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Water: Stage 2 DBP Rule

Initial Distribution System Evaluation Guidance Manual

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An Initial Distribution System Evaluation (IDSE) is required as part of Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR). IDSEs are an important part of the Stage 2 DBPR. They are one-time studies conducted by water systems to identify distribution system locations with high concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs). Water systems will use results from the IDSE, in conjunction with their Stage 1 DBPR compliance monitoring data, to select compliance monitoring locations for the Stage 2 DBPR.

Who does the IDSE apply to?
How do Public Water Systems (PWSs) meet the requirements of the IDSE?
Initial Distribution System Evaluation Guidance Manual
   Initial Distribution System Evaluation Guide for Systems Serving < 10,000 People (does not include SSS)
   Initial Distribution System Evaluation Guidance Manual (Comprehensive, for all system sizes and IDSE options)
   Initial Distribution System Evaluation Guidance Manual (Individual chapters)
IDSE Tool (electronic format allows you to complete plans/certifications/reports online)


Who does the IDSE apply to?
The IDSE applies to:

  • Use a primary or residual disinfectant other than ultraviolet light (UV), or consecutive systems that deliver water that has been treated with a primary or residual disinfectant other than UV.

AND

  • Are a community water system (CWS) of any size, or are a non-transient non-community water system (NTNCWS) that serves > 10,000 people.

IDSE requirements do not apply to NTNCWSs serving fewer than 10,000 people, although these systems have other requirements under the Stage 2 DBPR. Transient non-community water systems (TWSs) are not subject to any part of the Stage 2 DBPR.

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How do PWSs meet the requirements of the IDSE?
There are four options systems can use to comply with the IDSE requirements of the Stage 2 DBPR:

  1. Qualify for a Very Small System (VSS) Waiver
  2. Meet 40/30 Certification requirements
  3. Conduct a System Specific Study (SSS) using existing monitoring results or a hydraulic model
  4. Conduct Standard Monitoring

EPA has developed an IDSE wizard to help PWSs determine their requirements and eligibility for the IDSE options.

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IDSE Guidance Manual Errata

The IDSE Guidance Manual pdf files available on this website are up to date and reflect all corrections that have been identified as of April 21, 2006. For those who have already printed a copy, the Corrections Sheet available here reflects all updates that may have been made since you printed your copy.

Errata Sheet (PDF 1 pp, 11 K)

Initial Distribution System Evaluation Guidance Manual

If you are a system that serves < 10,000 people (ALL ABOUT PDF FILES)
EPA has developed the Initial Distribution System Evaluation Guide for Systems Serving < 10,000 People. You may find this manual more helpful as it is targeted to smaller systems and focuses on information they are most likely to use. It provides examples to help smaller systems as they proceed with satisfying IDSE requirements. It does not, however, discuss the IDSE System Specific Study (SSS) options.

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Initial Distribution System Evaluation Guidance Manual (Comprehensive) (ALL ABOUT PDF FILES)
The Initial Distribution System Evaluation (IDSE) Guidance Manual is comprehensive and includes IDSE requirements and technical guidance for all system sizes and types and all IDSE options. This is also available in modular format; see below.

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Initial Distribution System Evaluation Guidance Manual (Individual Chapters) (ALL ABOUT PDF FILES)
To help you find information quickly, EPA has designed the IDSE Guidance Manual in a modular format. The introductory materials contain information for all systems. The remaining chapters and appendices contain comprehensive requirements for each specific IDSE option.

EPA recommends that all systems first download the introductory materials for their system. Once you have read the introductory materials in Chapter 1, use the flowchart in Chapter 2 to determine the best IDSE option for your system. Then you can download only those chapters and appendices that you need to build a custom manual for your system.

Once you have determined which IDSE option you will use in Chapter 2, download the corresponding Chapters and Appendices listed below.

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