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Del Monte P8eds— Research Center <br /> 205 North Wiget Lane (94598-2458) <br /> P.O. Box 9004 <br /> Walnut Creek, CA 94598-0904 <br /> r Telephone: (510) 944-7300 <br /> FAX: (510) 945-7453 <br /> Overnight Delivery <br /> June 30, 1998 <br /> Ronald Rowe <br /> LOP/Site Mitigation Unit <br /> San Joaquin County Public Health Services <br /> Environmental Health Division J U L 0 1 1998 <br /> 304 E Weber Ave., Third Floor <br /> Stockton, CA 95202 ENV1R0Nk1FNTAL HEALTH <br /> PERW f i SERVICES <br /> Subject: Quarterly Monitoring Well Results—Del Monte Disco Site <br /> Dear Mr. Rowe: <br /> Attached are the last quarterly monitoring well results for the Disco site. The original samples <br /> were collected on April 16-17, 1998, and sent to Sherwood Lab for BTEX and PHC analyses, <br /> and BSK Analytical for 8260 oxygenate analyses. We used West Lab for oxygenate analyses the <br /> last quarter but Don Light,Del-Tech, changed laboratories because West Lab was very slow in <br /> returning hard copies of the results. Benzene was detected in the wells near the former tank area; <br /> oxygenates were nondetect. <br /> In reviewing the BSK data, we found they did not test for TBA. When we called to inquire <br /> about this,the BSK lab manager told us they had not undergone the EPA Method 8260 accuracy <br /> and precision demonstration for TBA and were not able to stand behind any test results. He also <br /> questioned the validity of TBA results as low as found in the three monitoring wells last <br /> December. Stewart Podolsky, the West Lab manager, told us that"TBA is difficult to interpret, <br /> and might be easily misidentified,but they would give it their best interpretation". He also <br /> claimed West Lab had completed the accuracy demonstration, and believed their results should <br /> be reliable. <br /> As a result of subsequent discussions with you about our concerns,Don Light resampled all the <br /> Disco site monitoring wells on 5/20-21/98 and had the samples analyzed for TBA by West Labs. <br /> (The same lab that tested for TBA last December.) The tests detected TBA in MW—1 at 30 ppb <br /> and SVE-S at 140 ppb. The three monitoring wells where TBA was found the last quarter(NP- <br /> 1-70,NP-1-90, and SVE-N)were all nondetect. <br /> We also found the groundwater rose 4-5 feet between the December 22, 1997 sampling and April <br /> 16, 1998, and another two feet by the May 20 sampling. Groundwater is now 49-51 feet below <br /> ground surface. <br />