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On December 29, 2000, the Federal Register published the Agreement in Principle which established the framework for more stringent regulation of disinfection byproducts (DBPs) and microbial contaminants. This agreement is commonly referred to as the FACA Agreement. The DBP portion of this agreement calls for a two-stage approach for more stringent DBP regulations. The first stage of this agreement lowered the MCL for total trihalomethanes from 100 ug/L to 80 ug/L. This rule also established an MCL for haloacetic acid (5 components) of 60 ug/L. Under the Stage 1 Rule, MCL compliance is to be determined as a four-quarter running annual average of four sites located in the distribution system. One of the four monitoring sites needs to be a site reflective of maximum DBP concentrations. The other three sites are to be from average DBP concentration sites. Stage 2 of the DBP regulation is in turn divided into two parts. Stage 2A will require monitoring at the same sites as Stage 1, but compliance will also be based on a locational running annual averages (LRAA). This means that compliance will not be determined by averaging all locations over the past four quarters, rather a four-quarter running average will be determined for each site. If any of the sites has a four-quarter average above the MCL, then the system will be out of compliance with the rule. For Stage 2A, the MCL for the LRAA will be set at 120 ug/L for THMs and 100 ug/L for HAAs. In addition to the LRAA MCLs, the running annual average of all the sites will still be regulated at 80ug/L just like in Stage 1. Compliance with Stage 2B of the DBP regulations will lower the LRAA MCLs to 80ug/L for THMs and 60 ug/L for HAAs. In addition, Stage 2B will require systems to first do a study of the distribution system to find the highest DBP sites in their distribution systems. This study is called the Initial Distribution System Evaluation (IDSE). If any of the sites has a four-quarter average above the MCL, then the system will be out of compliance with the rule. The selection of the sites to use for compliance with Stage 2B is complicated and depends on many factors that will have to be determined for each individual system. To assist systems with determining the location of these sites, the USEPA is currently developing a guidance manual. It is the intent of the USEPA to have this guidance manual available at the same time the Stage 2 DBP rule is proposed. The EPA has made available a draft of the guidance manual dated March 2002 and the information presented in this paper is based on that draft manual. Includes tables, figures.

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Edition: Vol. - No. Number of Pages: 11File Size: 1 file , 1.8 MB