United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-099 Jan. 1985
SEPA Project Summary
An Evaluation of the Disposal of
Flue Gas Desulfurization
Wastes in Coal Mines and the
Ocean: Mine Disposal
Demonstration Tests
Chakra J. Santhanam, James R. Valentine, and
Armand A. Balasco
This report gives results of an assess-
ment of a full-scale flue gas desulf uriza-
tion (FGO) waste disposal operation at
the Baukol-Noonan Mine near Center,
ND. FGD wastes from the alkaline fly
ash scrubbing system are disposed of in
the mine area in V-notches and in the pit
bottoms. A program of evaluating this
disposal operation consisted of place-
ment of monitoring wells, physical and
chemical sampling and analysis of
groundwater and wastes, and environ-
mental and engineering cost assessment.
The primary environmental effect
potential of FGD waste disposal in
mining may be in the generation of
leachates showing increased concentra-
tions of sulfate, sodium, magnesium,
and (to a lesser extent) calcium.
However, such FGD waste disposal
when properly practiced reduces poten-
tial effects of fly-ash-related leachate
generation. Placement of the FGD
wastes in V-notches appears preferable
to pit bottom disposal.
The capital cost for mine disposal of
FGD wastes (including thickening and
filtration prior to disposal) from a 438
MW (net) lignite-fired boiler is estimated
at about $10.85 million: the annual
operating cost is estimated at about
$10.70 per ton.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering in-
formation at back).
Program Purpose and Scope
This is a report on part of Phase III of a
project under EPA's Waste and Water
Program. The project consisted of investi-
gations of the feasibility of the disposal of
flue gas desulfurization (FGD) waste in
mines and at sea. In this program, the
FGD wastes studied were those from
non-recovery FGD systems and mixtures
of FGD wastes and coal ash.
Two earlier reports describe project
Phases I and II:
• Report EPA-600/7-77-051 gives
results of a preliminary assessment
of the environmental, technical,
regulatory, and economic aspects of
projected mine and at-sea disposal
operations.
• Report EPA-600/7-84-005 gives a
refinement of the preliminary assess-
ment based on additional evaluation
of selected impact issues identified
in the initial effort as requiring
further study.
The objectives of project Phase III,
described in this report, included monitor-
ing a full-scale FGD waste disposal op-
eration at the Baukol-Noonan mine near
Center, ND. The purpose was to evaluate
the environmental effects of full-scale
-------
FGD waste disposal in mines and develop
capital and operating costs of such
disposal operations.
This is the third (and final report) on
mine disposal and assesses the field
demonstration of a mine disposal opera-
tion. The mine supplies coal to and
receives waste from the Milton R. Young
Station, operated by the Minnkota Power
Cooperative.
Demonstration Project Descrip-
tion
The field studies were carried out at the
Center Mine, operated by Baukol-Noonan,
using FGD wastes from the Milton R.
Young Station, operated by the Minnkota
Power Cooperative near Center, ND.
There are two boilers, Units 1 and 2, at
this power plant; the latter, a 438-MW
(net) cyclone-fired boiler, has an FGD
system that uses alkaline fly ash from
both boilers as the principal source of
alkali for removal of sulfur oxides (SO*).
The FGD waste (as wet filter cake) was
transported to the mine area in rear-
dump trucks. To faciliate removal during
cold weather, boiler slag (3-4 tons) was
loaded into each truck to serve as a liner
for the 24-28 tons of FGD waste that was
subsequently added to the truck's load.
The FGD waste was placed in V-notches
(Vees) and pit bottoms.
The above waste disposal scheme
began in 1977, but was constantly
plagued with problems. Consequently, it
was decided to retire the thickener and
vacuum filter, and direct the scrubber
effluent directly to settling ponds for
dewatering. This interim pond/mine
disposal scheme has been in operation
since November 1981.
The environmental assessment part of
this project focussed on the original
operation. However, capital and operating
costs were estimated for both the orginal
and current process schemes.
The approach for environmental and
engineering/cost assessment involved a
series of sequential data gathering and
assessment steps designed to provide
both a data base and general guidance in
its assessment.
• Geological and geohydrological data
on the site and environs were
gathered during site development.
which included placement of water
wells and piezometers.
• Data on the composition and charac-
teristics of waters, wastes, and
geologic strata were obtained during
sampling and analysis.
• Using site data, data from the
laboratory tests, and existing back-
ground information on FGD wastes
and disposal effects, cause/effect
relationships are developed and
tested to fit the measured site data.
• The cause/effect hypotheses are
used to develop projects of the
generic implications of effects
observed at the test site to similar
FGD waste disposal scenarios.
Figure 1 shows the disposal-area location
of groundwater and leachate wells
installed after sludge disposal in the
bottom of the strip pit and in Vees formed
during removal of overburden (mining
spoil banks) from the strip pit.
Environmental Assessment
Table 1 provides an overview of some of
the data to illustrate the discussion of
environmental effects. Overall, it appears
Sludge Pit #3K
(Approx. Loc.-49 Loads)
Sludge Pit #3".0
(246 Loads)
Sludge Pit #20
tApprox. Loc.
101 Loads)
Sludge Pit #3M
Sludge 1*4*"" (139 Loads)
Pit #30 (Jft j
#32 Loads} J
Sludge Pit #3/V
(233 Loads)
Sludge Pit #3L
(106 Loads)
Sludge
Pit #20
(Approx. Loc.
157 Loads)
Sludge Pit n3H
(162 Loads)
Sludge Pit #2B
(255 Loads)
Sludge Pit H3A
(197 Loads)
Sludge
Pit #31
(49 Loads)
99 Sludge Pit #3B
21 (Second Lift is #3E)
(189 Loads)
Sludge Pit #3G
(40 Loads)
Sludge Pit #3F
(100 Loads)
Sludge Pit #3C
(41 Loads)
Sludge Pit #2A
(Approx. Loc.-233 Loads)
Sludge Pit 35L
(60 Loads)
Sludge Located in Vees
Sludge Located in Pit Bottom
I Piezometer (Well) Location
Approximate Mine Boundary
Figure 1. Location of groundwater and leachate wells installed after sludge disposal in Vees and dry pits.
2
-------
Table 1.
Well No.
99
94
79
102
Parameters of Interest for Wells Showing Evidence of FGD-Related Leachate
Chemical Analysis Data
Waste
Well
Locations
Vee 3C/
below waste
Vee 3F/
offset from
waste
Vee 3A/
below waste
Pit bottom
2B/below and
offset from
waste
Date
Sampled
3/27/80
6/09/80
9/09/80
3/27/80
6/09/80
9/09/80
6/09/80
9/09/80
3/27/80
6/09/80
9/09/80
Analyte Concentrations (mg/L)
Sulfate
4111
3811
3500
4917
3572
4980
1922
2891
1465
4343
5108
Sod/urn
960
1050
776
900
493
730
331
567
823
1845
2200
Magnesium
530
408
457
615
262
596
358
421
49.5
105
151
Calcium
215.5
393
331
195.3
307
404
215
416
65.8
186
560
Approximate Dates
Over-
Waste burden
Disposal Return
10/78 5/79
11/78 5/79
9/78 4/79
6/78 4/79
Data for Related Groundwater Wells-
76
Vee 3L/
below waste?
Aver age of
Aver age of
wells
Aver age of
wells
"spoils wells"
"below Hagel"
"Hagel Bed"
6/09/80
9/09/80
1978-79
1978-79
1978-79
222
148
1455
1217
668
322
377
361
568
297
34
30
232
80.4
74.3
65
58
348
153
105
3/79 5/79
that placement of FGD wastes from
alkaline-fly-ash FGD systems will result
in generation of liquors and leachates
which show increased concentrations of
sulfate, sodium, magnesium, and (to
some extent) calcium when compared
with the original coal bed. Of these, the
sulfate (and, consequently, total dissolved
solids—IDS) will be substantially above
drinking water limits (250 and 10,000
mg/L, respectively). At the same time,
the results indicate that, for FGD wastes,
trace elements in leachates are likely to
be within the allowable range for drinking
water.
The concentration of sulfate and
magnesium found in the groundwater
well samples are substantially lower than
the compositions of undiluted FGD waste
porewater. Sodium concentrations are
also lower than porewater except in the
pit bottom location where higher sodium
and correspondingly lower magnesium
concentrations may be the result of ion
exchange. Calcium appears to be under
solubility control by sulfate. These data
suggest two possible scenarios related to
FGD waste leaching: either the ground-
water (even near the waste) is a mixture
of waste leachate and other infiltrating
groundwater which bypassed or "chan-
neled" through the waste; or the contact
of infiltrating groundwater does not
'provide as efficient an extraction of
solubles as predicted by the laboratory
leaching column tests. While the cause
cannot be ascertained, for Vee disposal,
the net effect is the same: such disposal
may not result in the appearance of a
"plug" of full-strength FGD-waste pore-
water in the groundwater. Data for pit
bottom placement suggest that the
leachate concentration (i.e. the fraction of
leachate) is higher than for the Vees.
Data indicate that the major impact on
groundwater from FGD wastes generated
at the Milton R. Young plant stems from
the high concentrations of sulfate, and
those portions of other major species
which contribute to the dissolved solids.
These TDS contributors are present in the
wastes as soluble species readily available
for leaching.
A University of North Dakota study
(outside the scope of this study) also
focussed on characterization and assess-
ment of the environmental effects relating
to the disposal of alkaline fly ash itself.
This phase of the investigation indicates
that, in the absence of a working FGD
system, the alkaline ash was disposed of
in a mine in the same manner as the FGD
wastes. In contrast to FGD wastes,
alkaline fly ash appears to have a rather
significant potential to impact the environ-
ment, particularly in trace metal mobility.
Although the primary purpose of fly-ash
FGD systems is to reduce atmospheric
S02 contamination, the results indicate
that a potential secondary benefit of this
method of FGD is the conversion of fly ash
from a form that can cause groundwater
to acquire severe toxicity because of high
arsenic and selenium levels to a form that
causes increased sulfate concentrations
but generally no significant increases in
the more toxic elements. Placement of
these wastes in Vees appears to be highly
preferable to bottoms in most areas. Vees
are commonly above the postmining
watertable, and thus offer much less
opportunity for the dissolution and
leaching of soluble salts present in these
waste products.
Engineering/Cost Assessment
The original and current waste disposal
schemes are shown in Figures 2 and 3,
respectively. The original waste handling/
processing/disposal system, in operation
about 4 years at the Milton R. Young
plant, consisted of thickening and vacuum
filtering the fly ash/FGD scrubber
effluents from about 15 to about 65 wt%
solids. From the vacuum filter, the 65
wt% fly ash/FGD waste was directed by
belt conveyor to one of two surge bins.
The surge bins acted as temporary
storage for the waste until it was loaded
onto 35-ton coal haul trucks. These
trucks transported the waste to Baukol-
Noonan's Center Mine, about 5 miles
-------
From FCC
Scrubbers
Sludge
Thickener
Thickener
Overflow Tank
To FGD Scrubber
Thickener
Overflow Pump
Ftotary Drum Filter
Cake Wash Pumpp
Si
Thickener
Underflow Pump
Rota
Vacu
"^
\
ry Drum
jm Filter
. ^
1
/
jn
Screw Distributor
Rotary Drum Filtrate
Recycle Pump
FGD
Waste
Surge
Bin
Rotary Drum
Filter
Vacuum Pump
Emergency FGD Waste
Storage Area
To Mine for
Disposal
Dump Truck
Figure 2. Original Milton Ft. Young FGD waste processing/interim storage/transport (1977-78).
from the plant. At the mine, the waste
was deposited as a relatively dry soil-like
material in either: (a) pit bottoms prior to
the return of overburden; or (b) spoil
banks (Vees) before rough contouring.
The current scheme, shown in Figure
3, eliminates thickening and filtration.
Instead, the scrubber effluent is ponded
directly. Table 2 summarizes capital costs.
Tables 3 and 4 provide the basis for, and
summarize, annual operating costs for
both original and current schemes.
Mine disposal appears to be among the
lowest cost methods of FGD waste
disposal. In generic terms, mine disposal
may be 20-25% less expensive than
disposal in managed fill due to lower land
and mobile equipment costs; additionally,
reclamation is a normal part of mine
operation with or without waste disposal
and hence not charged to disposal
operation (since it is required in any case).
-------
Pond Effluent
Recycle Structure
From FGD
Scrubbers o
-JMXt-
Slowdown
Sump/Pump
Sludge
Pipeline
To Sludge
Thickener
(Original Scheme)
To Sludge
Thickener
Overflow Tank
(Original Scheme)
Pond Effluent
Recycle Structure
To Mine
for Disposal
Front End
Loader
(for Pond Dredging)
Dump Truck
Figure 3. Current Milton R. Young FGD waste handling/interim storage/transport (1980-81).
Table 2. Capital Costs — FGD Waste Disposal
Basis: 1. Operation of Baukol-Noonan Mine disposal.
2. All costs in 1981 dollars.
3. Unit 2 (438 MW net. cyclone-fired)
uses North Dakota lignite and has aklaline-fly-ash-based FGD system.
No.
1.
2.
Detail
Handling,
processing, and
storage
Transportation,
placement, and
disposal
Original
Scheme
Thickeners with
auxiliaries
Rotary vacuum
filter with
auxiliaries
Surge bin
By-pass con-
verger
Truck, loader
Dozers and
graders
Capital
Cost
$1000
10.000
850
Current
Scheme
Slowdown pump
and auxiliaries
Sewage Pond
Pipeline and
access road
Effluent recycle
lime
Dredging equipment
Capital
Cost
$1OOO
4.500
850
Total cost
10.850
5.350
-------
Table 3. Waste Disposal Engineering Operating Basis
Mi/ton Ft. Young (Unit 2)
Boiler
Capacity, MW
Annual load factor, %
Heat rate, Btu/kWh
Fly ash/bottom ash ratio
Coal
Heating value, Btu/lb
Sulfur content, %
Ash content. %
Emission Control
SOi removal, %
Paniculate removal, %
Wastes Generated
Fly ash*, tons/yr
FGD sludge, tons/yr
Total FGD waste, tons/yr
Total FGD waste, tons/yr
476
90
10.000
35/65
6,422
0.64
9.74
60
99+
157.300
58.475
217.775
332.00O
(dry basis)
(wet basis)
"Includes fly ash from Units 1 and 2, since fly ash from Unit 1 is used in alkaline fly ash scrubbing
operation. Capacity of Unit 1 is 265 MW.
Table 4. Annual Operating Cost Summary*
($ 1000s/year)
Original Scheme
Current Scheme"
Direct Costs
• Operating/ supervisory labor
• Maintenance (labor and materials)
• Utilities
- Water (@ $0.01/1000 gal.)
- Electricity (@ $0.03/kWh)
- Diesel fuel (@ $0.95/gal.)
$417.2
354.0
0.3
156.0
255.7
$496.8
214.0
0.3
54.0
332.4
Indirect Costs
• Plant overhead (@ 50% direct costs minus electricity)
• Administrative overhead (@ 16.5% of total capital cost)
• Capital charges (@ 16.5% of total capital cost)
Total Annual Operating Cost
• ($1000s/year)
• ($/ton)
513.6
59.4
1798.5
521.3
60.3
891.0
$3554.7
$ 10.70
$2570.1
$ 7.75
*ln 1981 Dollars.
"Thickening/Vacuum Filtration/Mine Disposal—Milton R. Young (Unit 2)
^Interim Ponding/Mine Disposal—Milton R. Young (Unit 2)
U. S. GOVERNMENT PRINTING OFFICE: 1985/559-111/10777
-------
C. J. Santhanam, J. R. Valentine, and A. A. Balasco are with Arthur D. Little. Inc.,
Cambridge, MA 02140.
Julian W. Jones is the EPA Project Officer (see below/.
The complete report, entitled "An Evaluation of the Disposal of Flue Gas
Desulfurization Wastes in Coal Mines and the Ocean: Mine Disposal Demon-
stration Tests," (Order No. PB 85-137 081; Cost: $26.50, subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
OCOC329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 S DEAR8CRN STREET
CHICAGO IL 60
------- |