The River Deerness not far from Durham had been polluted on three occasions since 2013 because of repeat flooding from sewer manholes. In light of this Northumbrian Water was granted planning permission in early 2018 for a £2.6 million upgrade to its sewer network at New Brancepeth in County Durham.
The nine-month project at Alum Waters saw the construction of a new precast concrete underground combined storm/sewer tank measuring 66M by 30M, with a depth of 2.1M.
The proposed solution to the flooding incidents mentioned was to:
- store storm flows in an online underground storage tank that would operate automatically under gravity, as and when required during rainfall events.
- the proposed Carlow tank would be a rectangular construction measuring 66x30x2.1M. A total storage of 4158CBM.
- have 2 compartments in the tank so that most of the time only a relatively small portion of it would be in use. The compartments would be divided by an internal wall that allow overspill when the larger capacity is required and this would drain out through a valve when the storm waters secede.
- the tank would be constructed largely below the existing ground level at the appropriate depth to be in line with the existing combined sewerage pipe.
- Once constructed the tank would be covered over with soils to a depth of between 1-5M. The finished landform would be 1M to 2M higher than it started out but would maintain a slope from South to North and could be put back into use for grazing.
The work was carried out by Northumbrian Water's supply chain partners ESH & Stantec with their framework supplier; Carlow Concrete who designed, manufactured and installed the new 4,000m3 underground precast concrete tank.
Around 300M of old sewer pipes were also replaced with larger pipes laid to increase the capacity of the network and help it deal with larger volumes of wastewater.
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