Drinking Water Research - January-March 2010 Volume 20, Number 1

The M/DBP Federal Advisory Committee
Act (FACA) began meeting in September
1999. Development of the rule options
progressed as occurrence data began
to emerge from the 18-month ICR data
collection period and subsequent quality
assurance/quality control procedures. The
FACA determined that there was adequate
basis for the Stage 2 DBPR to be based on a
concern that DBPs may lead to cancer. The
FACA indicated it was not appropriate for
the standard to be based on reproductive-
developmental health risk. Alternatives
to the initial 40/30 MCL placeholders
were considered and ultimately the goals
of reducing very high levels system wide
and of achieving more uniform reduction
in DBPs across the distribution system
became central to option selection. Hence,
the resulting Stage 2 DBPR provisions
water systems are currently responding to
include the following: conducting initial
distribution system evaluations (IDSEs) to
determine where high levels of TTHMs and
HAA5 occur, complying with an MCL based
on a locational-running annual average,
and a population-based sampling scheme.
The Stage 2 DBPR is accompanied by the
LT2ESWTR, which is a risk-based regulation,
where systems monitor their source water
and when observed occurrence exceeds
fixed thresholds the water treatment
plant must install additional treatment
(e.g., improved conventional removal;
add membranes; install ultraviolet
(UV); ozone; or chlorine dioxide). Just
as chloramination in combination with
enhanced coagulation shaped the cost-
benefit analysis for the Stage 1 and Stage
2 DBP rules, the widespread recognition
of UV disinfection as a treatment for
reduction of Cryptosporidium significantly
altered earlier expectations for the cost of
Cryptosporidium removal. In combination
with low realized Cryptosporidium
oocyst occurrence in the ICR and related
studies, affordable treatment without
known downside DBP risks set the stage
for agreement on the principle features
of LT2ESWTR. The M/DBP FACA reached
agreement in July 2000.

Stage 2 DBPR and LT2ESWTR were not finalized as rapidly as anticipated by the M/ DBP FACA, but were proposed on August 18, 2003 and September 22, 2003 respectively and subsequently promulgated as final rules on January 4, 2006. At present, water systems, depending on their size, are either in the midst of IDSEs and Cryptosporidium monitoring or determining what approach they will take to comply based on those studies. The M/DBP regulatory process will continue based on a second round of Cryptosporidium monitoring, which occurs in 2015 under the current LT2ESWTR and it is worthwhile to recognize that several DBPs (e.g., nitrosamines) are included in the agency’s latest Contaminant Candidate List published in the October 8, 2009 Federal Register.

Bibliography

Bellar, T.A., Lichtenberger, J.J., and Kroner, R.C., 1974. “The Occurrence of Organohalides in Chlorinated Drinking Water,” JAWWA, 66( 12):703-706.

Rook, J.J. 1974. “Formation of Haloforms
During Chlorination of Natural Water,”
Water Treatment and Examination,
23( 2):234-243.

Routt, J.C., Mackey E., Noack R. 2008. “Drinking Water Disinfection Practices Part 2 – Alternatives, Experiences & Future Plans,” JAWWA, 100( 11):110-126.