Ted
Duaime, John Sonderegger and Marek Zaluski
Montana Bureau of Mines and Geology
Montana Tech
Butte. MT 59701
Abstract--During
the past 7 to 8 years, the Colorado Tailings have been the site of numerous
studies on potential heavy metal contribution to Silver Bow Creek (SBC).
Three years ago the Montana Department of State
Lands-Abandoned Mine Lands Bureau (DSL-AML) initiated, through the Montana
Bureau of Mines and Geology (MBMG), a study of reclamation and removal
alternatives for this site. Since that time the tailings have received increased
interest with the placement of SBC on the Environmental. Protection Agency's
Superfund.
Numerous
studies predate the ongoing Superfund and MBMG studies, with contradictory
results. Loading rates in SBC have been reported to vary from 0 to 36 lb/day for
copper and 300 to 320 lb/day for zinc from above to below the tailings (4). Since
the initiation of the MBMG study, numerous changes have taken place upstream
which complicate comparisons with historic data; those being the Anaconda
Minerals Company zero discharge for the Weed Concentrator and the suspension of
mining in Butte.
Results from the MBMG study show a substantial degradation of
ground water quality from outside (upgradient) of the tailings through the
tailings, as do surface water results, but to a lesser degree, from above to
below the tailings.1
TAILINGS
ORIGIN AND LOCATION
The
Colorado Tailings are the waste products of the Colorado and Montana Smelting
Company's smelter and concentrator, which was located to the south of the
tailings area (fig.1) (2). The facility, operating from 1879 to 1905, was
enlarged and owned by numerous parties (7). The waste products (tailings) from
the facility were deposited north of the facility in a marshy area adjacent to
Silver Bow Creek (SBC).
Since the initial preparation of this manuscript and final
editing, a calibration error was found in Butte-Silver Bow's Metro Sewer
Treatment Plant's discharge rates. Modifying data to compensate for this has led
to moderate changes in some data from that presented at the April conference.
The
Colorado Tailings are located west of Butte and north of Interstate Highways
15-90, T. 3 N., R. 8 W., sec. 23, and lie between the Butte-Silver Bow Metro
Sewer Treatment Plant to the east, and Ranchland Packing Company to the west.
Silver Bow Creek forms the east, north, and west boundaries of the tailings (fig.2). The site consists of approximately 30 acres.
MATERIALS
AND METHODS
The initial study plan was designed with the assumption that the tailings would
be removed and deposited at a predetermined site (1). Since that time, the
reclamation plan was modified due to the suspension of mining in the Butte area.
Twenty-eight shallow, 2-inch observation wells were placed
through the center (east-west) east and west (north-south) portions of the
tailings area (fig. 2). These were installed by hand via a Giddings Core Barrel
to a maximum depth of 5 feet in an attempt to determine thickness and volume of
material to be moved. These wells were used also for static water level (swl),
specific conductance (sc), and pH measurements.
Twenty
4-inch wells were installed outside and within the main tailings area via the
MBMG Mobil 50 auger drill rig (fig. 2). The primary purpose of these
installations was to document existing ground water quality conditions,
upgradient, within, and downgradient of the tailings area. They were used for
water quality sampling, swl, sc, and pH measurements.
In
addition to the well drilling, sites were selected for surface water sampling
locations above and below the tailings in order to help quantify the effect of
the tailings on SBC water quality (fig.
2).
All water quality sampling
followed standard sampling and handling procedures, while trace metal samples
were field filtered through a 0.45 filter and preserved with nitric acid (1)
RESULTS
AND DISCUSSION
Drilling results
showed the presence of an organic layer underlying the tailings, which appears
to act as a semi-confining layer, based on swl measurements (fig.
3). This layer
does not exist beyond the north or south perimeters of the tailings.
Ground
water flow direction is from the southeast to the northwest, as shown in figure
4. Water quality deteriorates from the south to the north and from the east to
the west. Water from wells within the tailings most often exceeded recommended
or permissible limits (8,9) for iron, manganese, sulfate, cadmium, copper, zinc,
and arsenic, while well water outside (upgradient) the tailings generally
exceeded manganese and sulfate standards as shown in figures 5 and
6.
Surface water samples have been collected four times since
July 1983 for comparison of water quality above the tailings and below the
tailings. (All above-the-tailings samples include the addition of the
Butte-Silver Bow Metro Sewer Treatment Plant discharge.
Samples collected were grab, and handling procedures followed
that for the ground water sampling. In conjunction with the sample collection,
discharge (flow) measurements were performed at the same location.
In
most cases, concentration levels of metals were greater below the tailings than
above (figs. 7. 8.
9); the exception being a single occurrence for iron where
the opposite was true. For the same sampling periods, flow rates varied from a
10% loss to a 35% increase, as shown in figure 10.
Knowing concentration levels and flow, loading rates, in
kilograms per day (kg/d), were calculated showing changes once again from above
the tailings to below them (figs. 11,
12, 13). This showed the same trend as did
concentration (mg/L) only with sulfate being the one exception where loading
above was greater than below on one occasion. The average loading rate increases
varied from 15% for iron to greater than 70% for copper and zinc, with the
greatest increases occurring during the May period, which was also the time of
highest flow (spring runoff).
As was done with ground water, a comparison was made with
recommended or permissible limits (mg/L), but in this instance included instream
concentrations (1) along with drinking water standards. Instream quantification
is somewhat harder to compare because certain standards are based on lethal
concentrations (LC) or tolerance limits; i.e., copper, 0.1 x 96 hr LC50.
Manganese was the only constituent, which exceeded limits for drinking and
instream concentrations, while copper and zinc exceeded the concentration limit
for instream limits below the tailings.
In an effort to make sure that trends shown by the MBMG
sampling were actual, a comparison was made with data collected by the Montana
Department of Health and Environmental 5ciences-Water Quality Bureau (WQB) (6)
during an April 1983 sampling run and that collected by the MBMG during May
1984, which were both during high flows (fig. 10A). All comparisons were made
using dissolved concentration results for calculating loading rates. Values
compared were the percentage change from above to below for flow (Q), sulfate
(504), copper (Cu), and zinc (Zn). Trends and the percentage change (increase)
for the period of comparison were quite comparable and similar.
CONCLUSIONS
The
Colorado Tailings site contains highly mineralized and oxidized material, which
is highly erodable and has a high ground water table. These conditions lead to
the degradation of the local ground water quality as it flows through the
tailings area before discharging into Silver Bow Creek, thereby also affecting
surface water quality. While the exceedance levels of the surface water were not
as extreme as those shown in the ground water. The tailings are capable of
long-term and severe heavy metal addition to SBC.
In order to mitigate the tailings impact on surface and
ground water quality, the reclamation plan must reduce the amount of water,
which passes both through and over the tailings area.
ACKNOWLEDGMENTS
Bob
Bergantino, Herman Moore and Fred Schmidt provided valuable assistance with the
installation of the monitoring network and collection and interpretation of the
data while Tom Satterly aided in the preparation of the figures. Finally, this
investigation would not have taken place without the funding received from the
Department of State Lands. A special thanks to Dick Juntunen and Ben Mundie of
DSL for their assistance.
LITERATURE
CITED
1.
Administrative Rules of Montana, 16-2-87.
2.
Butte Special Folio. 1897. Geologic atlas of the United States. Department of
the Interior, United States Geological Survey.
3.
Duaime, T.E.; James, R.A.; Sonderegger, J.L., McClernan, H.G., and Lawson, D.C.
1982. Water monitoring and reclamation alternatives for the Colorado Tailings,
Butte, Montana. Montana Bureau of Mines and Geology.
4.
Hydrometrics. 1983. Summit and Deer Lodge Valleys long-term environ- mental
rehabilitation study, Butte-Anaconda, Montana. Vol. V, Colorado Tailings.
5.
Methods for Collection and Analysis of Water Samples for Dissolved Minerals and
Gases, Chapter A1. 1970. Techniques of Water- Resources Investigations of the
United States Geological Survey.
6.
Montana Water Quality Bureau. 1983. An intensive survey of Silver Bow Creek and
the upper Clark Fork River. Department of Health and Environmental Sciences.
7.
Smith, R.I. Montana. 1948.
History of the early reduction plants of Butte. Montana Bureau of Mines and
Geology.
8.
40CFR Part 141. 1975. Federal Register, Vol. 40, No.248, and ARM 16-2.14(10)
-814381 (Administrative Rules of Montana).
9.40CFR
Part
143. 1979. Federal Register, Vol. 44, No.140.