storm water overflow after heavy rain

storm water overflow after heavy rain

Sewage released over 100,000 times a year: what’s being done to stop it?

Published 13/06/2022   |   Reading Time minutes

Reports of sewer overflows operating illegally led to public outrage in late 2021. This resulted in a new legal duty on water companies in England, and a ‘major investigation’ by the Environment Agency. But, Natural Resources Wales isn't planning a similar investigation in Wales.

The Senedd’s Climate Change, Environment and Infrastructure Committee undertook its own investigation into sewage discharges, and their impact on water quality in early 2022.

This article looks what the Committee found in its investigation, and the response from the Welsh Government.

Our previous briefing gives a comprehensive overview of storm overflows and how they can impact water quality. It also gives further information on the new provisions in the UK Environment Act 2021 relating to English water companies.

Why is sewage is being released into the environment?

Combined sewers collect both sewage and run-off from drains and gutters. This wastewater is normally taken to a treatment works where it’s cleaned and returned to the environment.

Each sewer system has a maximum amount of wastewater it can accept. During heavy rainfall, if there’s more water than the system can cope with, it’s released at points called ‘Storm Overflows’ often referred to as ‘Combined Sewer Overflows’ or ‘Combined Storm Overflows’ (CSO).

The Committee heard that CSOs are operating more frequently due to a number of factors:

  • increasing frequency and intensity of extreme rainfall events due to climate change;
  • increases of impermeable surfaces i.e. urban creep;
  • increases in population attached to a sewer network;
  • blockages caused by the disposal of ‘unflushable’ items; and
  • collapses and deterioration of the sewer system.

How often is this happening?

Water companies acknowledged that CSOs are operating more frequently than is acceptable. The most recent data published by NRW shows just over 105,000 CSO discharges (or ‘spills’) recorded from 2,041 storm overflows.

The Committee found that whilst CSOs should be operating infrequently and in exceptional weather conditions, that isn’t the case. It calls for:

… action from the Welsh Government, in its leadership role, to ensure that the number and volume of discharges is reduced as a matter of urgency.

In response, the Welsh Government says “better information is required about discharge quality from overflows and the impact on the receiving water quality”:

Improved effluent monitoring at targeted sites, together with event duration monitoring already in place, will enhance evidence available and enable effective targeting and prioritisation of action.

How well is it understood?

The Committee heard that CSO monitoring has improved since water companies were instructed in 2012 to install Event Duration Monitoring (EDM), to record the frequency and duration of CSO discharges.

Dŵr Cymru has invested £10.5 million to improve monitoring of CSOs since 2015, and has EDM on almost 99% of its CSOs. Hafren Dyfrdwy has monitors on all 50 of its CSOs. EDM data is shared annually with NRW and is publicly available from both Dŵr Cymru and Hafren Dyfrdwy.

CSOs in Wales are permitted by NRW. Water companies may be breaching their permit conditions if a CSO operates when there isn’t heavy rainfall, or if they’re not treating enough sewage before it’s discharged. However the Committee heard how water companies must ‘self-report’ permit breaches/pollution incidents.

According to Annual Environmental Performance Assessments (EPA) by NRW, Dŵr Cymru’s self-reporting performance reached 80%, while Hafren Dyfrdwy self-reported 100% of pollution incidents.

However, a House of Commons Water Quality in Rivers inquiry found:

Citizen science analysis of water company data suggests that the true number of sewer overflow discharges may be considerably higher than those reported.

The Senedd Committee found public confidence in the regulatory and enforcement regime for storm overflows to be low. It recommended actions for NRW and water companies to tackle this. Both are yet to respond (at the time of writing).

What impact is it having?

CSOs can cause harm to the health of our rivers by worsening water quality, and harm to public health through preventing safe recreational use of those rivers.

The Welsh Government says CSOs have been identified as a reason for not achieving ‘Good Ecological Status’ (Water Framework Directive classification) in 3.7% of waterbodies across Wales.

Dŵr Cymru acknowledged it has “a major role to play in improving river water quality”. Hafren Dyfrdwy echoed this, but states that “unless the issue of agricultural pollution is also addressed, health of rivers in Wales are unlikely to improve materially.

The Welsh Government confirmed “agricultural pollution is one of the major factors causing waterbodies to fail”.

New rules on agricultural pollution came into force in 2021, and have been reviewed by the Senedd’s Environment, Trade and Rural Affairs Committee.

What action is being taken?

The Storm Overflow Evidence Project report, prepared for Water UK finds that to reduce harm from CSOs:

  • either more collected rainwater and wastewater must be retained in the system; or
  • the quantity of rainwater entering sewers must be reduced.

The Committee heard how Nature Based Solutions (NBS) and Sustainable Drainage Systems (SuDS) are important tools to tackle pressures on the sewer system, and recommended action to increase NBS for water management.

The Welsh Government highlights the Better River Quality Taskforce in taking forward a number of the Committee’s recommendations.

The taskforce is made up of NRW, the Welsh Government, Ofwat, both Welsh water companies, Afonydd Cymru and Consumer Council for Water. It will:

… evaluate the current approach to the management and regulation of overflows in Wales and to set out detailed plans to drive rapid change and improvement.

The Welsh Government says these plans will:

… support our understanding and identify whether changes are required to ensure water companies effectively manage and operate their network of sewers to meet current and future challenges.

The taskforce has identified a number of areas for change and improvement, and will publish a ‘storm overflows roadmap for Wales’ by 1 July. The Committee wants the roadmap to be ambitious with targets and timescales.

This will be published alongside River Basin Plans, which will set out a “comprehensive overview of all our waterbodies”, including pressures from CSOs and wider pollution sources.

The Committee’s findings will be debated in the Senedd on 15 June. You can watch it live on Senedd TV.

Article by Lorna Scurlock, Senedd Research, Welsh Parliament