Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/877922
24 | OCTOBER 2017 | WWT | www.wwtonline.co.uk The Works: Water Treatment With South West Water's Crownhill WTW reaching the end of its life, and operational and maintenance costs increasing year on year, the utility faced the choice between rebuilding or upgrading the existing site, or building an entirely new treatment works on a different site. One of main reasons for opting for the latter was the extent of development that has taken place in the area since Crownhill was built in the early 1950s. Much of this urban expansion has been on the higher ground to the north and east of the treatment works; this meant that around 14,500 properties (40,000 population) could only be served by pumping water up from Crownhill to Belliver service reservoir, on the hilltop. Siting the new works on the hilltop at Roborough will enable water to gravitate to a wider area, reducing costs and lowering South West Water's carbon footprint. The land at Roborough was already owned by the utility: part of it was bought by the then Plymouth Corporation in 1898, and was the site of an early treatment works before Crownhill was built. More was bought in 1991 in order to accommodate the service reservoir, which will be decommissioned once Mayflower WTW is operational. It was envisaged even at that stage that the site would be ideal for a future treatment works, and outline planning permission for such a works was granted by the local authority in 1991. While pumping will be required for raw water to reach the 97,852 square metre (24.18 acre) Roborough site, this is partially offset by the two new renewable energy generating features of the project, a hydro-electric turbine and solar PV panels. In the longer term, there is potential for the new works to link to South West Water's three other strategic supply areas (Colliford, Roadford and Wimbleball) boosting overall system resilience. The 800mm-diameter plastic pipeline between Roborough and Crownhill is being fitted inside the sleeve of an existing raw water pipeline which has been taken out of use, making the construction process simpler and reducing disruption. Before construction could start, great care had to be taken over the environmental profile of the site. An environmental survey was carried out on the site by EADN Ecology. Badgers, bats and snakes had made their home on the land and needed to be carefully relocated to alternative habitats and fences erected to keep them off the project site. l South West Water's Chris Rockey will be speaking about Mayflower WTW at WWT's Drinking Water Quality conference on Nov 2nd. For details of how to attend see: events.wwtonline.co.uk/drinking • THE SITE • CONTRACTOR VIEW Local children with the tunnelling machine for the pipeline section of the project Ken Nicholl, Contract Director, Balfour Beatty, H5O Alliance: "We are delighted to be delivering the Mayflower WTW Project as principal contractor through the H50 Alliance. Since works started in 2015, we have coordinated the building works with the installation of the process equipment, a challenge given the size of the equipment requiring installation in part-completed buildings. We strive for a lean and safe approach to project delivery, with bulk earthworks undertaken using GPS controlled excavators, removing the need for vehicle marshals and banksmen during this period of high vehicle movements. In addition to using innovative technology, we are also committed to recycling material excavated from site as backfill and landscaping bunds, decreasing the project's environmental impact."