Content uploaded by Mikko Lamminen
Author content
All content in this area was uploaded by Mikko Lamminen
Content may be subject to copyright.
Long-Term Behavior of Fixated Flue Gas Desulfurization
Material Grout in Mine Drainage Environments
Panuwat Taerakul1; Mikko Lamminen2; Yontian He3; Harold W. Walker, M.ASCE4; Samuel J. Traina5;
and Earl Whitlatch, M.ASCE6
Abstract: In this research, we examine the long-term (⬃4 years兲behavior of fixated flue gas desulfurization 共FGD兲material grout
following placement within the Roberts–Dawson underground coal mine. Surface water and groundwater samples were collected to
examine the impact of grouting on water quality, and core samples were obtained to assess the geochemical stability of the grout material.
Surface water samples collected from the main seep at the Roberts–Dawson mine indicated that 4 years after grout placement the
long-term fluxes of acidity, iron, sulfur, and calcium were slightly elevated compared to pregrout conditions. The long-term discharge of
these constituents was likely due to continued dissolution of grout material 共for Ca and S兲as well as changes in flow paths and subsequent
solubilization of metal salts accumulated within the mine voids 共for acidity, Fe, Al, and S兲. Although the fluxes of these elements were
elevated, no measurable deleterious impact was observed for the underlying groundwater or adjacent surface water reservoir. Groundwater
samples collected from monitoring wells installed within the grout material indicated that acid mine drainage waters were neutralized by
the grout material. Mineralogical analyses demonstrated minimal penetration of mine drainage water into the high strength fixated FGD
material grout, and little weathering of the material was observed. These data indicate that the high strength fixated FGD material grout
injected into the Roberts–Dawson mine was geochemically stable and could locally neutralize mine drainage waters. However, more
complete grouting and more extensive mine flooding is likely needed in order to bring about significant improvements in seep water
quality.
DOI: 10.1061/共ASCE兲0733-9372共2004兲130:7共816兲
CE Database subject headings: Acid mine water; Grouting; Drainage; Coal mines; Ground water pollution.
Introduction
The removal of sulfur oxides from coal combustion flue gas re-
sults in the production of over 25 million metric tons of flue gas
desulfurization 共FGD兲material every year 关American Coal Ash
Association 共ACAA兲2001兴. Flue gas desulfurization material is
the residual product of an FGD process with varying physical and
chemical characteristics depending on the FGD process used. In a
lime-based, wet FGD process, the resulting product consists of a
wet thixotropic sludge composed primarily of calcium sulfite, cal-
cium sulfate and water 共ACAA 2003兲. For handling purposes, this
material is often dewatered and stabilized with fly ash and lime,
and the resulting material termed ‘‘fixated FGD material.’’
Although a number of beneficial uses for FGD material are
available 共for a review, see Walker et al. 2002a兲, including the
production of FGD–gypsum for wallboard 共Drake 1997兲, amend-
ment of minespoil for abandoned mine land reclamation 共Stehou-
wer et al. 1995a,b兲, the replacement of clay in low-permeability
liners 共Butalia and Wolfe 1997; Wolfe and Butalia 1998兲and pads
for animal feed lots 共Wolfe and Cline 1995兲, the majority of this
material 共82%兲is disposed of in landfills 共Kalyoncu 1999兲. Be-
cause coal mines are often located near coal-fired power plants
and available landfill space is declining, there is interest in the
disposal of FGD material in deep mines following removal of
coal. Furthermore, placement of FGD material and other coal
combustion byproducts 共CCBs兲in deep mine environments may
potentially reduce the production of acid mine drainage if the
conditions that lead to acid mine drainage 共AMD兲are reduced or
eliminated 共e.g., exposed pyrite and the presence of water and
oxygen兲.
In a 1999 Report to Congress 关United States Environmental
Protection Agency 共U.S. EPA兲1999兴, the U.S. EPA recommended
that the disposal of fixated FGD material and other CCBs be
exempt from regulation as a hazardous waste under the Resource
Conservation and Recovery Act, Subtitle C. However, the recom-
mendation specifically excluded the placement of CCBs in deep
mine environments, indicating that regulation as a hazardous
1Graduate Research Assistant, Dept. Civil and Environmental Engi-
neering and Geodetic Science, The Ohio State Univ., 470 Hitchcock Hall,
2070 Neil Ave., Columbus, OH 43210. E-mail: taerakul.1@osu.edu
2Graduate Research Assistant, Dept. Civil and Environmental Engi-
neering and Geodetic Science, The Ohio State Univ., 470 Hitchcock Hall,
2070 Neil Ave., Columbus, OH 43210. E-mail: lamminen.1@osu.edu
3Graduate Research Assistant, School of National Resources, The
Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210. E-mail:
he.51@osu.edu
4Associate Professor, Dept. Civil and Environmental Engineering and
Geodetic Science, The Ohio State Univ., Columbus, 470 Hitchcock Hall,
2070 Neil Ave., Columbus, OH 43210. E-mail: walker.455@osu.edu
5Director, Sierra Nevada Research Institute, Univ. of California, P.O.
Box 2039, Merced, CA 95344. E-mail: sam.traina@ucop.edu
6Associate Professor, Dept. Civil and Environmental Engineering and
Geodetic Science, The Ohio State Univ., 470 Hitchcock Hall, 2070 Neil
Ave., Columbus, OH 43210. E-mail: whitlatch.1@osu.edu
Note. Associate Editor: Mark J. Rood. Discussion open until Decem-
ber 1, 2004. Separate discussions must be submitted for individual pa-
pers. To extend the closing date by one month, a written request must be
filed with the ASCE Managing Editor. The manuscript for this paper was
submitted for review and possible publication on September 25, 2002;
approved on June 23, 2003. This paper is part of the Journal of Envi-
ronmental Engineering, Vol. 130, No. 7, July 1, 2004. ©ASCE, ISSN
0733-9372/2004/7-816–823/$18.00.
waste under Subtitle C may be warranted for minefilling applica-
tions based on potential risks. The report noted that acid mine
drainage in deep mine environments may consume the acid neu-
tralizing capacity of the CCBs and result in prolonged release of
contaminants. Further, placement of CCBs in deep mines located
beneath a regional water table could result in contamination of
drinking water supplies. Prior to a final determination, the U.S.
EPA recommended that more information be gathered related to
the risks associated with the placement of CCBs in deep mine
environments.
In a previous paper 共Lamminen et al. 2001兲, we described the
short-term (⬃1 year兲impacts associated with the injection of
fixated FGD material grout at the Roberts–Dawson underground
coal mine. The fixated FGD material grout consisted of fixated
FGD material with added water. Immediately following grout in-
jection, increases in the concentration of acidity,Al, B, Ca, Co, K,
Li, Fe, Mg, Mn, Ni, Pb, S, Si, Sr, and Zn were observed in surface
water seeps as well as groundwater wells installed within the coal
layer. Field data and geochemical equilibrium speciation model-
ing suggested that the increase in concentration of a number of
these parameters was due to rerouting of mine drainage water
within previously inaccessible voids and the subsequent dissolu-
tion of accumulated solids, as well as the dissolution of fixated
FGD material grout. Following this initial increase, however, the
levels of these elements began to decline. While these data indi-
cated placement of fixated FGD material grout at the Roberts–
Dawson mine resulted in short-term degradation of water quality,
the long-term behavior of this material at the site remained un-
known.
In this paper, we report on the long-term impacts related to the
placement of fixated FGD material grout at the Roberts–Dawson
mine. Water quality monitoring was carried out for 4 years fol-
lowing the placement of fixated FGD material grout to assess the
impact of grouting on the groundwater in the immediate vicinity
of fixated FGD material grout, groundwater within the regional
aquifer, and surface water surrounding the site. In addition, core
samples were collected to examine the physical properties and
geochemical stability of fixated FGD material grout after pro-
longed exposure to AMD. These water quality and mineralogical
data provide important new information for assessing the risk
associated with the placement of fixated FGD material grout in
deep mine environments.
Site Description
This study was carried out at the Roberts–Dawson mine, a site
spanning an area of 0.059 km2共14.6 acres兲located in central-
eastern Ohio. The mine was closed in the 1950s following the
removal of approximately 6⫻104m3of coal. The hydrogeology
of the site was extensively characterized 共Bair and Hammer 1999兲
and consists of a perched aquifer in the Freeport Sandstone over-
lying the middle Kittanning 共No. 6兲coal layer which is 1–2 m
thick. The middle Kittanning No. 6 coal layer forms a second
perched water table overlying the regional water table within the
Clarion Sandstone 共see Fig. 1兲. The strike of the face and butt
cleats of the Kittanning coal are N10-20°E and N70-80°W, re-
ceptively 共Ver Steeg 1942兲.
Fig. 2 shows a map of the known mine voids in relation to the
main seep and adjacent receiving stream at the Roberts–Dawson
site. Fixated FGD material grout was injected into the down-dip
portions of the Roberts–Dawson mine between October 1997 and
January 1998 共Walker et al. 1999, 2002b兲. Two types of fixated
FGD material grout were injected into the mine: a high strength
grout and a low strength grout. The high strength grout was in-
jected into the shaded regions shown in Fig. 2, while the lower
strength grout was injected into the unshaded areas. Borehole
cameras used at the time of injection indicated that the high
strength grout effectively filled mine voids, at least within the
vicinity of the injection wells. The lower strength grout, on the
other hand, flowed over a more extensive area, coating exposed
pyritic surfaces but not filling mine voids. The design strengths of
the low strength and high strength FGD material grouts were 520
kPa (75 lbs/in.2) and 1,000 kPa (145 lbs/in.2) after 91 days, re-
spectively 共Damian and Mafi 1999兲. Laboratory testing of actual
grout mixes after 90 days yielded strengths of 1,180⫾500 and
1,960⫾651 kPa for the low and high strength grouts, respectively
共Wolfe and Butalia 1999兲; roughly twice the required design
strength. Fixated FGD material grout was also injected into lim-
Fig. 1. Representative geological cross section of Roberts–Dawson
site
Fig. 2. Site location and description
ited areas of the unmapped portion of the mine. A total of
18,182 m3of grout was injected through 317 boreholes 共Damian
and Mafi 1999兲.
The fixated FGD material grout injected at the Roberts–
Dawson site was a 1.25:1 mixture, on a dry mass basis, of class F
fly ash and dewatered scrubber sludge with an additional 5% lime
共CaO兲. The grout consisted primarily of calcium, silicon, iron,
sulfur, and aluminum 共Laperche and Traina 1999a,b兲. Minor ele-
ments also present in the grout included Sb, As, Ba, Be, B, C, Cr,
Cd, Cu, Pb, Mn, Ni, K, Na, Se, St, and Zn. The primary mineral
phases of the unweathered grout, detected by x-ray diffraction,
were hannebachite (CaSO3"1
2H2O), mullite (Al6Si2O13), quartz
(SiO2), hematite (Fe2O3), magnetite (Fe3O4), glass, and ettring-
ite (Ca6Al2(SO4)3(OH)12"26H2O) 共Laperche and Traina 1999a兲.
The high and low strength grouts varied only in water content.
The higher strength grout had lower water content to produce a
slump of 16–24 mm 共4–6 in.兲, while the lower strength grout had
greater water content and a slump of 31–39 mm 共8–10 in.兲
共Damian and Mafi 1999兲. Preliminary laboratory studies indicated
that the grout could neutralize acid mine drainage from the
Roberts–Dawson site 共Walker et al. 1999兲.
Materials and Methods
Sampling Locations and Techniques
Sampling of surface water and groundwater was carried out at the
Roberts–Dawson site before and after grouting. The major seep
discharging AMD from the known mine voids at the Roberts–
Dawson site is shown as Site 5 in Fig. 2. There was an additional
seep 共not shown on Fig. 2兲just south of Site 5 which drained the
unmapped portion of the mine. The seeps discharged into a re-
ceiving stream and flowed into a collection pond. Acid mine
drainage exited the collection pond and discharged through a cul-
vert to Wills Creek Reservoir. Flow at Site 5 consisted of seepage
over a large area, so flow measurements were calculated as the
difference in the upstream and downstream flow rates in the ad-
jacent stream. Stream flow rates were measured using the ‘‘bucket
and stopwatch’’technique for low flow rates and weirs installed at
the site for high flow rates. Water samples were taken at Site 5 by
collecting the most significant flow of drainage emerging in the
vicinity of the original mine opening and seep. Water samples
were collected on the opposite side of the reservoir 共sampling Site
12兲relative to the Roberts–Dawson AMD discharge point to as-
sess water quality impacts to Wills Creek Reservoir.
Surface water samples were collected using disposable 60 mL
Luer–Lok syringes 共Becton Dickinson, Franklin Lakes, N.J.兲and
placed in 60 mL polypropylene bottles. Samples were filtered
on-site with 0.45 m disposable sterile cellulose acetate mem-
brane filters 共Corning, Wilmington, N.C.兲to analyze for dissolved
constituents.
Groundwater monitoring locations are also shown in Fig. 2.
Well 9727 was installed prior to grouting operations in the lower
Clarion sandstone layer, 55 m below the ground surface and 29 m
below the Kittanning No. 6 coal layer. Well 9719 was also in-
stalled prior to grouting operations. This well was located in a
pillar of the Kittanning No. 6 coal layer.
Core samples were collected at the site of wells 9901, 9904,
9906, and 2002, 2–3 years after injection of fixated FGD material
grout. After collection of core samples, monitoring wells were
installed. Wells 9901, 9904, and 2002 were located in the down-
dip portions of the mine voids near the main seep 共surface water
Site 5兲. Well 9906 was located on the northwest edge of the
Roberts–Dawson site, near a grout injection hole that took
840 m3of low strength grout. Only core samples collected from
Wells 9906 and 2002 were confirmed to contain fixated FGD
material grout.
Wells 9719, 9727, 9901, 9904, and 9906 were constructed
with 5.1 cm 共2 in.兲schedule 40 PVC pipe in conformance with
ASTM standard D 5787-95. Monitoring well 2002 was installed
with 20 ft of 15.7 mm 共4 in.兲diameter PVC casing seated into the
top of rock with the remaining hole completed as an open bedrock
well.
Water levels in groundwater wells were measured with a
Heron™ water level probe 共Hamilton, Ohio兲. Prior to sample col-
lection, wells were purged using either dedicated submersible
Redi-Flow™ pumps 共Ben Medows Company, Canton, Ga.兲or by
using a Reel E-Z™ portable well pump 共Redmond, Wash.兲. Some
wells were purged manually using disposable 1 L, high-density
polyethylene bailers 共Timco Manufacturing, Prairie Du Sac, Wis兲.
Filtered and unfiltered samples for metals analysis, surface
water and groundwater, were acidified to 10% 共volume/volume兲
acid concentration using ultra pure nitric acid. After collection,
samples were stored either in a cooler or cold room (4°C) until
analysis.
Chemical Analysis of Water Samples
Surface water and groundwater samples were analyzed for pH,
conductivity, sulfate, arsenic, chloride, alkalinity, metals, and
other inorganic constituents. pH was measured using a Model
525A pH meter 共Thermo Orion, Beverly, Mass.兲, either in the
field or in the laboratory. Conductivity was measured in the labo-
ratory using a digital conductivity meter 共Fisher Scientific, Su-
wanee, Ga.兲. Alkalinity was determined by titration or by using a
Lachat Quickchem AE Autoanalyzer 共Milwaukee, Wis.兲. Chloride
and sulfate were determined using either the Autoanalyzer or an
Ion Chromatograph 共Dionex Corporation, Sunnyvale, Calif.兲.
The concentration of arsenic in surface water and groundwater
was determined using a Perkin–Elmer graphite furnace atomic
absorption 共GFAA兲spectrometer 共Norwalk, Conn., Model
4100XL兲or a Varian SpectraAA 880 zeeman GFAA spectrometer
共Walnut Creek, Calif.兲. Analyses for Al, Ba, Be, B, Cd, Cr, Ca, Cr,
Co, Cu, Fe 共total and dissolved兲, Pb, Li, Mg, Mn 共total and dis-
solved兲, Mo, Ni, P, K, Si, Na, Sr, S, and Zn were carried out using
an Inductively Coupled Plasma Optical Emission Spectrometer
共ICP-OES兲at the Ohio Agricultural Research and Development
Center STAR Laboratory in Wooster, Ohio, or in the Environmen-
tal Engineering Laboratory at the Columbus Campus of Ohio
State Univ. using a Varian Vista Pro ICP-OES 共Walnut Creek,
Calif.兲. The error in analyses was less than 5% based on duplicate
samples, and the percent difference in the anion–cation balance
was generally less than 10%.
Based on pH and the metals data, acidity 共mg/L as CaCO3)
was calculated as
acidity⫽50,000⫻共2关Fe2⫹兴⫹3关Fe3⫹兴
⫹3关Al3⫹兴⫹2关Mn2⫹兴⫹1关H⫹兴兲(1)
where the concentrations of iron, aluminum, manganese, and pro-
tons are in moles/Liter. Only soluble concentrations of these met-
als were used in the calculations. Because speciation of iron was
not carried out, calculations of acidity assumed that all the iron
was in the Fe3⫹oxidation state.
Analysis of Grout Core Samples
Grout core samples were collected from the site approximately 2
and 3 years after the grouting operation. Upon collection in the
field, core samples were immediately transported to Ohio State
Univ. for mineralogical analysis by x-ray diffraction 共XRD兲.
X-ray diffraction analysis was carried out using an x-ray diffrac-
tometer 共Phillips Analytical, Natick, Mass.兲using Cu K␣radia-
tion at 35 kV and 20 mA. Measurements were made using a step
scanning technique with a fixed time of 4 s/0.05° 2, from 5 to
70° 2. Prior to analysis, grout core samples were air dried and
ground with a synthetic sapphire mortar and pestle to ⭐250 m.
Crystalline phase assignments were made based on comparative
analyses of reference samples, searches of the International Cen-
ter for Diffraction Data, and data in the published literature.
pH values for the borehole cores were obtained in the follow-
ing fashion. For each depth increment, 5 g samples of ground and
dried core material were placed into 40 mL, screw-cap centrifuge
tubes along with 20 mL of HPLC grade H2O. These tubes were
then capped and shaken on an oscillating shaker to facilitate
equilibration of the solution phase with the solids present in each
sample. After a reaction period of 2 h, each sample was centri-
fuged at 4,000 rpm to separate the solid and solution components.
The pH of the resulting centrifugate was then measured with an
Orion–Ross pH electrode.
Results and Discussion
Long-Term Water Quality Trends
Surface water and groundwater monitoring was carried out to
characterize long-term impacts on water quality. Trends in the
flow rate of mine drainage and the flux of major AMD and grout
constituents at the main seep 共Site 5兲of the Roberts–Dawson site
are shown in Figs. 3 and 4, respectively. The bar in each graph
represents the grouting period. As can be seen in Fig. 3, the flow
rate at Site 5 decreased to less than 1.7⫻10⫺4m3/s 共10 L/min兲at
the end of grouting operations. However, shortly after grouting
was completed, a diffuse seep emerged approximately 50 m down
slope toward the receiving stream. As a result, the net contribu-
tion of flow to the receiving stream was not reduced at this site,
despite sealing of the original seep. After the new seep emerged,
the flow rate was seasonal, with high flow rates typically in Janu-
ary through April and lower flow rates during the summer
months.
As seen in Fig. 4, significant fluxes of acidity, sulfur, iron,
aluminum, calcium, and boron were observed at this new seep.
Acidity, iron and sulfate are all common constituents of acid mine
drainage, while the fixated FGD material grout contained cal-
cium, sulfur and boron. For all constituents shown in Fig. 4, there
was a large increase in flux immediately after grout injection,
which reflected both an increase in the concentrations of these
parameters and elevated flow rates from January through April. A
similar trend was observed for electrical conductivity, sulfate, Co,
K, Li, Mg, Mn, Na, Ni, Pb, Sr, and Zn. Previously, it was dem-
onstrated that the large initial increase in the concentrations of
acidity, iron, sulfur and aluminum was due to rerouting of mine
drainage flow, and the subsequent dissolution of accumulated iron
and aluminum sulfate salts and ferrihydrite 共Lamminen et al.
2001兲. The initial increase in calcium concentration after grouting
was attributed to the dissolution of fixated FGD material grout
and/or exchange of calcium from soil material due to the elevated
ion concentrations in the mine drainage water.
For all the chemical parameters shown in Fig. 4, except boron,
the initial sharp increase in flux was followed by a slower, long-
term decrease. For acidity, iron and sulfur, the long-term 共after
July 1999兲fluxes of these constituents stabilized at levels slightly
higher than levels observed prior to the injection of fixated FGD
material grout. Assuming Fe3⫹,Al
3⫹,H
⫹, and Mn2⫹were the
dominant species present, these constituents accounted for, on
average, 68, 21, 9, and 2% of the total flux of acidity, respectively.
The average pregrout and long-term flow rates were similar.
Therefore, the elevated fluxes were primarily a result of elevated
concentrations of acidity, iron, and sulfur in the mine drainage
waters. It is unlikely that the fixated FGD material grout was
responsible for the elevated levels of acidity and iron. More
likely, continued dissolution of soluble metal salts resulted in the
increased levels of acidity, iron, and sulfur in the mine drainage
water. For aluminum, the long-term flux was similar to flux val-
ues measured prior to FGD byproduct injection, possibly reflect-
ing lower amounts of accumulated aluminum salts within the
Fig. 3. Flow rate of mine drainage water at surface water Site 5
Fig. 4. Flux of acidity, sulfur, iron, aluminum, calcium and boron at
surface water Site 5, before and after placement of fixated flue gas
desulfurization material grout
mine voids. As of the last sampling date 共September 2001兲, the
flux of calcium remained elevated compared to pregrout levels,
but continued to decrease. The decrease in calcium flux indicates
that available calcium in the grout is also decreasing, due to the
prolonged dissolution and/or changes in the strength, permeabil-
ity, and mineralogical properties of the material. The flux of boron
increased immediately at the end of grouting but quickly returned
to near pre-grout levels, perhaps due to the lack of attenuation of
this element during transport.
While the concentrations of some contaminants at the main
seep 共Site 5兲were higher during the last year of the monitoring
program compared to pre-grout levels, little or no deleterious im-
pact on water quality was observed for either the surface water
reservoir 共Site 12兲or the underlying Clarion sandstone aquifer
共Well 9727兲. In Table 1, a list of parameters analyzed at the
Roberts–Dawson site for which either a primary or secondary
maximum contaminant level 共MCL兲has been established are
shown, along with the MCL value. As can be seen, all analytes
were within the range of acceptable values based on the MCLs,
except for manganese. In both the adjacent reservoir and the
Clarion sandstone aquifer, the concentration of manganese was
significantly higher than the established MCL. However, for both
the groundwater and surface water control sites, the concentra-
tions of manganese observed in April of 2001 were comparable or
lower than values detected prior to grouting operations.
Geochemical Stability of Fixated Flue Gas
Desulfurization Material Grout
To determine the geochemical stability of the fixated FGD mate-
rial grout upon exposure to acid mine drainage, mineralogical
analyses were carried out on well cores obtained from the
Roberts–Dawson site. The core sample obtained at the site of
Well 9906 in 1999 was only 21 cm long and had a fluid, paste-like
consistency, indicating a high moisture content 共moisture content
was not measured兲. A representative diffraction pattern for this
core is shown in Fig. 5. The diffraction pattern shown in Fig. 5
represents a subfraction of the core at a depth of 15–18 cm from
the top of the core.
It is apparent from the presence of hannebachite 2CaSO3
•(H2O) and ettringite (Ca6Al2(SO4)3(OH)12•26H2O), as well as
pH values ⬎9, that this core consisted entirely of fixated FGD
material grout material. The XRD pattern obtained from the
15–18 cm depth increment 共Fig. 5兲is strikingly similar to those
reported by Laperche and Traina 共1999a兲for unweathered fixated
FGD material grout. Laperche and Traina 共1999a兲did not observe
any Fe phases in fixated FGD material grout, unless the material
had reacted with mine drainage waters. Thus, the presence of
ferrihydrite clearly indicates the reaction of the fixated FGD ma-
terial grout with Fe-containing mine fluids. Indeed, the ambient
pH values present in the acidic mine drainage fluids should lead
to the formation of the mineral schwertmanite and not ferrihydrite
共Bigham et al. 1996兲. Whereas it cannot be determined if this
reaction occurred during or post grout emplacement, the former
seems most likely due to the low permeability one typically ob-
serves in solidified fixated FGD material grouts. Also, it should be
noted that although schwertmanite was not detected by powder
XRD, its presence could not be ruled out. Also, the pH of this
core was 9.6 which is at the lower limit of the stability field for
ettringite 共Myneni et al. 1998兲. Thus, a decrease in pH below this
point would likely lead to significant weathering of this material.
The core collected in 2000 at the site of Well 2002 was sig-
nificantly longer in length and contained a more varied mineral
assemblage than the core at 9906. The core from 2002 was well
consolidated and was much harder than the material from the
earlier sampling. A subsample within the central portion of the
core was dominated by hannebachite and ettringite followed by
lesser quantities of quartz 共see Fig. 6兲. The pH values in these
samples were all ⬎9.00. The elevated pHs (⬎9) and the pres-
ence of hannebachite and ettringite are diagnostic of fixated FGD
material grout. While muscovite is present throughout this core, it
is not commonly found in fixated FGD materials 共Laperche and
Traina 1999a兲nor is it likely to remain intact during coal com-
bustion. Thus, the presence of muscovite in the grout sections of
this core was either a result of micaceous materials from the mine
overburden and/or underclay or it was physically incorporated
into the matrix of the grout during grout injection.
Fig. 5. X-ray powder diffraction pattern of core sample collected
from Site 9906
Table 1. Concentrations of Contaminants with Either Primary Maxi-
mum Contaminant Level and/or Secondary Maximum Contaminant
Level 共MCL兲in Clarion Sandstone Aquifer and Adjacent Reservoir.
Data Are for Samples Collected in April, 2001. All Concentrations
Are in mg/L, Unless Noted
Parameter Primary
MCL Secondary
MCL Clarion
共Site 9727兲
Reservoir
共Site 12兲
pH 共pH units兲— 6.5– 8.5 7.28 8.06
TDS — 500 275 261
Sulfate 500a250 36 108
As 共ppb兲10 — 5.5 1.0
Al — 0.05–0.2 ⬍0.001 ⬍0.001
Ba 2 — 0.068 0.004
Be 0.004 — ⬍0.001 ⬍0.001
Cd 0.005 — ⬍0.001 ⬍0.001
Cl — 250 3 12
Cr 0.1 — ⬍0.001 ⬍0.001
Cu 1.3b1.0 ⬍0.002 ⬍0.002
Fe — 0.3 ⬍0.007 ⬍0.007
Mn — 0.05 0.981 0.120
Ni 0.1 — ⬍0.004 ⬍0.004
Pb 0.015 — ⬍0.006 ⬍0.006
Zn — 5 ⬍0.002 ⬍0.002
aMaximum contaminant level goal 共MCLg兲.
bAction level.
The presence of hannebachite in the core from 2002 is particu-
larly noteworthy in that this phase is from the FGD filter cake
共Laperche and Traina 1999a兲. Its long-term persistence in these
borehole samples indicates minimal altering of the fixated FGD
material grout in this particular location within the mine. Appar-
ently, there was little if any intrusion of acidic mine waters into
these samples when they were in place in the field. This conten-
tion is also supported by dramatic change in pH observed in the
subsample containing fixated FGD material grout (pH⫽9.35) and
the subsample immediately adjacent (pH⫽from 2.34兲. These data
indicate that the fixated FGD material grout in this region of the
mine maintained low permeability and has not reacted with local
acidic mine drainage water to any significant extent. It should be
noted, however, that the lower strength grout used to coat pyritic
materials likely had greater exposure to mine drainage waters,
and therefore, greater potential for weathering. As a result, a sig-
nificant reduction in the potential for grout weathering may occur
if all the mine voids were completely filled with grout.
Water Quality in Vicinity of Fixated Flue Gas
Desulfurization Material Grout
To better understand the interactions between acid mine drainage
and fixated FGD material grout, monitoring wells were installed
following the collection of grout core samples. These monitoring
wells were located directly within mine voids, and in some cases,
directly within fixated FGD material grout. The core samples col-
lected during well construction were analyzed in order to confirm
the presence of fixated FGD material grout. Wells installed prior
to grouting operations, on the other hand, were located within
coal pillars of the remaining Kittanning No. 6 coal layer, in order
to maintain hydraulic performance of the wells after inundation of
the mine voids with grout.
The data in Table 2 show the concentrations of important in-
organic constituents in wells installed within the mine void layer,
both prior to 共Well 9719兲and after 共Wells 9901, 9903, 9904,
9906, and 2002兲placement of fixated FGD material grout. Refer
to Fig. 2 for the locations of these wells at the Roberts–Dawson
site. Core samples collected from Sites 9906 and 2002 were con-
firmed to contain fixated FGD material grout. Grout was not de-
Fig. 6. X-ray powder diffraction pattern of core sample collected
from Site 2002
Table 2. Water Quality in Wells in Downdip Area of Mine, Installed Either before 共9719兲or after 共9901, 9904, 2002兲Grouting Operations. Water
Quality Data for Two Wells 共9903 and 9906兲Installed in Upper Mine Works after Grouting Are Also Shown. Concentrations Are in mg/L, Unless
Noted. All Concentrations Correspond to Average Values over Period April 2000–September 2001. Number of Sampling Dates (n) Recorded for
Each Well During This Period is Shown in Parentheses
Parameter 9719 (n⫽5) 9901 (n⫽5) 9903 (n⫽5) 9904 (n⫽2) 9906 (n⫽6) 2002 (n⫽4)
Acidity 共mg/L as CaCO3)284⫾34 124⫾134 2.7⫾2.5 99.2⫾48.2 9.1⫾4.6 21.1⫾36.7
Alkalinity 共mg/L as CaCO3)nd 102⫾83 296⫾35 67.8⫾12.1 262⫾98 8.7⫾3.1
pH 共pH units兲4.1 5.4 6.9 6.4 10.2 5.9
Conductivity 共S/cm兲1431⫾135 1352⫾381 1134⫾132 2200⫾296 1786⫾186 330⫾109
TDS 956⫾91 905⫾268 756⫾85 1450⫾221 1194⫾124 217⫾77
As 共ppb兲5.1⫾2.1 5.1⫾2.9 4.6⫾3.7 2.4⫾0.9 61.2⫾17.5 nd
Al 3.75⫾1.11 1.1⫾2.3 0.021⫾0.030 0.041⫾0.039 1.501⫾0.864 0.216⫾0.419
B 0.297⫾0.030 0.414⫾0.089 0.457⫾0.112 0.798⫾0.112 0.398⫾0.057 0.073⫾0.049
Ba 0.004⫾0.001 0.015⫾0.009 0.033⫾0.011 nd 0.020⫾0.010 0.021⫾0.012
Be 0.001⫾0.001 nd nd nd nd nd
Cd 0.021⫾0.028 0.004⫾0.008 nd 0.007⫾0.010 nd nd
Ca 184⫾14 216⫾63 193⫾34 365⫾31 78⫾48 36⫾12
Cl 27.6⫾9.1 52.9⫾19.7 23.4⫾15.4 217.8⫾87.4 409.4⫾64.6 10.2⫾5.3
Cr 0.001⫾0.002 nd nd 0.007⫾0.009 0.002⫾0.003 nd
Cu 0.093⫾0.089 0.027⫾0.061 nd 0.028⫾0.040 nd 0.007⫾0.010
Fe 共dissolved兲94.2⫾10.7 42.3⫾44.4 0.873⫾0.844 32.5⫾17.5 0.246⫾0.525 6.9⫾12.4
Mg 40⫾543⫾19 41⫾584⫾6 7.6⫾16.5 10.2⫾4.6
Mn 共dissolved兲2.74⫾0.44 2.37⫾1.85 0.392⫾0.105 6.31⫾0.71 0.077⫾0.148 0.59⫾0.61
Na 25⫾321⫾527⫾662⫾28 93⫾40 4.1⫾1.7
Ni 0.045⫾0.015 0.036⫾0.050 nd 0.046⫾0.022 0.003⫾0.006 0.008⫾0.011
Pb 0.010⫾0.022 0.005⫾0.011 0.013⫾0.024 nd 0.010⫾0.013 nd
S 284⫾24 232⫾111 123⫾128 343⫾23 71⫾17 44⫾24
Si 17.15⫾1.82 9.68⫾5.32 8.22⫾3.45 11.30⫾3.50 2.86⫾0.83 6.84⫾2.07
Zn 0.101⫾0.009 0.120⫾0.080 0.001⫾0.002 0.048⫾0.016 nd 0.020⫾0.017
Note: nd⫽none detected.
tected in core samples collected at well Sites 9901, 9903, and
9904, but these wells were confirmed to be within the mine void
layer. For wells located in the downdip portion of the mine voids,
the concentrations of most constituents was higher in wells in-
stalled prior to grouting 共9719兲compared to water quality in wells
installed at least 1 year after grouting operations were completed.
For example, the average pH values in Wells 9901, 9904, and
2002 were 5.4, 6.4, and 5.9, respectively, compared to an average
pH value of 4.1 for Well 9719. Also, wells installed in the down-
dip portions of the mine after grouting all had measurable alka-
linity 共average alkalinity from 8.7 to 101.7 mg/L as CaCO3)
while alkalinity was not detected in well 9719. Acidity, As, Al,
Be, Cd, Cu, Fe, Si, Pb, and Zn were all similar or lower in con-
centration in downdip wells installed after grouting compared to
wells installed prior to grouting. Calcium and boron, both con-
stituents present in the fixated FGD material grout 共Laperche and
Traina 1999a,b兲, were found at higher concentrations in wells
installed in the downdip portions of the mine after grouting, with
the exception of Well 2002.
The generally higher pH, higher alkalinity, and lower minor
and trace element concentrations in wells installed after grouting
in the downdip portions of the site reflects more extensive inter-
actions of AMD drainage waters with fixated FGD material grout.
These data indicate that AMD waters were partially neutralized.
This hypothesis is consistent with the lower iron and aluminum in
these wells, as these constituents would be precipitated as iron
and aluminum hydroxides as a result of interaction with calcium
hydroxide in the fixated FGD material grout and the increased pH
values. The levels of calcium and boron in these wells also gen-
erally support this hypothesis, although the processes controlling
these elements are not as straightforward as for iron and alumi-
num. For Wells 9901 and 9904 elevated levels of both calcium
and boron were observed, indicating dissolution of fixated FGD
material grout upon reaction with AMD waters. Interestingly, cal-
cium and boron concentrations in Well 2002 were lower than in
both 9901 and 9904, as well as 9719, which was installed prior to
grouting operations. The lower calcium and boron in Well 2002
indicates minimal penetration of AMD waters into the grout, or
possibly dilution from seepage into the open bedrock borehole
from the upper Freeport sandstone and fractured roof shale. For
Well 2002, neutralization of AMD waters likely occurred on the
outer edge of the water/grout interface, removing iron and alumi-
num 共as hydroxides兲, calcium and sulfur 共as gypsum兲, prior to
arriving at the monitoring well.
Well 9906 was located on the northwest section of the mapped
portion of the mine. The core sample collected from this site
indicated the presence of fixated FGD material grout, however,
the sample had little or no strength. This well had high pH and
high conductivity, with low levels of acidity, aluminum, cad-
mium, calcium, chromium, iron, manganese, and sulfur. Arsenic
levels in this well were high 共above 60 ppb兲for all sampling dates
except one 共July 2000兲. The high arsenic levels in this well may
be due to the enhanced solubilization of arsenic at high pH val-
ues, and also a reduction in the adsorption capacity of iron oxide
solids for arsenic anions under these conditions. Water quality in
Well 9903, also located on the northern side of the site, was
similar to 9906, except that water from 9903 had lower pH, ar-
senic, aluminum, and chloride, and higher calcium.
In comparing the water quality in wells installed prior to and
after grouting it should be noted that the grouting process altered
hydraulic flow paths within the mine voids. Therefore, samples
collected in wells installed directly within the fixated FGD mate-
rial grout may reflect water following a different flow path than
samples collected from wells installed in the coal pillars. Despite
the differences in well construction, however, the water quality
and mineralogical data clearly show significant neutralization of
mine drainage waters in the immediate vicinity of the fixated
FGD material grout and minimal physical and chemical altering
of the grout in the downdip portions of the Roberts–Dawson
mine.
Conclusions
Based on the water quality data and mineralogical analyses con-
ducted, placement of fixated FGD material grout within the
Roberts–Dawson mine resulted in little or no deleterious impacts
to water quality of the surrounding surface water or underlying
groundwater. Although significant neutralization of AMD waters
was observed in the immediate vicinity of the fixated FGD mate-
rial grout, no reduction in the concentration or flux of major ele-
ments in mine seepage, including acidity, iron, calcium, and sul-
fur was observed, largely due to changes in water flow paths and
subsequent dissolution of accumulated metal salts within the mine
voids. Little penetration of AMD waters within the high strength
grout occurred, and subsequently, little grout weathering. This
latter result indicates that the fixated FGD material grout was
geochemically stable over the period of study, despite the low pH
of the mine drainage waters. Weathering of the lower strength
grout used to coat mine surfaces was not determined but would be
expected to be greater.
Acknowledgments
This project was funded in part by the Ohio Coal Development
Office 共OCDO兲, Ohio Department of Development, under OCDO
Grant No. D-95-17. The writers thank Jackie Bird and Howard
Johnson at OCDO for their role in establishing a coalition of
funding for the project from federal, state and local agencies as
well as private industry. Additional support was provided by
American Electric Power, Ohio Environmental Protection
Agency, Ohio Dept. of Natural Resources, United States Dept. of
Energy, Dravo Lime Company, Office of Surface Mines, Corps of
Engineers, United States Environmental Protection Agency, and
The Ohio State Univ. The writers also thank Yu-Ping Chin and
James Wood at Ohio State Univ. who participated in Phase I of
this project, and John Massey-Norton, American Electric Power,
for serving as project manager.
References
American Coal Ash Association Inc. 共ACAA兲.共2001兲. ‘‘2001 coal com-
bustion product production and use 共short tons兲.’’ Aurora, Colo.
American Coal Ash Association Inc. 共ACAA兲.共2003兲. ‘‘Glossary of
terms concerning the management and use of coal combustion prod-
ucts 共CCPs兲.’’ Aurora, Colo.
Bair, E. S., and Hammer, M. J. 共1999兲. ‘‘Injection of FGD grout to miti-
gate acid mine drainage at the Roberts–Dawson underground coal
mine, Coshocton and Muskingum Counties, Ohio, Volume 2: Site
geology and hydrogeology.’’ Final Technical Rep., Submitted to Ohio
Coal Development Office, The Ohio State Univ., State of Ohio, Co-
lumbus, Ohio.
Bigham, J. M, Schwertmann, U., Traina, S. J., Winland, R. L., and Wolf,
M., 共1996兲. ‘‘Schwertmanite and the chemical modeling of iron in
acid sulfate waters.’’ Geochim. Cosmochim. Acta, 60, 2111–2121.
Butalia, T. S., and Wolfe, W. E. 共1997兲. ‘‘Re-use of clean coal technology
by-products in the construction of impervious liners.’’Proc., 1997 Ash
Utilization Symposium, Lexington, Ky.
Damian, M. T., and Mafi, S. 共1999兲. ‘‘Injection of FGD grout to mitigate
acid mine drainage at the Roberts–Dawson underground coal mine,
Coshocton and Muskingum Counties, Ohio. Volume 5: Grouting op-
erations.’’ Final Technical Rep. Submitted to Ohio Coal Development
Office, The Ohio State Univ., State of Ohio, Columbus, Ohio.
Drake, R., 共1997兲. ‘‘Wallboard plants to use 100% synthetic gypsum.’’
Rock Products, 100共8兲,7.
Kalyoncu, R. S. 共1999兲. ‘‘Coal combustion products.’’ U.S. Geological
Survey Minerals yearbook—1999, U.S. Geological Survey, Reston,
Va.
Lamminen, M., Wood, J., Walker, H., Chin, Y.-P., He, Y., and Traina, S.
J., 共2001兲. ‘‘Effect of flue gas desulfurization 共FGD兲by-product at an
underground coal mine.’’ J. Environ. Qual., 30共4兲, 1371–1381.
Laperche, V., and Traina, S. J., 共1999a兲. ‘‘Flue gas desulfurization by-
product weathering by acid mine drainage.’’J. Environ. Qual., 28共6兲,
1733–1741.
Laperche, V., and Traina, S. J. 共1999b兲. ‘‘Injection of FGD grout to miti-
gate acid mine drainage at the Roberts–Dawson underground coal
mine, Coshocton and Muskingum Counties, Ohio. Volume 7: Grout
weathering and chemical characterization.’’Final Technical Rep. Sub-
mitted to Ohio Coal Development Office, The Ohio State Univ., State
of Ohio, Columbus, Ohio.
Myneni, S. C. B., Traina, S. J., and Logan, T. J., 共1998兲. ‘‘Ettringite
solubility and geochemistry of the Ca(OH)2–Al2(SO4)3-H2O system
at l atm pressure and 298 K.’’ Chem. Geol., 148, 1–19.
Stehouwer, R. C., Sutton, P., and Dick, W. A., 共1995b兲. ‘‘Minespoil
amendment with dry flue gas desulfurization by-products: Plant
growth.’’ J. Environ. Qual., 24, 861–869.
Stehouwer, R. C., Sutton, P., Fowler, R. K., and Dick, W. A., 共1995a兲.
‘‘Minespoil amendment with dry flue gas desulfurization by-products:
Element solubility and mobility.’’ J. Environ. Qual., 24, 165–174.
United States Environmental Protection Agency 共U.S. EPA兲.共1999兲.
‘‘Report to Congress: Wastes from the combustion of fossil fuel. Vol-
ume 2. Methods, findings and recommendations.’’Rep. No. EPA 530-
R-99-010, United States Environmental Protection Agency, Cincin-
nati.
Ver Steeg, K., 共1942兲. ‘‘Jointing in the coal beds of Ohio.’’ Econ. Geol.,
37, 503–509.
Walker, H. W., Taerakul, P., Butalia, T. S., Wolfe, W. E., and W. A. Dick
共2002a兲. ‘‘Minimization and use of coal combustion by-products:
Concepts and applications.’’Handbook of pollution control and waste
minimization, A. Ghassemi, ed., Marcel–Dekker Inc., New York.
Walker, H. W., Wood, J. T., Lamminen, M., Chin, Y.-P., and E. E. Whit-
latch 共1999兲. ‘‘Injection of FGD grout to mitigate acid mine drainage
at the Roberts–Dawson underground coal mine, Coshocton and
Muskingum Counties, Ohio: Volume 5: Groundwater and surface
water quality.’’ Final Technical Rep. Submitted to Ohio Coal Devel-
opment Office, The Ohio State Univ., State of Ohio, Columbus, Ohio.
Walker, H. W., Taerakul, P., Lamminen, M., Y. He, Traina, S., and E. E.
Whitlatch 共2002b兲. ‘‘Injection of FGD grout to mitigate acid mine
drainage at the Roberts–Dawson underground coal mine, Coshocton
and Muskingum Counties, Ohio: Volume 9: Groundwater and surface
water quality, years 1–5, and mineralogical analysis of grout core
samples.’’ Final Technical Rep. Submitted to Ohio Coal Development
Office, The Ohio State Univ., State of Ohio, Columbus, Ohio.
Wolfe, W. E., and Butalia, T. S. 共1998兲. ‘‘Use of FGD as an impervious
liner.’’ Proc., 23rd Int. Technical Conf. on Coal Utilization and Fuel
Systems, Clearwater, Fla.
Wolfe, W., and Butalia, T. 共1999兲. ‘‘Injection of FGD grout to mitigate
acid mine drainage at the Roberts–Dawson underground coal mine,
Coshocton and Muskingum Counties, Ohio: Volume 4: Grout mix
design and physical characterization: OSU component.’’ Final Tech-
nical Rep. Submitted to Ohio Coal Development Office, The Ohio
State Univ., State of Ohio, Columbus, Ohio.
Wolfe, W. E., and Cline, J. H. 共1995兲. ‘‘A field demonstration of the use
of wet and dry scrubber sludges in engineered structures.’’Proc., 11th
Int. Symp. on Use and Management of Coal Combustion By-Products
(CCBs), American Coal Ash Association and Electric Power Research
Institute, Orlando, Fla.
