Water Resources Research Act Program

Details for Project ID 2002NV5B

Assessment of Ground Water Recharge in Mine Altered Regions of Nevada

Institute: Nevada
Year Established: 2002 Start Date: 2001-03-01 End Date: 2003-02-28
Total Federal Funds: $20,000 Total Non-Federal Funds: $40,000

Principal Investigators: Scott Tyler, Glenn Miller, Dirk Vanzyl

Abstract: This project proposes to determine the rate of ground water recharge beneath disturbed mine lands in Nevada, with particular attention to heap leach piles, waste rock dumps and the associated issues of water quality with these areas. In the first year of the project, we have focused on sampling known closed mine sites and designing a field monitoring laboratory to investigate the flow and transport processes in these complex materials. We have and continue to analyze heap leach pile drainage data to determine rates of recharge from these structures. As heap leach piles are lined and drainage can easily be measured, these structures act as very large lysimeters, intercepting ground water recharge before reaching the water table. The integrated fluxes through these structures, long after active leaching and rinsing has stopped represent deep infiltration. Data gathered to date from field investigations shows a complex relationship between surface morphology, precipitation and long-term drainage rate. At several sites, changes in surface cover or management practices have been reflected in declines in drainage rates below that expected for native vegetation at these sites. Water quality from the studies sites shows a wide variation in dissolved constituents, primarily reflecting the mineralogy of the primary ore and waste rock, as well as the rinsing and closure strategies employed.

As a result of efforts during the first year, we have developed a unique opportunity with Placer Dome Inc., to densely instrument a heap leach pad nearing completion. Currently, there does not exist any detailed, in-place monitoring and sampling facility to study the transport of water and contaminants through gold mining waste at the field scale. The planned facility represents a partnership between industry and the university of significant benefit to both. For industry, the facility will be used to demonstrate improvements in leach efficiency, design and test effective rinsing strategies and to test cover/closure performance. For UNR, the facility will allow, for the first time, detailed data on the fluid flow and contaminant transport mechanisms in mining facilities. We will also have, for the first time, detailed flow and geochemical data with which to test our numerical reactive transport models at the field scale. At this time, no similar facility exists in the world and will provide tremendous opportunities for future research into contaminant transport from mining waste.

Placer Dome will provide the cost of instrumentation and monitoring as in-kind services, with UNR's activities focused on laboratory analysis, data analysis and experimental design. The focus of this second year effort will be to quantitatively understand the water and geochemical evolution under heap leaching, rinsing and long-term closure using this field site. This site offers a unique opportunity, unavailable to us when the first year proposal was completed, to study in situ, 1) the evolution of wetting and drainage in an active heap leach pile, 2) the geochemical evolution of waters produced during leaching operations, 3) the short term drainage effluent quality following leaching 4) the efficacy of rinsing in reducing toxic species in the effluent waters and 5) to test various cover/closure options to reduce both water flow and toxic element release. During this second year of the project, #1-3 are expected to be completed, with rinsing studies to be initiated but may not be completed. Final cover analysis (#5) will not be completed in this second year, but funding from others sources will be developed to continue testing of rinsing and closure.

Information on anticipated long-term infiltration through heap leach piles and waste rock dumps at precious metal mines in Nevada is critical for assessing the potential impacts of these structures on ground water quality. Research completed in the first year of this grant have focused on extending the database of existing mine drainage rates (Objective 1) field investigations of previously documented sites (Objective 2) and the design, in collaboration with Placer Dome Mining, of a comprehensive field site for investigation of flow and transport through heap leach piles and waste rock.