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New Hampshire Department of Environmental Services

Frequently Asked Questions

Disinfection Byproducts (DBP) Rules Sampling Guidance

This guidance is for water system operators and sampling agents with specific questions on DBP sampling, and does NOT list the many other requirements required by these rules. Please refer to the additional information links and contacts at the end of this fact sheet for other questions and compliance requirements.

  • What are the microbial/disinfection byproducts (MDBP) rules and which ones apply to me?
    The MDBP requirements have been in place for close to 30 years and include the following federal rules:
    • Total Trihalomethanes monitoring and MCL, promulgated Nov 1979
    • Surface Water Treatment Rule, promulgated June 1989
    • Interim Enhanced Surface Water Treatment Rule and Stage 1 Disinfectants / Disinfection Byproducts Rule, promulgated Dec 1998
    • Filter Backwash Rule, promulgated June 2001
    • Long Term 1 Enhanced Surface Water Treatment Rule, promulgated Jan 2002
    • Long Term 2 Enhanced Surface Water Treatment Rule and Stage 2 Disinfectants / Disinfection Byproducts Rule, promulgated Jan 2006
    • Groundwater Rule, promulgated Nov 2006

The Disinfectants and Disinfection Byproducts (DBP) rules apply to all community and non-community water systems using a disinfectant such as chlorine, chloramines, ozone and chlorine dioxide. Compliance with the Stage 1 DBP requirements began in 2000. The Stage 2 DBP requirements began in 2006 with the Initial Distribution System Evaluation (IDSE). Compliance monitoring for the Stage 2 DBP begins in April 2012. See phased compliance schedule dependent on system population below.

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2) rule applies to all water systems using surface water, groundwater under the influence of a surface water, as well as groundwater/surface water blends. The LT2 requirements began in 2006 with the characterization of raw water Cryptosporidium and E.coli levels. Systems serving <10,000 monitor for E.coli only every two weeks for one year. Compliance with the LT2 requirements begin in April 2013.

The Groundwater Rule (GWR) applies to all public water systems using groundwater. The GWR requirements begin in March 2009 with 6-months investigative monitoring (IM) for source water E.coli, for systems currently applying disinfection only. All other requirements for the GWR begin in Dec 2009.

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  • What lab analysis/chain of custody form do I use for my DBP/LT2/GWR samples?
    All sampling forms for compliance sampling are provided with the water system Master Sampling Schedule links.

    DBP Quarterly and Triennial samples (currently Stage 1 samples) should be submitted on the DBP Analysis Form available from your Master Sampling Schedule, with the title,


    DBP-IDSE (Stage 2 distribution evaluation) samples and LT2 raw water E.coli samples must be submitted on the General System Evaluation Form (GSES), available from your Master Sampling Schedule, with the title,


    GWR-IM source water E.coli samples must be submitted on the General System Evaluation Form (GSES), available from your Master Sampling Schedule.
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  • What is the "Schedule numbers (1-4)" shown in the DBP section of my Master Sampling Schedule?
    The water system schedule is defined by its service population, and was created for the staged implementation of the M-DBP rule requirements. The larger "schedule 1 systems" are leading the way with requirements due first. The population categories and start of compliance dates are:
Schedule for M-DBP rules Water System Service Population Stage 2/LT2 requirements start Stage 2/LT2 compliance monitoring start
1 >100,000 October 2006 April 2012
2 50,000 - 99,999 April 2007 October 2012
3 10,000 - 49,999 October 2007 October 2013
4 < 10,000 April 2008 October 2013
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  • When do (did) I start the Stage 2 IDSE and/or LT2 raw water evaluation sampling?
Schedule Population Stage 2 IDSE
Sampling start by:
Stage 2 IDSE
Report due by:
LT2 Raw water E.coli
Sampling start by:
1 >100,000 October 1, 2007 January 1, 2009 October 1, 2006
2 50,000 – 99,999 April 1, 2008 July 1, 2009 April 1, 2007
3 10,000 – 49,999 October 1, 2008 January 1, 2010 April 1, 2008
4 < 10,000 April 1, 2009 July 1, 2010 October 1, 2008
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  • What sample numbers do I use for my IDSE samples?
    Any sequence such as A, B, C, etc. that will not be confused with your Stage 1 DBP (300-number series) compliance samples. The number of samples and locations is as approved by DES in your IDSE Plan.
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  • When do I submit my IDSE results?
    At the end of your one-year monitoring period with your IDSE report (see schedule above).
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  • When do I submit my LT2 E.coli results?
    By the 10th day of the following month with your monthly operating report.
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  • When and where do I measure chlorine residuals?
    Chlorine residuals in the distribution system must be taken at the same locations and times as all bacteria samples, whether routines or repeats. Chlorinating systems report free chlorine residuals, while chloraminating systems report total chlorine residuals. These residuals must be reported on the lab sample analysis forms (for the lab's information), and on your quarterly DBP reports to DES (for compliance purposes).

    In addition, surface water systems and groundwater systems that are required to disinfect to achieve 4-logs (99.99%) virus kill, must report daily minimum chlorine residuals at the entry point to the distribution system on their monthly operating reports to DES.

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  • How do I calculate the Running Annual Average (RAA)?
    The running annual average is the average of all compliance samples taken over the past 4 quarters (12 months).
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