In many parts of the country, but especially in areas that are/have been mined for coal, you may seen some watercourses that are bright red or orange.
Whilst the discharge itself is usually crystal clear, the bed of the watercourse below the discharge can be coated in a rusty deposit.
What is this rusty deposit! ?
Well to be frank it is just that! – Iron Oxide.
What causes this and why does the water look clear when it discharges into the watercourse?
In areas where there is coal the ground geology tends to contain high concentrations of Iron (sometimes in the form of Iron Pyrites “Fools Gold”). When coal is extracted, the mineral veins of Iron are exposed to the air. When groundwater flows through these coal workings, often after they are abandoned, the water will pick up these oxides of Iron in a Ferrous form. Although the water is rich in Iron it can still appear crystal clear at this point.
The Iron rich water, which can be slightly acidic, will then flow out into a watercourse, which is sometimes called “rebound” and once exposed to more oxygen and / or a pH increased in a fast flowing stream, it will rapidly deposit Ferric Iron Oxide.
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What can be done to prevent it?
The impact of these type of discharges can be varied, and in many cases, improvement work is being considered to treat the water and prevent the Iron Oxide being deposited in the watercourse.
If you want more information about Iron Ochre in the UK, you can download a report on Abandoned Mines and the Water Environment here:
our publication: Abandoned mines and the water environment
