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The U.S. Environmental Protection Agency (EPA) has conducted two Discharge Monitoring Report — Quality Assurance (DMR-QA) studies to evaluate the performance of laboratories doing analyses required in major National Pollution Discharge Elimination System (NPDES) permits. The object of these studies is to identify laboratories that appear to be having significant analytical problems and that should receive follow-up contact by the state or EPA region with primacy.
Participants receive a set of sample concentrates to be diluted to volume with distilled water. The resulting samples can be analyzed for 26 of the analytes most frequently limited in permits. Analytical results are submitted to EPA for evaluation against appropriate acceptance limits and a report is returned to each participant. The acceptance limits are constructed as 99% confidence intervals based upon the state-of-the-art analytical capabilities demonstrated by participating EPA and state laboratories. The statistical basis for the acceptance limits in the most recent study, DMR-QA Study 2, is discussed in detail.
DMR-QA Study 2 included data representing 5157 major NPDES permits and all 50 states. On the average, 22% of these data were beyond the acceptance limits, indicating there is considerable potential for improvement. Results from DMR-QA studies focus the limited follow-up resources of the primacy agencies to maximize the improvement in DMR data quality. Whether any improvement actually occurs, however, depends entirely upon the commitment of the responsible state and EPA enforcement offices, as well as the major NPDES dischargers, to make the changes necessary to improve the quality of monitoring data.
quality assurance, statistical properties, performance evaluation limits, major discharger, NPDES permitte
Statistician and DMR-QA Study Manager, Quality Assurance Branch, Environmental Monitoring and Support Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH