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ARCO Station 548 S E C O R. <br /> 1612 West Hammer Lane,Stockton <br /> Remedial Action Plan <br /> May 31,2006 <br /> extracted groundwater are air stripping and vapor abatement, liquid-phase GAC adsorption, <br /> and advanced oxidation. process (using UV radiation). Additionally, low petroleum <br /> hydrocarbon mass extraction rates are also typically observed during the treatment of <br /> groundwater. Therefore, groundwater extraction and treatment is implementable, but not a <br /> viable or cost effective remedial alternative. <br /> 6.1.4 Dual-Phase Extraction <br /> Dual phase extraction (DPE) involves concurrent extraction of groundwater and soil vapors <br /> from a common extraction well under vacuum conditions. A high-vacuum blower (liquid ring <br /> blower) is connected to a pipe (stinger) installed within a well that has openings only in the <br /> lower portion of the well. Once the soil vapor and groundwater are removed from the <br /> subsurface, they are partitioned aboveground by an air/water separator. The hydrocarbon- <br /> laden vapors and groundwater are then channeled to separate treatment systems. The soil <br /> vapors are typically treated with thermal or catalytic oxidizers, and groundwater is treated <br /> using granular activated carbon (GAC) vessels. <br /> DPE feasibility/treatability testing has not been completed. DPE may be a viable remedial <br /> alternative, however costs associated with completing remediation in this manner would be <br /> relatively high. Low petroleum hydrocarbon mass extraction rates, particularly in <br /> groundwater, might make this alternative viable and implementable, but cost prohibitive. <br /> DPE is not recommended based upon the associated cost, the relatively shallow groundwater <br /> elevation, and the magnitude of contaminant concentrations beneath the site. <br /> 6.1.5 In situ Biologic and/or Chemical Treatment <br /> Bioremediation is engineered degradation of petroleum hydrocarbons in soil and <br /> groundwater. Several methodologies are often used to accelerate the natural degradation of <br /> petroleum hydrocarbons in the subsurface. The most common limiting factor for natural <br /> biodegradation is oxygen. Methods of in-situ treatment include: injection of nutrients and <br /> cultured bacteria to stimulate biologic activity or injection of chemical oxidizers such as <br /> peroxide or ozone to directly destroy petroleum hydrocarbons and to stimulate biologic activity <br /> by increasing the dissolved oxygen (DO) concentrations. DO is not readily available for <br /> biodegradation in the subsurface. The lack of adequate DO limits the rgrowth of <br /> microorganisms necessary for biodegradation. Most engineered systems are designed to aid <br /> the natural process by supplying supplemental oxygen to the subsurface. <br /> Oxygen or air injection into groundwater is used to stimulate bacterial consumption of gasoline <br /> range petroleum hydrocarbons, benzene, and MtBE within the saturated zone. This remedial <br /> alternative is a cost-effective technology that can be applied at the site. The effectiveness can <br /> be monitored by evaluating contaminant concentration trends over future quarterly monitoring <br /> events. Air sparge (AS) is safer than ozone to use in the vicinity of underground structures, <br /> and based on relatively low contaminant concentrations beneath the site, would be an effective <br /> remedial alternative for on-site remediation. <br /> �l <br /> I:1BP-ARC0104 BP Valley Portfo1io15481Reports\RAP1548 RAP.doc 10 <br />