Database and Groundwater Model Analysis of the Oak Ridges Moraine, Ontario

Project Description:

Land development in the Greater Toronto Area (GTA) is encroaching on the high recharge areas of the Oak Ridges Moraine (ORM). The ORM provides drinking water for over 2 million residents and headwater streamflow for all the major rivers in the GTA. As part of provincial efforts to protect the moraine, Earthfx was hired to develop a database, regional scale groundwater flow model and sub-regional scale refined model of the GTA core area. The first major phase of this project, completed by Earthfx in 2006, set the foundation for ongoing groundwater management across the entire ORM area.

Earthfx began with the development of a comprehensive environmental database containing geologic, groundwater and surface water information spanning the entire ORM study area. Over 250,000 boreholes and 300 million water level measurements were compiled. Further, more than 3000 engineering reports were scanned to provide a definitive technical foundation for the analysis.

A 5-layer regional scale groundwater model was developed based on earlier mapping by the GSC. The regional model covered an area extending from the Niagara Escarpment eastward to the Trent River and southward from Lake Simcoe to Lake Ontario. A sub-regional model was developed using 100-m wide finite-difference cells to better represent stream/aquifer interaction and wellfield drawdowns. The two models were calibrated to observed heads and baseflow and provided regional water balances, refined recharge and aquifer property estimates, wellhead capture zones, and valuable insight into the sensitivity of the groundwater and surface water systems to development-induced change.

Key outcomes of the study included: a detailed understanding of the interaction between the rivers and the aquifer systems as well as identification of wellfield capture zones and aquifer vulnerability to contamination. Deliverables included the database and models, which have been used extensively for water supply assessment, Source Water Protection and engineering impact assessments. Earthfx has gone on to develop refined fully integrated SW/GW models for the Regions of York, Peel and many of the Conservation Authorities in the area.