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Site Assessment Work Plan <br /> 1022 Frontage Road, Ripon,California <br /> CONESTO SA-ROVERS March 7,2008 <br /> &ASSOCIATES <br /> 4.0 CONTAMINANT DISTRIBUTION <br /> 4.1 Petroleum Hydrocarbon Distribution in Soil <br /> Historical sampling results indicate that there were diesel leaks from the former diesel UST(T3),former <br /> diesel fuel dispensers,and former waste oil piping,all located in relatively close proximity to one another. <br /> Sampling results indicate that dissolved-phase TPHd concentrations extend southeast ofthe former USTs <br /> and likely beneath the tire shop/truck wash. Sampling results also suggest a diesel release approximately <br /> 175 ft southeast of the former UST cavity,in the vicinity of diesel pump station and/or MW-6.The lateral <br /> extent of TPHd-impacted soil and groundwater in the southeast portion of the site is not fully defined,and <br /> the source of the diesel release has not yet been confirmed.The vertical extent of TPHd-impacted soil and <br /> groundwater is adequately defined with hydrocarbon impact extending to a depth of app �1in <br /> iately 25 ft <br /> bgs,which coincides with the maximum historical depth_ 2.d 50 .1 ' I-{-��r' <br /> G� 1 L 0_'l jG <br /> 4.2 Petroleum Hydrocarbon Distribution in Groundwater D jai <br /> The extent ofTPHd plume near the former diesel UST is adequately defined in all directions except to the <br /> sou heast._beneath the tire shop/truck wash. The extent of the TPHd plume near the diesel pump <br /> station/ASTs and MW-6 is undefined to the west and northwest, and offsite to the south. <br /> Low dissolved-phase MTBE concentrations are detected beneath the former gasoline USTs(Tl and T2) <br /> and extend vertically to a depth of 44 ft bgs. Low dissolved-phase MTBE concentrations extend laterally <br /> towards the wesrThe extent of dissolved-phase MTBE is adequately defined both laterally and vertically. ? <br /> 5.0 PROPOSED SCOPE OF WORK �+l' 1 ��� i m TG��yl� <br /> �1L <br /> The objectives of the proposed scope of work are to: <br /> • Determine the source of the diesel-range hydrocarbons^icinity of the pump station and MW-6. _ <br /> • Assess the extent of diesel-range hydrocarbon impacted soil and groundwater,to the northwest, <br /> west,south,and southeast of the diesel pump station and MW-6. <br /> i <br /> To meet these objectives, CRA will conduct the following: <br /> • Advance approximately twelve direct push Geoprobe®borings in the vicinity of the diesel-pump <br /> station and MW-6 for the purpose of collecting soil samples in combination with grab <br /> groundwater samples. The locations of the proposed borings are shown on Figure 3'` <br /> 7 <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />