Situation and Compliance Report on the Disposal of Urban Wastewater and Sludge in Scotland 2018

5. Collection of Wastewater

As of 31 December 2018, Scotland had a total of 184 agglomerations with a generated load of around 6.36 million p.e.^[5] within the scope of the UWWTR, i.e. agglomerations with a p.e. of 2,000 or more.

All these agglomerations were served by WwTW (including four private wastewater systems) to which collecting systems were connected, as required by Regulation 4.

Some of the wastewater entering collecting systems will overflow to the environment via overflows before it undergoes full treatment.

Overflows are an integral part of Scotland’s sewer networks, ensuring sewers do not back up and flood homes, streets and sewage works during periods of heavy rainfall. Normally, wastewater from overflows has been highly diluted by rainwater.

Overflows associated with WwTW and sewer network licences are licensed by SEPA, and any unsatisfactory discharges are identified so that Scottish Water can invest to reduce the environmental impact. Scottish Water’s Improving Urban Waters Routemap sets out how it is investing to increase monitoring and reporting of overflow events, reduce overflow events, improve water quality and reduce sewer related debris in the environment.

Rather than permanent monitoring of all overflows, Scottish Water has carried out comprehensive modelling, in partnership with SEPA, to assess the impacts of its assets on water quality during the 2015 to 2021 investment period. The computer models Scottish Water developed allow it to understand when overflows will operate, under what rainfall conditions and the impact they will have on the environment. This allows Scottish Water to target its investments accordingly.

Scottish Water makes the data it collects on overflow events from overflows available in near real time via its Overflow Map. Annual overflow event data, including that required as part of its annual regulatory reporting to SEPA, is available from its website.