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Table of Contents
“We never know the worth of water till the well is dry.”
Thomas Fuller
Gnomologia, 1732
Introduction
One of the primary differences between rural and urban
housing is that much infrastructure that is often taken for granted by the urban
resident does not exist in the rural environment. Examples range from fire and police
protection to drinking water and sewage disposal. This chapter is intended to provide
basic knowledge about the sources of drinking water typically used for homes in
the rural environment. It is estimated that at least 15% of the population of the
United States is not served by approved public water systems. Instead, they use
individual wells and very small drinking water systems not covered by the Safe Water
Drinking Act; these wells and systems are often untested and contaminated [1].
Many of these wells are dug rather than drilled. Such shallow sources frequently
are contaminated with both chemicals and bacteria.
Figure 8.1 shows the change in water supply source in the United States
from 1970 to 1990. According to the 2003 American Housing Survey, of the 105,843,000
homes in the United States, water is provided to 92,324,000 (87.2%) by a public
or private business; 13,097,000 (12.4%) have a well (11,276,000 drilled, 919,000
dug, and 902,000 not reported) [2].
Water Sources
The primary sources of drinking water are groundwater and surface water. In addition,
precipitation (rain and snow) can be collected and contained. The initial quality
of the water depends on the source. Surface water (lakes, reservoirs, streams, and
rivers), the drinking water source for approximately 50% of our population, is generally
of poor quality and requires extensive treatment. Groundwater, the source for the
other approximately 50% of our population, is of better quality. However, it still
may be contaminated by agricultural runoff or surface and subsurface disposal of
liquid waste, including leachate from solid waste landfills. Other sources, such
as spring water and rain water, are of varying levels of quality, but each can be
developed and treated to render it potable.
Most water systems consist of a water source (such as a well, spring, or lake),
some type of tank for storage, and a system of pipes for distribution. Means to
treat the water to remove harmful bacteria or chemicals may also be required. The
system can be as simple as a well, a pump, and a pressure tank to serve a single
home. It may be a complex system, with elaborate treatment processes, multiple storage
tanks, and a large distribution system serving thousands of homes. Regardless of
system size, the basic principles to assure the safety and potability of water are
common to all systems. Large-scale water supply systems tend to rely on surface
water resources, and smaller water systems tend to use groundwater.
Groundwater is pumped from wells drilled into aquifers. Aquifers are geologic formations
where water pools, often deep in the ground. Some aquifers are actually higher than
the surrounding ground surface, which can result in flowing springs or artesian
wells. Artesian wells are often drilled; once the aquifer is penetrated, the water
flows onto the surface of the ground because of the hydrologic pressure from the
aquifer.
The Safe Drinking Water Act (SDWA) defines a public water system as one that provides
piped water to at least 25 persons or 15 service connections for at least 60 days
per year. Such systems may be owned by homeowner associations, investor-owned water
companies, local governments, and others. Water not from a public water supply,
and which serves one or only a few homes, is called a private supply. Private water
supplies are, for the most part, unregulated. Community water systems are public
systems that serve people year-round in their homes. The U.S. Environmental Protection
Agency (EPA) also regulates other kinds of public water systems—such as those at
schools, factories, campgrounds, or restaurants—that have their own water supply.
The quantity of water in an aquifer and the water produced by a well depend on the
nature of the rock, sand, or soil in the aquifer where the well withdraws water.
Drinking water wells may be shallow (50 feet or less) or deep (more than 1,000 feet).
On average, our society uses almost 100 gallons of drinking water per person per
day. Traditionally, water use rates are described in units of gallons per capita
per day (gallons used by one person in 1 day). Of the drinking water supplied by
public water systems, only a small portion is actually used for drinking. Residential
water consumers use most drinking water for other purposes, such as toilet flushing,
bathing, cooking, cleaning, and lawn watering.
The amount of water we use in our homes varies during the day:
- Lowest rate of use—11:30
pm to 5:00 am,
- Sharp rise/high use—5:00
am to noon (peak hourly use from 7:00 am to 8:00 am),
- Moderate use—noon
to 5:00 pm (lull around 3:00 pm), and
- Increasing evening use—5:00
pm to 11:00 pm (second minor peak, 6:00 pm to 8:00 pm).
Source Location
The location of any source of water under consideration as a potable supply, whether
individual or community, should be carefully evaluated for potential sources of
contamination. As a general practice, the maximum distance that economics, land
ownership, geology, and topography will allow should separate a water source from
potential contamination sources. Table_8.1 details
some of the sources of contamination and gives minimum distances recommended by
EPA to separate pollution sources from the water source.
Water withdrawn directly from rivers, lakes, or reservoirs cannot be assumed to
be clean enough for human consumption unless it receives treatment. Water pumped
from underground aquifers will require some level of treatment. Believing surface
water or soil-filtered water has purified itself is dangerous and unjustified. Clear
water is not necessarily safe water. To assess the level of treatment a water source
requires, follow these steps:
- Determine the quality needed for the intended
purpose (drinking water quality needs to be evaluated under the SDWA).
- For wells and springs, test the water for
bacteriologic quality. This should be done with several samples taken over a
period of time to establish a history on the source. With few exceptions, surface
water and groundwater sources are always presumed to be bacteriologically unsafe
and, as a minimum, must be disinfected.
- Analyze for chemical quality, including both
legal (primary drinking water) standards and aesthetic (secondary) standards.
- Determine the economical and technical restraints
(e.g., cost of equipment, operation and maintenance costs, cost of alternative
sources, availability of power).
- Treat if necessary and feasible.
Well Construction
Many smaller communities obtain drinking water solely from underground aquifers.
In addition, according to the last census with data on water supply systems, 15%
of people in the United States are on individual water supply systems. In some sections
of the country, there may be a choice of individual water supply sources that will
supply water throughout the year. Some areas of the country may be limited to one
source. The various sources of water include drilled wells, driven wells, jetted
wells, dug wells, bored wells, springs, and cisterns. Table_8.2
provides a more detailed description of some of these wells.
Regardless of the choice for a water supply source, special safety precautions must
be taken to assure the potability of the water. Drainage should be away from a well.
The casings of the well should be sealed with grout or some other mastic material
to ensure that surface water does not seep along the well casing to the water source.
In
Figure 8.2, the concrete grout has been reinforced with steel and a drain
away from the casing has been provided to assist in protecting this water source.
Additionally, research suggests that a minimum of 10 feet of soil is essential to
filter unwanted biologic organisms from the water source.
However, if the area of well construction has any sources of chemical contamination
nearby, the local public health authority should be contacted. In areas with karst
topography (areas characterized by a limestone landscape with caves, fissures, and
underground streams), wells of any type are a health risk because of the long distances
that both chemical and biologic contaminants can travel.
When determining where a water well is to be located, several factors should be
considered:
- the groundwater aquifer to be developed,
- depth of the water-bearing formations,
- the type of rock formations that will be encountered,
- freedom from flooding, and
- relation to existing or potential sources
of contamination.
The overriding concern is to protect any kind of well
from pollution, primarily bacterial contamination. Groundwater found in sand, clay,
and gravel formations is more likely to be safer than groundwater extracted from
limestone and other fractured rock formations. Whatever the strata, wells should
be protected from
- surface water entering directly into the top
of the well,
- groundwater entering below ground level without
filtering through at least 10 feet of earth, and
- surface water entering the space between the
well casing and surrounding soil.
Also, a well should be located in such a way that
it is accessible for maintenance, inspection, and pump or pipe replacement when
necessary. Driven wells (Figure
8.2) are typically installed in sand or soil and do not penetrate base rock.
They are, as a result, hammered into the ground and are quite shallow, resulting
in frequent contamination by both chemical and bacterial sources.
Sanitary Design and Construction
Whenever a water-bearing formation is penetrated (as in well construction), a direct
route of possible water contamination exists unless satisfactory precautions are
taken. Wells should be provided with casing or pipe to an adequate depth to prevent
caving and to permit sealing of the earth formation to the casing with watertight
cement grout or bentonite clay, from a point just below the surface to as deep as
necessary to prevent entry of contaminated water.
Once construction of the well is completed, the top of the well casing should be
covered with a sanitary seal, an approved well cap, or a pump mounting that completely
covers the well opening (Figure
8.3). If pumping at the design rate causes drawdown in the well, a vent
through a tapped opening should be provided. The upper end of the vent pipe should
be turned downward and suitably screened to prevent the entry of insects and foreign
matter.
Pump Selection
A variety of pump types and sizes exist to meet the needs of individual or community
water systems. Some of the factors to be considered in selecting a pump for a specific
application are well depth, system design pressure, demand rate in gallons per minute,
availability of power, and economics.
Dug and Drilled Wells
Dug wells (Figures
8.4 and
8.5) were one of the most common types of wells for individual water supply
in the United States before the 1950s. They were often constructed with one person
digging the hole with a shovel and another pulling the dirt from the hole with a
rope, pulley, and bucket. Of course, this required a hole of rather large circumference,
with the size increasing the potential for leakage from the surface. The dug well
also was traditionally quite shallow, often less than 25 feet, which often resulted
in the water source being contaminated by surface water as it ran through cracks
and crevices in the ground to the aquifer. Dug wells provide potable water only
if they are properly located and the water source is free of biologic and chemical
contamination. The general rule is, the deeper the well, the more likely the aquifer
is to be free of contaminants, as long as surface water does not leak into the well
without sufficient soil filtration.
Two basic processes are used to remediate dug wells. One is to dig around the well
to a depth of 10 feet and install a solid slab with a hole in it to accommodate
a well casing and an appropriate seal (Figures
8.4 and
8.5). The dirt is then backfilled over the slab to the surface, and the
casing is equipped with a vent and second seal, similar to a drilled well, as shown
in
Figure 8.6. This results in a considerable reduction in the area of the
casing that needs to be protected. Experience has shown that the disturbed dirt
used for backfilling over the buried slab will continue to release bacteria into
the well for a short time after modification. Most experts in well modification
suggest installing a chlorination system on all dug wells to disinfect the water
because of their shallow depth and possible biologic impurity during changing drainage
and weather conditions above ground.
Figure 8.7 shows a dug well near the front porch of a house and within 5
feet of a drainage ditch and 6 feet of a rural road. This well is likely to be contaminated
with the pesticide used to termite-proof the home and from whatever runs off the
nearby road and drainage ditch. The well shown is about 15 feet deep. The brick
structure around the well holds the centrifugal pump and a heater to keep the water
from freezing. Although dangerous to drink from, this well is typical of dug wells
used in rural areas of the United States for drinking water.
Samples should not be taken from such wells because they instill a false sense of
security if they are negative for both chemicals and biologic organisms. The quality
of the water in such wells can change in just a few hours through infiltration of
drainage water.
Figure 8.8 shows the septic tank discharge in the drainage ditch 5 feet
upstream of the dug well in
Figure 8.7. This potential combination of drinking water and waste disposal
presents an extreme risk to the people serviced by the dug well. Sampling is not
the answer; the water source should be changed under the supervision of qualified
environmental health professionals.
Figure 8.9 shows a drilled well. On the left side of the picture is the
corner of the porch of the home. The well appears not to have a sanitary well seal
and is likely open to the air and will accept contaminants into the casing. Because
the well is so close to the house, the casing is open, and the land slopes toward
the well, it is a major candidate for contamination and not a safe water source.
Springs
Another source of water for individual water supply is natural springs. A spring
is groundwater that reaches the surface because of the natural contours of the land.
Springs are common in rolling hillside and mountain areas. Some provide an ample
supply of water, but most provide water only seasonally. Without proper precautions,
the water may be biologically or chemically contaminated and not considered potable.
To obtain satisfactory (potable) water from a spring, it is necessary to
- find the source,
- properly develop the spring,
- eliminate surface water outcroppings above
the spring to its source,
- prevent animals from accessing the spring
area, and
- provide continuous chlorination.
Figure 8.10 illustrates a properly
developed spring. Note that the line supplying the water is well underground, the
spring box is watertight, and surface water runoff is diverted away from the area.
Also be aware that the water quality of a spring can change rapidly.
Cisterns
A cistern is a watertight, traditionally underground reservoir that is filled with
rainwater draining from the roof of a building. Cisterns will not provide an ample
supply of water for any extended period of time, unless the amount of water used
is severely restricted. Because the water is coming off the roof, a pipe is generally
installed to allow redirection of the first few minutes of rainwater until the water
flows clear. Disinfection is, nevertheless, of utmost importance. Diverting the
first flow of water does not assure safe, non-polluted water because chemicals and
biologic waste from birds and other animals can migrate from catchment surfaces
and from windblown sources. In addition, rainwater has a low pH, which can corrode
plumbing pipes and fixtures if not treated.
Disinfection of Water Supplies
Water supplies can be disinfected by a variety of methods including chlorination,
ozonation, ultraviolet radiation, heat, and iodination. The advantages and disadvantages
of each method are noted in Table 8.3.
The understanding of
certain terms is necessary in talking about chlorination.
Table_8.4 is a chlorination guide for specific water
conditions.
Chlorine is the most commonly used water disinfectant. It is available in liquid,
powder, gas, and tablet form. Chlorine gas is often used for municipal water disinfection,
but can be hazardous if mishandled. Recommended liquid, powder, and tablet forms
of chlorine include the following:
- Liquid—Chlorine
laundry bleach (about 5% chlorine). Swimming pool disinfectant or concentrated
chlorine bleach (12%–17% chlorine).
- Powder—Chlorinated
lime (25% chlorine), dairy sanitizer (30% chlorine), and high-test calcium hypochlorite
(65%–75% chlorine).
- Tablets—High-test
calcium hypochlorite (65%–75% chlorine).
- Gas—Gas
chlorine is an economical and convenient way to use large amounts of chlorine.
It is stored in steel cylinders ranging in size from 100 to 2,000 pounds. The
packager fills these cylinders with liquid chlorine to approximately 85% of
their total volume; the remaining 15% is occupied by chlorine gas. These ratios
are required to prevent tank rupture at high temperatures. It is important that
direct sunlight never reaches gas cylinders. It is also important that the user
of chlorine knows the maximum withdrawal rate of gas per day per cylinder. For
example, the maximum withdrawal rate from a 150-pound cylinder is approximately
40 pounds per day at room temperature discharging to atmospheric pressure.
Chlorine Carrier Solutions
On small systems or individual wells, a high-chlorine carrier solution is mixed
in a tank in the pump house and pumped by the chlorinator into the system.
Table_8.5 shows how to make a 200-ppm carrier solution.
By using 200 ppm, only small quantities of this carrier have to be added. Depending
on the system, other stock solutions may be needed to better use existing chemical
feed equipment.
Routine Water Chlorination (Simple)
Most chlorinated public water supplies use routine water chlorination. Enough chlorine
is added to the water to meet the chlorine demand, plus enough extra to supply 0.2
to 0.5 ppm of free chlorine when checked after 20 minutes.
Simple chlorination may not be enough to kill certain viruses. Chlorine as a disinfectant
increases in effectiveness as the chlorine residual is increased and as the contact
time is increased.
Chlorine solutions should be mixed and chlorinators adjusted according to the manufacturer’s
instructions. Chlorine solutions deteriorate gradually when standing. Fresh solutions
must be prepared as necessary to maintain the required chlorine residual. Chlorine
residual should be tested at least once a week to assure effective equipment operation
and solution strengths.
A dated record should be kept of solution preparation, type, proportion of chlorine
used, and residual-test results. Sensing devices are available that will automatically
shut off the pump and activate a warning bell or light when the chlorinator needs
servicing.
Well Water Shock Chlorination
Shock chlorination is used to control iron and sulfate-reducing bacteria and to
eliminate fecal coliform bacteria in a water system. To be effective, shock chlorination
must disinfect the following: the entire well depth, the formation around the bottom
of the well, the pressure system, water treatment equipment, and the distribution
system. To accomplish this, a large volume of super-chlorinated water is siphoned
down the well to displace the water in the well and some of the water in the formation
around the well. Check specifications on the water treatment equipment to ensure
appropriate protection of the equipment.
With shock chlorination, the entire system—from the water-bearing formation through
the well-bore and the distribution system—is exposed to water that has a concentration
of chlorine strong enough to kill iron and sulfate-reducing bacteria. The shock
chlorination process is complex and tedious. Exact procedures and concentrations
of chlorine for effective shock treatment are available [6,7].
Backflow,
Back-siphonage, and Other Water Quality Problems
In addition to contamination at its source, water can become contaminated with biologic
materials and toxic construction or unsuitable joint materials as it flows through
the water distribution system in the home. Water flowing backwards (backflow) in
the pipes sucks materials back (back-siphonage) into the water distribution system,
creating equally hazardous conditions. Other water quality problems relate to hardness,
dissolved iron and iron bacteria, acidity, turbidity, color, odor, and taste.
Backflow
Backflow is any unwanted flow of nonpotable water into a potable water system. The
direction of flow is the reverse of that intended for the system. Backflow may be
caused by numerous factors and conditions. For example, the reverse pressure gradient
may be a result of either a loss of pressure in the supply main (back-siphonage)
or the flow from a pressurized system through an unprotected cross-connection (back-pressure).
A reverse flow in a distribution main or in a customer’s system can be created by
a change of system pressure wherein the pressure at the supply point becomes lower
than the pressure at the point of use. When this happens, the water at the point
of use will be siphoned back into the system, potentially polluting or contaminating
it. It is also possible that contaminated or polluted water could continue to backflow
into the public distribution system. The point at which nonpotable water comes in
contact with potable water is called a cross-connection.
Examples of backflow causes include supplemental supplies, such as a standby fire
protection tank; fire pumps; chemical feed pumps that overpower the potable water
system pressure; and sprinkler systems.
Back-Siphonage
Back-siphonage is a siphon action in an undesirable or reverse direction. When there
is a direct or indirect connection between a potable water supply and water of questionable
quality due to poor plumbing design or installation, there is always a possibility
that the public water supply may become contaminated. Some examples of common plumbing
defects are
- washbasins, sterilizers, and sinks with submerged
inlets or threaded hose bibs and hose;
- oversized booster pumps that overtax the supply
capability of the main and thus develop negative pressure;
- submerged inlets and fire pumps (if the fire
pumps are directly connected into the water main, a negative pressure will develop);
and
- a threaded hose bib in a health-care facility
(which is technically a cross-connection).
There are many techniques and devices for preventing
back-flow and back-siphonage. Some examples are
- Vacuum breakers (nonpressure and pressure);
- Back-flow preventers (reduced pressure principle,
double gate–double check valves, swing-connection, and air gap–double diameter
separation);
- Surge tanks (booster pumps for tanks, fire
system make-up tank, and covering potable tanks); and
- Color coding in all buildings where there
is any possibility of connecting two separate systems or taking water from the
wrong source (blue—potable, yellow—nonpotable, and other—chemical and gases).
An air gap, which is a physical separation between
the incoming water line and maximum level in a container of at least twice the diameter
of the incoming water line. If an air gap cannot be installed, then a vacuum breaker
should be installed. Vacuum breakers, unlike air gaps, must be installed carefully
and maintained regularly. Vacuum breakers are not completely failsafe.
Other Water Quality Problems
Water not only has to be safe to drink; it should also be aesthetically pleasing.
Various water conditions affect water quality. Table_8.6
describes symptoms, causes, measurements, and how to correct these problems.
Protecting the Groundwater Supply
Follow these tips to help protect the quality of groundwater supplies:
- Periodically inspect exposed parts of wells
for cracked, corroded, or damaged well casings; broken or missing well caps;
and settling and cracking of surface seals.
- Slope the area around wells to drain surface
runoff away from the well.
- Install a well cap or sanitary seal to prevent
unauthorized use of, or entry into, a well.
- Disinfect wells at least once a year with
bleach or hypochlorite granules, according to the manufacturer’s directions.
- Have wells tested once a year for coliform
bacteria, nitrates, and other constituents of concern.
- Keep accurate records of any well maintenance,
such as disinfection or sediment removal, that require the use of chemicals
in the well.
- Hire a certified well driller for new well
construction, modification, or abandonment and closure.
- Avoid mixing or using pesticides, fertilizers,
herbicides, degreasers, fuels, and other pollutants near wells.
- Do not dispose of waste in dry or abandoned
wells.
- Do not cut off well casings below the land
surface.
- Pump and inspect septic systems as often as
recommended by local health departments.
- Never dispose of hazardous materials (e.g.,
paint, paint stripper, floor stripper compounds) in a septic system.
References
- Rhode Island Department
of Health and University of Rhode Island Cooperative Extension Water Quality
Program. Healthy drinking waters for Rhode Islanders. Kingston, RI: Rhode Island
Department of Health and University of Rhode Island Cooperative Extension Water
Quality Program; 2003. Available from URL:
http://www.uri.edu/ce/wq/has/html/Drinking.pdf.
- US Census Bureau. American
housing survey. Washington, DC: US Census Bureau; 2003. Available from URL:
http://www.census.gov/hhes/www/housing/ahs/nationaldata.html.
- US Census Bureau. Historical
census of housing graphs: water supply. Washington, DC: US Census Bureau; no
date. Available from URL:
http://www.census.gov/hhes/www/housing/census/historic/swgraph.html.
- National Ground Water
Association. Well system material. Westerville, OH: National Ground Water Association;
2003. Available from URL:
http://www.ngwa.org/pdf/wellsystemmaterials.pdf.
- US Environmental Protection
Agency. Spring development. Chicago: US Environmetal Protection Agency; 2001.
- Government of Alberta.
Shock chlorination - well maintenance. Edmonton, Alberta, Canada: Alberta Agriculture,
Food & Rural Development; 2001. Available from URL:
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/wwg411.
- Boulder GNS Water Well
Service and Supply. Chlorination of water systems. Boulder, CO: Boulder GNS
Water Well Service and Supply; 2002. Available from URL:
http://www.waterwell.cc/CHLORIN.HTM.
- Iowa State University
Diagnosing and solving common water-quality problems. Ames, IA: Iowa State University;
1994. Available from URL:
http://www.abe.iastate.edu/HTMDOCS/aen152.pdf.
Additional
Sources of Information
American Water Works Association. Available from URL:
http://www.awwa.org.
Drexel University: Drinking water outbreaks. Available from URL:
http://water.sesep.drexel.edu/outbreaks/.
US Environmental Protection Agency: Ground water and drinking water. Available from
URL: http://www.epa.gov/safewater.
Table 8.1. Recommended Minimum
Distance Between Well and Pollution Sources (Horizontal Distance) [1]
Pollution Source
|
Minimum Surface Distance from
Well
|
Septic tank
|
50 feet
|
Livestock yard silos
Septic leach fields
|
50
feet
|
Petroleum tanks
Liquid-tight manure storage
Pesticide and fertilizer storage and handling
|
100 feet
|
Manure stacks
|
250 feet
|
Table 8.2. Types of Wells for
Accessing Groundwater, Well Depths, and Diameters
Type of Well
|
Depth, in Feet
|
Diameter
|
Suitable Geologic Formations
|
Dug
|
0–50
typically less than 25
|
3 to 20 feet
|
Suitable in clay, silt, sand,
gravel, and soft fractured limestone
|
Bored
|
0–100
|
2 to 30 inches
|
Clay, silt, sand, gravel, boulders
less than well diameter, soft sandstone, and fractured limestone
|
Driven
|
0–50
|
1.25 to 2 inches
|
Clay, sand, silt, fine gravel,
and thin layers of sandstone
|
Drilled (rotary type)
|
0–1,000
|
4 to 24 inches
|
Same as above with percussion
type drilling
|
Table 8.3. Disinfection Methods
Disinfection Method
|
Advantages
|
Disadvantages
|
Boiling
|
Readily accessible
Well suited for emergencies
Removes volatile organic compounds
from water
Effective even on Giardia
and Cryptosporidium
|
Requires a great deal of heat
Takes time to boil and cool
Water tastes stale
Typically limited capacity
|
Chlorine
|
Provides residual treatment
Residual easy to test and measure
Readily available; reasonable
cost
Low electrical requirement
Useful for multiple water problems
Can treat large volumes of water
|
Requires contact time of 30 minutes
Turbidity reduces effectiveness
Gives water a chlorine taste
May form disinfection by‑products
Does not kill Giardia or
Cryptosporidium
Requires careful handling and
storage
|
Ultraviolet light
|
Does not change taste of water
Leaves no discernable odor
Kills bacteria almost immediately
Compact and easy to use
|
High electrical requirement
Provides no residual treatment
Requires pretreatment if turbid
Requires new lamp annually
|
Iodine
|
Does not require electricity
Requires little maintenance
Provides residual treatment
Residual easy to measure
|
Health side effects undetermined
Affected by water temperature
Gives water an iodine taste
|
Ozone |
Is a more powerful disinfectant than chlorine
Does not change taste of water
Leaves no discernable odor
|
Ozone gas is unstable and must be generated at point
of use |
Table 8.4. Chlorination Guide
for Specific Water Conditions
Chlorination Treatment for
|
Typical Dosage Rates
|
Algae
|
3 to 5 ppm
|
Bacteria
|
3 to 5 ppm
|
Biologic oxygen demand reduction
|
10 parts per million
|
Color (removal)
|
Dosage depends on type and extent
of color removal desired; may vary from 1 to 500 ppm dosage rate
|
Cyanide
|
|
Reduction to cyanate
|
2 times cyanide content
|
Complete destruction
|
8.5 times cyanide content
|
Hydrogen sulfide
|
|
Taste and odor control
|
2 times hydrogen sulfide content
|
Destruction
|
8.4 times hydrogen sulfide content
|
Iron bacteria
|
1 to 10 ppm, varying with amount
of bacteria to control
|
Iron precipitation
|
64 times iron content
|
Manganese precipitation
|
1 to 3 times manganese content
|
Odor
|
1 to 3 ppm
|
Taste
|
1 to 3 ppm
|
ppm: parts per million
|
Table 8.5. Preparing a 200-ppm Chlorine Solution
Carrier Solution
|
Amount of Chlorine per 100 Gallons (380 Liters)
of Water
|
5% chlorine bleach
|
3 pints
|
12%–17% chlorine solution
|
1 pint
|
25%–30% chlorine powder
|
⅔ pound
|
65%–75% chlorine powder
|
¼ pound
|
Table 8.6. Analyzing and Correcting
Water Quality Problems [8]
Symptoms
|
Probable Cause
|
Measurement
|
Corrective Action
|
Hardness
– Sticky curd forms when soap is added
to water
– Causes bathtub ring
– Requires more soap
– Glassware appears streaked, scale
forms in pipes
|
Calcium and magnesium
in the water, compounded with biocarbonates, sulfates or chlorides.
|
Hardness test kits, which
measure in grains per gallon (gpg) or parts per million (ppm). 1 gpg = 17.1
ppm
50 ppm is soft water; 50 to 100 ppm is moderately
hard water; 100 to 200 ppm is hard water; 200 to 300 ppm is very hard; over
300 ppm is extremely hard
|
If hardness creates problems,
a sodium zeolite ion exchange water softener or a reverse osmosis
unit can be used.
|
Dissolved iron
– Red stains (red water) on clothes
and plumbing fixtures
– Corrosion of steel pipes
– Metallic taste
– Clear water just
drawn begins to form red particles that settle to the bottom
|
Iron, from geologic formations
that groundwater passes through. Water, an excellent solvent, ionizes iron
and holds it in solution.
Iron is common in soft
water and when water hardness is above 175 ppm.
|
Atomic absorption (AA)
units or numerous colormetric test kits measure iron in ppm. Any measurement
above 0.3 ppm will cause problems.
|
To treat soft water that
contains no iron but picks it up in distribution lines, add calcium to
the water with calcite (limestone) units.
To treat hard water containing
iron ions, install a sodium zeolite ion exchange unit.
To treat soft water containing
iron, carbon dioxide must be neutralized, followed by a manganese zeolite
unit.
|
Iron bacteria (red slime
appears in toilet)
|
Caused by bacteria that
act in the presence of iron.
|
Check under toilet tank
cover for slippery jelly-like coating.
|
Kill bacteria by superchlorinating
pump and piping system.
|
Brownish
black water
– Fixture stains black
– Fabric stains black
– Bitter coffee and tea
|
Manganese is present
usually along with iron.
|
Colormetric tests for
manganese (concentrations above 0.05 mg/L cause problems).
|
Same methods as for iron.
|
Acidity (corrosion of
copper and steel in pumps, fixtures, piping and tanks)
|
Carbon dioxide forms
carbonic acid. Water may contain H2SO4, HCl,
or nitric acid, but unlikely.
|
Colormetric field titrametric
tests for acidity, pH and carbon dioxide (pH is determined at the titration
end point). A pH below 6.5 causes corrosion. Carbon dioxide should be less
that 10 mg/L or less than 5 mg/L if alkalinity is less than 100 ppm.
|
Soda ash solution is
fed into the well or suction line of a pump. May be fed along with chlorine
solution.
Limestone chips (calcite)
neutralize the water by increasing its alkalinity and hardness.
|
Odors and tastes
– Bitter taste
– Rotten egg odor
– Salty taste
– Flat, soda taste
– Salty taste
– Chlorine odor/taste
|
Very high mineral content
Sulfate-reducing bacteria,
hydrogen sulfide
High chloride levels
Bicarbonates
High total dissolved
solids (TDS)
High levels of di- or
trichloramines in water
|
Excess iron, manganese,
sulfate
Sulfate levels above
250 mg/L or any trace of hydrogen sulfide causes problem.
Problems at levels >250
mg/L
Carbonate hardness test
TDS levels above 500
mg/L may cause problems.
Check pH.
|
Methods mentioned above
Chlorinator and filter
Reverse osmosis unit
Aeration unit
Sand filter
Activated charcoal
filter
|
Turbidity (cloudy water) |
Silt, sediment, large number of microorganisms
or organic material |
Nephelometric turbidity units (NTUs) using
laboratory spectrophotometers. (Less than 5 NTUs is best, >10 not acceptable.) |
Fine filtering with sand filter or diatomaceous
earth filter. For ponds, coagulation and sedimentation are needed. |
Blue stain on porcelain fixtures |
Corrosion of copper pipes and fixtures due
to low pH, hardness, and alkalinity |
Langelier index determines proper balance
of pH, hardness, and alkalinity. |
Methods mentioned above to adjust pH, hardness,
and alkalinity. |
Lead contamination |
Leaching from lead service lines, solder,
or brass or lead fittings |
15 parts per billion |
Adjust pH
Filtration
Chemical treatment
|