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0 0 W r 3.0 EVALUATION MONITORING PROGRAM 3.1 EMP APPROACH The primary purpose of this EMP is to define and characterize the nature and extent of shallow groundwater impact. To understand the extent of release, it is essential to understand the groundwater flow patterns in the shallow aquifer beyond the existing landfill monitoring network and to determine whether or not impacts to the shallow aquifer are contained within the landfill property. To this end, it is essential to assess groundwater elevations to the northwest and northeast of the landfill property to determine if the interpreted groundwater flow conditions are the result of site-specific or more regional recharge conditions. If the investigation indicates that impacts are not migrating off site, but rather are being transported to the south beneath the landfill footprint, then the existing landfill gas extraction system, final cover system, and surface water management system would appear to be appropriate corrective actions. If significant evidence of release be identified in the offsite EMP wells proposed herein, then additional corrective action measures will be evaluated through a formal Engineering Feasibility Study. For this project, GLA recommends drilling three boreholes at locations to the north and west, beyond the existing monitoring network and property boundary (Figure 3). Boreholes will be advanced through Quaternary alluvium and terrace deposits and into the Corcoran Formation. Information obtained from past geologic and hydrogeologic investigations suggests that clays of the Corcoran Formation are approximately 50 feet thick at the site. Depending on the location, groundwater may be found within the Corcoran Formation clay at depths estimated to be between 40 and 80 feet. The proposed boreholes are estimated to be no more than 80 feet deep. Boreholes will be advanced using hollow -stem auger drilling techniques. Once groundwater is encountered, drilling will stop and a HydropunchT"° sampler will be driven up to 20 feet into the saturated zone . A groundwater sample will be collected using a disposable bailer lowered though the HydropunchTM casing. Samples will be analyzed for VOCs. The HydropunchTI tip and casing will remain in the borehole for up to two weeks to allow the groundwater equipotential surface to stabilize. After the water levels have equilibrated, the - static water level will be measured. If the sample indicates VOC impacts that are consistent with those observed in the existing site monitoring wells, then the HydropunchT^° sampler will be removed and borehole will be abandoned in accordance with requirements of the San Joaquin County Environmental Health guidelines. Another borehole will be drilled using the groundwater equipotential data to establish a downgradient direction and the chemistry data to extrapolate a distance where VOCs should be below the respective detection limits (i.e., at an approximate zero VOC concentration line). This process will be repeated as feasible until sample results 2011-0115 CHSL EMP Workplan Geo -Logic Associates Revision 1- August 24, 2011