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BUILDING 16 FORMER USTS GROUND WATER INVESTIGATION WORK PLAN PORT WEST COMPLEX, ROUGH AND READY ISLAND, PORT OF STOCKTON reported boundaries of the excavation, topography of the area may have been artificially raised, or the exaction extended further than was previously documented. Beneath the fill, clay and silt dominate to approximately 19 feet bgs, the maximum depth drilled at the Site. Only one boring location,B-9, encountered coarser grained silty sand lenses within the silt and clay matrix, between 11 feet and 16 feet bgs. Silty sand lenses were not observed in any other borings advanced at the Site. Therefore, coarser grained sandy units are local, discontinuous, and not pervasive beneath the Site. 2.3.2 Local Hydrogeology The four monitor wells installed at the Site are 10 feet deep and the screened zone intersects the shallow sandy fill. Similarly, grab ground water samples were collected from shallow borings intersecting the shallow sandy fill. Based on the geology and the artificial fill, ground water in the monitor wells and shallow borings does not appear to represent native hydrogeologic conditions. The depth to water measured in the monitor wells (Table 1) and shallow borings (Table 2) ranged from approximately 2 feet bgs to 8 feet bgs. In contrast, the deeper borings extended to approximately 19 feet bgs, intercepted ground water below the fill materials and appear to reflect the conditions in the native geology. These borings consisted yielded a depth to water of approximately 4 feet bgs. Based on the top of the piezometer screen at 14 feet bgs, the ground water in the native materials at the Site is confined, consistent with conditions throughout RRI. AGS referred to the shallow ground water collected in the monitor wells as the shallow water bearing zone (SWBZ) and the ground water collected in the deeper borings as Aquifer 2. 2.3.3 Ground Water Gradient The monitor wells intercept a local water table condition within sandy fill materials at the Site. Ground water elevation in the monitor wells has been measured on six occasions spanning the winter wet and summer dry seasons (Table 1). The ground water elevations in the monitor wells reflect seasonal influences, with higher ground water elevations in the rainy winter months and lower ground water elevations in the dryer summer months (Table 1). The ground water gradient direction in the sandy fill materials is consistently towards the west, ranging from towards the northwest to west-southwest. This direction is consistent with gradients throughout RRI, which are generally oriented towards the center of the island. The gradient magnitude is also consistent, ranging from approximately 0.003 feet per foot to 0.005 feet per foot. Figures 8 through 13 depict the ground water table for the six measurement dates. Environmental Risk Services,Corp.