Long Term Soil Development

Soil capping research has been a major focus for Syncrude Canada Ltd. (Syncrude) and has included a range of soil capping prescriptions. This project began in 1992 with the evaluation of the changes in soil physical properties associated with bison grazing in areas with different soil reconstruction techniques compared to relevant control sites and included soil moisture and soil density monitoring, soil penetration resistance, infiltration measurements, and climate monitoring. The program was subsequently expanded to include non-grazed areas with the objective of comparing the physical properties and moisture regime of the replaced soil covers with the undisturbed or naturally occurring soils in the region. Long term monitoring of volumetric soil water content and bulk density has been utilized to compare the physical status and moisture regime of the reconstructed soil covers with natural soils in the area. Evaluation of the long term patterns in moisture and density of the reclaimed soil covers provides a measure of performance of the various capping prescriptions as the landscape matures and moisture demands increase. Five different areas have been monitored since 1992 including the undisturbed forest and reclaimed areas where the soils were reconstructed using different replacement strategies.

The results from this project indicate that the reclaimed soil covers are capable of providing soil moisture to support the respective vegetation covers. Results demonstrated that greater amounts of secondary material in the reclamation cap resulted in less fluctuation during the growing season, however greater amounts of peat in the reclamation cap resulted in higher amounts of water being stored in the root zone. In addition, adding a peat-mix cap to a secondary cap over tailings sand increases AWHC. The data indicate that the soil covers all had bulk density values lower than 1.8 Mg m-3 which is considered limiting to root development and were equivalent to or lower than the values for the fine textured natural Luvisolic soils. The results of the monitoring program to date have shown that the reconstructed soils are recovering and performing well compared to the undisturbed sites. Recommendations pertinent to operational practices and the ongoing monitoring program are provided.