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Interim Corrective Action Plan <br /> Frontier Transportation, Inc. <br /> December 20, 2005 <br /> Page 3 <br /> In August 2005, BEA installed three additional shallow groundwater monitoring <br /> wells, screened from 5' bgs to 20' bgs Analytical results from the soil samples identified <br /> � �5 <br /> MTBE in each of the new wells, MW-19, MW-20 and MW-21 TPH-gas was identified in u1 <br /> MW-19 and MW-21 BTEX was identified in MW-21 at 10' bgs and 20' bgs MW-19 �'� <br /> contained ethylbenzene and xylene at 10' bgs <br /> 3.0) SITE GEOLOGY/HYDROGEOLOGY <br /> The site is located on the boundary of the Sacramento Valley and the San Joaquin <br /> Valley within the west-central portion of the Great Valley Geomorphic province of <br /> California The Great Valley has been filled with a sequence of older to younger alluvium of <br /> Pliocene to Holocene age which overlay sedimentary rocks of Cretaceous to Tertiary age <br /> These sedimentary units, in turn, overlay a crystalline basement of Paleozoic and Mesozoic <br /> I metamorphic and igneous rocks The shallow subsurface geology in the site vicinity is a <br /> heterogeneous mix of gravel, sand, silt, and clay (Reference, Site Characterization Report, <br /> Twining Laboratories, October 16, 1996) <br /> I� BEII encounteredp redominantly heterogeneous clays from 0' to 30' bg and fine- <br /> grained sands from 30' to 40' bg during well advancement ofMW-15 through MW-18 See <br /> Figures 7 and 8 <br /> First subsurface water was encountered at depths from 11' to 12' bg during tank <br /> removal and monitoring well installation at this site in 1995 and 1996 Since then, shallow <br /> subsurface water has been encountered beneath the site between 6' and 10' bg <br />' The past groundwater gradients included in quarterly groundwater monitoring reports <br /> have identified the flow of groundwater in a generally western direction beneath the site The <br /> Irecent groundwater gradient is included as Figure 3 <br />' 4.0) PROPOSED CORRECTIVE ACTION METHODS <br /> Stair reviews of three methods for efficient technically achievable and cost effective <br /> removal of the source of gasoline, aromatics and oxygenate (MTBE) migration identified <br /> groundwater injection of ozone (03) as the best available technology for this site The <br /> methods reviewed were ozone injection, soil vapor extraction and excavation <br /> I <br /> r <br />