Proposed Stage 2 Disinfectants and
Disinfection Byproducts Rule
Summary
EPA is proposing the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) to
reduce disease incidence associated with the disinfection 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 (DBFs). This proposed regulation will reduce DBF exposure and provide more equitable
health protection, and will result in lower cancer and reproductive and developmental risks.
Background
Chlorine and other chemical disinfectants have been widely used by public water systems as a
principal barrier to microbial contaminants in drinking water. DBFs are formed when certain
disinfectants interact with organic and inorganic materials in source waters. The levels of DBFs in
drinking water can vary signficantly from one point in a distribution system to another.
Epidemiology and toxicology studies have shown a link between bladder, rectal and colon cancers
and DBF exposure. Additionally, human epidemiology and animal toxicology studies report an
association between chlorinated drinking water and reproductive and developmental endpoints such
as spontaneous abortion, stillbirth, neural tube defects, pre-term delivery, intrauterine growth
retardation, and low birth weight. Because of the combined weight of evidence from the health data,
and consideration of the large number of people exposed to DBFs (approximately 254 million
Americans), EPA has proposed additional DBF control measures beyond those already required for
public water systems.
The proposed Stage 2 DBPR reflects a consensus Agreement in Principle of the Stage 2 M-DBP
Federal Advisory Committee. This Committee consisted of organizational members representing
EPA, State and local public health and regulatory agencies, local elected officials, Indian tribes, large
and small drinking water suppliers, chemical and equipment manufacturers, and public interest
groups. The Committee's activities resulted in the collection and evaluation of substantial new
information. The Committee signed an Agreement in Principle stating the consensus
recommendations of the group that was published by EPA in December, 2000.
About this Regulation
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.
Initial Distribution System Evaluation (IDSE): Under the Stage 2 DBPR, systems will conduct an
evaluation of their distribution system to identify the locations with high disinfection byproduct
concentrations. These locations will then be used by the systems as the sampling sites for DBF
compliance monitoring.
Locational Running Annual Average: Under the Stage 2 DBPR, compliance with the maximum
contaminant levels for two groups of disinfection byproducts (total trihalomethanes (TTHM) and
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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.
Other requirements: The Stage 2 DBPR would also require systems to determine if they are
experiencing short term peaks in DBF 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.
Environmental and Public Health Benefits
The Stage 2 DBPR will improve the control of disinfection byproducts in drinking water systems
with the highest risk levels. EPA estimates that full implementation of the Stage 2 DBPR will reduce
the incidence of bladder cancer cases by up to 182 cases per year, with an associated reduction of up
to 47 premature deaths. While the Stage 1 DBPR provided a major reduction in DBF exposure, new
national survey data suggest that some customers are receiving drinking water with elevated, or peak
DBF concentrations even when the average levels in their water distribution systems are in
compliance with the Stage 1 DBPR. Some of these peak concentrations can be substantially greater
than the Stage 1 DBPR maximum contaminant levels (MCLs). The new survey results also showed
that existing Stage 1 DBPR monitoring sites may not be the locations where the highest DBF
concentrations occur in distribution systems. EPA's analysis of this new information concludes that
significant public health benefits may be achieved through further cost-effective reduction of DBFs
in distribution systems. The new requirements provide for more consistent protection from DBFs
across the entire distribution system and the reduction of DBF peaks, requiring only those systems
with the greatest risk to make capital improvements. In addition, reduction of reproductive and
developmental health effects that may be associated with exposure to elevated DBF levels will come
from the provisions of this regulation, though these benefits have not been quantified.
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 average annual household cost is estimated to be $0.51 per year,
and over 99 % of households will experience annual costs of less than $12 per year.
How to Get Additional Information
For general information on the Stage 2 DBPR, contact the Safe Drinking Water Hotline, at (800)
426-4791. For copies of the Federal Register notice of the proposed regulation or technical fact
sheets, visit the EPA Safewater website, www.epa.gov/safewater/mdbp/st2/st2dbpr.html. The Safe
Drinking Water Hotline is open Monday through Friday, excluding legal holidays, from 9:00 a.m. to
5:30 p.m. Eastern Time.
Office of Water (4607M) EPA 815-F-03-006 July 2003 www.epa. gov/safewater
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