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Water - The lifeblood of our ecosystems
Tin mining is a part of Cornwall’s culture and heritage. It played a major role in our industrial history. There are hundreds of abandoned mine-workings scattered across the landscape and the trade in tin can be traced as far back as the Bronze Age. The location of many ancient mines and adits can only be guessed at, and more recent mines are not all fully documented. Most deep mines closed over 100 years ago but they still pollute our rivers, harming fish, insects and ecosystems.
Pollution from abandoned metal mines isn’t always obvious; it may not be visible and we can only tell if metals are present in rivers by measuring the water quality. Abandoned metal mines are responsible for over half the cadmium, zinc, lead, arsenic, mercury and copper found in UK rivers.
Image: Continuously overflowing mineshaft at the head of Porthleven Stream in the Flow Valley
Contamination
Contamination of groundwater and surface water is one of the consequences of metalliferous mining. Metals mix with water in the depths of a mine. They find their way to the surface in high concentrations and mix with organic materials and settle in the sediments of streams and rivers.
Most Cornish mines were closed many years ago when there was no burden of responsibility on the operators to deal with the consequences of closure. Mines were simply abandoned and allowed to flood with the result that contaminated water would flow unhindered from the mine adits into the streams and rivers. Though it is rarely discussed, this kind of pollution is present in most mining areas today and will continue for hundreds more years unless action is taken.
Mining companies spend a lot of money on pumping and water treatment when mines are active. The pollution problem arises after the mining operation is abandoned, when filtration systems are shut down and the mine floods.
Many people remember the Wheal Jane Pollution disaster in 1992 when a huge quantity of acidic metal laden water was released into the Carnon River The eventual remedy was the construction of a massive permanent treatment works that still falls short of filtering out all levels of contamination, but costs the tax payer £1.5million per year.
In January 2023 Parliament approved a new legally-binding target to halve the length of rivers polluted by abandoned metal mines by 2038. This target, explained in the Environmental Improvement Plan, will be achieved through the Water and Abandoned Metal Mines (WAMM) Programme.
Pollution has been identified in 1500 km of the UK’s rivers including 500 km in Cornwall. For more details of the government’s plan of action see this powerful article on the Environment Agency Blog : "Cleaning up rivers polluted by abandoned metal mines"
The scientific community generally accepts that climate change is bringing hotter drier summers, mild wetter winters, rising sea levels and more extreme weather. Droughts increase the severity of pollution because there is less dilution by cleaner water, and more erosion of mine wastes occurs after intense rainfall. Ancient shafts collapse, particularly when in-filled or capped a long time ago, releasing once-dormant pollution.
Porthleven Stream
Porthleven Stream one of the most polluted waterways in Cornwall.
Micro-organisms at the base of the food chain that find their way into contaminated streams and rivers are poisoned and cannot survive. Organisms higher up the chain become starved and die out. Insects, invertebrates, fish, amphibians, birds and small mammals lose their food source and either die or move elsewhere. This effect of contamination is generally irreversible and can cover a very large area. Biodiversity is eroded and will not recover unless the water is decontaminated.
This is the situation that exists in the Porthleven Stream, which is the principle waterway draining the Wheal Vor area.
The Porthleven Stream Catchment Area (https://environment.data.gov.uk/catchment-planning/WaterBody/GB108048002060) clearly states that the ‘reasons for not achieving good’ are the presence of elements resulting from abandoned mine workings. Some of these are ‘Priority Hazardous Substances’ which are stated as toxic, persistent and likely to bio-accumulate. According to the EU Water Framework Directive in 2000, emissions, discharges and losses of these substances need to be ceased or phased out. 24 years later, we still have these carcinogenic substances discharging into our local stream.
Protect Wheal Vor asked the Environment Agency to undertake and publicise baseline testing of Porthleven Stream, in spate and in drought, before Cornish Tin began their first phase of drilling. In the absence of a positive response, Protect Wheal Vor commenced water sampling from our local streams to establish a baseline.
Image: Pollution treatment at Wheal Jane