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• Soil Investigation and Backgrre Groundwater Monitoring Well Installation Workplan Addendum C A M B R I A February 2,2007 4. No more than 20-feet of well screen will be used to construct the monitoring wells. We plan to install no more than 5-feet of screen above static groundwater level in the well borings. 5. As stated on page 5, paragraph 3, of the workplan, a portland cement grout will be placed continuously from the top of the bentonite to approximately one foot below grade.In accordance with local regulations, a San Joaquin County Environmental Health Department representative will be contacted to observe and direct grouting activities.According to San Joaquin County Well Standards (Ordinance Code Section 9-1115.6), the grout will be placed on top of the hydrated bentonite transitional seal with a tremie pipe. ® 6. All groundwater samples collected for the initial four sampling events will be analyzed for total and dissolved metal concentrations. We will follow the sampling handling and filtration procedures outlined in the Designated Level Methodology for Waste Classification and Cleanup Level Determination document as requested.For dissolved metals,samples will be refrigerated to 4°C,filtered through a 0.45 micron(µm)filter in the laboratory within 24-hours of collection,and acidified to pH of<2 with nitric acid(HNO3) before analysis. Total metals are acidified in the field and refrigerated to 4°C prior to analysis. 7. 'Soil cuttings will be stockpiled on and covered with visqueen in the location of the proposed infiltration/evaporation pond.The soil cuttings will be incorporated with the material excavated during the construction of the pond and used to build the soil berm for this pond. Purged groundwater will be collected and discharged to the onsite standby storage pond. 8. As shown on Figure 1 and required in San Joaquin County Well Standards (Ordinance Code Section 9-1115.6)a 2 foot by 2 foot concrete surface seal will be constructed around the top ofthe monitoring well casings at the ground surface.The surface seal will be at least 4-inches thick and will be sloped to drain fluids away from the well. The surface seal will be continuous with the annular seal and the well cover. . 9. Based on your concerns that the proposed monitoring wells are located to close to the proposed infiltration/evaporation pond we propose moving both southern wells closer to the river,as shown on Figure 2.We propose moving the northern well north of East Buena Vista Road.Due to a large shear cliff road cut the only location accessible to install the well is near the facility gate on East Buena Vista Road(Figure 2). 2