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I i December 27, 1995 Page 3 Boring SB-10 were 2,400 ppm Maximum TPH-g concentrations at Borings SB-11, SB-12, and SB-13 were 240, 10,000, and 5,300 ppm, respectively The maximum TPH-g concentrations in each of the soil bonngs were detected at 25 to 30 foot bgs interval Groundwater monitoring wells that characterize the dissolved plume consist primarily of Well MW-9 located in the source area, Well MW-13 located within the dissolved plume ~ downgradient of the source, and Wells MW-12 and MW-14 located near the plume edge SVE will be used to address impacted vadose, and capillary-fringe sods in the area bounded by and beneath and downgradient of the USTs This impacted area is referred to on Figure 3 as the "remedial zone" Geologic cross-sections are shown on Figures 4 and 5 Figure 6 illustrates the conceptual site layout for the remedial system Hydrocarbon mass reduction will initially be accomplished using a combination of SVE and air sparging Initially, SVE and air sparging will be used to remove 'residual hydrocarbons from the vadose, capillary fringe and saturated zones Once the use of SVE and air sparging have been maximized, enhanced biodegradation (low flow air infection) will be utilized to complete remediation Screen intervals for each of the existing SVE wells extend from 14 to 44 feet bgs, but because of frictional resistance along the well screen, most of the vapor flow occurs over the upper portion of the well screen Additionally, the effects of frictional resistance are compounded because horizontal permeability to air flow is significantly greater than vertical permeability to air flow These factors result in mass removal localization near the top of the screen interval, at 14 feet bgs Soil Vapor Extraction Design Basis Current data suggests that the greatest petroleum hydrocarbon impact occurs at the 25 to 30 foot bgs interval In order to address this deeper impacted zone, PACIFIC proposes to construct three new SVE wells Newly proposed SVE Wells VW-1, VW-2 and VW-3 (Figures 7 and 8) are designed to more accurately address residual hydrocarbon impact remaining in vadose and capillary fringe zones Geologic cross- sections (Figures 4 and 5) show residual hydrocarbon impact data used to design wells for SVE The proposed SVE wells are screened from 25 to 35 feet to address the majority of residual hydrocarbon impact in that 10 foot interval Modifications to this screen interval may be recommended based on lithology encountered during well construction Previously, wells used for vapor-phase hydrocarbon removal were SVE Wells V-I through V-5, and Monitoring Wells MW-3 through MW 6 The vacuum radius of • influence was estimated to be in excess of 22 feet for SVE Wells V-1 through V-5 (EA, 3201333MV;Ri+PLN3