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"Acid sulphate soils (ASS) are naturally occurring soils and sediments containing
iron sulphides, most commonly pyrite.

When ASS are exposed to air the iron sulphides in the soil react with oxygen and water to produce a variety of iron compounds and sulfuric acid. Initially a chemical reaction, the process is accelerated by soil bacteria. The resulting acid can release other substances, including heavy metals, from the soil and into the surrounding environment.

If at all possible, do not disturb. ASS are benign when left in a waterlogged, undisturbed environment. Avoiding disturbance is often the most environmentally sustainable and economic option.

The impact of disturbing ASS

Without proper management, disturbing ASS can have serious environmental, economic, engineering, and health impacts, and can constrain development, construction and agriculture in affected areas. Activities that might disturb ASS in
high risk areas include:

• major earthworks - large scale excavations for canal developments and estates
• infrastructure earthworks - digging for clearways,
  roads and railways and
  excavating for sewage pipes, power lines and drainage channels
• maintenance dredging - boating channels and canal estates
• drainage channels - digging channels to manage water logging in agricultural areas, and
• lowering of the groundwater table - from low rainfall and over use of groundwater."