United States
Environmental Protection
Agency
Fact Sheet: sta§e 2
Disinfection Byproducts Rule
In the past 30 years, the Safe Drinking Water Act (SDWA) has been highly effective in
protecting public health and has also evolved to respond to new and emerging threats to safe
drinking water. Disinfection of drinking water is one of the major public health advances in the
20th century. One hundred years ago, typhoid and cholera epidemics were common through
American cities; disinfection was a major factor in reducing these epidemics.
However, the disinfectants themselves can react with naturally-occurring materials in the water
to form byproducts, which may pose health risks. In addition, in the past 10 years, we have
learned that there are specific microbial pathogens, such as Cryptosporidium, which can cause
illness, and are highly resistant to traditional disinfection practices.
Amendments to the SDWA in 1996 require EPA to develop rules to balance the risks between
microbial pathogens and disinfection byproducts (DBFs). The Stage 1 Disinfectants and
Disinfection Byproducts Rule and Interim Enhanced Surface Water Treatment Rule,
promulgated in December 1998, were the first phase in a rulemaking strategy required by
Congress as part of the 1996 Amendments to the Safe Drinking Water Act.
The Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) builds upon the
Stage 1 DBPR to address higher risk public water systems for protection measures beyond those
required for existing regulations.
The Stage 2 DBPR and the Long Term 2 Enhanced Surface Water Treatment Rule are the second
phase of rules required by Congress. These rules strengthen protection against microbial
contaminants, especially Cryptosporidium, and at the same time, reduce potential health risks of
DBFs.
Questions and Answers
What is the Stage 2 DBPR?
The Stage 2 Disinfection Byproducts Rule will reduce potential cancer and reproductive and
developmental health risks from disinfection byproducts (DBFs) in drinking water, which form
when disinfectants are used to control microbial pathogens. Over 260 million individuals are
exposed to DBFs.
This final rule strengthens public health protection for customers by tightening compliance
monitoring requirements for two groups of DBFs, trihalomethanes (TTHM) and haloacetic acids
(HAAS). The rule targets systems with the greatest risk and builds incrementally on existing
rules. This regulation will reduce DBF exposure and related potential health risks and provide
more equitable public health protection.
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The Stage 2 DBPR is being promulgated simultaneously with the Long Term 2 Enhanced
Surface Water Treatment Rule to address concerns about risk tradeoffs between pathogens and
DBFs.
What does the rule require?
Under the Stage 2 DBPR, systems will conduct an evaluation of their distribution systems,
known as an Initial Distribution System Evaluation (IDSE), to identify the locations with high
disinfection byproduct concentrations. These locations will then be used by the systems as the
sampling sites for Stage 2 DBPR compliance monitoring.
Compliance with the maximum contaminant levels for two groups of disinfection byproducts
(TTHM and HAAS) 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 also requires each system to determine if they have exceeded an operational
evaluation level, which is identified using their compliance monitoring results. The operational
evaluation level provides an early warning of possible future MCL violations, which allows the
system to take proactive steps to remain in compliance. A system that exceeds an operational
evaluation level is required to review their operational practices and submit a report to their state
that identifies actions that may be taken to mitigate future high DBF levels, particularly those
that may jeopardize their compliance with the DBF MCLs.
Who must comply with the rule?
Entities potentially regulated by the Stage 2 DBPR are community and nontransient
noncommunity water systems that produce and/or deliver water that is treated with a primary or
residual disinfectant other than ultraviolet light.
A community water system (CWS) is a public water system that serves year-round residents of a
community, subdivision, or mobile home park that has at least 15 service connections or an
average of at least 25 residents.
A nontransient noncommunity water system (NTNCWS) is a water system that serves at least 25
of the same people more than six months of the year, but not as primary residence, such as
schools, businesses, and day care facilities.
What are disinfection byproducts (DBFs) ?
Disinfectants are an essential element of drinking water treatment because of the barrier they
provide against waterborne disease-causing microorganisms. Disinfection byproducts (DBFs)
form when disinfectants used to treat drinking water react with naturally occurring materials in
the water (e.g., decomposing plant material).
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Total trihalomethanes (TTHM - chloroform, bromoform, bromodichloromethane, and
dibromochloromethane) and haloacetic acids (HAAS - monochloro-, dichloro-, trichloro-,
monobromo-, dibromo-) are widely occurring classes of DBFs formed during disinfection with
chlorine and chloramine. The amount of trihalomethanes and haloacetic acids in drinking water
can change from day to day, depending on the season, water temperature, amount of disinfectant
added, the amount of plant material in the water, and a variety of other factors.
Are THMs andHAAs the only disinfection byproducts?
No. The four THMs (TTHM) and five HAAs (HAAS) measured and regulated in the Stage 2
DBPR act as indicators for DBF occurrence. There are many other known DBFs, in addition to
the possibility of unidentified DBFs present in disinfected water. THMs and HAAs typically
occur at higher levels than other known and unknown DBFs. The presence of TTHM and HAAS
is representative of the occurrence of many other chlorination DBFs; thus, a reduction in the
TTHM and HAAS generally indicates a reduction of DBFs from chlorination.
What are the costs and benefits of the rule?
Quantified benefits estimates for the Stage 2 DBPR are based on reductions in fatal and non-fatal
bladder cancer cases. EPA has projected that the rule will prevent approximately 280 bladder
cancer cases per year. Of these cases, 26% are estimated to be fatal. Based on bladder cancer
alone, the rule is estimated to provide annualized monetized benefit of $763 million to $1.5
billion.
The rule applies to approximately 75,000 systems; a small subset of these (about 4%) will be
required to make treatment changes. The mean cost of the rule is $79 million annually. Annual
household cost increases in the subset of plants adding treatment are estimated at an average of
$5.53, with 95 percent paying less than $22.40.
What are the compliance deadlines?
Compliance deadlines are based on the sizes of the public water systems (PWSs). Wholesale
and consecutive systems of any size must comply with the requirements of the Stage 2 DBPR on
the same schedule as required for the largest system in the combined distribution system (defined
as the interconnected distribution system consisting of wholesale systems and consecutive
systems that receive finished water). Compliance activities are outlined in the following table.
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PUBLIC WATER
SYSTEMS
CWSs and NTNCWSs
serving at least 100,000
CWSs and NTNCWSs
serving 50,000 - 99,999
CWSs and NTNCWSs
serving 10,000 - 49,999
CWSs serving fewer
than 10,000
NTNCWSs serving
fewer than 10,000
ACTIONS
Submit IDSE
monitoring plan, system
specific study plan, or
40/30 certification
October 1, 2006
April 1, 2007
October 1, 2007
April 1, 2008
NA
Complete an
initial distribution
system evaluation
(IDSE)
September 30,
2008
March 3 1,2009
September 30,
2009
March 3 1,2010
NA
Submit IDSE
Report
January 1, 2009
July 1, 2009
January 1, 2010
July 1, 2010
NA
Begin subpart
V (Stage 2)
compliance
monitoring
April 1, 2012
October 1, 2012
October 1, 2013
October 1, 2013
October 1, 2013
* States may grant up to an additional two years for systems making capital improvements.
What technical information will be available on the rule?
The following Guidance Documents will be available:
• Initial Distribution System Evaluation (IDSE) Guidance Manual
• Operational Evaluation Guidance Manual
• Consecutive Systems Guidance Manual
• Small Systems (SBREFA) Guidance Manual
• Simultaneous Compliance Guidance Manual
Where can I fend more information about this notice and the Stage 2 DBPR?
For general information on the rule, please visit the EPA Safewater website at
http://www.epa.gov/safewater/disinfection/stage2 or contact the Safe Drinking Water Hotline at
1-800-426-4791. The Safe Drinking Water Hotline is open Monday through Friday, excluding
legal holidays, from 10:00 a.m. to 4:00 p.m., Eastern Time. For technical inquiries, email
stage2mdbp@epa.gov.
Office of Water (4607M) EPA 815-F-05-003 December 2005 www.epa.gov/safewater
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