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Alta Mine Remediation Project
July 2, 1999
December 20,
1999
Jefferson
Montana
46° 22' 24"
112° 05' 12"
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| Alta
Mine Site, circa 1890 |
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1.5 miles
SW of Corbin, MT
The total project construction
cost for the Alta Mine Lower Waste Rock Dump reclamation project
was $944,321.35. Construction costs included an initial bid of $624,266.00,
with four change orders resulting in an increase of $319,095.35.
The total engineering cost for the project, including site characterization
and environmental investigation, was $279,612.00. Costs associated
with the preparation of the reclamation work plans (PRC Environmental
Management, Inc. [PRC] 1996a) and final sampling and analysis plans
(PRC 1996b) for the Alta Mine were $38,868.00. Costs for conducting
and reporting the reclamation investigation were $72,079.00. These
investigation costs included the hydrogeologic investigation (PRC
1997a). The expanded engineering evaluation/cost analysis (EEECA)
for the Alta Mine (PRC 1997b and PRC 1998) cost $34,408.00. Costs
for engineering design and bid specification preparation cost, including
additional site characterization, (TtEMI 1999) were $42,422.00.
Construction inspection and management costs were $91,835.00.
Montana Department
of Environmental Quality, United States Department of the Interior,
Office of Surface Mining
Montana Department
of Environmental Quality
PRC Environmental
Management Inc. prepared the Reclamation Work Plans, the final Sampling
and Analysis Plan, the Hydrogeologic Investigation, and the Expanded
Engineering and Cost Analysis. Tetra Tech Environmental Management
Inc. performed the Engineering Design and Bid Specification, which
included additional site characterization.
Heavy metal contamination
and acid production from mine waste rock piles were affecting surface
water and ground water resources at the site, as well as potentially
exposing humans, wildlife, and plants to toxins in the wastes. Previous
surface water samples indicated elevated levels of antimony, arsenic,
cadmium, copper, iron, lead, mercury, and zinc (Pioneer 1993). The
primary contaminants of concern at the Alta Mine Lower Waste Rock
Dump were arsenic, lead, and manganese. The maximum measured arsenic
concentration was 4,400 parts per million (ppm) and the mean detected
concentration was 1,063 ppm. The maximum measured lead concentration
was 7,745 ppm and the mean detected was 3,238 ppm. The maximum measured
manganese concentration was 4,765 ppm and the mean detected was
1,711 ppm.
The primary objective of
the Alta Mine Lower Waste Rock Dump reclamation project was to protect
human health and the environment in accordance with the guidelines
set forth in the National Contingency Plan (NCP). Specifically,
the reclamation action selected was implemented to limit human and
environmental exposure to the contaminants of concern and reduce
the mobility of those contaminants to prevent impacts to local surface
The Alta Mine site
is an abandoned hardrock silver mine listed on the Montana Department
of Environmental Quality, Abandoned Mine Reclamation Bureau (DEQ/AMRB)
priority sites list. Shortly after the ore body at the Alta Mine
was discovered in 1869, the property was sold to the Alta Montana
Company. In 1883, the property was purchased by the Helena Mining
and Reduction Company (also known as the Helena and Livingston Smelting
and Reduction Company) which operated the mine until 1896. During
operation of the mine by the Helena Mining and Reduction Company,
between 150 and 200 tons of ore were mined per day. At the same
time, a concentrator was constructed in Corbin, approximately 1.5
miles northwest of the Alta Mine. In 1896, all mining operations
at Alta ceased.
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| The
Alta Mill Site drainage before remediation |
Some time after the closing of the mine, a concentrator was constructed
at the Alta Mine site (Roby and others 1960). In 1909 the mine was
purchased by the Boston and Alta Company (also known as the Boston
and Alta Mining Company). The Boston and Alta company sunk the Level
No. 8 shaft, also known as the Dick shaft, 665 feet. In 1925, the
Boston and Alta Company constructed a second concentrator about
one mile east of Corbin to treat the Alta mine tailings a third
time. The tailings were later hauled to Corbin Flats (Deckler 1982).
The Boston and Alta Company operated the mine until 1929. The mine
was leased to the Knickerbocker Mines Company in 1929 (Roby and
others 1960). In the late 1930s, much of the tailings at Corbin
Flats were hauled to the American Smelting and Refining Company
in East Helena.
Some time after 1949, the mine was leased to Ed Lahey (Lahey Leasing
Company) who operated an open cut on the vein on the crest of Alta
Mountain. From 1950 through 1956 the Lahey Leasing Company mined
low-grade ore from the upper mine area. This low grade ore was used
as silica flux in the smelter at East Helena.
Prior to 1893, it is estimated that the mine produced more than
1.25 million tons of ore. Between 1901 and 1948, another 10,000
tons of ore were produced.
The Alta mine area
was divided into the Upper Mine Area and the Lower Mine Area. The
volume of waste rock materials associated with the open pits in
the upper mine area was first estimated at 163,755 cubic yards (yd3).
The actual volume of waste rock was difficult to estimate because
the dumps were located on steep slopes, and the depth to bedrock
varies significantly across the site. The upper mine covered an
area of 494,406 square feet (ft2) (11.35 acres). The lower mine
area contained a waste rock dump, several adits, and one shaft.
The volume of waste in the lower mine area was estimated to be 151,502
yd3, and covered an area of 171,626 ft2 (3.94 acres).
Surface water at the site was shown to contain elevated concentrations
of heavy metal contaminants of concern. Previous analyses of water
from the discharge indicated very low pH (acidic) levels as well
as elevated metals concentrations. Previous surface water samples
indicated elevated levels of antimony, arsenic, cadmium, copper,
iron, lead, mercury, and zinc (Pioneer 1993).
Reconstructed stream channel at the Alta Mine following removal
of waste material.
The rip-rap stream channel is protected from sediment by straw
bales.
Terrace remain (upper left) where waste materials were removed
at the Alta Mine remediation project.
Surface water and depth to ground water were characterized at the
site during the reclamation investigation and the hydrogeologic
investigation. The main adit for the Alta Mine, adit Level No.8,
was located adjacent to the partially-collapsed hoist house. No
acid mine discharge was observed flowing from the adit during the
Spring 1996 field investigations. Depth to water measured in the
shaft during Spring 1996 was approximately 6 feet bgs. Water infiltrating
through the mine workings and from the shaft was likely recharging
the waste rock pile and was a source for the acid rock drainage.
Acid generation probably occurred within the sulfide-rich underground
workings and the waste rock pile. This acid probably leached metals
from the exposed wall rock and waste rock pile. Surface water at
the Alta Mine site is present in both the upper and lower mine areas.
The east side open pit contains a minor seep that is acidic and
appears to be associated with a collapsed adit. This seep may have
been a recharge area for the underground workings, although its
location near the ridge suggests that it is only seasonally present.
The lower mine area contains a significant discharge of water from
the waste rock pile located in the drainage.
Permits that may have been required to complete this project. (Table
1)
Site reclamation
involved removal of the waste rock, which was considered the principal
source of concern, from the Alta Mine Lower Waste Rock Dump. These
wastes were then placed in a repository constructed approximately
1 mile southeast of the Alta mine site. The Alta Gulch surface water
drainage was reconstructed through the former waste rock dump site
and lined with riprap. A total of seven straw bale barrier sediment
traps were constructed to reduce the quantity of residual wastes
that might erode onto and from the reclaimed area. Final reclamation
construction activities consisted of the following work: constructing
access roads; clearing and grubbing the work site; dismantling and
salvaging the mine headframe; constructing a 5.7 acre mine waste
disposal repository; excavating, transporting, and disposing of
154,000 cubic yards of mine waste in the repository; sealing the
mine shaft; reconstructing 900 linear feet of surface water drainage;
constructing 2,239 linear feet of diversion ditches; benching and
topsoiling (6,000 cubic yards) the former waste rock dump site;
applying and grading 19,000 cubic yards of cover soil on the repository;
fertilizing, seeding, and mulching 13 acres of excavation and construction
areas; constructing 4,727 linear feet of fences; and transporting
7,500 cubic yards of excess cover soil to the repository site.
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| Construction
of a mine waste repository at the Alta Mine near Jefferson City,
Montana. Placement of waste is occurring on top of a clay fabric
and drainage geogrid |
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| Dozer
pushes mine waste toward the edge of the repository liner. Multiple
geosynthetic fabrics were used in construction including a basal
clay fabric and overylying drainage grid |
The repository was constructed on United State Bureau of Land Management
(BLM) property approximately one mile southeast of the Alta Mine
. The total footprint area of the repository required to contain
the specified wastes was approximately 5.72 acres. Upon removal
of topsoil from the repository area, clean native soil was then
excavated to form the base of the repository. The base of repository
was completed using a geocomposite clay liner and leachate collection
system composed of a geocomposite filter fabric and leachate collection
piping. After the specified wastes were deposited and compacted
in the repository, a multi-layered lined cap was constructed overlying
the wastes, and the cap was seeded and mulched. Excavated material
unsuitable for use in the repository cap was used to backfill old
exploration pits and to reduce the slope break on the northwest
end of the repository. Ditches were constructed to divert runon
and runoff away from the repository. A 6-foot high woven-wire fence
was constructed to surround the repository to limit access by people
and allow for the establishment of vegetation without interference
from livestock or wildlife. In addition, a 4-wire barbed-wire fence
was constructed around the perimeter of the reclaimed waste rock
dump area to control livestock grazing until the revegetation became
established. Temporary roads constructed at the site were reclaimed
immediately after the mine reclamation activities were completed.
The successful
low bidder for the construction project was Smith Contracting Inc.
(Contractor) of Whitehall, Montana. The project manager for Smith
was Lee Barron. The on-site superintendent was Dave Smith. Smith¥s
address is as follows:
Smith Contracting, Inc.
1118 Highway 55
Whitehall, Montana 59759
(406) 287-3048
Yes
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| The
Alta Mill Site drainage before remediation |
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| Alta
Mill Site drainage following remediation |
The reclamation
of the Alta Mine Lower Waste Rock Dump was successfully completed.
All work was completed within the change order modified contract period
(one field season) and within the Engineer's cost estimate.
The site elevation
is 5600-6200 ft asl. Depth to water varies from 9 to 121 feet below
ground surface (bgs). Groundwater measurements in the open shaft in
the lower mine area indicate water can be as high as 6 feet bgs. During
construction, several issues developed that required extra effort
by the State, Engineer, and Contractor to resolve. These issues included
the presence of four large concrete foundations buried within the
waste rock dump; the inability to completely backfill the mine shaft
due to a blockage located only 35 feet below ground surface; and most
significantly, the greater than anticipated volume of waste rock.
All of these issues were resolved during construction.
For more information on this project, contact:
Mr. Dale Herbort
MDEQ/MWCB
P.O. Box 200901
Helena, Montana 59620-0901
Phone: (406) 444-1294
Fax: (406) 444-0443
Email: dherbort@state.mt.us
Available Documentation: (Table
2)
Submitted by: Montana Department of Environmental Quality
Summarized by: Mari Reeves, Reclamation Research Unit, Montana State
University
Date: 11/26/00
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