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A N A L Y T I C A L LABORATORIES April 1, 1999 i Del-Tech Geotechnical Services 10624 Olive Avenue f Oakdale, CA 95361 Attention: Don Light Dear Don: The following is an explanation of analytical results for monitoring wells at the Del Monte site. Four of the wells were sampled and analyzed twice, the first sampling event on ! 2/11/99, and the second on 3/19/99. The following table shows the results for TPH-Gasoline on three of the wells: I F i WELL ID 2/11/99 2/11/99 3119199 3/19/99 ORDER# RESULTS ORDER# RESULTS MW-5 98868 76 ug/L 104155 <50 ug/L MW-7S 98870 1 110 ug/L 104153 <50 ug/L MW-7D 98872 300 ug/L 104154 <50 ug/L The original results, which yielded reportable concentrations of gasoline, showed patterns consistent with the heavier, higher boiling point components of gasoline. The method blanks and adjacent injections to these samples did not reveal any carryover contamination. Closer examination of the raw data showed that the three sample stations that were used for these three samples had previously contained samples that were extremely high in hydrocarbon contamination, especially with the higher boiling point components. Even though the sample tubes are disposed for each analysis, and the purge lines are washed, these high levels of contamination probably adhered to the purge lines, and were able to contaminate the next set of samples analyzed at those stations. The subsequent re- sampling and re-analysis of these wells, giving no detectable levels of gasoline, is viewed as verification of the original sample contamination. The results for MW-2 were also viewed as problematic. because of its history of gasoline contamination. The BTEXG results for the two sampling events are summarized below, as well as BTEX results from the FID portion of the analytical run on the original sample: 1414 Stanislaus Street • Fresno, CA 93706-1623 • Phone 559-497-2888, In CA 800-877-8310 Fax 559-485-6935