Welsh Water CSOs : Morgan Sindall & Dwr Cymru (Welsh Water)
This was a large project, leading a team of surveyors from Morgan Sindall, to assess the impacts of Combined Storm Overflow (CSO) outfalls and storm overflow outfalls at Waste Water Treatment Works (WWTW) across Welsh Water's extensive holdings as part of the client's AMP 6 planning and responsibilities.
An initial pilot study (part of a larger national pilot study) was undertaken from August 2017 to March 2018 to finalise the SOAF method for the monitoring. Following this study, a network of intermittent discharges has been monitored throughout 2019, 2020 and 2021. Beginning mostly within the South Wales valleys, on the catchments of the Usk and Taff in 2019 and 2020, the programme has been expanded greatly in 2021 to encompass the whole of Wales. Some of the locations of the CSO outfalls were unknown to the water company and had not be visited for many years, hence the first task was to locate and document them using available sewer maps and data.
Once located surveys of both the aquatic and invertebrate communities of the watercourses into which the outfalls discharged, as well as their aesthetic impact (using the 466 survey method) were conducted upstream and downstream of each outfall to assess their environmental impact.
Receiving watercourses varied across the study area, from small streams to major rivers, within a diverse landscape, including outfalls in both rural and urban locations. Following collection, the invertebrate samples were analysed and extensive RICT (River Invertebrate Classification Tool) analysis was undertaken of the data for assessing and reporting the degree of impact for each outfall.
