Major Improvements Required To Sewer Overflow Monitoring And Management
4th September 2024
A new report published today (4 September 2024) by Environmental Standards Scotland (ESS) finds that action needs to be taken to improve monitoring, regulatory guidance and the operation of storm overflows in Scotland.
The report Storm overflows an assessment of spills their impact on the water environment and the effectiveness of legislation and policy sets out that:
there is no comprehensive, publicly available information on the scale and environmental impact of spills from storm overflows in Scotland.
Where there is data, it is clear that some sites spill much more frequently than should be expected, some of them hundreds of times a ESS' analysis of Scottish Water data reported to SEPA shows that in 2023, 49% of the 142 storm overflows and emergency overflows spilled over 50 times, 32% over 100 times and four spilled more than 500 times. As an example, one Combined Sewer Overflow (CSO) at the Meadowhead treatment works in North Ayrshire spilled waste water 365 times on 124 different days in 2023.
Current Scottish guidance is outdated and it is not sufficiently clear that spills from storm overflows should only occur in exceptional circumstances. This limits the effective implementation and application of the Urban Waste Water Treatment (Scotland) Regulations 1994.
The system of identifying, reporting, classifying and addressing environmental pollution incidents (EPIs) is one of the key ways of protecting the environment from pollution from storm overflows. ESS has therefore begun investigatory work on the legislation governing EPIs and the responsibilities of the Scottish Environment Protection Agency (SEPA) and Scottish Water.
Storm overflows are part of the sewerage system and are designed to reduce the risk of sewers flooding homes and businesses. However, spills from storm overflows can pose a risk to the environment and to human health. The Scottish Government, Scottish Water and the Scottish Environment Protection Agency (SEPA) all have responsibilities in relation to storm overflows in Scotland.
ESS finds that in 2023, data was publicly available for only 8% of storm overflows and emergency overflows. Furthermore, the guidance for the regulations that control the treatment of waste water in Scotland has not been updated since 1998, before devolution.
A revised Urban Waste Water Treatment Directive was formally adopted by the European Parliament on 10 April 2024. The Scottish Government will need to review the legislation relating to waste water management if it wishes to meet its commitment to keep pace with developments in European environmental policy and legislation.
Mark Roberts, CEO of ESS said, "Despite high levels of public concern, there is a lack of transparent information about the operation and impact of storm overflows in Scotland. We have outlined steps that the Scottish Government, SEPA and Scottish Water should take to improve data and monitoring on storm overflows in Scotland.
"We are also calling on the Scottish Government to publish up-to-date, clear and specific guidance about the exceptional circumstances when it is permissible for storm overflows to spill. Our analysis has found that while some storm overflows appear not to spill at all, others spill more frequently and for longer periods than can be considered exceptional. This situation must be addressed.
"ESS expects the Scottish Government, Scottish Water and SEPA to respond to the recommendations laid out in the report within six months."
Key findings, recommendations and further work
Key finding 1: There is no comprehensive, publicly available information on the scale and environmental impact of spills from storm overflows in Scotland. In 2023, data was publicly available for 8% of storm overflows and emergency overflows although Scottish Water is only required by licence to report the data to the Scottish Environment Protection Agency (SEPA) for 4%. Scottish Water is currently reviewing whether it has further monitoring data available. Scottish Water is also implementing plans to increase the number of event monitors. If completed by the end of 2024 as planned, Scottish Water expects this to cover at least 35% of storm overflows and emergency overflows. While the majority of spills are unlikely to lead to an environmental pollution incident (EPI) or licence non-compliance, more publicly available information on these topics is necessary. See paragraphs 5.1 to 5.23.
Recommendation 1: The Scottish Government, Scottish Water and SEPA must make data in relation to waste water spills, compliance with licences and environmental pollution incidents available to the public to provide a comprehensive and accessible picture of the scale of spills from storm overflows. This should include reporting where and when discharges occur, their scale and the reasons for any discharges, as well as more details on when these result in pollution incidents covering the source, reasons and links to licence compliance.
Recommendation 2: Scottish Water must complete installation of, and publish all data from, the more comprehensive network of monitors set out in its ‘Improving Urban Waters Routemap'. It should conduct and publish the results of targeted monitoring to assess the accuracy of predicted spill rates from its hydraulic modelling and in response to locations where environmental pollution incidents have occurred. In addition, monitors should be installed at all locations where storm overflows have been assessed as unsatisfactory and it should ensure that monitors are installed and operational wherever required by licence.
Further work by ESS: Environmental Standards Scotland (ESS) has begun to conduct investigatory work on the existing system for identifying, reporting and classifying environmental pollution incidents. This work will also examine whether, and to what extent, there are effectiveness issues with the law and the way it is being implemented or applied by the relevant public bodies.
Key finding 2: The Scottish regulations controlling waste water treatment (the Urban Waste Water Treatment (Scotland) Regulations 1994) derive from the 1991 European Urban Waste Water Treatment Directive. The Regulations require Scottish Water to ensure that sewerage systems for areas with a population equivalent to over 2,000, including storm overflows, meet the requirements of BTKNEEC (best technical knowledge not entailing excessive costs) to limit pollution. In addition, the Regulations require that, under normal climatic conditions, and taking into account seasonal variation, all urban waste water is collected and treated, except in exceptional circumstances. The European Court of Justice has made clear that this may only be departed from in exceptional circumstances. The Scottish guidance on this was last updated in 1998 and ESS finds that it fails to reflect the requirement for spills from storm overflows to be exceptional. This has had consequences for Scottish Water's operations and SEPA's regulatory activity and limits effective implementation and application of the law (see paragraphs 7.1 - 7.12).
Key finding 3: ESS' analysis of the limited data available demonstrates that, while some storm overflows appear not to spill at all, others spill more frequently and for longer periods than can be considered exceptional. This can occur without breaching existing licence conditions (see paragraphs 9.1 - 9.26).
Key finding 4: Climate change will increase the occurrence of extreme rainfall and alter what may be defined as exceptional circumstances. This, together with population changes and behaviour, will further increase the pressure on sewerage systems and, without intervention, is likely to lead to increased frequency and/or volume of spills (see paragraphs 7.10 - 7.12).
Recommendation 3: The Scottish Government should as a matter of priority: (1) prepare and publish up-to-date, clear and specific guidance about the exceptional circumstances in which it is permissible for storm overflows to spill; (2) ensure this guidance takes into account predicted future climatic conditions (commissioning further research if required); and (3) provide up to date information on BTKNEEC requirements.
Recommendation 4: SEPA should review and update its authorisation regimes and associated regulatory and operational guidance to reflect the Scottish Government's revised guidance and ensure that it remains up-to-date, publicly available and is in line with best practice.
Key finding 5: A small number of storm overflows are at risk of spilling during dry weather. This should not happen. ESS' analysis of the limited available data suggests Scottish Water and SEPA may not have identified all of the storm overflows that appear to spill in dry weather (see paragraphs 10.1 - 10.3). Dry weather spills are of greatest concern since their environmental impact is less likely to be diluted.
Recommendation 5: Scottish Water and SEPA should more routinely assess available rainfall, flow and spill event data to identify all instances of overflows which appear to spill in dry weather and prioritise these for investigation and improvement as soon as possible.
Key finding 6: In April 2024, the European Parliament adopted a revised Urban Waste Water Treatment Directive. The Scottish Government will need to review the legislation relating to waste water management to meet its commitment to keep pace with developments in European policy and legislation (see paragraphs 4.1 - 4.4).
Key finding 7: Overall, there has been significant progress in reducing the number of water bodies subject to pressure from waste water. In 2008, waste water was a pressure in 208 surface water bodies (out of a total of 2,013) in the Scotland River Basin District (all of Scotland, except the Solway and Tweed catchments). In 2020, it was a pressure in 48 surface water bodies (out of 2,827), particularly in more urban locations. Contaminants in storm overflows and treated sewage pose a potential risk to human health and to the environment which increases near and following a sewage discharge. This may not be identified in the monitoring of the overall quality of a water body (see paragraphs 12.1 - 12.7).
Further work by ESS: Later in 2024, ESS will begin work on the wider topic of water quality and river basin management planning. This will include examining whether the monitoring undertaken to classify whole bodies of water is adequate to identify more localised impacts from storm overflows.
Key finding 8: Scottish Water and SEPA have identified a small number of storm overflows (24 out of 3,674) as requiring enhancements to improve water quality of the wider receiving water body. Scottish Water indicate that there are a further 883 intermittent discharges currently identified as being unsatisfactory, mainly due to sewage related debris. Scottish Water are prioritising these for improvement. The scheduling of this improvement is subject to agreement with Scottish Ministers (see paragraphs 11.1 - 11.7).
Recommendation 6: Scottish Water should publish a comprehensive and accessible plan for all proposed improvement work specifying: (1) the locations of all these storm overflows; (2) the timetable when improvement work will take place; and (3) if the timetable for work has not been finalised, specify when a decision on whether to proceed will be made.
Environmental Standards Scotland
