Geology topics

Katherine Walton-Day

Publications and source records attributed to Katherine Walton-Day.

At least 55 records · Page 3Linked to original sources

USGS2012

Pre- and post-remediation characterization of acid-generating fluvial tailings material

Colorado↗

USGS2011

Evaluating remedial alternatives for an acid mine drainage stream: A model post audit

A post audit for a reactive transport model used to evaluate acid mine drainage treatment systems is presented herein. The post audit is based on a paired synoptic approach in which hydrogeochemical data are collected at low (existing conditions) and elevated (following treatment) pH. Data obtained under existing, low-pH conditions are used for calibration, and the resultant model is used to predict metal concentrations observed following treatment. Predictions for Al, As, Fe, H + , and Pb accurately reproduce the observed reduction in dissolved concentrations afforded by the treatment system, and the information provided in regard to standard attainment is also accurate (predictions correctly indicate attainment or nonattainment of water quality standards for 19 of 25 cases). Errors associated with Cd, Cu, and Zn are attributed to misspecification of sorbent mass (precipitated Fe). In addition to these specific results, the post audit provides insight in regard to calibration and sensitivity analysis that is contrary to conventional wisdom. Steps taken during the calibration process to improve simulations of As sorption were ultimately detrimental to the predictive results, for example, and the sensitivity analysis failed to bracket observed metal concentrations.

Colorado↗

USGS2011

Redox chemistry and natural organic matter (NOM): Geochemists' dream, analytical chemists' nightmare

Natural organic matter (NOM) is an inherently complex mixture of polyfunctional organic molecules. Because of their universality and chemical reversibility, oxidation/reductions (redox) reactions of NOM have an especially interesting and important role in geochemistry. Variabilities in NOM composition and chemistry make studies of its redox chemistry particularly challenging, and details of NOM-mediated redox reactions are only partially understood. This is in large part due to the analytical difficulties associated with NOM characterization and the wide range of reagents and experimental systems used to study NOM redox reactions. This chapter provides a summary of the ongoing efforts to provide a coherent comprehension of aqueous redox chemistry involving NOM and of techniques for chemical characterization of NOM. It also describes some attempts to confirm the roles of different structural moieties in redox reactions. In addition, we discuss some of the operational parameters used to describe NOM redox capacities and redox states, and describe nomenclature of NOM redox chemistry. Several relatively facile experimental methods applicable to predictions of the NOM redox activity and redox states of NOM samples are discussed, with special attention to the proposed use of fluorescence spectroscopy to predict relevant redox characteristics of NOM samples.

ACS Symposium Series↗

USGS2009

New light on a dark subject: On the use of fluorescence data to deduce redox states of natural organic matter (NOM)

This paper reports the use of excitation-emission matrix fluorescence spectroscopy (EEMS), parallel factor statistical analysis (PARAFAC), and oxidation-reduction experiments to examine the effect of redox conditions on PARAFAC model results for aqueous samples rich in natural organic matter. Fifty-four aqueous samples from 11 different geographic locations and two plant extracts were analyzed untreated and after chemical treatments or irradiation were used in attempts to change the redox status of the natural organic matter. The EEMS spectra were generated and modeled using a PARAFAC package developed by Cory and McKnight (2005). The PARAFAC model output was examined for consistency with previously reported relations and with changes expected to occur upon experimental oxidation and reduction of aqueous samples. Results indicate the implied fraction of total sample fluorescence attributed to quinone-like moieties was consistent (0.64 to 0.78) and greater than that observed by Cory and McKnight (2005). The fraction of the quinone-like moieties that was reduced (the reducing index, RI) showed relatively little variation (0.46 to 0.71) despite attempts to alter the redox status of the natural organic matter. The RI changed little after reducing samples using zinc metal, oxidizing at high pH with air, or irradiating with a Xenon lamp. Our results, however, are consistent with the correlations between the fluorescence indices (FI) of samples and the ratio of PARAFAC fitting parameters suggested by Cory and McKnight (2005), though we used samples with a much narrower range of FI values.

Aquatic Sciences↗

USGS2009

The use of fluoride as a natural tracer in water and the relationship to geological features: Examples from the Animas River Watershed, San Juan Mountains, Silverton, Colorado

Investigations within the Silverton caldera, in southwestern Colorado, used a combination of traditional geological mapping, alteration-assemblage mapping, and aqueous geochemical sampling that showed a relationship between geological and hydrologic features that may be used to better understand the provenance and evolution of the water. Veins containing fluorite, huebnerite, and elevated molybdenum concentrations are temporally and perhaps genetically associated with the emplacement of high-silica rhyolite intrusions. Both the rhyolites and the fluorite-bearing veins produce waters containing elevated concentrations of F - , K and Be. The identification of water samples with elevated F/Cl molar ratios (> 10) has also aided in the location of water draining F-rich sources, even after these waters have been diluted substantially. These unique aqueous geochemical signatures can be used to relate water chemistry to key geological features and mineralized source areas. Two examples that illustrate this relationship are: (1) surface-water samples containing elevated F - concentrations (> 1.8 mg/l) that closely bracket the extent of several small high-silica rhyolite intrusions; and (2) water samples containing elevated concentrations of F - (> 1.8 mg/ l) that spatially relate to mines or areas that contain late-stage fluorite/huebnerite veins. In two additional cases, the existence of high F - concentrations in water can be used to: (1) infer interaction of the water with mine waste derived from systems known to contain the fluorite/huebnerite association; and (2) relate changes in water quality over time at a high elevation mine tunnel to plugging of a lower elevation mine tunnel and the subsequent rise of the water table into mineralized areas containing fluorite/huebnerite veining. Thus, the unique geochemical signature of the water produced from fluorite veins indicates the location of high-silica rhyolites, mines, and mine waste containing the veins. Existence of high F - concentrations along with K and Be in water in combination with other geological evidence may be used to better understand the provenance of the water. ?? 2009 AAG/Geological Society of London.

Colorado↗

USGS2009

Investigating hydraulic connections and the origin of water in a mine tunnel using stable isotopes and hydrographs

Turquoise Lake is a water-supply reservoir located north of the historic Sugarloaf Mining district near Leadville, Colorado, USA. Elevated water levels in the reservoir may increase flow of low-quality water from abandoned mine tunnels in the Sugarloaf District and degrade water quality downstream. The objective of this study was to understand the sources of water to Dinero mine drainage tunnel and evaluate whether or not there was a direct hydrologic connection between Dinero mine tunnel and Turquoise Lake from late 2002 to early 2008. This study utilized hydrograph data from nearby draining mine tunnels and the lake, and stable isotope (δ 18 O and δ 2 H) data from the lake, nearby draining mine tunnels, imported water, and springs to characterize water sources in the study area. Hydrograph results indicate that flow from the Dinero mine tunnel decreased 26% (2006) and 10% (2007) when lake elevation (above mean sea level) decreased below approximately 3004 m (approximately 9855 feet). Results of isotope analysis delineated two meteoric water lines in the study area. One line characterizes surface water and water imported to the study area from the western side of the Continental Divide. The other line characterizes groundwater including draining mine tunnels, springs, and seeps. Isotope mixing calculations indicate that water from Turquoise Lake or seasonal groundwater recharge from snowmelt represents approximately 10% or less of the water in Dinero mine tunnel. However, most of the water in Dinero mine tunnel is from deep groundwater having minimal isotopic variation. The asymmetric shape of the Dinero mine tunnel hydrograph may indicate that a limited mine pool exists behind a collapse in the tunnel and attenutates seasonal recharge. Alternatively, a conceptual model is presented (and supported with MODFLOW simulations) that is consistent with current and previous data collected in the study area, and illustrates how fluctuating lake levels change the local water-table elevation which can affect discharge from the Dinero mine tunnel without physical transfer of water between the two locations.

Colorado↗

USGS2009

Geochemical data for Upper Mineral Creek, Colorado, under existing ambient conditions and during an experimental pH modification, August 2005

Mineral Creek, an acid mine drainage stream in south-western Colorado, was the subject of a water-quality study that employed a paired synoptic approach. Under the paired synoptic approach, two synoptic sampling campaigns were conducted on the same study reach. The initial synoptic campaign, conducted August 22, 2005, documented stream-water quality under existing ambient conditions. A second synoptic campaign, conducted August 24, 2005, documented stream-water quality during a pH-modification experiment that elevated the pH of Mineral Creek. The experimental pH modification was designed to determine the potential reductions in dissolved constituent concentrations that would result from the implementation of an active treatment system for acid mine drainage. During both synoptic sampling campaigns, a solution containing lithium bromide was injected continuously to allow for the calculation of streamflow using the tracer-dilution method. Synoptic water-quality samples were collected from 30 stream sites and 11 inflow locations along the 2-kilometer study reach. Data from the study provide spatial profiles of pH, concentration, and streamflow under both existing and experimentally-altered conditions. This report presents the data obtained August 21-24, 2005, as well as the methods used for sample collection and data analysis.

Data Series↗

USGS2008

Principal locations of major-ion, trace-element, nitrate, and Escherichia coli loading to Emigration Creek, Salt Lake County, Utah, October 2005

Housing development and recreational activity in Emigration Canyon have increased substantially since 1980, perhaps causing an observed decrease in water quality of this northern Utah stream located near Salt Lake City. To identify reaches of the stream that contribute to water-quality degradation, a tracer-injection and synoptic-sampling study was done to quantify mass loading of major ions, trace elements, nitrate, and Escherichia coli (E. coli) to the stream. The resulting mass-loading profiles for major ions and trace elements indicate both geologic and anthropogenic inputs to the stream, principally from tributary and spring inflows to the stream at Brigham Fork, Burr Fork, Wagner Spring, Emigration Tunnel Spring, Blacksmith Hollow, and Killyon Canyon. The pattern of nitrate loading does not correspond to the major-ion and trace-element loading patterns. Nitrate levels in the stream did not exceed water-quality standards at the time of synoptic sampling. The majority of nitrate mass loading can be considered related to anthropogenic input, based on the field settings and trends in stable isotope ratios of nitrogen. The pattern of E. coli loading does not correspond to the major-ion, trace-element, or nitrate loading patterns. The majority of E. coli loading was related to anthropogenic sources based on field setting, but a considerable part of the loading also comes from possible animal sources in Killyon Canyon, in Perkins Flat, and in Rotary Park. In this late summer sampling, E. coli concentrations only exceeded water-quality standards in limited sections of the study reach. The mass-loading approach used in this study provides a means to design future studies and to evaluate the loading on a catchment scale.

Utah↗

USGS2007

Quantification of changes in metal loading from storm runoff, Merse River (Tuscany, Italy)

The Merse River in Tuscany is affected by mine drainage and the weathering of mine wastes along several kilometres of its catchment. The metal loading to the stream was quantified by defining detailed profiles of discharge and concentration, using tracer-dilution and synoptic-sampling techniques. During the course of a field experiment to evaluate metal loading to the Merse, such data were obtained for both storm and pre-storm conditions, providing a unique opportunity for comparison. Iron, Cu, and Mn were chosen to illustrate changes resulting from the storm. The total-recoverable load of Fe increased 21-fold, while loads of Cu and Mn increased by 8- and 7-fold, respectively, during the storm runoff. The increases most likely resulted from flushing particulates from near the stream, resuspension of colloidal material from the streambed, and increased ground-water inflow to the stream. The increases in Cu and Mn loads results from their association with colloids. It is possible that in-stream colloids had relatively more Cu than Mn, while near-stream colloids had relatively more Mn. Each of the metals also increased as a result of increased ground-water discharge during the storm. Despite great increases in load, the filterable concentrations of these metals did not increase substantially, remaining below chronic levels of toxicity.

Tuscany↗

USGS2007

Field methods for measurement of ground water redox chemical parameters

An inexpensive, versatile, and portable system is presented, which facilitates rapid field determinations of redox potentials, pH, conductivity, ferrous and total iron, nitrite, specific conductance, dissolved oxygen, and temperature. Accuracy is facilitated by on‐site measurements of most parameters using specially constructed flow‐through cells and, for several analyses, sealed reagent ampoules, which can be broken and developed inside a flowing stream of ground water. Coupled with laboratory analyses of more stable ground water parameters, this system can provide accurate and relatively inexpensive determinations of redox conditions in ground water.

Groundwater Monitoring & Remediation↗

USGS2007

A simulation-based approach for estimating premining water quality: Red Mountain Creek, Colorado

Regulatory agencies are often charged with the task of setting site-specific numeric water quality standards for impaired streams. This task is particularly difficult for streams draining highly mineralized watersheds with past mining activity. Baseline water quality data obtained prior to mining are often non-existent and application of generic water quality standards developed for unmineralized watersheds is suspect given the geology of most watersheds affected by mining. Various approaches have been used to estimate premining conditions, but none of the existing approaches rigorously consider the physical and geochemical processes that ultimately determine instream water quality. An approach based on simulation modeling is therefore proposed herein. The approach utilizes synoptic data that provide spatially-detailed profiles of concentration, streamflow, and constituent load along the study reach. This field data set is used to calibrate a reactive stream transport model that considers the suite of physical and geochemical processes that affect constituent concentrations during instream transport. A key input to the model is the quality and quantity of waters entering the study reach. This input is based on chemical analyses available from synoptic sampling and observed increases in streamflow along the study reach. Given the calibrated model, additional simulations are conducted to estimate premining conditions. In these simulations, the chemistry of mining-affected sources is replaced with the chemistry of waters that are thought to be unaffected by mining (proximal, premining analogues). The resultant simulations provide estimates of premining water quality that reflect both the reduced loads that were present prior to mining and the processes that affect these loads as they are transported downstream. This simulation-based approach is demonstrated using data from Red Mountain Creek, Colorado, a small stream draining a heavily-mined watershed. Model application to the premining problem for Red Mountain Creek is based on limited field reconnaissance and chemical analyses; additional field work and analyses may be needed to develop definitive, quantitative estimates of premining water quality.

Colorado↗

USGS2007

Selenium and other elements in water and adjacent rock and sediment of Toll Gate Creek, Aurora, Arapahoe County, Colorado, December 2003 through March 2004

Streamwater and solid samples (rock, unconsolidated sediment, stream sediment, and efflorescent material) in the Toll Gate Creek watershed, Colorado, were collected and analyzed for major and trace elements to determine trace-element concentrations and stream loads from December 2003 through March 2004, a period of seasonally low flow. Special emphasis was given to selenium (Se) concentrations because historic Se concentrations exceeded current (2004) stream standards. The goal of the project was to assess the distribution of Se concentration and loads in Toll Gate Creek and to determine the potential for rock and unconsolidated sediment in the basin to be sources of Se to the streamwater. Streamwater samples and discharge measurements were collected during December 2003 and March 2004 along Toll Gate Creek and its two primary tributaries - West Toll Gate Creek and East Toll Gate Creek. During both sampling periods, discharge ranged from 2.5 liters per second to 138 liters per second in the watershed. Discharge was greater in March 2004 than December 2003, but both periods represent low flow in Toll Gate Creek, and results of this study should not be extended to periods of higher flow. Discharge decreased moving downstream in East Toll Gate Creek but increased moving downstream along West Toll Gate Creek and the main stem of Toll Gate Creek, indicating that these two streams gain flow from ground water. Se concentrations in streamwater samples ranged from 7 to 70 micrograms per liter, were elevated in the upstream-most samples, and were greater than the State stream standard of 4.6 micrograms per liter. Se loads ranged from 6 grams per day to 250 grams per day, decreased in a downstream direction along East Toll Gate Creek, and increased in a downstream direction along West Toll Gate Creek and Toll Gate Creek. The largest Se-load increases occurred between two sampling locations on West Toll Gate Creek during both sampling periods and between the two sampling locations on the main stem of Toll Gate Creek during the December 2003 sampling. These load increases may indicate that sources of Se exist between these two locations; however, Se loading along West Toll Gate Creek and Toll Gate Creek primarily was characterized by gradual downstream increases in load. Linear regressions between Se load and discharge for both sampling periods had large, significant values of r2 (r2 > 0.96, p < 0.0001) because increases in Se load (per unit of flow increase) were generally constant. This relation is evidence for a constant addition of water having a relatively constant Se concentration over much of the length of Toll Gate Creek, a result which is consistent with a ground-water source for the Se loads. Rock outcroppings along the stream were highly weathered, and Se concentrations in rock and other solid samples ranged from below detection (1 part per million) to 25 parts per million. One sample of efflorescence (a surface encrustation produced by evaporation) had the greatest selenium concentration of all solid samples, was composed of thenardite (sodium sulfate), gypsum (calcium sulfate) and minor halite (sodium chloride), and released all of its Se during a 30-minute water-leaching procedure. Calculations indicate there was an insufficient amount of this material present throughout the watershed to account for the observed Se load in the stream. However, this material likely indicates zones of ground-water discharge that contain Se. This report did not identify an unequivocal source of Se in Toll Gate Creek. However, multiple lines of evidence indicate that ground-water discharge supplies Se to Toll Gate Creek: (1) the occurrence of elevated Se concentrations in the stream throughout the watershed and in the headwater regions, upstream from industrial sources; (2) the progressive increase in Se loads moving downstream, which indicates a continuous input of Se along the stream rather than input from point sources; (3) the occurr

Colorado↗

USGS2007

Principal locations of metal loading from flood-plain tailings, Lower Silver Creek, Utah, April 2004

Because of the historical deposition of mill tailings in flood plains, the process of determining total maximum daily loads for streams in an area like the Park City mining district of Utah is complicated. Understanding the locations of metal loading to Silver Creek and the relative importance of these locations is necessary to make science-based decisions. Application of tracer-injection and synoptic-sampling techniques provided a means to quantify and rank the many possible source areas. A mass-loading study was conducted along a 10,000-meter reach of Silver Creek, Utah, in April 2004. Mass-loading profiles based on spatially detailed discharge and chemical data indicated five principal locations of metal loading. These five locations contributed more than 60 percent of the cadmium and zinc loads to Silver Creek along the study reach and can be considered locations where remediation efforts could have the greatest effect upon improvement of water quality in Silver Creek.

Utah↗

USGS2006

Quantification of mass loading to Strawberry Creek near the Gilt Edge mine, Lawrence County, South Dakota, June 2003

Although remedial actions have taken place at the Gilt Edge mine in the Black Hills of South Dakota, questions remain about a possible hydrologic connection along shear zones between some of the pit lakes at the mine site and Strawberry Creek. Spatially detailed chemical sampling of stream and inflow sites occurred during low-flow conditions in June 2003 as part of a mass-loading study by the U.S. Geological Survey to investigate the possible connection of shear zones to the stream. Stream discharge was calculated by tracer dilution; discharge increased by 25.3 liters per second along the study reach, with 9.73 liters per second coming from three tributaries and the remaining increase coming from small springs and dispersed, subsurface inflow. Chemical differences among inflow samples were distinguished by cluster analysis and indicated that inflows ranged from those unaffected by interaction with mine wastes to those that could have been affected by drainage from pit lakes. Mass loading to the stream from several inflows resulted in distinct chemical changes in stream water along the study reach. Mass loading of the mine-related metals, including cadmium, copper, nickel, and zinc, principally occurred from the discharge from the Gilt Edge mine, and those metals were substantially attenuated downstream. Secondary loadings of metals occurred in the vicinity of the Oro Fino shaft and from two more inflows about 200 m downstream from there. These are both locations where shear zones intersect the stream and may indicate loading associatedwith these zones. Loading downstream from the Oro Fino shaft had a unique chemical character, high in base-metal concentrations, that could indicate an association with water in the pit lakes. The loading from these downstream sources, however, is small in comparison to that from the initial mine discharge and does not appear to have a substantial impact on Strawberry Creek.

South Dakota↗

USGS2005

Geochemistry of Red Mountain Creek, Colorado, under low-flow conditions, August 2002

Red Mountain Creek, an acid mine drainage stream in southwestern Colorado, was the subject of a synoptic study conducted in August 2002. During the synoptic study, a solution containing lithium chloride was injected continuously to allow for the calculation of streamflow using the tracer-dilution method. Synoptic water-quality samples were collected from 48 stream sites and 29 inflow locations along a 5.4-kilometer study reach. Data from the study provide profiles of pH, concentration, and mass load with a high degree of spatial resolution. Despite the presence of 10 circumneutral inflows, pH remained below 3.4 at all stream sites. Concentration profiles indicate that dissolved concentrations of aluminum, cadmium, copper, lead, and zinc exceed chronic aquatic-life standards established by the State of Colorado along the entire study reach. Comparison of total recoverable and dissolved concentrations suggests that most constituents were transported conservatively. Exceptions to this pattern include arsenic, iron, molybdenum, and vanadium, four constituents that were subject to precipitation and(or) sorption reactions as the addition of a circumneutral tributary resulted in a slight increase in instream pH. Evaluation of data from the 29 inflow locations indicates a sharp contrast between the east and west sides of the watershed; inflows from the east side have high constituent concentrations and acidic pH, whereas inflows from the west side have lower concentrations and generally higher pH. Loading profiles, the product of streamflow and concentration, are used to rank potential sources of metals and acidity within the watershed. Four sources account for 83, 72, 70, 69, 64, and 61 percent of the aluminum, iron, arsenic, zinc, copper, and cadmium loading within the study reach, respectively. All four sources appear to be the result of surface inflows that have been affected by mining activities. The relatively small number of major sources and the fact that they are attributable to surface inflows are two factors that may facilitate effective remediation.

Colorado↗

USGS2005

Mass loading of selected major and trace elements in Lake Fork Creek near Leadville, Colorado, September-October 2001

A mass-loading study of Lake Fork Creek of the Arkansas River between Sugarloaf Dam and the mouth was completed in September-October 2001 to help ascertain the following: (1) variation of pH and aqueous constituent concentrations (calcium, sulfate, alkalinity, aluminum, cadmium, copper, iron, manganese, lead, and zinc) and their relation to toxicity standards along the study reach; (2) location and magnitude of sources of metal loading to Lake Fork Creek; (3) amount and locations of metal attenuation; (4) the effect of streamside wetlands on metal transport from contributing mine tunnels; and (5) the effect of organic-rich inflow from the Leadville National Fish Hatchery on water quality in Lake Fork Creek. The study was done in cooperation with the Bureau of Land Management, U.S. Department of Agriculture Forest Service, and U.S. Fish and Wildlife Service. Constituent concentrations and pH showed variable patterns over the study reach. Hardness-based acute and chronic toxicity standards were exceeded for some inflows and some constituents. However, stream concentrations did not exceed standards except for zinc starting in the upper parts of the study reach and extending to just downstream from the inflow from the Leadville National Fish Hatchery. Dilution from that inflow lowered stream zinc concentrations to less than acute and chronic toxicity standards. The uppermost 800 meters of the study reach that contained inflow from the Bartlett, Dinero, and Nelson mine tunnels and the Dinero wetland was the greatest source of loading for manganese and zinc. A middle section of the study reach that extended approximately 2 kilometers upstream from the National Fish Hatchery inflow to just downstream from that inflow was the largest source of aluminum, copper, iron, and lead loading. The loading was partially from the National Fish Hatchery inflow but also from unknown sources upstream from that inflow, possibly ground water. The largest sources for calcium and sulfate load to the stream were the parts of the study reach containing inflow from the tribu-taries Halfmoon Creek (calcium) and Willow Creek (sulfate). The Arkansas River and its tributaries upstream from Lake Fork Creek were the source of most of the calcium (70 percent), sulfate (82 percent), manganese (77 percent), lead (78 percent), and zinc (95 percent) loads in the Arkansas River downstream from the Lake Fork confluence. In contrast, Lake Fork Creek was the major source of aluminum (68 percent), copper (65 percent), and iron (87 percent) loads to the Arkansas River downstream from the confluence. Attenuation was not important for calcium, sulfate, or iron. However, other metals loads were reduced up to 81 percent over the study reach (aluminum, 25 percent; copper, 20 percent; manganese, 81 percent; lead, 30 percent; zinc, 72 percent). Metal attenuation in the stream occurred primarily in three locations (1) the irrigation diversion ditch; (2) the beaver pond complex extending from upstream from the Colorado Gulch inflow to just downstream from that inflow; and (3) the stream reach that included the inflow from Willow Creek. The most likely attenuation mechanism is precipitation of metal oxides and hydroxides (primarily manganese), and sorption or coprecipitation of trace elements with the precipitating phase. A mass-balance calculation indicated that the wetland between the Dinero Tunnel and Lake Fork Creek removed iron, had little effect on zinc mass load, and was a source for, or was releasing, aluminum and manganese. In contrast, the wetland that occurred between the Siwatch Tunnel and Lake Fork Creek removed aluminum, iron, manganese, and zinc from the tunnel drainage before it entered the creek. Inflow from the National Fish Hatchery increased dissolved organic carbon concentrations in Lake Fork Creek and slightly changed the composition of the dissolved organic carbon. However, dissolved organic carbon loads increased in the stream reach downs

Colorado↗

USGS2003

Use of an intact core and stable-metal isotopes to examine leaching characteristics of a fluvial tailings deposit

The upper Arkansas River south of Leadville, Colorado, USA, contains deposits of fluvial tailings from historical mining operations in the Leadville area. These deposits are possible non-point sources of acid and metal contamination to surface- and ground-water systems. We used stable-metal isotopes to help ascertain metal retention and release mechanisms that influence metal transport from the deposits to shallow ground-water systems. To accomplish this, we excavated an intact core from a small fluvial tailings deposit and performed laboratory column experiments to examine the amount of metals leaching through the core. Deionised water was continuously applied to the top of the core, and effluent was collected from the bottom of the core for a period of about two months. Three saturation conditions were used, including unsaturated, partially saturated, and fully saturated. Reducing conditions developed upon partial and complete saturation of the core. During the unsaturated leaching phase, core effluents were acidic (pH 2.8 - 3.5) and contained elevated metal concentrations. During a portion of the unsaturated leaching phase, stable-metal isotope spikes and conservative tracers were simultaneously applied to the top of the core. The isotopes provide a means to delineate metal behaviour within the core. During the unsaturated leaching phase, the isotope spikes did not exhibit breakthrough with simultaneously added conservative tracers. However, some of the stable-metal isotope spikes did break through when reducing conditions occurred in the core (during the partial- and completesaturation conditions). In this paper, we use Cd as an example of the utility of stable-metal isotopes in geochemical studies. In the case of Cd, after the core was partially saturated, the 111 Cd spike was released as evidenced by a change in the Cd isotope ratios in the effluent. This release continued during the fully saturated leaching phase, however, the total Cd concentration did not increase. These results suggest that the 111 Cd spike was retained inside the core during the unsaturated leaching phase, and only partially released as reducing conditions developed. Results from this core-leaching experiment indicate there is a large reservoir of water-soluble material within the fluvial tailings deposit, which yields elevated metal concentrations and high acidity, and which may degrade adjacent ground- and surface-water quality. Use of stable metal isotopes in this study facilitated the determination of different metal-retention processes, metal-release processes, and metal sources in the fluvial tailings deposit in response to changing geochemical conditions.

Conference Paper↗

USGS2003

Geochemistry of active and passive treatment processes used to treat mine drainage

No abstract available.

Book chapter↗