 Site is on the upper end of the Watts Bar Reservoir just
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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.
Ash
Storage
Kingston
Power
Plant
River
 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
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 Storage Cell
Ash
Pond
Plant Water Intake
Stilling
Basin
Ash pond solids
hydraulically
dredged to ash
storage cell
 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
Aerial
December
23, 2008
Day After Ash
Spill
Main channel filled
with over 30 feet of
ash
Ash Storage Cell
Emory River flowing
around the ash in
shallow impounded
water of Watts Bar
Reservoir
 Fly ash is the fine residue from the burning of coal that
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
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)
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
2.2 -2.4 range
Source: Federal Highway Administration
Grain Size Curve
SAND Sizes
SILT sizes
Grain Size of Ash in Dredge Pipeline from Pilot Test
 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
Emory River
Dredging
Segments
Upland
Rock Berm
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
 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
3.0 million cubic yards of ash.
 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
 Pilot testing of concept to hydraulically dredge to a
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Rim Ditch started late March 2009 and ran through
July 2009
Trans Ash of Cincinnati Ohio operated (3) Ellicott 370
10-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)
Trans Ash
Dredge
Dredges had twenty
foot, twenty-five foot
and thirty foot
ladders
Rim Ditch
and
Sluice Trench
Rim Ditch prior to
start of Pilot
Dredging
Ball
Field Area
Ash Sampling Locations
 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.
10.0
30.0
50.0
60.0
No Settling
40.0
Hindered
Settling
Depth to Interface (Inches)
20.0
Flocculent
Settling
0.0
70.0
80.0
0:00
3:00
6:00
9:00 12:00 15:00 18:00 21:00 24:00 27:00 30:00 33:00 36:00 39:00 42:00 45:00 48:00 51:00 54:00
Time (Hours)
100.0%
Concentration, % solids
65% Solids
10.0%
1.0%
0.010
0.100
1.000
10.000
100.000
1000.000
10000.000
Time, Hours
Concentration
 10-inch pump dredges were too small to complete the
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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
 Competitive bidding to dredge at full-scale operation
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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
20-Inch
Dredge
Subcontracted by
Sevenson to L.W.
Matteson
20-Inch
Dredge
Cutter Head
Approximately
4.5-ft. diameter
14-Inch
Dredge
Ellicott 670
owned by
Sevenson
 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
Sample Locations
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
Hydraulic Structure
Percent of Solids Retained
Rim Ditch
55%
Sluice Trench
11%
Ash Pond
34%
 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
% Solids
(by weight)
[%]
% Solids
(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
45.76
24.36
Sample ID
Average
% Solids
(by weight)
% Solids
(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
46.72
25.01
Sample ID
Average
 Ash Pond filled at rate of approximately 4,000
yd3/day (approximately 1/3 of the daily in-river
dredge volume)
 February 1, 2010 1.5 million cubic yards removed
under full scale dredging
 Ash Pond removal was undertaken in January 2010
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