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t <br /> Unocal Corporation <br /> Diversified Businesses <br /> 2000 Crow Canyon Place,Suite 400 <br /> San Ramon,California 94583 <br /> Telephone(510).867-0760 <br /> - , ;.. Facsimile(510),27 -2309 <br /> cr 1 M 9: 0 0 <br /> UN01MI . Lis <br /> February 7, 1997 <br /> West Region <br /> Environmental 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, California <br /> Dear Mr. Sasson: <br /> This letter is to transmit the.attached Remedial Action Performance Summary- October <br /> through 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 this 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. Please consider the following: <br /> 1) All 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 excavation under the tank pit area. The excavation extended to <br /> groundwater which 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 /> 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 fixture. <br />