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0 ' 4.1 Groundwater Pump and Treat Pump -and -treat is a proven ex -situ treatment technology for groundwater contaminated with dissolved phase chemicals such as petroleum hydrocarbons. As such, it is considered a potentially applicable treatment alternative for the site. If this alternative were selected, groundwater would be pumped from one or more 2 -inch to 4 - inch extraction wells into an aboveground treatment unit in which the contaminants would be removed. Treated effluent would then be discharged to a sanitary sewer operated by a publicly owned treatment works (POTW) under permit, as reuse of the treated water onsite would probably be not feasible. If discharge to POTW were not feasible, a permit request for re- injection of treated effluent into the ground would be made to CVRWQCB. As the COPCs are also categorized as volatile organic compounds (VOC), one typical aboveground treatment method would be by air stripping, followed by liquid phase carbon adsorption for polishing if discharge limits require. Offgas treatment would likely be required to remove the VOCs before release to the atmosphere to comply with the local air district regulations, in this case, the San Joaquin Valley Air Pollution Control District (SJVAPCD). A vapor phase carbon adsorption unit or a catalytic or thermal oxidizer would generally be used depending on the amount of hydrocarbons in the offgas stream. For this site, vapor phase carbon adsorbers would most likely be adequate. Additional pre-treatment of the groundwater might be required to address treatment issues caused by chemical species that are not COPCs; most common ones are suspended solids, calcium carbonate, iron, and manganese. These chemical species often cause plugging, scaling, and/or fouling of the air stripper and liquid phase carbon beds, and therefore require additional water treatment, such as solid filtration and addition of other chemical agents to prevent scaling and/or fouling. The need for, and the extent of, pre-treatment of the groundwater at this site is, however, not readily known until more general groundwater chemistry data is available for further evaluation. However, at a minimum, removal of suspended solids by filtration would be considered necessary. 4.1.1 Technical Effectiveness Groundwater pump -and -treat is capable of reducing the dissolved phase mass of TPH-g and BTEX within the contaminant plume at the site. This technology also has a potential of achieving the target cleanup goals. However, its effectiveness would be limited because of the presence of the more fine-grained soil (i.e., silts and clays) within the treatment area. Since a great portion of the residual hydrocarbon mass is expected to be adsorbed onto the silty and clayey soils in the saturated zone, it would undoubtedly require a longer period of time for groundwater pumping to operate before the residual mass is completely removed. In addition, FS Onsite Petroleum Hydrocarbon Remediation.doc 4-2 Shaw Environmental, Inc.