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~Bonestroo • 8 Rosene 11\11Anderlil<& 1 \11 Associates Engineers & Architects May 18, 1999 Mr. Paul Weinberger Assistant Zoning Administrator City of Orono Post Office Box 66 Crystal Bay, MN 55323 Re: Carriage Hill Subdivision File No. 139-2467 Dear Paul: Bonestroo, Rosene, Anderlik and Associates, Inc. is an Affirmative Action/Equal Opportunity Employer Principals: Otto G. Bonestroo, P.E. • Joseph C. Anderlik, P.E. • Marvin L. Sorvala, P.E. • Glenn R. Cook, P.E. • Robert G. Schunicht, P.E. • Jerry A. Bourdon, P.E. • Robert W. Rosene, P.E., Richard E. Turner, P.E. and Susan M. Eberlin, C.P.A., Senior Consultants Associate Principals: Howard A. Sanford, P.E. • Keith A. Gordon, P.E. • Robert R. Pfefferle, P.E. • Richard W. Foster, P.E. • David 0. Loskota, P.E. • Robert C. Russek, A.I.A. • Mark A. Hanson, P.E. • Michael T. Rautmann, P.E. • Ted K.Fieid, P.E. • Kenneth P. Anderson. P.E. • Mark R. Rolfs, P.E. • Sidney P. Williamson, P.E., LS. • Robert F. Kotsmith • Agnes M. Ring • Allan Rick Schmidt, P.E. Offices: St. Paul, Rochester, Willmar and St. Cloud, MN • Milwaukee, WI Website: www.bonestroo.com We have reviewed the grading, drainage and street construction plans for the proposed six: lot Carriage Hill subdivision. The site is located west of Brown Road South (C.R. 146), east of Willow Drive and south of the Webber Hills neighborhood in the northwest quarter of Section 10. We have the following comments in regards to engineering matters. 1. Access, Streets and Grading: The proposed King Street access from South Brown Road to Lot 1 is shown at over a 7% grade. This will present problems in the winter with stopping movements onto South Brown Road. We recommend that street grades on the easterly 50 feet of King Street not exceed 2% to provide a landing area for vehicles accessing South Brown Road. Proposed street elevations at the right-of-way on King Street and Carriage Lane should not be more than 6-inches higher than the centerline of the existing bituminous of the intersecting cross streets. We recommend that driveway grades into the proposed garage location on Lot 1 not exceed 2%, the profile shows the proposed driveway grade into the garage area at 5%. The proposed typical street section to serve Lot 1 provides only 4-inches of Class 5 base, we recommend the typical section be revised to show a minimum of 8-inches of Class 5 aggregate base. The proposed retaining wall height approaches 6 feet in some areas. Retaining wall details and design should be provided for review. 2. Drainage: The ponding and drainage calculations submitted appear to be acceptable. Carriage Lane st_reet/storm sewer design should include provisions to minimize flows onto Willow Drive. The pond grading detail should be revised to show the NWL above the 10: 1 bench at an elevation that intersects the 10:1 bench and the 3:1 slope. An outlet structure detail should be provided with the plan set. The proposed submerged 18" CMP outlet with apron may present problems with freezing and flooding. We recommend that the outlet structure utilize an orifice inlet and or weir to minimize problems with freezing. Riprap should be provided at all storm sewer outlets. Erosion control measures should be provided at the downstream end of the 18" CMP west of Willow Drive. The plans should show the location and elevation of the low point on Willow Drive to determine what freeboard is provided for the ponding area. We recommend that a minimum of 2 feet of freeboard be provided above the pond HWL. Street elevations on Willow Drive over the proposed 18" CMP should be shown on the plans to determine how much cover will be provided over the pipe. 2335 West Highway 36 • St. Paul, MN 55113 • 651-636-4600 • Fax: 651-636-1311