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ZA �J, /t/je-nlTro��n�C� r,✓� 1Jr2rLu�v6, rr✓sraAr.��ra� �� R�� The proposed onsite drilling program is intended to supply information sufficient to better define the following: o Present groundwater flow directions in the B, C, and D zones o Location of the eastern and western limits of the onsite groundwater contamination in the zones o The vertical extent of groundwater contamination The result of the onsite drilling program will be a delin- eation of the areal and vertical extent of groundwater con- tamination to the precision necessary to develop, evaluate, and implement remedial actions. Back round Twenty-two (22) monitoring wells exist on the M&B facility (Figure 4-1) : These wells monitor a series of permeable zones between the water table (at approximately 15 to 20 feet below ground surface [ft,bgs] ) and an apparently locally extensive sand and gravel aquifer (at a ely 250 feet, bgs) . The shallow system lies above theosand tand gravel aquifer, and consists of silt and clay with varying percentages of sand. Four sandy permeable zones have been identified from drill cuttings and electrical well logs; these are designated, starting with the shallowest water- bearing zone, as the A, B, C, and D zones (Figure 4-2) . The sand and gravel aquifer beginning at approximately 250 ft,bgs has been designated as the E zone. It is important to real- ize that the designation of the permeable Zones A, B, C, D, and E are for discussion only. The designations do not imply that the zones are hydrogeologically isolated from one another. Groundwater in the shallow system has been found to be con- taminated with chemicals used at M&B, including pentachloro- phenol and creosote compounds. The highest levels of con- tamination are found in the A zone in the old oily waste pond area and the track pit, track siding, and central pro- cess areas (Figure 4-3) . Contaminated groundwater has been detected in wells in the A, B, C, and D zones onsite. Con- taminants have not been detected in water from monitoring wells in the E zone on- and off-site. Groundwater in the A zone appears to be flowing east- southeastward at an estimated rate of a tel per year; the gradient in the E zone indicatesaeast-300 feet northeastward flow. Contamination detected offsite at the OS-3 location indicates that flow in the B and C zones has been southeastward prior to pumping of Wells A-8 , A-9 , and .7 4-2 a