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1 <br /> PUBLIC HEALTH SERVICES ° .`o� <br /> SAN JOAQUIN COUNTY e t� <br /> JOGI KHANNA M.D.,M.P H. <br /> Health Officer " �.., <br /> P.O. Box 2009 • (1601 East Hazelton Avenue) • Stockton, California 9520 <br /> 4CIFOP�sP <br /> (209) 468-3400 <br /> DAVE CORP COO <br /> �� <br /> UNOCAL AL CORPORATION <br /> 2000 CROW CANYON PLACE <br /> SUITE 400 FEB 0 4 1993 <br /> SAN RAMON CA 94583 <br /> RE: Unocal Service Station #6981 SITE CODE: 1217-123 <br /> 4707 Pacific Avenue <br /> Stockton CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed <br /> review of the "Problem Assessment Report" dated December 16, 1992 prepared by RESNA. PHS/EHD <br /> has the following comments for your consideration. <br /> Soil and Groundwater Contamination Investigation <br /> Soil investigation was initiated on May 13, 1988, prior to the removal of three underground storage <br /> tanks and the replacement with two underground storage tanks. The results of the soil investigation <br /> evidenced soil contamination associated with the eastern pump island at 4 feet below ground surface <br /> (bgs) of up to 382 ppm total petroleum hydrocarbons - gasoline (TPH-g) and 100 ppb benzene and at <br /> 19 feet bgs of up to 1407 ppm TPH-g and 2,300 ppb benzene. <br /> The tanks were removed on June 15, 1988. Soil samples collected at that time evidenced soil <br /> contamination at 22 feet bgs of up to 1,900 ppm TPH-g and 84,000 ppb benzene. During the tank <br /> removal process approximately 1,600 cubic yards of contaminated soil was removed, aerated and then <br /> transported to Forward Landfill in Stockton CA for disposal. Immediately following the tank removal, <br /> two underground storage tanks were installed in the same place the former tanks had occupied. There <br /> are no immediate plans to remove these tanks. <br /> A shallow soil vapor survey was conducted on December 1988 to investigate the parameter of the site. <br /> Thirteen soil vapor probes were placed along the boundaries of the site. The probes were placed at a <br /> depth of 12 feet and only one probe indicated contamination. Contaminates were detected using a <br /> Photovac 10S70. <br /> The soil and groundwater investigation continued on February 21, 1990 and consisted of the drilling and <br /> sampling of five soil borings, Bl - 135, all of which were converted to monitoring wells, MW1 - MWS. <br /> Soil contamination was detected during the installation of MW2, MW4, and MWS. Groundwater <br /> contamination was detected in all five wells. Confirmation sampling did not occur because the wells <br /> were reported dry October 18, 1990. The total depth of the wells were approximately 55 feet. The wells <br /> were screened from approximately 49 feet to 55 feet. <br /> The soil and groundwater investigation continued on March 2, 1992 and consisted of the drilling and <br /> sampling of seven soil borings, 136 - B13, four of which were converted to vapor wells, VW1 -VW4, and <br /> A Division of San Joaquin County Health Care Servmces 0 <br />