WATER seeping up from old mine workings has turned a tributary of the River Wear orange.
For more than three decades, discharge from a former mine shaft at Etherley Dene, near Bishop Auckland, has periodically caused pollution of the spring.
The Coal Authority has records of the discharge, which is coloured by iron reaching the surface and oxidising, dating back to at least 1986.
The issue is widespread across the region and those incidents that pose the greatest risk of pollution to watercourses are remedied, but this site is not a priority for the Environment Agency.
Government officials ask residents – many of whom have spotted it for the first time as they explore paths on their doorstep during the coronavirus lockdown – to report any significant changes on 01623-646333.
Thomas Mills, head of environment strategy at the Coal Authority, said: “We have records of the discharge being there since at least 1986 and have undertaken visual inspections and sampling.
“The orange-brown colour is probably due to naturally occurring iron within the water and our results show the levels of iron were stable and not rising at the time of sampling.
“Within the North-East region, we are aware of many discharges from former coal mine workings and any which have the potential to cause a significant impact to a watercourse are monitored routinely.
“Those with a greater impact on the environment are assessed and prioritised by the Environment Agency (EA).
“Although we do not have any statutory responsibility for mine water, we then use this ‘priority’ list as a guide for a treatment programme to assist in managing these flows.
“The discharge at Etherley Dene is not currently on the EA priority list for treatment and so, at the moment, is unlikely to be progressed for remediation.
“However, this list is regularly reviewed to take into account any changes in flow or impact and, as part of our role to make a better future for people and the environment in mining areas, wherever possible we work with other stakeholders to offer support or advice about making improvements to discharges such as this.”
The ‘orange river’ phenomenon is a legacy of the region’s former coal mining industry.
When mining activities stopped, so did the pumping of ground waters which allowed miners to operate in a dry environment underground.
Over time the water table has risen back to pre-industrial levels and when the water table rebounds it can reach the surface as a natural spring containing minerals from the abandoned coal layers.
When iron mixes with oxygen in the atmosphere it clings to the riverbanks and roots of trees, as seen in the photographs.
Groundwater levels of an anthropologically altered system via pumping Picture: PARKIN ET AL
Groundwater rebound occuring once pumping has ceased PICTURE: PARKIN ET AL
Mr Mills added: “People know their homes and local area best.
“If anyone living in a coal mining area sees something different or unusual, such as water seeping or bubbling where it didn’t before, please call our 24/7 hazard helpline on 01623-646333.”
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