Grantee Research Project Results
1999 Progress Report: Geochemical, Biological and Economic Effects of Arsenic and Other Oxyanions on a Mining Impacted Watershed
EPA Grant Number: R825289Title: Geochemical, Biological and Economic Effects of Arsenic and Other Oxyanions on a Mining Impacted Watershed
Investigators: Miller, Glenn C. , Anderson, Susan L. , Miller, Watkins W. , Shaw, Douglass , Papelis, Lambis , Hershey, Ron , Tyler, Scott
Institution: University of Nevada - Reno
Current Institution: University of Nevada - Reno , University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 1997 through December 31, 1999 (Extended to December 31, 2000)
Project Period Covered by this Report: January 1, 1998 through December 31, 1999
Project Amount: $767,805
RFA: Water and Watersheds Research (1996) RFA Text | Recipients Lists
Research Category: Watersheds , Water
Objective:
The objective of this research project is to investigate how large scale precious metals mining affects the Humboldt River watershed, which presently produces over half of the U.S. production of gold. Specifically, we are investigating the long-term chemistry and environmental risk of large pit lakes that will form after the mines close, the long-term drainage from cyanidization heaps, biological effects of arsenic and antimony, and the economic effects of long-term alteration of the watershed. The progress of each of the major objectives and the plans for the upcoming year are discussed below.Progress Summary:
Determination of Arsenic (As) Mobility in Precious Metals Mining Pit Lakes (Ron Hershey, Lambis Papelis). Presently, more than 30 open-pit mines in Nevada are operating below the premining groundwater table. Several are mining from 100 to 500 m into the local groundwater aquifers. When mining is completed and dewatering ceases, groundwater will flow into the pits and create standing bodies of water. Combined, these pit lakes will eventually contain more than an estimated one trillion liters of water. Research in 1999-2000 focused on collecting pit lake sediment samples for laboratory arsenic sorption experiments and obtaining access to an active mine to collect wall rock samples for detailed analysis of pyrite oxidation. Sediments were collected from three existing pit lakes that are representative of major ore body types found in the Humboldt River Basin. Sediments were collected from the former Anaconda pit lake in Yerington, NV, an example of a porphyry copper deposit; from the Dexter pit lake in Tuscarora, NV, an example of a quartz adularia type deposit; and from one of the Big Springs pit lakes north of Elko, NV, an example of a sediment-hosted Carlin type gold deposit. The Anaconda and Dexter pit lake sediments have very low amounts of leachable arsenic (<1 ppb As+3 and 3 ppb As+5 for Anaconda; 2 ppb As+3 and 3 ppb As+5 for Dexter) while the Big Springs pit lake sediment had higher amounts (10 ppb As+3 and 34 ppb As+5). Based on extensive discussions and review of the geochemistry of pit lakes, it now is increasingly apparent that pit lake development is dependent on the geochemistry of the dewatered cone of depression, rather than the rock immediately surrounding the pit. When water is withdrawn kilometers from a pit during mining, that water is replaced with air that oxidizes rock, sometimes far distant from the pit. This alternative model suggests that several constituents will be elevated, compared to the concentrations predicted by current pit lake models.Dissolution of Constituents from Heaps and Waste Rock Dumps (Scott Tyler, Wally Miller, Glenn Miller, and Dave Decker). Between 1 and 2 billion tons of precious metals heaps will have been extracted with cyanide and closed during the next 5-10 years in Nevada. From modeling and field data, it now is apparent that these heaps will release water whenever rain or snow melt is allowed to penetrate them. The drainage water contains a variety of constituents, including arsenic, antimony, selenium, sulfate, and vanadium. An important component of the subsurface phase of the research is the development of predictive models to estimate both the flux and concentration of transition and rare earth oxyanions produced from mining operations. In particular, we are focused on oxyanion production from typical heap leach piles and waste rock dumps both during mining activities, and following mine closure. For this effort, a fully coupled unsaturated flow and transport solver (UNSATCHEM), combined with a reaction path geochemical model, has been adapted to heap leach and waste rock dump environments. We have modified both the 1-D and 2-D versions of this code to include the dissolution of solid phase arsenic (orpiment) and pH-dependent adsorption. In support of the modeling effort, a series of arsenic oxyanion adsorption experiments have provided the pH-dependent sorption isotherm for arsenate for two mine heap leach materials. A method has been developed that accomplishes the detection of arsenate and arsenite together in the same fluid sample. The results of batch reactor experiments to date are that the two heap samples that we are studying exhibit strongly pH-dependent arsenate adsorption behavior. At low (pH 2) or high (pH 10) pH, arsenate is desorbed, whereas in the middle of the pH 2-10 range, arsenate readily adsorbs and is described by a Langmuir isotherm model. At high pH, arsenate desorption occurs due to hydroxyl ligand groups loading onto the adsorption sites. These data can be best represented by a pH-dependent isotherm surface that is then easily incorporated into the numerical model.
Effects of Arsenic on Aquatic Organisms (Susan L. Anderson). DNA damage from arsenic in aquatic species could result in changes in fertility and fecundity, and abnormal development. In the past year, we have completed studies on the induction of genotoxic damage by arsenic to an aquatic vertebrate, the fathead minnow (Pimephales premelas). We used an alkaline single cell gel electrophoresis assay (comet assay) to examine DNA strand breaks in erythrocytes. We conducted 14-day dose-response studies to arsenic (III) and arsenic (V), as well as time-course studies with arsenic (III). Blood was sampled by heart puncture and preserved at -70?C. Following electrophoresis, slides were stained with ethidium bromide and analyzed using fluorescence microscopy and an image analysis program. Damage was expressed as "percent tail", or the amount of damaged DNA that has migrated away from the nucleus divided by the amount of DNA in the entire nucleus x 100. Significant strand-breaks were observed at 2-4 mg/L arsenic (III), indicating that responses in fish may occur at lower doses than previously believed. In the time-course studies, significant effects were observed after 8 days of exposure at 4 mg/L arsenic (III). These data indicate that significant effects might be observed at lower doses if longer exposure times are used. We also observed greater damage induced by arsenic (III) versus arsenic (V).
Economic Impacts (Douglass Shaw and Noelwah Netusil). All of the data have been collected for this project, including data for a recreational analysis of the Rye Patch Reservoir, a programming model to allow estimation of impacts of flow changes on the Humboldt River, and the contingent valuation study. The recreation data are mostly at the county level of aggregation. The former data were scant for the Humboldt River Basin and had to be supplemented using crop data for Southern Idaho, which is similar in many ways to this region. The contingent valuation data set is smaller than desired, but low response rates across the State of Nevada were anticipated.
The recreational data were analyzed using an aggregated recreation demand model. A manuscript was submitted, accepted, and published in the November issue of the journal Water Resources Research. The programming data were analyzed using a simple dynamic, stochastic programming approach.
Public Outreach. As indicated in previous reports, this project has received a large amount of interest in the regulatory and mining communities. This project was in part responsible for development of interest in having a pit lake workshop in Reno, NV, during March 2000. The proceedings of the workshop on Closure, Remediation and Management of Precious Metals Heap Leach Facilities was published.
Additionally, the Principal Investigator (PI) and Co-PIs have developed a good working relationship with staff interested in mining in the U.S. Environmental Protection Agency's (EPA) Region 9. This has been particularly useful as the Toxic Release Inventory has been released as well as for issues with regard to closure of precious metals heaps.
Future Activities:
Currently, we are focusing on identifying a pyrite rich abandoned pit where we may sample by contacting the appropriate state or federal agency responsible for the abandoned mine. Unfortunately, wall rocks collected from such a pit will not ever have been below the water table and then dewatered. However, we feel that valuable information on the depth of oxygen diffusion into the pit wall and the amount and rate of pyrite oxidation can still be obtained under these conditions. Once an appropriate sampling location is identified, samples will be collected and analysis will commence.To incorporate both an arsenate and an arsenite isotherm into the numerical flow and transport model, an additional modification to the UNSATCHEM code is planned. The modification will incorporate the Fe(II)/Fe(III) redox couple system together with iron/arsenopyrite dissolution. The Fe(II)/Fe(III) system will serve as a surrogate redox couple that will allow the model to speciate arsenic via a redox-dependent relationship. The incorporation of arsenopyrite dissolution will allow the model to simulate arsenic transport for a wider range of Carlin-type gold deposits. Additionally, we will incorporate the geochemistry for an iron precipitate, Jarosite, which can coprecipitate with arsenic. Jarosite is stable within a range of pH and redox potentials observed in Carlin-type heap leach operations.
The acceptance and publication of the programming and contingent valuation manuscripts will mark the conclusion of the economic analysis. It is anticipated that both manuscripts will be accepted by the end of the year 2000.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 37 publications | 19 publications in selected types | All 10 journal articles |
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Decker DL, Tyler SW. Evaluation of flow and solute transport parameters for heap leach recovery materials. Journal of Environmental Quality 1999;28(2):543-555. |
R825289 (1999) R825289 (Final) |
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Supplemental Keywords:
watershed, heavy metals, arsenic, geochemistry, modeling, Nevada, NV, Humboldt River, mining wastes., RFA, Scientific Discipline, Geographic Area, Water, Water & Watershed, Geochemistry, Arsenic, State, Economics, Ecological Risk Assessment, Biology, Watersheds, fate and transport, epidemiology, human health effects, genotoxic research, pit lakes, mine tailings, geochemical efffects, Nevada (NV), economic effects, aquatic ecosystems, water quality, arsenic exposure, biological effects, mining impacted watershedProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.