Compiled Reference Document - MCU25/0020 (As Published)

7.4          ASS Investigation Results
A total of 32 samples were recovered and assessed by pH field screen analyses. Existing soil pH (pHF)
ranged from 6.5 to 11, indicating mostly alkaline to slightly acidic conditions are present at the site. It is
noted that the alkaline conditions may be a result of previous ASS treatment of the fill materials
(i.e. addition of lime during the canal construction works), which was also evidenced by Acid Neutralising
Capacity (ANC) being present in all of the quantitative laboratory test results.
Quantitative laboratory analyses were completed on six samples using the Chromium Reducible Sulfur
(CRS) suite of testing to quantify the severity and nature of any acidity or potential acidity present in the
soil profile. Actual acidity was assessed using Titratable Actual Acidity (TAA), and potassium-chloride
extractable sulfur (SKCl) was used to assess the nature of the measured actual acidity. Potential acidity
was measured by the CRS method which specifically measures inorganic oxidisable sulfur. These
methods are set out in the QASSIT guidelines and associated ASS management documents. Based on
the nature of the proposed disturbance, an action criterion of 0.03%S (18 mol H+ per tonne) was
adopted for comparison with the combined actual and potential acidity results.
It is noted that the potential acidity exceeded the action criteria in two of the six samples tested, both of
which were in existing fill materials recovered from borehole BH1. However, all of the samples tested
returned ANC values exceeding the combined net acidity, which is inferred to be due to previous ASS
treatment.
The combined actual and potential acidity therefore did not exceed the action criteria in any samples.
ASS laboratory test results are summarised in Table B1 in Appendix B along with laboratory certificates.


7.5          Risk Characterisation
Laboratory test results indicate that the site soils above 4 m BGL have minimal acid generating capacity
given that the existing ANC levels exceeded the net acidity levels. As such, these soils do not require
specific management strategies under Queensland’s ASS legislation and guidelines. However, the soils
excavated below 4 m BGL, up to 7 m to 8 m BGL, would likely include ASS for which an ASS management
plan would be required and is included herein.


8.           Acid Sulfate Soil Management
The primary objective of this management plan is to provide a framework to allow the proposed works
to proceed without adverse environmental impacts related to the disturbance of ASS. To successfully
achieve this objective, the following issues shall be addressed:
    Confirmation of lime treatment rates for soils excavated from 4 m up to 8 m BGL by laboratory
     characterisation testing.
    Mitigation of risk associated with ASS present in disturbed soil (via neutralisation of disturbed soil
     and successful verification testing);
    Containment, testing and treatment (where necessary) of any water collected during the excavation
     and/or during the treatment processes; and
    Limitation of any alteration to the existing groundwater conditions and appropriate treatment of any
     collected groundwater before re-use, offsite discharge or disposal.




Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                                  21