Distribution of Organic Carbon in the Berkeley Pit Lake, Butte, Montana

Abstract.  The concentration of dissolved organic carbon (DOC) in the Berkeley pit lake water ranges from 2 to 4 mg/L, and is comparable to that of its inflow waters. On the dates sampled, the DOC concentrations decreased towards the surface of the lake, in a manner similar to the concentration of dissolved Fe. This may reflect adsorption of DOC onto newly formed ferric precipitates in the epilimnion of the lake. The total organic carbon (TOC) content of the lake sediment is 0.20 to 0.33%, and is on the low end of TOC in natural aquatic sediments. In contrast, the DOC concentrations of sediment pore waters are unusually high, ranging from 50 to 380 mg/L, and are much higher than DOC values of pore waters from typical marine or lacustrine sediments. The high DOC concentrations are explained by release of adsorbed organic carbon from ferric precipitates as they age and recrystallize, coupled with the relative scarcity of heterotrophic bacteria in the acidic and heavy metal-rich waters that would otherwise consume DOC through reduction of sulfate.     

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.     

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.     

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.     

The Limnology of Summer Camp Pit Lake: A Case Study

Abstract.  Surface water bodies are expected to form in several pits at the Getchell Open Pit Mine after mining has ceased due to inflowing surface and ground water. Predicting the long-term geochemical behavior of the pit water is important in assessing potential environmental effects. One of the pits, the Summer Camp Pit, began to develop a pit lake in 1991 when dewatering ceased and the pit was used to store water pumped from underground operations. This provided a field-scale opportunity to identify the controls on lake water chemistry and determine the effects of seasonal mixing events on long-term chemical behavior. During a five-year period (1996-2001), a number of physical, chemical and mineralogical characteristics of the lake were monitored with the intent of using this information as a basis for predicting long-term geochemical behavior of future lakes in the other pits. Seasonal and multiyear cycles were identified within the water column. These cycles were influenced by climatic changes and element and sediment loadings of inflow to the lake. Stratification occurred, with the metalimnion or active layer of the lake evolving from a low total dissolved solids (TDS), alkaline water to a high TDS, neutral to mildly acidic water, until turnover occurred due to density variations between the metalimnion and epilimnion, completely mixing the layers. A hypolimnion that formed has the potential to stabilize metals in the basal sediments as sulfide minerals below a chemolimnion in the lake. Longer-term events also appear to involve the hypolimnion.The monitoring program demonstrated the dynamic nature of a pit lake and how the complex limnology can affect seasonal water quality. Such considerations are important in interpreting water quality from pit lakes and in selecting monitoring data to use when constructing mathematical models for predicting changes in water quality.     

Geochemistry and Isotopic Composition of H2S-rich Water in Flooded Underground Mine Workings,Butte, Montana,USA

Abstract.   Groundwater being pumped from the flooded West Camp mine workings of Butte, Montana, is elevated in hydrogen sulfide (H₂S), has a circum-neutral pH, and has high arsenic but otherwise low metal concentrations. The daily flux of H₂S and As pumped from the extraction well are each estimated at roughly 0.1 kg. Isotopic analysis of coexisting aqueous sulfide and sulfate confirms that the H₂S was produced by bacterial sulfate reduction. the mine waters are close to equilibrium saturation with amorphous FeS, amorphous ZnS, siderite, rhodochrosite, calcite, and goethite, but are undersaturated with orpiment (As₂S₃). The higher solubility of orpiment relative to other mental sulfides allows concentrations of dissolved arsenic (~ 100 g/L) that are well above human health standards. The West Camp waters differ markedly from the acidic and heavy metal-rich mine waters of the nearby Berkeley pit-lake. These differences are partly attributed to geology, and partly to mining history.     

A Screening-Level Laboratory Method to Estimate Pit Lake Chemistry

Abstract.  An analog pit lake (APL) test has been developed to predict pit lake water quality following closure of an equatorial copper-gold mine. The juvenile (0-9 years after closure) pit lake (JPL) water budget will comprise 10% rainfall; 26% surface runoff; 40% wallrock runoff, and 24% deep groundwater inflow. The mature (>65 years after closure) pit lake (MPL) will consist of 39% rainfall; 29% surface runoff; 15% wallrock runoff; 3% deep groundwater inflow, and 1% shallow groundwater inflow, with the balance (13%) contributed by the JPL. Wallrock runoff due to incident precipitation was replicated in humidity columns, subaqueous wallrock leachate by leaching columns of each rock type with groundwater, rainwater by addition of sea salt to deionized water, and surface runoff by a sample from a local creek. The solutions were combined in aquaria and the appropriate fraction evaporated, 7% for the JPL and 36% for the MPL. Electron microprobe analysis of precipitates identified clays and Al, Cu, and Zn adsorbed to ferrihydrite surfaces. A preliminary pit design resulted in an acidic (pH 3.3) JPL containing 7 mg/L Cu. However, by modifying the design to exclude a potentially acidgenerating andesite unit, the JPL water quality improves (e. g., pH 6.7; Cu 0.002 mg/L). The MPL pH with the andesite would be 6.1 (Cu = 2.2 mg/L), while the final design results in a pH of 7.1 and 0.22 mg/L Cu. The APL test can also be used to corroborate numerical models predictions and assess the efficacy of mitigation alternatives.     

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.     

Development of the Sleeper Pit Lake

Abstract.  The Sleeper open pit gold mine operated from the mid-1980s through the mid-1990s. Operations were mostly sub-water table and extensive dewatering was required to lower groundwater levels by 180 m. Dewatering flows peaked at 930 L/s, with most flow contributed from an alluvial aquifer. After completion of mining, the pit was rapidly filled with water pumped from the alluvial aquifer to reduce the exposure time of sulfide wall rocks and waste rocks in the ultimate pit. The pumped alluvial groundwater provided a large volume of low total dissolved solids (TDS), high alkalinity water that controlled the early chemistry. The rising lake waters were amended with lime to buffer excess acidity contributed to the lake from reactive pit wall rocks during submergence. The pore water contained in submerged waste rock at the base of the pit was elevated in TDS and subsequently of higher density that the lake water. The density contrast and waste rock location limited contributions of waste rock pore water to the main body of the lake. Some stratification of the early lake occurred, with shallow water characterized by higher pH, low dissolved metals, and sulfate; deeper water had lower pH and higher dissolved metals and sulfate. The reservoir of alkalinity in the shallow layer mixed with the deeper waters and created a stabilized lake with a homogenized column that exceeded water quality expectations. Current water quality meets all Nevada primary drinking water standards with the exception of sulfate, TDS, and manganese, which are slightly elevated, as predicted. Chemistry has remained stable since development of the initial lake.     

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 Comprehensive Realistic Yearly Pit Transient Infilling Code (CRYPTIC): A Novel Pit Lake Analytical Solution

Abstract.  Permitting of open pit mines that intersect the groundwater table necessitates the use of sophisticated numerical models to determine the temporal impact of pit lake hydraulics. However, while mine feasibility and the potential environmental influences of open-pit dewatering can be estimated using conventional screening-level methods, to date there have been few published transient analytical solutions to estimate the pit lake recovery duration and inflow rates. The Comprehensive Realistic Yearly Pit Transient Infilling Code (CRYPTIC) described here is based on the Jacob-Lohman equation, modified to include the pit geometry and effects of precipitation and evaporation from the pit lake surface as well as the input/output of external flows. It assumes that the aquifer is homogeneous and isotropic with laterally extensive horizontal flow but differs from other methods in that it includes transient inflows. CRYPTIC was used to successfully model the Berkeley Pit Lake (Butte, Montana) recovery data and its predictions also compared favorably with results from the Pipeline Pit (north-central Nevada) numerical model. However, while this analytical approach provides useful hydraulic insights at the feasibility stage of mine planning, more detailed analysis is required to determine critical mine permitting requirements. For example, the lateral extent of the drawdown cone, time to maximum extent of dewatering, and temporal effects on springs and seeps require deployment of a full numerical code and substantially more data.     

Opportunities for Sustainable Mining Pit Lakes in Australia

Abstract.  Due to operational and regulatory practicalities, pit lakes will continue to be common legacies of mine lease relinquishments. Unplanned or inappropriate management of these geographical features can lead to both short- and long-term liability to mining companies, local communities, and the nearby environment during mining operations or after lease relinquishment. However, the potential for pit lakes to provide benefit to companies, communities, and the environment is frequently unrecognised and yet may be a vital contribution to the sustainability of the open-cut mining industry. Sustainable pit lake management aims to minimise short and long term pit lake liabilities and maximise short and long term pit lake opportunities. Improved remediation technologies are offering more avenues for pit lakes resource exploitation than ever before, at the same time mining companies, local communities, and regulatory authorities are becoming more aware of the benefit these resources can offer.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Youghiogheny River Basin,Pennsylvania, USA

Abstract.  Nighttime high-resolution airborne thermal infrared imagery (TIR) data were collected in the predawn hours during Feb 5-8 and March 11-12, 1999, from a helicopter platform for 72.4 km of the Youghiogheny River, from Connellsville to McKeesport, in southwestern Pennsylvania. The TIR data were used to identify sources of mine drainage from abandoned mines that discharge directly into the Youghiogheny River. Image-processing and geographic information systems (GIS) techniques were used to identify 70 sites within the study area as possible mine drainage sources. The combination of GIS datasets and the airborne TIR data provided a fast and accurate method to target the possible sources. After field reconnaissance, it was determined that 24 of the 70 sites were mine drainage. This paper summarizes: the procedures used to process the TIR data and extract potential mine-drainage sites; methods used for verification of the TIR data; a discussion of factors affecting the TIR data; and a brief summary of water quality.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Kettle Creek and Cooks Run Basins,Pennsylvania, USA

Abstract.  High-resolution airborne thermal infrared (TIR) imagery data were collected over 90.6 km² (35 mi²) of remote and rugged terrain in the Kettle Creek and Cooks Run Basins, tributaries of the West Branch of the Susquehanna River in north-central Pennsylvania. The purpose of this investigation was to evaluate the effectiveness of TIR for identifying sources of acid mine drainage (AMD) associated with abandoned coal mines. Coal mining from the late 1800s resulted in many AMD sources from abandoned mines in the area. However, very little detailed mine information was available, particularly on the source locations of AMD sites. Potential AMD sources were extracted from airborne TIR data employing custom image processing algorithms and GIS data analysis. Based on field reconnaissance of 103 TIR anomalies, 53 sites (51%) were classified as AMD. The AMD sources had low pH (<4) and elevated concentrations of iron and aluminum. Of the 53 sites, approximately 26 sites could be correlated with sites previously documented as AMD. The other 27 mine discharges identified in the TIR data were previously undocumented. This paper presents a summary of the procedures used to process the TIR data and extract potential mine drainage sites, methods used for field reconnaissance and verification of TIR data, and a brief summary of water-quality data.     

Water Management Aspects of the Britannia Mine Remediation Project,British Columbia,Canada

Abstract.  The Province of British Columbia, Canada, is undertaking environmental remediation at Britannia Mine, located approximately 45 km north of Vancouver. Britannia Mine operated for 70 years and produced mainly copper and zinc concentrates. During its operating life, and since its closure in 1974, the mine has discharged large volumes of acidic water with elevated concentrations of potentially toxic metals, including copper, zinc, and cadmium. Prior to the recent remedial efforts, metal loadings to Howe Sound averaged 300 kg/day each of copper and zinc. In addition to the acid rock drainage, mine infrastructure and mineral processing activities provide secondary sources of metal contamination of soils, sediments, ground water, and surface water. Effective water management is key to the remedial plan for the mine: ground water and surface water are the primary transport pathways for the metal contamination reaching the local receptors of Britannia and Furry creeks, and Howe Sound. The remedial concept includes diversion of clean water from entering the mine, use of the mine workings as a storage reservoir to balance seasonal flows to a water treatment plant, prior to discharging to Howe Sound via a deep outfall, and the interception of a metal-contaminated ground water plume.     

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.     

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.     

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.     

The Use of Measured and Calculated Acidity Values to Improve the Quality of Mine Drainage Datasets

Abstract:  The net acidity of a water sample can be measured directly by titration with a standardized base solution or calculated from the measured concentrations of the acidic and basic components. For coal mine drainage, the acidic components are primarily accounted for by free protons and dissolved Fe²⁺, Fe³⁺, Al³⁺, and Mn²⁺. The base component is primarily accounted for by bicarbonate. A standard way to calculate the acidity for coal mine drainage is: Acid^calc = 50*(2*Fe²⁺/56 + 3*Fe³⁺/56 + 3*Al/27 + 2*Mn/55 + 1000*10^-pH)—alkalinity, where acidity and alkalinity are measured as mg/L CaCO₃ and the metals are mg/L. Because such methods of estimating acidity are derived by independent laboratory procedures, their comparison can provide a valuable QA/QC for AMD datasets. The relationship between measured and calculated acidities was evaluated for 14 datasets of samples collected from mine drainage discharges, polluted receiving streams, or passive treatment systems, containing a total of 1,484 sample analyses. The datasets were variable in nature, ranging from watersheds where most of the discharges contained alkalinity to ones where all of the discharges were acidic. Good relationships were found to exist between measured and calculated acidities. The average acidity measurement was 239 mg/L CaCO₃ and the average acidity calculation was 226 mg/L CaCO₃. Linear regressions were calculated for individual datasets and for the entire dataset. The linear regression for the entire dataset was: Acid^calc = 0.98 * Acid^meas – 8, r² = 0.98. The good correlation between calculated and measured acidity is the basis for an easy and inexpensive QA/QC for AMD data. Substantial variation between measured and calculated acidities can be used to infer sampling or analytical problems.     

Underground Mine Water for Heating and Cooling using Geothermal Heat Pump Systems

Abstract  In many regions of the world, flooded mines are a potentially cost-effective option for heating and cooling using geothermal heat pump systems. For example, a single coal seam in Pennsylvania, West Virginia, and Ohio contains 5.1 x 10¹² L of water. The growing volume of water discharging from this one coal seam totals 380,000 L/min, which could theoretically heat and cool 20,000 homes. Using the water stored in the mines would conservatively extend this option to an order of magnitude more sites. Based on current energy prices, geothermal heat pump systems using mine water could reduce annual costs for heating by 67% and cooling by 50% over conventional methods (natural gas or heating oil and standard air conditioning).