Presented by:Tim Harrington, P.E. - Hard Hat Services

Ash RecoveryAt

Kingston Fossil PlantKingston, Tennessee

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.

KingstonPowerPlant

AshStorage

Clinch

Emor

y

River

Overall Site Location MapRiver

Fly Ash Storage HistoryOriginally, 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

AerialFall 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 Rive

r

Ash Storage Cell

Plant Water Intake

AshPond Stilling

Basin

Sluice

Trenc

h

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

Ash Release

AerialDecember 23, 2008Day 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

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)

What is Fly Ash?

Fly Ash Magnified

2000xFly 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

Grain Size of Ash in Dredge Pipeline from Pilot Test

SILT sizes

SAND Sizes

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

Purpose of Ash 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.

Time Line for Progress

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

Ash Recovery by Hydraulic Dredging

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 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)

Pilot Test Operation

Trans Ash Dredge

Dredges had twenty foot, twenty-five foot and thirty foot ladders

Rim Ditchand

Sluice Trench

Rim Ditch prior to start of Pilot

Dredging

BallField Area

Sluice Trench

Rim Ditch

Ash Sampling Locations

Average percent dry solids to the ditch 8.4%Flocculent Settling Rate 14 in/hourSolids Content after 12 hours of quiescent

settling 65%Rim Ditch removal rate of 90% when the flow

was under 10,000 gpmWith higher flows more solids to the Sluice

TrenchConstant agitation of the Rim Ditch by backhoe

results in a thickened solids content of 30-35% in the water column of the ditch.

Results of Pilot Test

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

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Time (Hours)

Dep

th to

Inte

rfac

e (In

ches

)

Floc

cule

ntSe

ttlin

g

No

Settl

ing

Hin

dere

dSe

ttlin

g

Settling Curve – Ash Pond Sample

Time Versus Concentration

0.010 0.100 1.000 10.000 100.000 1000.000 10000.0001.0%

10.0%

100.0%

ConcentrationTime, Hours

Con

cent

ratio

n, %

sol

ids

65% Solids

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

Dredging Results

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

Full Scale Dredging Operation

20-Inch Dredge

Subcontracted by Sevenson to L.W. Matteson

20-Inch Dredge Cutter Head

Approximately 4.5-ft.

diameter

14-Inch DredgeEllicott 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

Full Scale Operations

Sample Locations

Sample Point

Percent Solids

% Sand Size Ash

% SiltSize 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

Performance in Rim Ditch

Hydraulic Structure Percent of Solids Retained

Rim Ditch 55%

Sluice Trench 11%

Ash Pond 34%

Performance Metrics

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

Observations

Ash Pond Samples

Performance In Fly Ash PondP1 Sample With Depth

Sample ID% Solids % 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

Performance In Fly Ash PondP2 Sample With Depth

Sample ID% Solids % 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

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

Summary of Full Scale Performance

Thank Youto

Jacobs Engineering Group, Inc.&

Tennessee Valley Authorityfor

Permission to Presentat

WEDA 2010Midwest Chapter Annual

Meeting