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Yr <br /> A S S O C I A T E S I N C <br /> others, 1993, McAllister and Chiang, 1994, Borden and others, 1995, Buscheck and Alcantar, <br /> 1995) Through these studies and on-going research on the factors which control biodegradation, <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 /> 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 itucroorgamsms 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 a oxygen) is reduced (accepts electrons) There are several <br /> compounds that can serve as electron acceptors including oxygen, nitrate, iron oxides, sulfate, <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 /> Groundwater samples collected from each of the site's monitoring wells have not been analyzed <br /> ' for the indicator parameters noted above It is likely that intrinsic bioremediation is occurring <br /> within the dissolved petroleum hydrocarbon plume at the subject site to some degree but it is not <br /> known at what the rate of reduction is <br /> 5.2 Groundwater Extraction with Soil Vapor Extraction <br /> Groundwater extraction with soil vapor extraction, or dual-phase extraction, uses pumps to <br /> remove a combination of impacted groundwater and hydrocarbon vapor from the subsurface <br /> Dual-phase extraction systems are typically designed to maximize extractions rates but this <br /> method also stimulates biodegradation by increasing the supply of oxygen in the subsurface <br /> In order to determine the effectiveness of groundwater extraction and soil vapor extraction, pilot <br /> testing was performed at the site Results indicated that both of these methods are feasible <br /> alternatives for remediation of the site even though the pilot tests were not performed <br /> ' concurrently Data provided by the pilot studies could be used to properly design a full-scale <br /> groundwater extraction and soil vapor extraction system The pilot studies have also provided <br /> information on the concentrations of volatile organic compounds (VOCs) that are likely to be <br /> extracted during the early stages of the operation <br /> ' 5_3 In-Situ Air Snarging with Soil Va or Extraction <br /> In-situ air sparging with soil vapor extraction has proven effective in reducing VOCs and certain <br /> semi-volatile compounds In brief, air is infected into the saturated zone The air forms bubbles <br /> i that rise to the unsaturated zone, carrying trapped and dissolved contaminants Vapor extraction <br /> wells in the unsaturated zone capture sparged air If necessary the effluent air can be treated <br /> using a variety of vapor treatment options This method also stimulates biodegradation by <br /> increasing the supply of oxygen in the subsurface <br /> W 167574 Mpilot fa=pod doc 9 <br />