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CMP Part 3A. Environmental Protection Plan <br /> The spring thaw of snow and ice can have an impact as great as or greater than <br /> rain. Pollutants trapped by ice and snow are released together with the <br /> melt-water to produce a flush effect when temperatures rise enough to melt <br /> significant amounts of ice and snow. <br /> Other factors affecting pollutant migration include the storm pattern; physical <br /> factors such as soil type, land slope, and type of vegetation ground cover; <br /> infiltration into drainage systems; and amount of temporary storage available in <br /> the watershed. The worst time for an urban stormwater runoff to occur is during <br /> a period of low flow, high temperature and low wind, when design loads for <br /> point source inputs have not taken into account nonpoint inputs. These <br /> conditions overstress the ability of the stream or lake to assimilate the <br /> pollutants. <br /> Pollutants behave in various ways during stormwater runoff events. A typical <br /> storm would contribute extremely variable amounts of sediment. The largest <br /> amount of sediment per volume of runoff would follow a first flush behavior, <br /> that is it would correspond with the greatest flow of water and then diminish. <br /> Associated with, and often adhered to this sediment are several harmful <br /> pollutants, including metals, nutrients, bacteria, pesticides, and PCB's. <br /> Pollutants that adsorb to sediment generaily tend to adsorb to the fine fraction, <br /> thus increasing mobility and management difficulties. <br /> The question of scale between individual runoff parameters becomes important <br /> in analyzing the effects of urban runoff. For pollutants such as COD and <br /> bacteria, the immediate areas downstream must be considered critical soon after <br /> an event. Pollutants such as metals and nutrients, however, migrate far <br /> downstream and have lonb lasting effects." <br /> The 208 Study concluded that urban stormwater runoff pollution is potentially a <br /> significant portion of total annual loading far the Metropolitan Area. Further <br /> water pollution abatement programs must consider this source of pollutant input <br /> and change to a balanced approach from the historic practice of considering only <br /> point sources of pollution if future water quality goals are to be reached. Future <br /> upgrading of municipal treatment plants and industrial dischargers should be <br /> viewed in light of potential large capital expenditures for treatment structures <br /> versus reduced expenditures for minimum-structural or source control of <br /> nonpoint sources of pollution. The study recommendation was that "abatement of <br /> nonpoint pollution from urban runoff should receive high priority in future water <br /> pollution programs". <br /> The Minnehaha Creek Watershed District's overall plan (1969) noted that: <br /> "Urban development rapidly increases the amount of storm run-off in an <br /> area because the hard-surfacing of streets and construction of buildings <br /> reduces the amount of water absorbed by the soiL In addition, urban <br /> areas are usually graded and drainage provided to prevent accumulation <br /> of surface water. Since ground water aquifers are normally recharged by <br /> City of Orono Community Management Plan 2008-2030 Page 3A-19 <br />