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. Request for 5de Closure 3 I Chevron U 5 A Products Company,2400 Airport Way Stockton,CA Januar ry 15,1996 Analytical results for MW-1 and MWs-3 through-5 support the conclusion that groundwater under the majority of the site Is not Impacted by petroleum hydrocarbons The historical groundwater gradient is summarized on Figure 3 EXISTING SITE CONDITIONS The site is currently an unpaved lot lacking buildings or improvements As of July 27, 1995, groundwater levels were approximately 49-to 51-feet BGS at the site Figure 1 shows the site location,topography, and surrounding features A survey of Department of Water Resources well records for groundwater wells located in the area is summarized in Table 3 Figure 3 is a site map showing the general site layout, current location of groundwater monitoring wells and the former location of the service station building, USTs and soil borings RATIONALE FOR SITE CLOSURE Current site conditions Indicate that environmental concerns at the site are of no immediate or future threat to current and potential beneficial uses of groundwater beneath the site As stated in the Addendum to Appendix B of the Tn-Regional Guidelines(CRWQCB-NCR, SFB, CVR, 1990), a rationale for site closure should be included with the request for closure Based on a review of the results of past investigations and risk assessment,two compelling reasons exist as a basis for no further environmental action, including ■ Non-extensive hydrocarbon impact and immeasurably small mass of hydrocarbons remaining in the subsurface ■ Lack of significant leachate potential Non-Extensive Hydrocarbon-impacted Soil Based on the data provided by the four site investigations conducted during the period 1989 through 1994 and subsequent quarterly groundwater monitoring and sampling events, conclusions can be drawn as to the extent of hydrocarbon-impacted material currently in place at the site Non-detectable concentrations have been observed in borings drilled to the west of the former station building/UST area (131-1-3, MW-4),to the east(MW-3),and to the north (131-1-1, MW-2 and MW-5) The two boreholes with soil samples showing hydrocarbon impact, BH-2 and MW-1, are located at the former station building/central UST area, a suspected hydrocarbon source BH-2,drilled in April 1989, contained 0 083 ppm benzene and 0 350 ppm TPH-G at a depth of 20 feet BGS, and MWA, drilled in August • 1989, contained 0 230 ppm TPH-G at a depth of 45 feet BGS (near the capillary zone at time of soil otaklos Rn(crv-56) 1:11:1®GROUNDWATER 01:1 TECHNOLOGY