Acid sulfate soils are naturally occurring soils, sediments or organic substrates (e.g.
peat) that are formed under waterlogged conditions. These soils contain
iron sulfide minerals (predominantly as the mineral
pyrite) or their
oxidation products. In an undisturbed state below the water table, acid sulfate soils are benign. However, if the soils are drained, excavated or exposed to air by a lowering of the water table, the sulfides react with
oxygen to form
sulfuric acid.