Connisbrough Castle in south Yorkshire holds a warm place in the heart of ETM - it marks the site of the firm's 150th combined sewer outfall. It is also special for being Yorkshire Water's only 'double decker'.
The brief demanded the improvement of two aesthetically unsatisfactory CSOs sitting at the base of the castle. The first - Burcroft Hill No 1 CSO - was relatively simple, consisting of a rebuild within Yorkshire Water land at Burcroft Sewage Treatment Works.
But the second overflow (Low Road) did not have such an obvious solution and provided many significant health and safety challenges. The existing CSO is located on a dangerous bend in the carriageway of the A6023.
This busy road is the main link between Mexborough and Doncaster and is a bus route.
The Capital Solutions Team agreed to attempt a solution that would provide safer maintenance access for operational staff in addition to meeting the demands of the Environment Agency.
Initial ideas included extending or re-orientating the CSO to move the access openings away from the highway. But trial holes confirmed the area was littered with existing services. 'We established that even with extensive service diversions the construction work would have a huge impact on the traffic and therefore the local community, ' says ETM team leader Phil Press.
This option would also still have long term maintenance problems.
To complicate matters further Doncaster Council indicated that a road closure would not be readily approved. To achieve the output in year four an alternative had to be found. Moving to the adjacent grassed area was not an option - the land being part of the Scheduled National Monument that is Conisbrough Castle.
The final solution was a unique two level CSO. 'The overflow pipe from the Low Road CSO passes close to the proposed Burcroft Hill No 1 CSO, ' says Press. 'We realised that we could screen the overflows in this new chamber within the STW boundary. This would require a short length of new sewer but would eliminate the need to work in the carriageway at Low Road CSO.'
Further hydraulic investigations led to the design of a new chamber at Burcroft STW to house two independent sets of screens;
one to screen the overflows from Low Road CSO, and one to replace Burcroft Hill No 1 CSO.
The chamber was substantially completed in time for the year end, with final landscaping now under way.