Kingston Ash Slide
Eckman Dredge and Visual Observations Survey
For Portions of the lower Emory River, Clinch River, and Tennessee River
Tennessee Valley Authority
May 22 and June 2, 2009
Report of Results
TVA sampled the substrate in the lower Emory, Clinch and Tennessee Rivers on Friday, May 22, 2009 and Tuesday, June 2, 2009 to supplement data obtained from TVA bathymetry measurements. Both the bathymetry and the substrate sampling were utilized to assess the additional extent of ash migration from the primary spill area in the Emory River that was caused by a high-flow event that occurred in the Emory River on May 4, 2009. The bathymetry data identified changes in river bottom elevations compared to previous bathymetric surveys. The substrate sampling provided additional visual data regarding the presence of ash on the river bottoms.
The observations are limited by the capacity of the dredges and their ability to penetrate the substrate. Where a sample containing all ash was collected, observed, and measured, it could not be determined to what extent the ash thickness was greater than the capacity of the dredge or depth of penetration. Those results are reported as “>” the recorded value. That situation would occur if the depth to which the dredge penetrated the substrate either (a) completely filled the dredge with ash, or (b) did not completely fill the dredge but also did not penetrate to the bottom of the ash. Situation (a) occurred for some of the upstream samples collected January 26, 2009. Situation (b) occurred for some May 22 and June 2 samples.
TVA had previously performed similar substrate sampling and visual observations on January 26, 2009 following a period of elevated Emory River flows. The main intent of the January survey was to document the presence or absence of ash in order to assess the extent of fly ash migration downstream from the spill. Eckman grab samples also were collected during that survey but often only at mid-channel and the thickness of the ash was estimated by visual inspection rather than by measurement.
The observations from the January survey are included in the data/observation summary. Note that the January survey was a single-point dredge drop at mid-channel. The May/June survey was performed along cross-channel transects with multiple drops, providing additional coverage.
- A small quantity of ash (1-6 mm in four of five samples) was found at Tennessee River Mile (TRM) 563. In January, a trace of ash (~12 mm) was found at TRM 564, with none observed at TRM 563. This indicates only a trace movement of ash one mile further down the Tennessee River.
- A surface layer of silt above the ash, ranging from <1mm to 10 mm, was observed in all samples collected on May 22 in the Emory, Clinch, and Tennessee Rivers. This indicates that the ash settled out more quickly than the natural river silt. It can be concluded that a significant amount of natural river sediment moved during the event. This silt deposition may explain the bathymetry results.
- In the lower Emory River (Emory River Miles 0.5, 0.3, and 0.1), the thickness of ash was found to increase from the west bank (shallow) to the east bank (deep). For all but two samples (on the east bank of Emory River Mile 0.5), a surface layer of silt was observed above the ash. The observations indicate that most of the ash deposition in this area occurred in the main river channel.
May 22, 2009
Grab samples were collected at eight locations (i.e., river miles) using Eckman dredges. The survey followed a left-bank descending (river mile) sequence. At each location, a line-of-sight transect was established across the width of the reservoir, and grab samples were collected at 5 to 10 equally-spaced points along each transect. Two concurrent Eckman grab samples were collected at each sample point; one from the left side of the boat and one from the right side of the boat. The contents of the Eckman samples were deposited side-by-side into a large pan for visual comparison and measurement of ash depth. A ruler was used to measure the total depth of the substrate collected and the total depth of the ash.
Approximate river miles of May 22, 2009 sample transects are summarized below.
June 2, 2009
Additional substrate was sampled in the lower Emory on June 2, 2009. Grab samples were collected at three locations using Eckman and handheld Ponar dredges. Ponar dredges were used to try to gain deeper penetration of substrate, but folding of the sampled material by this device and comparable results resulted in primarily using the Eckman dredges. Transects were established in the same manner as the May survey, with 10 points sampled along each. Two concurrent grab samples were collected, until it was determined (drop 3 at ERM 0.3) that substrate retrieved was similar for both Eckman and Ponar dredges. One Eckman was used for remainder of sampling. Contents of Eckman samples was measured and observed in the same manner as May survey.
Approximate river miles of June 2, 2009 sample transects are as follows:
May 22, 2009
The May survey documented ash at all river miles. The thickness of the ash in individual grab samples varied from 0 to >75 mm, with the thickness of the ash decreasing from upstream to downstream. All samples had a surface layer of silt above the ash that ranged in thickness from <1mm to about 10 mm.
Results were similar to those found on January 26, 2009, except at TRM 563.0. In January, a single sample was collected at TRM 563.0 and no ash was found. In May, grab samples were collected at 5 points across the channel at this location. In four of the five samples collected, the ash thickness was 1 mm or less; in one sample ash thickness was about 6 mm.
June 2, 2009
The June survey found thickness of ash to vary from 5 to >100mm, with thickness of the ash found to increase from the west bank to east bank of the Emory River. Samples along the east bank were nearly 100 percent ash and in defined layers, while samples collected on west bank were estimated to contain 90 percent organics/sand/sediment and mostly mixed ash and silt.
Attachment 3 provides detailed results for all observations.
Page Updated October 4, 2009 8:22 PM