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Water Resources <br />Construction of the courthouse would require a large excavation that could encounter perched <br />ground water at either of the alternative sites. Even if ground water is not encountered, <br />dewatering may be necessary to prevent stormwater from ponding in foundation construction <br />areas at the bottom of the excavation. Therefore, dewatering during construction may be <br />necessary under either of the alternatives. Dewatering in excavation areas would cause an <br />increase in the flow volumes discharged from the site during construction, compared to existing <br />runoff volumes. Because existing storm drainage systems in the project area have sufficient flow <br />conveyance capacity, the dewatering discharges are not expected to cause localized flooding <br />problems. Water quality impacts associated with excavations and dewatering typically include <br />an increase in the transport of solids offsite, and an increase in turbidity of runoff entering <br />receiving waters. <br />If ground water is contaminated in the vicinity of the alternative sites, dewatering discharges <br />could potentially contain elevated levels of pollutants. Without proper controls, receiving water <br />quality impacts could result from dewatering activities. <br />Operation of heavy equipment requires fueling and engine maintenance activities that involve <br />oil, grease, solvents, and other toxic engine fluids. These materials can be entrained in <br />stormwater runoff through leaks in material storage areas, spills resulting from improper <br />handling of liquids, miscellaneous accidents, drips from the undercarriages of vehicles, <br />wastewater used to clean equipment and control dust, and improper disposal of waste liquids. <br />Soils that become contaminated by spills, drips, .leaks, equipment washwater, and miscellaneous <br />accidents can carry the adsorbed contaminants offsite if eroded by wind or runoff or transported <br />by vehicles. The types of contaminants that could be adsorbed to soil and sediments include <br />nutrients naturally present in the soils, heavy metals, petroleum hydrocarbons, and organic <br />compounds. Elevated concentrations of nitrogen and phosphorus in construction site runoff <br />could contribute to production of algae in the Willamette River and subsequent water quality <br />problems related to algal decay. However, nitrogen and phosphorus in the onfite soils are not a <br />significant concern, because algal growth should not be stimulated in the Willamette River due <br />to the large flow volumes relative to site runoff flows. <br />Damage to aquatic life in the Willamette River could occur if an uncontrolled spill of fuel or <br />other toxic material occurs on the construction site and stormwater runoff or dewatering carries <br />the material offsite. Heavy equipment used for construction could increase the potential for <br />spills of fuel or other related products. Spilled material could also contaminate ground water <br />beneath the construction site. Lesser impacts could be caused by the cumulative effects of <br />miscellaneous leaks and drips of fuel, antifreeze, solvents, concrete curing compounds, asphalt <br />emulsifier, paints, and other materials used during construction. <br />If any of the proposed sites are found to have contaminated soils, construction activities could <br />also result in disturbance of these soils, potentially leading to offsite contamination by soil <br />particles carried in stormwater runoff. The potential severity of this type of contamination and <br />. the resultant water quality impacts depend on the extent of contamination at the selected site. A <br />phase II environmental assessment performed at Norm's Auto Repair (Alternative, Option A) <br />indicated the presence of contaminated soils associated with underground gasoline storage tanks. <br />New Federal Courthouse 49 Final EIS <br />