Frequent Questions

How is compliance with the MCL's calculated in the 3 quarters leading up to the first LRAA calculations? There is a mix of sample data from Stage 1 and Stage 2 sites. Is a system wide average (like Stage 1) used for compliance during this interim period?

Once a system is required to begin Stage 2 quarterly compliance monitoring under 40 C.F.R. 141.620(c), it must no longer be required to perform monitoring pursuant to its Stage 1 TTHM and HAA5 monitoring plan. Under Stage 2, systems must perform four consecutive quarters of monitoring before making a Stage 2 compliance determination (except if any of the results exceed four times the MCL before the fourth quarter). Systems will continue to conduct LRAA compliance calculations at the end of each subsequent quarter.  
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