Answers to Questions about the Stage 2 Disinfection Byproducts Rule
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).
- 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.