Chapter 02 · Nature, land & waterWater, Waste & Pollution
Acid mine drainage
Definition
The formation and movement of highly acidic water rich in dissolved heavy metals. It forms when surface water and shallow groundwater react with sulphur-bearing minerals — especially pyrite — exposed by mining, producing sulphuric acid that leaches metals from surrounding rock; bacterial action can substantially accelerate the process (US EPA).
References
Formation mechanism (sulphur-bearing minerals → sulphuric acid → metal leaching); prevalence among drainage types; toxicity; Section 319 grant context.
Pyrite/iron-sulphide oxidation chemistry; USGS-observed pH range of 2.5–4.4; rust-coloured sediment description.
Overview
What it means
It is the most prevalent form of mine drainage, alongside alkaline and metal mine drainage. The US Geological Survey has observed drainage with pH as low as 2. 5–4. 4. Resulting fluids can be highly toxic to humans, animals and plants, and often leave rust-coloured iron sediments on streambeds.
How it is used
The term anchors monitoring, remediation and funding programmes: in the United States it is addressed through nonpoint-source programmes (including Clean Water Act Section 319 grants) and abandoned mine land reclamation, using active or passive treatment systems. Risk prediction and prevention are standard parts of mine permitting and closure planning.
Why it matters
Acid mine drainage can continue for decades or longer after mining stops, degrading streams, groundwater and fisheries and imposing long-run treatment costs. It is one of the main mechanisms by which legacy mines continue to harm communities and ecosystems.
Definitions and controversy
"Acid rock drainage" stresses that the process can occur without mining (natural weathering of sulphide rock); "mine drainage" is the broader umbrella, as not all mine drainage is acidic.