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9110 Thornton Road, Stockton, California April 27, 1994 <br /> The Southland Corporation Page 8 <br /> in the subsurface materials without requiring additional site activities or <br /> cleanup Based on <br /> calculation for the leaching potential using Table 2-1 from the LUFf manual (Attachment 7), the site <br />' is characterized as having medium to high potential for leaching of hydrocarbons to groundwater <br /> One site characteristic which greatly increases the potential for leaching is the large number of <br /> monitoring wells at the site Removing the wells would greatly reduce the potential for leaching of <br /> hydrocarbons <br /> CONCLUSIONS <br /> Groundwater Technology recommends site closure for the referenced site based on <br /> ■ The presence of separate-phase hydrocarbons has been removed from the on-site <br /> groundwater monitoring wells in the source area <br /> ■ Evidence of only a limited vertical and lateral extent for low concentrations of <br />' residual petroleum hydrocarbons impacting subsurface soils suggests a low driving <br /> mass and low potential for migration to groundwater <br /> ■ Analytical results from groundwater sampling indicate levels of hydrocarbon <br /> constituents have been at or below California action levels for drinking water since <br /> 1989 <br /> ■ Site conditions have been characterized using the LUFT manual calculation table as <br /> currently having medium to high potential for leaching of hydrocarbons to <br /> groundwater (Attachment 2) The leaching potential for the site would be reduced if <br /> the on-site wells would be abandoned <br /> ■ The surface at the site is capped by uninterrupted asphalt paving limiting percolation <br />' from precipitation <br />' Groundwater Technology requests that the SJCPHS forward a copy of this report to the <br /> CRWQCB-CVR with recommendations for site closure Upon approval of site closure, Groundwater <br /> Technology will proceed with the abandonment of the on-site and off-site monitoring wells in <br />' accordance with SJCPHS requirements <br /> GROUNDWATER <br /> �i TECHNOLOGY <br />