PARTICLE SIZE VARIATION AND GEOCHEMICAL SIGNATURES OF COAL ASH DEPOSITION IN HYCO LAKE, NC

In North Carolina, impounded lakes supplying cooling water for coal fired power plants are also used for recreation and fishing. Sediment cores collected from Hyco Lake document the presence of coal fly ash released from Roxboro power plant ash storage ponds following the lake impoundment in 1964. A suite of gravity cores was collected near the ash pond point of discharge and along an 8 km transect downstream to the dam. Here we present a multi-proxy dataset from 3 cores dated using ²¹⁰Pb and ¹³⁷Cs. Each core was sampled at 1-cm intervals extending into the pre-lake sediments. We measured particle size via laser particle analysis and calculated mean grain size and degree of sorting using GRADISTAT statistical software. These data were compared with ash content determined from optical point counting, sediment geochemistry, and magnetic susceptibility (χ). At all core sites, the boundary between pre-reservoir and post-impoundment sediments is shown by an up-core shift to finer sediments with better sorting, which corresponds with the detection of ash in optical point counts. At Hyco Core 1, closest to the ash storage ponds, the mean particle size ranges from 4 to 20 µm. The coarsest particles (14 to 20 µm) occur at the base of the post-impoundment sediment. Larger ash particles coincide with higher χ and a lower concentration of trace elements, such as Se and As. This corresponds to the release of larger Fe-enriched amorphous fly ash particles from ash ponds into the lake until the late 1970’s. Beginning in 1980, mean particle size fines to 8 µm as smaller spheres become the predominant ash type retained at the plant and released into the lake due to implementation of the Clean Air Act. Clear spherical ash contains higher concentrations of trace elements such as As, Se, Tl, U, Mo, and Sb. Hyco Core 3, collected nearest the dam, displays a finer, 2 to 6 µm range, and better sorted particle size distribution than Hyco Core 1. The abundance of clear spherical ash explains elevated As concentrations and finer particle sizes. These observations demonstrate temporal and spatial changes in fly ash particle morphology, particle size, and geochemistry in Hyco Lake sediment, which are likely related to waste management practices and sediment transport processes.