Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | OCTOBER 2015 | 17 Project focus Tanks United Utilities opt for mega-tank in Mersey project Project focus T he Mersey has never been known for being the cleanest of England's rivers: in the mid-1980s, the Mersey Estuary was declared the most polluted estuary in the UK. But today it is cleaner than it has been for more than a century, and a series of projects from United Utilities is about to improve matters still further. UU is currently undertaking a massive programme of work to improve wastewater treatment and the sewer network in the Mersey catchment area. This includes an ambitious £200M extension (now nearing completion) to Liverpool's wastewater treatment works at Sandon Dock. But further upstream other, equally impressive, improvement work is ● Major programme to protect Mersey from CSO discharges ● Giant precast detention tank at Widnes is 140 metres in length ● Single tank design avoided flotation problems ● Stormwater retention required to reduce CSO discharges into Mersey ● Single large scale tank best able to accommodate flows ● Off-site manufacture preferred to save time and cost • Drivers measure 140m by 43m – covering a substantially bigger area than a football pitch - and will be capable of storing the equivalent of 36 million pints of water. "Over the past few years we've created extra storm storage in our sewer network across the Merseyside area. This will help improve the River Mersey by reducing the number of times the local sewer system overflows in heavy rains," says Hepworth. The project – officially known as the HAL0037 Ash Lane UID (unsatisfactory intermittent discharge) scheme – is one of a number of jobs associated with the overall AMP5 Change Protocol C (CPC) Knowsley, Huyton and Widnes (KHW) programme of works. Besides HAL0037, the AMP5 KHW CPC Catchment UID programme also included another six jobs, five of which, now complete, comprised Phase 1. Phase 2 comprises construction of 23,500 cubic metres of additional storm storage at Huyton WwTW, now also complete, leaving the Ash Lane UID as the last scheme to be delivered in the KHW programme. Temporary storage flow The existing Ash Lane CSO is a stilling pond type located in a field adjacent to Ash Lane, Widnes. During heavy rainfall, spill flows discharge through also underway. United Utilities and its framework contractor KMI (a joint venture between Kier Infrastructure, J Murphy & Sons, Interserve Construction and consulting engineer Mouchel) are currently engaged in several large scale engineering works, not least the installation of what it believed to be the largest pre-cast concrete detention tank ever seen in England. United Utilities project manager Eric Hepworth says: "The detention tank is being built just off the Knowsley Expressway, in Widnes, and will vastly increase the capacity of the local sewer for safely retaining storm water, which might otherwise ended up flowing into the river Mersey via Ditton Brook." The rectangular detention tank will The precast concrete tank, seen here being constructed, measures 140m x 43m • Innovations ● Huge scale tank has internal measurements of 140 metres by 43 metres ● Flows collected when rate exceeds 274 litres per second ● Silt and other contaminants allowed to settle before water is discharged under controlled conditions

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