**[Appendix Table of Contents]**

## Appendix D - Calculation of UTL Without the High Lead Value (Sample ID SS57)

At the direction of Peter Lodde, per our January 10, 2002 meeting with TNRCC, the lead UTL was recalculated without the high value of 212.59 mg/kg (Sample ID: SS57) to investigate the effect this high value had on the UTL. Without the value the Lead UTL is 74.6 (See table D.1) and including the high value the UTL result was 84. It is unusual practice to throw a high value out of the dataset without proper justification (e.g., poor laboratory analytical procedure, or the sample was really not in the background). This value was not a statistical outlier (See Table B.6) and, even if it were, there is a well-known admonition associated with omitting a value that is a statistical outlier without real evidence that this value does not belong in the dataset. In his book, __Statistical Methods for Environmental Pollution Monitoring,__ in Section 15.2 “Treatment of Outliers” the author R. O. Gilbert states, “It is important that no datum be discarded on the basis of a statistical test.” Since this high lead value was not a statistical outlier and there was no non-statistical justification for throwing omitting it, it is our position that this datum should be included in the UTL calculation of 84 mg/kg.