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Water Resources <br />runoff flow rates and volumes resulting from the conversion of impervious surfaces into pervious <br />surfaces. <br />Because the Alternative 1 and 2 sites are located outside the Willamette River 500-year and 100- <br />year floodplain boundaries (FEMA 1999), the project should not result in impacts on flood <br />storage in the Willamette River (see Figure 8). <br />For either Alternative 1 or Alternative 2, the smaller site option (option B) would have impacts <br />similar to the larger site option (option A). <br />No Action Alternative <br />Impacts on water resources would not change under the no-action alternative. Stormwater would <br />continue to drain from either of the alternative sites and to be discharged untreated into the <br />millrace or the Willamette River. Loadings of pollutants from the uncovered parking lots on the <br />Alternative 1 and 2 sites would continue at current levels. <br />Potential Mitigation Measures <br />Construction-phase water quality protection efforts could emphasize appropriate erosion and <br />sedimentation controls; prevention of spills, leaks, and drips of toxic materials; and proper <br />storage and handling of fuels and construction products that are potential sources of <br />contamination. Although the city of Springfield has not yet developed a comprehensive <br />stormwater management plan, stormwater management practices similar to those outlined by the <br />city of Eugene standards may be considered. <br />City of Eugene standards call for preparation of a construction site management plan identifying <br />potential water quality impacts and stipulating measures to eliminate or minimize impacts, as <br />part of the construction planning process. GSA would consider developing such a plan. The <br />plan normally would include details on controls that minimize erosion and offsite sediment <br />transport and reduce potential water quality impacts in storm drainage systems and receiving <br />waters. Several erosion and sedimentation controls that could be included in the plan are the <br />following: <br />Construct sediment control facilities prior to other site disturbances. <br />Provide protection for existing storm drain inlets in the site area using <br />filter fabric screens beneath the inlet grates or straw bales to surround each <br />inlet. <br />^ Install silt fencing downslope of work areas. for perimeter protection, <br />particularly in the vicinity of drainage ditches and storm drain inlets. <br />New Federal Courthouse 51 Final EIS <br />i <br />