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DSW-4C. Rates of migration in these deeper zones are not known. Scope of Work Eight groundwater monitoring wells will be installed. The proposed locations are discussed in the following paragraphs and shown in Figure 4-1 . DSW-2D and 2E. Wells will be installed in the D and E zones at the DSW-2 cluster location. The DSW-2 location is down- gradient from the contaminant plume in the central plant region. The central plant area is the probable source area of groundwater contamination in the D zone. Based on the existing electric log (E-log) of the DSW-2 pilot hole (Figure 4-2) , the D-zone well will be screened in the sandy zone located between 157 and 168 feet below ground surface. The E zone will will be screened from 200 to 220 ft,bgs in the sand indicated on Figure 4-2 . DSW-4D. A D zone well will be installed near the site boundary at the DSW-4 location. This well will be screened from 153 to 169 ft,bgs in a permeable zone of interbedded sand, silt, and clay (Figure 4-2) . This zone appears to be the same zone monitored by Well DSW-1D and will provide the third well needed to determine the direction of flow in the D zone groundwater. DSW-6B and 6C. Two wells will be installed to monitor the B and C zones, respectively, at the location of the existing A-5 well. Prior to drilling and installing the wells , a pilot borehole will be drilled to a depth of 250 feet below y, ground surface, for obtaining geologic and geophysical logs. These geophysical logs will provide the stratigraphic con- trol to construct hydrogeologic cross sections and select screened intervals for the B and C zone wells. DSW-7A, 7B, and 7C. A monitoring well cluster (DSW-7) will be installed at a location near the site boundary between DSW-2 and DSW-4 (Figure 4-1) . Prior to drilling and in- stalling the wells, a pilot borehole will be drilled to a depth of 250 feet to obtain geologic and geophysical logs. Screened intervals for the A, B, and C zone wells at the DSW-7 location will be selected using these logs. Additional Wells. The drilling program outlined above is expected to a ineate the areal and vertical onsite ground- water contamination to the precision necessary to develop, evaluate and implement remedial actions. It is possible, however, that the findings from the new wells may raise additional concerns about the full areal and vertical extent of onsite groundwater contamination. If so, McCormick and 4-3