Both CSOs had been identified as failing the Environment Agency regulatory requirement for spills to watercourses with respect to the Bathing Water Directive and the Shellfish Waters Directive.
The overall project involves construction of underground storage tank, together with the transfer of continuation flows, via a new rising main crossing the River Lune which will connect into the existing storage tanks at Riverside Pumping Station.
VolkerStevin were contracted by UU to install the pipeline across the river within the 2011 window for in-river disturbance works.
The works provided under the contract were as follows:
The 560mm diameter polyethylene rising main within the main channel was butt fusion welded on land into a 140m long length. This was the placed within a 120m long protective steel tube sleeve to prevent damage from river erosion and propellers of pleasure craft.
A temporary causeway was established across the river bed from which excavators dug a trench into which the pipe string would be laid.
The pipe string was carried across the river by five tracked excavators and lowered into the trench.
Precast concrete "anti-flotation blocks were placed over the pipe and the trench back-filled before removing the temporary causeway.
Shorter polyethylene pipe sections were butt welded and connected to each end of the pipe string within the river banks.
The pipe was pressure tested end to end and then sealed, then the site was re-landscaped.