Town Responds to Drilling Mud Entering into Brook Creek

Environmental remediation efforts underway

Cobourg, ON (November 19, 2025) – Town of Cobourg Public Works and Engineering staff are working to remediate the impact of drilling fluid (mud) entering Brook Creek.

Staff are working with the contractor who is using a micro-tunnel boring machine to install a trunk sanitary sewer on Brook Road North.

Yesterday afternoon (November 18, 2025) an incident occurred where pressurized drilling fluid (mud) used in the micro-tunnelling process entered the east tributary of Brook Creek (approximately 350m north of the railway tracks).

Drilling mud is a pressurized fluid used in micro-tunnelling to lubricate the tunneling equipment and carry away the soil that is removed as the tunnel is constructed (drilled).  The drilling mud being used on Brook Road North is an inert, non-hazardous product that is certified to NSF/ANSI 60 (drinking water standards) and consists of bentonite clay and water.

Bentonite clay is a natural material that forms from volcanic ash. It is highly absorbent and has properties that allow it to be easily pumped. Bentonite clay is also commonly used to create seals for water wells and ponds, as a clarifying agent in food production processes and as an absorbent in products such as pet litter.

The water in Brook Creek has a visually milky appearance in some locations, while in other locations the bentonite clay has settled and the water appears clear.

Environmental Services staff are working with the Ganaraska Region Conservation Authority (GRCA), the Ministry of the Environment, Conservation and Parks (MECP) and the Department of Fisheries and Oceans (DFO) to review the incident and requirements and options for any remediation activities.

The Town of Cobourg will issue a further Public Notice with additional information as it becomes available.