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---- <br /> E- <br /> IG <br /> ChV,_ j%LTC ` <br /> / <br /> A S S O C I A T E S I N C <br /> Several detailed field studies have been performed examining indicators of intrinsic bioremediation <br /> and identify factors which significantly effect the rate and extent of bioremediation (Buscheck and <br /> and others 1995• Buscheck and Alcantar, <br /> others, 1993; McAllister and Chiang, 1994; Borden ;. <br /> -: 1995). Through these studies and on-going research on the factors which control biodegradation, s <br /> it is now understood that dissolved petroleum hydrocarbons in groundwater will biodegrade, <br /> without artificial enhancement, due to the presence of naturally occurring (indigenous) <br /> F;} microorganisms. Technical protocols for implementing and monitoring intrinsic bioremediation <br /> studies in groundwater have been developed by the US Air Force and Chevron Corporation. <br /> Intrinsic bioremediation in brief, is the use of indigenous microorganisms to degrade contaminants <br /> which have been released into the subsurface. The biodegradation of the contaminants is <br /> essentially an oxidation-reduction (redox) reaction where the hydrocarbon is oxidized (donates an <br /> electron) and an electron acceptor (i.e. oxygen) is reduced (accepts electrons). There are several <br /> rs including oxygen, nitrate, iron oxides, sulfate, <br /> compounds that can serve as electron accepto <br /> water, and carbon dioxide (Borden and others, 1995). Aerobic microorganisms use oxygen as the <br /> electron acceptors. Anaerobic microorganisms use other compounds such as nitrate, iron oxides <br /> (ferric iron), and sulfate as electron acceptors. <br /> r'' Groundwater samples collected from each of the borings and each of the site's monitoring wells <br /> ' 3 <br /> were analyzed for the indicator parameters noted above. Several of the geochemical parameters <br /> indicate intrinsic bioremediation may be occurring within the dissolved petroleum hydrocarbon <br /> F- plume at the subject site. The results of these chemical analyses are presented in Table 2. <br /> Geochemical trends from the results are discussed below and are summarized in Table 5. <br /> 7_2 Soil Excavation <br /> Excavation of shallow soil contamination and on-site aeration or off-site disposal to a certified <br /> waste disposal facility would remove the potential source for groundwater contamination. <br /> Additionally, standing water in the open excavation can be remediated by pumping the water into <br /> E. an on-site holding tank for either on or off-site treatment and/or disposal. As shown on Figures 2 <br /> _A and 11, underground utilities and above ground structures have impeded further excavation of the <br /> petroleum affected areas and extensive shoring and/or demolition of the structures would be <br /> required. <br /> 7.3 In-Situ Air SParging with Soil Vapor Extraction <br /> In-situ air sparging with soil vapor extraction (SVE) has proven effective in reducing volatile <br /> organic compounds (VOCs) and certain semi-volatile compounds. In brief, air is injected into the <br /> F saturated zone. The air forms bubbles that rise to the unsaturated zone, carrying trapped and <br /> dissolved contaminants. Vapor extraction wells in the unsaturated zone capture sparged air. If <br /> necessary the effluent air can be treated using a variety of vapor treatment options. <br /> i <br /> w:1951221rcporlslparcap.doc 8 <br />