Geo-environmental Investigation · MCU25/0020

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
(SCR) 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. An ASS
management plan is therefore not required, and no lime treatment is necessary for soils above 4 m BGL.
Should excavations exceeding 50 m3 extend below 4 m BGL, Tectonic should be notified to assess the
implications associated with ASS and treatment strategies.


7.6          Water Quality Management
Erosion and sediment control measures are expected to be applied in accordance with current industry
best practice to contain and control site runoff waters during construction.
Water collected by dewatering works and from other site areas is to be contained, tested and treated (if
necessary) prior to discharge off-site or re-use on-site. Uncontrolled discharge of water from excavation
areas, or exposed works areas must not be allowed to occur. If discharge from the site is required,
performance criteria detailed in Table 6 overleaf below must be met prior to release.




Geo-environmental Investigation Proposed Residence
11 March 2025 | 25040-001-Rev0                                                                              21