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1-5:Aurora Donald Interchange(Exit 278) <br /> Interchange Area Management Plan for Marion County Approval <br /> ODOT KN19062 <br /> Oregon Department of Transportation—Region 2 <br /> by the Calapooya Mountains.The Willamette River meanders through the valley from south to north. Faults <br /> exist on the eastern and western margins of the Willamette River basin. <br /> Sedimentary deposits have filled the Willamette Valley and generally consist of conglomerate,gravel,sand,silt, <br /> and some clay from volcanic,fluvial,and lacustrine material. Quaternary alluvial deposits cover much of the <br /> surface within the vicinity of the subject property area. These sedimentary deposits overlie Miocene basalt flows <br /> of the Columbia River Basalt Group.The Columbia River Basalt Group overlies lava flows and volcanic breccias of <br /> Oligocene age(Ma et al. 2009). <br /> The study area is located at an elevation of 193 feet above mean sea level. Topography is primarily flat,with the <br /> exception that Ehlen Road passes beneath 1-5 below grade. The surrounding Willamette Valley also primarily <br /> consists of low topographic relief but includes many gently sloping hills and valleys. Shallow soil in the area <br /> consists of fine-grained soils that include silts, loams, and clays. Depth to groundwater in the vicinity of the <br /> project area is expected to range from approximately 20 to 40 feet below ground surface. Groundwater flow in <br /> this portion of the Willamette Valley is highly variable and can be significantly impacted by local creeks and <br /> rivers.The nearest surface water body is Senecal Creek, approximately 0.5 mile to the south.The Willamette <br /> River lies approximately 3 miles to the northwest. <br /> 2.4.2 Floodplains <br /> There are no Federal Emergency Management(FEMA)-mapped floodplains with the study area (see Figure 2-4). <br /> July 2020 1274-3012-031 2-9 <br />