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• • GROUND WATER MONITORING WORK PLAN DREDGE MATERIAL DISPOSAL SITE 1,ROBERTS ISLAND,PORT OF STOCKTON ■ MW-6-is located downgradient from DMD1 to assess persistent impacts to ground water quality, if any, associated with the dredge materials. ■ MW-7-is located cross gradient from DMD1 and will monitor background ground water quality near DMD1. 3.2.2.1 Monitor Well Construction The boreholes for the monitor wells will be advanced using hollow-stem auger drilling equipment. The monitor wells will be constructed within the hollow-stem auger. Soil samples will be collected continuously in a 2-inch diameter split-spoon sampling device. The soil samples will be described and log as detailed in Task 2 above. Soil samples collected from the borehole are not proposed for laboratory analysis. The anticipated depth of the borings for monitor wells completed in the shallow sandy aquifer ranges from 25 feet to 35 feet bgs; this depth will be known with greater accuracy following the completion of Phase 1. Based on the schematic geologic cross-section beneath DMD1, as depicted in Figure 3, the monitor wells will be screened in the upper 5 feet of the underlying shallow sandy aquifer. The two additional monitor wells proposed at MW-2 will be screened as described above. The monitor wells will be constructed using 2-inch diameter schedule 40 PVC. The screen will contain factory slots of 0.010-inches and will be surrounded with a sand filter pack of Lonestar 12-16 sand, or similar. The sand pack will be "set" using a bailer to gently surged the water within the well screen. At least 2 feet of hydrated bentonite will be placed above the sand pack to provide a well seal. A cement-bentonite slurry will be placed above the bentonite seal to ground surface. Depending on the requirements of the local farmers, the well may be completed flush or above ground surface. In either case, the well casing will be protected with concrete, and within a water tight, traffic rated, locking Christy box, or similar. Figure 6 is a schematic for a typical monitor well. 3.2.2.2 Well Development The monitor wells will be developed by bailing. The development water will be monitored for electrical conductivity, pH, and turbidity. When these parameters have stabilized to within 10 percent of successive measurements, the well will be considered adequately developed. All bailed development water will be contained in drums for proper disposal. Disposal options will be identified based on the analytical results of water samples to be collected from the monitor wells. January 2005 Page 18 Environmental Risk Services,Corp.