Southern Water is working in the Lavant Valley again to complete further improvements to its sewer network.
The company has invested £12 million during the past two years to survey and seal the sewers in 60 towns and villages prone to groundwater flooding and is spending a further £2 million this year. More than £1 million has been invested in improvements in the Lavant Valley alone.
When incessant rainfall occurs, the water table can rise to the surface causing groundwater flooding. This affects the sewer network as groundwater infiltrates it. Sewer manhole covers pop up and toilets back up, potentially causing releases of sewage into streets, gardens and properties. Without immediate action many communities cannot drain their domestic wastewater – including flushing toilets, taking baths and showers.
In the Lavant Valley Southern Water has surveyed nearly seven kilometres of sewer pipes, drains and manholes, identifying where leaks were allowing groundwater into the system when the water table is high. That’s about one third of all sewer pipes in the catchment.
Most of the repairs have been completed but the company returned to the Valley again recently to repair a sewer in East Dean where surveys showed that significant amounts of groundwater were entering the network. Although a single repair, it accounted for the major part of the groundwater infiltrating the sewer network in the village. Indeed, since repair, flows have dropped dramatically.
Earlier this year Southern Water installed a Biological Treatment Tank at the Singleton Relief Combined Storm Overflow (CSO). This provides an improved system of treatment of the wastewater lifted from the sewers before it is pumped into the Bourne when the CSO is operative during storm conditions.
Southern Water was the first water and wastewater company in the UK to design and use these tanks which offer better protection of our watercourses during emergency weather conditions. Such is their success that they are attracting the interest of the water industry and have already been adopted by another water company. Given that the wastewater they treat is heavily diluted by groundwater, these mobile tanks offer a system of treatment comparable to that of a standard wastewater treatment works – a marked improvement on the system of screening previously in use at the Singleton CSO.
Southern Water again came back to the Valley last month to seal lateral drains in Singleton and Charlton. That work is being completed this month.
Several of the sewer repairs in the Lavant Valley have been carried out on customers’ lateral drains, including one which had completely collapsed. These drains are key sources of groundwater entering the spine sewer network which serves the Valley.
Said Southern Water’s Director of Operations Phil Barker: “Of course, the performance of any sewer system can never be guaranteed due to ground movements, the invasion of tree roots and the like but we are confident that, after such a significant investment, the performance of the Lavant Valley sewer network will have improved considerably should the winter that is nearly upon us prove to be wetter than usual.
“Meanwhile, we have updated the Infiltration Reduction Plan (IRP) for the Valley which has been submitted to the Environment Agency (EA). IRPs were never heard of until the EA, in its Regulatory Position Statement, required water companies across the UK to publish plans which effectively set out their strategies for dealing with groundwater flooding of the sewer network. Southern Water has responded by publishing the first IRPs to be agreed by the EA in the UK. They now form the template for other water companies to follow.”
The company has also tightened its maintenance regimes and has made improvements to its pumping stations to make sure that, should groundwater enter the network, it can be got away as quickly as possible.
Concluded Phil Barker: “Naturally, we are hoping for a drier than usual winter during 2015/16, but if the elements conspire against us we’re confident that our ongoing investment in the sewer system will again stand us – and our customers - in good stead.”