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URS <br /> 5� <br /> Mr Mike Infurna Page 5 <br /> oaqum County Environmental Health Department <br /> 6,2003 <br /> r 1,000 feet from the site,URS concludes that the impacted groundwater at the site does not pose <br /> a threat to either of these municipal wells <br /> ���\������� • Groundwater conditions at the site have benefited from the historical use of SVE and air injection <br /> Q SVE has contributed to the remediation of soil and groundwater by source removal Air injection has <br /> contributed to the remediation of groundwater through the introduction of oxygen to the subsurface to <br /> encourage the growth of naturally occurring bacteria and associated aerobic biodegradation <br /> • The remaining hydrocarbon impacts identified in groundwater are in the vapor extraction wells in the <br /> vicinity of the USTs and dispenser islands,particularly in well VW-10,located approximately 10 feet <br /> south of the western dispenser island TPHg and benzene were reported at 14,000 gg/L and 2,800 <br /> gg/L in VW-10 during the December 2002 sampling event <br /> • Because of the relatively low permeability soils(predominantly silts)and the relatively low hydraulic <br /> gradient(approximately 0 0015 ft/ft),the remaining hydrocarbon impacted groundwater is unlikely to <br /> migrate vertically or laterally to a significant extent <br /> If you have any questions or comments regarding this letter,please call Mr Vernon Elarth at(916)679-2299 <br /> Sincerely, <br /> URS Corporation Americas ����� GE4< <br /> `� pN PAUL <br /> a y <br /> _ No 7120 <br /> r Scott Lookmgbill Vernon Elarth, R G Exp <br /> Project Geologist Project Manager �T'9TF OF CA��F���\e <br /> Attachments Figure 1 Site Location Map with Production Well Locations <br /> Figure 2 Site Plan <br /> Figure 3 Site Lithology <br /> Figure 4 TPHg Distribution in Soil at Depths of 15 to 40 Feet <br /> S 12130 Site Conceptual Model doe <br />