Longue Hougue reservoir fully available after contamination by pesticide declines
- Longue Hougue reservoir has been cleared for full use following the decline of metamitron levels.
- The pesticide was isolated after being detected during routine sampling.
- Guernsey Water took immediate action, resulting in a 90% reduction in metamitron levels.
- Enhanced water management strategies included dilution and carbon dosing.
- No water use restrictions are currently anticipated despite the dry conditions.
The Longue Hougue reservoir in Guernsey has returned to full availability following a significant decline in metamitron levels.
The now-banned pesticide was discovered in the reservoir earlier this year during routine sampling and was immediately isolated from the water supply.
Swift action by Guernsey Water led to a reduction of metamitron levels by over 90%, allowing the reservoir to resume maximum capacity for supplying the island's water needs.
Key measures taken included enhanced sampling and analysis, dilution of the Longue Hougue supply with water from other reservoirs, and the introduction of carbon dosing at the Juas water treatment works to thoroughly eliminate traces of metamitron.
Prior to the recent actions, the normal daily transfer of around 10 million litres from Longue Hougue reservoir to Juas was restricted to approximately three million litres due to the contamination.
It is estimated that less than half a litre of metamitron was responsible for contaminating the reservoir's total of 1.1 billion litres.
When at full capacity, Longue Hougue accounts for 27% of Guernsey's stored water, and the reduction in its output placed additional strain on water resources, especially during an exceptionally dry year.
Carbon dosing, which effectively removes pesticides and other organic compounds from water through adsorption, successfully eliminated all traces of metamitron from treated drinking water.
The source of metamitron remains unknown, and there have been no detections of the pesticide elsewhere.
Water Quality Risk Manager Daffyd Griffiths highlighted the essential role of stream monitoring in identifying the pesticide early.
“Although investigations were inconclusive and we were unable to determine where the pesticide originated, robust sampling identified it and enabled us to prevent it from becoming a danger to the drinking water supply,"said Griffiths.
He also pointed out the challenges posed by the dry weather.
“This example underlines the importance of our stream monitoring, which allowed us to identify and respond to this issue in time to protect drinking water.”
He urged residents to adhere to guidelines for using pesticides, herbicides, fungicides, and insecticides, advising against spraying if rain is forecast and ensuring proper disposal of any chemicals or containers at the Longue Hougue recycling centre.
Despite the challenging circumstances, Guernsey Water has confirmed that there are currently no plans for water use restrictions.
Updates regarding the island's water resource status will be posted on the Guernsey Water Facebook page bi-weekly.
Comments ()