PowerPoint Presentation

Introduction to Minewater PollutionAbandoned mines are a significant pollution threat to watercourses in Britain. Many thousands of abandoned mines now discharge minewater into watercourses. Recently closed mines are still filling up with groundwater and will start discharging in the future.Nine percent of rivers in England and Wales, and two percent in Scotland are at risk of being labelled failing because of abandoned mines. (Source EA Aug 2008)

So who is responsible?Mining output peaked in the 18th and 19th centuries after the industrial revolution, when demand for coal and metal ores was at its highest. Only a few mines are still working. As is often the case, the potential long-term consequences were just not known when mining operations began.The legal position in the UK is such that no-one can be held liable for the pollution from the majority of mines. Only since 1999 has the operator of a mine had any legal obligation to deal with the consequences of abandonment.

A scarred landscape

The area of land below contains some of the most contaminated water in the country.

From a distance

It all looks very green and pleasant.

Appearances can be deceptiveIn red is the area which contains the remains of past mining activity.

What mining activities took place?Predominantly, coal was extracted, mainly by drift mining. Much evidence of these mining activities can still be seen on Todmorden Moor.In the North, between Cornholme and Cliviger, Galena (Lead Ore) was mined.Towards the South of Todmorden Moor, Fireclay was also extracted and together with the local supply of coal was used in brickmaking and the manufacture clay sewer pipes.

How does pollution occur?Pollution of water generally arises from the disturbance of land.Different mining practices may provide different specific pathways for the pollution to occur.Discharges are generally point sources of pollution, but reactions covering many square kilometres are responsible for the water quality.Groundwater and run-off from surface waste (spoil heaps), are the main sources of contaminated water.

Drift mining

Drift mining was the most widespread method in this area.

Groundwater build-up in drift mine

A real minewater discharge

What causes the pollution?Water flowing through old mine workings and seeping through the ground becomes loaded with minerals, including compounds of Iron (Fe), such as Iron Pyrites (FeS2).Iron Pyrites is commonly found associated with coal beds and when exposed to Oxygen and water, decomposes into iron oxides and sulphates. Some of these are soluble and get picked up by the water where they may undergo further reactions upon exposure to Oxygen. Other mechanisms may also be at work.

Iron Pyrites

Nodule containing PyritesPyrite crystal

Very generally it is the following reaction that produces the Iron Sulphate in a soluble form and acidifies the water by producing Sulphuric acid. At this point it is not unusual for the water to look absolutely unnaffected.

2 FeS2+ 7 O2+ 2 H2O 2 FeSO4+ 2 H2SO4

Upon further exposure to Oxygen, typically where the mine water meets the surface, the Iron Sulphateoxidises to becomeferric Iron- a hydrolysis (in the presence of water) reaction which causes the precipitation of Iron III Hydroxide - Fe(OH)3- these particles are not soluble in water and coat river and stream beds. This is what gives the characteristic Red/Brown staining.

The Iron III Hydroxide for most creatures, is not a poison in itself, but it coats aquatic plants and prevents photosynthesis from taking place which reduces the amount of dissolved Oxygen in the water. It can also block the gills of aquatic invertebrates so they take in less of the Oxygen that is still available.

So what can be done?The Coal Authority (CA) has a responsibility to manage the historic legacy of coal mining which includes treating mine water discharges from old mines and preventing the pollution of watercourses. The CA in partnership with the Environment Agency (EA) monitors mine water levels and have an agreed national programme of mine water treatment schemes.These schemes can be:-PassivePumped-passiveActive

Passive treatment

A passive scheme captures the water at source and it is transferred by gravity through either settlement ponds and reedbeds, or just reedbeds. It depends upon the water quality. Settlement ponds are usually 3 metres deep with steep sides and are fenced off. Reedbeds are only 30-50cm deep and these are either surrounded with post and wire fencing or not fenced at all.

Passive-pumped treatmentA pumped-passive scheme is similar to the passive scheme, but with a pump installed to assist with the movement of the water. Such a scheme is in operation at Clough Foot, on Midgelden Brook in Todmorden.

Active treatmentAn active scheme is more industrial in nature, and can require large fibreglass tanks, centrifuges, portacabins, skips and hard standing.

Monitoring Clough Foot

The Main Culprit

Sampling Sites

Site Context

Site 1:- Midgelden Brook (Above treatment works, but with some mine discharge) very poor score.Site 2:- Adjacent to mine discharge but untreatedSite 3:- After treated minewater is reintroduced

Results so far

Results so far