SUPERSEDED Reference Document

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ASS includes actual acid sulfate soils (AASS) and potential acid sulfate soils (PASS). AASS and PASS
are often found within the same soil profile, with AASS generally overlying PASS. AASS are highly
acidic resulting from the oxidation of soil materials that contained sulfides. PASS are soils that
contain iron sulfides or sulfidic materials, which have not yet been oxidised.

       6.6.2    Criteria for Evaluation of ASS

The criteria on which the results of screening tests (pH f and pHfox) were assessed as indicative of
possible AASS or PASS were based on the following:
•   pHf of less than 4 may indicate oxidation of sulfides has probably occurred in the past,
    indicating the presence of AASS. Three samples from Bore 1 from between 4.25 m and 5.25 m
    depth returned a pHf value of less than 4.
•   pHf between 4 and 5.5 indicates the soils are acidic. This may be as a result of limited oxidation
    of sulfides, but may also be as a consequence of the presence of organic acids. Generally
    samples tested from Bore 1 from 3.25 m to 5.50 m depth, except for the samples mentioned
    above, returned pHf values of between 4 and 5.5.
•   pHf of greater than 5.5 indicates the soil has little or no actual acidity; however this can be
    common with PASS materials or marine-influenced samples The majority of the samples
    tested from Bore 1, except for the samples mentioned above, and all samples from Bore 2
    returned pHf values equal or greater than 5.5.
The pHf test method does not detect acidity bound within sulfides, however the pH fox test gives
an indication of any potential acid release. Results of the pHfox are summarised as follows:
•   pHfox of less than 3, plus a pHfox reading at least one pH unit below pHf, plus a strong reaction
    with peroxide, strongly indicates the presence of PASS. All samples tested from Bore 1 from
    3.25 m depth and one sample from Bore 2 returned pHfox values of less than 3.
•    pHfox between 3 and 4 indicates the possibility of PASS material and a pH fox between 4 and 5
     may indicate the presence of small amounts of sulfide or fine carbonates. All the samples
     tested, expect the ones mentioned above, returned pHfox values of between 3 and 5.
To provide confirmation of the above qualitative testing, quantitative analytical testing was
carried out on selected samples, generally with the greatest difference in pH f and pHfox readings
and strongest reaction using the Chromium Suite method.
•    Chromium reducible sulfur (SCR) values where greater than 0.01 %S indicates a significant
     level of sulfide, and where greater than 0.03 %S then the soil has a potential acidity level
     exceeding the action criteria. Three samples tested from Bore 1 and one sample tested from
     Bore 2 returned SCR values greater than or equal to 0.03%S.
•    Titratable actual acidity (TAA) values greater than 18 mol/t indicates the soil has an acidity
     level exceeding the action criteria. None of the samples tested returned TAA values greater
     than 18 mol/t.

Generally, the action criterion from the chromium suite of tests, which triggers a requirement for
ASS disturbance to be managed, derived from the Soil Management Guidelines (Dear, et al., 2024)
are as follows:
•    Net Acidity (TAA + SCR + SNAS) of greater than or equal to 0.03.%S for soils greater than 1000
     tonnes of disturbance.




Proposed Residence                                                                   229073.00.R.001.Rev0
13 Mermaid Quay, Noosaville                                                                    June 2024