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Water Resources <br />The site is currently undergoing cleanup procedures. A phase II assessment has not yet been <br />performed for the AutoCraft body shop (Alternative 2). In either case, the impacts on receiving <br />waters are likely to be minor because extensive soil erosion is not expected. Any contaminated <br />soils disturbed durin construction would re wires ecial handlin and dis osal in accordance <br />g q P g P <br />with applicable regulatory requirements. <br />Removal of existing structures could result in short-term impacts from dust and debris associated <br />with demolition activities. Water quality impacts typically associated with demolition activities <br />include increased debris loadings to stormwater conveyance systems and increased particulate <br />loadings in runoff entering receiving waters. Excessive debris loadings to offsite drainage <br />systems may clog drainpipes and decrease the flow conveyance capacity, and may also reduce <br />the ability of catch basins to trap other pollutants. Contaminants associated with dust particles <br />may be transported to the Willamette River via wind or surface runoff, resulting in increased <br />pollutant loadings. Therefore, proper controls are needed to prevent water quality impacts <br />resulting from demolition activities. <br />Long-Term Operational Impacts <br />Alternatives 1 and 2 <br />Currently, the Alternative 1 and 2 sites are covered almost entirely by impervious surfaces, <br />including mostly rooftops and pazking lots. The Alternative 1 site (the Riverfront site) consists <br />of slightly less impervious azea than the other site, because of a greater amount of trees and <br />landscaped areas. However, it is still heavily dominated by impervious surfaces. <br />Based on preliminary designs, construction of the courthouse on either of the alternative sites is <br />expected to either maintain or slightly reduce the amount of impervious surface area on the site. <br />The net change for each site would depend on the amount and type of open space areas <br />incorporated into the site, which could consist of pervious surfaces such as grass lawns, or <br />impervious surfaces such as terraces or fountains. <br />Stormwater runoff from either of the alternative sites would be collected and dischazged via the <br />existing storm drains that empty into the millrace or the Willamette River. Slight long-term <br />decreases in the peak rates of flow and volumes of stormwater runoff from the sites could be <br />expected due to the potential for reduced impervious surface area. The net change in stormwater <br />runoff would depend upon the final plans for the selected site. <br />Because the new courthouse is expected to have underground or covered pazking for courthouse <br />personnel, it is anticipated that stormwater runoff would lazgely originate from the courthouse or <br />pazking structure roofs. Generally, roof runoff contains lower concentrations of suspended <br />solids, nutrients, fecal coliform bacteria,. petroleum hydrocarbons, grease, and heavy metals than <br />pazking lot runoff. Therefore, construction of the facility could result in reduced pollutant <br />loadings from the site compazed to current conditions, due to a decrease in uncovered pazking lot <br />runoff and an increase in roof runoff. No public parking azeas are included in the proposed <br />project under these alternatives. Either of the alternatives could result in a slight reduction in <br />Final EIS 50 New Federal Courthouse <br />