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09102 '00 WE0 16 50 FAX 18259409968 ERMWEST IC I1007 <br /> EnvMemorandum d�.m Resou x►tnental <br /> 1lesot�ces <br /> Management <br /> Jun Adams,Catellus Development Corporation 1777 Botelho Drive <br /> Suite 260 <br /> Pro= Ara,Cbembuxkar,r E Project Engineer wanut Creek,CA 94596 <br /> (925)94"455 <br /> Date: 9 February, 2000 (975)94f.-9%8(fax) <br /> Subject: Chenucal Mass Calculat mis.- <br /> Former Tank Sates#1 and#2 <br /> 1515 and 1.325 West Weber Avenue, <br /> Stockton,California <br /> ERM, <br /> In response to a regional Water[duality Control Board request, <br /> lEnvtronrnental Resources Management (ERM)has performed calculations <br /> to estimate the mass of chemicals of concern(COCl) in ground water at <br /> 1515 and 1325 West Weber Avenue Tlus memorandum sun marnzes the <br /> results and methodology of these calculations (Tables 1 and 2). <br /> As a first step in determining the mass of CC►Cs,ERM estimated the <br /> volume of water in the ground water systern. Figures 1 and 2 present the <br /> est wted dimens ons of impacted ground water at both sites_ The plumes <br /> at tluew sites ace roughly elliptical ERM applied the mathematical <br /> . equation for the surface area of an ellipse to deter mne the surface area of <br /> each of the plurrrrses Estirnates for the malar and nuinor axes as well as the <br /> calculated surface areas are presented in fables 1 and 2 for Tank 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(EFA Technical Frofocul fur Eraaluahng Natural Attenuation of <br /> Gdlonnated Solvents in Ground Water,Appmdzx C-Data Interpretation and <br /> CWculattons, EPA jbl]UJR-98 j1.2b,September 1998),ERM calculated the <br /> volume of water eontamed 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 monrtormg event(22 July 1999)were <br /> averaged to estimate the rmss of COCl remaining in ground water For <br /> samples in which COCl were not detected,concentrations were assumed <br /> to be equal to half the detection lurdt The average concentration for the <br /> plume was multiplied by the volume of water in the vmd space of the <br /> ground water system The result was an esbmate of the mass of COCl <br /> remaining in the ground water Results of these mass calculations for Site <br /> • #1 and Site #2 are presented in Tables 1 and 2,respectively. <br />