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a ME .. r: The placement Of the wells is designed both to determine the areal and vertical extent elow the of lite groundwater contamination and to determine the groundwater gradient b site. Shallow wells will be screened within the upper aquifer (first groundwater) to investigate the distribution of floating product. The deep wells will be screened within the next aquifer encountered to investigate the distribution of product dissolved in groundwater with depth. Three of the six shallow wells, Mw-IS. MW-2S and MW-2S will 'tie located adjacent to to three of the deep wells, MW-ID, MW-2D and MW-3D, to form three (3) two-well cluster wells. The purpose of these wells will be to determine contaminant extent as well as to determine if a vertical groundwater gradient is present below the site. One deep well, MW-4 D, will be placed in the center of the plume of -floating product in order to evaluate the vertical extent of contamination. The well incorporates surface casing in its construction to eliminate the potential for cross contamination between the upper aquifer and the next lowest aquifer. 3.2.2 Monitor Well Installation Borings for the monitor wells will be drilled using a hollow-stem auger drilling rig. Shallow well borings will be advanced 5 feet below the existing groundwater table to a depth of approximately 20 feet. Deep well borings will be advanced ten feet into the t" next lowest aquifer or to a maximum depth of 50 feet. For geological logging, soil samples will be taken at the surface and at 5-foot intervals with a split-spoon sampler. The sampler will be driven by a 140 Ib hammer falling a distance of 30 inches. Soil samples will be described according to the Unified Soil Classification System under the direct supervision of a Geologist registered in California. Blow counts will be recorded at each sampling interval in accordance with a standard penetration test (ASTM D1586). The design for a typical monitor well is presented in Figure 3.2-2. The monitor weils will be constructed with 4-inch diameter, Schedule 40 polyvinyl chloride (PVC) flush- threaded casing. The shallow monitor wells will be scicened with approximatcly 10 feet of machine-slotted PVC well screen with 0.020 slot size. Slotted casing will - --- rxtcnd-3--feet.-into-..the.-aqu'tfcr_.and:_.risc_5._f eet-above_._th.c.-_water..-_t.a31c_in-_the shallow wells. Deep wells will be constructed with a 10 foot screen length also; however, the e6660.01/03132/uruox.2 6 40