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P <br />i <br />I I <br />0 <br />n <br />'I <br />F" <br />u <br />11 <br />u <br />C <br />When the background data set contains greater than 50 percent but less than 100 percent <br />nondetect values and/or its distribution is not normal (or transformed normal), Sanitas applies the <br />nonparametric tolerance limit method. However, this method requires a large number of samples <br />to achieve a false positive rate of 1 percent or less, which is required by CCR Title 23, Chapter <br />15, Article 5 guidelines. Thus, when the alpha level was higher than 1 percent, the concentration <br />limit was not established and data was compared to established limits in the Waste Discharge <br />Requirements. <br />When the background data set contains 100 percent nondetect values, Sanitas applies the <br />nonstatistical approach. This approach takes into consideration that if historically a constituent <br />has not been detected, any detection of that constituent would be considered an exceedence. <br />Thus, in these situations (100 percent nondetected values), the tolerance limit is set at "detect", <br />meaning that if a value is detected above its method detection limit, this value is an exceedence <br />of the concentration limit. <br />North County RC&SL D_2 Public Works/Solid Waste <br />2ntl Semester and Annual 2013 Groundwater Monitoring County of San Joaquin — January 25, 2014 <br />