Understanding CSO Discharge Impacts
The key (and open) question this proposal will address is whether or not, under a range of hydrological conditions the spilled water from CSOs presents a significant risk to environmental and/or human health.
The majority of SWW’s sewer network utilises a combined sewer system, amalgamating foul sewage and stormwater runoff within the same pipes. Such systems are designed with sufficient capacity to convey effluent flows during day-to-day operations of all domestic and trade sources, as well as during design standard rainfall events, safely delivering to waste water treatment works (WwTW) for processing. However, combined systems are vulnerable to high water inputs, therefore these systems are designed to utilise Combined Sewer Overflows (CSO) to prevent sewer flooding by spilling excess water into the environment.
Recent studies have highlighted that aging legacy infrastructure, increasing loads, development, misconnections, infiltration and increasing rainfall intensity are leading to more frequent CSO events throughout the region, with similar findings across England. Climate change is likely to further exacerbate these problems.
This question needs to be addressed as water companies move towards a more transparent risk-based approach for long-term Drainage and Wastewater Management Planning (DWMP).
The project will run in two phases:
1) Pilot studies in three major catchments (Exe, Tamar and Torbay) to study CSO spills (chemical and microbial), their frequency and volumes, and their potential for impacting (including (eco)toxicological) on receiving waters to help understand both the possible scale and nature of the problem of CSO across these catchments
2) In-depth study in collaboration with South West Water of one chosen catchment, working towards recommendations and establishing a modelling technique for future use
