Lean Oil Sands Review of Gravimetrically Heavy Hydrocarbons in Closure Landforms

Reclamation requirements for LOS are vague in most EPEA Approvals – beyond specs on analysis methods, LOS is referred to only in one clause as a potential impervious condition requiring capping. However, LOS of different PHC percentages look and behave differently depending on whether it is in sand, tar ball or organic material format. It is possible LOS presents a risk to soil development and revegetated cover success on reclaimed surfaces; however, duration and severity of this risk needs to be quantified to develop a monitoring framework to guide management decisions. The objective of this study is to describe the behavior of gravimetrically-heavy, long-chain hydrocarbons (particularly F4 and F4G fractions, as most likely to trigger exceedance guidelines) in LOS near the surface on reclaimed landforms to provide support for Imperial’s approach to capping and reclamation soil requirements in areas that may contain LOS in underlying materials.

(1) accurate analysis protocols are time-consuming, but important to differentiate between anthropogenic and petrogenic PHCs until guidance provided by AER and/or CCME; (2) shorter-chain PHC fractions (F1 and F2) volatilize in a few days to a few months, depending when they are released as products of degradation; (3) longer-chain PHC fractions weather, oxidize and biodegrade to a recalcitrant fraction within 120-180 days, and because of insolubility and immobility don’t pose significant risks of bioavailability or imperviousness; (4) there is a gap in CCME guidelines about how naturally-occurring LOS should be analyzed/ treated – decreasing risk posed by gravimetrically heavy PHCs seems related more to timing (for weathering and degradation processes) than spatial separation by capping; (5) recognizing background hydrocarbon concentrations (from LOS) in overburden would support use as a reclamation material, if potential beneficial effects (reducing percolation/increasing water storage in reclamation soil layers) are substantiated; (6) placement depth and distribution will be an important part of reclamation planning for overburden containing LOS.