09-19-1994 Planning Packet - Laserfiche WebLink

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Zoning File #1962 September 15, 1994 Page 5 It is clear from the discussions on water quality aixl the wetland and marsh requirements that assimilative capacity of Orono’s existing wetlands is, overall, less than that required to assimilate all expected phosphorus loading. Staff gives guarded credeiKe to the numbers but accepts the concept that open water has less assimilative capacity than dryer tvpes of wetlands, as noted in the follow ing excerpt; “Permanent standing water has assimilative capacity of 4 lbs. per acre per year. Permanent standing water was defined as areas of the narsh having cattails and other emergent vegetation. The dryer areas of the marsh, which have water in them only interminently, absorb a greater amount of phosphorus and have an assimilative rate of 20 lbs. per acre per year". In Table 2 of that document uiKler Wetland Marsh requirements, the wetlands upstream of Dayton’s driveway are defined as Basin "LL12A". This subwatershed has a drainage area of 105 acres, permanent water of 20 acres and intermittent water of 10 acres for |i an assimilative capacity of 280 lbs. of phosphorus. The ps^lluiion potential of that portion of the subwatershed is 363 lbs. (under an urbanized development setting, which does not exist in this watershed) therefore 130% of the existing assimilative capacity would be necessary to prevent discharge of phosphorus to Long Lake. One can make the argument then that changing 7 1/2 acres of relatively “intermittent" water into "permanent" water may decrease the assimilative capacity' of that marsh system, and potentially more phosphorus would discharge to Long Lake if the watershed were to be intensely developed. A fair statement might be that in this watershed under the current density of development, the project w ill have a much lower impact than if the watershed was highly urbanized. Staff would appreciate comments from the MCWD as to how this project might fit in with their efforts to upgrade the water quality of Long Lake. Comments/Concems of Other Agencies • Minnesota DNR has submitted a letter indicating no objection to the project and requiring no permit. • The US Army Corps of Engineers has. according to Mr. Bowen, indicated they will not require a permit for this project. Staff has requested that a written confirmation from Corps of Engineers be submitted. • The Minnehaha Creek Watershed District has preliminary' reviewed the application and tabled it requesting additional information. The Watershed District is expected to review this again on September 22nd.