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\ GIR, <br /> Southwest, Inc. <br /> of the extent and degree of TPH-d impact to the underlying groundwater across the site is <br /> recommended. <br /> 12.4 PCB Contamination and Concerns <br /> The Phase II has identified PCB contamination at levels exceeding the PRG for industrial soil <br /> in the shallow soils in many areas of the site. PCBs detected near the documented August <br /> 2007 spill may be attributable to this release, but the widespread detection of PCB <br /> contamination over much of the Learner site indicates multiple releases, consistent with <br /> historical site usage. PCBs detected in the groundwater grab samples do not conclusively <br /> confirm that groundwater has been impacted by PCBs. Further investigation is recommended <br /> to determine the extent and degree of PCB impact to the on-site soil and to confirm or refute <br /> that groundwater has been impacted by PCBs. <br /> 12.5 Surface Staining and Documented Petroleum Releases <br /> Petroleum O&G, TPH-mo and TPH-d contamination of the soil has been confirmed in many <br /> areas of the site. The soil samples collected from one and three feet bgs display a higher <br /> degree of impact than those collected at five feet bgs suggesting the contamination originated <br /> • predominantly at the surface. Levels of O&G exceeding the ESL were found in shallow soils <br /> in or near areas where surficial staining was noted, including locations where motor blocks <br /> have been historically stockpiled, near the ASTs, near the equipment wash pad and <br /> maintenance shop, and in locations used for stockpiling and processing of metals. Soil TPH-d <br /> concentrations in excess of the ESL were detected in the vicinity of historical motor block <br /> stockpiling and in an area used for metal stockpiling and processing. TPH-d and TPH-mo <br /> were detected in the majority of the groundwater grab samples at concentrations exceeding <br /> ESLs, particularly in the northwestern and eastern parts of the site. Further investigation is <br /> recommended into the extent of O&G, TPH-mo and TPH-d impact to soil and groundwater <br /> across the site. <br /> 12.6 Equipment Wash Area and Disposal of Wash Water <br /> A petroleum O&G concentration exceeding the ESL, a PCB concentration exceeding the PRG <br /> and zinc, copper and lead concentrations exceeding reference levels detected in shallow soil <br /> near the equipment wash area indicate activities in this area have impacted soil conditions. <br /> Additional investigation in this area is recommended. A link between the use of treated wash <br /> water for dust control on the Learner site and surface contamination was not found. <br /> • <br /> 704. PRIM 31 July 21, 2008 <br />