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Iy Unocal Corporation J <br /> Diversiliea Businesses <br /> 2000 Crow Canvon Place Suite 400 <br /> San Ramon California 94583 <br /> Telepnone(5101 867 0760 <br /> Facsimde 1510)277 2309 <br /> r <br /> UNOCAL76 <br /> I <br /> February 7, 1997 <br /> Iwest Reoian <br /> cnvironmentai Remediation Services Mr Steven Sasson <br />' San Joaquin County Public Health Services <br /> Environmental Health Division <br /> PO Box 388 <br />' Stockton, California 95201-0388 <br /> Former Unocal Service Station 92859 <br />' 1665 Pacific Avenue <br /> Stockton, Califorrua <br />' Dear Mr Sasson <br /> This letter is to transmit the attached Remedial Action Performance Summary- October <br /> rthrough December 1996 prepared by Pacific Environmental Group, Inc for the above <br /> referenced site The soil vapor extraction (SVE) system at the site was shut down on <br /> November 6, 1996 following a long-term pilot test, and the attached report provides the <br /> final round of monitoring data from the test <br />' I would also like to take thus opportunity to respond to your letter of January 9, 1997 In <br /> that letter, you recommend that additional assessment be performed and that a feasibility <br /> study and corrective action plan be prepared for the site PIease consider the following <br />' 1) Ali underground storage tanks and product piping have been removed <br /> In 1988, 1,100 cubic yards of hydrocarbon-impacted soil were removed <br />' from an excavat-on under the tank nit area The excavation extended to <br /> groundwater whuch was encountered at a depth of 30 feet In addition, <br /> about 2,745 pounds of gasoline and 12 pounds of benzene were <br />' removed by the SVE system from the dispenser island area The <br /> majority of the source of contamination has been removed <br /> z <br />' 2) Depth to groundwater has fluctuated over the years from 30 feet bgs in <br /> 1988 to over 50 feet bgs in 1990 through 1992 This smear zone was <br /> largely submerged during the operation of the SVE The SVE system <br /> was properly designed and operated well Unfortunately, the system <br /> was not able to impact contaminated soil located below the <br /> groundwater Based on recent weather patterns, I do not anticipate any <br /> significant drop in the level of groundwater in the near future <br />