United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 832-F-00-079
September 2000
Decentralized Systems
Technology Fact Sheet
Septic Tank Systems for Large Flow Applications
DESCRIPTION
A septic tank system is a traditional wastewater
treatment technology utilizing treatment in a tank
system followed by soil absorption. The system
operates on gravity and has been used in residential
areas for decades. A modification to the traditional
system is an enlargement to accommodate many
homes and/or commercial discharges. This is
accomplished with individual septic tanks followed
by a community collection and subsurface disposal
system, or a community collection system followed
by a single treatment system. Commercial
establishments, such as restaurants, nursing homes,
hospitals and other public use areas do not generally
use septic tank systems due to oil & grease, odor,
and flow issues.
The primary device in treatment is a septic tank
enclosed in a watertight container that collects and
provides primary treatment of wastewater by
separating solids from the wastewater. The tank
removes solids by holding wastewater in the tank
and allowing settleable solids to settle to the bottom
of the tank while floatable solids (oil and grease)
rise to the top. In large commercial systems, a
separate oil/grease removal system is applied to the
commercial waste before introduction to the septic
tank. The tank should hold the wastewater for at
least 24 hours to allow enough time for the solids to
settle.
Some solids are removed from the water and stored
in the tank while some are digested. Up to 50
percent of solids retained in the tank decompose
while the remainder accumulate as sludge at the
tank bottom and must be removed periodically by
pumping the tank.
Three main types of septic tanks are used for
wastewater treatment:
• Concrete.
• Fiberglass.
• Polyethylene/plastic.
All tanks must be watertight because groundwater
entering the system can saturate the soil absorption
field, resulting in a failed system. Furthermore, in
instances where septic tanks precede a secondary
treatment process, excess groundwater may
inundate the downstream process, causing it to
perform poorly.
From the septic tank, the clarified wastewater
passes through the tank outlet and enters the soil
absorption field. The most common outlet is a tee
fitting connected to the pipe leading to the soil
absorption field. The top of the tee retains floatable
solids (scum, oil, and grease) that might otherwise
clog the absorption field. An effluent filter can be
placed in the outlet tee for additional filtering of
wastewater. The effluent filter removes additional
solids, keeping them from clogging the absorption
field and causing premature failure. Effluent filters
must be cleaned regularly.
Soil Absorption Field
The soil absorption field provides final treatment
and distribution of the wastewater. A conventional
system consists of perforated pipes surrounded by
media such as gravel, chipped tires, or other
material, covered with geotextile fabric and loamy
soil. This system relies heavily on the soil to treat
wastewater, where microorganisms help remove
organic matter, solids, and nutrients from the water.
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As effluent continually flows into the soil, the
microbes eating the components of the wastewater
form a biological mat. The mat slows the
movement of the water through the soil and helps
keep the area below the mat from becoming
saturated. The water must travel into unsaturated
soil so microbes there and in the mat can feed on
the waste and nutrients in the effluent. The grass
covering the soil absorption system also uses the
nutrients and water to grow.
Backfill 1-3'
Barrier Material
6-12" gravel
Perforated
Distribution Pipe
Source: Robillard and Martin, 2000
FIGURE 1 SECTION OF TRENCH SOIL
ABSORPTION SYSTEM
Treatment
Used properly, the septic tank and soil absorption
system works well, reducing two parameters
commonly used to measure pollution: (1)
biochemical oxygen demand, which is lowered by
more than 65 percent; and (2) total suspended
solids, which are cut by more than 70 percent. Oil
and grease are typically reduced by 70 to 80 percent
(EPA 1980).
Using a septic tank to pretreat sewage from
commercial sources also makes other secondary
treatment systems more effective. The effluent
from the septic tank is consistent, easy to convey,
and easily treated by either aerobic (with free
oxygen) or anaerobic (without free oxygen)
processes.
Common Modifications
Septic tanks for large flow systems may be
followed by traditional soil absorption systems or
by one of several alternate technologies such as
constructed wetlands or slow sand filtration.
Pressure sewers and small diameter gravity sewers
may also be used as alternate collection systems for
transport of effluent to central treatment facilities.
These systems are discussed in other fact sheets
(see Reference section). This fact sheet focuses on
the traditional septic tank system applied to
commercial waste and multiple sources, using
subsurface infiltration for wastewater disposal.
Subsurface Infiltration
Subsurface wastewater infiltration systems (SWISs)
are subgrade land application systems most
commonly applied in unsewered areas by individual
residences, commercial establishments, mobile
home parks, and campgrounds (EPA, 1992). The
soil infiltration surfaces are exposed in buried
excavations that are generally filled with porous
media. The media maintain the structure of the
excavation, allows the free flow of pretreated
wastewater to the infiltrative surfaces, and provides
storage of wastewater during times of higher flows.
The wastewater enters the soil where treatment is
provided by filtration, adsorption, and biologically
mediated reactions which consume or transform
various pollutants. Ultimately, the wastewater
treated in the SWIS enters and flows with the local
groundwater.
Various SWIS designs have been developed for
various site and soil conditions encountered. The
designs differ primarily in where the filter surface
is placed. The surface may be exposed within the
natural soil profile (conventional or alternative
technology) or at or above the surface of the natural
soil (at-grade or mound systems) (see related Fact
Sheets). The elevation of the filter surface is
critical to provide an adequate depth of unsaturated
soil between the filter surface and a limiting
condition (e.g. bedrock or groundwater) to treat
wastewater applied.
The geometry of the filter surface also varies, with
long, narrow filter surfaces (trenches) much
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preferred. Wide filter surfaces (beds) and deep
filter surfaces (pits and deep trenches) do not
perform as well, although they require less area.
Subsurface infiltration systems are capable of high
levels of treatment for most domestic wastewater
pollutants. Under suitable site conditions, they
provide nearly total removal of biodegradable
organics, suspended solids, phosphorus, heavy
metals, and virus and fecal indicators.
The fate of toxic organics and metals is not as well
documented, but limited studies suggest that many
of these constituents do not travel far from the
system. Nitrogen is the most significant wastewater
parameter not readily removed by the soil. Nitrate
concentrations above the drinking water standard of
10 mg-N/L are commonly found in groundwater
immediately below SWISs (EPA 1992), but these
concentrations fall with distance down-gradient of
the SWIS.
APPLICABILITY
Community Establishments
Septic tanks are usually the first component of an
on-site system and are the most widely used on-site
wastewater treatment option in the United States.
Currently, about 25 percent of new homes in the
United States use septic tanks for treatment prior to
disposal of home wastewater.
Septic tanks for single family homes are generally
purchased as "off the shelf items, which means
that they are ready for installation and based on a
standard flow. The wastewater characteristics used
to design septic tanks are generally those for a
typical residence.
Commercial Establishments
For many commercial establishments, the
wastewater-generating sources are sufficiently
similar to the wastewater-generating sources in a
residential dwelling. For other establishments,
however, the wastewater characteristics may be
considerably different from those of typical
residential wastewater.
Commercial establishments can take advantage of
a centralized system if the flows and capacities are
sufficient and adequate pretreatment is available.
Wastewater must be pretreated prior to being
discharged to a soil absorption system. Wastewater
is most commonly pretreated by an on-site septic
tank when a soil absorption system is used for
treatment/disposal. In areas where soil and
groundwater conditions are favorable for
wastewater disposal and land costs are low, a
community soil absorption system is usually the
most cost effective wastewater treatment/disposal
option for flows below 35,000 gallons per day.
Careful application of the effluent to the soil
absorption system ensures uniform application of
effluent over the filtration surface. Distribution
laterals should be provided with cleanouts for
access and flushing. Ponding monitors should be
installed in trench areas to allow observation of
liquid level in trenches.
Subsurface Infiltration
In some instances, it is desirable to bury the
absorption system. Buried systems, known as
subsurface wastewater infiltration systems (SWISs),
are advantageous because the land above a SWIS
may be used as green space or park land, and
because they provide groundwater recharge.
Subsurface infiltration systems are well suited for
treatment of small wastewater flows. Small SWISs,
commonly called septic tank systems., are
traditionally used in unsewered areas by individual
residences, commercial establishments, mobile
home parks, and campgrounds. Since the late
1970s, larger SWISs have been increasingly used by
clusters of homes and small communities where
wastewater flows are less than 25,000 gpd. They
are a proven technology, but require specific site
conditions to be successfully implemented. SWISs
are often preferred over on-site mechanical
treatment facilities because of their consistent
performance with few operation and maintenance
requirements, lower life cycle costs, and less visual
impact on the community.
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DESIGN CRITERIA
Pretreatment of Wastewater for Commercial
Septic Tank Systems
The most serious operational problem encountered
with commercial septic tank systems has been the
carry-over of solids, oil and grease due to poor
design and lack of proper maintenance. The
carryover of suspended material is most serious
where a disposal field is to be used to dispose of
septic tank effluent without further treatment.
Recognizing that poor septic tank maintenance is
common, some regulatory agencies require the
addition of a large septic or other solids separation
unit before collected septic tank effluent can be
disposed of in subsurface disposal fields. The use
of oil and grease traps reduces the discharge of TSS
and oil and grease significantly. The presence of oil
and grease in effluents from septic tanks servicing
restaurants has led to the failure of downstream
treatment processes such as intermittent and
recirculating sand filters. As a consequence of
these problems, pretreatment is recommended.
Pretreatment in centralized treatment systems
involves coarse screening, comminution, grit
removal, oil and grease removal, flow equalization,
and TSS removal.
increase in different types of oils and greases
available for cooking. The problem is further
complicated because many of these oils are soluble
at relatively low temperatures, making their
removal more difficult. Typically, skimming or
interceptor tanks (grease traps) are used to trap
greases and oils. Figure 2 shows a schematic of an
oil and grease trap with an external sampling
chamber.
Note: 1 in = 2.54 cm
Source: Crites and Tchobanoglous, 1998
FIGURE 2 SCHEMATIC OF OIL AND
GREASE TRAP WITH EXTERNAL
SAMPLING CHAMBER
Pretreatment for Oil and Grease Removal
Wastewater from restaurants, laundromats, and
other commercial establishments may contain
significant amounts of oils and grease which may
be discharged to the soil absorption system when
they enter a septic tank. Oils and greases tend to
accumulate on the surface of the soil absorption
system, reducing the infiltration capacity. Oils and
greases are especially troublesome because of their
persistence and low rate of biodegradation. To
avoid problems in decentralized wastewater
treatment and disposal systems, the effluent oil and
grease concentration should be reduced to less than
about 30 mg/L before it is introduced to the soil
absorption system (Crites and Tchobanoglous
1998).
The problems associated with the removal of oils
and greases become more complex with the
Several commercial oil and grease traps are
available. Most commercial units are rated by
average flow rather than instantaneous peak flows
observed in the field from restaurants and laundries.
The use of conventional septic tanks as interceptor
tanks has also proven to be effective in removing
oil and grease. Depending on the tank
configuration, some replumbing may be necessary
when septic tanks are used to trap grease.
Typically, the inlet is located below the water
surface while the outlet is placed closer to the
tank's bottom. The larger volume provided by the
septic tank helps achieve the maximum possible
separation of oils and greasy wastes. For
restaurants, the use of a series of three interceptor
tanks is effective to separate oil and grease. High
concentrations of oil and grease associated with
restaurants make the use of three interceptor tanks
in series necessary to reduce this concentration to
acceptable levels.
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Volumes for grease interceptor tanks typically vary
from one to three times the average daily flowrate.
For example, if a restaurant serves 100
customers/day at an average flow of 38
liters/day/customer (10 gallons/day/customer), the
size of the grease interceptor tank should be
between 3,800 and 11,400 liters (1,000 and 3,000
gallons). Depending on the activities at a given
facility, accumulated sludge and scum should be
removed every three to six months (Crites and
Tchobanoglous 1998).
Septic Tanks
A septic tank must be the proper size and
construction and have a watertight design and stable
structure to perform successfully.
• Tank size. The required size of a septic
tank for a commercial establishment
depends on anticipated flows from the
facility, coupled with additional flow from
residences or other inputs, if on a
community system.
Tank construction. A key factor in septic
tank design is the relationship between the
amount of surface area, its sewage storage
capacity, and the amount and speed of
wastewater discharge. These factors affect
the tank's efficiency and the amount of
sludge retention. Tank construction must
also assure a watertight structure.
A key to maintaining a septic tank is placing risers
on the tank openings. If a septic tank is buried
below the soil surface, a riser must be used on the
openings to bring the lid to the soil surface. These
risers make it easier to locate and maintain the tank.
Septic tank effluent may be applied to the soil
absorption field by intermittent gravity flow or via
a pump or dosing siphon. Periodic application
using a dosing siphon maintains an aerobic
environment in the disposal field, allowing
biological treatment of the effluent to occur more
rapidly. Dosing siphons are particularly desirable
for fields composed of highly permeable soils
because they help maintain the unsaturated flow
conditions necessary to achieve effective biological
treatment of effluent.
Subsurface Infiltration
Important considerations in designing subsurface
infiltration systems include:
• Soil texture. There are three sizes of soil
particles: sand, silt and clay. Texture
reflects the relative percentage of each of
these soil particles at a particular site. Soil
texture affects the rate at which wastewater
infiltrates into and percolates through the
soil (called hydraulic conductivity). These
factors determine how large an absorption
field is needed. Sand transmits water faster
than silt, which is faster than clay.
Hydraulic loading. This is the amount of
effluent applied per square foot of trench
surface or field, an important factor in
septic tank design. Because water filters
through clay soils more slowly than through
sand or silt, the hydraulic loading rate is
lower for clay than for silt, and lower for
silt than for sand. Because clay soils have a
very low conductivity, they may easily
smear and compact during construction,
reducing their infiltration rate to half the
expected rate.
Site Selection
Selection criteria for a site on which wastewater
treatment and renovation is to occur must consider
two fundamental design factors. These are the
ability of a site to assimilate the desired hydraulic
load and the ability of the site to assimilate the
process load. The process load consists of the
organic matter, nutrients, and other solids contained
in the wastewater. The hydraulic assimilative
capacity of a site is often determined by the texture
of the soil material on a site. Sites with sandy
textured soils generally are assigned high hydraulic
loadings while sites with fine textured clay are often
assigned low hydraulic assimilative capacities.
This typical hydraulic loading scenario often results
in excessive loadings of the process constituents on
a sandy site.
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Sandy textured soils generally exhibit rapid
permeability. This suggests that these soils will
drain rapidly and reaerate quickly. These
characteristics allow moderately high organic
loadings onto these soils, but limit the potential for
these soils to attenuate soluble pollutants such as
nitrogen and phosphorus. The fine textured soils -
those that contain clays - exhibit high potential to
attenuate soluble pollutants, but exhibit very limited
capacity to transmit liquid; consequently the
hydraulic loadings applied to these soils must be
very conservative. No soil provides the optimum
characteristics to assimilate all constituents applied
and the challenge to the onsite wastewater
professional is to balance the loadings applied with
the total assimilative capacity of the designed
receiver site. Treatment objectives must be utilized
to optimize system design.
When large volumes of wastewater are designated
for application onto a site, then a groundwater
mounding analysis may be required. This analysis
is required to assure that the separation distance
between the bottom of the trench and the shallow
groundwater is adequate to provide necessary
treatment. Large systems should be designed so
that the longest dimension of the trench is along site
contour lines and the shortest dimension crosses
field contours. This generally results in systems
designed with hydraulic gradients that facilitate
treatment.
Soil and site conditions on which wastewater will
be treated will vary from location to location. Sites
selected as receivers for wastewater must exhibit
characteristics that facilitate treatment and
renovation of wastewater. Sites for wastewater
treatment and renovation must be selected based on
criteria established by local regulatory agencies as
acceptable
Trench bottom application rates range from 0.2 to
1.2 gpd/ft2 depending on soil conditions. Table 1
contains suggested rates of wastewater applications
for trench and bed bottom areas.
TABLE 1 SUGGESTED RATES OF
WASTEWATER APPLICATION
Soil Texture
Gravel, coarse
sand
Coarse to
medium sand
Fine to loamy
sand
Sandy loam to
loam
Loam, porous
silt
Silty clay loam,
clay loam
Clay, colloidal
clay
Percolation
Rate (m in/in/
min/cm)
<1/
<0.4
1 -51
0.4-2.0
6 -157
2.4-5.9
16-307
6.3-11.8
31 - 607
12.2-23.6
61 - 1207
24.0-47.2
>120/>47.2
Application
Rate (gpd/ft2/
Lpd/m2)
not suitable
1.27
0.049
0.87
0.033
0.67
0.024
0.457
0.018
0.27
0.008
not suitable
Notes: 1) min/in x 0.4 = min/cm
2) gpd/ft2 x 40.8 = Lpd/m2
Source: Crites STchobanoglous, 1998.
Hydraulic Loading Rate
The design hydraulic loading rate is determined by
soil characteristics, groundwater mounding
potential, and applied wastewater quality. Clogging
of the infiltrative surface will occur in response to
prolonged wastewater loading, which will reduce
the capacity of the soil to accept the wastewater.
However, if loading is controlled, biological
activity at the infiltrative surface will maintain
waste accumulations in relative equilibrium so
reasonable infiltration rates can be sustained.
Selection of the design hydraulic loading rate must
consider both soil and system design factors.
Typically, design rates for larger SWISs are based
on detailed soil analyses and experience, rather than
measured hydraulic conductivities.
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Wastewater Pretreatment
Disadvantages
At a minimum, wastewater treatment in a septic
tank is required before application to a SWIS.
Figure 3 presents a schematic of a dual soil
absorption system. Higher levels of treatment such
as achieved with an aerobic treatment unit (ATU)
can reduce SWIS size or prolong system life, but
this must be weighed against the increased costs of
pretreatment and potential damage from poor
maintenance of the system.
Source: Barrett and Malina, 1991
FIGURE 3 PLAN VIEW OF DUAL SOIL
ABSORPTION BED SYSTEM
ADVANTAGES AND DISADVANTAGES
Advantages
Subsurface infiltration systems are ideally suited for
decentralized treatment of wastewater because they
are buried. They are often the only method of
wastewater treatment available for rural homes and
business establishments. Some communities
choose subsurface infiltration systems to avoid
costly sewer construction. Where individual lots
are not suited for their use, remote sites may be
used to cluster homes onto a single SWIS, limiting
the need for sewers. Alternatively, wastewater from
entire communities may be treated by a SWIS.
Because the system is buried, the land area can be
used as green space or park land. In addition,
SWISs provide groundwater recharge.
Use of SWISs is limited by site and soil conditions.
Because the infiltrative surface is buried, it can be
managed only by taking it out of service every 6 to
12 months to "rest", requiring the construction of
standby cells with alternating loading cycles.
Therefore, larger SWISs are usually restricted to
well-drained sandy soils to reduce land area
requirements. Because nitrogen is not effectively
removed by SWISs, pretreatment may be necessary
to prevent nitrate contamination above drinking
water standards in underlying groundwater.
Flows from commercial establishments greater than
the design capacity of the system may overwhelm
the SWIS and produce overflow conditions and
objectionable odors.
PERFORMANCE
Septic tanks and other pretreatment units must be
properly maintained to keep a SWIS system treating
sewage efficiently. As the septic tank or ATU is
used, sludge accumulates in the bottom of the
treatment unit. As the sludge level increases,
wastewater spends less time in the tank and solids
may escape into the absorption area. Properly sized
septic tanks generally have enough space to
accumulate sludge for at least three years. ATUs
require aggressive sludge management.
The frequency of tank pumping depends on:
• The capacity.
• The amount of wastewater flowing into the
tank (related to size of household).
The amount of solids in the wastewater (for
example, more solids are generated if
garbage disposals are used).
The soil absorption field will not immediately fail
if the tank is not pumped, but the septic tank will no
longer protect the soil absorption field from solids.
If the tank or ATU is neglected for long, it may be
necessary to replace the soil absorption field.
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One example of septic tank/absorption field system
failure is found in Missouri. Several statewide
surveys have shown that 70 percent (150,000) of
systems are not functioning properly, causing nearly
60 million gallons of untreated or semi-treated
sewage per day to reach groundwater supplies
(Schultheis and Hubble). Based on the general soils
map of Missouri, 60 to 99 percent of counties in the
Ozarks region show severe limitations in the use of
absorption field systems.
Many studies of failing septic tank systems have
been conducted. The Lower Colorado River
Authority (LCRA) received a grant from the Texas
Water Commission (TWC) to identify clustered
sites of on-site wastewater treatment and disposal
facilities in the Lavaca and Colorado coastal basins
that may be failing. Information from this study
will identify areas which may qualify for funding
under Section 319 of the Clean Water Act.
A study was conducted by the Texas Water
Commission (TWC) to gauge whether septic tanks
were polluting Lake Granbury in Hood County,
Texas (TWRI Spring 1993). Because so many
septic tanks were in use near the lake, there was
additional concern of fecal coliform contamination.
Analysis of samples taken in coves along the lake
showed that 10 percent of tested areas had more
than 200 colony-forming units per 100 milliliters,
indicating that the lake is highly contaminated with
fecal coliform bacteria.
Increasingly stringent discharge regulations have
led many communities to turn to more effective on-
site means to treat waste. One example is Eagle
Mountain Lake near Fort Worth, Texas, where the
Tarrant County Water Control and Improvement
District (WCID) is taking strides to improve the
effluent quality of the 2,500 local on-site
wastewater systems at Eagle Mountain Lake. Many
homes in this area are weekend homes, with septic
tanks designed for limited use. WCID is designing
the on-site system to be large enough for full time
use to improve effluent quality.
In the Texas Panhandle, the Texas Natural
Resource Conservation Commission (TNRCC) has
used innovative on-site technologies to solve
wastewater problems in the region associated with
failing septic tank systems due to rapid growth in
the region. In the 1980s, the town of Umbarger
installed a 44,000-gallon septic tank and a 30,720-
square foot drainfield to serve its 325 residents.
This community system replaced the collection of
many smaller septic tanks distributed throughout
the town, many of which had previously
experienced failures.
OPERATION AND MAINTENANCE
Subsurface Infiltration
A well-designed SWIS requires limited operator
attention. Management functions primarily involve
tracking system status, testing for solids
accumulation, evaluating pump performance,
monitoring system controls, and monitoring
performance of pretreatment units, mechanical
components, and wastewater ponding levels above
the filtration surface. Operator intervention may be
required if a change is noted. Routine servicing of
SWIS is generally limited to annual or semiannual
alternating of infiltration cells.
Another maintenance task to prevent a system from
backing up is to clean the screen on the effluent end
of the septic tank. This filter must be cleaned
periodically by removing the filter from the outlet
and spraying it with a hose directed back into the
septic tank.
Soil absorption fields must be protected from solids
and rainfall. If a tank is not pumped, solids can
enter the field. Rainfall running off roofs or
impermeable surfaces such as concrete areas should
be diverted around the soil absorption field to
prevent it from becoming saturated with rainwater.
Fields saturated with rainwater cannot accept
wastewater. Planting cool-season grasses over the
soil absorption field in winter can help remove
water from the soil and keep the system working
properly.
COSTS
Subsurface Infiltration
Land and earthwork are the most significant capital
costs. Where fill must be used to bed the primary
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infiltrative surface, the cost of transporting the
material also becomes significant. Other costs
include pretreatment and transmission of
wastewater to the treatment site.
Other factors that affect septic tank costs include
subsurface site conditions, location of and access to
the site, and the type of tank used. Costs of tanks,
including installation, typically range from $1.00 to
$4.00 per gallon of tankage. Pumping septic tanks
ranges from $150 to $200 per 2,000 gallons. If a
tank is pumped once every 3 1A years, the
maintenance cost will be about $50 per year, with a
pump and haul cost of $175.
REFERENCES
Other Related Fact Sheets
Mound Systems
EPA 832-F-99-074
September 1999
Pressure Sewers
EPA 832-F-00-070
September 2000
Small Diameter Gravity Sewers
EPA 832-F-00-038
September 2000
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. Barret, Michael E. and J. F. Malina, Jr.
Sep. 1, 1991. Technical Summary of
Appropriate Technologies for Small
Community Wastewater Treatment Systems.
The University of Texas at Austin.
2. Corbitt, Robert A. 1990. Standard
Handbook of Environmental Engineering.
McGraw-Hill, Inc. New York.
3. Community Environmental Services, Inc.
Septic Tank. Fact Sheet. City of Austin, TX.
4. Crites, R. and G. Tchobanoglous. 1998.
Small and Decentralized Wastewater
Management Systems. WCB McGraw-Hill,
Inc. Boston.
5. Robillard, Paul D. and Kelli S. Martin.
Septic Tank Soil Absorption Systems.
Agricultural and Biological Engineering
Fact Sheet. Penn State, College of
Agriculture. Site accessed 2000.
http://www.klinesservices.com/psl.cfm.
6. Schultheis, Robert A. and Gwen Hubble. A
Homeowner's Guide: Septic
Tank/Absorption Field Systems. Extension
Service, U.S. Department of Agriculture,
Project Number 90-EWQI-1-9241,
publicationWQ0401.
7. Texas On-Site Insights, Volume 2, Number
1: Spring 1993, Measuring the Impact of
Septic Tanks on Lake Granbury. Texas
Water Research Institute.
8. Texas On-Site Insights, Volume 2, Number
2: Summer 1993, LCRA Receives Grant to
Study On-Site Systems in Colorado, Lavaca
Coastal Basins. Texas Water Research
Institute.
9. Texas On-Site Insights, Volume 4, Number
2: Spring 1995, Managing On-Site
Wastewater Programs at Eagle Mountain
Lake. Texas Water Research Institute.
10. Texas On-Site Insights, Volume 6, Number
2: June 1997, Texas Panhandle is Site of
Many Innovative On-Site Systems. Texas
Water Research Institute.
11. U.S. Environmental Protection Agency.
1980. Design Manual: Onsite Wastewater
Treatment & Disposal Systems. EPA Office
of Water. EPA Office of Research &
Development. Cincinnati. EPA 625/1-
80/012.
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ADDITIONAL INFORMATION
Lower Colorado River Authority
Burt Carter
P.O. Box 220
Austin, TX 78767
Tarrant County WCID
David Jensen
10201 North Shore Drive
Fort Worth, TX 76135
Texas Natural Resource Conservation Commission
Lezlie Cooper or Steve Green
3918 Cany on Drive
Amarillo, TX79109
Texas Natural Resource Conservation Commission
Wilson Snyder
6801 Sanger Avenue, Suite 2500
Waco, TX 76710
David Venhuizen, P.E.
5803 Gateshead Drive
Austin, TX 78745
The mention of trade names or commercial
products does not constitute endorsement or
recommendations for use by the United States
Environmental Protection Agency (EPA).
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, NW
Washington, D.C. 20460
MTB
Excelence fh tompfance through optfhial tethnltal solutfons
MUNICIPAL TECHNOLOGY BRANCH
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