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OXIDATION AND DISINFECTION 10.9

The requirements of these two rules are similar, with the IESWTR applying to public wa-
ter systems (PWS) serving more than 10,000 people and the LT1ESWTR specifying re-
quirements for systems serving fewer than 10,000 people. Both rules are applicable only
for systems using surface water or groundwater under the direct influence of surface wa-
ter, and they establish a limit on finished water turbidity of 0.3 ntu as well as turbidity
criteria for individual filters. Also for systems that filter, at least a 2-log removal of Cryp-
tosporidium was mandated; but if the system complies with the turbidity limit, the 2-log
removal requirement will be met. The rules also include triggers for disinfection bench-
marking, disinfection profiling, and filter profiling.
The pending Stage 2 Long-Term Enhanced Surface Water Treatment Rule will in-
crease the minimum removal/inactivation requirement for Cryptosporidium to 3-log. Raw
water monitoring will determine if additional removal/inactivation beyond 3-log will be
necessary. If so, the results of the monitoring dictate the additional treatment and/or in-
activation required. USEPA will provide guidance regarding credit received for various
treatment processes including inactivation from ozone, chlorine dioxide, and UV. Con-
ventional, and probably direct filtration, plants will receive a 3-log removal credit if tur-
bidity limits are met.

Regulation of Disinfection By-products
All oxidation-reduction reactions will form by-products from the reaction, and the by-
products formed from many common oxidants used in water treatment are now subject
to regulation. In 1979 trihalomethanes, a group of by-products of chlorination, were reg-
ulated at 0.10 mg/L. Further by-product regulation is proceeding under Stages 1 and 2 of
the Disinfectants/Disinfection By-product Rules (Stage 1 DBPR and Stage 2 DBPR).
The Stage 1 DBPR was promulgated at the end of 1998, and it set limits for the con-
centrations of both disinfectants and disinfection by-products, as shown in Table 10.5. If

TABLE 10.5 Regulated Levels for Disinfectants and Disinfection
By-products

MCLG/MRDLG,* MCL/MRDL,*
Parameter mg/L mg/L
Trihalomethanes (total THMs) 0.080
Chloroform 0
Bromodichloromethane 0
Bromoform 0
Dibromochloromethane 0.06
Haloacetic acids (HAA5) 0.060
Dichloroacetic acid 0
Trichloroacetic acid 0.3
Bromate 0 0.010
Chlorite 0.8 1.0
Chlorine 4.0 4
Chloramines 4.0 4
Chlorine dioxide 0.8 0.8
*MCLG = maximum contaminant level goal, MRDLG = maximum residual disinfec-
tam level goal, MCL = maximum contaminant level, MRDL = maximum residual disin-
fectant level.