To support Yorkshire Water in meeting Environment Agency storm capacity targets under the WINEP programme, Seymour was appointed to design and construct a new stormwater attenuation system. The scheme repurposed four disused below-ground Primary Settlement Tanks (PSTs) as storm storage—an innovative, sustainable alternative to the originally planned lagoon.
Project Scope
The works included:
- Site establishment and segregation from live operations using 2m-high Heras fencing
- Removal of redundant guardrails and metal gantries
- Mass fill to raise tank bases to required levels
- Placement of aggregate within tank bases
- Installation of 250mm-thick structural concrete slabs laid to falls
- Coring and track sawing to create inter-tank connections
- Installation of 1m runs of 300mm diameter pipework between tanks
- Installation of 5m of 300mm pipework connecting PSTs to the existing storage tank
- Installation of new perimeter guardrail system
Design & Construction
Before construction, each tank was surveyed by a structural engineer to confirm integrity. Redundant infrastructure was removed, and trenches were excavated and fully shored for new pipework connecting the PSTs to the existing stormwater network.
Inside the tanks, recycled aggregate was placed to design levels, reinforcement mesh was installed, and concrete bases were poured to enable gravity drainage, eliminating the need for mechanical pumping. Tanks were cored to accommodate 300mm pipework, which was lifted, installed, and interconnected with the existing storm tank.
New perimeter guardrails replaced the original deteriorated system to meet current safety standards.
Challenges Overcome
The original lagoon-based attenuation design was revised after a rising main was discovered within the proposed footprint. In collaboration with Yorkshire Water and Lynas Engineers, the team developed a more sustainable, cost-effective solution by re-purposing the redundant PSTs, reducing carbon, cost, and operational complexity.
Additionally, 11kV overhead cables crossed the site. Permits were secured, height restrictions enforced, and goal posts installed for physical and visual protection. All activities were closely supervised to maintain safety.
Added Value
The project enabled Yorkshire Water to meet UIMP6 and WINEP stormwater capacity requirements, supporting wider environmental objectives. By re-purposing existing infrastructure, the solution delivered long-term operational efficiency, cost savings, and reduced environmental impact.
