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.     

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.     

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.     

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.     

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.     

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.     

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.     

Summary of Deepwater Sediment/Pore Water Characterization for the Metal-laden Berkeley Pit Lake in Butte, Montana

Abstract.  Unconsolidated sediment at the bottom of the Berkeley pit lake is a mixture of detrital silicate minerals derived from sloughing of the pit walls and secondary minerals precipitated out of the water column. The latter include gypsum and K-rich jarosite. The pore waters have a similar pH to the overlying lake waters (pH 3.1 to 3.4), and have similarly high concentrations of dissolved heavy metals, including Al, Cd, Cu, Mn, Ni, and Zn. Sediment cores show that the top meter of the sediment column is moderately oxidized (jarosite-stable). Petrography, chemical analysis and geochemical modelling all suggest a transformation of poorly crystalline ferric compounds such as schwertmannite and/or ferrihydrite near the sediment surface to jarosite with depth in the core. No evidence of bacterial sulfate reduction was found in this study, despite the presence of 0.3 to 0.4 wt% organic carbon in the pit lake sediment.     

Radionuclide Contamination of Surface Waters, Sediments, and Soil Caused by Coal Mining Activities in the ruhr District (Germany)

Abstract.   The discharge of highly mineralised mine waters with enhanced ²²⁶Ra and ²²⁸Ra activity concentrations has affected creeks, rivers, sediments, soils, and plants along the Lippe River and its tributaries. ²²⁶Ra activity concentrations were elevated in all water samples receiving mine water, with activity concentrations gradually decreasing with increased distance from the colliery due to dilution and chemical precipitation of radium with barium. Increased concentrations of radium and radium decay products were also measured in sediments and flood-affected soils. The sediments show an enrichment of ²²⁶Ra up to a factor of 750, while the contaminated soils only reach a factor of 10. In aquatic plants, a 4-fold increase in ²²⁶Ra activity concentrations was measured downstream of the discharge points. The contamination of the river banks and adjacent floodplain with radium is responsible for enhanced gamma dose rates, which, along with the incorporation of soil by playing children, provide potential radiation exposure to the public.     

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.     

Microbial Alkalinity Production to Prevent Reacidification of Neutralized Mining Lakes

Abstract.  Microbial alkalinity production was evaluated as a method to prevent reacidification of neutralized mining lakes by acidic ground and seepage water. We used 60 L mesocosms to represent the sediment and water column of a shallow acidic mine lake. To enhance alkalinity production, acidic and neutralized lake waters were treated with either phosphorus (controlled eutrophication) or organic matter (controlled saprobization). Controlled eutrophication could not produce enough autochthonous biomass as substrate for microbial alkalinity production to change the acidity of the water. Chemical pre-neutralization of the acidic water caused the inorganic carbon concentration to increase, but at the same time, hindered algae growth by reducing the availability of phosphate by sorption to the freshly precipitated iron hydroxide. This effect was so strong that even high phosphorus additions could not increase the algae biomass production. In contrast to controlled eutrophication, controlled saprobization produced significant alkalinity. Despite inhibition of the most important alkalinity producing process, namely microbial sulfate reduction, by low pH values, the microbial alkalinity production rate was not affected by pre-neutralization of the water column. Other alkalinity producing processes raised the pH in the reactive zone until sulfate reduction was no longer inhibited.     

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).     

Heavy Metals in Stream Sediments from the Coquimbo region (Chile): Effects of Sustained Mining and Natural Processes in a Semi-arid Andean Basin

Abstract.   Active sediments from the Elqui River in Chile were sampled 4 times at 10 sites during 2000. Concentrations of Ag, Ba, Cd, Co, Cr, Hg, Mn, Mo, Ni, Pb, Sr, Ti, V, Al, Ca, Fe, K, Mg, Na, P, and S were normal. Zinc levels were clearly high, and those of Cu (hundred to thousands ppm) and As (tens to hundreds ppm) were highly anomalous. Dissolved Cu (0.1-12.7 ppm) and Zn (0.2-2.2 ppm) levels were also very high. The anomalies of the upper tributaries are due to the El Indio–Tambo Au-Cu-As district and large hydrothermal alteration zones at altitudes between 3500–4500 m. Lower on the river, old and active tailing waste deposits and on-going mining operations in the Talcuna Cu (Pb) district are responsible. Partially eroded tailing deposits in the alluvial plain of the Elqui River and its tributaries, and especially in the El Indio-Tambo district, after mine closure in 2000, warrant special attention.     

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.     

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.     

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.     

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.     

Environmental Risks Associated with Beneficial End Uses of Mine Lakes in Southwestern Australia

Abstract  Lakes develop when pits from open cut mines are left to fill with groundwater. In recent years, mining companies, mining communities, and regulatory agencies have begun to consider potential beneficial end uses for mine lakes. Beneficial end uses are unlikely to be without environmental impacts, however, and a proper consideration of the total benefit to the community should consider them. This paper briefly reviews potential beneficial end uses and possible environmental impacts that might arise with them for mine lakes in the Collie Basin, a coal mining region in Western Australia. We identified eight distinct, but not necessarily incompatible, end uses from a search of the literature on mine lakes throughout the world: recreation and tourism, wildlife conservation, aquaculture, irrigation, livestock water, potable water, industrial water, and chemical extraction. Recreation, conservation, and possibly aquaculture use the mine lake directly, whereas the other end uses utilise extracted water. All end uses have the potential to have environmental effects, with the most common being an actual or perceived impact on human health and safety. A semi-quantitative risk assessment, using published literature sources, identified wildlife conservation as the end use with the least environmental risk, and irrigation as the end use with the greatest environmental risk. Such risks need to be balanced against economic and social benefits. There is an urgent need for a regulatory framework to address mine lake options.     

Evaluation of the Effluent Water Quality Produced at Phosphate Mines in Central Jordan

Abstract.   The effluent water produced by the washing process at the Al-Hisa and Al-Abyad phosphate mines in central Jordan was investigated in summer 2002. Twenty-four effluent and 10 ground water samples were collected and analyzed. There was a significant difference in water chemistry between input (groundwater) and output (effluent water) but, although the investigated area is highly fractured, the stable isotopic results indicated little or no mixing between the effluent water and groundwater in the area. This is attributed to the precipitation of clay-sized particles along the drainage channel. The quality of the effluent from the Al-Hisa mine was better than at the Al-Abyad mine, with electrical conductivity averaging 1474 µS/cm at Al-Hisa and 3250 µS/cm at Al-Abyad. The difference in effluent quality is attributed to slight lithological differences. At both mines, chloride was the predominant ion in the effluent water, with an average concentration of 669 ppm and 1299 ppm at the Al-Hisa and Al-Abyad mines respectively. The concentrations of heavy metals in the high-pH effluent water were very low, presumably due to precipitation and absorption onto suspended fine-grained particles. The effluent water from both mines was found to be relatively low in sodium and radiation, and suitable for the irrigation of salt tolerant plants.     

Modelling the Long-term Release of Sulphate from Dump Sediments of an Abandoned Open Pit Lignite Mine

Abstract.  The generation of acid drainage from overburden spoil piles at open-pit lignite mines impacts water quality in large parts of the Lusatian mining area in Germany. The Lohsa Mine was exploited until the early 1990s and is to be flooded by 2005. It will then be used as a reservoir basin for the river Spree. Future acidity and sulphate concentrations in the surface water are of great interest because considerable amounts of the bank filtrate of the river are used to supply drinking water to communal water plants downstream. In our study, the input of sulphate from the unsaturated zone of the heap into the groundwater was calculated using the one dimensional reactive transport code SAPY. The SAPY program, which had been calibrated for effective diffusion and tortuosity using oxygen breakthrough curves of a column experiment with original heap sediments, was scaled up to field conditions and verified by measuring the oxygen and sulphate profile of the heap. Scenarios for a period of 80 years were simulated for different distances of the groundwater level to the subsurface, and the mass input of sulphate from the unsaturated zone into the groundwater was calculated in terms of specific fluxes for different times. Plans are to use the calculated source terms in a regional three-dimensional model to predict the evolution of the ground- and surface water in the area.