Abstract:

Teck Coal’s Regional Water Quality Model (RWQM) is a tool that is used to understand past, current and future impacts of mining on water quantity and quality in the Elk River Watershed, British Columbia, Canada. Although it is generally accepted that the geochemical characteristics of Teck Coal’s waste rock are very consistent across the different mine impacted tributaries, monitoring data suggests a large spread in constituent release rates across those same tributaries. To address this issue, the RWQM was updated to move away from empiricism and incorporate increasingly mechanistic processes, leveraging results from multi-year research on waste rock hydrology. A coupled surface water and groundwater budget, and an unsaturated waste rock hydrogeochemical module where developed. Pore water nitrate from blasting residuals and from naturally occurring nitrogen was used as a tracer to calibrate the basal seepage rates from waste rock piles while sulphate was used as a conservative tracer to close the mass balance further downstream of the operations. The calibrated model shows that solute transport within the Elk Valley coal waste rock piles is largely driven by advective flow within the finer grain size matrix. Geochronology of waste placement and initial moisture content are essential inputs to simulating the long-term water quality trends. The seasonal loading distribution to the receiving environment is mostly driven by lateral runoff into a waste rock pile from upstream catchments. Reducing the uncertainty in the local and regional scale water balance successfully reduced the uncertainty in the geochemical source terms.

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Al Hossain