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09/02 '00 NED 16 40 FAX 18289489968 ERNnST WC - — �JD07 <br /> Memorandum Fnvirenruentar <br /> Resources <br /> Management <br /> To: Jim Adams,Catellus Development Corporation 1777 Bohtffio eve <br /> Suate 260 <br /> From: Arun Chemburkar,P Es Project Engineer walnut Creek,CA U596 <br /> (925)946-0455 <br /> Dater 9 February,2:000 (925)946-9968(fait) <br /> Subject; ChermcaEl Mass Calculations <br /> Former Tank Sites#1 and #2 <br /> 1515 and 1325 West Weber Avenue, <br /> Stockton, California <br /> ERM,O <br /> In response to a Regional Water Quality Control Board request, <br /> Environmental Resources Management(ERM)has pedonned calculations <br /> to estmmate the mass of chenucals of concern(COCl)in ground water at <br /> 151.5 and 1325 West:Weber Avenue This memorandum surnrrianzes the <br /> results and methodology of these calculations (Tables 1 and 2). <br /> As a first step in determining the mass of COCl, BRIM estimated the <br /> volume of water in the ground watex system Figures 1 and 2 present the <br /> estimated dimensions of impacted,ground water at both sites The plumes <br /> at these sites are roughly elliptical ERM applied the n-mthematical <br /> equation for the surface area of an ellipse to determine the surface area of <br /> each of the plumes Esbmates for the major and mirror axes as well as the <br /> calculated surface areas are presented in Tables 1 and 2 for'Banjo Sites #1 <br /> and #2,respectively <br /> ERM assumed an average thickness of 15 feet for the aquifer at Sites #1 <br /> and#2- Total volumes for the plumes were calculated by multiplying the <br /> surface area of each plume by the depth of the aquifer- Assuming a <br /> porosity of 0 3 (EPA. Technical protocol far Evaluahng Natural Aamuldwn of <br /> Chlonnateal S Ivents in Ground Water, Appendix C-Data Interpretation and <br /> Calculations, EPA/600jR-98/128, September 1998), ERM calculated the <br /> volume of water contained within the void space(total volume multiplied <br /> by the porosity,Tables 1 and 2) <br /> For each site,analytical results reported for each sample collected during <br /> the most recent ground water morutoring gent(22 July 1999)were <br /> averaged to estimate the mass of COCs remaining in ground water For <br /> samples in which COCl were not detected,concentrations were assumed <br /> to be equal to half the detection limit The average concentration for the <br /> plume was multiplied by the volar m of water in the void space of the <br /> ground water system The result was an estimate of the mass of COC9 <br /> remaining in the ground water Results of these mass calculations for Site <br /> #1 and Site 42 are presented in Tables 1 and 2, respectively <br />