Determination of Critical Soil Water Content and Water Repellency in Soils.

Soil water repellency (SWR) has an adverse effect on environmental quality due to reduced infiltration, increased overland flow, increased preferential flow, decreased water storage and increased soil erosion.  The presence of SWR is reported in all types of soils at variable degrees. As such its role in soil hydrology is extremely important. Water repellency in soils is controlled by the critical soil water content (water content at which soils changes from a repellent to a wettable state). The purpose of this study is to determine the critical soil water content from soils from the Athabasca Oil Sands.  Soil samples were collected from natural and reclaimed sites located in the Athabasca Oil Sands region, as well as two soils from Saskatchewan for texturally contrast comparison.  Soil samples were sieved through 2 mm and initial soil water content was determined.  Additional water was added to obtain a series of uniform water contents (OD, AD, 2.5%, 5%, 7.5%, 8.5%, 10%, 12.5%, 15% and 17.5%).  Using the modified sessile drop method, contact angles were measured on the surface of the soil.  Soil water contents were determined immediately after measurements by drying at 105°C for 24 hours.  Critical water content (θ_CR) between the soils ranged from 0 % - >17 %.  A number of these soils had high critical water content (θ_CR >12%), suggesting a significant concern of SWR in these soils.  Due to the presence of SWR in all types of soils, the critical soil water content must be taken into consideration when understanding the hydrology of a water repellent soil.