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I <br />I <br />I <br />k' * <br />r <br />i: <br />i: <br />K <br />I <br />than those of raw sewage, with predominant sources of sediment being <br />erosion, atmospheric fallout and vehicular deposition. The detrimental <br />effects of sediment include decreased light penetration, settling on lake or <br />stream bottoms, transport of adhered pollutants, clogging of fish gills and <br />decreased aesthetics. In general, urbanization will increase sediment loads, <br />with areas of rapid development contributing the largest loads, but with fully <br />developed areas also contributing large sediment volumes. <br />Oxygen-demanding substances introduced by urban runoff threaten receiving <br />water bodies with oxygen depletion resulting from biological and chemical <br />degradation of oxidizable material. Oxygen demand is best represented <br />through chemical oxygen demand (COD), but biochemical o,xygen demand <br />(BOD) has historically been used as the most convenient means of reporting <br />demand. BOD and COD concentrations occurring in stormwater runoff are <br />approximately equal to those of secondary treatment effluent. The degree to <br />which oxygen is lost as a result of this demand depends upon the amount of <br />degradable material in the stormwater, benthic oxygen demands and the <br />physical nature of flow in the receiving water body. <br />Nutrient (nitrogen and phosphorus) input resulting from urban runoff <br />is critical, since it becomes a contributing factor in eutrophication of <br />downstream inactive waters. Nutrient input levels are generally less than <br />inputs from municipal treatment sources, but nevertheless are significant to <br />the total water quality condition. Phosphorus input to water bodies, <br />particularly lakes, has in most cases been found to be the limiting element <br />in determining algal productivity. Nutrient character in the stomi water <br />runoff is highly dependent upon oxygen conditions. pH and physical <br />conditions such as sediment and organic content in the water. <br />Toxic hca\y metal loading from urban runoff merits attention as a potential <br />nondegradable aid to stream deterioration. Metals are capable of reaching <br />critical levels in quiet areas where they are able to accumulate in bottom <br />sediments. Loading of heaNy metals during a storm contributes a signi ficant <br />portion of the entire load to urban streams. <br />Other constituents of urban runoff of concern, but of variable severity, <br />include bacteria, chlorides (C1) from road salt, oil and grease, pesticides and <br />PCB’s. These pollutants can be locally severe depending upon receiving <br />water conditions and proximity to source areas. <br />The major identified sources of urban stormwater pollution include: <br />vehicular and industrial emissions and leakages, combined sewer overflows, <br />skid control grit and deicing salts, street and construction litter, vegetation <br />and animal droppings, improperly applied pesticides, atmospheric fallout and <br />CMP 3A - 14