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r <br /> Site Delineation and RAP Addendum Proposal April 16,2008 <br /> Former Canteen Facility—1500 Shaw Rd Page 4 <br /> AREAS OF CONCERN <br /> Based upon the ongoing system O&M and groundwater data, a number of areas should be addressed for <br /> additional assessment. Details of the separate areas are presented below: <br /> Area between MW-3 and MW-13-Series Wells <br /> As of the latest groundwater events, the cluster of MW-13 wells generally had concentrations below <br /> reportable levels, with some lingering concentrations of benzene, TBA, and MTBE on the shallow and <br /> median wells (MW-1 3 and MWA3A, respectively). The MW-3 well cluster show concentration trends that <br /> increase with the total depth or the well series. <br /> Therefore, the area between the MW-3 and MW-13 well series requires additional impacts delineation. <br /> This area has received minimal treatment from the AS-SVE System (currently only one AS well is in this <br /> area)and may be harboring residual concentrations that continue to`feed'the MW-3 wells. <br /> Delta therefore proposes two wells of different screened intervals in this area(see Figure 1): <br /> • MW-14M—Screened from 55'-70'bgs <br /> • MW-14D—Screened from 80'-85'bgs; <br /> Note(*): The deeper well may serve as an AS well if a System Upgrade is required. <br /> Down-Gradient of MW 11 <br /> Off-site monitor well MW-11 continues to show concentrations of MTBE and 1,2-DCA above California <br /> Maximum Concentration Levels.The nearest down-gradient location for additional wells is on the other <br /> side of the Lane Masters building, along Shaw Road(see Figure 1). <br /> Delta proposes two wells of different screened intervals in this area: <br /> • MW-15M—Screened from 55'-70'bgs <br /> • MW-15D—Screened from 70'-85' bgs <br /> Soil AssessmentlConfirmaflon <br /> A review of the soil analytical results for the site revealed a few areas of past concern, as summarized in <br /> the table below: <br /> Sample ID I Smpl Date Depth Results <br /> Locatlon (mm-yy) ( ) (mg/kg) <br /> UST—S.Wall Nov-92 14 Benzene=63,TPH=16,100 <br /> UST—SE Wall 19 Benzene=203,TPH=17,600 <br /> SB-2 Feb-93 41 Benzene=1.50,TPH=17.8 <br /> 46 Benzene=1.70,TPH=18.3 <br /> SB-3 46 Benzene=1.40,TPH=7.7 <br /> SB-4 46 Benzene=1.45,TPH=15.9 <br /> MW-3 May-93 71 Benzene=1.40,TPH=13 <br /> 79 Benzene=1.60,TPH=12 <br /> SB-13D May-99 26.5 Benzene=<0.05,TPH=390 <br /> 46.5 Benzene=22,TPH=1,400 <br /> 71.5 Benzene=<0.02,TPH=140 <br />