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Comet Mine Reclamation Project, Phase I
September
3, 1997
July 8, 1998
Jefferson
Montana
Legal Description: South ½ of Section 36, Township
7 North, Range 5 West
Nearest Town and Distance: Basin, Montana which lies
about six miles to the southwest |
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| Comet
Mine Site Before Reclamation Construction |
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Location: The Comet Mine and Millsite is located in the
northeastern part of the Basin/Cataract Mining District in Jefferson
County, Montana. The Comet Mine Site is located adjacent to High
Ore Creek, approximately six miles northeast of the town of Basin,
Montana. The site is located on privately owned, patented mining
claims within and bordered by lands administered by the U.S. Department
of the Interior/Bureau of Land Management (BLM), Butte District.
The site elevation ranges between 6,100 and 6,400 feet above mean
sea level.
Project Schedule: The construction phase of the project
started on September 3, 1997. Work at the site continued through
December 19, 1997, when winter shutdown occurred. The work resumed
the following spring, beginning on May 11, 1998 and continued through
July 7, 1998. The final inspection was given by the State DEQ/MWCB
on July 8, 1998.
Project Costs: The construction cost for the project was
$1,268,623.83. Shumaker was awarded the contract with an original
bid of $903,580.00; quantity increases and change orders increased
the cost by $365,043.83. The total engineering costs associated
with the project were $296,967.26.
Project Sponsor(s): Montana Department of Environmental
Quality, Mine Waste Cleanup Bureau and the United States Department
of the Interior, Office of Surface Mining
Oversight Agency: Montana Department of Environmental Quality,
Mine Waste Cleanup Bureau (DEQ/MWCB)
Project Partners: Under contract with the DEQ/MWCB, Pioneer
Technical Services, Inc. (Pioneer), was responsible for preparing
the final design and engineering specifications for the project,
and for overseeing construction. Pioneer performed all quality control
activities for the project.
Reasons for Action: Problems at the Comet Mine Site include
high concentrations of metals and arsenic in waste materials on-site
(mill tailings and waste rock dumps) and in surface water and stream
sediments downgradient from the site. Exposed waste materials had
potential to result in significant ecological effects. Concern for
fisheries, aquatic life, wetlands, terrestrial wildlife, and native
terrestrial plant communities has resulted in the remedial actions
taken at the Comet Mine and Mill Site. The downstream Boulder River
is an important recreational trout fishery. Wetlands of any size
are of concern as they can support a diverse ecologic community.
Terrestrial wildlife may use this area as part of their summer range,
including deer and elk. Wildlife could consume both water and evaporative
salts that form on the wastes. This exposure posed a potential for
contaminant accumulation and consequent health effects in the wildlife
populations that visit the site. Native terrestrial plant communities
are notably absent on many of the waste sources at the Comet Site.
Native vegetation has not become established on the tailings or
the waste rock dumps.
Objectives: The reclamation project was designed to reduce
human, livestock, wildlife, and environmental exposure to the contaminants
of concern, as well as reduce the mobility of the contaminants to
limit impacts to the local surface water and groundwater resources.
History of Site: The Comet Mine is one of the oldest mines
in the Basin/Cataract Mining District. It was first mined in about
1880 by the Alta-Montana Mining Company. In 1883, the Alta-Montana
Mining Company sold the Comet Mine, the Alta Mine, and several other
mines to the Helena Mining and Reduction Company. The majority of
the production from the Comet Mine occurred from 1883 to1893 under
the Helena Mining and Reduction Company. In 1907, the Montana Consolidated
Copper Company deepened the Comet Mine shaft to 600 feet and continued
to operate the mine for another 20 years. The Basin Montana Tunnel
Company acquired the Comet Mine in 1926 and constructed a 200-ton
flotation mill to process Comet ore as well as custom mill ores
from other mines in the district. The mill was closed and dismantled
in 1941.
The Comet Mine is credited with production valued at $13,000,000
prior to 1911. Since 1902, the Comet Mine has produced 496,000 tons
of ore, yielding 42,000 ounces of gold; 3,000,000 ounces of silver;
28,000,000 pounds of lead; 23,000,000 pounds of zinc; and 2,000,000
pounds of copper. The mine consists of a 900-foot vertical shaft
with drifts at nine levels. In total, the mine comprised 20,000
feet of lineal workings.
Site Description: The Comet Mine Site encompasses an area
of approximately 35 acres, and includes two tailings impoundments
located in the High Ore Creek floodplain, three waste rock piles
(two of which are in the floodplain), five waste rock dumps on Silver
Hill, a large open pit mine area, and numerous abandoned buildings
and structures associated with the mine and the town of Comet. The
mill tailings deposits have been eroding into the creek for many
years. Mitigation measures have been completed on the site in the
past, primarily to minimize contact between High Ore Creek and the
tailings deposits. In 1990, the Montana Department of Fish, Wildlife
and Parks (MDFWP) sponsored reconstruction of a pre-existing creek
diversion around the waste rock piles and mill tailings, and sedimentation
ponds to control the release of mine waste sediments from the tailings
impoundments into High Ore Creek. Most recently, DEQ/MWCB initiated
interim reclamation activities at the site to improve sediment and
erosion control of the tailings deposits.
The Comet Mine is located on a mountainous hillside. Shrubland,
riparian, and timbered plant communities occur at the mine site.
The potential natural community of the shrubland is Artemisia tridentata/
Agropyron spicatum. The potential for the timbered areas is Pseudotsuga
menziesii/ Calamagrostis rubescens. No sensitive, threatened, or
endangered plants were found on-site. The following four species
of noxious weeds occur at the site: Musk thistle, Canada thistle,
Spotted knapweed, and Dalmatian toadflax. None of these occur in
populations large enough to be considered infestations. Riparian
areas occur along High Ore Creek. The riparian zone below the mine
site is a Populus tremuloides/Poa pratensis community type. The
riparian area above the mine site is a Populus tremuloides/Cornus
stolonifera habitat type. Both communities have been heavily browsed
and contain early seral species. The riparian area above the mine
is functioning, but at risk due to grazing pressure. Below the mine,
the riparian area is not functioning because of tailings in the
stream channel and grazing. Where the creek has been diverted, no
riparian community exists along the new channel.
Waste Sources: The Comet Mine Site was divided into two
distinct subunits based on the waste types, locations, and applicable
reclamation technologies. These subunits consist of: 1) the solid
media, including waste rock dumps and tailings ponds, and 2) the
aqueous media, which encompasses adit discharges, seepage, and drainage
water.
Waste Rock Dump #1 (WR1) was located on the southside of
the High Ore Creek diversion, to the west of the lower pit, and
has an estimated volume of 142,000 cubic yards (cy). Waste Rock
Dump #1 (WR1) covered an area of approximately 14,200 square yards
with steep and high banks along the entire west end. Waste Rock
Dump #1 (WR1) was accessible by vehicles and comprised one of the
largest waste volumes. Waste Rock Dump #1 (WR1) was one of the most
significant sources of COCs (Contaminants of Concern) to the surface
and ground water. Concentrations of the following metals were significantly
elevated above background (>3X) in the dump: antimony, arsenic,
cadmium, copper, lead, manganese, silver, mercury, and zinc. Waste
Rock Dump #1 (WR1) was considered a potential acid producer and
approximately 70 tons of lime per acre would have been required
to successfully establish vegetation on this material, assuming
a 12-inch depth of incorporation. The pH ranged from 4.2 to 7.2
in the five separate test pits samples from WR1. According to the
TCLP data obtained for WR1, the concentration of lead measured in
laboratory-generated leachate exceeded the regulatory limit for
hazardous waste classification.
Waste Rock Dump #2 (WR2) was also located to the south of
the High Ore Creek diversion and to the southwest of WR1. This dump
was estimated to be 85,000 cy, a little more than half the size
of WR1, and covered an area of approximately 10,200 square yards.
Waste Rock Dump #2 (WR2) was relatively devoid of vegetation and
the west bank was steep and high. Waste Rock Dump #2 (WR2) was easily
accessible by vehicles. Concentrations of the following metals were
elevated above background (>3X) in the dump: antimony, arsenic,
cadmium, copper, manganese, lead, mercury, silver, and zinc. The
pH ranged from 5.7 to 7.0 in samples taken from the three separate
test pits. According to the TCLP data obtained for WR2, concentrations
measured in laboratory-generated leachate did not exceed the regulatory
limit for hazardous waste classification.
Waste Rock Dump #3 (WR3), located east of the upper pit,
was the largest dump with an estimated volume of 150,000 cy and
covered an area of approximately 16,300 square yards. The dump was
both steep and high, with some vegetation on the surface. Vehicles
were able to access the top of this dump. Waste Rock Dump #3 (WR3)
was the source area of least concern, primarily because it was isolated
from both surface water and ground water. Concentrations of the
following metals were elevated above background (>3X) in the
dump: arsenic, cadmium, copper, lead, manganese, mercury, silver,
and zinc. The pH ranged from 5.6 to 6.8 in samples obtained from
the three separate test pits. According to the TCLP data obtained
for WR3, concentrations measured in laboratory-generated leachate
did not exceed the regulatory limit for hazardous waste classification.
Tailings Pile #1 (TP1) was located east of WR2 and extended
beneath WR1. Tailings Pile #1 (TP1) had a volume estimated at 38,500
cy of material and covered an area of approximately 7,650 square
yards. There was no vegetation on TP1 and it is accessible to vehicles.
Tailings Pile #1 (TP1) and TP2 were the largest source areas of
concern, primarily because they were located in the floodplain of
High Ore Creek. Concentrations of the following metals were elevated
above background (>3X) in the pile: antimony, arsenic, cadmium,
copper, iron, lead, manganese, mercury, silver, and zinc. The fire
assay tests conducted on three discrete samples from TP1 detected
gold concentrations at 0.09 oz./ton, 0.102 oz./ton, and 0.116 oz./ton.
The pH measured ranged from 5.2 to 6.0 in the test pit samples.
According to the TCLP data obtained for TP1, concentrations measured
in laboratory-generated leachate did not exceed the regulatory limit
for hazardous waste classification.
Tailings Pile #2 (TP2) was located west of TP1 and extended
beneath WR2. Tailings Pile #2 (TP2) was the largest waste source,
with an estimated volume of 158,000 cy of material, and covered
an area of approximately 18,950 square yards. There was some vegetation
on TP2 and it was accessible to vehicles. Concentrations of the
following metals are elevated above background (>3X) in the dump:
antimony, arsenic, cadmium, copper, iron, lead, manganese, mercury,
silver, and zinc. The fire assay tests conducted on samples from
TP2 detected gold concentrations at 0.021 and 0.029 oz./ton. The
pH was measured from <3.5 to 7.0 in the test pit samples.
Six separate waste rock dumps with a combined estimated volume
of 2,000 cy are located on Silver Hill. The majority of the rock
volume is in the two lower waste rock dumps. All of the waste rock
dumps are north of the main road on the south slope of Silver Hill.
The lower two waste rock dumps are the only dumps accessible by
vehicle. Concentrations of the following metals are significantly
elevated above background (>3X) in the dumps: antimony, arsenic,
cadmium, copper, lead, manganese, silver, and zinc. The ABA and
SMP buffering capacity results indicate that the Silver Hill waste
rock dumps are considered potential acid producers and approximately
12 tons of lime per acre would be required to successfully establish
vegetation on this material, assuming a 12-inch depth of incorporation.
The pH value was 5.2 for the composite sample. According to the
TCLP data obtained for the Silver Hill waste rock dumps, concentrations
measured in laboratory-generated leachate did not exceed the regulatory
limit for hazardous waste classification.
Waste Source Characteristics for the Comet Mine Site: (Table
1)
Contaminant Concentrations for the Comet Mine Site: (Table
2)
Effects on Surface Water: A downstream surface water sample
in High Ore Creek had total metals concentrations greater than three
times an upstream sample concentration for the following elements:
arsenic, barium, cadmium, copper, iron, lead, magnesium, manganese,
silver, and zinc. The downstream sample exceeded the following water
quality standards: Maximum Contaminant Levels (MCLs) for arsenic,
cadmium, antimony, lead, and zinc; acute and chronic aquatic life
standards for arsenic, cadmium, antimony, lead, and zinc; and chronic
aquatic life standards for iron and mercury. Montana Human Health
Standards (HHSs) were exceeded for antimony, arsenic, cadmium, iron,
lead, manganese, and mercury. Comparing total metals to the dissolved
metals at the downstream station shows the following distribution:
9% of the arsenic, 56% of the cadmium, 2% of the copper, 9% of the
iron, 0% of the lead, 20% of the antimony, and 80% of the zinc are
in the dissolved phase.
The sediment sample downstream in High Ore Creek had total metals
concentrations greater than three times the background soils concentrations
for the following elements: arsenic, cadmium, copper, lead, manganese,
mercury, silver, and zinc.
Two groundwater discharges potentially associated with mine workings
were identified and characterized during this sampling episode.
A sample of a spring at the base of the diversion channel dike,
probably associated with an adit discharge from the Silver Hill
area, and a sample of water emanating from the ground within the
northern-most erosion channel in the lower tailings exceeded MCLs
for arsenic and cadmium, and Montana HHSs for arsenic, cadmium,
iron, lead, manganese, and mercury. Comparing total metals to the
dissolved metals for the two water samples shows the following metals
are in the dissolved phase: arsenic - 82% and 85%, cadmium - 100%
and 93%, copper - 75% and 7%, iron - 96% and 88%, lead - 45% and
2%, and zinc - 97% and 97%, respectively. Intermediate samples taken
downgradient of these two samples generally show lower concentrations
of dissolved phase metals and higher concentrations of the solid
phase (particulate) metals.
Water Quality and Sediment for Comet Mine Site: (Table
3)
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| Comet
Mine Site Prior to Reclamation Construction, Phase I |
Construction Narrative: The purpose of the Phase I Comet
Mine Reclamation project was to excavate Tailings Piles #1 and #2
and Waste Rock Dumps #1 and #2 and dispose of them in the open pit
located on the east side of the site. The wet tailings were to be
disposed of in the deepest portion of the pit on the east side,
and dry tailings and waste rock were to be disposed of in the shallower
west section of pit or the bench area in the north section of the
pit. Sediments contained in Settling Pond #1 were to be completely
excavated and disposed of in the open pit. A portion of the High
Ore Creek diversion embankment was to be excavated and disposed
of in the shallower areas of the pit. Run-on control ditches (type
A, B and C) were to be constructed to protect excavated areas from
erosion.
Prior to Change Order #1, WR3 was to be excavated (approximately
35,000 cubic yards) and graded to attain target maximum slopes of
2H:1V. Excavation of WR3 was to be used to form an interim final
cover over the consolidated mine wastes in the pit. The dump was
to be then amended with lime and compost, fertilized and seeded,
and covered with erosion control mat. Change Order #1 instructed
the Contractor to remove the entire amount of waste rock from WR3
and dispose of it in the repository. Waste Rock Dump #3 (WR3) was
also to be enclosed by a wire fence after revegetation procedures
were complete.
Phase I of the project was completed over two construction seasons.
The majority of the waste removal and placement was done during
the 1997 construction season (September through December). The remaining
work was completed in the early months of the 1998 construction
season (May through July).
Items completed during the 1998 construction season: (Table
4)
Phase I of the Comet Mine Reclamation Project is 100 percent complete.
Most of the contaminant sources that were responsible for negatively
impacting the High Ore Creek drainage have been permanently removed,
which alleviates the majority of the environmental problems associated
with the site. The repository was constructed by backfilling the
upper and lower pits with the waste material. The existing High
Ore Creek diversion ditch to be removed in Phase II of the Comet
Mine Reclamation Project overlies a considerable amount of tailings;
however, a portion of these tailings were removed during Phase I.
The WR3 area is back to its original native slopes; compost, fertilizer,
seed, and erosion control mats were added to the slope. When last
observed in July 1998, the WR3 area contained a significant amount
of vegetation.
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| Comet
Mine Site Under Reclamation Construction, Phase I, View 1 |
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| Comet
Mine Site Under Reclamation Construction, Phase I, View 2 |
Services/Contractors Used: The Contractor utilized from
seven (7) to eighteen (18) employees on the job site at various
times. The majority of the labor involved with this project was
in the removal of the tailings and waste rock which took two to
three excavators, three to four haul trucks, four scrapers and two
to four dozers. A team of four people was brought in to construct
the ditches. The fencing was contracted out to Smith River Fencing
of White Sulphur Springs, Montana. Other employees on site included
the superintendent, mechanic, construction company owner, and project
manager (on occasion).
The successful low bidder for the project construction was Shumaker
Trucking and Excavating Contractors, Inc. Contact information is:
Shumaker Trucking and Excavating Contractors, Inc.
P.O. Box 1279
Great Falls, MT 59403
Telephone: (406) 727-3537
Was this Project Successful? Yes
Comet Mine Site Reclamation Project Before and After Restoration.
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| Before
Restoration |
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| After
Restoration |
Supplementary Narrative: Final inspection and approval
was conducted on July 8, 1998. Attendance included Ben Quiìones
and John Koerth of DEQ/MWCB, Gene Shumaker of Shumaker, and Dawn
Clark and Steve Pierce of Pioneer. All construction activities were
approved except for the following items: 1) the east side of the
fence surrounding WR3 needed an additional panel and a deadman;
and 2) straw bales placed on the buttress slope of the repository
needed to be restaked.
Other issues involved with the site reclamation activities included
the following:
-
Equipment would often get stuck in the saturated
tailings in the drainage area and upper pit causing some delays
in the project. On October 10, the Contractor had four pieces
of equipment stuck at the same time, which delayed the job for
almost an entire day. In order to attain the moisture
specification for the tailings placed in the repository, the
Contractor continuously mixed the wet tailings with dry waste
rock or dry tailings. Moisture tests were taken with a nuclear
density gauge. To attain the moisture specification, the tailings
had to be within 4% over the optimum moisture content of 19%;
as it turned out, the material had to be significantly less
than 19% before the equipment could operate in it.
- Engineers also decided that it would be better to go with dozer
basins on a covered waste rock pile, instead of run-on control
ditches as originally planned.
- Some scrap metal at the site was found to be radioactive by
the steel mill, to which it was sent, in Salt Lake City, Utah.
For more information on this project, contact:
Mr. Ben Quiìones
MDEQ/MWCB
2209 Phoenix Avenue
Helena, MT 59620
Phone: (406) 444-2074
Email: bequinones@state.mt.us
Submitted by: Montana Department of Environmental Quality
Summarized by: Mari Reeves, Reclamation Research Unit, Montana
State University
Date: 12/03/00
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