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Remedial Action Plan <br /> Frontier Transportation <br /> June 17, 2004 <br /> Page 9 <br /> Mass of Impacted Groundwater = n x 50 feet x 100 feet x 8 feet (thickness of <br /> groundwater) x 0.5 (porosity) = 61280 ft' <br /> Mass of Impacted Groundwater = 6,280 ft3 x 7.481 gallons/ft3 = 46,981 gallons <br /> Based on the groundwater sample results, it is estimated that 47,000 gallons of <br /> I l impacted groundwater exist in the subsurface. Although a significant mass of impacted <br /> groundwater was calculated to exist beneath the site, historically the dissolved petroleum <br /> hydrocarbons have been confined to the site due to the discontinuous sandy clay lenses <br /> l and the relatively flat hydraulic gradient. However, accelerated migration of the MTBE <br /> !- in particular to approximately 175-feet west of the former UST location was identified. <br /> Lateral and vertical concentration fluctuations in dissolved TPH-g, BTEX and MTBE <br /> support an imminent threat to on and off-site receptors. Impact to nearby receptors is <br /> anticipated. <br /> j 6.0) PROPOSED REMEDIAL ACTION <br /> Based on the soil conditions encountered at the site, BEII proposes to excavate the <br /> extent of impacted soil as identified by laboratory analytical results from subsurface <br /> testing at the site. The soil will be excavated using a backhoe or excavator. Stained soil <br /> or soil with vapors over 50 parts per million (ppm) as measured by a photoionization <br /> J detector will be stockpiled in hazardous waste bins for disposal under manifest. <br /> Unstained soil will be stockpiled on visqueen for waste characterization via soil sample <br /> collection and analysis. Soil samples will be collected at one sample per 10 tons of soil ? <br /> for waste characterization. <br /> Previous excavation performed at the site identified water seepage at 11 ' bgs, the <br /> first water. The proposed excavation will, therefore, require shoring through the first <br /> water to maintain the structural integrity of the pit for deeper excavation (greater than 15 ' <br /> - bgs). Groundwater infiltrating the excavation pit will be evacuated using pumps and <br /> stored on-site in Baker tanks for disposal under manifest. An on-site mobile laboratory will be present to analyze soil samples to define the extent of excavated soil. <br /> Furthermore, BEH proposes to pump the impacted groundwater and treat it <br /> through an air stripper. A minimum of fouzgroundwater, monitoring wells will be <br /> - � selected for groundwater pumping. Each well will contain a dedicated 2-inch stainless <br /> steel submersible pump, which will be piped to an air stripper for treatment. Additional <br /> wells may be required for groundwater extraction. Baker tanks will be on hanTto contain I <br /> groundwater should more than one air stripper treatment cycle be needed. Sample <br /> collection frequency from the treated water will be determined by the PHS/EHD . The <br /> groundwater effluent will be discharged to the sewer. <br /> i <br />