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MWMC FACILITIES PLAN have the potential to influence fish and other aquatic organisms. In the discussion regarding bacteria, nutrients, and heavy metals, data obtained from ambient monitoring programs in rivers and streams have been separated from data obtained by sampling stormwater discharges during wetweather events. Typically, pollutant concentrations of bacteria, nutrients, and heavy metals are higher in wet weather stormwater discharges than in rivers and streams. The water quality monitoring programs that generate data used for this study do not include analysis for pesticides. Because the mainstem of the Willamette River is the water body that would be most directly affected by potential expansion of major MWMC facilities, this section only examines selected characteristics for water quality in the mainstem. For a more detailed description and comparison of treated wastewater discharge and water quality in the Willamette River in the vicinity of the WPCF outfall, see section 5.3, Water Quality Impact. It should be noted that the following discussion on water quality was adapted from a description on water quality originally published in the Aquatic and Riparian Habitat Assessment for the Eugene-Springfield Area, September 2002, Final Report, by the Eugene- Springfield MECT (MECT, 2002). Natural Influences on Water Quality Streams in the MWMC study area (e.g., Amazon Creek, Willow Creek) are influenced primarily by the geology of the flat valley floor, a landscape that does not promote infiltration of water or delayed release of winter precipitation into the dry season. These water bodies tend to warm quickly in the summer and are relatively high in sediment and nutrients at other times of the year. Water quality in the mainstem of the Willamette River is directly affected by underlying surface geology. Creeks and rivers that flow into the Willamette mainstem upstream of the MWMC service area (i.e., McKenzie River and Middle Fork Willamette River) originate in the Cascade Mountains in porous rock that is young in geologic age and favors deep infiltration and delayed transfer of water to channels, where there are few opportunities for warming and incorporation of nutrients or other substances. Further downstream, these two rivers flow through rock of older geologic age consisting of porous, fractured basalt that also promote deep infiltration of runoff and delayed transfer of water to the rivers, although the effect is not as significant as further upstream. Upon reaching the flat valley bottoms, groundwater influx to the rivers is low, warming accelerates, fine-grained substrates that line the stream banks are readily incorporated, and nutrient-rich lenses of water within the Missoula flood deposits leach into the rivers. Human Influences on Water Quality In addition to structural modifications to water bodies in the area such as channelization and dredging, human influence on the fiver includes non-point source discharges from stormwater runoff and permitted point source discharges. Permitted discharges include discharge of treated sanitary wastewater into the Coast Fork downstream of Cottage Grove, and into the Willamette River downstream of Eugene. In addition, cooling water is discharged from power generation facilities at the University of Oregon into the Eugene Mill Race (an artificial side channel of the Willamette River), and from both treated and non- contact process water from numerous industries in both Eugene and Springfield that 2-18 MWMC_2.0_REV23.DOC