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, � . . � . ♦ . � � May 3, 1995 Lyle Oman City of Orono PO Box 66 Crystal Bay, MN 55323-0066 Re: 1650 North Farm Road Dear Mr. Oman: At Terry Dahlstrom's request I have reviewed Barr Engineering's study, dated July 10, 1995, of the small pond on this property. Mr. Dahlstrom has asked for alternatives to raising the proposed house to an elevation 3" above the low point of Long Lake Road or constructing an emergency overflow swale through the wooded site to the south. Both of these alternative would have negative impacts on the aesthetics of the home site. The issue appears to be two fold: what happens if the culvert under Long Lake Road becomes plugged and secondly, what happens if there is an event in excess of the 100 year event. It is my belief that both concerns can be addressed by the installation of a second culvert under Long Lake Road. The culvert should be set 4 inches higher than the existing culvert. This will help prevent sediment from collecting in the second pipe, since under typical situations it will remain dry. The culvert should be 18" in diameter to minimize the potential for clogging. The pipe material should be double wall corrugated polyethylene (MNDOT 3247), which provides a smooth inner wall, again to minimize clogging. Polyethylene pipe should be bed in sand to prevent deforming the pipe. A bedding detail is attached. As an added precaution I recommend that the house be raised six inches. This will allow storage for a second 100 year rainfall event, in the event that both culverts are blocked. As a reference point a visable permanent marker (i.e. a boulder, fence post, etc.) should be placed near the proposed home by Mr. Dahlstrom's surveyor at the outlet elevation of the pond (986.7). Standing water above the marker could alert the homeowner to a blocked culvert. Within a day of most rainfall events the water level should return to the outlet elevation If you have any questions feel free to contact me. Sincerely, LANDFORM ENGINEERING COMPANY , !/'� Step n M. Jo ston,P.E. /sMJ Landform Engineering Company,905 Twelve Oaks Center,I5500 Wayzata Blvd.,Wayzata,Minnesota 55391,(612)475-3272,Fax/Data(612)475-3159