Southeast Collector Trunk Sewer Route Selection: The Regional Municipalities of York and Durham, Ontario, Canada

The York-Durham Sewage System (YDSS) is a large regional sewer system carrying approximately 80 percent of the wastewater flows from York Region as well as the communities of Ajax and Pickering in Durham Region. The Southeast Collector (SeC) trunk sewer is the primary outlet sewer to Duffin Creek Water Pollution Control Plant and as such is a critical component of the YDSS. The system will convey the wastewater flows from 1.5 million people by design year 2036. York and Durham Regions completed an Individual Environmental Assessment (IEA) in support of a major trunk sewer capacity upgrade of the SeC trunk sewer. The IEA was the first of its kind required by Ontario's Ministry of the Environment (MOE) for a major wastewater project. The IEA addressed key environmental and public concerns including groundwater impacts from construction/tunneling and public and agency opposition related to pipe construction. To address these concerns, baseline conditions were established and a three-stage methodology was implemented to identify and subsequently evaluate the alternative trunk sewer routes and alternative design methods (e.g., earth pressure balance tunnel technology versus open cut, use of sealed shaft construction, provision of dedicated haul roads and spoil sites, etc.). The IEA recommended the construction of a 15 kilometre, 3000-millimetre diameter sewer by tunnelling (using earth pressure balancing machine (EPBM) and sealed shaft construction). The project involves significant tunneling (five to 40+ metres below grade) under sensitive watercourses (cold water fishery) and associated tributaries and the protection of major groundwater aquifers serving local wells. The IEA document was approved by the MOE in August 2010 and the new sewer is currently under construction. This paper will focus on the political/regulation challenges the team faced and how approvals for this project were obtained. Specifically, a well-documented process was implemented to develop the alternative sewer routes, screen and select a shortlist of alternative routes and finally, select the preferred route. This process contributed to the various political and regulatory agencies approving this significant project.