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Water Resources <br />these developed sites originates from parking lot runoff. Runoff from parking lots such as these <br />typically .contains elevated concentrations of suspended solids, nutrients, fecal coliform bacteria, <br />petroleum hydrocarbons, grease, and heavy metals. These existing pollutant loads can add to <br />cumulative water quality problems if appropriate stormwater treatment systems are not <br />functioning or are not in place, as is the case with these sites. Nonetheless, existing pollutant <br />loads from the individual sites make up a negligible portion of the total loads to the Willamette <br />River. <br />Willamette River Water Quality <br />The Willamette River characteristically exceeds state water quality standards (Oregon <br />Administrative Rules [OAR] 340-41-445) for temperature and fecal coliform bacteria (Sales <br />1997 personal communication). Maximum temperatures are usually reached in August, when <br />water temperatures as high as 23 degrees Celsius (73 degrees Fahrenheit) have been recorded <br />(USGS 1994). The maximum fecal coliform bacteria concentration is typically reached during <br />January and has been recorded at 450 organisms per 100 milliliters (compared to the state <br />criterion of 406 organisms per 100 milliliters for a single sample). The high fecal coliform <br />concentrations have been attributed to combined sewer overflows (Sales 1997 personal <br />communication). <br />In addition, the dissolved oxygen concentration in the river drops to a minimum during the <br />lower-flow months of July and August, when it is typically in the range of 7 to 8 milligrams per <br />liter (compared to the state criterion of greater than or equal to 8 milligrams per liter). Turbidity <br />(i.e., reduction in water clarity) is typically elevated during high flows and has been recorded as <br />high as 23 nephelometric turbidity units. <br />Peak flows for the Willamette River occur in December when the average discharge rate is <br />63,490 cubic feet per second. Minimum average flows are typically reached in August, when the <br />- average discharge rate is 8,335 cubic feet per second (USGS 1994). <br />Ground Water Conditions <br />The Eugene/Springfield area is underlain by deposits of alluvium consisting largely. of sand and <br />gravel with mixtures of silt and clay. Ground water in the area occurs approximately 20 to 30 <br />feet below the surface, depending on the season and precise location (USGS 1973). Ground <br />water in the vicinity of the Alternative 1 and 2 sites generally flows north to northwest. The <br />direction of ground water flow is influenced by precipitation, variations in the water level of the <br />surrounding streams and rivers, and local characteristics of subsurface materials. These <br />differences also influence the depth and velocity of ground water flow. <br />Based on available geologic information and preliminary construction plans for the project, it is <br />. ' likely that excavation for construction of the courthouse building under either of the <br />development alternatives would extend into a local shallow aquifer. Therefore, it is anticipated <br />that dewatering would be necessary during the construction phase of the project. <br />;_ <br />i` <br />New Federal Courthouse 47 Final EIS <br />