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• 0 California and County of San Joaquin Environmental Health Department (EHD) guidelines. Boreholes were abandoned by removing the PVC casing, drilling out the temporary well materials, and backfilling the annular space with a neat cement grout. Abandonment was conducted under the supervision of GLA's field geologist and an EHD inspector. 5.0 PRELIMINARY FINDINGS - NATURE AND EXTENT OF RELEASE The following sections describe the preliminary findings concerning groundwater flow and contaminant distribution that were developed using field measurements and analytical results from the temporary monitoring wells and existing on-site monitoring well data. 5.1 Groundwater Flow Conditions After installation of the casing and filter pack materials, the depth -to -water was measured with a decontaminated electronic water level sounder. The field geologist observed increasing water levels between October 10 and 13, 2011. As a result, the temporary wells were left to equilibrate for one week before "static" water levels were measured on October 19, 2011. Groundwater monitoring information is summarized on the following table: Well ID First Groundwater (ft) Static Groundwater (ft) Groundwater Elevation (ft amsl) MW -9 88.6 66.4 230.52 MW -10 75 66.7 219.63 MW -11 69.5 67.2 216.07 Groundwater equipotential contours were developed using October 2011 data combined with the third quarter (Summer) 2011 monitoring data from wells SB -1, MW -4, MW -5, and MW -8. As shown on Figure 3, the equipotential data suggest the presence of a groundwater flow divide along the northern edge of the landfill. Groundwater to the south of the divide flows in a southerly direction at a gradient of 0.05 foot per foot, which is consistent with the historical interpretation of groundwater movement in the shallow aquifer. To the north of the flow divide, data from the temporary wells suggest that groundwater flows to the northeast with an apparent slight convergence along the centerline of Corral Hollow Road. 5.2 Groundwater Sampling and Analytical Results Samples from temporary wells MW -10 and MW -11 were collected on October 13, 2011. As a result of slow movement of groundwater at temporary well MW -9, sampling of this well was conducted on October 19, 2011. Groundwater samples were collected using a EMP Report — Phase 1Ge0-Log0 Page ■ 7 Corral Hollow Sanitary Landfill ASSOCIATES February 1, 2012