NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: water quality, hydrology, geochemistry, waste rock

Objective(s): To investigate the processes related to water quality and quantity (collected at different scales) draining from country rock stockpiles that are located in areas of continuous permafrost.

Project Description: This research study is designed to investigate the processes related to water quality and quantity (collected at different scales) draining from country rock stockpiles that are located in areas of continuous permafrost. The quality of water draining from a country rock stockpile is determined by the combined effects of oxygen transport in the air phase, biogeochemical processes that control mineral weathering rates, the release of heat and dissolved constituents due to sulfide mineral oxidation, and hydrologic processes that control unsaturated water flow. The transport of dissolved constituents is further affected by the precipitation and subsequent dissolution of secondary minerals. Three instrumented country rock stockpiles were constructed from 2004 to early 2007. Instruments in the pile include: -thermistors (connected to dataloggers for continuous measurement of internal pile temperatures) -time domain reflectometry (TDR) probes (connected to dataloggers for continuous measurement of internal pile water content and movement) -soil water solution samplers (SWSS) (sampled manually for internal pore water geochemical composition) -air permeability probes (sampled manually to determine rock pile permeability to air) -thermal conductivity access ports (a custom thermal conductivity probe can be lowered into the conduits to measure rock pile thermal conductivity properties) -gas sampling ports (sampled manually using a multi-port oxygen and carbon dioxide analyzer to obtain levels within the pile) -air pressure transducers (connected to dataloggers to measure air pressure changes) -microbiology access conduit an pyrite growth medium (installed during construction; tea bag-sized growth media samples removed from access conduit annually and analyzed for microbiological populations) All three test piles were constructed on an impermeable HDPE liner that ensures all water that infiltrates the piles and reports to the bottom is collected. In addition, 12 lysimeters (water collection boxes) were constructed on the liner to collect spatially discrete water samples. All water from the base and from the lysimeters is directed to heated instrumentation shacks where the water discharges through a series of flow-through cells. The flow-through cells have probes to measure pH and electrical conductivity, as well as a cell to collect water samples. Water is then direct to tipping bucket rain gauges to measure flow. Water samples for geochemical analysis are collected approximately every second day during peak water flows, and less frequently when flows decline. Several parameters are measured in the field, and additional analyses are conducted on samples shipped to the University of Waterloo. Three boreholes are scheduled to be drilled into the North Country Rock Pile at the Diavik site in early 2010 to install instruments similar to those in the test piles. The drilling will be arranged and supervised by Diavik and the research group will plan and install the instrumentation. The North Country Rock Pile drilling will provide an additional scale of research. The study is undertaken entirely as a graduate research program through the Universities of Waterloo, British Columbia and Alberta. Students and staff working on the project are all affiliated with the universities (students, researchers, technicians, professors, support staff). Seasonal Diavik staff from the north may be able to learn about the project through exposure to the site and research team members, and possibly, in assisting with some research activities. Test Piles Researchers attend the annual Geoscience Forum in Yellowknife, prepare annual progress reports, and prepare papers and conference presentations. Environmental Monitoring Advisory Board site visits include a brief discussion of test piles. The fieldwork for this study will be conducted from July 4, 2013 to December 31, 2013.