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wells cannot be accurately measured The vacuum distribution appears to <br /> effective at addressing VOCs in the vicinity of the former wards facility Dissolved <br /> concentrations of petroleum hydrocarbons in groundwater, PID readings from <br /> vapor samples and lab analysis of vapor samples from SVE wells indicate <br /> captures of vapor <br /> c Are monitoring points distributed adequately to determine vacuum <br /> distribution, flow paths, or containment'? Are monitoring points distributed <br /> adequately to determine if adequate air flow or vapor capture is achieved in <br /> three dimensions? (!n most cases, vacuum monitoring points set at <br /> multiple depths are needed to verify vertical flow components) Monitoring <br /> points provide adequate control of distribution, flow paths and containment on the <br /> wards site However, the radius of influence for individual wells has not been <br /> measured There are no monitoring points located on the former Unocal facility <br /> d Construct concentration versus time graphs for all contaminants of <br /> concern in each extraction well Construct isopleth maps of the current <br /> soil gas concentrations for each contaminant of concern Have <br /> contaminant concentrations been declining Mn most of the target zone? <br /> After evaluating concentration versus time graphs for the SVE wells, it is evident <br /> that concentrations are stable to declining in the target zones ENSR has not <br /> constructed isopleth maps for current sod gas concentrations Based on <br /> concentration of dissolved petroleum hydrocarbons in groundwater, it appears <br /> that the center of the plume is located in the vicinity of the northwest portion of <br /> the former Montgomery Ward's site and southwest portion of the former Unocal <br /> site <br /> e Have individual wells or the system as a whole reached a consistent <br /> asymptote on the concentration versus time graph without significant <br /> rebound? (Significant Rebound may be defined as an increase of 25-50% <br /> above the asymptote concentration value) The SVE system as a whole did <br /> achieve a consistent asymptote during the first and second quarter 2003 The <br /> SVE system was shut down in October 2003 based upon the decreasing <br /> groundwater trends and low influent concentrations from the soil vapor wells <br /> during the first and second quarter 2003 However, concentrations rebounded <br /> during the first and second quarter 2004 resulting in the restart of the SVE <br /> system in September 2004 <br /> f Are the well depths and screened intervals adequate to optimally direct air <br /> throuah the tarnet zone? Is there evidenra of preferential fln_A, pathe nr <br /> hydrogeologic boundaries that were not considered in the system design'? <br /> (Prepare hydro-geologic cross sections using available well boring logs, <br /> including the extraction wells, if cross sections of the area of concern are <br /> not available) Well depth and screened intervals are adequate to address <br /> target areas at the wards site There are no SVE wells located on the former <br /> Unocal site There is no evidence of preferential flow paths Cross sections that <br /> ID include boring log data from extraction wells are available are attached 6 <br />