SITE INFORMATION AND CORRESPONDENCE_1988-1991

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David Wang, P.E. , Chief Page 10 March 6, 1991 10. Figures 5. 4-29 through 5. 4-40 These figures are head difference maps indicating vertical flow potential between the A- and C-zones for the period of January 1988 through December 1988 . The maps indicate a downward flow potential between the A- and C-zones persists over nearly the entire site for the period. Recommendation: Similar analyses of the potential between the A- and B-zones and the B- and C-zones may be more useful than the analyses presented. C. Chapter 7 , Groundwater Treatment Program 11. Page 7-6, Geometry of Withdrawal Cone - South Balloon Area The report states "Figures 6. 1-9, 6. 1-10, and 6. 1-11 show the A-, B-, and C-zone cones of depression created by the treatment system groundwater withdrawal . " The referenced figures do not show A-, B-, and C-zone cones of depression. The ground water elevation contours are based on head data averaged over two years. o Figure 6. 1-9 (A-zone) shows a trough coinciding with the western portion of Plume 1 and a mound centered near Well 426-A (near the upgradient 100 ug/L contour) . The degree of hydraulic control resulting from the treatment system is not clear from the figure. o Figure 6. 1-10 (B-zone) shows the two-foot contour closing around well B-2 but the degree of control achieved beyond that is not clear. o Figure 6. 1-11 (C-zone) doesn't indicate any hydraulic control resulting from the three C-zone extraction wells. Recommendations: a. The scale of these maps should be increased to at least 1: 2 ,400 (one inch equals 200 feet) . b. The ground water elevation contour interval should be reduced so that flow lines can estimated to clearly show the influence of the extraction system. C. The data (chemical and water level elevations) used for contouring should be provided.