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D-2 <br />Non-parametric Tolerance Limit <br />When the background data set contains greater than 50 percent but less than 100 percent <br />non-detect values and/or its distribution is not normal (or transformed normal), Sanitas <br />applies the non-parametric tolerance limit method. However, this method requires a large <br />number of samples to achieve a false positive rate of 1 percent or less, which is required <br />by CCR Title 23, Chapter 15, Article 5 guidelines. Thus, when the alpha level was higher <br />than 1 percent, the concentration limit was not established and data was compared to <br />established limits in the WDRs. <br />Non-statistical Approach <br />When the background data set contains 100 percent non-detect values, Sanitas applies <br />the non-statistical approach. This approach takes into consideration that if historically a <br />constituent has not been detected, any detection of that constituent would be considered <br />an exceedance. Thus, in these situations (100 percent non-detected values), the <br />tolerance limit is set at “detect”, meaning that if a value is detected above its method <br />detection limit, this value is an exceedance of the concentration limit.