A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Technology
News & Trends
EPA 542-N-14-005 I Issue No. 69
Spring 2015
This issue of Technology News & Trends highlights innovative approaches for remediating sites that are
contaminated due to the presence of mining-influenced water (MIW) or solid waste associated with the mining of
hard rock, coal or uranium. About 14,000 active and 500,000 abandoned mining sites are estimated to exist across
the United States. Whether past or ongoing, mining operations can create a host of contamination issues, including
the release of contaminants of concern such as arsenic, cadmium, copper, lead and zinc, into soil, groundwater
and surface water. Much of the contamination is associated with acid rock drainage (ARD) that is generated when
surface water or groundwater comes into contact with acid-generating mine wastes or with bedrock exposed by
mining processes.
Federal partners such as the U.S. Bureau of Land Management (BLM), Environmental Protection Agency (EPA)
and Forest Service are working with state agencies, tribes and other stakeholders such as watershed groups to
find solutions for mining sites. EPA also is working with industry to identify cost-effective and low-maintenance
treatment systems for mine site cleanups. Factors affecting selection of a treatment technology for a mining site
commonly include the site's available land surface, topography, remoteness, access to power and other utilities, and
climate regime. Other factors concern the treatment system's anticipated longevity, maintenance needs, flow rate
and performance criteria.
EPA continues to foster broader restoration and reuse of mining sites. Rebuilding of plant and animal habitat, for
example, enables ecological land reuse of mining sites and restores associated ecosystem services to a
community. When aligned with the community's vision, development of renewable energy offers additional means
for returning past mining sites to sustainable and beneficial use.
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FEATURED ARTICLES
Pilot-Scale Operation: Bacteria-Inoculated Limestone Treatment of AMD on National
Forest Land
Contributed by Mike Nicklow and Shiv Hiremath. Ph.D., U.S. Department of Agriculture Forest Service
The Kimble Creek remediation site in the Wayne National
Forest of southeastern Ohio is one of several abandoned coal
mine sites responsible for acid mine drainage (AMD) pollution
of ground and surface water in the region. Ongoing release of
AMD with high concentrations of metals such as iron, aluminum
and manganese and associated conditions such as high
surface water acidity were found harmful to the aquatic life. In
2003, a pilot-scale remedy was constructed at the Kimble Creek
site (Figure 1) to test performance and economics of an
underground treatment system employing metal-oxidizing
bacteria adsorbed onto limestone rocks. Based on its
performance, the system was enlarged in 2005 to handle a
higher rate of influent flow. Intermittent tests over the past nine Figure 1. Surface of the underground
years indicate the treatment system is functioning as expected. limestone/microbial treatment system (in
foreground) positioned upgradient of
The AMD became evident after a 1995 rainstorm, when orange- Kimble Creek
tinted water was observed in Kimble Creek and a fish kill occurred farther downstream in Pine Creek. Water
samples from Pine Creek exhibited iron hydroxide precipitate, abnormal surface water chemistry and lack of
normal stream fauna. A preliminary assessment and site inspection and an engineering evaluation and cost
analysis (EE/CA) concluded that a 0.4-acre area within the former underground coal mine along Kimble Creek
was partially filled with approximately 168,000 gallons of acidic water.
The EE/CA surveyed 14 removal action options and investigated three in detail: (1) mine dewatering with
expanded flow diversion; (2) mine dewatering with limited flow diversion and bioaugmentation; and (3) an
underground treatment system involving a microbiological treatment system known as the Pyrolusite Process®.
The microbiological treatment system was selected due to its previous effectiveness at other sites, as well as
potential technical difficulties in implementing the first two options. The system was designed by Wayne National
Forest personnel over 10 months in 2002 with assistance from the Forest Service's Northern Research Station.
The project is located on a moderately steep, forested, southwest-northeast trending hill with three mining-
related benches crossing the hillside. Three portals are known to exist in this area, and another portal may exist
along the lowermost bench. All three portals drain into Kimble Creek, which ultimately flows into the Ohio River.
Coal waste known as "gob piles" near or downhill from these portals contribute to the emerging AMD. The AMD
crosses the bench and flows downhill through gob, consequently coalescing into a single flow path at the toe of
the gob. Flow measurements showed that the water volume increases from the portal to the gob toe, indicating
that subsurface flow through the gob is augmenting surface flow. The highest AMD flow measured at the toe to
date is 15 gallons per minute (gpm).
The treatment system consists of a limestone bed inoculated with selected aerobic bacteria. As the bacteria grow
on rocks, they etch away the limestone, releasing calcium carbonate that neutralizes the AMD acidity and
oxidizes metals. Manganese removal under these conditions is achieved at pH 6 to 7; in contrast, other chemical
treatment methods typically require a pH rise to 9.5. These conditions also enable removal of iron, a major
component of AMD, as a dense, crystalline, low-volume oxide. Normally, iron in AMD precipitates out as a
voluminous hydroxide (yellowboy) that easily clogs a treatment system. When pH increases, this technology also
removes aluminum through abiotic processes.
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Use of limestone in the treatment bed offered the advantages of high calcium content, low cost, ease of use and
formation of a dense, easily handled sludge as an end product. Expected disadvantages of using limestone
included slow reaction time, loss in system efficiency due to coating of the limestone particles with iron
precipitates, difficulty in treating AMD with a very high ferrous-ferric oxide ratio, and ineffectiveness in
manganese removal. Introduction of microbes was anticipated
to mitigate most disadvantages.
Construction of the treatment system began in March 2003
and was completed in two months. A conventional trackhoe
was used to dig a trench approximately 50 feet wide, 15 feet
long and 7 feet deep. The bottom of the trench was lined with
a layer of synthetic, water-proof fabric that was baffled by PVC
pipes to form three cells (Figure 2). A mini-excavator was
"walked" into the cell to avoid liner damage and spread the
material into areas exceeding the trackhoe reach. Each cell
received approximately 500 cubic yards of limestone obtained
from a local quarry. The cells also received approximately 1
cubic yard of rocks already exhibiting bacterial growth due to
earlier inoculation. Six ports were installed for water and rock
sampling.
Figure 2. Limestone emplaced in three lined,
underground treatment cells at the Kimble
Creek site
Within days of completing construction, a mixture of five
strains of metal-oxidizing bacteria was introduced to the
limestone beds via buckets at each of six inoculation ports
(Figure 3). One re-inocoluation of the same bacterial solution
was performed at each port over the following 12 months.
The pilot-scale system was designed to treat an average AMD
flow of 2 to 4 gpm. Pipes at the upgradient end of the
treatment system collected the AMD. To achieve a "wave" of
AMD flow through different depths of the limestone beds,
AMD entered at the bottom of the first cell then passed
Figure 3. Inoculation of bacteria solution
into a port extending into limestone
emplaced at the Kimble Creek site
through the remaining cells via pipes at the top and bottom of
each cell. The water exited the system at the top of the third
cell, on the northeast (downgradient) end of the treatment
area. From there, the effluent traveled through a series of
diversion pipes extending under two adjacent roads and ultimately to Kimble Creek for discharge. The limestone
beds were annually flushed to collect accumulated sludge, which was stored in an adjacent aboveground cell for
ultimate offsite disposal.
Two major changes were made to the treatment system during its first year of operation. Due to significant
clogging in the influent pipe, an upgradient manifold was added to aerate the influent AMD and direct it to the top
instead of the bottom of the first treatment cell. Also, after suboptimal bacterial growth was observed on the
limestone at the ground surface, an upgradient vegetation-covered holding cell was installed to provide additional
carbon sources that could provide more bacterial nutrients. This design aspect was not previously incorporated
since the site is thickly vegetated.
Determining the system's performance focused on evaluating pH and metal content of the influent and effluent,
the bacterial growth and metal deposition on rock surfaces, and the sludge generated by the treatment process.
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Monthly sampling during the first year of operation indicated the system operated effectively. For example,
effluent pH was significantly higher than influent pH during each sampling event, with an average pH increase of
approximately 2 standard units (s.u.) (Figure 4). Also, acidity of the influent was almost completely removed
through the treatment process (Figure 5). Concentrations of metals similarly decreased; for example,
concentrations of aluminum (the second most common contaminant at this site) in the influent were as high as
100 milligrams per liter (mg/L) but decreased to almost non-detect levels in the effluent samples.
H-nfimvpH
•outflow pH
*
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colorimetric method was used to approximate Fe+^ and Fe+J percentages. This method showed that
approximately 90% of the iron was Fe+3, indicating the bacteria were effectively oxidizing ferrous hydroxides to
the desired crystalline ferric form. Additionally, toxicity characteristic leaching procedure (TCLP) digestion
analysis of the sludge samples indicated that hazardous constituents were below detectable levels, thereby
allowing future disposal of the sludge elsewhere within the Wayne National Forest as nonhazardous solid waste.
In 2005, the pilot-scale system was replaced by a larger treatment system (Figure 6) capable of handling up to
15 gpm AMD. Limestone was removed from the three existing cells and 12 additional cells were constructed
using the same techniques used earlier. The 15 treatment beds were inoculated and a drainage system was
installed to divert clean surface water away from the treatment beds.
Influent and effluent sampling about 18 months later indicated that the treatment system continued to increase
pH and decrease metal concentrations in the AMD (Figure 7). Based on the average flow, the enlarged system
has effectively treated nearly 20 million gallons of AMD over the past nine years. Implementation costs to date
total approximately $300,000, including $220,000 for the limestone bed, $20,000 for the bacterial inoculants, and
$60,000 for monitoring over the first six years of operation.
Treatment System Influent and Effluent
(December 28, 2006)
Parameter
Influent Effluent
Flow (average)
pH su
Iron (dissolved), mg/L
Zinc (dissolved). mg/L
Calcium (dissolved). rrsg/L
Aluminum (dissofved). mg/L
Manganese (dissolved), mg/L
Sulfate, rn^L
4.0 gpm
A f\r\
1.UO
22,700
137
94
10;200
510
344
7.26
69
<10
172
<2QO
350
552
Fiaure 7. Performance of the limestone/bacterial treatment beds at the Kimhle Creek Kite annrnyimatelv 1 5
years after the system expanded to 15 treatment cells
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Full-Scale Operation: Biochemical Reactor Treats ARD Near Lake Shasta
Contributed by Brad Shipley, U.S. Department of Agriculture Forest
Service, and James Gusek, Sovereign Consulting Inc.
The Golinsky Mine is an abandoned underground base metal mine in
Shasta County, California, within the Shasta-Trinity National Forest. In
2010, a biochemical reactor (BCR) with a treatment capacity of 10
gallons per minute (gpm) was constructed to address onsite acid rock
drainage (ARD). Construction of the BCR was significantly challenged by
the site's remote location and rugged terrain as well as precipitation,
which also influences the rate at which the BCR now treats ARD. The
fully passive treatment system has functioned unattended since
installation and is achieving approximately 95% metal removal and a
more neutral pH. Projected longevity of the BCR media is approximately
20 years. Annualizing the $1.3 million construction cost, which was funded
by the American Recovery and Reinvestment Act, over the total expected
flow for two decades in dicates a unit treatment cost of about 1.3 cents per
gallon of ARD.
Figure 1. Vintage World War II
landing craft used for transport
across Lake Shasta
The Golinsky Mine was last active in the early part of the 20th century, when copper and zinc and small amounts
of precious metals were recovered. The site comprises the mine as well as a milling and smelting complex
situated in mountainous terrain. Access to this site is by boat (Figure 1), typically traveling three miles across
Lake Shasta. Three former mine adits known as the Upper Portal, Lower Portal, and Portal 3 (Figure 2) exist.
Concrete bulkheads were installed in 2001 at the upper and lower portals to flood the mine workings and
suppress pyrite oxidation and ARD by perpetual submergence. Portal 3 indirectly connects to workings that are
bulkheaded through natural fractures.
Portal 3
Valve (typ)
Lower Portal
Upper Portal
1-toKJog Tank
Buried 6* HOPE pipeline
Flow control vatw &
(not twin)
Trapezoidal Flume
(BCR Influent samping pom!)
Reactor (SCR)
Modutoi
a! Quarry
By-Pas* Flow PipO
(not installed)
'-Acce» Road
: To Lak* Sha*l.i
ll Beach Head
Figure 2. Schematic of BCR infrastructure at the Golinsky Mine
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Geochemistry of the main mine ore, in workings of the Upper Portal and Lower Portal, is dominated by pyrite and
other sulfides, which results in an ARD pool exhibiting a pH of 2.5 to 4 and containing metals such as iron,
aluminum, copper, zinc, cadmium and manganese. Portal 3 reportedly exhibited ARD with a neutral pH and trace
levels of metals prior to installation of the concrete bulkheads; however, the condition deteriorated soon after
bulkhead construction and persisted until the BCR was installed and the main mine pool was drained down. The
change was attributed to a rising level of ARD in the main mine pool, which induced ARD migration through
natural fractures toward the Portal 3 workings.
In late 2003, Region 5 of the U.S. Forest Service investigated methods of treating and discharging the main mine
pool water behind the two concrete bulkheads and to collect and treat ARD discharging from Portal 3. The
measures aimed to improve water quality in Little Backbone Creek, a tributary to Lake Shasta. Passive treatment
methods were preferable due to the site's limited access and lack of electricity and other infrastructure. Onsite
bench- and pilot-scale testing (Figure 3) in 2003 indicated a BCR could effectively treat the ARD.
Figure 3. Bench-scale testing (left) and pilot-scale application of a BCR treating ARD at a rate of approximately 1
gpm (right) at the Golinsky Mine
Figure 4. Barge delivery of sacks filled
with organic media or other construction
materials such as drainage gravel and rip
rap needed for the Golinsky Mine BCR
Space to construct a full-scale BCR adjacent to the draining
mine adits was insufficient due to very steep terrain. Therefore,
it was constructed at a nearby abandoned limestone quarry. In
2004, a 1.5-mile-long pipeline was constructed to collect the
ARD from the two bulkheaded adits and Portal 3 and deliver it
by gravity to the quarry.
During construction, high water levels in Lake Shasta caused by
high precipitation in the spring necessitated use of a distant boat
ramp, which added nearly six miles of cross-lake commute.
Most construction equipment and materials were transported on
a prefabricated barge (Figure 4). Construction materials were
offloaded from the barge with a rented crane and transferred to
a flatbed truck for the one-mile trip to the quarry. Due to limited
quarry space, more than 2,000 fabric sacks of the imported
materials were stored along an access road (Figure 5).
Similar to the pilot application, the full-scale BCR cell was configured as a vertical flow bioreactor with flow
entering the top of the cell and flowing out the bottom. The BCR contains approximately 1,700 cubic yards (yd3)
of organic media comprising rice hulls (10% by weight), wood chips (50%), hay (10%) and limestone (30%). This
recipe was similar to the pilot recipe with the exception of using wood chips to save costs in place of organic
matter purchased from a local biomass-fueled power facility. Approximately 4 yd3 of composted or fresh animal
manure was tilled into the top six inches of the BCR media to provide the necessary initial bacterial community;
experience in other BCR bench-scale tests suggested that such a relatively small amount could achieve the
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desired bacterial inoculation while minimizing the volume
needing to be imported. About 2 yd3 of media saved from the
pilot-scale BCR during its decommissioning was
simultaneously tilled into the top soil to provide microbes that
had already adapted somewhat to the site conditions.
The original design assumed that ARD from all three portals
would be combined and treated in the BCR. In the intervening
years between draining of the main mine pool (in concert with
the 2004 pilot project) and commissioning of the full-scale
BCR, the chemistry of Portal 3 water had improved enough that
it did not require treatment. Additionally, the main mine pool had
drained to the extent that the Upper Portal remained dry. As a
result, the design was modified for BCR receipt of ARD only
from the Lower Portal, which flowed at a rate averaging 10 gpm.
Figure 5. Construction materials stockpiled
along a quarry access road near the
Golinsky Mine
In October 2010, the organic materials and limestone were proportioned, mixed, and placed in the BCR trench,
which was lined with 1.5-millimeter geomembrane (Figure 6). Diversion of the Portal 3 ARD to the quarry area
also began at that time; due to its improved chemistry, that ARD was used for fire suppression, dust control on
haul roads, and moisture control in earthwork fill placement.
Commissioning of the BCR was anticipated to involve filling it
with a mixture of Portal 3 and Lower Portal ARD that would
allow bacterial incubation to commence. During the last week
of construction and the following two weeks, however, the site
received approximately 11 inches of rainfall that filled the BCR.
The startup procedure was consequently modified to include
addition of Epsom salt and agricultural gypsum. Sampling
indicated that sulfate concentrations in the influent rebounded
within two months, enabling the microbial community to begin
the sulfate reduction process.
The BCR effluent flows via gravity into either of two flow
dispersion zones (FDZs). Each FDZ consists of an unlined
percolation trench equipped with a series of standard flow
infiltration chambers, which are commonly used in residential
septic systems. Although a single FDZ was initially used, frequent backup of the BCR effluent prompted
construction of a new FDZ to fully handle the design flow rate of 10 gpm. The original FDZ, which was found to
include a thin soil layer that limits effluent infiltration into underlying bedrock, now serves as an auxiliary system
to handle excess from higher flow rates or other temporary conditions. Based on sampling results and
observations during the pilot-scale operations, the infiltrated BCR effluent generally follows subsurface bedrock
fractures or runs along the bedrock-colluvial contact before mixing with and becoming indistinguishable from
other subsurface drainage that may periodically surface within an unnamed ephemeral tributary to Little
Backbone Creek, near its confluence with Shasta Lake.
Figure 6. Placement of media in the
Golinskv Mine BCR
Germination of vegetation from seed in the hay component of the media occurred soon after the onset of
inclement weather in the following autumn. Within five years, willows up to 16 feet tall and other plants had
colonized the BCR surface (Figure 7). This vegetation may be suppressed in the future if oxidizing micro-
environments in the root zone are found to suppress sulfate reduction.
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Figure 7. Progression of revegetation above the Golinsky Mine BCR, at three months after construction
completion (left) and four years later (January 2015, right)
The BCR was designed to provide an ARD residence time of about nine days at the design flow rate.
Semiannual monitoring demonstrates consistent water quality in BCR effluent, with a pH rise from approximately
4 to 6.5 and significant removal of metals (Figure 8), with the exception of manganese. Experiences at other
sites indicate that BCRs typically do not remove manganese and that naturally-occurring manganese in the
organic substrate is commonly mobilized (rinsed) from the substrate, especially at startup. The mobilized
manganese is likely deposited as manganese oxide (known as "desert varnish") on the rock surfaces in and
adjacent to the FDZs. Trace levels of other metals that elude removal in the BCR are expected to adsorb to
these rock surfaces, providing additional passive polishing of the BCR effluent.
BCR Influent and Effluent
(March 11,2011)
Parameter Influent Effluent
Flow
pH s.u
Iron (dissolved), mg/L
Copper (dissolved), mg/L
Zinc (dissolved), mg/L
Cadmium (dissolved), mg/L
Aluminum (dissolved), mg/L
Manganese (dissolved), mg/L
Sulfate mg/L
7.2 gpm
2.8
34
9
18
0.15
15
0.24
340
7.8
1.4
0.002
0.03
0.006
0.02
1.6
100
Figure 8. Observed How and chemistry of ARD entering and exiting the Golinsky Mine BCR four months after its
commissioning
The BCR has required no maintenance over the five years of operation. During storm events, the pipeline used
to collect ARD at the Lower Portal has experienced some scaling and clogging by sediment. Flanges were
installed on the pipes to allow easier and speedier cleaning when needed, which has occurred twice to date.
Also, some scaling in the inlet flume box has slightly impacted accuracy of the pressure transducer used for
continuous flow measurements.
Due to the prevailing drought in California, adit drainage has completely stopped from late spring to early fall
during the past three years. The near stagnant conditions appear to have no measurable effect on water
chemistry or metal removal within the BCR. Low or no flow of adit drainage under the anoxic conditions existing
in the BCR may result in a low rate of cellulosic bacteria degradation of the organic matter, potentially increasing
longevity of the BCR.
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Remedy Optimization: ARD Treatment Plant Combined with Source Control at the Gilt
Edge Mine
Contributed by Joy Jenkins, U. S. EPA Region 8
Cleanup at the 360-acre Gilt Edge Mine Superfund site in the
northern Black Hills of South Dakota involves an acid rock
drainage (ARD) collection and conveyance system and a
water treatment plant that has operated since 2000. The
most significant ARD source in 2000, when the site was
listed on the National Priorities List, was the Ruby Mine
Waste Dump left behind by past mining activities. Re-grading
and capping of the former dump was completed in 2006. In
2016, significant earthwork will begin addressing ARD sources
remaining within the primary mine disturbance area, which
includes acid-generating waste rock and fills, spent ore, exposed acid-generating bedrock in mine pit highwalls
and sludge (Figure 1).
Figure 1. Aerial view of Gilt Edge Mine
Superfund site
A recent five-year review and optimization study indicate
that the treatment plant, which uses a lime-based
precipitation process, operates effectively. The review also
confirmed that the planned ARD source control work should
significantly reduce the volume of water requiring treatment
in the future. Current optimization activities focus on
reducing the cost of operating the treatment plant and
preparing for future earthwork that prevents precipitation
and runoff from contacting ARD-generating material.
Additionally, plans for site drainage structures were recently
modified to accommodate updated predictions of severe Fjgure 2. Spent ore from the cyanide
storm events at this site. heap leachjng process formerly used at
the Gilt Edge Mine
The contaminants of concern in surface water, groundwater,
soil and sediment include metals (arsenic, cadmium, chromium, copper, lead, nickel, silver, thallium and zinc) as
well as sulfate contributing to total dissolved solids. Cyanide and nitrates were a concern for a time after
termination of the mining activities, which included a cyanide heap leach process (Figure 2) and rock blasting to
extract gold and silver ore. Sampling indicated that the source of these contaminants was eliminated when active
mining ceased.
The rate of ARD generation at this site varies considerably, due to variable precipitation rates influenced by
orographic effects as well as regional weather patterns. For example, in 2012 and 2013 the site received
approximately 19 inches and 49 inches of precipitation, respectively. Hydrologic modeling indicates that each
inch of precipitation at this site generates approximately 34 million gallons of ARD requiring treatment.
To reduce migration of metals and acidic water to streams, the ARD seeps and surface water runoff are collected
and conveyed to the water treatment plant. The plant's lime-based precipitation process (Figure 3) is capable of
accommodating a flow of about 325 gallons per minute (gpm). Collected ARD exceeding this capacity is stored in
onsite impoundments, including former mine pits. Treated water is discharged onsite to Strawberry Creek. The
cost to collect and treat the ARD ranges from $2 million to $2.4 million per year.
10
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The treatment plant and site are staffed 24 hours per day,
with a minimum of two operators to operate and monitor the
ARD collection and conveyance systems and water treatment
plant. Full-time staff also is needed to address potential
problems such as storm-related power outages that could
result in release of untreated water. The optimization study
recommended installation of upgraded equipment enabling
remote operation and monitoring of the treatment plant, which
could eliminate the need for nighttime staff. The upgrades
would include a supervisory control and data acquisition
(SCADA) system, additional alarms and call-outs, pumps
operated on level indicators and auto-start generators.
Conversion to a fully automated water treatment plant is
expected to cost approximately $500,000. The study also
recommended short-term operation in a batch rather than a
continuous treatment process to reduce staffing needs.
Figure 3. Addition of lime to high density
sludge treated at the Gilt Edge water
treatment plant
As of May 2012, when the optimization study was conducted, 12 million gallons of high-sulfate ARD and 4.1
million gallons of low-sulfate ARD were stored in the onsite impoundments, which have a total capacity of 253
million gallons. Under the current ARD-generating conditions and average annual precipitation (29 inches), the
treatment plant would need to operate approximately 200 days per year at a rate of 325 gpm to treat the ARD
volume generated each year. Completion of the future earthwork is expected to reduce ARD generation more
than 67%. Based on these findings, the study estimated that the treatment plant could operate fewer than 70
days per year in the future.
Approximately $315,000 were saved in 2012 due to a modified
operating plan involving a four-month suspension in treatment
plant operations and in staffed overnight monitoring. In 2013,
approximately $102,000 were saved through this approach; the
operations and monitoring suspensions were held to 1.5
months due to the higher than average precipitation. An
additional $26,400 savings was achieved in 2013 as a result of
reducing water-sampling frequency (from weekly to monthly) at
surface water locations with a long history of sampling.
Additionally, a previous energy audit revealed measures that
could reduce electricity usage and costs. Post-audit
modifications included installing a lower-power pump for
handling discharge at the Strawberry Creek pump house (Figure
4) and installing a bladder tank and smaller pump for delivering
process water from the treatment plant. Also, the electricity purchasing rate charged by the utility provider was
negotiated to a lower rate. These changes resulted in approximately $37,000 in electricity savings per year.
Figure 4. The Strawberry Creek pumping
station, one of three primary facilities for
water management at the Gilt Edge Mine
Prior to the upcoming earthwork, approximately 14 million gallons of high-sulfate water stored in two pits (Figure
5) will require processing in the water treatment plant. During processing, the mixing of high-sulfate water with
treatment lime generates gypsum that forms a cake that tends to clog the multi-media filters, the final treatment
component. Recent test-scale operations suggest that slowing the treatment flow to 100 gpm enables
precipitation of the gypsum in the system's clarifiers, thereby reducing burden on the multi-media filters. Slowing
the treatment rate would therefore allow the pit water to be more efficiently treated in the treatment plant and
avoid the alternate pre-treatment approach of adding lime to the pits , which would generate additional sludge.
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Figure 5. One of two onsite pits holding
high-sulfate water at the Gilt Edge Mine
site
In the Ruby Mine Waste Dump capping area, the waste rock
was re-graded in place in the upper portion of Ruby Gulch prior
to cap construction. The composite cap consists of an
impermeable low-density polyethylene liner placed directly
above the waste rock. A layer of crushed rock serving as a
protective layer above the liner is covered with approximately
three feet of clean soil; the soil and rock were sourced from
excess materials at a nearby highway construction project. In
the topsoil, a mix of native prairie grasses such as wheatgrass,
fescue and clover were seeded to promote re-vegetation. The
capping system includes a complex series of lateral drainage
structures that divert runoff water to uncontaminated drainage
ditches and limit infiltration and prevent erosion of the cap
(Figure 6). The cap is inspected periodically to assure its
integrity; no significant erosion problems have been identified to
date.
Approximately three years after cap construction, more work
was initiated to further reduce or eliminate surface water
infiltration into the capped waste repository, which was found to
receive water leaking from the drainage ditches. Certain ditch
sections were sealed through pressurized concrete grouting,
and other ditch sections were lined with impermeable
geomembranes. Approximately 3,200 linear feet of ditch have
been grouted, and 660 linear feet of ditch have been lined. Two
smaller repairs will be completed during the planned source
control earthwork.
The earthwork will involve excavating and consolidating mine
waste throughout the 290-acre disturbed area into three open
mine pits. The pits will be backfilled with waste and covered with
impermeable caps consisting of clean soil and vegetation,
similar to the Ruby Mine Waste Dump cap. Newly exposed soil
will be amended with lime to neutralize accumulated acidity and
then vegetated. The earthwork also will involve grading to
convey clean surface water throughout the site toward the historical (pre-mining) path of Strawberry Creek.
Additionally, a lined water management facility will be constructed to handle the site's ARD in the future, rather
than continuing to use mine pits that allow waste communication with groundwater. During years with an average
amount of precipitation, these efforts are anticipated to reduce the annual ARD generation from 97 million
gallons to approximately 30 million gallons. ARD due to groundwater-waste interaction in the bottom of the Ruby
repository (as well as the "Dakota Maid" pit), however, is anticipated to continue.
Figure 6. Five uppermost slopes and
drainage channels along the capped Ruby
Gulch waste repository, approximately
three months after seeding
To account for updated predictions of precipitation frequency and intensity at this site, including those concerning
potential climate change, the drainage structures planned in the earthwork design were modified to sustain 7.3
inches of precipitation within a 24-hour period. This specification is based on the most recent projections from the
National Oceanic and Atmospheric Administration, which estimates that 7.04 inches of precipitation within a 24-
hr period at this location have a 1% chance of occurring in any given year, which constitutes a 100-year storm. In
contrast, 4.3 inches of precipitation in a 24-hour period was the predicted 100-year storm taken into
consideration during initial remediation activities. The 4.3-inch/24-hour scenario is now considered a 25-year
storm, with a 4% chance of occurring in any given year.
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RESOURCES
Interagency Website: Abandoned Mine Lands Portal
The Abandoned Mine Lands Portal serves as an information repository about abandoned mine lands (AMI) and
their associated environmental, health and safety issues, with a focus on federal, state, local and tribal efforts in
AMI cleanup and reclamation. This website provides links to key guidance and technical resources concerning a
range of AMI topics such as voluntary cleanup under EPA's Good Samaritan Initiative, bat protection, innovative
cleanup or reclamation technologies, greener cleanup strategies and leverage of renewable energy
development. The portal also provides links to numerous case studies developed by BLM, EPA, or the National
Park Service.
EPA Website: Abandoned Mine Lands
EPA's Abandoned Mine Lands program identifies ways to protect human health and the environment by using all
of the non-regulatory and regulatory approaches available to the Agency. These approaches include voluntary
cleanups, Agency-managed emergency responses, involvement of brownfield partners, integration of site
cleanup with site redevelopment/revitalization, listing on the National Priorities List (NPL) and enforcement
activities. The Abandoned Mine Lands website offers news about mine sites and provides links to selected
resources.
CLU-IN Website: Mining Sites
This website provides information on site characterization, cleanup technologies, and revitalization and reuse of
mining sites, whether abandoned, closed, or active. Cleanup technologies addressed in this resource are
categorized by their applicability to solid waste, MIW or both. This website also provides links to upcoming
Internet seminars, workshops or conferences concerning mining sites and to archives of past seminars, videos
and courses on related topics.
EPA Reference Guide: Treatment Technologies for Mining-Influenced Water
This report (EPA 542-R-14-001) focuses on cost and maintenance reductions that may be attained through
passive treatment or through recently developed technologies utilizing hybrid passive-active treatment. It
provides detailed information on 16 technologies identified through review of technical literature or by subject
matter experts. For each technology, the report summarizes the treatment process, system operation, applicable
contaminants, scale of implementation, long-term maintenance requirements, limitations, costs and
effectiveness.
New Report: Operation and Maintenance of Passive Acid Mine Drainage Treatment
Systems; A Framework for Watershed Groups
Recognizing that funding for AMD treatment is limited, the West Virginia Department of Environmental Protection
recently compiled this report as a framework for encouraging watershed groups to develop operation and
maintenance (O&M) plans for their passive treatment projects. The framework addresses institutional practices
supporting O&M; O&M considerations through the project life cycle; best management practices (BMPs) for AMD
remediation; post construction inspection, monitoring, and operation; and post-construction major maintenance.
Particular BMPs discussed in this report include settling ponds and aerobic wetlands, anoxic limestone drains,
anaerobic vertical flow wetlands, self-flushing limestone leach beds and steel slag beds.
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Applied Research and Development: Passive Treatment of Mine Impacted Water In Cold
Climates: A Review
The Yukon Research Centre of Canada recently evaluated the challenges encountered and the adaptations
required to successfully use passive treatment systems for MIW in cold climates. The primary challenges
concern a mining site's typically remote location, limited access in winter, freezing pipes, variable seasonal flow,
and low productivity of microbial and macrophytic communities. Many adaptations have been implemented to
address these challenges, such as pipe burial to avoid hydraulic failure, pipe insulation to avoid freezing surface
waters, bypasses and overflows to maintain constant flow, summer establishment of microbial and macrophytic
communities, and addition of liquid carbon sources to offset reduced organic matter decomposition in cold
temperatures.
Upcoming and Recent CLU-IN Webinars: Mining Sites
EPA's Office of Superfund Remediation and Technology Innovation is presenting a series of webinars dedicated
to the topic of mining sites. Recent events for which archived materials are available on CLU-IN include a June 4
webinar about remedial action, remedy performance and long-term land management at the Anaconda Smelter
NPL site in Montana, and May 19 and May 20 webinars on "Mine Tailings Fundamentals: Current Technology
and Practice for Mine Tailings Facilities Operations and Closure." Archives of previous webinars in this series
can be viewed at www.cluin.org/mininq under Training and Events. On June 18, 2015, the Interstate Technology
and Regulatory Council will hold a CLU-IN webinar on Biochemical Reactors for Treating Mining Influenced
Water.
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and
alternative treatment technologies and techniques. The Agency does not endorse specific technology vendors.
Contact Us:
Suggestions for articles in upcoming issues of Technology News and Trends may be submitted to
John Quandervia email at quander.johng&.epa.gov.
Past Issues:
Past issues of the newsletter are available at httoV/www.clu-in.ora/Droducts/newsltrs/tnandt/.
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