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i IUsing the current laboratory data, the volume of remaining gasoline can be calculated to be approximately 184 gallons This represents a 93 9% reduction These two methods of calculating the volume of remaining hydrocarbons yield very similar results 5.2 Hydrocarbon Imapcted Groundwater IMonitoring wells MW-8 and MW-9 were installed to investigate the extent of hydrocarbons in groundwater In 1988, free product was present in MW-1 and MW-2 The groundwater gradient at that time was to the north to northeast Because of interim soil remediation and the sharp drop in groundwater depths, no groundwater monitoring activities took place between October 1988 and June 1994 No petroleum hydrocarbons were detected in water samples from MW-8 or EW-1 This indicates a dramatic decrease in petroleum hydrocarbons The process of vapor extraction in the vicinity of these wells, combined with natural degradation is most likely responsible for the sharp decrease in petroleum hydrocarbons Low concentrations of toluene and xylenes were detected in the sample from MW-9 Low concentrations of petroleum hydrocarbons were previously reported in MW-3 However, concentrations of toluene and xylenes detected during the July 1994 sampling are very low, and are below the State of California Action Level (AL) and Maximum Contaminant Level (MCL) for drinking water Two methods of transferring contaminants from the soil to the water are through the downward leaching of water and through the direct contact of groundwater with contaminated soil The surface directly above the effected soil is covered with concrete and asphalt, preventing significant migration of surface water through the impacted zone No I petroleum hydrocarbons were detected in soil samples below 40 feet, groundwater depth is currently near 60 feet It is unlikely that groundwater will rise above high enough to come in contact with contaminated soil 5.3 Site Closure A Closure Summary Report (CSR) should be prepared summarizing all activities conducted at the site The CSR should include the problem assessment, analytical results for all soil and groundwater sampling, remediation activities and the results and findings of these activities A final monitoring event should be scheduled for mid-September 1994 The results of this monitoring should be included in the CSR 6.0 LIMITATIONS Our professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities The findings were based upon analytical results provided by an independent laboratory Evaluations of the geologic/hydrogeologic conditions at the site for the purpose of this investigation are 0-1baht A.d.1 3.ry 1- 13 0—B.lary OFR 90 t