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No hydrocarbon impacts remain in soils between 0 and 10 feet bgs Therefore, it is unlikely that workers or the general public would come into direct contact with impacted soils or constituents of concern However, there would be no assurance that changes in future land use resulting in exposure to the impacted material would not occur 5 3 2 Limited Action Groundwater Monitonng---Option 2 This Limited Action option consists of an extensive groundwater monitoring program la designed to provide early warning of rising groundwater levels The groundwater table beneath the site was recently measured at 61 feet bgs, approximately 26 feet below the deepest identified diesel-impacted soil (Dames & Moore, 1994) If the groundwater table beneath the site rises to and maintains its historical maximum of 34 feet bgs (recorded in 1987), groundwater impacts could potentially occur Option 2 includes quarterly monitoring of groundwater elevations in on-site monitoring wells (including the new well to be constructed in 1994), annual groundwater sampling and analysis for the five wells, and preparation and submittal of annual monitoring reports to the PHS/EHD and RWQCB Groundwater samples would be analyzed for TPH/D, and BTEX The annual groundwater monitoring report would include hydrographs for each well, analytical laboratory data for groundwater samples collected during the previous year, and an evaluation of groundwater elevation and quality trends In addition, based on criteria developed by AFPC, PHS/EHD, and the RWQCB, the agencies would be notified within a specified period if significant, sustained increases in groundwater elevation or groundwater quality impacts occur beneath the site For the purpose of this study, it is assumed that the groundwater monitoring and reporting program would continue for a period of five years I Additionally, as with Option 1, the existing asphaltic concrete pavement would act as a cap to enhance surface runoff in the area of impacted soils The pavement would limit percolation through impacted soils, thereby reducing potential for migration of diesel constituents to the groundwater table Because Option 2 does not include pavement maintenance, the pavement may deteriorate somewhat over time, and could gradually become a less effective barrier to infiltration An additional mitigating factor is that naturally occurring soil microbes would continue to degrade the hydrocarbons SAC127 10 13 DAMES &MOORE