346 ENVIRONMENTAL HEALTH
so as to be in the direct line of drainage from sources or pol-
lution. 2. If a handpump is provided it should be of sanitary
design, installed with a watertight connection.
Note: 1. Locations. Wells should be located at least 100
ft and preferably 200 ft from privies, barnyards, leaching
pits, cesspools, tile fi elds, and other sources of pollution.
Wells should not be located downgrade so as to be in the
direct line of drainage from sources of pollution. Concrete.
Mix one bag of cement, 2 cu ft of sand, and 3 cu ft of gravel.
Then add 5 gal of water, for moist sand, and mix again.Water TreatmentAs an aid in determining the treatment that should be given
water to make it safe to drink, the United States Public Health
Service has classifi ed waters into several groups.^20 The treatment
required by this classifi cation is based upon the most probable
number (MPN) of coliform bacteria per 100 milliliters (ml) ot
sample. The classifi cation is summarized in Table 5. It needs
to be supplemented by chemical, physical, and microscopicexaminations. For water to be generally acceptable, other
treatment may be required in addition to that necessary for the
elimination of disease-producing organisms. People expect the
water to be safe to drink, attractive to the senses, sort, non-
staining, and neither scale-forming nor corrosive to the water
system. The various treatment processes employed to accom-
plish these results are shown in the fl ow diagram in Figure 8.
The untrained individual should not attempt to design a water
treatment plant for life and health will be jeopardized. This is a
job for a competent sanitary engineer.
Plant capacity—50 to 100% greater than average daily
demand, with clear well. Possible chemical combinations:
A—Chlorine. B—Coagulant; alu minum sulfate (pH 5.5–8.0),
ferrous sulfate (pH 8.5–11.0), ferric chloride (pH 5.0–11.0),
sodium aluminate and or other (activated silica) (polyelec-
trolytes). C—Alkalinity adjustment; lime, soda ash, or poly-
phosphate. D—Activated carbon. E—Dechlorination; sulfur
dioxide, sodium sulfi te, sodium thiosulfate. F—Fluoridation
treatment. X—Chlorine dioxide.
Note: The chlorinator should be selected to pre-chlorinate
surface water at 20 mg/l and post-chlorinate at 3 mg/l. Provide
for a dose of 3 mg/l plus chlorine demand for ground water.WASTEWATERDefinitionsExcreta is the waste matter eliminated from the body, includ-
ing feces, urine, and sweat. Domestic sewage is the used
water from a home or community and includes toilet, bath,
laundry, lavatory, and kitchen-sink wastes. Sewage from
a community may include some industrial wastes, ground
water and surface water, hence the more inclusive term
wastewater is coming into general usage. Normal sewage
from a private sewage disposal system contains about 99.8%
water and 0.2% total mineral and organic solids. Domestic
sewage contains less than 0.1% total solids. The strength of
wastewater is commonly expressed in terms of 5-day bio-
chemical oxygen demand (BOD), suspended solids and
chemical oxygen demand (COD).
The biochemical oxygen demand of sewage, sewage
effl uents, polluted waters, industrial wastes or other waste-
waters is the oxygen in parts per million (ppm) or milligrams
per liter (mg/l) required during stabilization of the decom-
posable organic matter by aerobic bacterial action. Complete
stabilization requires more than 100 days at 20°C. Incubation
for 5 or 20 days is not unusual but as used in this chapter
BOD refers to the 5-day test unless otherwise specifi ed.
Suspended solids are those which are visible and in sus-
pension in water. They are the solids which are retained on
the asbestos mat in a Gooch crucible.
The chemical oxygen demand (COD) is also used, par-
ticularly in relation to certain industrial wastes. The COD is
the amount of oxygen expressed in parts per million (ppm)
or milligrams per liter (mg/l) consumed under specifi c con-
ditions in the oxidation of organic and oxidizable inorganic
material. The test is relatively rapid. It does not oxidize
some biodegradable organic pollutants (pyridine, benzene,TABLE 5
A classifi cation of waters by concentration of coliform bacteria and
treatment required to render the water of safe sanitary qualityGroup No.Maximum permissible
average MPN coliform
bacteria per monthb Treatment requireda1 Not more than 10% of all
10-ml or 60% of
100 ml portions
positive; not more than
1.0 coliform bacteria
per 100 ml.No treatment required of
underground water, but a
minimum of chlorination
required to surface water,
advised for ground water.2 Not more than 50 per
100 ml.Simple chlorination or
equivalent.
3 Not more than 5000 per
100 ml and this MPN
exceeding in not more
than 20% of samples.Rapid sand fi ltration
(including coagulation) or
its equivalent plus
continuous chlorination.
4 MPN greater than 5,000
per 100 ml in more
than 20% or samples
and not exceeding
20,000 per 100 ml in
more than 5% of the
samples.Auxiliary treatment such as
30–90 days storage,
pre settling,
pre-chlorination, or
equivalent plus complete
fi ltration and chlorination.5 MPN exceeds group 4. Prolonged storage or
equivalent to bring within
groups 1–4.a Physical, inorganic and organic chemicals, and radioactivity concentrations
in the raw water and ease of removal by the proposed treatment must also
be taken into consideration. See Table 3, Water Quality Criteria, Report of
the National Technical Advisory Commitee, to the Secretary of the Interior.
April 1, 1968, Washington, DC. And Manual for Evaluating Public Drinking
Supplies U.S. Department of Health, Education, and Welfare, Public Health
Service, Environmental Control Administration, Cincinnati, OH 1969.
b Fecal coliforms not to exceed 20% or total coliform organisms. The monthly
geometric mean of the MPN for group 2 may be less than 100 and for group
3 and 4 less than 20,000 per 100 ml with the indicated treatment.
Adapted from Environmental Sanitation, Joseph A. Salvato, Jr., John
Wiley & Sons, Inc., New York, 1958.C005_009_r03.indd 346C005_009_r03.indd 346 11/18/2005 10:24:48 AM11/18/2005 10:24:48 AM