EFFECTS OF PETROLEUM HYDROCARBON CONCENTRATION AND BULK DENSITY ON THE HYDRAULIC PROPERTIES OF LEAN OIL SAND OVERBURDEN AND WATER STORAGE IN OVERLYING SOILS

Abstract

Coarse textured soils with low water and nutrient retention are commonly the only available materials for reclamation of the projected 480,000 hectares of disturbed land in the Alberta oil sands. It is important to understand the processes in the soils being used for reclamation to be able to re-create conditions that occurred prior to disturbance. Extensive research has been conducted to understand the hydraulic processes in mineral soils, however much of the soils that are used for reclamation in the Alberta oil sands are impregnated with petroleum hydrocarbons (PHCs). Little is known of the effects of PHCs on soil hydraulic properties. Lean oil sand (LOS) is an overburden material that contains PHCs, and is considered mine waste. LOS must be reclaimed, and is currently being tested as the base soil layer for some of the reclamation being conducted in the Alberta oil sands. It is important to understand how the hydraulic properties in the LOS as well as in the overlying reclamation soils will be affected by PHCs. The main objective of this thesis is to determine the efficacy of using LOS as a base soil layer on the successful reclamation of disturbed land in the Alberta oil sands. This was done by: 1) Evaluating how PHCs and bulk density influence the hydraulic properties of LOS and 2) Determining how the soil hydraulic properties in the layers overlying the LOS are affected by the heterogeneity of PHC concentration and bulk density of the LOS. Soil cores were packed with LOS with varying PHC concentrations and bulk densities to test water retention curves and saturated hydraulic conductivity of the LOS. Soil columns were packed with a base LOS layer and reclamation cover soils that are used in the Alberta oil sands. The soil columns were used to test water and nutrient dynamics in the reclamation soil profile. It was found that both bulk density and PHC concentration had an effect on the hydraulic properties in LOS as well as in the overlying reclamation profile. The porosity of soil is largely affected by bulk density, so as bulk density of the LOS increased, it lead to lower water retention at saturation, but higher water retention at soil suctions associated with field capacity and permanent wilting point (PWP). This led to LOS at higher bulk densities having higher available water holding capacity (AWHC) and lower Ks, providing the overlying soil profile with more water and nutrients for a longer time for plants to access. Furthermore, PHCs reduced water retention in LOS due to plugging mainly the soil micropores pores and connecting porosity. This lead to lower Ks of the LOS, which resulted in an increased water and nutrient retention in the overlying soil profile. Results show that the use of LOS in the reclamation of coarse textured soils in the Alberta oil sands can aid in creating suitable soil conditions leading to reclamation success.