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03/07/95 09:39 $503 224 7820 WOODWARD -CLYDE 10005/022 <br /> mechanism for providing continuous education and updated guidance to City <br /> staff and engineers/designers in the private sector. <br /> Baelekround: - Development Impacts on Water Quality and Flood Control- - <br /> New development and redevelopment have increasingly been recognized by EPA and <br /> the City as significant sources of pollutants to stormwater runoff. Pollutants are <br /> discharged both during construction activities and after construction is complete, over <br /> the life of the project. During construction, there is the potential for discharge of <br /> sediment from erosion and stockpiled materials, oil/grease and heavy metals from <br /> heavy equipment use, and nutrients and organics from use of fertilizers and pesticides <br /> to establish landscaping. After construction, the pollutants discharged in site runoff <br /> will vary, depending on the land use. Table 1 presents various pollutants and their <br /> typical sources, by land use category. Temporary and permanent controls can be <br /> installed on newly developing properties to reduce the amount of pollutants in site <br /> runoff. <br /> When an area develops, the natural water balance is disrupted. There is a transition <br /> from natural surfaces to more impervious surfaces such as roofs, driveways, parking <br /> lots, sidewalks and streets. There are fewer trees and plants to intercept the rain and to <br /> transpire water back into the air. Paved and other impervious surfaces prevent water <br /> from soaking into the ground and increase the volume and flow rate of stormwater <br /> runoff. Runoff reaches streams and rivers more quickly; and typically there is less <br /> recharge to groundwater to contribute baseflow to streams and rivers. As a result, <br /> stream geometry changes, altering plant and animal habitats. In addition to <br /> downstream impacts, the increase in volume and flow rate of runoff from a newly <br /> • developing site can intensify erosion problems. With this comes an increase in the <br /> amount of pollutants carried off the site, since pollutants such as heavy metals tend to <br /> attach themselves to sediment. <br /> Background: What Guidance is Currently Provided? <br /> As stated previously, Eugene has existing standards for stormwater quantity (e.g., <br /> flood) control, but no standards yet for water quality control, since the latter need only <br /> be constructed on a voluntary basis at the present time. The existing flood control <br /> standard is specified in Appendix A (Table 4.1) of Procedures for Privately <br /> Engineered Projects (April 1993), based on the Eugene Areawide Drainage Master <br /> Plan (1990) by OTAK. It requires design of drainage facilities for design storm <br /> recurrence intervals of 5 to 50 years, depending on the type of drainage unprovement <br /> and the size of the drainage area. In addition to the existing water quantity standard, <br /> a recommendation or standard for a water quality design storm will be required before <br /> S1945042na \task02001onsitc controls\techmcm.ck 4 <br />