Agenda - Council - 09/25/1990 - Laserfiche WebLink

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I '1 I ! I I I I I I I I I I I I I I I The "Phase IA Technical Memorandum" (July 1988), indicated the presence of buried outwash or tunnel valley deposits between the Grantsburg Till and bedrock at MW-3BB on cross section A-A' (Figure 1.21). The interpretation has now been changed to indicate the presence of Superior Till between the Grantsburg Till and bedrock at this location with no buried outwash deposits. Cross-sections C-C' and G-G' (Figures P.E.7 and P.E. 11) show that there is an isolated island or mound of Superior Till directly beneath SB-3 which is surrounded laterally by buried outwash deposits. The basis for the apparent changing of this interpretation was not made clear. Based on an inspection of the boring logs and geophysical logs presented on the cross-sections, it is not always apparent as to how the contacts between various geologic units were determined. While the geophysical logs appear to be useful in some situations, the logging results do not provide clear contacts at all locations. Furthermore interpretations of various contacts have changed since the "Phase IA Technical Memorandum." In general, the geologic contact interpretations presented in the EIS cross-sections appear to be reasonable; however, because all drilling logs were not provided, we were unable to prepare our own interpretation for comparison. Section F: Site Hydrogeology For all of the wells which have been installed near Site P, it is hard to believe that "flow directions could not be determined on-site within the buried outwash or bedrock aquifer due to limited water level data" (p. P-132). While the general direction is regionally known, site specific variations could be important since both of these aquifers could be impacted by potential groundwater contamination from the Site P landfill development.