542N06002
^ news/effer abouf so/7, sediment, and ground-water characterization and remediation technologies
Issue 23 March 2006
This issue of Technology News and Trends highlights innovative technologies used to treat con-
taminants affecting soil, ground water, and surface water at mining sites. In addition to complex
problems associated with acid rock drainage (ARD), these sites typically involve remote locations,
limited access, extreme climates, a predominance of heavy metal contaminants, and large volumes
of contaminated tailings. The U.S. EPA is working with other federal and state agencies, academia,
and private industry to demonstrate innovative technologies and associated performance mea-
sures for use at these sites.
Hydraulic Conductivity Loss at the Monticello PRB Leads to Trial
Use of Ex-Situ Treatment Cell
Performance monitoring of the permeable reactive
barrier (PRB) that has operated since 1999 at a
former mining/milling site near Monticello, UT,
recently revealed significant reductions in the
system's ability to treat contaminated ground
water. The PRB had successfully reduced high
concentrations of target radioactive and metal
contaminants to non-detectable levels during the
first four years of operation [see June 2000 Ground
Water Currents and July 2003 Technology News
and Trends online at http://www.cluin.orgl. During
the past two years, however, hydraulic
conductivity throughout the treatment area
decreased and caused ground water to mound
upgradient of the PRB. The U.S. Department of
Energy (DOE) and U.S. EPA subsequently
investigated the system's reduced performance
and identified a supplemental remedy for ground-
water treatment.
The original 100-ft-wide by 6-ft-thick PRB was
designed to treat ground water containing uranium,
selenium, vanadium, and other contaminants with
concentrations exceeding maximum contaminant
levels (MCLs) by as much as a factor of 100. The
PRB was constructed with a 2-ft-thick upgradient
zone containing 13% (by volume) zero-valent iron
(ZVI) mixed with pea gravel and a 4-ft-thick
downgradient zone containing 100% ZVI. Though
contaminant concentrations in ground water
exiting the PRB remain below MCLs after seven
years of operation, hydraulic conductivity in the
downgradient ZVI zone has decreased by nearly
three orders of magnitude.
In February 2002, after 30 months of PRB
operation, 70 cores were collected from the
reactive media. Analytical results of 279 random
samples indicated that more than 8,000 kg of
calcium carbonate and 24 kg of uranium- and
vanadium-bearing minerals had deposited in the
PRB. Nearly all the uranium and vanadium
precipitated in the upgradient gravel/ZVI zone;
however, calcium was found throughout both
the gravel/ZVI and ZVI zones, indicating that
precipitation rates of calcium carbonate require
longer residence times than uranium and
vanadium. Solid-phase chemistry data were
used in combination with dissolved-phase
ground-water chemistry to estimate an average
ground-water flow rate of 6-9 gpm.
Results of a second round of coring 18 months
later, in August 2003, indicated that uranium and
calcium continued to precipitate in the PRB. On
the basis of the increased concentrations of
uranium and calcium since the first coring,
ground-water flux through the PRB was
estimated to consistently average approximately
5 gpm. Electron microprobe analysis of the core
samples indicated that ZVI grains in the
upgradient gravel/ZVI zone had corroded but
that much of the original ZVI mass remained.
Mixtures of iron oxides and carbonates had
replaced and coated the ZVI grains and/or
crystallized in interstitial space.
To evaluate trends in hydraulic conductivity,
gas-injection slug tests were conducted in June
Contents
Hydraulic Conductivity
Loss at the Monticello
PRB Leads to Trial Use
of Ex-Situ Treatment Cell page 1
Resources on Mining
Technologies page 3
Compost-Free
Bioreactors Remove
Metals from Acid Rock
Drainage page 3
Evaluation of Mining
Technologies Needs
Standardized
Performance-Based
Measures page 4
PRB Containing
Processed Fish Bones
Sequesters Metals from
Ground Water page 5
MWTP Demonstrates
Integrated Passive
Biological System for
Treating Acid Rock
Drainage page 7
Mine Waste Technology
Program (MWTP)
As a joint program sponsored
by the U.S. DOE and U.S.
EPA, the MWTP works with
academic organizations and
private industry to conduct pilot-
scale demonstrations and
technology transfer related to
mine waste issues. Project
summaries, solicitations, and
networking opportunities are
available online at http://
www.epa.gov/
minewastetechnology.
-------
Figure I. Long-
tenn monitoring
showed
nnanlieipated
1 OE-02
f
live/ran lie
eonduclivi/v
within the I007c
ZVI zone of the
Monticello PRB.
1 OE-03
o
O
o
1 OE-04
•Jun-00
QAug-03
• Nov-04
HNov-05
Alluvium
Gravel/ZVI
[continued from page 1]
2000, August 2003, November 2004, and
November 2005. The number of wells tested
in each event varied from 30 to 45. Tests
revealed that hydraulic conductivity values
had remained nearly constant within the
upgradient alluvium and the gravel/ZVI zone
but decreased 3 orders of magnitude in some
wells within the ZVI zone during this period
(averages shown in Figure 1).
After 44 months of PRB operation, upgradient
ground-water mounding had advanced to
approximately 1 foot of ground surface. As a
result, an extraction well immediately
upgradient of the PRB (within the area of
mounded ground water) and a supplemental
ex-situ treatment cell were installed last June
to help alleviate the mounding and ensure
continued treatment of ground water. The
treatment cell consists of a 6-ft-diameter by 5-
ft-deep concrete cylinder located immediately
downgradient of the existing PRB.
On the basis of earlier site-specific tests
showing enhanced longevity of a gravel/ZVI
mixture over ZVI alone, the cell's reactive
medium consists of 2 tons of ZVI mixed with
pea gravel (Figure 2). Contaminated ground
water is pumped into the bottom of the
treatment cell and allowed to flow up through
the reactive media at a typical flux of 4-5 gpm.
Real-time measurements of influent pressure,
flow rates, ground-water levels, and pH of the
system are recorded every 5 minutes and
transmitted to the DOE Office of Legacy
Management in Grand Junction, CO, for
evaluation.
Ground-water levels upgradient of the PRB
decreased from nearly ground surface to 5 feet
below ground surface (bgs) within five months
of treatment cell operation, and hydraulic
conductivity of the treatment cell has not
changed since the cell installation. Analysis of
weekly and monthly ground-water samples
indicates that uranium concentrations entering
the system range from 100 to 250 jog/L and that
effluent water is meeting State of Utah ground-
water standards for uranium (less than 45
u.g/L). Concentrations of selenium currently
Extraction Well
Concrete Valve Box
Treatment Cell
C
<
Fill
;' I
•To Breather
Alluvium
fc-
Figure 2. Contaminated ground water at the
Mon/icello site is now extracted from a well
upgradient of the PRB and routed to an
adjacent ex-situ treatment cell.
decrease from 25 {ig/L in (he cell influent to 0.7
jog/L in the effluent.
The site ground-water flow model predicts that
the contaminant plume will move
downgradient of the PRB by 2015. Due to the
PRB's current function as a physical barrier,
its use will continue for source control and to
provide a mound of ground water to feed the
treatment cell. PRB coring will be conducted
this spring to observe mineralization that now
causes nearly complete blockage of ground-
water flow. High concentrations of dissolved
salts in the ground water are partially
responsible for the mineralization in the ZVI
zone, which causes the reduction in hydraulic
conductivity and imminent failure of the PRB.
Although design-phase treatability studies
had indicated the potential for mineral
precipitation, the use of gravel-dominated
media in the upgradient zone was expected
to increase the likelihood that the PRB would
function for the 10-15 years needed to flush
contaminants from the aquifer.
Long-term results indicate that the PRB
effectively treated ground water for
approximately four years. Limited data from
operation of the supplemental treatment cell
indicate that the system may be capable of
treating contaminated ground-water flux to an
extent similar to the PRB's. The treatment cell
has treated 700,000 gallons of contaminated
ground water during its first six months of
operation, while the PRB treated approximately
8.2 million gallons of water during its six years
of operation.
Cost analysis indicates that treatment cell
construction was completed for approximately
$50,000 versus more than $lmillion for PRB
construction. To achieve a comparable level
of confidence, performance monitoring also
will cost significantly less for the treatment
cell than for the PRB. In addition, treatment
cell decommissioning costs are estimated at
less than $5,000 while PRB decommissioning
costs are estimated at more than $50,000.
Due to the hydrogeological conditions and
economics, the U.S. DOE and EPA will
consider replacing the ZVI reactive media in
[continued on page 3]
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[continued from page 2]
the treatment cell (for less than $2,000) when
the cell no longer adequately treats the
contaminants of concern (uranium and
vanadium) or when hydraulic conductivity in
the cell decreases and causes mounding
upgradient of the PRB. Replacement of reactive
material in the PRB gate, which would cost
approximately $700,000, is not considered a
viable alternative.
Paul Mushovic US. EPA Region 8
(mushovic.paul@epa.gov or 303-312-
6662), Tim Bartlett, S.M. Stoller Corp.
(tim.bartlett@RJo.doe.gov or 970-248-
7741), and Stan Morrison, PhD., S.M.
Stoller Corp. (stan.morrison@gjo.doe.gov
or 970-248-6373)
Resources on Mining Technologies
Abandoned Mine Lands (AML) Web Page: This on-line resource (http://www.epa.gov/aml) is updated by the U.S. EPA regularly in order
to provide a comprehensive source of AML information such as federal and state policies, technical guidance, and site inventories.
Hard Rock 2006-Sustainable Modern Mining Applications: The U.S. EPA Office of Research and Development (ORD)/NRMRL will
hold this conference on November 14-16,2006, in Tucson, AZ, to discuss sustainable opportunities for extraction and utilization of mining
resources. Conference abstracts are due April 7,2006. More information is available on the AML web page.
Jump-Starting Ecosystem Restoration-Beyond Hydro-Seeding: The U.S. EPA Land Revitalization Office and Technology Innovation
and Field Services Division offer this new series of Internet seminars as an opportunity to leam about the role of ecological restoration in
the cleanup of sites, including mining sites; the relationship among land disturbance, functioning ecological systems, and restoration
project management; and techniques for implementing ecosystem restoration. Upcoming training schedules and archived seminars are
available on CLU-IN (http://www.cluin.org/training).
Copper Basin Mining District-Case Study: This publication describes joint efforts among the U.S. EPA, the State of Tennessee, and
private industry to clean, reforest, and stabilize lands affected by extensive ore processing in the Copper Basin Mining District, TN. The
case study can be downloaded from the AML web page.
Compost-Free Bioreactors Remove Metals from Acid Rock Drainage
The U.S. ERA's National Risk Management
Research Laboratory (NRMRL) recently
completed a two-year evaluation of a full-
scale, compost-free bioreactor system
operating at the Leviathan Mine Superfund
site in northeastern California. The
technology uses a liquid-carbon source in a
rock matrix, rather than compost or wood
chips, which is consumed by bacteria and
collapses over time. Preliminary performance
tests (reported in the May 2004 issue of
Technology News and Trends') indicated 91 -
99% efficiency in removal of target metals
from ARD. Performance results over the past
two years confirmed that the system achieved
a target-metal removal efficiency of 95%.
The treatment system consists of two
bioreactors, two settling ponds, and an
aeration channel. It treats up to 30 gpm of
ARD year-round in either gravity-flow or
recirculation mode. Operation in gravity-flow
mode causes metals to precipitate in both the
bioreactors and settling pond, which requires
frequent flushing and disturbs bacteria in the
bioreactors. In recirculation mode, metals
precipitate in the settling pond, and the pond
effluent is recirculated through the bioreactors,
thereby reducing the need for bioreactor
flushing. Overall, the recirculation mode places
less stress on the bacteria, reduces sodium
hydroxide consumption, and improves
handling of solids.
Thirteen sampling events were conducted
between November 2003 and July 2005. During
each sampling event, NRMRL collected metals
data from the system influent and effluent and
from flows between the five system
components; calculated reductions in metals,
sulfate, and acidity between the components;
and measured the system's operating
parameters. Final evaluations of the system
were based on removal efficiencies for target
metals, the ability of effluent concentrations to
meet EPA discharge standards, and the
characteristics (including disposal
requirements) of end-product solid wastes.
Results indicate that the system reduced
concentrations of sulfate ion in the ARD more
than 17%, and increased ARD pH from
approximately 3.0 to 7.0. Treatment effectively
reduced concentrations of all target metals
(excluding iron) in the ARD to below EPA
interim discharge standards, achieving an
average removal efficiency of 95% (Table 1).
Iron concentrations met the discharge
standards when base addition was optimized.
Solids generated by ARD treatment were
determined to be non-hazardous under state
and federal solid waste regulations. Over the
20 months of operation, the system generated
a total of 17 yd3 of dewatered sludge (80%
moisture) per million gallons of ARD treated.
The system treated 2.44 million gallons of
ARD in gravity-flow mode during the first six
months of the study, using 2,440 gallons of
sodium hydroxide (in 25% solution) and
1,180 gallons of ethanol. The average removal
efficiency exceeded 94% over six sampling
events. During the following 14 months, the
system operated in a recirculation mode and
treated 5.81 million gallons of ARD, using
[continued on page 4]
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[continued from page 3]
approximately 5,820 gallons of sodium
hydroxide and 2,805 gallons of ethanol.
Removal efficiency in this mode exceeded 96%
over seven sampling events. No difference in
sulfate removal efficiencies was found between
the two operational modes.
Capital costs for construction of the system
were approximately $836,600 for gravity-flow
operations and $864,100 for recirculation
operations. Based on an average ARD flow
rate of 9.45 gpm, operation and maintenance
costs during these research activities were
$19.45 per 1,000 gallons oftreatedARD.
NRMRL determined that compost-free
bioreactors provide a constant source of readily
oxidized ethanol and effective control of
biological population dynamics. Rock
substrate bioreactors also offer the advantage
of being non-compressible, which stabilizes
hydraulic conductivity, enhances precipitate
flushing, and avoids short-circuiting of
untreated ARD through the bioreactor.
The technology was limited more by weather
conditions than operational issues. Though
slower biological activity decreased the rate
of sulfate reduction during the winter, effluent
discharge standards were met year-round.
Winter snow pack limited access to this remote
site, requiring consumable materials such as
sodium hydroxide, ethanol, and diesel fuel to
Table 1. Although influent concentrations
exceeded interim discharge standards as
much as 580-fold, the Leviathan Mine
bioreactor svslein reduced concentrations
in ARD to levels I- to 43-fold lower than
standards.
be transported to the site and stored in bulk
during the summer. Similarly, equipment
replacement, sludge dewatering, and sludge
transfer needed to be performed during the
summer months. The system required routine
maintenance once each week, considerably less
than alternative ARD remedies such as lime
treatment.
The study determined that successful full-scale
implementation of this technology relies on
adequate space for the system components,
staging areas, and support facilities. Application
at the Leviathan Mine required approximately
0.75 acre. The system required less than 0.6
kilowatt hour (KW) of electricity for continuous
operation in the recirculation mode. In gravity-
flow mode, it required less than 0.1 KW of
energy that was supplied by a solar panel and
storage batteries.
Based on these results, the bioreactor system
will continue in recirculation mode to treat ARD
at the Leviathan Mine. The system is
continually optimized to reduce the quantity of
alcohol and caustic chemicals needed in the
treatment process. System enhancements
during 2006 will include development of
alternate power sources for the recirculation
pumps, installation of redundant recirculation
pumps to be available in the event of pump
failure, and additional protection of the ARD
recirculation lines by relocating them below
grade. A comprehensive innovative
technology report will be available later this
summer through EPA's Superfund Innovative
Technology Evaluation Program (online at
http://www.epa.gQiV/ORD/SITE/).
NRMRL anticipates that pilot-scale testing,
which typically is required for bioreactors
employing compost and wood chip matrices,
is unnecessary for this technology at other
ARD-impacted sites because uncertainties
related to carbon availability, sulfate reduction
efficiency, matrix compaction, and solids
flushing are essentially eliminated. Instead,
bench-scale tests can be used to optimize the
ethanol dose necessary for sulfate reduction,
to optimize the base type and dose required
for acid neutralization, and to determine the
volume of metal sulfide precipitate that will
be generated by the treatment process.
Contributed by Edward Bates, NRMRL
(bates.edward@epa.gov or 513-569-
7774), Dr. Tim Tsukamoto, University of
Nevada-Reno (timothyt@unr.edu), Glenn
Miller, Ph.D., University of Nevada-Reno
(gcmiller@unr.edu), and Matt Udell,
Tetra Tech EM Inc. (matt.udell@ttemi.com
or 916-853-4516)
Average Concentrations of Target Metals
Aluminum
(mg/L)
Copper
(mg/L)
Iron
(mg/L)
Nickel
(mg/L)
Zinc
(mg/L)
Gravity-Flow Mode
[ Influent
Effluent
\ Removal Efficiency (%)
I Recirculation Mode
I Influent
Effluent
Removal Efficiency (%)
EPA Standard
375
01
997
40
0.05
999
20
069
0005
993
117
49
958
049
007
866
072
002
97.8
079
0005
994
0016
116
27
977
1 0
0.53
007
868
0094
0.78
001
989
021
Evaluation of Mining Technologies Needs Standardized Performance-Based Measures
The U.S. EPA laboratories and program
offices continue to evaluate methods for
determining the adequacy of site
remediation. As part of this effort, EPA's
Environmental Response Team Center
(ERTC) evaluated performance-based
measures that are needed for demonstrating
reductions in mobility and bioavailability of
contaminants (particularly metals) in soil. The
evaluation identified a range of physical/
chemical, biological, and health risk-based
tests as well as their advantages and
limitations. Although test protocols for some
of these technical performance measures
(TPMs) are not fully standardized, all of
the methods use statistically designed
sampling plans and interpretations based
on site-specific data.
The study highlights bioavailability
concerns commonly encountered during
[continued on page 5]
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[continued from page 4]
evaluation of remediation technology at hard-
rock mining sites, particularly those
employing organic soil amendments such as
biosolids. In-situ biosolid technology
involves introducing organic materials such
as compost, manure, wood chips, or wood
ash and nonorganic material such as lime to
establish surface-soil structure and
conditions amenable to plant growth. These
materials are incorporated directly into
contaminated soil or placed on top of the soil,
which facilitates contaminant immobilization
by chemical/biological processes such as
adsorption. Iron and magnesium oxide
concentrations, as well as the organic matter
itself, render the biosolids particularly
amenable to cadmium, lead, and zinc
immobilization. Application of this in-situ
technology does not reduce the
concentrations of contaminants but it will
reduce their bioavailability, mobility, and
leachability. Typical regulatory tests
determining total concentrations of
contaminants do not illustrate the technology
effectiveness. As a result, a broad suite of
TPMs is needed to evaluate the ability of a
technology to meet remediation goals
involving contaminant mobility and/or toxicity
reductions.
Physical/chemical extraction techniques
identified during the ERTC evaluation include:
> Pore-water measurement obtained by
analyzing contaminant concentrations in soil
solution, which offers an absolute measure-
ment of contaminant solubility.
> Sequential extraction that quantifies metal
distributions in different solid phases of soil,
allowing pre-remediation and post-
remediation comparisons to be made.
Biological-based techniques include:
> Gastrointestinal absorption procedures for
measuring contaminant uptake in human
colon cells through the study of membrane
transport mechanisms and associated con-
taminant interactions.
> Mineralization and assimilation assays
employing microbial mineralization and re-
lated carbon dioxide evolution to compare
contaminant-free controls against soil/slurry
solutions containing hydrophobic organic
compounds.
> Plant bioassays involving analysis of plant
tissue to determine if contaminants are
present at elevated or potentially toxic lev-
els, with the capability to measure
bioavailability of a wide range of organic
and inorganic compounds.
> Earthworm assays involving tests on sur-
vival, reproduction, growth, or contamina-
tion bioaccumulation of earthworms, which
serve as important indicators of contami-
nant bioavailability in soil due to direct der-
mal contact.
Health risk-based techniques include:
> Physiological-based extraction test
(PBET) testing, an in-vitro test network
using grastrointestinal tract parameters
representative of a human to predict
bioavailability of metals from contaminated
soD.
> In-vitro extraction test, a simplified PBET
using an aqueous solution to simulate gas-
trointestinal fluid into which contaminated
soil is introduced.
ERTC worked with field staff to demonstrate
use of these TPM's for evaluating organic-
amendment technology at mining sites in
Leadville, CO, Jasper, MO, Kellogg, ID, Picher,
OK, and Prescott, AZ. Although regulatory
concurrence on technology effectiveness
varies, consistent application of TPMs allows
for efficiency comparisons across similar
technologies involving similar costs. EPA is
working with other organizations such as the
Interstate Technology and Regulatory Council
to establish cost-effective and consistent
protocols for using these TPMs.
Contributed by Harry Compton, US. EPA
ERTC (compton.harry@epa.gov or 732-
321-6751), Mark Sprenger, U.S. EPA
ERTC (sprenger.mark@epa.gov or 732-
906-6826), and Scott Fredericks, U.S. EPA
Office of Solid Waste and Emergency
Response (fredericks .scott@epa .gov or
703-603-8771)
PBB Containing Processed Fish Bones Sequesters Metals from Ground Water
Over the past decade, the U.S. Department
of Defense, U.S. EPA, and other government
or academic agencies sponsored
demonstrations employing biogenic apatite
as a reactive agent for remediation of soil and
ground water. Early applications involved
circulating pumped ground water into
treatment tanks containing processed fish
bones (known as Apatite II™) or the direct
mixing of apatite into soil (see the March 2002
issue of Tech Trends, online at http://
www.cluin.org/products/newsltrs/ttrend/
archive.cfm). More recently, apatite served
as the reactive medium in a PRB demonstration
at the Success Mine and Mill site in northern
Idaho. Evaluation of the system's performance
over four years indicates that the PRB reduced
concentrations of target metals in ground water
99%, significantly above the anticipated 75%
reduction, but experienced difficulty maintaining
a constant flow of water.
The PRB was installed in 2001 to address
leaching of metals from approximately 500,000
tons of mine tailings at a former disposal area
adjacent to a tributary of the Coeur d'Alene
River. Below the tailings, an alluvial layer
extends to bedrock at 16-20 feet bgs.
Investigations indicated that soil contained
lead, zinc, and cadmium in concentrations
ranging from 1,000 to 4,000 mg/kg. Ground-
water and surface seeps also contained
elevated concentrations of the metal
leachates, reaching 1.25 mg/L for cadmium,
1.44 mg/L for lead, and 177.0 mg/L for zinc.
Biogenic apatite was selected as the reactive
medium due to its ability to stabilize metals in
water through precipitation, co-precipitation,
sorption, or biological stimulation. In
addition, the organic carbon in apatite could
[continued on page 6]
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[continued from page 5]
serve as both an electron donor and carbon
source for sulfate-reducing bacteria that
accelerate precipitation of metal (particularly
zinc) sulfides directly onto the reactive medium
surface. Based on the results of bench-scale
tests performed by the Idaho Department of
Environmental Quality (IDEQ), fish-bone
apatite was selected for the PRB rather than
alternate forms such as synthetic
hydroxyapatite, mineral apatite from
phosphate rock, or cow bones.
Construction of the PRB involved excavation
of a 15-ft-wide trench extending 14 feet bgs
and 50-ft-long and between the tailings pile
and creek. The trench was lined with type-V
Portland cement in a baffled pattern to create a
two-cell vault that would uniformly receive
seep and alluvial ground-water flow. Each cell
contains five 6-ft-wide, 9-ft-long chambers
separated by plywood baffles that bring ARD
into optimal contact with the reactive medium.
j Both cells were filled with 100% Apatite n.
!
j The vault was plumbed and valved to allow
sampling and potential replacement of the
reactive media. A1,200-ft grouted containment
wall and hydraulic drain were installed
upgradient of the PRB to divert water to the
treatment vault while reducing migration of any
contaminants bypassing the system. Captured
ARD flows from the drain through
underground piping and into the vault, where
the water is split and piped into each of the
two cells for parallel treatment. Upon exiting
the vault, treated water discharges to a rock
apron that routes it into the nearby creek. Water
passes through the vault at a rate of
approximately 5 gpm, resulting in a total
residence time of approximately 24 hours.
After a year of operation, one of the cells
exhibited plugging. A 1:1 mixture of pea
gravel and apatite was mixed into the cell to
increase porosity and the rate of treatment flow.
Data collected over four years of monitoring
indicate that water exiting the PRB contains lead
and cadmium in average concentrations below
the detection limits of 0.005 mg/L and 0.002 mg/
L, respectively. Zinc concentrations also
decrease as a result of treatment, to below the
average background level of 0.100 mg/L.
Concentrations of these metals in the effluent
consistently meet the State of Idaho criteria for
drinking water. In addition, pH of the water
increases from 4.5 before treatment to 6.5-7.0
upon exiting the PRB. Slightly elevated
concentrations (approximately 10 ppm) of
chemical byproducts such as ammonia and
phosphate exist in water exiting the vault but
decrease after passing through the rock apron.
Sample analysis also shows that water entering
the vault contains an average sulfate
concentration of 250 mg/L, while sulfate in
water exiting the system ranges from 35 to 150
mg/L. X-ray diffraction analysis performed by
Idaho National Laboratory (INL) confirmed
high concentrations of sulfate in precipitates
formed in the media. Detailed analyses of
microbial communities within the PRB suggest
that sulfate-reducing Enterococd bacteria are
the primary drivers of sulfate reduction in the
ARD. Analysis of the treated water indicates
that these microbial populations do not exist in
Results of a Representative Sampling Event
pH Metal Concentration (ppm)
5-
Eh
L0001
'50
01
Inlet [sulfate]=216 ppm
[nitrate]=0 58 ppm
[phosphorous]=0 04 ppm
Chamber 1
Chamber 2
Chamber 3 Chamber 4 Chamber 5
Outlet [sulfate]<0 05 ppm
[mtratej<0 02 ppm
[phosphorous]~9-10 ppm
\50l-
the system effluent. Changes in key ground-
water parameters indicate that a
corresponding increase in metal precipitation
is caused by the sulfate-reducing bacteria
within the PRB (Figure 3).
Although influent initially entered the PRB
at a rate of approximately 30 gpm, it quickly
decreased to and remained at 5 gpm due to
intake buildup of suspended alluvial silica
and breakdown of the apatite. Subsequent
system optimization conducted by
researchers from INL and IDEQ involved
replumbing of the intakes, which had little
effect on the rate of treatment flow. In
addition, INL injected air into both treatment
cells during a single event last spring in order
to aerate the apatite medium and to decrease
overflow at both of the cell inlets. Air
sparging resulted in a 7- to 15-fold temporary
increase in treatment flow and cessation of
the overflow. Overall results indicate that
mixing of apatite with pea gravel did not
improve the rate of treatment flow or decrease
performance of the system.
A total of approximately 150 pounds of lead,
100 pounds of cadmium, and 10,000 pounds
of zinc were sequestered in the vault during
the demonstration, over 80% of which
collected in the first two treatment chambers
of both cells. As of mid 2005, field
investigations suggested that about 40% of
the barrier was spent. The reactive media
consequently were removed from the apatite/
gravel cell and disposed onsite as non-
hazardous waste later in the year. The cell
was re-filled with limestone in the first
chamber and a mixture of apatite and plastic
packing rings (to provide additional aeration)
in the remaining four chambers.
Due to its extremely high concentrations
relative to lead or cadmium, zinc is expected
[continued on page 7]
Figure 3. Changes in key ground-water
parameters within the Apatite II PRB indicate
thai pH of the ARD is buffered during
treatment and that metals are sequestered from
ARD primarily within the first two treatment
chambers.
Dissolved
Oxygen (DO)
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[continued from page 6]
to serve as the indicator of PRB break-
through. Longevity of the PRB will depend
upon the ability to reduce system plugging
and maintain an adequate rate of treatment
flow. Construction of the PRB cost more than
$500,000, including $35,000 for 100 tons of
Apatite II.
Similar performance results were demonstrated
for an apatite PRB at the Nevada Stewart Mine
Site near Wallace, ID, where routine air
injections are performed to reduce system
plugging. Animal toxicity studies conducted
by the IDEQ at that site (using the invertebrate
Ceriodaphnia dubia and the fathead minnow
Pimephalespromelas,) demonstrated complete
toxicity removal for both species from
contaminated water that had passed through
the PRB. Additional microbiological studies
recently conducted at New Mexico State
University (NMSU) suggest that apatite can
induce biodegradation of contaminants such
as perchJorate, TNT, and RDX.
Contributed by Bill Adams, EPA Region
10 (adams.bdl@epa.gov or 206-553-
2806), Neal Yancey, INL
(neal yancey@INL.com or 208-526-
5157), James Conca, Ph.D., NSMU
(jconca@cemrc.org or 505.706.0214),
and Judith Wright, Ph D., PIMS NW, Inc.
(judith@pimsnw.com or 505.628.0916)
MWTP Demonstrates Integrated Passive Biological System for Treating Acid Rock Drainage
The U.S. EPA and U.S. DOE recently
completed a four-year, pilot-scale
demonstration of a passive biological system
for treating ARD at the Surething Mine near
Elliston, MT. Mining of gold, zinc, and lead at
this mine from the late 1800's until the mid
1950's exposed sulfide mineralization to the
environment, which led to ARD discharge
from the mine adit. In addition to being highly
acidic, the ARD contained elevated
concentrations of iron, aluminum, copper,
zinc, lead, arsenic, cadmium, and manganese.
This demonstration was one of several
sponsored by the Mine Waste Technology
Program to identify effective source-control
technologies for retarding or preventing acid
generation at mining sites.
The technology's multi-stage process at the
Surething Mine involved sequential passage
of ARD from the mine adit through three
adjacent anaerobic reactors and an aerobic
reactor. Anaerobic treatment relied on sulfate-
reducing bacteria that reduced dissolved
sulfate to hydrogen sulfide, which reacted
with dissolved metals to form insoluble metal
sulfides. This bacterial metabolism also
produced bicarbonates that increased pH of
the ARD and limited dissolution of metal.
Seven of the eight target metals were
addressed through the anaerobic process.
The treatment system was constructed in the
summer of 2001. It was designed to treat a
maximum ARD flow rate of 2 gpm, although
rates varied due to seasonal influences and
reached 10 gpm during spring runoff. The
first anaerobic reactor through which ARD
passively flowed was constructed of a mixture
of cow manure and walnut shells. Cow manure
provided a source of easily degradable organic
carbon and large populations of sulfate-
reducing bacteria. The walnut shells provided
a longer-term source of organic carbon and
the structural strength needed to maintain
permeability of the mixture. Bench-scale tests
indicated that this initial reactor would
successfully establish the sulfate-reducing
conditions needed for the overall system, but
also that it would be the first to fail due to
bacterial incompatibility with the low pH of feed
water. Sulfate-reducing capabilities also were
challenged by the presence of iron ion in the
ARD, 95% of which existed in the ferric state.
Drainage water then flowed passively through
the second anaerobic reactor, which was
constructed of limestone cobbles that added
alkalinity to the water. Earlier laboratory tests
indicated that the previous cell's reduction of
ferric iron to ferrous iron reduced the extent of
limestone "armoring" from ferric iron
precipitates during ARD residence in this
reactor. The third adjacent reactor, containing
the same cow manure/walnut shell mixture as
the first, served as the primary driver of sulfide-
precipitating reactions that removed metals
from solution. With the exception of
manganese, concentrations of all target metals
in water exiting this reactor were below state
water quality standards.
Drainage water leaving the final anaerobic
reactor was aerated by routing it through 300
feet of corrugated pipe "riprap" (a sequence
of small partitions placed in the pipe to
increase reaction-time solution mixing). The
water was allowed to aerate 2-3 hours more in
an above-ground tank before passively
flowing into the fourth reactor for aerobic
treatment. This final reactor was constructed
of a shallow, baffled limestone bed that
provided an environment for indigenous
manganese-oxidizing bacteria to thrive and
for subsequent removal of manganese as a
precipitate. After modifications were
performed to the final reactor, 99% removal
[continued on page 8]
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Washington, DC 20460
Phone:703-603-7198
Fax: 703-603-9135
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I
{****/
s.«^
United States
Environmental Protection Agency
National Sen/ice Center for Environmental Publications
P.O Box 42419
Cincinnati, OH 45242
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-06-002
March 2006
Issue No. 23
Presorted Standard
Postage and Fees Paid
EPA
Permit No. G-35
Official Business
Penalty for Private Use $300
Table 2. Sequential biological treatment
of ARD ai the Snrethini; Mine through both
anaerobic and aerobic processes resulted in
an average metal reduction oj'997f.
[continued from page 7]
of the manganese was achieved and
secondary MCLs were met.
Due to the ARD's relatively long residence
time in the reactor network, testing of influent
and effluent concentrations of target metals
and of water quality parameters was
conducted only monthly. Performance
monitoring included sampling of the ARD for
pH and metals analysis, as well as equipment
tests to ensure an adequate rate of ARD flow.
During 2002-2003, intermittent plugging
occurred in pipes that connected the first and
second reactors, but the problem was solved
by reconfiguring the feed system. Later in 2003
and 2004, aeration of water flowing into the
final reactor was enhanced by installing 200
additional feet of corrugated pipe with waterfall
weirs.
1
ARD Parameter
aluminum
arsenic
cadmium
copper
iron
lead
manganese
zinc
sulfate
ammonia/nitrogen
pH (standard units)
Feed
Concentration
(mg/L)
29.5
0.127
0.208
2.35
15.0
0.151
26.7
22.7
591
0.11
2.58
Discharge
Concentration
(mg/L)
<0.04
<0.01
<0.00009
<0.003
<0.014
0.004
0.037
O.007
239
0.37
7.31
State Standard
(mg/L)
0.087
0.010
0.00076
0.037
0.31
0.015
0.0501
0.338
2501
4.612
6.5-8.5
1 EPA secondary MCL 216°C, pH 7.3
The demonstration concluded in October 2005
when MCLs were attained for all target metals
and pH of the water returned to a neutral range
(Table 2). During four years of operation, the
system treated approximately 3 million gallons
of ARD.
Construction of this system cost approximately
$250,000. The evaluation results show that this
technology provides an effective alternative to
pumping and ex-situ treatment of ARD. Detailed
information on this demonstration will be
available in a final report to be issued by the
U.S. EPA ORD later this year (at http://
www.epa.gov/ORD/NRMRL/pubs/).
Contributed by Diana Bless, U.S. EPA
ORDINRMRL (bless.diana@epa.gov or
513-569-7647), Helen Joyce
(helen.joyce@mse-ta.com) and Brian
Park (brian.park@mse-ta.com), MSE
Technology Applications, Inc. (406-494-
7232)
EPA is publishing this newsletter as a means of disseminating useful Information regarding innovative and alternative treatment techniques and
technologies. The Agency does not endorse specific technology vendors.
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