Magnetic susceptibility measurements to detect coal fly ash from the Kingston Tennessee spill in Watts Bar Reservoir

An estimated 229 000 m3 of coal fly ash remains in the river system after dredging to clean-up the 2008 Tennessee Valley Authority (TVA) spill in Kingston, Tennessee. The ash is heterogeneous with clear, orange and black spheres and non-spherical amorphous particles. Combustion produces iron oxides that allow low field magnetic susceptibility (χLF) and percent frequency dependent susceptibility (χFD%) to be used to discriminate between coal fly ash and sediments native to the watershed. Riverbed samples with χLF greater than 3.0 × 10−6 m3/kg, have greater than 15% ash measured by optical point counting. χLF is positively correlated with total ash, allowing ash detection in riverbed sediments and at depth in cores. The ratio of ash sphere composition is altered by river transport introducing variability in χLF. Measurement of χLF is inexpensive, non-destructive, and a reliable analytical tool for monitoring the fate of coal ash in this fluvial environment.

► Coal fly ash is composed of spheres (clear, orange, black) and amorphous particles. ► Black spheres dominate the magnetic susceptibility signal (χLF). ► The river sorts ash but maintains a ratio of clear: orange: black ash. ► χLF measurements can predict % ash spheres from simple linear regression. ► χLF can be used to track coal ash in the riverbed and in sediment cores.