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.1(. . -1- 203 LITTLB CANADA ROAD SUITB laO SAINT PAUL MINNBSOTA H111 TEL: 61l.~90.9266 PAX: 6Il,~90-9l6S H'I&:CI~l"CJlIU.:.VII!@ ">'OFESSIONAL ENGINEERING CONSULTANTS INCORPORATED February 5, 1998 Mr. Dale Joel. Schaferichardson, Inc. 420 North Fifth Street, Minneapolis, Minnesota Suite 530 55401 Subj: Parking Lot Addition Healy-Ruff Company Roseville, Minnesota Dear Mr. Joel: Attached you will find the drainage calculations for the proposed addi tional paving at the Healy-Ruff site. These calculations provide for the required detention ponding at the northwest corner of the site.' At present I the site drains to the west onto the n~ighboring property and then toward the north and west, according to the City. You 'are required to provide detention storage on your si te so that your proposed new parking area does not create a runoff rate exceeding the present runoff rate with the existing paving .' You will see on the last sheet that the runoff rates are so similar that we had to even further reduce the detention runoff in the computer model in order to get the program to compute. However, we took the runoff from the coinciding lOO-year storms in ord~r to compute a volume for detention ponding. A strict cut from elevation ,962.0' yields a pond bottom of approximately 960.51. Instead of cutting to elevation 960.51, we recommend that a rock filter berm be placed near the west property line to a height of at least 11 above grade. Then a very slight depression should be made below the 962.' elevation within the noted 962' contour. This will provide you with the necessary detention ponding but will also allow the detention area to filter back to a dry pond condition as is presently the case immediately west of the west property line.