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DEC— 1 5-135 PR I 8 1 1 ITA S T <br />fOV1il:114GEti(yI1FIR% December 15, 1995 <br />File: 230-270-11 <br />1326 Engy Pork Drive <br />1, 1995, and the final plat. Our comments are as follows: <br />St' Pavl &AN 56108 <br />Mr. Steve Ach <br />6 12 644 4389 <br />City Planner <br />1 800-888-2923 <br />City of Elk River <br />Pte:61N" 9446 <br />13065 Orono Parkway <br />h;m wA5 P <br />P.O. Box 490 <br />seutrueA, <br />Elk River, MN 55330 <br />P A U L <br />RE: WEATHERWOOD SUBDIVISION REVIEW <br />Dear Mr. Ach: <br />P - 5 2 <br />We have reviewed the revised Grading/Drainage Plan with a revision date of December <br />In the past, the City has required Developers to calculate the high-water leseis for <br />a 100 -year snowmelt event (7.2 inches over 10 days), rather than a 6 -inch rainfall <br />event. For wetland or stormwater areas with no constructed outlet, the snowmelt <br />event is often the critical event. The volume of runoff is greater due to the frozen <br />,iFICES IN: ground conditions at the time of runoff. We would recommend requiring the saune <br />HNNEAPOUS type of analysis for the Weatherwood Development. <br />PRIOR LAKE <br />ST. PAUL <br />WA,SECA <br />1, 1995, and the final plat. Our comments are as follows: <br />_rORoNAr,ENtAt-Grading <br />and Drainage Plan <br />N C!PAL <br />m NrrNG <br />■ The Developer has shown the proposed building site and two septic system <br />h;m wA5 P <br />locations on each lot. Several of the proposed septic sites are shown to be placed <br />seutrueA, <br />on steep slopes. If these systems are to be drainfield, they can be terraced down <br />URVE'•NG <br />the slopes and around trees. But if the soils would not permit this type of <br />'RAFFic <br />drainfield and a mound system were to be used, these locations on steep slopes <br />TRANSPMATION <br />would not permit the mounds to be built. The mound system requires a 12:1 side <br />slope, which could not be constructed on a 3:1 existing slope. The Developer <br />EIECtRiCALAMKHAIKM <br />ENGINEERING. <br />should be required to submit the proper soil testing to guarantee that these lots <br />have a buildable area for the septic systems. <br />WA` <br />Pc`AIR MTRI40,0 <br />SCAUA <br />■ We have reviewed the proposed Weatherwood Development with resl?ect to <br />;,ETEMcrWRa: <br />drainage issues. Some of the wetland areas are labeled with a 100 -year event <br />runoff volume, as well as a 100 -year high-water level. The runoff volumes were <br />calculated using a runoff coefficient of 0.4 for a 6 -inch rainfall over the watershed <br />area for a specific wetland. <br />In the past, the City has required Developers to calculate the high-water leseis for <br />a 100 -year snowmelt event (7.2 inches over 10 days), rather than a 6 -inch rainfall <br />event. For wetland or stormwater areas with no constructed outlet, the snowmelt <br />event is often the critical event. The volume of runoff is greater due to the frozen <br />,iFICES IN: ground conditions at the time of runoff. We would recommend requiring the saune <br />HNNEAPOUS type of analysis for the Weatherwood Development. <br />PRIOR LAKE <br />ST. PAUL <br />WA,SECA <br />