Here come da tunnels, page-42

20.7.3 Acid Sulfate Soil and Rock

As noted in Section 20.5.3, there is a high likelihood of Melbourne Metro encountering potential and actual acid sulfate soil and acid sulfate rock. This means that a high proportion of the spoil excavated from the tunnels (about 221,000 m³) would be expected to be acid sulfate soil or acid sulfate rock. The potential impacts from disturbing acid sulfate soil and acid sulfate rock include human health impacts, adverse effects on aquatic environments and the corrosion of concrete and steel infrastructure from acidified groundwater.
Acid sulfate impacts would be managed in accordance with EPA guidelines and the Industrial Waste Management Policy (Waste Acid Sulfate Soils). This would include implementing an environmental management plan that includes:

Identification of the location and extent of any acid sulfate soil and rock (primarily Fresh Melbourne
Formation rock and Coode Island Silt) within the project boundary

Assessment of the potential environmental risks of disturbance

Identification of suitable sites for the re-use or disposal of any acid sulfate material.

Prevention of acid generation is the preferred management option. However, a number of off-site waste management options are available for treating acid sulfate material extracted during tunnelling activities, where prevention is not possible. These options include:

Treating spoil with limestone

Inhibiting oxidation of pyrite in spoil by underwater disposal or by encapsulation within a water saturated engineered cover

Preventing leaching of pyritic spoil by encapsulation within a long-term containment system designed to limit infiltration.

Further testing would be undertaken during the project’s detailed design and construction phases to determine the most effective management option.

Acid sulfate soil can only be disposed of or re-used on sites that have an EMP approved by the EPA or at a landfill with the appropriate licence. On-site re-use of this material is not considered practical.

20.7.4 Temporary Stockpiling of Spoil

The Spoil Management Plan for Melbourne Metro would require spoil to be removed to an off-site location in an expeditious manner and would require pre-categorisation of spoil where practical. Temporary stockpile areas would be provided in the event that unexpected conditions or spoil materials are encountered. It is envisaged that these areas would be located at all construction work sites, with larger facilities at the western portal, Arden station and the TBM southern launch site (Domain or Domain and Fawkner Park).
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Any off-site facility accepting acid sulfate soils and rock would need to have an EPA-approved Environmental Management Plan in place.

Sound like anyone, we know.