12-11-2000 Council Packet - Laserfiche WebLink

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d. e. f. A majority of the runoff from the site (and from the roads to be constructed within the Garden Lane corridor and within the site) will be directed to a stormwater pond above the northerly ravine. This pond will serve both water quantity and quality functions, and will result in flow rates in this ravine that are no greater than the pre development condition. Reasons for directing a majority of the flows to this ravine include that it has a flatter gradient with less erosion potential, and adding flows to this ravine will have minimal impact to properties downstream as compared to the potential impact if all flows were directed to the southeasterly ravine per the existing natural drainage areas. Further, this ravine discharges to a wetland hydraulically separated from Lake Minnetonka by a driveway and culvert, hence further treatment of runoff will naturally occur within this wetland. Both stormwater ponds are designed to meet National Urban Runoff Program (NURP) standards for water quality. NURP ponds are designed to result in an average reduction of phosphorus of 60%. Additionally, covenants will be established requiring the property owners within the plat to use phosphorus-free fertilizers for lawn maintenance. The water discharged from tliese ponds is not likely to be a significant source of added pollution to Forest Lake Bay. Road and utility construction and site grading will be occurring primarily in areas where existing slopes are relatively level. Tlie site plan has been revised a number of times to incorporate changes suggested by the City staff and by the area residents, resulting in decreased road lengths, minimization of disturbance of sensitive slopes, and retention of existing vegetation within the ravine areas and on most of the slopes exceeding 12%. Virtually all previous development in the Saga Hill area was completed prior to the adoption of development requirements for managing stormwater runoff As a result, there has been a need to retrofit stormwater management facilities into the neighborhood. An example is the storm pond constructed just west of the south end of Tonkaview Lane; another example is the sediment and rate control berra required of the recently constructed home at 4685 Tonkaview. Additionally, the draft Orono Surface Water Management Plan indicates the need for new water quality ponds to protect the quality of Forest Lake. The ponds proposed with this development will reduce the magnitude and property impacts of those future ponds by trapping pollutants and retaining runoff higher in the watershed. Page 4 of 8