Appendix B - Geotech and Acid Sulfate report - MCU19-0030

Gympie Terrace Noosaville Pty Ltd



7.0      ACID SULFATE SOIL ASSESSMENT
The development of ASS is commonly the result of marine or estuarine deposition of sulfate and iron bearing
sediments in the presence of an abundant source of readily decomposable organic matter resulting in the
deposition of pyrite. This pyrite is stable within the soil so long as anoxic conditions prevail. Oxidation of this
material produces acidic conditions and oxidation typically occurs as the material is exposed above the water
table by excavation, and by lowering the water table during dewatering processes.
Previous experience and available guidelines indicate that ASS are normally restricted in extent to recent
(Holocene to Pleistocene age) soil horizons deposited in a saline environment below RL 5 m AHD. The State
Planning Policy, July 2014 (SPP14) applies to land, soil and sediment at or below 5 m AHD where the
natural ground level is less than 20 m AHD. Within such areas the SPP14 applies to development involving
any of the following:

     Excavating or otherwise removing 100 m³ or more of soil or sediment; or

     Filling of land involving 500 m³ or more of material with an average depth of 0.5 m or greater.
The topography of the site is consistent with the above criteria (i.e. the surface elevation is below RL 5 m
AHD) and the proposed development involves excavations that would exceed the above trigger levels.
SPP14 is therefore applicable to the proposed development and an assessment of potential disturbance of
ASS is required.
The aims of this investigation were to:
     Conduct an ASS assessment in general accordance with SPP14 and the Queensland Sampling
      Guidelines
     Quantitatively identify the presence or absence of ASS across the site
     If necessary, assess the likely impact of the proposed development on ASS and groundwater
     If necessary, provide prudent management measures so that the release of acid leachate from
      disturbed soil and groundwater does not have significant adverse effects on the natural and built
      environment or human health.
Details and results of the ASS assessment are provided in Appendix C, along with laboratory test
certificates. The outcome of the ASS assessment is summarised in Section 7.1.

  7.1 ASS Summary
The results from this investigation indicate that low levels of existing acidity and potential ASS (PASS) are
distributed throughout the natural sands across the site.
The SPP14 Guidelines require that the level of treatment for management of ASS is based on treatment of
all existing and potential acidity. The results of the laboratory testing have been accumulated in an Acid-
Base Account to give the Net Acidity for each sample in units of mol H+/tonne as presented in Table C1.
This value has been calculated from sulfur trail potential acidity (SCr) plus actual acidity (TAA).
Liming rates have been calculated in kg CaCO3/m³ using a factor of safety (fineness factor) of 1.5 and an
assumed bulk density of 1.8 tonne/m3. Calculation of liming rates required for full neutralisation of combined
existing and potential acidity are presented in Table 4.
Table 4: Liming Rates
 Material Type                            Depth                         Treatment Rate

                                          0 m – 1 m BGL                 5 kg CaCO3/m³
 Natural Sands
                                          Below 1 m BGL                 15 kg CaCO3/m³


Given the anticipated volume of soils that will be disturbed and required lime treatment, management of



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