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Qi <br />7. Figure 5.4.1-8, which shows the A zone piezometric surface, suggest that there may <br />be a recharge area in the vicinity of Monitoring Well 508A. A region of heavy <br />pumping is indicated between Well 508A and 423A. If the water level data from <br />these areas are accurate, the permanence of these features and the implications of <br />the data need to be further evaluated. Perhaps additional piezometers should be <br />installed in this area' to better define the piezometric surface. Based on the <br />piezometric surface indicated in Figure 5.4.1-8, it appears that there is insufficient <br />control downgradient of the apparent source area of the plume in the vicinity of <br />Well 407A. Both Well 407A and 506A are water table wells, while Wells 508 and 518 <br />are screened deeper in the A zone. Low levels of TCE observed in Wells 518A and <br />506A may originate from the source area in the vicinity of Well 407A, but may <br />represent the western edge of a plume moving in the directory of Wells AGW6 and <br />AGW4. SHAD should address the possibility that the central part of this plume may <br />be moving undetected off -base into deeper aquifer zones. <br />17 <br />