A large urban development of 10,000 units is proposed for the nutrient-sensitive Willow Creek watershed in central Ontario.

HESL completed:

• An Assimilative Capacity Study for the WWTP as part of a Class Environmental Assessment for Municipal Servicing.
• A whole-watershed phosphorous model to address water quality protection as part of the Master Drainage Plan for the development.
• Assessment and protective measures for aquatic species at risk in the planning area.

The development was planned and approved under intense public and regulatory scrutiny, focused on protection of the nutrient-sensitive Minesing wetland and Nottawasaga River downstream.

We conducted the project in a cumulative effects assessment framework, which included:

• Protection of water quality in Willow Creek through state-of-the-art effluent limits for the WWTP.
• Estimating phosphorus loadings from stormwater runoff and developing Low Impact Development Techniques to provide an assessment of cumulative loadings from the development, achieve a target of “no net increase” or “net zero loading” for the Willow Creek watershed and inform the need for phosphorus offsetting to mitigate increased loadings in the creek.
• Developing a cumulative effects monitoring and adaptive management framework for water quality and phosphorus loading for the Willow Creek watershed, centred on stormwater management from three settlement areas plus the wastewater treatment plant discharge.
• Assessing potential impacts to the nearby Minesing Wetland and phosphorus loading to and from the wetland from all sources.

The Class Environmental Assessment was approved by the Province of Ontario and a request for a “bump up” to a full EA turned down. The Master Drainage Plan is being developed in cooperation with the Nottawasaga Valley Conservation Authority and construction is scheduled to start in early 2021.