Paper No. 279-5
Presentation Time: 9:05 AM
ORIGIN AND FATE OF NITRATE DERIVED FROM BLASTING IN COAL WASTE-ROCK SPOILS IN BRITISH COLUMBIA AND ALBERTA, CANADA
Explosives used for blasting during mining operations contain nitrogen (N) compounds. The release of N from blasting residuals may result in elevated nitrate (NO3) concentrations in freshly blasted waste rock which could subsequently leach from waste-rock spoils. The distribution of NO3 in older spoils can also be used to characterize the flushing of these spoils (rates and efficiencies), and when used in conjunction with the d15N and d18O in the NO3, can confirm the source of the NO3 and identify if denitrification is occurring within the spoils themselves. This study used multiple datasets of NO3 and d15N and d18O of NO3 collected in the Elk Valley from waste-rock spoil piles ranging in age from 1982 to present day to define the source, distribution, and fate of NO3 in waste-rock dumps and rates of water flushing (recharge) through the dumps. Preliminary analyses showed that NO3 concentrations in post-blasting rock were greater than pre-blast rock. Isotopic analyses on NO3 confirmed that the source of NO3 in the spoils is N used in blasting. The high-resolution porewater profiling of NO3 through unsaturated spoils exhibited variability with depth (attributed to heterogeneity in leaching of the spoils) but also illustrated a decrease in NO3 concentrations with increasing dump age. The historic NO3 concentrations from rock drains indicates flushing of NO3 from the waste rock spoils. There was no indication of denitrification within unsaturated waste rock or in the underlying rock drains evaluated; however, the stable isotope data collected from saturated waste rock suggests denitrification occurs under saturated conditions. This study is part of a multi-year R&D program identifying key controls on waste rock chemistry, hydrology, and water quality in this region.