Sources of groundwater and subsoil contamination include:

Natural processes

• Dissolution of rock salt during the percolation of groundwater, which results in an increase in chlorides, sulphates, nitrates and iron ions concentration.
• Increase in salt concentration during evapotranspiration of shallow perched groundwater.
• Exposure of acid sulfate soils to oxygen through drainage or disturbance. Acid sulphate soils are widespread along the NSW coast.

Human activities related to waste management

• Industrial liquid waste stored in surface reservoirs, as in the case of Hinkley, CA mentioned earlier (Figure 2.6).
• Urban and industrial solid waste deposited in aboveground and underground repositories, as in the case of Love Canal mentioned earlier.
• Treated or untreated urban sewage deposited into the soil.
• Solid and liquid waste industrial byproducts e.g., tailings or flying ash deposited into the soil.
• Improperly disposed livestock waste.

Other human activities/Accidents

• Agriculture: use of pesticides, insecticides and fertilisers.
• Accidents during transportation or deposition e.g., derailing of a train transporting environmentally hazardous materials.
• Failure of engineering projects e.g., rupture of a sewage pipeline during an earthquake.
• Leakage of contaminants through their storage facilities/tanks.
• Uncontrolled waste disposal.