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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 non-transient 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 began 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 sampled for E.coli only every two weeks for one year. Compliance with the LT2 requirements began in April 2013.

The Groundwater Rule (GWR) applies to all public water systems using groundwater. The GWR requirements began 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 began 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 should be submitted on the DBP Analysis Form available from your Master Sampling Schedule under the DBP section, with the title,


    GWR-IM source water E.coli samples must be submitted on the Investigative Monitoring (IM) Form (GSES), available from your Master Sampling Schedule, under the “Groundwater Rule” section.
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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 your routine bacteria samples. Chlorinating systems report free chlorine residuals, while chloraminating systems report total chlorine residuals. These residuals must be reported on the lab sample analysis forms to be transmitted electronically to NHDES, and on your quarterly DBP reports for DBP rule compliance purposes. This form is available from your Master Sampling Schedule under the DBP section, with the title, “D/DBP QUARTERLY REPORT”

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 NHDES.

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  • How do I calculate the Locational Running Annual Average (LRAA)?
    The locational running annual average is the average of all compliance samples taken over the past 4 quarters (12 months) at each sampling site.
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NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
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