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

Abstract

An estimated 229,000 m(3) 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 (χ(LF)) and percent frequency dependent susceptibility (χ(FD)%) to be used to discriminate between coal fly ash and sediments native to the watershed. Riverbed samples with χ(LF) greater than 3.0 × 10(-6) m(3)/kg, have greater than 15% ash measured by optical point counting. χ(LF) 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 χ(LF). Measurement of χ(LF) is inexpensive, non-destructive, and a reliable analytical tool for monitoring the fate of coal ash in this fluvial environment.

Characterization of coal ash released in the TVA Kingston spill to facilitate detection of ash in river systems using magnetic methods

“…Magnetospheres average 10 lm in diameter [8] but range from a few microns to 50 lm. BSE images show different types of bright surface textures on dark spheres (Fig.…”

“…The slide was fixed using Loctite Gel Control Superglue. Five hundred points were counted at 200Â magnification using a Zeiss Point Counter mounted on a petrographic microscope [8]. Following our previous PLM methods we identified particles as spherical or non-spherical.…”

“…Samples with v LF 6 1.0 Â 10 À7 m 3 /kg were devoid of ash or had negligible ash content, and samples with v LF > 3.0 Â 10 À6 m 3 /kg were composed of greater than 15% ash. Samples with v LF P 1.0 Â 10 À5 m 3 /kg were composed of >80% ash [8]. In the initial study, we identified that the magnetic component occurred within the spherical fraction of coal ash but we could not determine from statistical analysis of the bulk samples whether it was preferentially within the black, orange, or clear spheres.…”

“…Within the area affected by the spill, we determined that v LF is positively correlated with the measured percent total ash determined with PLM in the Watts Bar Reservoir system [8]. Samples with v LF 6 1.0 Â 10 À7 m 3 /kg were devoid of ash or had negligible ash content, and samples with v LF > 3.0 Â 10 À6 m 3 /kg were composed of greater than 15% ash.…”

“…We have demonstrated that a time efficient and cost effective method of distinguishing ash from background watershed sediment could be developed by measuring the mass-normalized low field magnetic susceptibility (v LF ) of riverbed sediment [8].…”