Long-term Reclamation Outcomes after using Varying Depths of Subsoil to Cap Sodic Overburden

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Kevin Renkema , Dean MacKenzie and Dan Kuchmak

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Capping sodic overburden with subsoil or other non-sodic material is a common practice in mining to create a suitable growth medium for vegetation. Several studies were conducted in the 1970s, 80s and 90s to determine an optimal placement depth of subsoil to balance vegetation growth with costs associated with subsoil handling. These studies concluded that depths of 50 to 100 cm would provide a suitable rooting depth for vegetation and buffer against upward migration of sodium from the overburden. These conclusions were generally based on results obtained 5 to 10 years after subsoil was placed over sodic overburden. As development of soil processes and movement of elements in soil can take decades to centuries, the conclusions can be considered preliminary. As some of these previous study locations are still intact, it is possible to remeasure these locations to obtain longer term results and verify earlier conclusions. One such study was set up on agricultural land at Highvale Coal Mine, Alberta, Canada in 1982. It was monitored between 1982 and 1987, in 2001 and most recently in 2016 (34 years after subsoil capping). Migration of sodium into the subsoil cap was minimal between 1987 and 2016 and a capping depth of 55 cm plus 15 cm of topsoil produced a similar crop yield to capping depths thicker than 300 cm. Long-term results support previous conclusions that 50 to 100 cm of capping over sodic overburden can sustain crop productivity.

Resource Type:
Conference Presentation, SER2021

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