In this policy brief, Dr Theodorous Giakoumis recommends that combined sewer overflow regulation should move beyond spill duration metrics towards assessments of the pollution load and risks to the waterbodies they flow into.
The increasing frequency of Combined Sewer Overflows (CSOs) has heightened public concern, triggered government action, and driven water authorities worldwide to commit to major infrastructure upgrades. The Storm Overflows Discharge Reduction Plan sets out legally binding targets under the Environment Act 2021 for upgrading priority CSOs in England by 2035 and ensuring that by 2050 CSOs operate only during unusually heavy rainfall or to cause no ecological harm.
Research by Dr Giakoumis and colleagues at Brunel University of London and Imperial College London reveals that CSO discharges represent a more significant source of pollution pressure on England’s waterbodies than previously recognised, challenging the assumption that they are only intermittent or secondary contributors to waterbody pollution.
Policy Brief recommendations:
- Integrate pollutant-load assessments into the regulatory framework for CSOs
- Adopt a system-level risk classification to prioritise interventions, rather than a CSO by CSO assessment
- Align CSO and Wastewater Treatment Works regulations within a unified environmental-outcomes framework
See the full policy brief here