SPIRITWOOD BURIED VALLEY AQUIFER MANITOBA: EMERGING UNDERSTANDING FOR GROUNDWATER MANAGEMENT

The Geological Survey of Canada is mapping buried valley (BV) aquifers in prairie provinces of Canada as part of an assessment of 30 key Canadian aquifers. A number of buried valleys are identified from water well records in southwest Manitoba. The Spiritwood BV is the largest of these valleys, extending northwest from North Dakota to west of Brandon, Manitoba. A Basin Analysis study integrating geophysical, sedimentological, geochemical and hydrogeological data is being completed on the Spiritwood BV. The study goal is to use geological and groundwater modeling to assess sustainable groundwater use.

A helicopter time-domain electromagnetic survey (AEM) was carried out over a 1062 km sq area to map the bedrock geometry and character of the buried valley fill. The AEM data reveal a complex succession of nested buried bedrock interface valley relationships as well as shallower obliquely-orientated, sediment-hosted valleys. The survey has significantly improved understanding of the location, orientation and complexity of the Spiritwood BV in the survey area.

High-resolution, three-component seismic surveys (46 line km) were completed within the AEM survey to provide ground-truth data and a more detailed characterization and depth control of the valley geometry and fill. Ground-based resistivity surveys were completed parallel to a number of seismic lines to provide higher resolution conductivity data in the valleys fills. Where feasible, shallow and deep (> 100 m) boreholes were drilled to intersect and sample the sedimentary succession and permit downhole geophysical data collection. Multi-parameter geochemical analysis is being completed to permit chemo-stratigraphic analysis and to characterize aquitards. Nested peizometers were installed to monitor the identified BV structure and to supplement data available from the Manitoba groundwater monitoring network. Integration of the AEM data with seismic depths is providing control on the geological modelling of bedrock valleys and their fills. The geological model and the monitoring data will be used for numeric groundwater flow modelling to provide an enhanced framework for data collection and provide a realistic assessment of sustainable groundwater management.