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Atlantic Richfield Company _ _ _ __ Page 15 <br /> • ARCO Station No 4932 Stockton California August 29,2002 <br /> levels, and(2)to prevent further off-site migration of the dissolved petroleum hydrocarbon <br /> and MtBE plume <br /> 6.2 Evaluation of Remedial Alternatives <br /> Several technologies for remediating petroleum hydrocarbons and MtBE in soil and <br /> groundwater have been evaluated <br /> Passive bioremediation (natural attenuation), enhanced bioremediation, and excavation alone <br /> are not feasible alternatives for addressing the high concentrations of TPHg, BTEX, and <br /> MtBE in wells MW-4 and MW-b, and EW-1 Excavation is not feasible based on the extent <br /> of dissolved petroleum hydrocarbons and MtBE, impact to operations, and the associated <br /> cost <br /> DPE is not feasible because it will not control off-site plume migration <br /> Based on the results of aquifer testing, GWE in conjunction with SVE are feasible <br /> remediation technologies for application at the site for expediting the reduction and removal <br /> of subsurface petroleum hydrocarbon and MtBE impacts The application of GWE would <br /> generate decreased localized groundwater levels, exposing petroleum hydrocarbon-impacted <br /> soils for remediation by SVE Through reversing hydraulic gradient, GWE would also <br /> • prevent off-site migration of petroleum hydrocarbons and MtBE dissolved in groundwater <br /> AS technology is another practical remedial application that can later be introduced if <br /> needed, and used in conjunction with GWE and SVE, to accelerate the reduction/removal of <br /> petroleum hydrocarbons and MtBE beneath the site The installation of an enhanced <br /> GWE/SVE system to include AS would facilitate the introduction of increased oxygen levels <br /> into the subsurface, creating a favorable environment for biodegradation of petroleum <br /> hydrocarbons and MtBE in soil and biodegradation of volatilized petroleum hydrocarbons <br /> from petroleum hydrocarbon-impacted groundwater AS feasibility testing would have to be <br /> performed to determine the design of an enhanced GWE/SVE/AS. system <br /> 6.3 Remedial Alternative Recommendation <br /> A combination of GWE and SVE was selected as the most feasible cost-effective <br /> remediation alternative for mitigating subsurface impacts to below remediation goals, nd to <br /> prevent off-site migration of the dissolved petroleum hydrocarbon and MtBE plume GWE <br /> and SVE will provide control of the dissolved hydrocarbon/MtBE plume and will remove <br /> dissolved petroleum hydrocarbons and MtBE from beneath the site <br /> The results of aquifer pump testing suggest that continuous GWE from well EW-1 and EW-2 <br /> and proposed wells EW-3 through EW-7 should significantly affect dissolved petroleum <br /> hydrocarbons and MtBE beneath the site Based on calculated capture zones of <br /> approximately 31 feet and 48 feet in the downgradient and crossgradient directions, <br /> 11ARCO\49321PAR\PAR doc <br />