Geochemistry of Perched Water in an Abandoned Underground Mine, Butte, Montana

Abstract.  The Lexington tunnel is the last accessible underground mine working in the Butte, Montana mining district. Used as recently as 1993, the tunnel and adjacent workings have been abandoned for over 10 years. Although the Lexington tunnel is over 200 m above the regional water table, perched water is present over much of its extent. Mine water near the portal is moderately acidic (pH 4 to 5), with extremely high concentrations of metals, including Cu (up to 1000 mg/L) and Zn (up to 1400 mg/L). In the middle reaches of the tunnel, the quality of the water is much better, with near-neutral pH, high bicarbonate alkalinity, and lower concentrations of heavy metals. The low acidity and metal content is attributed to a lack of pyrite and other sulfides in this portion of the mine, as well as the presence of carbonate minerals, such as rhodochrosite (MnCO₃), in exposed veins. Sulfide minerals are more widespread further back in the tunnel, and are now oxidizing rapidly, leading to pockets of severe acid drainage (pH< 3, dissolved Zn up to 5000 mg/L). Geochemical modeling suggests that the near-neutral waters—the most voluminous type encountered in the Lexington tunnel—are close to equilibrium saturation with rhodochrosite and hydrous Zn-carbonate (ZnCO₃•H₂O). The Eh of these waters is most likely controlled by redox reactions involving dissolved Mn²⁺ and secondary, Zn-rich, hydrous Mn-oxides. In contrast, the Eh of the acidic waters appears to be controlled by reactions involving Fe²⁺ and Fe³⁺. Most of the acidic waters are saturated with K-jarosite, which forms delicate, straw-like dripstones at several localities. Decaying mine timbers could be an important renewable source of organic carbon for heterotrophic microorganisms, such as iron- and sulfate-reducing bacteria, especially deeper in the mine workings where the ground is saturated with anoxic ground water.     

Removal of Sulphate, Metals, and Acidity from a Nickel and Copper Mine Effluent in a Laboratory Scale Bioreactor

Abstract  Mine effluents should be treated so that they can either be re-used (e. g. for mining activities or irrigation purposes) or discharged into a river system. The results of this study showed that applying laboratory scale biological sulphate removal technology to a nickel/copper mine effluent (BCL mine, Botswana) consistently lowered sulphate concentrations from an average of 2000 to 450 mg/L, and increased the pH from 5.8 to 6.5. During this period, the hydraulic retention time varied from 24 to 12 h. The Ni and Zn concentrations were reduced from a maximum of 5.86 to 0.15 mg/L and from a maximum of 38 mg/L to 0.03 mg/L, respectively, presumably precipitated as metal sulphides.     

Giant Mine: Identification of Inflow Water Types and Preliminary Geochemical Monitoring during Reflooding

Abstract:  Between 1948 and 1999, gold ore containing high concentrations of arsenopyrite was mined at the Giant Mine near Yellowknife, Canada. Processing resulted in 215,000 kg of gold and approximately 237,000 tonnes of highly soluble arsenic trioxide, a by-product of the roasting process. The arsenic dust was collected and placed underground in 15 shallow chambers and stopes (within 75m of the surface) with the understanding that the ground would revert to permafrost conditions once mining was completed. Subsequent studies have shown that the ground is unlikely to refreeze naturally; therefore, it has been proposed to actively freeze the arsenic trioxide storage areas to hydraulically isolate them from the post-closure ground water system. However, other arsenic sources (backfilled tailings, etc.) exist deeper in the mine (600 m total depth), so there is a concern that arsenic will leach into the minewater system and ultimately into the environment when the mine is allowed to flood. Therefore, the development and implementation of a remediation plan for the site requires a good understanding of the arsenic distribution and expected release to the mine water. To gain this understanding, a detailed program of surface and underground sampling was carried out to identify or “type” the inflow sources to the mine, and their interaction with arsenic sources both on the surface and within the mine workings. As of July 2005, the mine has been allowed to begin reflooding to reduce pumping costs and remove the need for servicing pumps at the bottom of the mine, thus allowing the main shaft to be taken out of service. Prior to starting reflooding, a multi-level monitoring system was installed in the main shaft and is currently being used to monitor reflooding levels and water chemistry. Samples can be collected from each mine level intersecting the shaft. The system will monitor reflooding rate and test how underground arsenic sources (backfilled tailings, etc.) are affecting water quality in the mine. This geochemical information will be used to assess long-term arsenic loading from sources outside the frozen zone and predict how long mine water treatment will be needed before natural ground water flow can be allowed.     

Pollution of Water and Stream Sediments Associated with the Vale De Abrutiga Uranium Mine,Central Portugal

Abstract.   The Vale de Abrutiga uranium deposit, located in Central Portugal near the Aguieira dam reservoir, was surface mined. Low-grade ore and waste rock were deposited on permeable ground, close to the mine, and were not revegetated. A lake has formed in the open pit. Surface waters draining the mine site are acidic, have high conductivity, and high concentrations of U, SO42-, Zn, Fe, Mn, Ra, Cu, Th, and Pb. The groundwater and the water from the reservoir cannot be used for human consumption or irrigation. The sampled waters show higher contaminant concentrations in winter than in summer. Stream sediments have high geoaccumulation indices for U, Fe, Ag, Zn, Cr, Co, and Pb. In general, sediments bordering the dam reservoir have higher metal contents in winter than in summer.     

A Survey of the Geochemistry of Flooded Mine Shaft Water in Butte, Montana

Abstract.  This paper outlines general trends in the geochemistry of the more than 10,000 km of flooded underground mine workings in the Butte mining district. The waters in question range in pH from 4 to 8, are all moderately to strongly reducing, and show a huge range in concentration of dissolved metals such as Al, As, Fe, Mn, and Zn. Metal concentrations and total acidity are highest in the Kelley mine shaft, which was the main dewatering station used to pump ground water from the underground mine complex during active mining operations. In contrast, metal concentrations are much lower in the outer portions of the district where many of the mines contain hydrogen sulfide formed by sulfate-reducing bacteria. In comparison to the other heavy metals, concentrations of Pb and Cu are quite low in the flooded mine shafts. An interesting inverse correlation between pH and water temperature is noted, which may be partly caused by exothermic pyrite oxidation reactions in the central portion of the district.     

Geophysical Investigation of the Sulphur Bank Mercury Mine Superfund Site, Lake County, California

Abstract.  Airborne geophysical reconnaissance was used to identify potential flow paths for mercury-rich, acidic water entering Clear Lake near the Sulphur Bank Mercury Mine. Airborne magnetic and electromagnetic conductivity surveys were conducted over a 12.3 km² (4.75 mi²) area that included the Oaks Arm of Clear Lake and the old mine. These surveys identified four magnetic and/or conductive anomalies that may represent groundwater conduits towards or away from the Herman Impoundment. An anomaly that extended from Herman Impoundment through a waste rock dam and into Clear Lake was selected for a more detailed ground electromagnetic conductivity survey. The combined results of the airborne and ground surveys provided a detailed, lateral depiction of conductive zones, the most probable pathways for groundwater flow. These surveys also identified near-surface areas that may contain elevated concentrations of sulfide minerals that weather to produce acid groundwater.     

Use of Pb, <Superscript>18</Superscript>O,and <Superscript>2</Superscript>H Isotopes in Mining-related Environmental Studies

Abstract.   An isotopic and geochemical study of surface water and groundwater was undertaken at the Sullivan Mine, a sediment-hosted Pb-Zn massive sulphide deposit with a well-defined homogeneous Pb isotopic composition. The Pb isotopic composition of surface water and groundwater samples from near the mine site define a mixing line between Sullivan Pb and at least one other end member. The ¹⁸O and D isotopic results fall along an evaporation line that shows mixing between water from evaporative sources with water from meteoric sources.     

Using a Water Balance to Determine the Source of Water in the Flooding Underground Mine Workings of Butte

Abstract.  Nearly 10,000 miles (16,000 km) of underground mine workings began flooding on April 22, 1982 when the large pumps used to dewater the mines of Butte, Montana were shut off. In the first few months, water levels in the workings rose hundreds of meters. Flooding continues to this day at a slower rate, nearly 25 years later. An early evaluation of the water chemistry in the flooding mines suggested that the initially poor water quality was the result of flushing of a reservoir of stored acidity and metals. However, a detailed water balance for the Berkeley pit, underground workings, and associated mining features suggests an alternative explanation. During the early period of mine flooding, acidic surface water from the deactivated heap leach operations and nearby acid rock drainage were routed into the empty Berkeley Pit, and thence drained downward and outward into the underground mine workings, causing widespread degradation of water quality in the underlying workings. After 21 months, the hydraulic gradients in the system reversed, causing a change in the direction of ground water flow and a gradual improvement in water quality of the mine shafts.     

Mine Water Literature in ISI’s Science Citation Index Expanded™

Abstract.   Scientists in most countries are assessed by the number of papers published in journals that are cited in the Science Citation index. This article reviews the mine water related entries in the Science Citation Index Expanded and discusses the results. Mine water relevant literature is spread over more than 900 journals, with 13 of them accounting for 25% of all relevant papers. No journal focused on mine water relevant issues can be found in the Index.     

Long Term Changes in the Limnology and Geochemistry of the Berkeley Pit Lake, Butte, Montana

Abstract.  The Berkeley pit lake in Butte, Montana is one of the largest accumulations of acid mine drainage in the world. The pit lake began filling in 1983, and continues to fill at a rate of roughly 10 million liters d^-1. This paper details how changes in mining activities have led to changes in the rate of filling of the pit lake, as well as changes in its limnology and geochemistry. As of 2005, the Berkeley pit lake is meromictic, with lower conductivity water resting on top of higher conductivity water. This permanent stratification was set up by diversion of surface water—the so-called Horseshoe Bend Spring—into the pit during the period 2000 to 2003. However, the lake may have been holomictic prior to 2000, with seasonal top-to-bottom turnover events. The present mining company is pumping water from below the chemocline to a copper precipitation plant, after which time the Cu-depleted and Fe-enriched water is returned to the pit. Continued operation of this facility may eventually change the density gradient of the lake, with a return to holomictic conditions. A conceptual model illustrating some of the various physical, chemical, and microbial processes responsible for the unusually poor water quality of the Berkeley pit lake is presented.     

Effects of a Barite Mine on Ground Water Quality in Andhra Pradesh,India

Abstract.  An investigation was undertaken to determine the effects of a large barite mining operation on local ground water quality near Mangampeta,Andhra Pradesh, India.Water samples were collected from drinking water wells in the mining and adjacent regions. The drinking water in the mining region had sulphate concentrations that ranged from 211 to 589 mg/L, compared to sulphate concentrations of 25 mg/L or less in the non-mined areas. The natural existence of barite and the widespread mine waste dumps at Mangampeta are believed to be responsible for the higher levels of sulphate in the ground water.     

Contaminated Alluvial Ground Water in the Butte Summit Valley

Abstract.  Ground water in alluvial sediments of upper Silver Bow Creek is chronically contaminated with heavy metals, including Cd, Cu, Fe, Mn, and Zn. Most of this contamination stems from slag, mill tailings, and waste rock from the Butte mining district that had been deposited along the ancestral Silver Bow Creek floodplain. Much of this mine waste is now buried by fill, topsoil, buildings, or parking lots. Although the pH values of most wells in the region are in the 5.5 to 7.0 range, a cluster of monitoring wells near the site of a former mill and smelter contain water that is strongly acidic (pH < 4.5), with extremely high dissolved metal concentrations (Cu up to 750 mg/L; Zn up to 490 mg/L). Ground water discharging from the area is currently collected by a subsurface French drain and conveyed to a treatment facility where lime is added to precipitate metals from solution.     

The Chemistry of Waters Associated with Metal Mining in Macedonia

Abstract  Pollution from current and past mining is a significant problem in several parts of the former Yugoslav Republic of Macedonia. Water from six different mining areas in Macedonia was analysed to assess the effects of metalliferous mining activities. Drainage sediments at all locations show evidence of physical and chemical contamination; water compositions, however, were more variable. Low pH water associated with mining has led to the dissolution of minerals and the mobilization of metals from the ores and the host rocks. Only Sb was noted to exhibit enhanced mobility in higher pH waters. The Zletevo Pb-Zn mine discharges low pH water that has high levels of several metals, including Al, Zn, Cd, and Fe; sediment concentrations are grossly elevated for several km downstream. Toranica and Sasa Pb-Zn mines exhibit similar sediment contamination of Pb, Zn, Cd, and other ore-related metals. However, concentrations of metals in waters are far lower at both of these mines, due to less pyrite in the ore and the buffering of the acid waters by carbonate host lithologies. At the Buchim copper mine, waters are both acidic and high in dissolved solids; Cu concentrations exceed 100 mg/L. Krstov Dol and Alshar are small, disused As-Sb mines that discharge waters that exceed potable values for some contaminants (e. g. As), but this may be related to the mineralization of the bedrock rather than the mines. In general, metal concentrations decreased downstream from the source due to dilution from other rivers and coprecipitation of metals on other mineral phases (e. g. Fe-, Al- and Mn-oxides, and hydroxides).     

Resistivity Level Runs to Detect Water-filled Mine Voids between Drill Holes

Abstract.  Resistivity level runs are collected by lowering a current source down one well and measuring the resulting voltage at the same depth in another well. Mine voids between the wells that contain acid water appear as conductive anomalies on the resulting apparent resistivity profiles. Resistivity level runs can be collected rapidly and without lowering expensive equipment down holes of unknown stability. The data can be interpreted on-site, and are relatively insensitive to positioning errors. The method is well suited to sites where several drill holes have failed to intersect a known mine void. We demonstrated the feasibility of resistivity level run profiling at an abandoned mine complex in central Pennsylvania, where resistivity level runs were successfully used to locate haulage ways containing mine water.     

A Computer-Aided System for Design of Drainage Facilities in Surface Mining

Abstract.   Drainage systems in large surface mines are designed to accomplish three basic objectives: keeping working conditions dry, stable and safe; lowering hydrostatic pressure and increasing the effective stress of soil to improve slope stability; and ensuring pit floor workability. This can be achieved with drainage facilities that include channels, water collection sumps, and pump stations. We report the development of a computer-aided system called Dewatering of Open Pit Mines (DEWOP), which can assist open pit mine designers to solve water-related problems. The system was developed in a Visual Basic object programming language, taking advantage of multi-user, open database connectivity, such as Microsoft Access, for storage and processing of information. In tests at coal and copper surface mines, it reduced drainage facilities costs by 8%.     

Removal of Sulfate,Zinc, and Lead from Alkaline Mine Wastewater Using Pilot-scale Surface-Flow Wetlands at Tara Mines,Ireland

Abstract.    Passive treatment systems have primarily been used at abandoned mines to increase pH and remove metals from the drainage water. Two pilot-scale treatment wetlands were constructed and monitored at an active lead/zinc mine (Tara Mines) in Ireland to treat alkaline mine water with elevated sulfate and metal levels. Each system comprised three in-series surface-flow cells that contained spent mushroom compost substrate. Typically, aqueous concentrations of 900 mg L^-1 sulfate, 0.15 mg L^-1 lead, and 2.0 mg L^-1 zinc flowed into the treatment wetlands at c. 1.5 L min^-1. During a two-year monitoring period, removal of sulfate (mean of 10.4 g m^-2 day ^-1 (31%), range of 0-42 g m^-2 day ^-1 (0-81%)), lead (mean of 1.9 mg m^-2 day ^-1 (32%), range of 0-6.6 mg m^-2 day ^-1 (0-64%)) and zinc (mean of 18.2 mg m^-2 day ^-1 (74%), range of 0-70 mg m^-2 day ^-1 (0-99%)) were achieved. These contaminants were somewhat associated with the vegetation roots but more significantly with the substrate. Communities of colonizing macroinvertebrates, macrophytes, algae, and microorganisms contributed to the development of a diverse ecosystem, which proved to be a successful alternative treatment process. The interacting processes within the wetland ecosystems responsible for wastewater decontamination are being further elucidated and quantified using a systems dynamic model.     

Hydrogeological and Hydrochemical Characteristics of the Partially Flooded Piaseczno Opencast Sulphur Mine in Southeastern Poland

Abstract.  The basic chemical properties of Tertiary (T) and Quaternary (Q) aquifers near the Piaseczno opencast sulphur mine and the water in the open pit, along with the stratigraphy and hydrogeology of the area, were characterized to assess the feasibility of inundating the mine with ground water. Ground water quality varied markedly in the opencast area. A distinct stratification was noted in the pit water; total dissolved solids, calcium, chloride, hardness, and hydrogen sulphide increased from the top water level to the bottom of the pit lake. The concentrations of SO₄^2- and Cl^- in the opencast water were very high, especially in the hypolimnion zone. Based on our preliminary analysis, it appears that an artificial lake formed in the Piaseczno open pit could be used in the future as a fish and wildlife habitat as well as for recreational purposes.     

Predicting Groundwater Rebound in the South Yorkshire Coalfield,UK

Abstract:  The semi-distributed model GRAM (groundwater rebound in abandoned mineworkings) has been applied to part of the South Yorkshire Coalfield, UK, to predict the pattern of groundwater rebound, in particular the timing and rates of changes in mine water flows between abandoned collieries. The model is based upon the mining hydrogeologist's concept of ‘ponds’ (discrete volumes of interconnected workings) and calculates water balances over time for all ponds in a multi-pond mined system. GRAM was successfully calibrated against observed groundwater levels over a 5 year period from 2001 to 2005 before being used to predict future rates of groundwater rebound, in accordance with different scenarios, including average, low, and high rainfall scenarios. The results reveal that it could take up to 22 years before an inflow of water occurs into the last remaining colliery in the area at Maltby, with the first surface discharge expected in approximately 15 years time from an old mine shaft. If Maltby is closed and pumping ceases across the area, then it could be 100 years before groundwater rebound is complete.     

Using the DRASTIC System to Assess the Vulnerability of Ground Water to Pollution in Mined Areas of the Upper Silesian Coal Basin

Abstract  An attempt was made to use the U.S. EPA DRASTIC ranking system to assess the vulnerability of ground water in the Upper Silesian Coal Basin. Analysis of the various system components indicate that several DRASTIC factors would have to be modified to consider the effects of mining, subsidence, and ground water rebound.     

Injection of Fluidized Bed Combustion Ash into Mine Workings for Treatment of Acid Mine Drainage

Abstract  A demonstration project was conducted to investigate treating acid mine water by alkaline injection technology (AIT). A total of 379 t of alkaline coal combustion byproduct was injected into in an eastern Oklahoma drift coal mine. AIT increased the pH and alkalinity, and reduced acidity and metal loading. Although large improvements in water quality were only observed for 15 months before the effluent water chemistry appeared to approach pre-injection conditions, a review of the data four years after injection identified statistically significant changes in the mine discharge compared to pre-injection conditions. Decreases in acidity (23%), iron (18%), and aluminum (47%) were observed, while an increase in pH (0.35 units) was noted. Presumably, the mine environment reached quasi-equilibrium with the alkalinity introduced to the system.