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V <br /> Car-dno� 1117 Lone Palm Avenue,Suite 201 <br /> Modesto,California 95351 <br /> ATC 209-579-2221 <br /> Shaping the Future Fax:209-579-2225 <br /> V <br /> analyzed, there appear to be two areas of impacted soil beneath the site. The first area is located <br /> immediately beneath one of the former USTs and limited to depths ranging from approximately 5 and 15 <br /> feet bgs. The second impacted area is larger in size and is located closer to the water table and/or <br /> capillary fringe and laterally away from the former UST system at depths ranging from approximately 30 <br /> to 45 feet bgs. The estimated lateral extent of BTEX compounds and TPHg in soil samples collected <br /> from the vadose zone is depicted on Figures 7 through 9. <br /> For purposes of obtaining a conservative estimate of BTEX and TPI-Ig mass in the vadose zone,the lateral <br /> extent of petroleum impacted soil was assumed to be the shape of an ellipse. The vertical thickness of <br /> petroleum impacted soil within the two horizons, referenced above, was estimated to be 10 feet and 15 <br /> feet,respectively. Average concentrations over the estimated area of impact for each analyte were used in <br /> mass balance calculations. Estimates did not take into account biodegradation that may have occurred <br /> naturally over time or as a result of the extended ozone pilot test. <br /> To estimate the contaminant mass in groundwater, a similar process to that of soil was used to determine <br /> the area and volume of impact. Ellipsoid shaped isoconcentration boundaries were developed using the <br /> average concentration from each monitoring well from the most recent monitoring events. <br /> Isoconcentration maps were prepared for select compounds(refer to Figures 12 through 14)which depict <br /> the lateral extent of dissolved contaminant. An average water bearing unit of 60 feet was assumed based <br /> on boring logs and a cone penetrometer test boring completed at the site. <br /> The following equations and parameters were used to determine the mass of site contaminants in soil and <br /> groundwater. Appendix C provides a detailed summary of each calculation. <br /> Area of ellipse: (A)=rl* ('/za) * ('/zb) Mass(Mg)in Groundwater=V * n *ACC <br /> Volume of ellipse: (V)=Area(A) * d Mass(Ms)in Soil=V* p *ACC <br /> v <br /> Where: <br /> 11=Pi or 3.14159 A=Area of medium <br /> 6" p=soil bulk density V=Volume of medium <br /> * = multiplication sign d=depth interval or thickness of medium <br /> a=short axis of ellipse n=porosity <br /> b=long axis of ellipse ACC=Average Chemical Concentration <br /> 6.0 SENSITIVE RECEPTOR SURVEY <br /> ATC conducted a sensitive receptor survey (SRS) within a 2,000-foot radius of the site in 1999. <br /> Information regarding the SRS was submitted ATC's Well Survey for Eggiman, Andrew and Edith Trust, <br /> for the Property at 1112 East Harding Way, Stockton, California dated April 9, 1999. A summary of the <br /> SRS is provided below. <br /> Groundwater well construction logs of wells located within 2,000 feet of the site were obtained from the <br /> Department of Water Resources (DWR) and San Joaquin County PHS/EHD groundwater well <br /> construction logs and reviewed. Fourteen wells were identified within 2,000 feet of the site. <br /> A well located at the northeast corner of the State Hospital is the closest to the site(within approximately <br /> S:Enviromental\22493U2eports\Eggiman Closure Report.doc 8 <br /> w.+ <br /> Y <br /> v <br />