In 2015, a control system failure at Thames Water’s Bruern Road, Chipping Norton pumping station led to a sewage leak that affected a 50-metre stretch of a brook in West Oxfordshire that killed several hundred fish. Thames Water was recently fined £2 million for the pollution incident by the Environment Agency.
The Miltern Bruern Sewage Pumping Station operates a wet well that uses two submersible pumps to propel the sewage of approximately 550 people from the villages of Idbury and Fifield to Milton-Under-Wychwood sewage treatment works. The site is fitted with a standby generator in case of loss of supply, telemetry equipment for remote monitoring, a pump controller that operates the station based on level, and a backup control to protect against pump control loss.
However, on the day in question, the site suffered a loss of telemetry, resulting in lack of remote visibility of the operation of the site. Within the time the telemetry fault was present, it appears that the pump operation failed, according to the utility.
Since the incident, the organisation has been strengthened in three ways. Thames Water puts it simply: more people, more maintenance, and more training.
First, it had, in fact, implemented a new sewage pumping station management structure, increasing management oversight of assets, shortly before the Bruern Road incident occurred, although Thames Water admits that this has taken time to mature fully.
Second, maintenance planning processes have been optimised and improved, with more activity undertaken to plan across the pumping station estate. This has led to an increase in pump availability; the utility states that it is now consistently achieving levels of 98% to 99% overall. So important is this method that the company has set it as an official KPI, or ‘outcome delivery incentive’, in the next operating period PR19 (2020-25) with regulator OFWAT.
Third, engineers have also been trained in commissioning and using a new generation of pumping station controllers.
Furthermore, changes have been made via better systems and management of data. The company has invested in bespoke software and additional analytical capability and capacity across this and other areas of its operations. It introduced the iHub tool in 2016/17, which collects operational data across the utility to give control centre staff and operators a richer view of station and catchment level performance data. It has also continued to develop improved risk models that monitor a wider range of leading performance indicators to help plan to deal with issues at sites as they develop.
Thames Water adds that its record shows improvement since 2015. For example, in its most recent complete regulatory year of 2017, 17 incidents occurred from its 4,000 pumping stations.
Operational performance manager Stephen Pattenden adds:“We’ve already made a big step change, which is reflected in our performance and pollution incident numbers. The risk we carry operationally is now reduced; we have improved visibility of our assets, and have developed new software and analytical approaches to understand and manage operational and asset risk more effectively still in the future.”
Thames Water claims to have reduced pollution by 69% since 2013 and, as part of the company’s £11.7 billion business plan, it is investing record amounts on improving resilience, service and efficiency. The plan also includes a commitment to reduce by 18% pollution incidents that are defined by the Environment Agency as causing some harm to water courses by a further 18% in 2020-2025. This is based on the company’s performance in 2016 (as a base year due to its long business planning cycle).
“The majority of pollution incidents come from our network of gravity foul water sewers, as this is by far our most extensive asset. The performance in the sewer network will be specifically targeted to achieve this reduction with pollution incidents from sewage pumping stations minimised. Mechanical assets will always be prone to some failures, and we will continue to minimise the risk of this through effective maintenance and renewal of these assets,” explains Pattenden.
Operational planning for 2020 onwards is still ongoing; however, an increase in capital investment (replacing and upgrading equipment) is proposed in the business plan, particularly replacing older telemetry and control equipment.