1. Ash Recovery At Kingston Fossil Plant Kingston, Tennessee
Presented by:
Tim Harrington, P.E. - Hard Hat Services

2. Site History
Site is on the upper end of the Watts Bar Reservoir just north of Interstate 40.
The coal-fired generating station was constructed in the 1950’s.
The generating station draws cooling water from the Emory River and discharges to the Clinch River which in turn enters the Tennessee River.
Slack water from the Watts Bar Dam envelopes the mouth of both the Clinch and the Emory River.
Prior to the ash spill the main channel of the Emory River at the Site is approximately 30-feet deep.

3. Overall Site Location Map
River
Emory
Ash
Storage
Kingston
Power
Plant
Clinch
River

4. Fly Ash Storage History
Originally, ash was sluiced wet from the plant to a basin constructed in the Watts Bar Reservoir
The basin is contained by a clay dike that is raised three times to eventually impound 60-feet thickness of ash
Starting in the 1980’s, accumulating ash was dredged and stored in an engineered storage cell constructed on top of the filled basin
By late 2008, the storage cell reached 60-feet height and covered approximately 90 acres

5. Aerial Fall 2008 Prior to Ash Pond Release
Bottom ash removed in sluice trench
Fly ash settled in Ash Pond
Water quality obtained in stilling basin
Ash pond solids hydraulically dredged to ash storage cell
Emory River
Ash Storage Cell
Ash
Pond
Stilling
Basin
Sluice Trench
Plant Water Intake

6. Ash Release
Early morning of December 22, 2008 a dike failure near the northwest corner of ash storage results in static liquefaction of nearly 2/3 of the stored ash
The flowing ash water mixture flows into the Emory River moving both upstream and downstream
When the flow stopped, the main channel of the river was filled with ash
The Emory flows around the ash in a shallow area of the Watts Bar Impoundment

7. Aerial December 23, 2008 Day After Ash Spill
Main channel filled with over 30 feet of ash
Emory River flowing around the ash in shallow impounded water of Watts Bar Reservoir
Ash Storage Cell

8. What is Fly Ash?
Fly ash is the fine residue from the burning of coal that escapes with the combustion gas and is removed by air treatment equipment
With bottom ash it is 10% by weight of the coal at Kingston
The majority of fly ash is within the size range of 100 to 1 micron (fine sand and silt particle size)
The particles are spherical with some particles forming as hollow spheres known as cenospheres
Because of the cenospheres the solid specific gravity may be lower than for earth minerals (as low as 2.0)

9. Specific gravity of fly ash at Kingston in the 2.2 -2.4 range
Fly Ash Magnified 2000x
Fly Ash consists primarily of oxides of silicon, aluminum iron and calcium (85-90% by weight).
Magnesium, potassium, sodium titanium, and sulfur oxides make up most of the remaining weight with traces of heavy metals .
Specific gravity of fly ash at Kingston in the range
Source: Federal Highway Administration

10. Grain Size of Ash in Dredge Pipeline from Pilot Test
Grain Size Curve
SAND Sizes
SILT sizes
Grain Size of Ash in Dredge Pipeline from Pilot Test

11. Purpose of Ash Removal
Time Critical Removal was to open Main Thalweg of the Emory River
Non-Time Critical work on land and in embayments separated from Time Critical by a landside rock berm.
Opening river channel to approximate original contours was goal of removal
It was recognized that further dredging may be required in later stages of the ash recovery after completion of the Time Critical Removal

12. Emory River Dredging Segments
Segment 1: Ash Filled Full Channel
Segment 2: Full Channel but With Some Flotation Water
Segment 3: Underwater Rock Berm to Prevent Further Downstream Movement.
Segment 4 & 5: Thinning Ash Thickness with Flotation Water
Upland
Rock Berm

13. Time Line for Progress
It was considered time critical that the main channel be open by no later than Spring 2010.
Avoid impact from the Spring flood season of 2010.
Besides the logistics of dredging and dewatering the ash, the logistics of removing the ash from the site had to be resolved to complete the removal.
It was estimated that the time critical work involved million cubic yards of ash.

14. Ash Recovery by Hydraulic Dredging
Experience at the site was already good with hydraulic dredging for building the ash storage cell
It was believed that the ash would settle out quickly in a rim ditch removal method as was used to build the ash storage cell
The production rate using mechanical dredging was slower with the same level of manpower and equipment
The existing ash pond and sluice ditch were available for hydraulic operation

15. Pilot Test Operation
Pilot testing of concept to hydraulically dredge to a Rim Ditch started late March 2009 and ran through July 2009
Trans Ash of Cincinnati Ohio operated (3) Ellicott inch pump swinging ladder dredges with booster pumps
Rim Ditch 1,800-ft. long, 40-ft. wide and 10-ft. deep
Solids delivered to Rim Ditch at 4,000 dry tons per day
Total flow in Rim Ditch of 8,300 gpm (10 MGD)

16. Trans Ash Dredge
Dredges had twenty foot, twenty-five foot and thirty foot ladders

17. Rim Ditch and Sluice Trench
Rim Ditch prior to start of Pilot Dredging
Rim Ditch
Ball
Field Area

18. Ash Sampling Locations

19. Results of Pilot Test Average percent dry solids to the ditch 8.4%
Flocculent Settling Rate 14 in/hour
Solids Content after 12 hours of quiescent settling 65%
Rim Ditch removal rate of 90% when the flow was under 10,000 gpm
With higher flows more solids to the Sluice Trench
Constant agitation of the Rim Ditch by backhoe results in a thickened solids content of 30-35% in the water column of the ditch.

20. Settling Curve – Ash Pond Sample

21. Time Versus Concentration
65% Solids

23. Dredging Results
10-inch pump dredges were too small to complete the work within the timeline goals
Substantial problems with plugging from trees and other debris
Ash is very abrasive and results in heavy maintenance impact on operation.
Three 10-inch dredges moved on average 4,000 cubic yards per day
Problems with dredges from fast river currents
At end of pilot 375,000 cubic yards removed

24. Full Scale Dredging Operation
Competitive bidding to dredge at full-scale operation defined as completing 1.5 million cubic yards to open the main channel by February 28, 2010.
Required production rate of approximately 12,000 cubic yards per day 6-days per week
Competitive bidding for the work with Sevenson Environmental selected for the work.
Dredging equipment initially on site was one 20-inch cutterhead dredge and one 14-inch cutterhead dredge
Later supplemented with a 16-inch cutterhead dredge

25. Subcontracted by Sevenson to L.W. Matteson
20-Inch Dredge
Subcontracted by Sevenson to L.W. Matteson

26. 20-Inch Dredge Cutter Head
Approximately ft. diameter

27. Ellicott 670 owned by Sevenson
14-Inch Dredge
Ellicott owned by Sevenson

28. Full Scale Operations
20-inch River Dredge average 470 cubic yards per hour
16-inch dredge average 230 cubic yards per hour
14-inch dredge average 160 cubic yards per hour
Rim ditch is operated at twice its hydraulic capacity (on average 20 MGD)
Substantial solids carryover to sluice trench and ash pond

29. Sample Locations

30. Performance in Rim Ditch
Sample Point
Percent Solids
% Sand Size Ash
% Silt
Size Ash
Sand Size(tons/day)
Silt Size(tons/day) A
14.6 21 79
2500
9200 B
11.1 12 88
1080
7620 C
8.8
1.5
98.5
100
6700

31. Performance Metrics Hydraulic Structure Percent of Solids Retained
Rim Ditch
55%
Sluice Trench
11%
Ash Pond
34%

32. Observations
Rim Ditch operated at 20 MGD 100% above its hydraulic capacity determined during the pilot test
Efficiency of the Rim Ditch was reduced from the pilot operation and the fly ash pond was required to store ash
With the use of a coagulent, the stilling basin continued to produce acceptable water for discharge (permit limit average TSS of 29 ppm)
Using a dredge to remove ash from the fly ash pond and cycle back to the Rim Ditch provided little improvement of performance

33. Ash Pond Samples

34. Performance In Fly Ash Pond
P1 Sample With Depth
Sample ID
% Solids
(by weight)
(by volume)
[%]
P1-6 ft.
34.22
16.41
P1-8 ft.
44.60
23.3
P1-10 ft.
46.06
24.37
P1-12 ft.
47.62
25.54
P1-14 ft.
48.71
26.38
P1-16 ft.
53.37
30.16
Average
45.76
24.36

35. Performance In Fly Ash Pond
P2 Sample With Depth
Sample ID
% Solids
(by weight)
(by volume)
[%]
P2-6 ft.
37.93
18.74
P2-8 ft.
45.05
23.63
P2-10 ft.
46.93
25.02
P2-12 ft.
47.65
25.57
P2-14 ft.
49.24
26.79
P2-16 ft.
53.55
30.32
Average
46.72
25.01

36. Summary of Full Scale Performance
Ash Pond filled at rate of approximately 4,000 yd3/day (approximately 1/3 of the daily in-river dredge volume)
February 1, million cubic yards removed under full scale dredging
Ash Pond removal was undertaken in January to develop new pond capacity to complete Emory River removal goal
Goal of opening river channel is obtained with very little reserve capacity in ash pond

37. Thank You to Jacobs Engineering Group, Inc
Thank You to Jacobs Engineering Group, Inc. & Tennessee Valley Authority for Permission to Present at WEDA 2010 Midwest Chapter Annual Meeting