SITE INFORMATION AND CORRESPONDENCE

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Greg K. Vaughn • -6- • 11 May 1988 Only horizontal gradients in the uppermost aquifer have been determined. Vertical ground water gradients must also be determined and flow paths should be reported on geologic cross sections as well in plan view. Measurement of vertical gradients will require the installation of piezometer clusters screened at different depths in the uppermost aquifer. The wells installed to date have screen lengths of 30 feet (20 feet in well 4) . This screen length is too long to characterize the vertical extent of waste constituents in ground water, and depending on hydrostratigraphy and pump location, may be missing the maximum concentrations of contaminants. Future well clusters for identification of vertical gradients and vertical extent of contaminants should have screen lengths on the order of five to ten feet. o Aquifer properties The velocity calculations on page 3 .8-10, the discussion of transmissivity on page 3 .8-11 and the discussion of storage coefficient on page 3 . 8-12 of the HAR are all inadequate. Again, while the knowledge of how a pumping test should be conducted is demonstrated, no test was run. The textbook values based on visual inspection of sediment properties are not acceptable for a site investigation the scope of the HAR. Pore velocity is calculated as 5. 2 (10-4) ft/day - 26. 0 (10-4) ft/day (page 3 . 8-10) . Assuming a 30-year lifetime for the pond, the first leachate, after traveling through the vadose zone, would have travelled a mean distance of only 5.7 - 28 . 5 feet horizontally in this time. Downgradient wells MW-1 and MW-2 are over 100 and 300 feet from the pond respectively, but both have been impacted by waste constituents. This illustrates the inadequacy of the velocity estimates. The argument is made several times in the HAR (pages 3 . 8-12 , 3 .8- 14) that aquifer tests are not necessary unless ground water remediation will be undertaken. Accurate estimates of aquifer properties, derived from aquifer tests, are necessary to determine the effectiveness of the monitoring system. o Water Quality The entire discussion of downgradient water quality is contained in two paragraphs on pages 3 . 10-6 and 3 . 10-7 . While this discussion does address information previously presented in monthly monitoring reports, the entire database has not previously been analyzed and interpreted. Concentrations of waste constituents in ground water over time should be analyzed and presented in tabular and graphic forms. Concentrations of major ionic constituents should be interpreted in relation to background water quality and presented in trilinear or similar diagrams. The presence and possible source of nitrate concentrations exceeding drinking water standards must be addressed.