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DEC-15-95 F R I S- 1 1 M S A S T P A U L <br />- December 15, 1995 <br />4XMITINGOGITUS File: 230- 270 -11 <br />1326 Eriet2y Park 0&0 <br />St. Paul, MN 55108 <br />612.644.4389 <br />800.888 -2923 <br />fax: 613 =644 °9446 <br />_V. ENaNEEQ;`•dG. <br />_r. /I ONAANT AL <br />OICIPAL <br />V„ s,NNNG <br />D wASrf <br />S RUC'URA; <br />LIRVE{IN IG <br />'RAFFIC <br />TRANSPORTATION <br />ELECTRICALImECF -UMC AL <br />ENG?NUR:NG: <br />WAC <br />Pa PER I s"NUTION <br />SCAUA <br />SYKEM CCNTRCLE <br />WICES IN: <br />;MINNEAPOLIS <br />PRIOR LAKE <br />ST. PAUL <br />WASECA <br />Mr. Steve Ach <br />City Planner <br />City of Elk River <br />13065 Orono Parkway <br />P.O. Box 490 <br />Elk River, MN 55330 <br />RE: WEATHERWOOD SUBDIVISION REVIEW <br />Dear Mr. Ach: <br />P - a 2 <br />We have reviewed the revised Grading /Drainage Plan with a revision date of Dezember <br />1, 1995, and the final plat. Our comments are as follows: <br />11U71-rint 7.1 <br />■ The Developer has shown the proposed building site and two septic system <br />locations on each lot. Several of the proposed septic sites are shown to be placed <br />on steep slopes. If these systems are to be drainfield, they can be terraced down <br />the slopes and around trees. But if the soils would not permit this type of <br />drainfield and a mound system were to be used, these locations on steep slopes <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 />should be required to submit the proper soil testing to guarantee that thtse lots <br />have a buildable area for the septic systems. <br />We have reviewed the proposed Weatherwood Development with resjaect to <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 levels for <br />a 100 -year snowmelt event (7.2 inches over 10 days), rather than a 6 -inch rallifal.l <br />event. For wetland or stormwater areas with no constructed outlet, the snowraelt <br />event is often the critical event. The volume of runoff is greater due to the frozen <br />ground conditions at the time of runoff. We would recommend requiring the smile <br />type of analysis for the Weatherwood Development. <br />