NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: contaminants, water quality, hydrology, groundwater, microbiology, biogeochemistry

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 sulphide 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 and 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 high-density polyethylene 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 directed 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. Test Piles Researchers try to attend and present at least one presentation at the annual Geoscience Forum in Yellowknife. In addition, the research team prepares annual progress reports, and papers and conference presentations. Site visits include a brief discussion of test piles. The fieldwork for this study will be conducted from January 1, 2014 to December 31, 2014.