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• 5.3 Nature and Extent of Groundwater Impacts The nature of release was assessed, but the locations of the temporary wells did not allow for precise determination of the extent the release; therefore, additional monitoring wells will be constructed as "Phase II" of this investigation. Chlorinated aliphatic compounds; namely, PCE, TCFM, and DCDFM, were detected in samples from each temporary monitoring well. Concentrations ranged from estimated, trace levels to measured levels below Maximum Contaminant Levels. These results are consistent with those found historically in samples from monitoring wells MW -5 and MW -8. Isoconcentration contours of DCDFM, TCFM, and total VOCs (Figures 4, 5, and 6, respectively) were constructed using the temporary monitoring well data as well as the third quarter (Summer) 2011 data from the existing site monitoring network to assess the distribution of groundwater impacts in the shallow aquifer. As shown on these figures, groundwater impacts appear to generally migrate outward from the northern corner of the landfill in a northeasterly direction, with the largest concentrations measured at well MW -5. The findings of direction and source of migration from this data is consistent with the on-site monitoring results presented in previous reports. 6.0 ADDITIONAL EMP FIELD WORK The results of the initial EMP field work (now referred to as Phase 1) indicate the presence of a groundwater flow divide near the northern edge of the landfill. To the southwest of the divide, groundwater flows to the southwest, toward the landfill. To the north of the divide, groundwater generally flows to the northeast, carrying VOC- impacted groundwater away from the site. The data collected during the Phase I investigation suggest that VOCs will diminish to non-detectable levels within approximately 800 feet beyond the landfill limit. Additional wells are required to verify this hypothesis. The County has committed to constructing three additional step -out wells as part of the Phase II EMP field work. The approximate location of each well is shown of Figure 7. Wells will be drilled, constructed, and sampled using the approved methods described in the EMP Workplan. 7.0 REVISED EMP SCHEDULE As previously stated, assessment of the extent of groundwater impact requires the drilling and sampling from additional groundwater locations, which in turn requires EMP Report— Phase IGeo-Loic Page ■ 9 Corral Hollow Sanitary Landfill A S f O C I AT E 5g February 1, 2012