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u f] Temporary monitoring wells MW -9, MW -10, and MW -11 were constructed in October 2011 as part of this EMP. Samples from each of these wells contained low, but measurable concentrations of VOCs, specifically tetrachloroehtene, trichlorofluoromethane, and dichlorodifluoromethane. The results could not be used to fully characterize the extent of VOC impacts, and as a result, the temporary wells were abandoned and replacement offsite monitoring wells are proposed. 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 (MW -9A, MW -10A, and MW - 11A) 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 90 feet. The proposed boreholes are estimated to be no more than 95 feet deep. Boreholes will be advanced using hollow -stem auger drilling techniques. Once groundwater is encountered, the+borehole will advance approximately five additional feet and a temporary well will be installed. A well casing and screen, filter pack, and bentonite chip seal will be installed, but the sanitary seal postponed, and the well will be developed and sampled. A groundwater sample will be collected using a disposable bailer, and samples will be analyzed for VOCs. After the water levels have equilibrated, the static water level will be measured. 2011-0115 CHSL EMP Workplan Revision 2 — January 11, 2012 5 Geo -Logic Associates