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News Centre > Friday 15 November 2019

Investigation of herbicide use at Guernsey Airport

St Saviours Reservoir

Margaret McGuinness, Water Quality Risk Manager, Guernsey Water: "Last week we received the analysis results from stream samples taken in October from the St Saviour's reservoir area, which showed unusually high levels of two herbicide chemicals.

"Subsequent samples taken from drinking water from the St Saviours water treatment works also showed trace levels of these chemicals, but within the legally permitted level in the UK. However as a precaution, we took the decision to cease supply from St Saviour's Reservoir while we investigated the source of the chemical and determined the levels in the raw water within the reservoir. Drinking water supplies are being maintained from the island's other reservoirs.

"A further sample taken last week from King's Mills water treatment works identified a concentration of one herbicide slightly above the UK limit for that chemical. At the time that sample was taken this treatment works was still being fed from St Saviour's Reservoir, which is no longer the case. The treated water from King's Mills would subsequently have been blended with water from the Juas treatment works, which is unaffected, so we are confident that there was no significant risk to health.

"We believe the source of the chemicals was Guernsey Airport, where herbicides were applied to the airfield some days before October's water samples were taken. The airport has procedures in place covering the application of herbicides, which have been agreed with Guernsey Water. These procedures are designed to prevent chemicals that have to be used on the airfield, for operational reasons, from entering St Saviour's Reservoir. Airport management is currently investigating whether those procedures were followed.

"There are two streams that run through the airport, neither of which is currently flowing into St Saviours Reservoir. We have bypasses that can be used to divert these incoming flows and discharge that water directly to sea. They were installed to protect the reservoir in the event that there is any chemical spillage at the airport. Both are currently in operation while we await the results of further samples from the raw water within the reservoir. In the meantime, St Saviour's reservoir is offline and drinking water supplies are being maintained from the island's other reservoirs."

"We regularly sample water from all our water sources and analyse it at different stages of the water supply process for around 130 different chemicals, to ensure that our water at all times is safe and good to drink. This rigorous testing, which includes all catchment streams, reservoirs and treatment works, is designed specifically to identify issues such as this. Now that the source has been isolated, any chemical concentrations within the reservoir will be naturally diluted by the water entering from other streams. Continued sampling will ensure that it is not brought back into supply before this happens.

"The Office of Environmental Health & Pollution Regulation was notified when the elevated levels of the chemical were first detected, and they have been kept abreast of the actions that we have taken to ensure there is no risk to the public."

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