Implications of Establishing Effluent Guidelines at Usepa Minimum Levels, 1995 Environmental Conference Proceedings

Steven W. Hinton

NCASI - Tufts University

USEPA "non-detect" approach for establishing BAT maximum daily effluent guideline limitation values when no observations exceed the analytical chemistry minimum level is described and evaluated. It was found to have serious technical shortcomings and to ignore useful information contained in the data. Given the sample sizes used by USEPA, the "non-detect" approach effectively establishes limitations at approximately the 96th percentile value of possible discharge conditions instead of the customarily-used 99th percentile value. Rational estimates for a facility’s 99th percentile discharge condition can be made, however, by scaling the maximum value of a data set based on its cumulative probability; the procedure for making such calculations is described. The material presented has direct applicability to the derivation of site-specific permit limits, the interpretation of compliance monitoring data and the analysis of situations involving only one fully quantified observation.