SITE INFORMATION AND CORRESPONDENCE_FILE 1

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PUBLI : HEALTH SERVICES SAN JOAQUIN COUNTY ENVIRONMENTAL HEALTH DIVISION Ernest M. Fujimoto, M.D., M.P.H., Acting Health Of 304 E.Weber Ave., 3rd Floor • P. O. Box 388 • Stockton, CA 95141-03 209/468-3420 BOB BOUST MAILED OCT 31195' UNOCAL 2000 CROW CANYON PL STE 400 SAN RAMON CA 94583 RE: 437 East Miner Ave SITE CODE: 1181 Stockton CA 95202 San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed review of the "Quarterly Data Report" dated August 25, 1995 which was prepared by MPDS Services and the "Well Installation and Soil Boring Report" dated October 9, 1995 which was prepared by GeoStrategies. PHS/EHD has the following comments for your consideration. The "Quarterly Data Report" included the results of the August 9, 1995 sampling of monitoring wells U-1 - U-3 which continued to evidence significant groundwater contamination at approximately the same levels as detected during previous sampling events. The "Well Installation and Soil Boring Report" included the results of soil sampling on July 19 and 20, 1995 during the drilling of soil boring U-N, U-O, and U-P which was subsequently converted into vapor extraction well UV-1, along with soil sampling during the installation of monitoring wells U-4 - U-8. Soil contamination was detected in samples collected from U-N-25, U-0-1 5, and U-P-25, 35 and 40, as well as from U-4-10. It is likely that tanks and piping were in various locations throughout the site. As part of the corrective action plan preparation process, please include isoconcentration maps at various depths, along with cross-sections, so that the distribution of petroleum hydrocarbons can be better understood. Subsequent to the installation of monitoring wells U-4 - U-8, groundwater samples were collected on July 31, 1995 for analysis. Significant contamination was detected in an apparently upgradient well, U-7, which is located off site and south of the site. Benzene at 620 ppb was detected in U-7 which was considerably higher than the 9.8 ppb which was detected in U-2 the most southern on site well. Information is available to suggest that there may have been an underground storage tank located on the property located at the southwest corner of East Miner and California. Prior to PHS/EHD requiring the property owner of APN 139-250-05 (situs address 242 North Sutter) to initiate an investigation, PHS/EHD requests that you have the wells resampled to confirm the analytical results reported and that isoconcentration maps of the groundwater contamination be prepared. As PHS/EHD indicated in prior correspondence the groundwater gradient reportedly has shifted from the west in August 1994 to the north in November 1994 and most currently to the northeast in August 1995. PHS/EHD suggests that monthly groundwater elevation measurements be collected. A Division of San Joaquin County Health Care Services