South Bison Hill (Clearwater Overburden) Soil Capping Research Synthesis

Elevated salinity and sodicity of Clearwater overburden pose a risk to the reclamation cover soil materials by negatively impacting the suitable rooting zone for vegetation growth. The South Bison Hills research watershed was reclaimed over 5 years (1998-2003). Research began in 1998 on an instrumented soil capping trial consisting of 1 h plots with thicknesses of 35, 50 and 100 cm. This multi-disciplinary study focused on the questions: (1) what are the measured and predicted responses to reclamation material depth over Clearwater overburden from data collected to date on the SBH study site? and (2) what is the minimum reclamation cover depth required to support reclamation vegetation requirements on saline-sodic Clearwater overburden?

A soil cover of 75 cm provides sufficient soil-water to vegetation during drought conditions and an acceptable level of salt migration into cover. Soil covers >100 cm is likely to reduce the amount of water released downstream to receptors (wetlands), while allowing more salt ingress in soil. Additionally, the project offers a scientific risk-based approach applicable for any soil capping/cover questions (including tailings), while specific findings offer (1) a benchmark site for comparing risk profile of other materials (including tailings) and (2) directly applicable findings for areas with Clearwater overburden as a surficial material.