Kingston Ash Release
Emory River High-Flow Event
of May 4, 2009
On May 4, 2009 a heavy rainfall caused the rivers near the Kingston Fossil Plant to flow rapidly, and some ash, along with sand, sediments and other debris, was swept downstream from the main channel of the Emory River into the Clinch and Tennessee Rivers. TVA, TDEC and U.S. EPA are researching the incident, and we are using the information gained from this research thus far to make changes that will help us minimize movement of ash in the river in the future. Future steps include:
- TVA will keep the area in the vicinity of the intake channel and the near-by underwater weir below the ash spill as clear of ash as possible in order to help reduce ash and sediment movement in future high-flow events.
- TVA will continue to perform different model calculations of river flows throughout the system to help better understand how to dredge in a way that will reduce the possibility that ash will move downstream during high river flows.
- Improved understanding of how river flows affect the migration of ash will help TVA manage the Emory, Clinch, and Tennessee Rivers to reduce the impact of high-flow events on ash near the plant.
- In mid-June, EPA in coordination with TVA will contract with a company that provides a sub-bottom profiler, a piece of equipment that uses sonar to bounce sound waves off the bottom of the river to differentiate ash from river sediment and rock. The sub-bottom profiler will map the river bottoms from five miles upstream of the spill to the Tennessee River, about nine miles downstream of the spill. This will provide a more accurate baseline of the location of ash in the river than the former method of measuring only the topography of the river bottom. TVA will periodically use the sub-bottom profiler to take readings to watch for subtle changes in the river bottom.
The following describes the background of the rainfall event, the research that followed it, and the results of that research.
On May 4, 2009 a heavy rainfall (3-4 inches) in the Emory River headwaters caused the river to flow rapidly, up to a peak of nearly 70,000 cubic feet per second. The normal Emory River flow is between 700 and 1,300 cubic feet per second.
The high flows carried sand, sediments, and debris downstream. Along with sand and sediments from further upstream, ash from the main channel of the Emory River was swept downstream into the Clinch and Tennessee Rivers. By the afternoon of May 4, the Emory and the portion of the Clinch immediately downstream of the Emory was noticeably gray in color. The rest of the Clinch and the Tennessee River turned a muddy brown color, as is normal after rains.
Since May 4, TVA, TDEC, and the U.S. EPA have been collecting information to evaluate the extent of ash movement from the main spill area in the Emory River. Several approaches are being used, including:
- Collecting surface water samples as soon as it could be safely done after the high flows (performed by both TVA and TDEC on May 5).
- Conducting surveys to map the physical contours of the bottom of the river to compare with pre-May 4 bottom contours. This will determine where and how much the shape of the bottom of the river changed during the high flows due to deposits of sediment, mud, ash and debris.
- Collecting sediment samples in the Emory, Clinch, and Tennessee rivers to measure the depths of the redeposited materials and the composition (ash and sediment). These results will be compared to similar sampling performed in January 2009 as well as pre-spill data where available. This will determine how the ash migrated during the high flows.
In addition, TVA, along with EPA, is researching historical data on storm-related sediment transport in the Emory, Clinch, and Tennessee Rivers, and is having a contractor perform sediment transport modeling based on the May 4 flows. This work uses a complex series of mathematical formulas that predict how flows increase in these rivers after different amounts of rain and transport mud and sediments from the river bottom.
Some of the investigations are nearly complete—those results are discussed below. Others will take more time to complete. All together, these investigations help TVA, TDEC, and EPA evaluate where material moved and what actions can be taken to reduce ash movement during future high-flow events.
From the information that is available, we can draw the following conclusions:
- Sediment, mud, ash and debris moved downstream during the event. Exactly how much ash moved is difficult to determine since we do not have good information on how much river sediment (not ash) was washed in from areas further upstream on both the Clinch and Emory Rivers. However, the changes in bottom contours show that there were localized areas near the spilled ash where small amounts of a few inches up to several feet of material were picked up by the rushing waters, and areas downstream where material was deposited, increasing the bottom elevations by a few inches to a few feet.
- Most of the ash and other material washed downstream were re-deposited in the lower 1.5 miles of the Emory River. However, some ash was washed into the Clinch River.
- The areas immediately upstream and downstream of the underwater weir had several feet of ash scoured away due to the turbulent waters in the vicinity of the weir. The weir remained intact and the scour was localized around the weir. TVA will modify its dredging practices to keep those areas as clear of ash as possible in order to help minimize the amounts of ash washed downstream by future high-flow events.
- Small amounts of ash were washed long distances downstream. The sediment sampling showed small amounts of ash as far downstream as Tennessee River Mile 563.5, approximately 10 river miles downstream from the spill. Results were similar to the investigation conducted after a heavy rainfall event in January, 2009, when small amounts of ash were observed in the reach of the Tennessee River just downstream of Kingston.
- Chemical analysis results for river water samples collected May 5, one day after the highest flows and while the river was still in a moderately high-flow condition, showed that levels of suspended solids and turbidity were quite high on that date, as is typical of high flow. Despite the high concentrations of sediments suspended in the river, concentrations of arsenic, selenium, and mercury did not exceed state drinking water standards.
New information on river bottom contours is available, but TVA plans to collect additional data to improve the quality of that information for use in evaluating future high-flow events. Results of the investigation of historical data on sediment movement in these rivers and the mathematical modeling to predict sediment transport during storms are not yet available.
Page Updated June 16, 2009 3:19 PM