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Former Discovery Chevrolet March 20, 1998 <br /> Tracy. lifornia Problem AssessmentReport <br /> groundwater through time. It appears, from the groundwater quarterly monitoring analytical <br /> results, that passive remediation has been occurring at this site. <br /> 7.2.2 _Aboveground Treatment <br /> This remediation alternative typically involves the extraction, treatment, and disposal of <br /> groundwater. Recovery wells or interceptor trenching may be used for groundwater <br /> removal. Removal of hydrocarbons from the groundwater may utilize product/water <br /> separation, air-stripping of volatiles, carbon absorption, biotreatment, or ultraviolet light <br /> degradation. After treatment, groundwater may be discharged to the storm or sanitary sewer <br /> system, depending on local discharge regulations. <br /> 7.2.3 In-Situ Bioremediation <br /> This remediation alternative involves the stimulation of microflora or bacteria to degrade <br /> hydrocarbons. Stimulation of the microbes is achieved by introduction of nutrients and <br /> oxygen through existing wells or trenches. Groundwater is usually pumped and recirculated <br /> to control migration of the dissolved petroleum constituents and to distribute oxygen and <br /> nutrients. <br /> 7.2.4 Air-Sparrging <br /> A recent innovation in remedial technology has extended the utility of soil vapor extraction <br /> to water-saturated soils. This technology is referred to as air-sparging. In this process, air is <br /> injected under pressure below the water table. The air bubbles which have been formed <br /> traverse horizontally and vertically through the soil column creating transient air-filled <br /> regimes in the saturated zone. Volatile compounds that are exposed to this sparged air <br /> environment"evaporate" into the gas phase and are carried by air movement into the vadose <br /> zone where they can be captured by a soil vent system. <br /> 3001-12.par 14 HORIZON ENVIRONMENTAL INC. <br />