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Date sent: Wed,22 Apr 1998 16:09:07-0500 To: "Mark Roffers, Planning,6-4021"<roffers @co.dane.wi.us> From: Ken Bradbury<krbradbu @facstaff.wisc.edu> Subject: Re: Comments on Herfel Pit CUP Dear Mark: I have now completed my review of the materials related to the proposed sand and gravel extraction at the Herfel Property south of Verona. The materials I looked at include the Hydrologic Investigation submitted by Woodward-Clyde(dated 1/29/98)and an additional map of groundwater modeling results submitted by Rob Montgomery at our meeting at the county Land Conservation office on April 1, 1998. In addition, I have had several conversations with Rob Montgomery and his colleagues at Woodward-Clyde about this project. In my opinion the conclusions reached in the Hydrologic Investigation are reasonable and supportable. In particular, I agree with the conclusion that the proposed construction of the two extraction ponds will have negligible impact on surrounding groundwater flow. The ponds will cause local groundwater levels to rise slightly(about 1 foot)on their down-gradient end and to lower slightly(about 1 foot) on their up-gradient end. These effects will decrease rapidly as one moves laterally away from the ponds. It is interesting to note that local annual water-table fluctuations are probably in the range of a foot or so(though we don't have data from this exact site). The data presented in the Hydrologic Investigation are consistent with data we (the Wisconsin Geological and Natural History Survey)and others have collected in Dane County over the past few years. • I also agree with the conclusion that construction and operation of the ponds as proposed in the Hydrologic Investigation should not adversely affect groundwater or surface water quality. The main potential source of groundwater and surface water contamination will be accidental spills and leaks from equipment and materials around the • pits. It will therefore be important that the applicant have adequate pollution prevention and spill management plans. One comment that I raised at the meeting on 4/1/98 concerns the contour lines on the map of modeled groundwater elevations presented by Rob Montomery. That map shows equipotential lines running straight across the two proposed ponds. This is an impossible configuration of contours. If the consultants assume that the ponds are directly connected to the water table, then the free water surface of the ponds will be perfectly horizontal and will represent the water table. The contours need to wrap around the ends of the ponds, not be drawn through them. However, I think this is just a mistake in map contouring; it will make no difference in the final analysis of the problem. Mark, let me know if you would like to discuss these comments. I can put them in the form of a formal memo if you like. Sincerely, Ken Bradbury Hydrogeologist Wisconsin Geological and Natural History Survey 3817 Mineral Point Road Madison,Wi 53705 Phone:608-263-7921 Email: Krbradbu @facstaff.wisc.edu