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.74, • r<tt- Howarc R. Green Company L CONSULTING ENGINEERS August 17, 1999 File: 807640J-0240 Mr. Scott Harlicker City of Elk River 13065 Orono Parkway Elk River, MN 55330 RE: PRESERVE ESTATES Dear Mr. Harlicker: As requested we have reviewed the preliminary plat and preliminary grading/drainage plan for the Preserve Estates project located on north Tyler Street. Based on our review and comments received at the staff review meeting we would offer the following comments. 1. No drainage calculations have been submitted for this project. There are a number of questions that are raised when reviewing the grading plan relative to drainage concerns. For instance, on Lot 4 Block 2 there is a high point that naturally flows both directions. The • portion that flows to the east flows through a swale located on Lots 5 and 6, ultimately going under 201st Avenue in a storm sewer pipe. There are no easements provided for this swale and the swale crosses the proposed septic system sites on Lots 5 and 6. This obviously is a concern. Another example is once this pipe crosses 201st Avenue it goes into a wetland on Lot 7. If you follow the natural contours, this wetland will overflow to either the north or the east to another wetland. Ultimately crossing under Polk Street, then flowing to a storm water pond prior to outleting to the Trott Brook area. Again, no easements are provided, no storm sewer calculations for the pond have been provided. Also, it is not acceptable to discharge runoff from the road directly into wetlands without first providing a sedimentation pond. One other example of this would be at the west end of 201st Avenue, a proposed storm sewer would collect the runoff and discharge it to the north onto Lot 1 to existing wetland. There is no indication of where the wetland would overflow from here or if it sufficient capacity for the amount of runoff. Following the natural contours, if it overflows it could end up into a low area located on Lot 1, north of this development. Again, a sedimentation pond should be provided prior to discharging to the wetland. We would recommend that the storm water calculations be submitted, reviewed and approved prior to approval of this development. 2. There are a number of areas, including those listed above, where additional easements are needed but not shown on the plan. In addition, all the wetlands in Outlot A and Outlot B should be provided with drainage and utility easements to protect the wetland areas. O:\PROJ\807640j10240\640-1705.august99.doc 1326 Energy Park Drive • St. Paul, MN 55108 • 651/644-4389 fax 651/644-9446 toll free 888/368-4389