Increasing sewer capacity and renewing pipeline to protect Coundon Burn

Coundon Burn Pollution Risk Reduction

Northumbrian Water Group (NWG) wanted to reduce pollution risk to Coundon Burn, a small but environmentally sensitive tributary of the River Wear in County Durham, and improve the resilience of the wastewater network. They reached out to our team, via the Esh-Stantec joint venture framework, to help.

Our team designed plans to increase sewer capacity and renew the existing sewer pipeline to help protect the environment. We led hydraulic modelling, option appraisal, and design development for underground stormwater storage, sewer diversions away from the watercourse, and the rehabilitation of the existing combined sewer to extend the life of existing assets.

The sewer pipeline passed through highly sensitive environments including centuries-old ancient woodland, ecological habitats, and a Grade II listed former railway arch. Working closely with Natural England, the Environment Agency, Durham County Council, and the Auckland Project, we developed a detailed construction mitigation strategy to protect wildlife and ecology such as bats, otters, and protected waxcap fungi. Our strategy has been adopted by NWG as a template for their future AMP8 schemes.

We carefully designed the sewer route to reduce environmental impact and selected no dig, trenchless methods including horizontal directional drilling and auger boring. This helped decrease ground disturbance in the ancient woodland to avoid disrupting biodiversity and eliminate the risk of complex temporary works. Over 1 kilometre (0.6 miles) of existing sewer within the ancient woodland was relined using cured-in-place pipe instead of replacing whole sections of cracked and disjointed pipework.

We also designed a new gravity-based storm tank to store stormwater. This removed the need for pumping or power, while reducing operational carbon and the need for future maintenance.

The project was delivered four months ahead of schedule, achieved a 25 percent cost savings and exceeded the 25 percent carbon reduction target. It has since improved water quality in the Coundon Burn and provided resilience to the existing wastewater network, while protecting the local environment.