The Stage 2 Disinfection Byproducts Rule (DBP2) was adopted by
EPA December 15 2005 to build on existing rule requirements. This
Web page answers questions you may have about the new rule.
What are disinfection byproducts (DBPs)?
Chlorine 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.
Unfortunately, disinfectants can react with naturally occurring
materials in the water to form disinfection byproducts (DBPs),
which may pose health risks. The specific DBP regulations that are
discussed here are for two DBP families: trihalomethanes (THMs) and
haloacetic acids (HAAs).
How will the DBP2 rule help protect public health?
This final rule strengthens public health protection for
customers by tightening compliance monitoring requirements for two
groups of DBPs, trihalomethanes (TTHM) and haloacetic acids (HAA5).
The rule targets systems with the greatest risk and builds
incrementally on existing rules. This regulation will reduce DBP
exposure and related potential health risks and provide more
equitable public health protection. The DBP2 rule is being
promulgated simultaneously with the Long Term 2 Enhanced Surface
Water Treatment Rule (LT2) to address concerns about risk tradeoffs
between pathogens and DBPs.
What is the history of DBP regulation?
In November 1979, EPA set an interim maximum contaminant level
(MCL) for total THMs of 0.10 milligrams per liter (mg/L) as an
annual average for community public water systems (PWSs) serving
10,000 or more people. The Stage 1 Disinfectants and Disinfection
Byproducts Rule (DBP1) was promulgated in December 1998 as the
first phase in a rulemaking strategy required by Congress as part
of the 1996 Amendments to the Safe Drinking Water Act. DBP1 lowered
the MCL for THMs to 0.080 mg/L, and added an MCL for HAAs of 0.060
mg/L, both based on an annual average. The Stage 2 Disinfectants
and Disinfection Byproducts Rule (DBP2) of December 2005 builds
upon the DBP1 to address higher risk public water systems for
protection measures beyond those required for existing
regulations.
What are the requirements of DBP2?
The DBP2 rule requires system to determine the highest risk
sample sites for DBPs in their distribution system, then changes
the compliance calculation to look at each sample site
individually. The two main parts of the rule are the Initial
Distribution System Evaluation (IDSE) for finding highest risk
sites and locational running annual average (LRAA) for calculating
compliance at every sample site.
What are the benefits of the rule?
Quantified benefits estimates for DBP2 are based on reductions
in fatal and nonfatal bladder cancer cases. EPA has projected that
the rule will prevent approximately 280 bladder cancer cases per
year in the United States. Of these cases, 26 percent are estimated
to be fatal. Based on bladder cancer alone, the rule is estimated
to provide annual monetized benefit of approximately $763 million
to $1.5 billion savings.
What are the costs of the rule?
The Initial Distribution System Evaluation (IDSE) is a one-year
period of sampling that will increase sample costs for systems that
don’t receive a waiver. The approximate cost of a paired DBP
sample (TTHM and HAA5) is $287. The approximate amount of
additional sampling during the one-year IDSE period is three times
current compliance sampling for DBP1. A PWS can determine the exact
increased cost by figuring out how many IDSE samples they are
required to take, using the rule language and tools provided by
TCEQ’s Public Drinking Water Section. Systems that exceed the
MCLs may have to incur capital cost to fix the problem.
What systems must comply with DBP2?
All community public water systems (PWSs) must comply with the
rule. Very small community PWSs (population less than 500) may be
eligible for waivers to the Initial Distribution System Evaluation.
Nontransient noncommunity (NTNC) public water systems have to
comply with DBP2, but NTNC systems that serve fewer than 10,000
people do not have to do the Initial Distribution System
Evaluation.
Will the MCLs be lowered?
The maximum contaminant levels (MCLs) for total THMs and HAAs
will remain the same. The MCL for the sum of the concentration of
the four regulated THMs (TTHM) will stay 80 micrograms per liter
(µg/L); the MCL for the sum of the five regulated HAAs (HAA5)
will stay 60 µg/L. The LRAA will be used starting in about
2012.
What is an LRAA?
After the DBP2 sites are set through the IDSE process,
compliance determination will change to use a locational running
annual average (LRAA) instead of a running annual average (RAA) for
all sites in the system. An LRAA is the yearly average of all the
results at each specific sampling site in the distribution
system.
What is the IDSE?
The Initial Distribution System Evaluation (IDSE) is a special
sampling activity to find highest areas for DBP formation. The IDSE
process will result in selection of new DBP2 compliance sample
sites to replace the DBP1 compliance sample sites. There are four
ways to comply with the IDSE:
- Do standard IDSE sampling.
- Serve fewer than 500 people (small system waiver).
- Have less than 40 µ/L TTHM and less than 30 µ/L
HAA5 in all DBP1 compliance samples (40/30 waiver).
–or–
- Do a system-specific study as described in the rule.
We will send you more information on these options.
What are the specific requirements of the IDSE?
The first requirement is to figure out which of the four ways to
comply is appropriate for a water system. TCEQ will send Texas PWSs
a letter saying which method we believe is appropriate, and give
you a chance to confirm or correct our data. If you serve more than
500 people, and have had sample results over 40 µ/L for TTHM
or 30 µ/L for HAA5, you will either have to do IDSE sampling
or a system-specific study. If you have to do the IDSE sampling,
you will need to complete the IDSE plan that TCEQ sends you. If you
want to do the system-specific study, you should review the DBP2
rule language with your engineer and submit a plan to TCEQ. The
DBP2 rule has very specific requirements for system-specific
studies, including specifications for the required hydraulic
modeling, and requirements for sampling.
How will TCEQ help with the IDSE?
TCEQ will send you letters summarizing your system’s data,
and the IDSE compliance method that data indicates. The letters
will guide you through the process. For any reports you need to
generate, TCEQ will send you a report form to sign, certifying that
our data is correct. If you find that TCEQ’s data is
incorrect, you will have the opportunity to submit changes. Most
systems should not have to hire a consultant to complete the IDSE
(except for those doing system-specific studies) though some
systems may find it helpful. TCEQ will collect IDSE samples using
our normal contract samplers.
What letters will TCEQ send PWSs?
We will send the following letters:
- Confirmation of Interconnects. In this letter,
we will tell you who, according to our records, your PWS provides
water to or receives water from. These letters will be sent to PWS
Responsible Parties in early 2007. If our information is correct,
you will sign the report and return it, keeping a copy for your
Monitoring Plan. If our information is incorrect, you will strike
through canceled interconnects, or write in new ones, sign the
report to certify that the data is good, and send that new data
back for us to correct in our database.
- IDSE Plan and Confirmation of DBP1 Sites (IDSE Sampling
/ Small System Waiver / 40/30 Waiver). When your
compliance time gets close, TCEQ will send a letter that says which
method each system will use to comply with the IDSE: IDSE Sampling,
Small System Waiver, or 40/30 Waiver. This letter will also list
the sample sites that you are using now for compliance. If we send
you a letter providing a waiver, you will need to sign that waiver
certifying that the data is correct, send the original to TCEQ, and
keep a copy for your Monitoring Plan. The waiver may require you to
select additional sample sites for DBP2, in which case you will be
given instructions, and asked to list those. If you must do IDSE
Sampling, you will need to fill out the IDSE Sample Site Selection
form (following the instructions that TCEQ provides), return it to
TCEQ, and keep a copy for your Monitoring Plan.
- IDSE Report. When the IDSE is over, TCEQ will
send a letter summarizing the results. This will include the IDSE
Report Form that lists the proposed DBP2 compliance sites and
current DBP1 compliance sites. You will need to check to make sure
you agree with the sites, sign and return the report, or propose
different sites with justification. After these sites have been
certified by the PWS and TCEQ, the system can not change sample
locations without TCEQ approval.
Will IDSE sampling results count for compliance?
No. Until the LRAA calculation becomes effective in about 2012,
only samples collected at DBP1 routine compliance sample sites will
be used to determine compliance. So, you can see how important it
will be to verify those sites with TCEQ when you get our
letter.
How many sample sites will my system need for IDSE?
The number of IDSE sample sites will be based on population and
type of water. Larger systems will be required to set more sites
than small systems; systems that treat or purchase surface water
(or groundwater under the direct influence of surface water) will
set more sites than systems that just use groundwater. Tables of
sample sites will be available on our Web site.
When will my water system have to comply?
Compliance deadlines are based on the sizes of the public water
systems. Large systems, and the systems connected with them, have
to comply first. Wholesale and consecutive systems of any size must
comply with the requirements of the DBP2 on the same schedule as
required for the largest system in the “combined distribution
system.” Smaller systems’ compliance dates will be
phased in over the next few years. IDSE activities will happen in
2006 through 2008. The new LRAA calculations will start being used
in 2012.
What is a “combined distribution system?”
The combined distribution system is defined as the
interconnected distribution system consisting of all systems that
provide water and the systems that receive finished water. The
population of the largest system in the group sets the schedule for
the whole group. The population cutoffs for scheduling are 100,000,
50,000, and 10,000. The four scheduling groups for DBP2 are:
- DBP2 Group 1: Systems that serve 100,000 or
more people and combined distribution systems that include a system
that serves 100,000 or more people
- DBP2 Group 2: Systems that serve 50,000 to
99,999 people and combined distribution systems whose largest PWS
member serves 50,000 to 99,999 people
- DBP2 Group 3: Systems that serve 10,000 to
49,999 people and combined distribution systems whose largest PWS
member serves 10,000 to 49,999 people
- DBP2 Group 4: Systems that serve 9,999 or
fewer people and combined distribution systems in which all PWS
members serve 9,999 or fewer people
Note that this is based on population, not
connections. Also, if a PWS has no interconnects, that PWS
just follows the population cutoffs as given, and does not have to
worry about the combined distribution system concept.
What is a “combined distribution system?”
The combined distribution system is defined as the
interconnected distribution system consisting of all public water
systems (PWSs) that provide water and the systems that receive
finished water. The population of the largest system in the group
sets the schedule for the whole group.
Does the sum of the populations in the combined distribution
system set the schedule?
No. The sum of the populations of the interconnected
distribution system has no impact on schedule.
Does the combined distribution system determine the number of
sample sites?
No. The number of sample sites for DBP2 is determined only by
the population of the individual system.
What schedule does a system with no interconnections
follow?
A PWS with no interconnects follows the population cutoffs as
given. For example, a system that serves 110,000 people and has no
interconnects is in Group 1; a system that serves 900 people and
has no interconnects is in Group 4.
What is a provider?
Usually a provider sells water to a receiver, based on a
contractual agreement between the two PWSs. Sometimes the provider
is a true wholesaler that does not operate a distribution system of
its own. More often the provider is a community PWS that sells
water to other PWSs. Sometimes, a PWS provides water for no cost,
which is why TCEQ refers to “providers” instead of
“sellers.”
What is a receiver?
A receiver is a PWS that gets potable water from a different PWS
and distributes it. Most receivers in Texas are known as true
purchased water systems because they don’t have any wells or
surface water treatment plants of their own. However there are also
many PWSs that buy some water, but also operate their own sources.
Sometimes, a PWS does not have a contract for their potable water
source (for example, a school that operates wells), so TCEQ calls
these “receivers” instead of
“purchasers.”
EPA guidance refers to “consecutive systems” and
“wholesalers.” What does that mean?
If you read the EPA guidance material, they use slightly
different terms. TCEQ wanted to use terms that Texas PWSs were
familiar with. Generally, a consecutive system is the same as a
“receiver,” and a wholesaler is just one type of
“provider.”
What are the types of interconnect?
Interconnections are classified as Operational (O), Demand (D),
or Emergency (E). Operational interconnects are generally used
frequently, for example daily. Demand wells are routinely used for
higher-demand situations, such as annual summer usage peaks.
Emergency interconnects are not normally used; usually it would
require some maintenance — such as insertion of a spool piece
— for an emergency interconnect to be used.
Do emergency interconnects count for the combined distribution
system?
Your system may have a contractual agreement with a neighboring
system to provide water under emergency conditions. A true
emergency interconnect is not used annually; it is only used every
few years at most. If you certify that an interconnection is for
emergency use, TCEQ will not consider it an interconnect for the
scheduling purposes of DBP2.
Do demand interconnects count for the combined distribution
system?
Yes, demand interconnects usually count for the scheduling
purposes of DBP2.
Will true wholesalers be required to comply with the DBP2?
Under DBP2, systems that just sell water but do not have any
retail connections will be required to sample at the points where
water is transferred to their purchasers or other receiving systems
starting in 2012.
When will the Initial Distribution System Evaluation (IDSE)
requirements apply to my system?
The first thing that will apply to your system is the IDSE. TCEQ
will send letters to PWSs when their start time is near:
- DBP2 Group 1: Fill out and return IDSE Sample
Plan or Waiver by October 1, 2006.
- DBP2 Group 2: Fill out and return IDSE Sample
Plan or Waiver by April 1, 2007.
- DBP2 Group 3: Fill out and return IDSE Sample
Plan or Waiver by October 1, 2007.
- DBP2 Group 4: Fill out and return IDSE Sample
Plan or Waiver by April 1, 2008.
How will compliance be calculated under DBP2?
Compliance with the maximum contaminant levels for two groups of
disinfection byproducts (TTHM and 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.
What is an “Operational Evaluation Level?”
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 DBP levels, particularly those
that may jeopardize their compliance with the DBP MCLs.
Why is compliance based on a running annual average?
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. Because the
identified health effects result from a long period of contact, it
is appropriate to base compliance on a long-term calculation rather
than single samples.
