SITE INFORMATION AND CORRESPONDENCE_1988-1991

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David Wang, P.E. , Chief Page 9 March 6, 1991 8 . Figures 5. 4-10 through 5.4-27 The figures illustrate November 1984 , 1985, 1987 , 1988 , and 1989 ground water elevation contours for the WBZs underlying the site. On Page 4-20, the report identifies 9 wells (514A, 437B, 507B, 511B, 435C, 437C, 445C, 507C, and 412C) as not providing suitable head data for contouring. Recommendation: The report should clarify why data from these wells are used in Figures 5.4-10 through 5. 4-27 . The A-zone contours for November 1987 , 1988 , and 1989 reflect complex and unusual ground water flow patterns. As discussed in the report, these patterns are complicated by wells completed at various depths responding to vertical gradients. Recommendations: Before presenting monthly ground water contour maps, well completion depths should be reassessed. The cross-sections (Figures 2 . 1-3 through 2 . 1-13) should be amended to illustrate well screen and filter pack intervals. Construction of qualitative flow nets along the axes of plumes should better illustrate the operation and effectiveness of extraction systems and the distribution of contaminants. The horizontal spacing of the wells on Figures 2 . 1-3 through 2 . 1-13 and the plume cross sections in Chapter 6 should be corrected. 9 . Page 5-61, Vertical Gradients Head differences measured at three well clusters (401, 402 , and 407) are presented to illustrate the effect of the South Balloon Area extraction system. Figure 5 . 4-28 indicates a decreased downward vertical gradient and sometimes an upward vertical gradient between the B-, and C-zones at Wells 402 and 407 . However, the figure also indicates an increased downward vertical flow potential from the A-zone to the B-zone in the wells. Recommendation: To illustrate the effect of the extraction system vertical flow potential at all wells in the area should be presented.