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1 0 0 <br />4.2.1.2 Drilling methodology <br />Each boring will be advanced using 8 -inch outside diameter hollow stem <br />augers. Soil samples will be collected from the borings using a 2.5 -inch <br />inside diameter California modified split -spoon sampler containing three <br />' brass tube liners. The sampler will be driven through the augers <br />approximately 18 inches beyond the tip of the lead auger by a 140 -pound <br />hammer dropping 30 inches. The number of blows required to advance the <br />sampler each six-inch interval will be recorded by the geologist to aid in <br />defining the strata encountered. The brass sample tubes will then be <br />extracted from the sampler. The ends of the samples in the two brass tubes <br />' closest to the shoe (leading tip) of the sampler will be examined by the <br />geologist and logged according to the Unified Soil Classification System <br />prior to being labeled, capped, sealed and placed in cooler chests with ice. <br />' The soil collected in the brass tube farthest from the shoe will be logged <br />by the geologist, extruded from the brass sample tube, placed in a zip -lock <br />I3542a/BAV102 8 <br />4.2.1 Define the vertical and horizontal distribution of gas plant <br />residues in soils within the site property boundaries <br />4.2.1.1 Soil boring locations <br />Due to the lack of historical information on the operations of the Tracy gas <br />TES the <br />manufacturing plant, will. conduct an unbiased survey of site, using <br />an offset grid pattern to select soil boring locations. Borings will be <br />drilled approximately 50 feet apart around the site perimeter and 100 feet <br />apart throughout the interior of the property. This pattern has been <br />selected to maximize data collection aimed at analyzing the potential for <br />offsite migration of gas plant residues. <br />A total of 31 borings will be drilled within the property boundaries. The <br />proposed boring locations are shown in Figure 2. Four of the borings will <br />be <br />completed as monitoring wells. In the event that subsurface obstructions <br />do not allow completion of a soil boring to the specified depth, the boring <br />will be filled with a cement/bentonite slurry, and a new boring advanced at <br />the closest practical location. At locations where overhead obstructions <br />(such as electrical wires) exist, a low clearance drill rig will be used, <br />where possible, to advance the borings. <br />4.2.1.2 Drilling methodology <br />Each boring will be advanced using 8 -inch outside diameter hollow stem <br />augers. Soil samples will be collected from the borings using a 2.5 -inch <br />inside diameter California modified split -spoon sampler containing three <br />' brass tube liners. The sampler will be driven through the augers <br />approximately 18 inches beyond the tip of the lead auger by a 140 -pound <br />hammer dropping 30 inches. The number of blows required to advance the <br />sampler each six-inch interval will be recorded by the geologist to aid in <br />defining the strata encountered. The brass sample tubes will then be <br />extracted from the sampler. The ends of the samples in the two brass tubes <br />' closest to the shoe (leading tip) of the sampler will be examined by the <br />geologist and logged according to the Unified Soil Classification System <br />prior to being labeled, capped, sealed and placed in cooler chests with ice. <br />' The soil collected in the brass tube farthest from the shoe will be logged <br />by the geologist, extruded from the brass sample tube, placed in a zip -lock <br />I3542a/BAV102 8 <br />