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CMP Part 3B. Land Use Plan <br /> Ponds in the Twin Cities area designed according to NURP standards have total <br /> phosphorus removal efficiencies of 47 to 68 percent according to the Walker <br /> Model. Possibilities for improving this include (1) increasing mean pond depth; <br /> (2) promoting infiltration; (3) promoting plug flow conditions(i.e. multiple cell <br /> ponds); (4) applying chemicals to precipitate out the orthophosphorus (alum <br /> treatments); (5) encouraging growth of certain aquatic plants; and (6) design of <br /> outlet structure to provide extended detention of large runoff events. Whether <br /> each of these enhancements can or should be incorporated is dependent on the <br /> desired level of control and other site specific conditions. <br /> Constructed wetlands have potential benefits as well as drawbacks. Locating <br /> ponds in the most efficient locations could have significant impacts on certain <br /> already developed properties. Design and construction of ponds in residential <br /> areas will be scrutinized by the public to ensure safety concerns are addressed and <br /> a natural character is maintained. Additionally, the cost of constructing <br /> stormwater ponds and storm sewer systems is enormous compared to the cost of <br /> wetland preservation. Orono's ?89� Surface Water Management Plan indicates <br /> that a complete system of supplementary ponds to provide adequate levels of <br /> phosphorus removal under the proposed development densities would have a <br /> price tag in the range of $10 million. Only a fraction of this cost could be paid <br /> through the development of remaining vacant lands, and this ultimately places a <br /> heavy burden on the general taxpayer. Increasing development density to help <br /> pay the costs of stormwater infrastructure would in turn raise the cost of such <br /> infrastructure to accommodate added flow rates and pollutant loads. <br /> LAKE POLLUTION <br /> NQV-POINT SOURCE • <br /> INCREASED HARD COVER <br /> MORE RUN-OFF <br /> MDRE POLLUT4NT5 FROM LAKE POLLUTION <br /> �.AWN- FERTIUZATIOM� � PpNT SOURCE 9 <br /> VEHICLE EXHAUST, lMMINENENT <br /> DE-iCE1NG, AND STREET HEALTH HAZARD <br /> SWEEPING <br /> � <br /> ALTERNATIVES STUOIED <br /> SEWER EXTENSION <br /> ORDERED <br /> LAIVD sueoivisiorv � <br /> TO SPftEAD UNIT <br /> COSTS OF ASSE55- <br /> MENTS <br /> PROPEFiTY ASSESSMENTS <br /> POSE FINANCI4L BUROEN <br /> DtJE TO SPECIAL CONSTRUG- <br /> TION IN WETLANO TERRAIN, <br /> LARGE LOT 4CREAGE AND <br /> SC1\TTEREO DEVELOPMENT <br /> Figure 3B-1. THE URBANIZATION SPIRAL <br /> Illustrates the Development Paradox that faces <br /> Orono if municipal services are extended into rural areas. <br /> City of Orono Community Management Plan 2008-2030 Page 3B-6 <br />