DETERMINING THE AMOUNT AND LOCATION OF FLY ASH RELEASED INTO A RIVER USING CORING AND POINT COUNTING

During the early morning of December 22, 2008, a failure in an earth dike at Tennessee Valley Authority’s Kingston Power Plant, released about 4.1 million cubic meters of coal fly ash slurry into the waters and proximate riparian areas draining into Watts Bar Reservoir, principally into the Emory River. Within 3.2 km the Emory River discharges into the Clinch River, which flows into the Tennessee River after several kilometers.

Since the ash slurry release, both the Tennessee Valley Authority and researchers at Appalachian State University have been coring the river systems to track the ash deposits in the river. The problem we face is how to determine what is and what is not ash. During the spill and subsequent deposition, the ash mixed with native sediments to varying degrees, producing a spectrum of ash/sediment mixtures. The ash/sediment mixtures are difficult to distinguish by eye. To help determine the amount of ash in the sediment, we developed a method, with the help of Ryan Hall of the R.J. Lee Group Inc., for point-counting ash. Point-counting is a commonly used technique in petrography for determining percentages of minerals in a rock sample. We have adapted the method as an efficient way to accurately estimate the amount of ash in a given sediment sample by counting the number of ash spherules in a sediment samples.

Results from the point-counting of core samples show that the ash in the ash/sediment mixtures is at most 53% ash. Most ash/sediment mixtures are between 15% and 30% ash. Ash is concentrated in the Emory and Clinch Rivers, with a higher percentage of ash more proximal to the spill site. The ash is also concentrated between approximately 0 and 10 cm below the sediment/water interface. There are, however, exceptions where there are significant amounts of ash up to 50 cm below the sediment/water interface, and small amounts of ash present at depths up to 1m below the sediment/water interface. Coring also shows that there are ash/sediment mixture deposits on submerged terraces in the lower Emory River that are capped by mat of organic materials, possibly trapping these deposits and preventing downstream movement.