Hydrogeological Assessments for Development Projects in Ontario

By: Salima Jaffer, B.Sc.
sjaffer@pggroup.com

Dewatering permits have become a common pain point in development projects lately. 

Hydrogeological (groundwater) assessments are part of development applications in Ontario. The expectations are higher in greenfield areas where there are natural heritage features or water supply aquifers nearby. But they are still required, even in dense urban settings, for developments with multiple levels of underground parking. The assessments cover construction dewatering volumes and estimate long-term dewatering volumes.

But the study itself isn’t the only important thing. Municipalities are increasingly concerned with sewer capacity as our climate continues to warm and we experience more frequent high-intensity storm events and flooding. In Toronto, where there are old “combined” sewers in the downtown core, development projects are starting to encounter push-back on long-term dewatering connections to the sewer system. Toronto Water has been increasingly requesting that developments waterproof their foundations and “tank” their projects.

Not all hydrogeological studies are equal. We highly recommend a pre-consult with the stakeholder that requested the study to understand the objective. What do they see as a risk that is driving their request for the study? It’s important to know roughly what the proposed development is (e.g., strip plaza vs. residential tower), number of underground levels being proposed, and where it is situated. Sites near a natural setting (i.e., woodlot, watercourse with fish habitat) or maybe in an area where drinking water is sourced from groundwater wells will face greater obstacles to dewatering.

Based on what is being proposed and where it is situated, a hydrogeological study may include an evaluation of groundwater infiltration and recharge, groundwater discharge and baseflow, dewatering estimates for excavations, groundwater elevations and flow paths, water quality and temperature, cumulative watershed impacts, coldwater fisheries supported by groundwater discharge, and impacts to the city’s drinking water sources. Knowing what the stakeholder requires means that the scope can be tailored down to the specific needs of the project.

Engaging the local conservation authority early to confirm requirements is a necessary step especially if you are within their regulated area. Another piece of the puzzle is understanding municipal and provincial requirements for construction dewater discharge. The deeper the excavation, the more water is usually generated during construction. Not identifying the cost and timeline for these permits can lead to project delivery delays.

Knowing how to negotiate with the various approving bodies is a key factor in not overspending on these items.  Also, start the conversation early, the conversation and expectations have been changing, so it’s easier when time is on your side.