PCWS Water Quality Monitoring - Disinfection By-Products (DBPs)
This page was designed specifically to offer a brief introduction to disinfection by-products, the Federal Rules regulating these, and to provide you with what you will need to complete a Stage 2 DBP Compliance Monitoring Plan. As either the administrative contact or the operator of an NTNC, or Community Public Water System that either chlorinates drinking water or purchases drinking water already chlorinated, you likely collected DBP data under the Stage 1 Disinfection By-product Rule (DBPR)(can we link to this document? is it a separate document?). Stage 1 DBP monitoring requirements sunset September 30, 2013. Beginning October 1, 2013 systems will become responsible for Stage 2 Compliance Monitoring.
All systems affected by the Stage 2 Disinfection By-product Rule (DBPR) are required to submit Stage 2 DBP Compliance Monitoring Plans (can we link to a PDF or sample plan?) These plans must include recommendations on a compliance monitoring schedule and sampling locations in accordance with the schedule, below:
1 All systems must take at least one dual sample set during the month of highest DBP concentrations or warmest water temperature.
The Science of Disinfection By-products (DBPs)
Disinfection byproducts (DBPs) form when water that contains natural organic matter (NOM) is mixed with certain forms of chlorine. NOM, referred to as a DBP precursor, is most commonly found in surface water where organic matter frequently enters the water body from runoff and aquatic organisms. All public water systems using surface water must disinfect the water prior to delivery to customers. DBPs are harmful to human health and are regulated under the Safe Drinking Water Act (SDWA). In 2001, USEPA published the STAGE 1 DISINFECTANTS AND DISINFECTION BYPRODUCT RULE (Stage 1) to address DBPs in treated water (surface water or otherwise). There are many USEPA GUIDANCE DOCUMENTS on Stage 1 available. Stage 1 created Maximum Contaminant Levels (MCL) for DBPs, monitoring requirements and DBP precursor removal requirements.
The most common DBPs are Trihalomethanes, Haloacetic Acids, Bromate and Chlorite (plants using chlorine dioxide). The Maximum Contaminant Level (MCL) for Trihalomethanes is for Total Trihalomethanes (TTHM). The MCL for Haloacetic Acids is for the five most common Haloacetic Acids, referred to as HAA5. The MCLs for TTHM, HAA5 and Bromate is based on the Running Annual Average (RAA) of the all the samples collected over a twelve month period. The MCLs for these DBPs are as follows:
Trihalomethanes typically continue to form in the distribution system over time so the highest concentrations of these are most often found at the outermost edges of a distribution system (furthest from the water treatment facility) where the "oldest" water is found. Thus, this is where sampling locations for TTHMs are most appropriately located (the Maximum Retention Time or MRT Site). Haloacetic Acids, on the other hand, tend to degrade in the distribution system after treatment and thus are often found at their highest levels more centrally within the distribution system. Other factors influencing DBP formation include pH (higher pH favors THM production, lower pH favors HAA production) and temperature (higher temperature favors DBP production so summer time often sees higher DBP concentrations).
The Regulation of Disinfection By-products (DBPs)
In 2006, USEPA published the STAGE 2 DISINFECTANTS AND DISINFECTION BYPRODUCTS RULE (Stage 2). This rule built on and strengthened Stage 1. One big change is that the MCL was and will be based on the local running annual average (LRAA) which means that concentrations are averaged at individual sampling locations rather than over the entire distribution system as in Stage 1.
Normal Organic Matter (NOM) is measured in the form of Total Organic Carbon (TOC). Individual treatment plants are required to achieve a specified percent removal of influent TOC between the raw water sampling point and the treated water TOC monitoring location. The percentage reduction depends on the influent TOC and the alkalinity (the percent reductions recognize that TOC removal is more difficult with increasing alkalinity). The TOC reduction requirements are found in the following table:
Transitioning to Stage 2 DBP from Stage 1 DBP Compliance Monitoring
The Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 Rule) sets new monitoring requirements for total trihalomethanes (TTHM) and haloacetic acids (HAA5). USEPA published the Stage 2 Rule in January 2006. The Stage 2 Rule applies to all community and non-transient, non-community (NTNC) public water systems that deliver water continuously treated with a primary or residual disinfectant other than ultraviolet light (including those that purchase treated drinking water). The Stage 2 Rule does not apply to water systems that only use these disinfectant chemicals temporarily, such as after facility cleaning or repair.
FREQUENTLY ASKED QUESTIONS:
How do I know which Stage 2 Rule due dates apply to my system?
1 Public water systems that have non-emergency interties with other water systems must comply with the deadlines for the largest water system in their combined distribution system.
2 An Initial Distribution System Evaluation (IDSE) document is a standard monitoring plan or system-specific study plan. NTNC water systems serving < 10,000 people are exempt.
3 Ground water systems and surface water systems that did not have to do Cryptosporidium monitoring under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR).
4 Surface water systems that also did Cryptosporidium monitoring under LT2ESWTR.
What are the differences between Stage 1 and Stage 2?
Which monitoring do I need to do – Stage 1 or Stage 2 – and when?
What changes are there for my bromate, chlorite, and disinfectant residual monitoring?
How do I determine my Stage 2 DBP Compliance Monitoring locations?
I completed the IDSE. What do I do next?
I received a VSS Waiver, a 40/30 Certification, or my system is a NTNC – What do I do next?
Stage 2 DBP Compliance Monitoring Plan Guidance (in Brief and Detailed)
The Stage 2 compliance monitoring plan must be completed by the date routine Stage 2 DBP monitoring begins. Meeting this deadline will ensure you are ready to start the Stage 2 DBP compliance monitoring in 2012, 2013, or 2014, whichever applies to your water system.
Monochloramines and Chloramination:
For some systems, one treatment option for minimizing DBP formation is to avoid using chlorine as the disinfectant. Another disinfectant considered effective in minimizing regulated DBPs is monochloramine. The following resources should help in learning more about monochloramines and chloramination:
DBP Stage 2 - Additional Resources
The following reference and guidance documents may prove useful to you in better understanding and minimizing the formation of Disinfection Byproducts:
Resources for Maintaining Compliance with the DBPR:
Best Management Practices (BMP) for DBP Minimization:
Directions for Electronic Submission of your Stage 2 DBP Compliance Monitoring Plan
When you have completed your Stage 2 DBP Compliance Monitoring Plan- you can submit it electronically directly to the Vermont Drinking Water & Groundwater Protection Division. Save the completed digital plan form first to your computer’s hard drive (you may also wish to save a printed copy), then submit it as a file attachment e-mailed to the following with Stage 2 DBP Compliance Monitoring Plan in the subject line: firstname.lastname@example.org.
PLEASE attach also a distribution system schematic with ALL selected monitoring location(s) clearly labeled.
Upon review, systems will either be contacted with a request for additional information OR sent a letter of approval.
drinkingwater.vermont.gov groundwater.vermont.gov septic.vermont.gov wastewater.vermont.gov
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