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#2596 Brenshell Homes EAW Need Determination December 6, 2000 Page 4 The portions of the parcel which will be disturbed by development activity are located primarily on slopes of 0-12%, uphill from steeper slopes leading down to Forest Lake Bay of Lake Minnetonka. Runoff from the site either is in the form of sheet flows over the relatively uniform slopes just above Wildhurst Trail, or in the form of channelized flows in two ravines, the smaller (“south ravine ”) located at the southeasterly comer of the site, the larger (“north ravine ”) heading northeastward from the northwesterly comer of the parcel. Both ravines are wooded with mature hardwoods. Soils on a majority of the site per the Hennepin County Soil Survey are of the Kilkenny series, being primarily Kilkermy loam. The Soil Sur\'ey classifies these soils within “Building Site Group 7". The soils in Group 7 have "'moderate I imitationsfor residential and commercial development with public sewer systems where slopes are less than 12%. In areas where slopes are more than 12%, these soils generally have severe limitations for commercial and residential development because of the high cost of installing utilities and grading streets and building sites. Proper design of buildings, site planning, and minimal grading reduce erosion and sedimentation. Where slopes are more than 18%, these soils are better suited to uses that enhance the natural beauty of the area than to most other uses ". The proposed development has been designed w ith these limitations in mind. Consider the following aspects of the development intended to minimize or eliminate erosion concerns: a)A majority of the slopes in excess of 18% on Lots 2 and 3 will not be disturbed by grading and will have existing vegetation retained. These sloped areas will be protected from excess runoff by a swale which will direct runoff to the proposed retention pond on Lot 1 above the southeasterly ravine. Easements and covenants will be put in place to ensure the swale will be retained and maintained on a permanent basis. The proposed retention pond on Lot 1 will result in a decrease of the mnoff flow rates w the southeast ravine. Due to the steep gradient of the existing ravine, the watershed area tributary to this ravine has been reduced significantly and redirected to the northerly stormwater pond, thereby decreasing the mnoff rates and volumes reaching the southeast ravine lo a level lower than pre-development conditions. The pond in Lot 1 will also serve as a water quality pond, meeting NURP standards for sediment and nutrient removals prior to discharge to the ravine. Also, because the southeast ravine has steep bank slopes, the protected area where no grading is allowed will encompass the entire ravine area within Lot 2. In order to eliminate disturbance of the steeper slopes on Lots 2 and 3, installation of sanitary sewer along the common lot line as well as within Wildhurst Trail will be via directional boring methods to avoid open cuts which would potentially affect slope stability.