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SECTION 2 Study Area Characteristics quality standards, and the data meet listing guidelines, DEQ must assume that the water body is water quality limited. Water bodies with no information, or information incompatible with the EPA guidelines, are not included on the 303(d) list. The 303(d) list is updated and revised every two years. Once a water body is included on the 303(d) list, DEQ is required to develop a total maximum daily load (TMDL) requirement for both point and non -point sources of the pollutants of concern. It is anticipated that DEQ will develop TMDL requirements for all designated water quality limited water bodies in the State of Oregon sometime within the next ten years. No water bodies in the River Road Santa Clara basin appear on the 303(d) list. However, two subbasins drain to the Amazon Creek and all subbasins in River Road Santa Clara eventually drain to the Upper Willamette River. Amazon Creek appears on the 303(d) list for bacteria, arsenic and lead. The Willamette River appears on the 303(d) list for bacteria, temperature and mercury. A TMDL was issued for the Willamette River basin in September 2006 for bacteria, mercury, and temperature. Lane County and the City of Eugene have each developed TMDL implementation plans outlining specific actions and programs to address water quality problems in the Willamette Basin. Lane County's plan was approved by the DEQ on June 17, 2008. The City of Eugene's plan was approved on December 23, 2008. 2.6.3 Natural and Built Conditions Evaluating the natural and built conditions that influence water quality can be useful in indirectly assessing water quality conditions in the basin. As urbanization occurs, negative impacts to the health of receiving waters result from changes in the quality of stormwater runoff. Natural features such as riparian areas, wetlands, and open drainage systems have the ability to treat stormwater pollutants, prevent waterway scour by slowing down runoff rates, settle out sediments, and protect stream banks from erosion. However, with research showing that water quality degradation occurs at relatively low levels of imperviousness (10 -20 percent), the implications of development on water quality is significant.' Figures 2 -6, 2 -7, and 2 -8 examine natural and built conditions relative to the other Eugene drainage basins. 1 Tom Schueler, et al. Site Planning, for Urban Stream Protection: The Importance oflmperviousness, 1995. 0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 11 -23