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Problem Assessment Report Page 15 Ranch Market,23569 South Santa Fe Road,Riverbank,CA November 8,2000 fringe In addition, the sandy nature of the sediments underlying the site would be expected to yield a significant amount of water that would require treatment 0 Dual Phase Extraction and Water Treatment- DPET was not selected because the depth to groundwater is greater than 26 feet and the potential that the sandy lithology would produce water at rates in excess of the DPET capacity • Soil Vapor Extraction combined with Air Sparging — Based on results of the SVE ' test, operation of a SVE system will effectively remove the gasoline adsorbed to soil within the vadose zone Operation of the air sparging will actively strip dissolved gasoline from the groundwater The air sparging will also increase the dissolved ' oxygen concentration in the groundwater and stimulate the in-situ destruction of gasoline by aerobic bacterial activity • In-situ Biologic and/or Chemical Treatment — In-situ bioremediation or chemical treatment was eliminated because it would not be effective in the destruction of hydrocarbons in the vadose zone In-situ destruction of hydrocarbons in the ' groundwater may be used to supplement operation of the SVE/AS system Methods of in-situ treatment include 1) Injection of nutrients and cultured bacteria to stimulate ' biologic activity, and 2) Injection of chemical oxidizers such as peroxide or ozone to directly destroy hydrocarbons and to stimulate biologic activity by increasing the dissolved oxygen concentrations lie 9.3 Remedial Alternative Recommendation ' Soil vapor extraction combined with air sparging was selected as the most cost effective remedial alternative to mitigate subsurface impacts to below risk-based levels Soil vapor extraction will remove the gasoline from the vadose zone and air sparging will remediate t groundwater and saturated soils by stripping organics, and introducing dissolved oxygen to stimulate biodegradation Results of the AS/SVE feasibility test indicate SVE will recover the petroleum hydrocarbons from the vadose zone and that air sparging was effective in increasing dissolved oxygen concentrations in the offsetting wells 9.4 Conceptual Remedial Alternative Design 1 The goal of the remediation project is removal and/or in-situ destruction of the gasoline adsorbed to soil and dissolved in groundwater to concentrations below site-specific risk based ' levels Using an SVE radius of influence of 40 feet, a total of 10 soil vapor extraction wells are proposed to remove the hydrocarbons from the vadose zone and to capture the air injected into the air sparging wells Assuming a 30-foot radius of influence for the air sparging wells, ' a total of 7 air sparge wells are proposed to either remove or stimulate in-situ biologic destruction of the petroleum hydrocarbons in the saturated zone The location of the existing and proposed SVE and AS wells are shown on Figure I I ' During the SVE/AS feasibility test the individual well flows ranged from 30 to 130 scfm at 75 in H2O The combined flow from the 6 wells averaged ranged from 165 to 220 scfm with ' File PAR-report doc S1COR International Incorporated