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H. S. Weinberg
precursor material was in a different form and would not generate the same byproducts. Indeed, the levels of chlorine doses could often be reduced since there
was less of a demand for the disinfectant byproduct precursors and hence more
active species available for the purpose for which it was originally added, namely
disinfection. In some cases, replacing chlorine with a slightly less potent
disinfectant ( chloramine) had a similar effect without the expense of retrofitting or
rebuilding the treatment plant. In other cases, chlorine dioxide was the preferred
disinfectant choice. However, in cases where alternative chemical addition was
employed, there soon became concern about alternative byproduct formation, their
persistence in drinking water, and their potential impact on human health.
The USEPA conducted a regulatory negotiation (reg neg) in 1992-1993 and
1996-1997 in order to develop a consensus-based future regulation for
disinfectants and DBPs (DIDBPs). Although the reg neg was initiated to develop
one rule, three rules actually came out of the negotiations: (1) a DIDBP rule,
(2) an enhanced surface water treatment rule (ESWTR), and (3) an information
collection rule (lCR). Because of the limited scientific data available on the
occurrence, health effects, and treatability of DBPs and microbial pathogens, the
reg neg Advisory Committee decided to develop a two-stage DIDBP rule, with
linkage to an ESWTR to prevent potential increases in microbial risk.
Furthermore, the cost impacts of the long-term ESWTR and Stage 2 of the DIDBP
rule are substantial.
The DIDBP rule includes stage 1 maximum contaminant levels (MCLs) of
80 Jlg rl for total trihalomethanes (TTHMs), 60 Jlg rl for five of the haloacetic
acids (HAAS), and 10 Jlg rl for bromate (USEPA 1994). In addition, utilities
treating either surface water or groundwater under the direct influence of surface
water that use conventional treatment (i.e., coagulation, sedimentation, and
filtration) will be required to remove DBP precursors by enhanced coagulation or
softening. The removal of TOC will be used as a performance indicator for DBP
precursor control. The stage 2 proposal - which will be reevaluated in the next
negotiated rule-making process - originally proposed lower MCLs of 40 Jlg rl for
TTHMs, 30 Jlg rl for HAAS, and S Jlg rl for bromate as "placeholders." In
addition, the best available technology (BAT) proposed for stage 2 is treatment
with granular activated carbon (GAC) for the removal of DBP precursors, with
chlorination for primary and residual disinfection. However, it is recognized that
even when treatment is practiced efficiently, traditional disinfection is not always
capable of protecting the consumer against a whole slew of emerging pathogens.
Table 1 summarizes what is known about such microorganisms and the threat they
pose. Our greatest concern has to be that even with new technologies, some of
these pathogens, if they are not prevented from reaching water sources, may
survive treatment and seriously threaten the health of consumers.
H. S. Weinberg
precursor material was in a different form and would not generate the same byproducts. Indeed, the levels of chlorine doses could often be reduced since there
was less of a demand for the disinfectant byproduct precursors and hence more
active species available for the purpose for which it was originally added, namely
disinfection. In some cases, replacing chlorine with a slightly less potent
disinfectant ( chloramine) had a similar effect without the expense of retrofitting or
rebuilding the treatment plant. In other cases, chlorine dioxide was the preferred
disinfectant choice. However, in cases where alternative chemical addition was
employed, there soon became concern about alternative byproduct formation, their
persistence in drinking water, and their potential impact on human health.
The USEPA conducted a regulatory negotiation (reg neg) in 1992-1993 and
1996-1997 in order to develop a consensus-based future regulation for
disinfectants and DBPs (DIDBPs). Although the reg neg was initiated to develop
one rule, three rules actually came out of the negotiations: (1) a DIDBP rule,
(2) an enhanced surface water treatment rule (ESWTR), and (3) an information
collection rule (lCR). Because of the limited scientific data available on the
occurrence, health effects, and treatability of DBPs and microbial pathogens, the
reg neg Advisory Committee decided to develop a two-stage DIDBP rule, with
linkage to an ESWTR to prevent potential increases in microbial risk.
Furthermore, the cost impacts of the long-term ESWTR and Stage 2 of the DIDBP
rule are substantial.
The DIDBP rule includes stage 1 maximum contaminant levels (MCLs) of
80 Jlg rl for total trihalomethanes (TTHMs), 60 Jlg rl for five of the haloacetic
acids (HAAS), and 10 Jlg rl for bromate (USEPA 1994). In addition, utilities
treating either surface water or groundwater under the direct influence of surface
water that use conventional treatment (i.e., coagulation, sedimentation, and
filtration) will be required to remove DBP precursors by enhanced coagulation or
softening. The removal of TOC will be used as a performance indicator for DBP
precursor control. The stage 2 proposal - which will be reevaluated in the next
negotiated rule-making process - originally proposed lower MCLs of 40 Jlg rl for
TTHMs, 30 Jlg rl for HAAS, and S Jlg rl for bromate as "placeholders." In
addition, the best available technology (BAT) proposed for stage 2 is treatment
with granular activated carbon (GAC) for the removal of DBP precursors, with
chlorination for primary and residual disinfection. However, it is recognized that
even when treatment is practiced efficiently, traditional disinfection is not always
capable of protecting the consumer against a whole slew of emerging pathogens.
Table 1 summarizes what is known about such microorganisms and the threat they
pose. Our greatest concern has to be that even with new technologies, some of
these pathogens, if they are not prevented from reaching water sources, may
survive treatment and seriously threaten the health of consumers.