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Extraction and venting wells would be installed with screened intervals at zones of impacted soil <br /> A vacuum would be applied to the air extraction wells to draw fresh air through the venting <br /> wells to the impacted soil The system would be designed based on site-specific stratigraphy, <br /> soil physical parameters, soil permeability to air, and the extent of impacted soils <br /> Soil bloventing has alimnted ability to significantly reduce hydrocarbon concentrations <br /> under conditions of limited moisture and nutrients, and its effectiveness would depend on the <br /> following factors <br /> • Ability to maintain a suitably moist environment, given that relatively dry air is <br /> being pulled through the soil, <br /> • Natural presence of sufficient nutrients to encourage microbial growth, <br /> • Expectations of the final cleanup level, and <br /> • Bioventing system operating life <br /> The conceptual design of the bioventing system includes 16 venting wells approximately <br /> 40 feet deep and 3 air extraction wells approximately 44 feet deep, and is based on our current <br /> understanding of Site conditions For this study, a radius of influence for venting and extraction <br /> wells of 30 feet has been preliminarily estimated to be appropnate Underground piping would <br /> be used to connect the extraction wells to a blower located near the existing lunchroom/electrical <br /> building <br /> It is estimated that bioventmg could achieve a cleanup level of about 2,000 mg/kg, <br /> beyond which little further reduction in hydrocarbons would be expected, however, O&M of the <br /> system could be expected to continue for a minimum of approximately 12 years Soil bonngs <br /> would be periodically advanced into areas of known soil impacts to monitor the progress of this <br /> remedial option Soil samples would be analyzed to assess hydrocarbon concentrations <br /> Bioventing would continue until petroleum hydrocarbon concentrations stabilize, indicating that <br /> the system has achieved the maximum practical level of cleanup Because of the relatively slow <br /> response expected, soil sampling and testing would be performed every two years <br /> Option 4 also includes quarterly monitoring of groundwater elevations in on-site <br /> monitoring wells (including the new well to be constructed in 1994), annual groundwater <br /> sampling and analysis of the five wells, and preparation and submittal of annual monitonng <br /> SAc127 to 15 <br /> DAMES &MOORE <br />