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Kent’s presentation focused on a small scale (~10 m x 10 m plot) study in which he developed three distinct site conceptual models for a fractured bedrock site, using different depth-discrete hydraulic and tracer transport measurements.
Kent reiterated the point that “tracking where contamination has gone is easy (now); predicting where it will go next, [is] much more difficult”. While defining what a conceptual site model is, Kent emphasized the fact that a model should be able to accurately predict off-site migration of contaminants and allow for risk analysis.
The first site model was based on single-well tests. Constant-head tests were performed in 87 depth-discrete intervals, amongst 5 boreholes drilled in a star formation at the field site. Discrete fractures were interpreted using a borehole camera and cores.
The second model was based on inter-well tests. 61 pulse interference tests were done between two boreholes.
The third model was based on inter-well tracer experiments. Three different methods were employed for these experiments: radial divergent, natural gradient, and injection-withdrawl. A total of 11 experiments were performed using a fluorescein dye.
When comparing the conceptual site models from each method, it was found that the first two methods identified three pervasive horizontal sheeting fractures. Method two, however, showed an additional sub-horizontal fracture and smaller fracture apertures (lower hydraulic conductivity).
The tracer test method identified three discontinuous horizontal sheeting fractures, and one sub-horizontal fracture. It was found that the fracture features are not connected between all boreholes.
In the end it was found that the constant head method over-predicted the fracture connections. While the pulse interference methods did provide a better estimate of solute transport, it still over-predicted fracture connections. The tracer methods, however, showed that even though pressure is transmitted between boreholes, those fractures don’t necessarily transport solutes. Kent noted that a similar study needs to be done on a larger scale with inclined boreholes.
ABOUT THE SPEAKER – Kent Novakowski, Ph.
Queen’s University
Kent Novakowski obtained his PhD from the University of Waterloo in 1992. He joined the Department of Civil Engineering at Queen’s University in August of 2000 and was appointed Head of the Department in 2009. Prior to Queen’s, Dr. Novakowski led the Groundwater Contamination Project at the National Water Research Institute in Burlington, Ontario. He has published more than 200 papers and abstracts on the hydrogeology of fractured rock in a variety of proceedings and refereed journals. The majority of his research has focused on the development of characterization methods for improving the understanding of fundamental flow and transport processes in discrete fractures at the field scale. He is currently an Associate Editor of the Journal of Contaminant Hydrology, and is a past AE for Ground Water, Water Resources Research, and the Canadian Geotechnical Journal. He has served on two expert panels and chaired a third which was focused on Sustainable Water Well Infrastructure in Ontario. Dr. Novakowski also leads the Water Research Group at Queen’s, an affiliation of more than 40 faculty members from a broad range of disciplines who conduct research in water-related areas.
