personnel are permitted to handle gaseous chlorine. Chlorination by means of chlorine
gas is found only in permanent (fixed) installation water treatment faciIities and is done
only by highly qualified operators.
(2) Calcium hypochlorite is the standard chlorine compound used for
disinfection of Army water supplies. It is a dry granule or powder which is relatively
stable, readily soluble, and which contains approximately 70 percent available chlorine
by weight. It is relatively nontoxic even in concentrations used against the most
resistant organisms (10 mg/l). In fact, it produces nausea and is unacceptable to the
taste in concentrations much lower than those that cause serious toxic effects. Added
to water in sufficient quantities to destroy microorganisms (chlorine demand), it has
some remaining to serve as a continuing disinfectant (chlorine residual). The most
effective disinfection occurs between the pH of 5.5 to 6.5. After 30 minutes, chlorine
residual of at least 5.0 ppm and a pH value between 6.5 and 7.5 is desirable. In normal
concentrations, the taste is not noticeable to people who are accustomed to drinking
water from city water systems; however, it may be slightly unpalatable to persons who
have never drunk chlorinated water. Even the latter group will become accustomed to
the taste. One of the major advantages of chlorine--in any form--is that its presence in
water can be determined by simple tests.
Section III. WATER TREATMENT FACILITIES
1-16. MUNICIPAL (GARRISON) WATER TREATMENT FACILITIES
Garrison, or fixed installation, water treatment faciIities are essentially the same
as civilian municipal faciIities. The size and design of the faciIities depend upon the
population served, the space available, and the amount of treatment required. For
example, a city, which services a metropolitan area of approximately 800,000 people
(including an installation), treats its public water supply only by chlorination. This is
because the source may have a deep underground aquifer from which water is obtained
by driIIing deep wells. Other smaller communities within a 35-miIe radius test water
from surface sources and require complete treatment. Garrison or municipal water
treatment faciIities uses one of the following combinations of processes.
a. Slow Sand Filtration Plant. The slow sand fiItration plant is generally
accompanied only by chlorination following the filtration process. This type of plant is
decreasing in popularity and is seldom buiIt today because of the ever-increasing
scarcity of land and the large land requirement for this type of fiIter.
b. Rapid Sand Filtration Plant. The rapid sand fiItration plant is the most
common type of municipal or garrison water treatment plant. The rapid sand fiItration
plant requires some type of pretreatment to prevent excessive clogging of the fiIters and
the resulting requirement for frequent backwashing. Pretreatment may consist of the
standard coagulation, flocculation, and sedimentation process or, in some of the more
modern plants, utiIize the solids contact process. FiItration is usually accomplished by
means of an open (gravity type) rapid sand fiIter in some small communities, although
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