Pumping the polluted water from mines
Water contaminated with metals and chemicals still sits in dozens of disused mines across England, Scotland and Wales. But how do you ensure those millions of litres are kept out of rivers and streams?
A twisting array of pipes emerges Hydra-like from the depths of the disused Wheal Jane mine, near Truro in Cornwall.
Contaminated water, laden with iron, zinc, cadmium and arsenic, is pumped out of the mine at the rate of at least 110 litres a second out of a maximum of nine pumps, depending on the rainfall at the time.
All nine were called on to deal with last winter's floods.
There is no sound - the pumps are 63m (207ft) below the surface where miners once dug for arsenic, copper, tin, iron and zinc.
Pumps at Wheal Jane work round-the-clock, sending contaminated water for treatment where it is mixed with lime to neutralise its acidity, mixed with a chemical to bond the metal particles together or into a settling tank.
The remaining sludge is pumped into clay-lined impermeable lagoons and clean water is ejected into a stream which emerges into the River Fal.
"After a mine closes, you are no longer pumping water out so the water rises within the mine," said Jeremy Crooks, the Coal Authority's principal contracts manager
"It absorbs metals and minerals from the surface of the workings and when they come to the surface they can be released and you can have a highly-polluted water."
The authority's job is to make sure the residues from Britain's mining past are treated in 51 processing plants.
Coal mines produce less acidic iron-polluted water, which can coat river beds, choking plants and killing fish by getting in their gills.
The Wheal Jane plant was built after a catastrophic release of contaminated water in 1992, a year after the mine was closed and its pumps turned off.
A drainage tunnel, or adit, near the surface had collapsed and more than £45m litres of acidic mine water poured into the Carnon River and the Fal Estuary.
Former Cornish miner Mark Kaczmarek said: "When I first saw the pictures on TV I could not believe it.
"You can still see the marks on the river bank near the Pandora Inn on the river.
"Cornwall is used to mining effluent, the Red River at Godrevy is named after the iron from the mines, but it was shocking seeing the Fal stained red."
Mr Kaczmarek, now a Cornwall councillor, campaigns to maintain adits from former mines in the county.
There have been no other incidents of such widespread pollution since, but the Coal Authority deals with about three "blow-outs" a year across England, Scotland and Wales.
They happen when the collapse of a shaft leads to a build-up of water pressure and contaminated water is released.
In the 1980s a shaft became blocked at Glyn Castle - situated above the town of Resolven, Neath Port Talbot - leading to mine water contaminating the Clydach Brook for 0.62 miles (1km).
The shaft was blocked up to prevent further blow-outs until a treatment site was built in 2005 using new boreholes.
Pumps usually fail about once every two or three years, either because of mechanical failure of a power cut and are replaced or reset by contractors such as waste firm Veolia on the Wheal Jane site.
Last winter torrential rain overwhelmed the Wheal Jane pumps and Cornwall Fire Brigade brought in its own pumps to keep the water at bay.
The Coal Authority called it a "one-in-a-246-year event".
"It was a tense period," said Mr Crooks.
"We were pumping four times more water than usual and with the fire brigade's pumps we were able to control that.
"It was not designed for that kind of quantity, but all the water was treated."
The staining effect from iron and other metals is still visible at in the old tailings lagoons at the Wheal Maid Mine, near Wheal Jane.
The Coal Authority says the levels of metal contamination in the mine water at Wheal Jane will gradually reduce as the water washes the contaminants away from the exposed surfaces of the old mine.
It says the treatment process is likely to last for another 50 years and there is "ample" storage capacity in the sludge lagoons.
Wheal Jane, the biggest and most expensive operation, costs the government about £1.5m a year to run, out of total running costs of £8.5m around the UK.
But there are hopes of cutting the cost in a £1m pilot scheme led by Newcastle University.
The university has joined a Defra-funded partnership with the Coal Authority, Environment Agency and National Trust to design and build the UK's first large-scale "passive" treatment system - using compost and limestone to treat metal-rich mine water at the former Force Crag mine near Keswick in Cumbria.
The aim is to remove the three tonnes of zinc, cadmium and lead which is being discharged every year into Bassenthwaite Lake.
Mining expert Dr Melanie Brown, who advised the authorities on treatment of water from Wheal Jane, after the 1992 incident, said the current treatment was "very expensive and unsustainable".
The graduate of Camborne School of Mines, said: "I can understand why they went for it, it is a tried and tested method and they had to get something in place, but there are ways to do it more ecologically.
"Carting all that limestone from Derbyshire to Cornwall is crazy and unsustainable.
"There could also be the possibility of reclaiming some of the metals."
Dr Adam Jarvis, reader in Environmental Engineering at Newcastle University said: "Abandoned metal mines are by far the biggest source of metals pollution to the freshwaters of England and Wales.
"Between 2,500 and 3,000km of our streams and rivers are estimated to be impacted (about 6%), with major pollutants including zinc, cadmium and lead.
"This pollution has a major impact on the health of freshwater ecosystems, the amenity value of streams and rivers, and the potential uses of waters downstream of the abandoned mines.
"Monitoring of the Force Crag system will help to establish whether it will be possible to build similar treatment systems for other metal mine water discharges across the UK, and therefore address this major source of freshwater pollution on a national scale."