COMPTE-RENDU DU COLLOQUE

TABLE I
VOCs: FINAL MCLGS AND MCLS (IN mg/Ii(cr)
EPA EPA Final Final
ranking category MCLG MCL
Trichloroethylenc B2 I Zero 0.005
Carbon tetrachloride 02 r Zero 0.005
Vinyl chloride A i Zero 0.002
1.2-Dichloroethane 02 i Zero 0.005
Benzene A i Zero 0.005
para-Dichlorobenzene C ii 0.075 0.075
1,1 -Dichloroclhylcnc C n 0.007 0.007
1,1,1 -Trichloroetha ne D m 0.2 0.2
U.S. NATIONAL DRINKING WATER REGULATIONS
The U.S. Safe Drinking Water Act requires that EPA set drinking water standards
n two steps after it makes a determination that a substance "may" have any adverse
-.fTect on health. First, it must determine the MCLG, the level in drinking water that
vould result in "no known or anticipated adverse cfTect on health" with a margin of
afety. Second, the MCL is the enforceable standard to be set as close as feasible to
he MCL taking costs into consideration. The statute does not formally.dcscribe that
i risk assessment is part of the process and the final standards arc technology based,
lot risk/benefit or cost/benefit based.
FIGURE 13
UNIT COSTS
Cost estimates ranged from SO. 10 to $0.85 per 1000 gallons of production for GAC
and S0.05 to $0.30 per 1000 gallons for PTA.
TOTAL COSTS
EPA estimated that 1300 community water suppliers in the United States would
have to install treatment at a total cost of $280 million for the MCLs at 0.005 mg/
liter. MCLs at 0.001 mg/litcr would involve 3800 systems at a cost of $ 1300 million.
It concluded that the latter costs were not warranted considering the incremental
national costs.
ANALYTICAL CONSIDERATIONS
The practical quantitation levels (PQLs) were defined as the lowest levels that can
be reliably achieved within specified limits of precision and accuracy during routine
laboratory operations. These were ±40% of true value for concentrations less than
0.010 mg/Iiterand ±20% of true value for concentrations greater than 0.010 mg/Iiter.
RISK CONSIDERATIONS
After the above conclusions were considered, the MCLs for the probable carcinogens
(except vinyl chloride) were set at 0.005 mg/litcr and established for most of the
VOCs in this group. EPA then examined the putative risks at the MCL. levels to
determine whether they would be acceptable from a safety standpoint
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