Frequent Questions

What are the purpose and options for the requirement in 40 CFR Part 141, Subpart U, to complete an initial distribution system evaluation (IDSE) under the Stage 2 Disinfectants and Disinfection Byproducts Rule?

The IDSE is intended to identify sample locations for Stage 2 compliance monitoring that represent distribution system sites with high disinfection byproduct (i.e., THM and HAA5) concentrations (71 FR 388, 419; January 4, 2006).  A system may meet the IDSE requirement by conducting standard monitoring or a system specific study, certifying to the state that they meet the 40/30 certification criteria, or qualifying for a very small system waiver (40 CFR 141.600(d)).

More information about the Stage 2 Disinfectants and Disinfection Byproducts Rule is available at http://water.epa.gov/lawsregs/rulesregs/sdwa/stage2/regulations.cfm.
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