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1 <br /> ' 01 June 1999 <br /> AGE-NC Project No 95-0137 <br /> Page 6 of 26 <br /> ' The analytical results indicate two areas of hydrocarbon-impacted soil, an eastern area south of the <br /> AST enclosure on the Jimco site and a western area near the former UST area and transnussion shop <br /> The eastern area is primarily impacted by diesel fuel hydrocarbons,The former UST area is impacted <br /> ' by diesel fuel compounds, but also is impacted by significant concentrations of gasoline fuel <br /> compounds The hydrocarbon-impacted soil plumes of the two areas may be partially comingled <br /> ' Hydrocarbon-impacted ground water in the former UST area has higher average TPH-g TPH-d <br /> rations (0 702 - 1 852) compared to ground water in the eastern area (0 089 and 0 104), indicating <br /> a greater contribution to ground water of TPH-g in the former UST area The eastern ground water <br /> ' has greater proximity to and an up-gradient position relative to the domestic well on the Jimco site <br /> ' 4.0. POTENTIAL IMPACT ON NEARBY SURFACE AND GROUND WATER <br /> ' Typically, ground water represents the migration medium for contaminants over significant <br /> horizontal distances Sites Iocated in up-gradient or equi-gradient(cross-gradient) directions from <br /> the subject site are not likely to be negatively Impacted by the petroleum hydrocarbon release on the <br /> subject site Since the closest surface water feature to the site Is the Stamslaus River located <br /> approximately 9,000 feet south and up-gradient of the site, impacted water at the site does not pose <br /> a significant threat to beneficial uses of the Stamslaus River Stanlslaus River water is primarily used <br /> ' for agricultural use and recreational boating <br /> Drinking water near the site is supplied by domestic wells and Municipal wells A City of Rapon <br />' municipal well is located within 1,000 feet of the site The Jimco site has a well within the dissolved <br /> TPH-d plume The first encountered ground water(20 feet to 50 feet) is not used for drinking water <br /> and is probably not utilized for Irrigation, however, all ground water in the Central Valley is <br />' considered to be of potential beneficial use Detection of benzene at concentrations as high as 1,400 <br /> µg/1 in ground water samples from MW-2,Iocated approximately 45 feet up-gradient of the domestic <br /> water well on the Jimco site Is the primary remediation concern addressed in the CAP Reduction <br /> ' of the diesel-range petroleum hydrocarbons, which do not have clean-up standards, In soil and <br /> ground water are an important, but secondary concern The goal of this CAP is to reduce BTEX <br /> ' compounds to MCL concentrations and to reduce the mass of TPH-g and TPH-d hydrocarbons <br /> Several sites with impacted ground water are located down-gradient and cross-gradient to the subject <br />' site The plumes from other sites do not appear to have impacted the sub)ect site <br />' 5 0. SOIL REMEDIATION ALTERNATIVES <br /> Based on the distribution and concentrations of petroleum hydrocarbons in soil and ground water <br /> on the subject site and on the adjacent Jimco site, and on site-specific conditions, AGE believes soil <br /> Advanced GeoEnvironmentel,Inc <br />