Stage 2 Disinfectant Byproducts Rule
The Environmental Protection Agency (EPA) proposed the Stage
2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) to reduce
disease incidence associated with dangerous chemical byproducts that form
when public water supply systems add disinfectants. The Stage 2 DBPR will
supplement existing regulations by requiring water systems to meet disinfection
byproduct maximum contaminant levels (MCLs) at each monitoring site in the
distribution system. The proposal also contains a risk-targeting approach
to better identify monitoring sites where customers are exposed to high
levels of disinfection byproducts (DBPs). This proposed regulation will
reduce DBP exposure and provide more equitable health protection, and will
result in lower cancer and reproductive and developmental risks.
Chlorine and other chemical disinfectants have been widely used by public
water systems as a principal barrier to microbial contaminants in drinking
water. DBPs are formed when certain disinfectants interact with organic
and inorganic materials in source waters. The levels of DBPs in drinking
water can vary significantly from one point in a distribution system to
another. Epidemiology and toxicology studies have shown a link between bladder,
rectal and colon cancers and DBP exposure. In consideration of the large
number of people exposed to DBPs (approximately 254 million Americans),
the EPA has proposed additional DBP control measures beyond those already
required for public water systems.
The Stage 2 DBPR will protect public health by supplementing existing drinking
water regulations with risk-targeted monitoring and compliance determinations
for current disinfection byproduct MCLs. This regulation will apply to all
systems that add a disinfectant other than ultraviolet
light. Under the Stage 2 DBPR, systems will conduct an Initial Distribution
System Evaluation (IDSE) to identify locations with high disinfection byproduct
concentrations. These locations will then be used as the sampling sites
for DBP compliance monitoring.
Under the Stage 2 DBPR, compliance with the maximum contaminant levels for
two groups of disinfection byproducts, total trihalomethanes (TTHM) and
haloacetic acids (HAA5) will be calculated for each monitoring location
in the distribution system. This approach, referred to as the locational
running annual average (LRAA), differs from current requirements, which
determine compliance by calculating the running annual average of samples
from all monitoring locations across the system. The Stage 2 DBPR would
also require systems to determine if they are experiencing short term peaks
in DBP levels referred to as significant excursions. Systems
experiencing significant excursions would be required to review their operational
practices and work with their state to determine actions that may be taken
to prevent future excursions.
The new requirements provide more consistent protection from DBPs across
the entire distribution system and the reduction of DBP peaks, requiring
only those systems with the greatest risk to make capital improvements.
Cost of the Regulation
The Stage 2 DBPR will result in increased costs to public water systems
and states. The annual cost of the rule is expected to be $54.3 to $63.9
million. Public water systems will bear approximately 98 percent (equivalent
to $53.1 to $62.8 million) of this total cost, with states incurring the
remaining 2 percent ($1.1 to $1.2 million).
The proposed Stage 2 Disinfectants and Disinfection Byproducts Rule was
published in the August 18, 2003 Federal
Register. The comment period was extended by 60 days, and comments were
accepted until Friday, January 16, 2004. Subsequent to review of comments,
a final rule will be published. However, it may be 12-18 months before the
final rule takes effect.
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