Mining impacts and rehabilitation: HSC Earth and Environmental Science Module 8
“Analyse the environmental impacts of mining and waste disposal and the methods used to manage and rehabilitate them, including but not limited to acid mine drainage, tailings, land degradation and site rehabilitation in the Australian context”
Mining disturbs large areas (open-cut pits, waste dumps, subsidence), destroys habitat and heritage, and generates waste. Acid mine drainage, formed when exposed sulfides oxidise to sulfuric acid, dissolves heavy metals and can pollute waterways for decades after closure. Tailings dams store toxic processing slurry and risk failure. Rehabilitation reshapes landforms, replaces stockpiled topsoil, revegetates with natives and manages water quality, and in Australia is enforced through bonds and completion criteria. It works best when planned from the start, though some damage cannot be fully reversed.
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What this dot point is asking
NESA wants you to analyse the environmental damage caused by mining and waste disposal and the methods used to manage and repair it. You need specific impacts (land disturbance, acid mine drainage, tailings, water and dust), the techniques used to rehabilitate sites, and Australian examples. This builds on the ore deposits of Module 5 and the sustainability theme of Module 8.
The answer
Mining extracts the ore deposits described in Module 5, but it disturbs large areas of land, generates huge volumes of waste, and can pollute water and air for long after the mine closes. Modern management aims to minimise these impacts during operation and to rehabilitate the site afterwards, increasingly under legal requirements and financial bonds.
Land disturbance
Open-cut mining, common for Australian coal and iron ore, removes vegetation, soil and overburden to reach the ore, leaving large pits and waste-rock dumps. This destroys habitat (including, in some cases, Aboriginal cultural heritage), alters drainage and landforms, and exposes fresh rock to weathering. Underground mining disturbs less surface but can cause subsidence, where the ground sags as worked-out voids collapse.
Acid mine drainage
When sulfide minerals such as pyrite are exposed to air and water during mining, they oxidise to form sulfuric acid. This acid runs off, dissolving heavy metals from the rock and lowering the pH of nearby streams and groundwater, killing aquatic life and contaminating water supplies. Acid mine drainage can continue for decades after a mine closes, making it one of the most persistent mining impacts. It is managed by sealing sulfide waste away from air and water, neutralising acid with lime, and treating discharge.
Acid mine drainage is the acidic, metal-rich runoff produced when sulfide minerals exposed by mining react with air and water to form sulfuric acid. Because the reaction continues as long as sulfides are exposed, it can pollute waterways for decades after a mine closes, which is why it is a major focus of mine planning and rehabilitation.
Tailings and waste
Processing ore produces tailings, a slurry of finely ground waste rock, water and residual chemicals, stored behind dams. Tailings dams can fail catastrophically, releasing toxic sludge, and even intact they can contaminate groundwater and harm wildlife. Mining also generates large volumes of waste rock and, for coal, methane and dust. Safe long-term storage of tailings is a central challenge of resource management.
Rehabilitation
Rehabilitation aims to return mined land to a safe, stable and productive state. Typical steps are reshaping the landform to blend with surroundings and control erosion, replacing stored topsoil (which is stripped and stockpiled before mining), revegetating with native species, and managing water quality until acid drainage and contamination subside. In Australia, mining companies are generally required to lodge rehabilitation bonds and meet legal completion criteria before a site is signed off. Some former mines become farmland, wetlands or conservation areas; not all damage, particularly to deep aquifers and to Aboriginal heritage, can be reversed.
Consider a coal open-cut in the Hunter Valley. Before mining, topsoil is stripped and stockpiled. During mining, overburden is removed and stored, the coal is extracted, and water and sulfide waste must be managed to prevent acid drainage. After mining, the pit and dumps are reshaped, topsoil and native vegetation are replaced, and water is monitored until it meets standards. Analysing this shows that rehabilitation is most effective when planned from the start (saving topsoil, isolating sulfides) rather than attempted only at closure, which is the key judgement markers look for.
- Forgetting that acid mine drainage persists
- It can pollute waterways for decades after closure; it is not a problem confined to the operating life of the mine.
- Treating rehabilitation as full restoration
- Rehabilitation returns land to a safe, stable, useful state, but some impacts (deep aquifers, cultural heritage) cannot be fully reversed.
- Ignoring topsoil
- Stripping and storing topsoil before mining is essential for later revegetation; without it, rehabilitation largely fails.
Try this
Q1. Explain how acid mine drainage forms and why it can persist long after a mine closes. [3 marks]
- Cue. Exposed sulfide minerals oxidise with air and water to sulfuric acid that dissolves metals; the reaction continues as long as sulfides remain exposed, so it persists for decades.
Q2. Analyse why successful rehabilitation depends on actions taken before and during mining, not only after closure. [4 marks]
- Cue. Stripping and storing topsoil and isolating sulfide waste during operation enable revegetation and prevent acid drainage; leaving rehabilitation to closure makes restoring soil and water quality far harder.
Exam-style questions
Questions in the style of NESA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
2024 HSC-style5 marksComplete the table to justify how TWO reclamation methods could be used to address TWO environmental concerns associated with non-operational mines.Show worked answer →
For 5 marks, pair each environmental concern with a reclamation method and justify why each method is effective at addressing that concern.
Concern 1: soil erosion and river sedimentation from open pits. An abandoned open pit leaves bare, unstable ground exposed to erosion, and the eroded sediment washes into local waterways. Reclamation method: backfill the pit with waste rock and other material, then plant native vegetation. Justification: backfilling removes the exposed face and the plant roots bind and stabilise the soil, minimising erosion and keeping sediment out of waterways.
Concern 2: collapse of offshore mining infrastructure damaging ecosystems. Leaving an offshore oil rig to rust and collapse would destroy the ecosystem that has established on its submerged structure. Reclamation method: remove the above-water portion of the rig and recycle it onshore, while leaving the submerged section as an artificial reef. Justification: this prevents a damaging collapse yet preserves the established reef community.
Marks reward an explicit link from each method to why it solves its concern, not just listing methods.
2021 HSC-style1 markA diagram shows a method for small-scale mining of a lake to extract gold (a barge with a pump and sluice box dredging the lake bed). Which rehabilitation strategy would be the most environmentally sustainable at the conclusion of mining? A. Fill in the holes and replant native aquatic vegetation. B. Introduce more pollution tolerant species of fish and plants. C. Fill in the lake and use the reclaimed land as playing fields. D. Cover the area with a thick layer of clay to seal it against leakages.Show worked answer →
The correct answer is A: fill in the holes and replant native aquatic vegetation.
The most environmentally sustainable rehabilitation restores the disturbed site as closely as possible to its original, self-sustaining ecosystem. Filling the dredged holes repairs the lake bed, and replanting native aquatic vegetation re-establishes the local habitat and food web so the lake ecosystem can recover and persist.
B introduces non-native pollution-tolerant species, which can disrupt the ecosystem; C destroys the lake habitat entirely by converting it to playing fields; D seals the area artificially rather than restoring a living ecosystem. Only A rebuilds the natural system.