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• . GROUND WATER MONITORING WORK PLAN DREDGE MATERIAL DISPOSAL SITE 1,ROBERTS ISLAND,PORT OF STOCKTON should be readily distinguished from the lighter colored clay, silt, and sand that characterize the dredge materials. Standard single wall boring equipment is anticipated to be adequate to advance the boreholes to the desired depth. Care will be taken to assure that water in overlying dredge materials do not mix in the borehole with water in the peat layer. Similar care will be taken to assure that water in the dredge material and peat layer does not mix in the borehole with water in the sandy aquifer. The primary method of care will include advancing the single wall boring equipment into the clay underlying the dredge materials and evacuating the water from the borehole. If water continues to enter the borehole, indicating that an adequate seal between water bearing units cannot be achieved, then separate boreholes may be advanced to enable collection of water samples from discrete geologic materials. If necessary to maintain sample integrity, dual wall boring equipment may be utilized. This method entails setting the outer wall of the dual wall system in the clay underlying the dredge sediments to prevent water in the dredge sediments from mixing with water in the underlying peat. Once the outer wall is set in the clay, the inner wall will be extended to facilitate a sample of the peat and associated water. Similarly, the outer wall may then be extended into the clay underlying the peat, and then the inner wall will be extended to the underlying sandy aquifer to enable collection of samples. 3.1.2.3 Water Level Measurements The depth to water encountered in each geologic layer will be measured to the nearest 0.01 feet using an electric water level probe. Observations of both the depth to saturation and the depth to the potentiometric or water table surface will be recorded. Repeated measurements will be made over a period of 5 to 10 minutes to establish the equilibrated depth to water. Measurements will continue until the depth to water is stable to within 0.05 feet over a 5 minute period. The purpose of these measurements is to determine possible differences in head pressures within each geologic unit. Water samples will be collected according to the methods provided below and after measurements of depth to water are complete. 3.1.2.4 Soil Sampling As described above, the borehole will be advanced sequentially into and through each of the geologic materials: dredge materials, foundation soil and peat, and sandy aquifer. Soil samples will be collected continuously and described with regard to soil type, relative moisture, and color in accordance with the Unified Soil Classification System. Soil samples will be collected within clear acetate tubes lining the inside of the boring equipment. Once the total thickness of the dredge materials is known, the sample intervals will be identified according to Table 1 and as depicted in the geologic cross-section schematic on Figure January 2005 Page 10 Environmental Risk Services,Corp.