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Significantly contaminated in the area immediately north and west of the site building Soil contamination beyond this area appears to be confined to the 5-foot thick smear zone where concentrations of TPHg are likely much less significant (<100 ppm) Soil contamination in the vadose zone beneath the site is visibly evident as impacted soil is gray- colored, whereas native soil is light to medium brown Soil beneath the groundwater-bearing zone (approximately 20 feet below ground surface), although not contaminated, is a naturally occurring medium gray color 6 12 Groundwater Contamination Because groundwater is relatively shallow beneath the site, the release of petroleum hydrocarbons to the subsurface has significantly impacted groundwater Evaluation of the extent of groundwater contamination has indicated that impacted groundwater extends mainly southwestward from the apparent onsite source location Although clean limits have been established to the north and east of the source location, it is likely that impacted groundwater is present beneath Monte Diablo Avenue and potentially 10 to 15 feet offsite towards the east Impacted groundwater does not appear to have rmgrated across the southern property line except for possibly at the southwestern corner of the site It appears that the migration of contaminated groundwater has occurred mainly across the western property line and extends southwestward for approximately 150 feet Concentrations of total petroleum hydrocarbons as gasoline in groundwater are highest beneath the . asphaltic-concrete covered parking area directly north of the site building, beneath Buena Vista Avenue, and beneath the eastern edge of the two adjacent properties to the west of the site Concentration of TPHg are approximately two orders of magnitude greater beneath the site than beneath these two adjacent properties 6 13 Soil Vapor Extraction Test The soil vapor extraction pilot test performed at the site indicated that vapor extraction likely will be a viable and effective approach to removing contaminants from impacted vadose zone soil The data collected during the test implied that adequate flow and hydrocarbon recovery rates can be achieved by applying a vacuum to the subsurface 6 1 4 Aquifer Pump Test Data collected during the aquifer pump test indicated that pumping and treating groundwater is not likely a viable alternative for remediation of contaminated groundwater The data implied that hydraulic conductivity of the relatively narrow groundwater-bearing zone is low and could not produce a flow rate great enough to affect a cost-effective method for hydrocarbon removal It is possible that flow was impeded or obstructed by a defect in the older monitor well (MW 1) used as the extraction well, however, it is our opinion that the thin groundwater-beanng zone has low hydraulic conductivity because of lateral discontinuities in the soil stratigraphy • SEACOR 014-01-1 par 20