Herbicides found in water at St Saviour’s reservoir

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ST SAVIOUR’S reservoir has been cut off from water supplies after a pollution incident which has been linked to the use of herbicides at the airport.

St Saviour’s reservoir has been polluted by herbicide sprayed at the airport. (Picture by Peter Frankland, 26368741)

When analysed, stream samples taken from the St Saviour’s reservoir area in October showed abnormally high levels of two herbicides, MCPA and Mecoprop, while further samples taken from St Saviour’s water treatment also showed trace levels.

These were within legal UK limits, but the precautionary decision was taken to cut supply from the reservoir while Guernsey Water investigated the source of the chemical and determined the levels in the raw water.

A further sample taken from Kings Mills’ water treatment works identified a concentration of one herbicide slightly above the UK limit for that chemical.

However, Guernsey Water said that they are confident there would have been no ‘significant risk’ to health – the sample was taken before the reservoir supply was cut off and water in Kings Mills from there would blend with water from the unaffected Juas treatment works.

Environmental Health said it was investigating an incident and Guernsey Water said it notified the office as soon as the first sample was analysed.

Guernsey Airport confirmed it was notified of the incident on Friday last week, it said: ‘Since we have been alerted about these results, Guernsey Airport has started its own internal investigation to establish the circumstances of why and how this has happened.

‘Guernsey Airport believes these results may have been caused by the application of approved herbicides for weed control. The use of such products is an established part of our Wildlife and Habitat Management Programme for the airfield.’

Margaret McGuinness, water quality risk manager, Guernsey Water, said: ‘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 Saviour’s reservoir.

In 2011 bypasses that can be used to divert these incoming flows and discharge that water directly to sea were installed to protect the reservoir in the event of any chemical spillage at the airport.

Both are currently in operation while Guernsey Water await the results of further samples from the raw water within the reservoir.

In the meantime, St Saviour’s reservoir is not operational and drinking water supplies are being maintained from the island’s other reservoirs.


Ms McGuinness continued: ‘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.’

St Saviour’s reservoir had 15.4% of the island’s total water storage by the end of October - 676 megalitres.

Longue Hougue is the biggest storage facility, it currently holds 1,110 megalitres, 25.3%.

The four other large reservoirs are at Gross Hougue, Hougue Ricart, Juas and St Andrews.

At the end of October stored water totalled 3,746 megalitres, 85.43% of total capacity.

Yves Le

By Yves Le
News reporter

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