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Work Plan and Time Schedule for Analyses of Background Groundwata Quality City of Stockton Regional Wastewater Control Facility Page 9 Analysis Plan (revised) in Appendix 4. Vehicular access to all proposed Geoprobee boring and sampling sites is possible by following established paved and unpaved roads(Figure 5). The rationale for the sampling locations is described below. 9.1.1 Oxidation Ponds Background Groundwater Quality Sampling To assess natural background variability, groundwater samples will be collected at nine (9) sites over a wide area south of the current ponds. Proposed sample sites labeled El through E9 are located southwest of MW-15 as shown on Figure 5. Additional samples will be collected at four (4) sites in an array west (downgradient) of the ponds shown as sites E10 through E13 on Figure 5. In order to correlate grab samples at these locations to the monitoring well data, identical sample procedures will be conducted at each of the monitoring wells located outside the groundwater interceptor system. These sample sites are designated as W3, W15, W18, W7, and W16 on Figure 5. All data from these areas will be statistically evaluated across all samples combined with samples grouped by depth and area. These data will be used to determine whether background water quality values can be applied to all COC or whether intra-well comparison must be used. 9.1.2 Eastside Background Groundwater Quality Sampling To assess spatial variability along flow paths east of the SJR, samples will be collected along four transects, designated as A, B, C and D. These are shown on Figure 6. Transect A will evaluate groundwater along a flow path from MW-11. Transect B will evaluate groundwater along a flow path from MW-14. Transect C will evaluate groundwater along a flow path removed from the facility and will be used to represent background conditions. Transect D includes samples that are approximately equidistant from the river and will provide an opportunity to test degradation rates derived from the other transects. Transects A,B, and D include grab sampling pairs at well locations. As in the Oxidation Ponds Background program, these samples provide an opportunity to correlate grab sampling with the longer monitoring histories at each monitoring point and to assess the impact screen submergence can have on background thresholds. 10.0 WEST SIDE UPGRADIENT MONITORING NETWORK 10.1 HOLLOW STEM AUGER WELL INSTALLATION PROGRAM Hollow stem drilling methods will be employed to install additional groundwater monitoring wells. Drilling permits will be obtained from the SJCEHD prior to drilling and the areas will be marked for USA 72 hours prior to drilling. A site specific health and safety plan has been prepared(Appendix 5) and will be reviewed and signed by all field workers prior to commencing activities. The work will be completed by a C-57 licensed contractor under the supervision of a field geologist working under the direct supervision of a California Professional Geologist. Drilling equipment will be cleaned between borehole locations. Cuttings will be discharged to the surface near the boring locations. Vehicular access to all proposed monitoring well locations is possible by following established paved and unpaved roads(Figure 7). Wells will be completed in accordance with typical completion diagrams provided on Figure 8 and Figure 9. Any filter sands used in construction must not generate high saline solutions when mixed with water. A saturated paste extract from construction sand and tap water must not result in an electrical conductivity measurement greater than 500 uS/cm. Each batch of sand brought to the construction site will be field tested by the supervising geologist. At least 48 hours after well completion, the wells will be developed by surging and bailing until the water is clear to the unaided eye. Development water will be discharged to the surface near the wells. Sample collection and shipping methods are described in the Sampling and Analysis Plan(revised) in Appendix 4. The wells will be surveyed by a licensed surveyor to GeoTracker standards.The rationale for the sampling locations is described below. A ti� COND