Hydrocarbons in the Root Zone: Soil Vapour and Respiration Monitoring at an Overburden Material Repository in the Oil Sands Region

This project investigates the presence and behaviour of naturally occurring hydrocarbons, or "tarballs," in soils salvaged for reclamation in the Athabasca Oil Sands Region. It aims to determine the composition and hydrocarbon content of tarballs and evaluate whether they pose risks when reused in reclamation. A column study was conducted to examine the degradation and leaching potential of hydrocarbons from these soils, building on earlier batch study research. Key objectives include identifying distinguishing characteristics of tarballs for field classification and understanding their degradation pathways. The study also measures soil vapour constituents, respiration rates of hydrocarbons at the overburden surface, and changes in gaseous emissions over time.

The study found that tarballs have high hydrocarbon concentrations, especially in the F4G fraction, but field traits like depth and grain size did not predict content. Tarballs retain much more moisture than surrounding soils yet degrade slowly and leach minimally under unsaturated conditions, indicating low hydrocarbon mobility. Field gas flux measurements showed variable CO₂ and CH₄ emissions with spatial and seasonal changes, including occasional high methane levels. Laboratory column tests confirmed low leaching and slow degradation rates, which decreased at lower temperatures. Hydrocarbon degradation was estimated at 60 g/year at room temperature and 15 g/year at cooler temperatures, with negligible volatilization. Lab and field gas fluxes correlated and increased linearly with temperature. Additional studies are examining how capping materials affect methane oxidation.