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Upper Cretaceous Nanaimo Group of Vancouver Island as a potential bedrock aquifer zone: summary of previous literature and concepts

A new inquiry into the groundwater potential of the Nanaimo Lowlands is being jointly undertaken by concerned municipal, provincial and federal agencies. Rapid population growth and expanding industrial development are, and will continue to, put pressure on the limited groundwater
resources. The bedrock component of the project focuses on the characterization of the aquifer potential of the Upper Cretaceous Nanaimo Group, as a likely target of importance. This unit is a thick succession of 11 intertonguing sandstone-dominated and shale-dominated formations, of which only the
lower 8 are present in the defined study area. As a preliminary step in the analysis, this report summarizes the most relevant information for these 8 units from the previously published geological literature, in order to focus attention on the zones and areas of most likely groundwater potential.
The sandstone- and conglomerate-dominated units of the Comox, Extension and Protection formations have significant aquifer potential due to their potential for porosity and permeability, fracturing, and extensive development at reasonable depths over wide areas (with minor potential in the De Courcy
Formation, present only near the surface in a small part of the study area). Conversely, the interbedded shale-dominated units of the Haslam, Pender, Cedar District and Northumberland formations are important because they may provide significant aquitard seal units, overlying the potential aquifer
zones over wide areas of the Nanaimo Lowlands. Further study of the thickness, geographic and stratigraphic distribution, fracturing, and internal stratigraphic complexities of these 8 units of the Nanaimo Group will provide a more scientific basis for evaluation of the bedrock aquifer potential in
the Nanaimo Lowlands region.

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