A Statistical Approach for Performing Water Quality Impairment Assessments Under the TMDL Program
نویسنده
چکیده
A statistical approach for making impairment determinations in the Section 303(d)listing process is developed. The method is based on the 100(1 a ) percent lower confidence limit on an upper percentile of the concentration distribution. Advantages of the method include: (1) it provides a test of the null hypothesis that a percentage of the true concentration distribution fails to meet a regulatory standard, (2) it is appropriate for a variety of different concentration distributions (i.e., normal, lognormal, nonparametric), (3) it directly incorporates the magnitude of the measured concentrations in the test of the hypothesis that a percentage of the true concentration distribution exceeds the standard, and (4) it has explicit statistical power characteristics that describe the probability of detecting a true impairment conditional on the number of samples, the concentration distribution, and the magnitude of t,he exceedance.
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