
Chamber Design
Structural loadings should be considered in the WQIdesign (Berg, 1991).WQIs are available
in pre-manufactured units or can be cast-in-place. Reinforced concrete should be used to construct below-
grade WQIs. The WQIs should be water tight to prevent possible ground water contamination. The first
and second chambers are generally connected by an opening covered by a trash rack or by a PVC or other
suitable material pipe (Berg, 1991). If a pipe is used it should also be covered by a trash rack or screen. The
opening or pipe between the first and second chambers should be designed to pass the design storm with out
surcharging the first chamber (Berg, 1991).' The design storm will vary depending on geographical location
and is generally definite by local regulations. ;
When the combined length of the first two chambers exceeds 12 feet, the chambers are typically
designed with the length of the first and second chamber being 2/3 and 1/3 of the combined length
respectively. Each of the chambers should have a separate manhole to provide access for cleaning and
inspection. ' ,
The State of Maryland design standards indicate that the combined volume of the first and second
chambers should be determined based on 40 cubic feet per 0.10 acre draining to the WQI. In Maryland, this
is equivalent to capturing the first 0433 inch of runoff from the contributing drainage area. The combined
volume includes the volume of the first and second chamber up to the top of the ulterior walls and the volume
of the permanent pool (Berg, 1991).
Permanent pools within the chambers help prevent the possibility of sediment resuspension. The first
and second chambers should have permanent pools with 4-foot depths. If possible, the third chamber should
also contain a permanent pool (NVPDC, 1992).
In the standard WQI, an inverted elbow is installed between the second and third chamber. The
elbow should extend a minimum of 3 feet into the second chamber's permanent pool in order to retain oil
(NVPDC, 1992). The elbow should be capable of passing the design storm to prevent frequent discharge of
accumulated oil. The size of the elbow or number of elbows can be adjusted to accommodate the design flow
(Berg, 1991).
-MAINTENANCE
WQIs should be inspected after every storm event to determine if maintenance is required. At a
minimum each WQI should be cleaned at the beginning of each change in season (Berg, 1991). The required
maintenance will be site-specific due to variations in sediment and hydrocarbon loading. Maintenance should*
include clean-out and disposal of the sediments and removal of trash and debris. The clean-out and disposal
techniques should be environmentally acceptable and in accordance with local regulations. Since WQI
residuals contain hydrocarbon by-products they may require disposal as a hazardous waste. Many WQI
-------
owners contract with waste haulers to collect, and dispose of these residuals. Since WQIs can be relatively
deep, they may be designated as confined spaces. Caution should be exercised to comply with confined space
entry safety regulations in the event that entry into the WQI is required.
COSTS
The construction costs for WQIs will vary greatly depending on the size and depth required. The
construction costs On 1993 dollars) for cast-in-place WQIs range from $5,000 to $16,000, with the ayerage
WQI costing around $8,500 (Schueler, 1992). For the basic design and construction of WQIs, the pro-
manufactured units are generally less expensive than those cast-in-place (Berg, 1991).
Maintenance costs will also vary greatly depending on the size of the drainage, the amount of the
residuakcSected, and the clean-out and disposal methods available (Schueler, 1992). The cost of residuafe
removal, analysis and disposal can be major maintenance expense, particularly if the residuals are toxic and
are not suitable for disposal hi a conventional landfill. ' :
WQIs can effectively trap trash, debris, oil and grease, and other floatables that would °*erwfcetoe
discharged to surface waters (Schueler, 1992). The 1993 MWCOG study founIthat poUutanfc^he WQI
sediments were similar to those pollutants found in downstream receiving water sedunents (the tidal Anacostm
River). This information suggests that downstream sediment contamination is linked to contaminatedhrunoff
(MWCOG, 1993). A properly designed and maintained WQIs can be an effectively BMP for reducing
hydrocarbon contamination in receiving water sediments.
WOIs Eenerally provide limited hydraulic and residuals storage. Due to the limited storage, WQIs
do not provide adequate storm water quantity control. The WQI residuals require frequent^rem°^d may
raraire disposal as a hazardous waste. The 1993 MWCOG study found that the residuals from WQIs
typically contain many priority pollutants, including polyaromatic hydrocarbons, trace metals,- pthaiatcs,
pheSULe, and possibly metnylene chloride (MWCOG, 1993). During periods of high flow, the residuals
may be resuspended and released from the WQI to surface waters.
1. Rbresep Limited, not dated. Informative literature on the Stonnceptor System. Oakville, Ontario,
Canada. ,
2. Schueler, T.R. 1992. A Current Assessment Of Urban Best Management Practices. Metropolitan
Washington Council of Governments.
3. Berg, V.H. 1991. Water Quality fri*« mil/Grit Separators). Maryland Department of the Environment,
Sediment and Storm Water Administration.
4. American Petroleum Institute (API) 1990. Monnpraphs on Refinery Environmental Control -_
Tf Water Discharp ~ rPesign and Option of Oil-Water Separators). Publication 421, First
5. Northern Virginia Planning District Commission (NVPDC) and Engineers and Surveyors Institute, 1992.
Northern Virginia BMP Handbook.
6 Metropolitan Washington Council of Governments (MWCOG), 1993. The Quality of Trapped Sediments
and Pool Water Within OH Grit Separators in Suburban Maryland. Interim Report.
tto BMP to shea v«pccp»m! bythe Municipal Technology Breach (4204), US EPA, «1
SW, Wad^oo, DC. 20460
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STORM WATER BMP:
WET DETENTION PONDS
MUNICIPAL TECHNOLOGY «RANCH
DESCRIPTION . .'..'". ~
Wet detention ponds provide both retention and treatment of contaminated storm water runoff. A
typical wet detention pond is shown in Figure 1 below. A wet detention pond maintains a permanent pool
of water where pollutant removal is achieved through physical, biological and chemical processes. Storm
water runoff is detained in the pond until runoff from the next storm event mixes with and displaces some
of the treated water before discharge to receiving waters. Discharge from the pond is controlled by a riser
and an inverted release pipe. .
toPrtwnlQogging
Riser with Trash Rack
Emergency
Spillway
Riprap
Cutoff Tranch
SOURCE: Reference 2
Deep Water Zone tor
Gravity Settling
Riprap tor Snoretae
Protection
Emergent Aquatic
Plants
Sediment Forebay
Concrete
Base
Low Flow Drain lor Pond Maintenance
(Should te dMigiMd to pnwid* M*y MCOM wd IB
raid dogging by ftppMj
FIGURE 1: TYPICAL LAYOUT OF A WET DETENTION POND
Wet detention ponds remove sediment, organic matter and metals by sedimentation and remove
dissolved metals and nutrients through biological uptake. Effective pollutant removal can be achieved if the
pond is properly designed and maintained (SEWPRC, 1991).
COMMON MODIFICATIONS
A typical wet pond may be enhanced with the addition of a sediment forebay, as shown in Figure 1,
.or by constructing shallow ledges along the edge of the permanent pool. Runoff passes through the sediment
forebay where the heavier sediments drop out of suspension, while additional removal of lighter sediments
occurs in the permanent pool. The shallow, peripheral ledges contain aquatic plants that trap pollutants as
they enter the pond. Biological activity also increases due to the aquatic plants, and results in increased
nutrient removal. Perimeter wetland areas can also be created that will aid in pollutant removal. The ledges
also act as a safety precaution from accidental drowning and provide easy access for maintenance to the
permanent pool.
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Treatment within a pond can be enhanced through extending the detention time hi the permanent
pool. This allows for a more gradual release of collected runoff from a design storm over a specified tune
(Hartigan, 1988). This results in increased pollution removal .?< well as control of peak flows.
CURRENT STATUS
Wet detention ponds have been widely used throughout the U.S. for many years to treat of storm
water runoff. Many of these ponds have been monitored to determine their performance. EPA Region V
Is currently performing a study on the effectiveness of SO to 60 wet detention ponds. Other organizations,
such as the Washington, D.C., Council of Governments (Wash COG) have also conducted extensive
evaluations of wet detention pond performance (Schueler, 1992). Wet detention ponds provide the benefit
of both storm water quantity and quality control. In general, a higher level of nutrient removal and better
storm water quantity control can be achieved hi wet detention ponds than can be achieved with other best.
management practices (BMPs), such as infiltration trenches or sand filters. However, proper maintenance
is essential to maintaining these higher levels of treatment.
LIMITATIONS
Wet detention ponds must be able to maintain a permanent pool. Therefore, ponds should not be
constructed in areas where there is insufficient precipitation or on soils that are highly permeable. In wetter
regions, a small minimum drainage area may be adequate, where as, in more arid regions, a larger drainage
areas may be required In order to ensure sufficient water to maintain the permanent pool. In some cases,
soils that are highly permeable may be compacted or overlaid with clay blankets to make the bottom less
permeable. Land constraints, such as small sites or highly developed areas, may also preclude the use of a
pond. In addition, the local climate (i.e., temperature) may affect the biological uptake in the pond. With
out proper maintenance, the performance of the pond will drop off sharply. Regular cleaning of the forebays
is particularly important. Maintaining the permanent pool is also important hi preventing the resuspension
of trapped sediments. In most cases no specific limitations have been places on disposal of sediments removed
from wet detention ponds. Studies to date indicate that pond sediments are likely to meet toxicity limits and
can be safely landfilled (Schueler, 1992). Some states have allowed sediment disposal on-site, as long as the
sediments are deposited away from the shoreline, preventing their reentry into the pond.
PERFORMANCE
The primary pollutant removal mechanism in a wet detention pond is sedimentation. Suspended
pollutants, such as metals, nutrients, sediments, and organics, are partly removed by sedimentation. Other
pollutant removal mechanisms include algal uptake, wetland plant uptake and bacterial decomposition
(Schueler, 1992). Dissolved pollutant removal occurs as a result of biological and chemical processes
(NVPDC, 1992).
The removal rates of conventional wet detention ponds (i.e., without the sediment forebay or
peripheral ledges) are well documented and are shown in Table 1 below. The wide range in the removal rates
is a result of varying hydraulic residence tunes (HRTs), which is further discussed in the Design Criteria
section. Increased pollutant removal by biological uptake and sedimentation is correlated with increased
HRTs. Proper design and maintenance also affect pond performance.
Studies have shown that more than 90 percent of the pollutant removal occurs during the quiescent
conditions (i.e., the period between the rainfall events) (MD, 1986). However, some removal occurs during
the dynamic period (i.e., when the runoff enters the pond). .
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TABLE 1: REMOVAL EFFICIENCIES FROM WET DETENTION PONDS
Parameter
Total Suspended Solid
Total Phosphorus
Soluble Nutrients
Lead
Zinc
Biochemical Oxygen Demand or
Chemical Oxygen Demand
1 hydraulic residence tune varies
2 hydraulic residence itime of 2 weeks
SOURCE: Reference 1
SOURCE: Referuue 2
Percent Removal
Schueler. 19921 Hartigan. 19882
80-90
50 - 90
30-90
40-80
70 - 80
40-50
20-40
50-70
DESIGN CRITERIA
Well designed and properly maintained ponds can function as designed for 20 years of more.
Concrete risers and barrels have a longer life than corrugated metal pipe risers and barrels and are
recommended for most permanent ponds (Schueler, 1992). The accumulation of sediments in the pond will
reduce the storage capacity and cause a decline in performance. Therefore, the bottom sediments in the
permanent pool should be removed every 2 to 5 years or as necessary. The design of the pond should allow
easy access to the forebays for frequent sediment removal'. .
All local, state and federal permit requirements should be established prior to starting the pond
design. Depending on the location of the pond, required permits and certifications may include wetland
permits, water quality certifications, dam safety permits, sediment and erosion control plans, waterway
permits, local grading permits, land use approvals, etc.(Schueler, 1992). Since many states and municipalities
are still in the process olf developing or modifying storm water permit requirements, the applicable
requirements should be confirmed with the appropriate regulatory authorities.
Prior to designing the pond, a site should be selected that is able to support the pond environment.
The cost effectiveness of locating a pond at that site should also be carefully evaluated. The site must have
adequate base-flow from the groundwater or from the drainage area to maintain the'permanent pool.
Typically, underlying soils: with permeability between Kr5 and 10* cm/sec will be adequate so that a
permanent poor can be maintained. In addition, the pond should be located where the topography of the site
allows for maximum storage at minimum construction costs (NVPDC, 1992). Land constraints to avoid
include existing utilities (e.g., electric or gas) that would be costly to relocate and excavation of bedrock that
would require expensive blasting operations. • .
The design of wet detention ponds should serve two functions: storm water quantity control and
storm water quality control. Storm water quantity requirements are typically met by designing the pond to
control post-development peak discharge rates to pre-development levels. Various routing models (i.e., Soil
Conservation Service TR-20 or EPA SWMM) can be used to calculate the required storm water storage.
Usually the pond is designed to control multiple design storms (e.g., 2- and/or 10-year storms) and safely pass
the 100-year storm event. However, the,, design storm may vary depending on local conditions and
requirements. , .
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Storm water quality control is achieved in the permanent pool, which is designed by either the
eutrophication method or the solids settling method (Hartigan, 1988). Several models are available for both
methods The solids settling method accounts for pollutant removal through sedimentation, whereas the
eutrophication method accounts for dissolved nutrient removal that occurs as a result of biological Presses.
Equations for the Walker eutrophication model are shown in Table 2 below. The solids settltag niethod
fadlcate that two-thirds of the sediment, nutrients and trace metal loads are removed by sedimentationwithin
SSertloi. are supported by the results of the EPA's 1993 National Urban Runoff Program
However, other studTes indicate that a hydraulic residence time (HRT) of 2 ^ j^equirec
rffflcant phosphorus removal (MD, 1986). This longer HRT is similar to the HRT determined
by thTeutropbication method. In some cases, the HRTs calculated by the eutroph.cat.on method are up to
three timTgVeater than HRTs calculated by the solids settling method. These longer HRTs appear to be due
oTe7owe?rLtion rates associated with the biological removal of dissolved nutoiente. This r^U^Uva
permanent pool that is approximately three times larger than the permanent pool calculated ********
models (Hartigan, 1988). Other design methods, such as sizing the permanent pool to collect a spedfic
volume of runoff from the drainage area, have been tried with varying degrees of success, and are not
described in this fact sheet.
TABLE 2: WALKER EUTROPHICATION MODEL '
K2 « (O.OS6)(QS)(F)-V(QS + 13.3) (1)
R « 1+(1-(1+4N)M)/(2N) (2)
where:
K2 = Second order decay rate V(m3/mg-yr)
QS - Mean .overflow rate (m/yr) = Z/T
F = Inflow ortho P/total P ratio
Z = Mean depth (m)
T = Average HRT (yr)
R = Total P retention coefficient = BMP efficiency
N = (K2)(P)(T)
P t= Inflow total P (ug/L)
SOURCE: Reference 3
Other key factors to be considered in the pond design are the volume and area rataos. Thevolume
ratio, VB/VR, is the ratio of the permanent pool storage (VB) to the mean storm runoff (VR). The area
ratio A/As, is the ratio of the contributing drainage area (A) to the permanent pool surface area (As). Both
rX t^Zritad important in thelesign of the pond and are correlated with treatment effic.enc.fis.
LW VBs and smaller VRs provide for increased retention and treatment between storm events Low
YEA* ratios result in poor pollutant removal efficiencies. The eutrophication model ****<***• «*
VB/VR ratio should equaU.0 tor maximum efficiency (Hartigan, 1988). However, ^.^J^^
set VB/VR equal to 2.5 (Hartigan, 1988). The area ratio is also an md.cator of pollutant
toZ.lrTvious studies, indicates that area ratios less than 100 typically have better
efficiencies
-------
One way to increase the HRT is to increase the depth of the permanent pool. However, the
permanent pool depth should not exceed 20 feet. The optimal depth ranges between 3 and 9 feet for most
regions, given a 2 week HFlt (Hartigan, 1988). Ponds with shallower depths will have shorted HRTs. It is
important to maintain a sufficient.permanent pool depth in order to prevent the resuspension of trapped
sediments (NVPDC, 1992). Conversely, thermal stratification and anoxic conditions in the bottom layer might
develop if permanent pool depths are too great. Stratification and anoxic conditions may decrease biological
activity. Anoxic condition!, may also increase the potential for the release of phosphorus and heavy metals
from the pond sediments (NVPDC, 1992).
In general, pond designs are unique for each site and application. Ponds should always be designed
to complement the natural topography (NVPDC, 1992). The pond should be constructed with adequate slopes
and lengths. JVhile, a length-to-width ratio is usually not used in the design of wet detention ponds for storm
water quantity management, a 2:1 length-to-width ratio is commonly used when water quality is of concern.
In general, high length-to-width ratios (greater than 2:1) will decrease the possibility of short-circuiting and
enhance sedimentation within the permanent pool. Baffles or islands can also be added within the permanent
pool to increase the flow path (Hartigan, 1988). Shoreline slopes between 5:1 and 10:1 are common and allow
easy access for maintenance, such as mowing and sediment removal (Hartigan, 1988). In addition, wetland
vegetation is difficult to establish and maintain on slopes steeper than 10:1. Ponds should be wedge-shaped
so that flow enters the pond and gradually spreads out. This minimizes the potential for zones with little or
no flow (Urbonas, 1993). ,
The design of the wet pond embankment is another key factor to be considered^ Proper design and
construction of the embankments will prolong the integrity of the pond structure. Subsidence and settling
will likely occur after an embankment is constructed. Therefore, during construction the embankment should
be overfilled by at least 5% (SEWPRC, 1991). Seepage through the embankment can also affect the stability
of the structure. Seepage can generally be minimized by adding drains, anti-seepage collars and core
trenches. The embankment side slopes can be protected from erosion by using minimum side slopes of 2:1
and by covering the embankment with vegetation or rip-rap. The embankment should also have a minimum
top width of 6 feet to ease maintenance.
Normal flows willl be discharged through the wet pond outlet, which consists of a concrete or
corrugated metal riser and! barrel. The riser is a vertical pipe or inlet structure that is attached to the base
with a watertight connection. Risers are typically placed in or adjacent to the embankment rather than in
the middle of the pond. This provides easy access for maintenance and prevents the use of the riser as a
recreation spot (e.g., diving platform for kids) (Schueler, 1988). The barrel is a horizontal pipe attached to
the riser that conveys flow under the embankment. . -
Typically, flow passes through an inverted pipe attached to the riser, as shown hi Figure 1, with
higher flows will pass through a trash rack installed on the riser. The inverted pipe should discharge water
from below the pond water surface to prevent floatables from clogging the pipe and to avoid discharging the
warmer surface water. Clogging of the pipe could result in overtopping of the embankment and damage to
the embankment (NVPDC,, 1992). Flow is conveyed through the near horizontal barrel and discharged to the
receiving stream. Rip-rap, plunge pools, or other energy dissipators should be placed at the outlet to prevent
scouring and minimize eirosion. Rip-rap also provides a secondary benefit of reaeration of the pond
discharges.
.. ' '*.,'' ' ' / ' - • • . ,
The design and construction of the riser and barrel should consider the design storm and the material
of construction. Generally, the riser and barrel are sized to meet the storm water management design criteria
(e.g., to pass a 2-year or a 10-year storm event). In many installations the riser and barrel are designed to
convey multiple design storms (Urbonas, 1993). The riser and barrel should be constructed of reinforced
concrete rather than corrugated metal pipe to increase the life of the outlet. The riser, barrel and base should
also have sufficient weight: to prevent flotation (NVPDC, 1992).
In most cases, emergency spillways should be included ira the pond design. Emergency spillways
should be sized to safely pass flows that exceed the design storm flows. The spillway prevents pond water
levels from overtopping the embankment, which could cause structural damage the embankment. The
-------
* ' *
emergency spillway should be located so that downstream buildings and structures will not be negatively
impacted by a spillway discharges. The pond design should include a low flow drain, as shown in Figure 1.
The drain pipe should be designed for gravity discharge and should be equipped with an adjustable gate
valve. ' ' -,
MAINTENANCE
Wet detention ponds function more effectively when they are regularly inspected and maintained.
Routine maintenance of the pond includes mowing of the embankment and buffer areas and inspection for
erosion and nuisance (e.g., borrowing animals, weeds, odors) problems (SEWPRC, 1.991). Trash and debris
should be routinely removed to maintain an attractive appearance and also to prevent the outlet from
becoming clogged. In general, wet detention ponds should be inspected after every storm event. The
embankment and emergency spillway should also be routinely inspected for structural integrity, especially
after major storm events. Embankment failure could result in severe downstream flooding. .'
When any problems are observed during routine inspections, necessary repairs should be made-
immediately. Failure to correct minor problems may lead to larger more expensive repairs or even powd
failure. Typically, maintenance includes repairs to the embankment, emergency spillway, inlet and outlet,
removal of sediment and control of algal growth, insects and odors (SEWPRC, 1991). Large vegetation or
trees that may weaken the embankment should be removed. Periodic maintenance may also include the
stabilization of the outfall area (e.g., add rip-rap) to prevent erosive damage to the embankment and the
stream bank. In most cases sediments removed from wet detention ponds are suitable for landfill disposal.
However, where available, on-site disposal od. removed sediments will reduce maintenance costs.
coins
The total cost for a pond includes permitting, design and construction and maintenance costs.
Permitting costs may vary depending on.state and local regulations. Typically, wet detention ponds are less
costly to construct in undeveloped areas than retrofitting into developed areas. This is due to the cost of latad
and the difficulty in finding suitable sites in developed areas. The cost of relocating of pre-existing utilities
or structures is also a major concern in developed areas. The construction costs for wet detention ponds in
1989 for undeveloped areas are shown hi Figure 2 below. These costs include mobilization and demobilization
of heavy equipment, site preparation (e.g., clearing and excavation), site development (e.g., seeding and inlet
construction) and contingencies (e.g., engineering and legal fees) (SEWPRC, 1991). Several studies have
shown the construction cost of retrofitting a wet detention pond into a developed area may be 5 to 10 times
the cost of constructing the same size pond in an undeveloped area.
Operation and maintenance costs in 1989 are presented in Figure 3 below (SEWPRC, 1991). Annual
maintenance costs can generally be estimated at 3 to 5 percent of the construction costs (Schueler, 1992).
Maintenance costs include the costs for regular inspections of the pond embankments, grass mowing, nuisance
control, debris and liter removal, inlet and outlet maintenance and inspection, and sediment removal aind
disposal. Sediment removal costs can be decreased by as much as 50 percent if an on-site disposal areas are
available (SEWPRC, 1991). ,
ENVIRONMENTAL IMPACTS
Wet detention ponds provide both storm water quantity and quality benefits. Benefits obtained from
the use of wet detention ponds include decreased potential for downstream Hooding and stream bank erosion.
Water quality is also unproved due to the removal of suspended solids, metals, and dissolved nutrients. In
general, the positive impacts from a wet detention ponds will exceed any negative impacts from a pond,
assuming the pond is properly designed and maintained.
-------
TABLE 3: CONSTRUCTION COSTS (198S>)
USMMLL
MAMTENAMCE'
I ' ^ ^
X* / ^'^ •i
«M-r ' —• _-^^ • -•
SOURCE: Rcfenmce4
•TrOritimaNIASMWTBI VOLUME M THOUSANDS OF CMK FEET
TABLE 4: OPERATIONS AND MAINTENANCE COSTS (1989)
SOURCE: Rrfe
However, wet detention ponds that are improperly designed, sited or maintained may have potential
adverse affects on water quality, groundwater, cold water fisheries, or wetlands. Improperly designed or
maintained ponds may result in stratification and anoxic conditions that can promote the resuspension of
solids and the release of nutrients and metals from the trapped sediments. During construction, precautions
should be taken to prevent damage to wetland areas. Ponds should also not be sited in areas where warm
water discharges from the pond will adversely impact cold water fishery. The potential groundwater
contamination should be carefully evaluated. However, studies to date indicate that wet detention ponds do
not significantly contribute to groundwater contamination (Schueler, 1992).
-------
s. MetropoUtan
WJKERENCES.
1. Schuder, T.R., 1992. A Current Assessment of Urban Best Management
Washington Council of Governments. . ' .
2. Maryland, Department of the Environment (MID), 1986. Feasibility and Design of Wet Ponds to Achieve
Water Quality Control. Sediment and Storm Water Administration.
3. Hartigan, J.P, 1988. "Basis for Design of Wet Detention Basin BMPS" in Design of Urban Runoff
Quality Control. American Society of Engineers.
4. Southeastern Wisconsin Regional Planning Commission (SEWPRC), 1991. Costs for Urban NonPoint
Source Water Pollution Control Measures. Technical Report No. 31.
5. Northern Virginia Planning District Commission (NVPDC) and Engineers and Surveyors Institute, 1992.
Northern Vire^"
6. Urbonas, Ben and Peter Stahre, 1993. Storm Water Best Management Practices and Detention for Water
Quality. Drainage, and CSO Management. PTR Prentice Hall, Englewood Cliffs, New Jersey.
1W« bet rittrt w* prepared by «he MmUdpd Teduubgjr Branch (4204), US EPA, 401M Street, SW. Wnttiigtoa, DC, 20460
-------
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tear it out, fold it, staple it, put a stamp on it and mall it. Otherwise, it may be
faxed to 202-260-01116
MTE
Office of Wastewater Management '
MUNICIPAL TECHNOLOGY BRANCH
MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS ADDENDUM:
STORM WATER BEST MANAGEMENT PRACTICES
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FOLD HERE
Municipal Technology Branch (4204)
United States Environmental Protection Agency
401 M Street, SW
Washington, DC, 20460
FOLD HERE
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