Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | XXXX 20XX | 17 In essence, the solution we're imple- menting involves creating a new pump- ing station to handle wastewater from Persimmon Homes' development, along with diverted flows from a number of ex- isting surrounding villages that discharge into the trunk sewers. This takes pres- sure off the existing sewers and ensures flows from the new houses enter it at a downstream point north of Grove, where capacity isn't a problem. To implement this, Persimmon Homes agreed to undertake the early construc- tion of part of the planned foul sewer through their development, and to also upsize it to accommodate the diverted flows. As a result, this 'spine sewer' through the development area is available to intercept flows from the existing pump- ing station at East Challow, which serves several villages to the west of Wantage. In that way, sewage from these com- munities no longer needs to flow into the trunk sewer through Wantage, freeing up capacity to serve future housing in and around the town centre. Persimmon Homes' spine sewer – which has a diameter of up to 450mm – discharges into a new pumping station we've built on the former airfield on land donated by Persimmon Homes. This transfers flows, via a 300mm diameter new rising main, back into the trunk main at a point upstream of the sewage treat- ment works. The new pumping station, originally designed to cope with flows of 73 litres per second, has since been increased to deal with 105 litres per second, allowing it also to handle the diverted flows from East Challow and beyond. The approach we agreed with Persim- mon Homes has great advantages for everyone. They will benefit from a robust and timely solution to their drainage needs whilst total cost of the work is reduced; it's more efficient to do the work in this way; and local residents avoid disruptive work in Wantage and Grove. In addition, developers building new homes locally over the next 15 years will be able to connect into the trunk sewer generally without concerns over capacity. To the north of the airfield develop- ment, we've employed a no-dig technique to lay the rising main that connects the new pumping station into the trunk main. We'd normally have used an open-cut method, but this would have disrupted traffic on a busy road – in addition to a number of issues highlighted by our envi- ronmental screening work. This showed the presence nearby of a Roman road, along with an ancient hedgerow and an area of common land. It therefore made practical sense to employ a no-dig pipe installation technique along the whole route of the new rising main. This in turn removed the need for pipe bedding materials to be brought to site and soil taken away, which again meant less impact on local residents and motorists. The overall project has shown the huge benefits that can result from identifying growth hotspots, by establishing when and where developers intend to connect to our sewers. Partly as a result of the approach we've taken at Wantage, Thames Water has now established a dedicated 'growth' team. They look to identify clusters of devel- www.wwtonline.co.uk | WWT | AUGUST 2018 | 17 opments, so we can provide additional wastewater capacity in more efficient ways and, where feasible, also take the opportunity to tackle operational prob- lems for our customers, such as sewer surcharging posing risk of flooding and pollution. In order to achieve this, our developer services team have worked cross-function- ally with colleagues in asset planning, finance and network modelling teams, among others. Thames Water are looking for op- portunities to take a similar approach elsewhere in our region. For example, in Three Mile Cross, near Reading in Berk- shire, we worked with developers Taylor Wimpey to ensure there is sufficient pumping station capacity for a trebling in the village's population. SEWER NETWORKS