Assessing Groundwater Supply Sustainability in the Multi-Layer Aquifer System of the Waterloo Moraine

Stephen Di Biase, Jen Hancox, John Petrie, George Schneider, Amy Domaratzki

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Regional Aquifer Characterization III

ABSTRACT: The Region of Waterloo, with a population exceeding 500,000, is the largest municipality in Canada that is dependent on groundwater for its water supply. Within the core urban area of the Region, approximately 100 groundwater production wells are operated, providing a firm capacity of approximately 45 million imperial gallons per day. The water source for many of these production wells are the overburden aquifers associated with the Waterloo Moraine, an interlobate moraine formed by the convergence of four glacial lobes. Due to successive advances and retreats of the ice lobes, the overburden stratigraphy within the Waterloo Moraine represents a complex depositional sequence. Within the City of Waterloo, moraine deposits generally reflect four interstadial granular deposits (aquifers), separated by five glacial till deposits (aquitards). The thickness, continuity and hydraulic properties of these soil deposits are highly variable. As a result, extensive studies have been undertaken to understand the glacial history and conceptual geological model of the area. The Region has recently completed a hydrogeological investigation to assess the sustainability of groundwater pumping from three new municipal test wells completed in intermediate and deep aquifers located in the northwestern portion of the City of Waterloo. This area is located on the eastern flank of the moraine and includes environmentally sensitive lands, water features and habitat. Key components of the hydrogeological investigation included flow monitoring in local surface water courses, an assessment of aquatic habitat and a 42-day groundwater pumping test. To assess the individual and cumulative effect of pumping from the three municipal test wells, the pumping test was structured with staged start-up and shut-down of the municipal test wells. The effects of groundwater pumping were monitored at a total of 136 locations, including 39 municipal monitoring well nests, 7 stream flow stations, 6 wetland piezometers and 26 private wells. The structure of the pumping test and comprehensive monitoring program allowed for an improved understanding regarding the lateral extent, transmissivity and confined condition of two water supply aquifers, as well as the vertical hydraulic conductivity of a regionally extensive aquitard. The Environmental Assessment process concluded that sustainable groundwater supply would be possible from two of the three municipal test wells. This presentation will review the interpretation of the field study results, the conclusions of the hydrogeological study and rationale for establishing sustainable groundwater supply sources.

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