Calls have been made for Powys County Council to fully explain a “substantial” pollution incident at one of its high schools.

The council has revealed, following questions by Plaid Cymru group leader, Cllr Elwyn Vaughan that 800 tonnes of soil has had to be dug out and taken away from Gwernyfed High School.

In May last year kerosene oil was found in the drainage system next to the sports hall at the school.

The leak could have been going on for several years and the cost of dealing with the incident is said to be £140,000.

Cllr Vaughan said: “In view of the importance of environmental matters to this authority, it is imperative that a full report on the situation is presented to councillors especially the education (Learning and Skills) scrutiny committee to ensure complete transparency and openness.

“Having to move 800 tonnes of soil implies it is substantial pollution and we not only need assurance that none went into the local watercourses but also confirmation of full costs and any other future liability.

“If the tank was removed in 2011, then the pollution must have been ongoing for a number of years and begs the question why nobody noticed years ago.”

He added that private polluters would face prosecution by Welsh Government environment body Natural Resources Wales and that question needed to be answered.

A Powys County Council spokesman said “In May 2023, kerosene was found in the drainage system next to the sports hall building at Gwernyfed High School.

“The oil had emanated from a decommissioned oil tank next to the sports centre building that had been removed in 2011.

“There has been 800 tons of contaminated material removed from Gwernyfed High School to a specialist and licensed tip.

“This area has been backfilled with stone and is due to be reinstated with topsoil, a new grass surface as well as a new pedestrian access pathway.

“The overall cost of the re-mediation work is approximately £140,000.”

He added that the Welsh Government’s environment body NRW have been informed and “kept updated” with the situation.