Modeling a Complex Multi‐Aquifer System: The Waterloo Moraine

Abstract

Abstract The Regional Municipality of Waterloo in Ontario, Canada (population 250,000) depends on ground water for most of its water supply. The ground water is extracted from the Waterloo Moraine, an extensive and complex glacial aquifer system extending over a 400 km 2 area. A methodology is being developed to inventory the ground water resource, to define its susceptibility to contamination, and to create the basis for optimal management and protection strategies. A key component of this methodology is a three‐dimensional conceptual hydrogeologic model based on the geologic characteristics of the multiple‐aquifer Moraine system. The steps in the development of the model include screening of the large database, interpretation and interpolation of the data to define the variable hydrostatigraphy and to generate consistent hydraulic conductivity functions, and model calibration. The numerical basis is a fully three‐dimensional finite element model that provides flexibility and adaptability in representing the natural boundaries, the highly irregular stratigraphy, and the numerous wellfields. The model has the capability to automatically find the location of the water table consistent with given recharge and pumping conditions, and to direct recharge from low‐permeability areas to higher‐permeability areas. Capture zones generated by the model are found to be highly sensitive with respect to the geologic structure, in particular the presence or absence of windows in the aquitard units. Professional judgment is found to be an essential component of the modeling process.