The Drinking Water Inspectorate has published the findings from an investigation into the presence of perfluorooctane sulphonate (PFOS) in drinking water supplies in Cambridgeshire.

The report provides the outcome of the investigation by the Inspectorate into the supply of water from Duxford Airfield/Sawston Mill works and the blending arrangements with water coming from Abington Park/Hinxton Grange, joining with Babraham pumping station (PS) and the Cherry Hinton reservoirs system feeding into the Cambridge rural zone which includes the villages of Great Shelford, Hinxton and Stapleford.

The investigation followed notification to DWI on 8 February 2022 and as a result of a media article which appeared in the Guardian Newspaper on the same day by Cambridge Water, part of the South Staffordshire Plc group.

The Inspectorate found that PFOS was detected in the supply arising from Duxford airfield due to historical firefighting activity where PFOS was commonly used in firefighting foam on aircraft and the airfield. The runoff of the foam penetrated the aquifer contaminating the raw water used for abstraction.

The DWI said the water company was not responsible for the ground contamination but was aware of its presence in historical data. Historically, the company blended water from Duxford with that of Abington Park/Hinxton Grange as a supply/resource arrangement incidentally reducing the level of PFOS in supply. The Inspectorate described the blending configuration of the network as “long-standing and complex arrangements.”

Prior to February 2022, the Inspectorate had issued precautionary guidance on PFOS and more widely Poly and Perfluorinated Alkyl Substances (PFAS) in January 2021. PFAS represent a group of over 9,000 different fluorinated chemicals, some of which, such as PFOS and perfluorooctanoic acid (PFOA), are already highly restricted. Once in the environment, PFAS are persistent. There is increasing evidence about the occurrence of PFAS in the environment and growing concern about the potential risks to human health.

"Actions by the company following January 2021 guidance far short of the minimum expectations of a water supplier"

The report by the DWI states:

“The actions by the company following the guidance of January 2021 were far short of the minimum expectations of a water supplier because of incorrect assumptions, errors, delays, and incorrect information which allowed the inadequate blending arrangement to continue to June 2021.”

In addition, the Inspectorate says the confidence of consumers in their supplier was brought into question.

Cambridge Water was served with a precautionary prohibition notice on 21 February 2022,to protect water quality based upon the potential to fail wholesomeness requirements. The action was taken to ensure the supply could not be returned to service even in times of water stress in the region unless proven treatment could be installed to remove with certainty PFAS to below 0.1 µg/l in the public interest.

As part of the investigation, DWI also sought expert toxicological advice which concluded that it was unlikely that the concentrations supplied would give rise to a significantly increased probability of harm compared to exposures of up to 0.1 µg/l. The report states:

“The conclusion by the toxicologists, based upon the limited water quality data available, is that it is inconclusive that the concentrations would cause a significant probability of harm to consumers, compared to exposure of PFOS concentrations up to 0.1 μg/l guidance limit. “

The Water Industry Act 1991 and the Water Supply (Water Quality) Regulations 2016 set the framework for wholesomeness which are either set by a standard or, where a substance has the potential to cause harm to human health.

Based on the toxicological advice, the Inspectorate said the investigation did not identify evidence to conclude that drinking water was unwholesome as defined by the Regulations.

DWI recommendations include need to put robust measures in place to ensure accuracy of future statements so consumers can be correctly informed and public confidence maintained

However, following the incident, the Inspectorate has made a number of recommendations intended to address failings in Cambridge Water’s processes, including:

• The company should consider the risk associated with an unknown peak concentration, as well as the potential risks to the aquifer, when designing the new process, to ensure that there are sufficient control measures in place for the continued supply of wholesome water.
• The company reviews and amends its risk assessment processes so that all available information is appropriately considered, and timely actions are taken to ensure public health is protected.
• The company ensures that future blending calculations, for any type of blending arrangement, are robust and consider worst-case scenarios and actual flow data to demonstrate the blending arrangements are always adequate.
• The company reviews the sampling requirements associated with any change of analysis to ensure the requirements are understood, the appropriate sampling equipment is available and that the changes are clearly communicated to sampling staff.
• The company reviews its laboratory triggers for unusual results for all its parameters to ensure an appropriate and timely response to any failures.
• The company puts in place robust measures to ensure the accuracy of future statements and letters so that consumers can be correctly informed and public confidence maintained.

Click here to download the DWI report in full