Page 91 - Water and Wastewater Engineering Design Principles and Practice

2-34 WATER AND WASTEWATER ENGINEERING

Compliance with the regulations is also based on the quality of the water at the consumer’s
tap. Monitoring is required by means of collection of first-draw samples at residences. The num-
ber of samples required to be collected will range from 10 per year to 50 per quarter, depending
on the size of the water system.
The SDWA amendments forbid the use of pipe, solder, or flux that is not lead-free in the
installation or repair of any public water system or in any plumbing system providing water for
human consumption. This does not, however, apply to leaded joints necessary for the repair of
old cast iron pipes.

Disinfectants and Disinfectant By-Products (D-DBPs). The disinfectants used to destroy patho-
gens in water and the by-products of the reaction of these disinfectants with organic materials in the
water are of potential health concern. One class of DBPs has been regulated since 1979. This class is
known as trihalomethanes (THMs). THMs are formed when a water containing an organic precursor
is chlorinated. In this case it means an organic compound capable of reacting to produce a THM. The
precursors are natural organic substances formed from the decay of vegetative matter, such as leaves,
and aquatic organisms. THMs are of concern because they are known or potential carcinogens. The
four THMs that were regulated in the 1979 rules are chloroform (CHCl 3 ), bromodichloromethane
(CHBrCl 2 ), dibromochloromethane (CHBr 2 Cl). and bromoform (CHBr 3 ). Of these four, chloroform
appears most frequently and is found in the highest concentrations.
The D-DBP rule was developed through a negotiated rule-making process, in which indi-
viduals representing major interest groups concerned with the rule (for example, public-water-
system owners, state and local government officials, and environmental groups) publicly work
with EPA representatives to reach a consensus on the contents of the proposed rule.
Maximum residual disinfectant level goals (MRDLGS) and maximum residual disinfectant lev-
els (MRDLS) were established for chlorine, chloramine, and chlorine dioxide ( Table 2-15 ). Because
ozone reacts too quickly to be detected in the distribution system, no limits on ozone were set.
The MCLGs and MCLs for disinfection byproducts are listed in Table 2-16 . In addition
to regulating individual compounds, the D-DBP rule set levels for two groups of compounds:
HAA5 and TTHMs. These groupings were made to recognize the potential cumulative effect of
several compounds. HAA5 is the sum of five haloacetic acids (monochloroacetic acid, dichloro-
acetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid). TTHMs (total
trihalomethanes) is the sum of the concentrations of chloroform (CHCl 3 ), bromodichloromethane
(CHBrCl 2 ), dibromochloromethane (CHBr 2 Cl), and bromoform (CHBr 3 ).
The D-DBP rule is quite complex. In addition to the regulatory levels shown in the tables,
levels are established for precursor removal. The amount of precursor required to be removed is a
function the alkalinity of the water and the amount of total organic carbon (TOC) present.

TABLE 2-15
Maximum residual disinfectant level goals (MRDLGs) and
maximum residual disinfectant levels (MRDLs)
Disinfectant residual MRDLG, mg/L MRDL, mg/L

Chlorine (free) 4 4.0
Chloramines (as total chlorine) 4 4.0
Chlorine dioxide 0.8 0.8