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Geofagicaf7'echnics inc. <br /> City of Escalon Page 4 <br /> Project No. 750.3 <br /> w <br /> October 31,2000 <br /> The pilot test showed the subsurface at the site to be high in petroleum hydrocarbon vapors <br /> and low in oxygen. It is expected that the vapor extraction system will have to be run at <br /> reduced flows for up to one month until oxygen has been introduced into the subsurface <br /> through the passive air recharge/monitoring wells. <br /> Maintenance of the VETS will include monthly monitoring of the oil levels in the blower, <br /> condition and tightening of the pulley belts on the blower, cleaning of the filter and any other <br /> items deemed necessary by the mechanic. <br /> Monitoring is described in Section 4.2.2 below. <br /> 4.0 ASSESSMENT OF REMEDIAL EFFECTIVENESS <br /> 4.1 Effectiveness Testing <br /> Once the system is operational, its effectiveness will be evaluated. All vapor extraction and <br /> air recharge wells will be monitored for vacuum pressure in various operating configurations <br /> oth the shallow and deep soil zones). GTI shall confirm that vacuum pressure drawdown <br /> extends beyond targeted hydrocarbon-impacted zones and demonstrate that the extraction <br /> system will reach the goals of the remedial action. <br /> Ud <br /> 4.1.1 Radius of Influence <br /> GTI shall calculate the radius of influence (zone of capture) by measuring vacuum pressure <br /> from the extraction well and rate of vacuum pressure drawdown in surrounding wells. This <br /> work can be performed during the effectiveness testing. <br /> 4.1.2 Rate of Contaminant Removal <br /> Concentrations of volatile organic compounds from each extraction well will be measured on <br /> a monthly basis to demonstrate remedial effectiveness and to comply with the Authority to <br /> Construct (AtoC). <br /> 4.2 Monitoring and Laboratory Analysis <br /> Monitoring during the remedial process will satisfy permit conditions and provide valuable <br /> information needed to optimize the vapor extraction system during the remedial process. <br /> Measuring extracted soil vapor for volatile organic compounds by field instruments and <br /> laboratory analysis is useful in -determining-hydrocarbon concentrations remaining in the <br /> �. trea nt areas and determining when alternative treatment technologesinay lie appropriate. <br /> Quarterly testing of groundwater by laboratory analysis will also provide useful information <br /> to complement the vapor influent data. <br /> 4.2.1 Groundwater Monitoring <br /> Monthly Groundwater Elevation Measurements <br /> The groundwater elevations in all of the monitoring wells will be measured once a month <br /> until a complete annual cycle has been obtained. ZXhusafter, the groundwater elevation <br /> measurements wi 1'be-c-oTTe—d-eT during quarterly groundwater monitoring. This information <br /> will help to evaluate the effect of groundwater mounding in response to vacuum extraction <br /> �, and possible groundwater level changes as influenced by pumping of City wells in the area. <br />