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.>s of vapors toward the extraction wells. The extraction rate is dependent upon the bulk <br /> permeability of the formation and the advection and diffusion of vapor from the hydrocarbon- <br /> impacted zone. Based on the relatively small area and volume of subsurface hydrocarbon <br /> impaction, soil- vapor extraction is not recommended due to higher costs associated with the <br /> equipment, installation, and operation of a soil-vapor extraction/off-gas treatment system. <br /> Petroleum hydrocarbons like gasoline are generally biodegradable, given that certain naturally- <br /> occurring micro-organisms, utilizing the fuel as a carbon source, are provided an adequate <br /> r supply of oxygen and basic nutrients. This biodegradation process is dependent on natural <br /> oxygen diffusion rates through the subsurface soil as well as proper temperature and pH of the <br /> surrounding subsurface soil, for example. Enhancement of this natural biodegradation process <br /> (bioventing)could well be the most cost-effective remediation method for hydrocarbon-impacted <br /> a soils. <br /> Bioventin is a bioremediation process in which oxygen is delivered b forced air movement to <br /> g p Yg Y <br /> the contaminated subsurface sobs in order to stimulate biodegradation. Although somewhat <br /> similar to soil-vapor extraction, bioventing is designed to maximize biodegradation of <br /> r aerobically-biodegradeable compounds, regardless of their molecular weights, with minimal <br /> volatilization. In contrast, soil-vapor extraction is designed to maximize the volatilization of <br /> low-molecular-weight compounds, with minimal biodegradation. Bioventing utilizes a number <br /> `C of injecting and monitoring wells to provide and maintain an aerobic environment for naturally- <br /> occurring micro-organisms. The major advantage is the relatively low cost of installation and <br /> =, .. operation because no off-gas treatment is required. Irwin recommends bioventing for Village <br /> i West. <br /> Ground-Water Remediation Alternatives <br /> Air-sparging is an in-situ remediation technology used to remove gasoline and volatile organic <br /> i compound contamination in the saturated zone. The air-sparging process involves injection of <br /> air into the saturated zone using relatively low-flow blowers or compressors. The air stream <br /> contacts the adsorbed- and dissolved-phase contaminants. The contaminants adsorbed in the soil <br /> =1 in the liquid phase are then transferred to the air stream and transported into the unsaturated <br /> F zone, where they are captured by the soil-vapor extraction system. <br /> The ground-water pumping-and-treatment process involves recovering ground water using <br /> pneumatic or electrical pumping systems and treating extracted ground water prior to clean <br /> discharge. A typical ground-water extraction and treatment system consists of recovery pumps <br /> and an aboveground, ground-water treatment system comprised mainly of an air stripper and <br /> -� activated carbon vessels. <br /> W.W. Irwin, Inc. <br /> } Project No. 33016.07 <br /> ' December 1995 7 <br /> I <br />