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s Mr Ronald Rowe August 17, 1999 C A M B R I A March 1990 Soil Vapor and Groundwater Extraction Tests Ground water pumping and vapor extraction tests were conducted during March 1990 to obtain hydrogeologic data, hydrocarbon concentration levels, and flow parameters for remedial system design April 1990 Free Product Skimming System A free product skimming system was installed to collect free product from well MW-2 in April 1990 The skimmer was later moved to well MW- 7 Approximately 180 gallons of free product were skimmed from the wells July 1991 Well Installation Off-site ground water monitoring well MW-10 was installed in July 1991 Soil Vapor Extraction System Installation - —-- Figure A A soil vapor extraction (SVE) system was E TPHg Concentrations in SVE Influent installed and operated full time from E 16 000 70 September 1992 to September 1993 The S 12 000 --_---T-- - -__- 65 system was operated intermittently through 8000 _ d _ __ so November 1996 As indicated in Figure A, 4000 ry -- -- - - ss total petroleum hydrocarbons as gasoline (TPHg) concentrations decreased ra idl ti 5 5 5so within a few months of system startup, which 141 r_ is very typical for SVE system performance ©mn�entTPH9 GwE InfRrI.16 Mw 5 The San Joaquin County Public Health Services asserted in previous documents that the rapid TPHg concentration decrease was due to a rising water table However, as indicated in Figure A, TPHg concentrations had decreased prior to any increase in water table elevation Furthermore, although groundwater elevations increased to near or slightly above the top of the well screen, groundwater elevations also decreased to near original elevations the following year Since there was no corresponding increase in TPHg influent concentrations as the water table elevation decreased, it is evident that groundwater elevation did not adversely affect SVE performance Therefore, the decrease in TPHg concentrations was due to mass removal and not due to rising water tables The system removed an estimated 14,980 pounds of hydrocarbons from the subsurface during the first year of operation Hydrocarbon Distribution in Soil No hydrocarbons were detected in up-gradient well MW-1, cross-gradient well MW-6, cross- gradient borings SB-6, SB-7 and SB-8, and down-gradient well MW-10 (Attachment A) The only area where the horizontal extent of hydrocarbons has not been defined is east of well MW- 5 However, the adjacent motel made additional lateral definition problematic 2