11 October 2010
Waste water treatment is flowing more smoothly in Wigan thanks to a multi-award-winning facility that Costain helped create.
United Utilities needed to replace its inlet works in the town as the existing works had reached the end of its design life. It had already started design work on the new plant when it called in the IA+ joint venture (jv) that includes Costain to continue the process.
The project, which was designed to have a throughput of up to 408 million litres a day, consisted of coarse and fine screens to filter out debris, a high lift pumping station and grit 'detritors', which remove particles from the flow.
The jv developed a completely redesigned system that involved relocating different plant from the type initially envisaged. In doing so, they succeeded in reducing United Utilities' budgeted £22.4million scheme to just £17.67million, saving in excess of £10million on the original scheme (original scheme was estimated be to in excess of £30million).
An early problem arose when the originally-allocated brownfield site within the existing treatment works was no longer available. This meant the team had to move to a small, triangular plot adjacent to the existing inlet works. As an added challenge, the new inlet works had to be built beside the operational site without any disruption to its operations.
With the limited space available, the traditional cofferdam approach to building the deep inlet pumping station was not viable. A less obtrusive secant bored pile walling arrangement was adopted instead.
The volume of concrete used on the project was also able to be reduced by using polystyrene void formers, while the structure of the high-level inlet screens plus the detritor structure was simplified to ease construction, maximising efficiency and cost-effectiveness.
The project has picked up a string of awards over the past year, most recently winning the Capital Project Management Award from Utility Week, repeating its 2009 success in this contest.
The job was also highly commended in the 'Best Construction Project 2009' prize from Construction News in the £10 - £50million category.