Based upon field observations and sediment core data, the Gorge Dam impoundment has different characteristics downstream and upstream of the former power plant (Fig. 2). Downstream of the former power plant, cores C1 through C6, C12, and C13 contain sediment, having high magnetic concentration, and are readily correlated (Fig. 4). Upstream of the former power plant, cores C11, C10, and C8 contain sediment, having lower magnetic concentration (Fig. 4). To confirm the magnetic susceptibility correlations, 18 distinctive GW-572016 concentration lithologic

marker beds or laminations were identified and correlated among most cores. Not all of the key beds/laminations could be extended upstream of the former power plant to sites 11, 10, and 8 because there is a change in sediment type. Downstream of the former power plant the impoundment is wide, deep and slow-flowing (Fig. 2). The water cross sectional area decreases from about

900 m2 closest to the dam to about 320 m2 at cross section 11 as both the pool width and depth decrease (Fig. 5). Cores C1 through C4 recovered between 550 and 580 cm of sediment and terminated at bedrock. Cores C3 and C4 were collected within 5 m of each other and contain identical sediment. Correlative sediment GSK1120212 price from C3 was spliced into the gap of no sediment recovery between core drives 1 and 2 in core C4 to create a complete composite sediment section (Fig. 6). This composite section is representative of the impoundment fill downstream of the former power plant. The composite section contains, dark brown to black mud having organic-rich layers, between 0 and 225 cm below lake floor (cmblf); an abundance of dark gray CCP and black mud layers between 225 and 460 cmblf; and dark

grayish-brown mud, having abundant light gray to tan clay laminations, between 460 and 545 cmblf (Fig. 6). Directly above bedrock is a 9 cm thick layer of muddy, sandy gravel. Moving upstream toward the former power plant, the uppermost mud unit, having low magnetic concentration, thins and contains more fibrous plant material PLEK2 (Fig. 4). Wet and dry bulk density increase toward the bottom of the cores, and sediment organic content is between 4 and 8%. The largest magnetic susceptibility values correspond to the sediment layers having abundant CCP (Fig. 6). The combustion of coal produces slag, synthetic gypsum, fly-ash, and bottom-ash that are collectively called coal combustion products (CCPs) (Kalyoncu, 2000 and Jones et al., 2012). Although spherule fly-ash particles were identified by ESEM, we did not attempt to distinguish the different CCP particle types, so we use the term CCP in this study. Further study of representative subsamples supplements the lithologic descriptions presented above. The median grain-size (d50) for the impoundment fill is in the silt-size range. Samples at the core top and in the CCP-bearing layers have between 4 and 14% sand (Fig. 6).