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GROUND WATER MONITORING WORK PLAN • DREDGE MATERIAL DISPOSAL SITE 1,ROBERTS ISLAND,PORT OF STOCKTON 3.1.2.1 Boring Locations The boring locations have been selected based on (1) a local shallow ground water gradient toward the interior of the island, and (2) land use. Five transects (A, B, C, D, E) consisting of three borings each are proposed that extend from the surface water body, through DMD1 (Transects B, C,D), and onto agricultural lands (Figure 4). Transects A and E are located beyond the limits of the DMD1 and parallel to the expected ground water gradient direction. Therefore, samples of geologic materials and water collected from Transect A and E borings are expected to represent background conditions. In addition, while the borings in Transect A are located close to surface water in the San Joaquin River and Burns Cutoff, the borings in Transect E increase in distance from the San Joaquin River. Accordingly, comparing ground water quality along these two transects is expected to differ due to differences in distance from the recharge zone. Transects B, C, and D extend in similar fashion across DMD1. The three borings along these transects are located near the center of DMD1, just beyond the inland levee bounding DMD1, and approximately 500 feet southwest from DMD1. Locations have been adjusted to allow the borings to be completed through the local earthen roads and avoid damage to the agricultural fields. Another feature of this sampling design is the ability to compare conditions across DMD1 and equidistant from DMD1 within the agricultural field. Comparing the chemical characteristics of the various samples is anticipated to adequately indicate if significant impacts to ground water from DMD1 has occurred. 3.1.2.2 Boring Advancement The borings will be advanced using hydraulic direct push equipment to approximately 30 feet to 40 bgs within DMD1 and to approximately 20 feet to 30 feet bgs beyond of DMD1. These are estimated maximum depths; the actual boring depth will be determined in the field. The borings will be advanced into the upper 10 feet of, or to the base of, the first shallow relatively permeable geologic unit that is at least 2 feet thick and encountered beneath the peat layer, whichever is less. A relatively permeable geologic unit is anticipated to consist predominantly of sand or silty sand. Clay layers are not interpreted to represent significant water bearing units. The borehole will be advanced sequentially into each of the geologic materials: dredge materials, foundation soil (including clay and peat layers), and sandy to silty sand aquifer (Figure 3). Proposed soil and water samples will be collected in the borehole prior to advancing to the next underlying geologic layer. The geologic materials comprising the Delta Islands, which are typically dark to black colored layers of clay, silt, and organic rich peat and clay, January 2005 Page 9 Environmental Risk Services,Corp.