You must submit monitoring locations and dates with your compliance monitoring plan. These should be the same locations and dates proposed in your water system’s IDSE report or match any modifications made by the State, unless your system has made significant changes in treatment, distribution system operations and layout, or other factors that may affect TTHM or HAA5 formation. If there are any changes to the monitoring locations, you must replace existing compliance monitoring locations with expected high TTHM or HAA5 levels. Selecting the Highest TTHM Location You should choose your high TTHM site to represent areas in the distribution system where you expect to find higher levels of TTHM throughout the year as compared to other sites. Higher temperatures and increased residence time typically lead to higher TTHM concentrations. Low disinfectant residual usually indicates longer residence time sites. The best TTHM sites are typically located at the ends of the distribution system. Selecting the Highest HAA5 Location Your high HAA5 site should be chosen to represent areas in the distribution system where you expect to find higher levels of HAA5 throughout the year as compared to other sites. Higher temperatures and increased residence time can lead to higher HAA5 concentrations. However, HAA5 can biodegrade when disinfectant residual levels are low or non-existent. Therefore, a high HAA5 site will not necessarily be the site with the longest residence time. Typically, the best HAA5 sites are located near the center of the distribution system. Select the Location with:
Download the EPA’s TTHM and HAA5 Selection Worksheet. *Systems on quarterly monitoring must: take dual sample sets every 90 days at each monitoring location, except for Subpart H systems serving 500-3,300. *Systems on yearly monitoring and Subpart H systems serving 500-3,300 are required to take individual TTHM and HAA5 samples instead of dual sample set at the locations with the highest TTHM & HAA5 concentrations, respectively. Only one location with a dual sample set per monitoring period is needed if highest TTHM & HAA5 concentrations occur at the same location and month. Remember, all TTHM and HAA5 samples collected for Stage 2 DBPR compliance must be analyzed by a certified laboratory. Several States control the sampling process. In some States, samples are analyzed by State laboratories. If either of these situations occurs in your State, you should contact the State drinking water program before contacting the laboratory or before filling in the TTHM and HAA5 Sample Collection and Handling Checklist.