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V 1117 Lone Palm Ave,Suite 201 <br /> r Modesto,CA 95351 <br /> Phone:209-579-2221 <br /> «..ii Fax: 209-579-2225 <br /> r 3.1.2 Enhanced Natural Attenuation <br /> L Natural attenuation, discussed in 3.1.1 above, can be enhanced or augmented by a variety of <br /> chemical or mechanical means. Both aerobic and anaerobic processes can be assisted by the <br /> addition of chemical substances to promote -specific chemical reactions that break down the <br /> contaminants present in the subsurface. It is also possible to supplement the micro-organism <br /> populations in the subsurface through augmentation. <br /> While the objective of augmentation is normally applied to groundwater contamination, the <br /> process can be engineered to target soil contamination. Groundwater augmented with a <br /> microbial solution is recirculated into vadose zone wells or an infiltration gallery. Lateral <br /> "injection" wells deliver the solution within the unsaturated soils through infiltration and/or <br /> percolation. <br /> Augmented natural attenuation can be applied so that a limited area in the vicinity of the <br /> injection gallery is affected. Subsurface conditions should be evaluated to determine the <br /> physical soil properties. Soil conditions must -be suitable to allow for percolation'and/or <br /> infiltration. Soils with high effective permeability and porosity, such as sand and gravel are <br /> preferred. Collection of geophysical soil parameters and performing a percolation test would be <br /> required. Additionally, heterotrophic plate counts would be necessary to estimate the live <br /> bacteria, which provides an estimate of the bacterial load in the soil. The advantages are: <br /> • Readily available equipment and easy installation. <br /> • Implementation with minimal disturbance to aboveground activities. <br /> • Cost effective under optimal conditions. <br /> • Isolated areas of treatment are possible. <br /> 3.1:3 Soil Vapor Extraction (SVE) <br /> SVE is a proven technology for effectively -reducing concentrations of volatile organic <br /> compounds (VOCs) and certain semi-volatile compounds in soil. .SVE is an in-situ unsaturated <br /> P ) p <br /> zone, soil remediation technology in which a vacuum is applied to the vadose zone soil to extract <br /> soil gas and remove volatile compounds in the vapor phase from the soil. The extracted soil gas <br /> is then treated as required before discharge to the atmosphere. This technology can be applied to <br /> remediate in-situ soils which are inaccessible to excavation. Additionally this technology is well <br /> suited to remove high vapor pressure, low boiling point compounds, such as those present in the <br /> petroleum hydrocarbon-impacted soil at this site. <br /> t SVE is not particularly effective at extracting low vapor pressure, high boiling point compounds, <br /> such as diesel and heavier oils, which are also present at this site. This method is also space <br /> s:\environmental\22493\reports\feasibility.doc 8 <br />