RFI - Attachment G - Acid Sulfate Soils Investigation

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    pHf of less than 4 indicates oxidation of sulfides has probably occurred in the past, indicating the
     presence of actual acidity. None of the samples tested 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. The majority of
     the samples tested returned pHf values of between 4.5 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. Only surficial fill material samples
     tested returned pHf results greater than 5.5.

The pHf test method does not detect acidity bound within sulfides; however the pHfox 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. The majority of the natural sand and clay
     samples tested in the upper 2.0 to 2.5 m from Bores 1 to 3 tested returned a pHfox value of less
     than 3.
    pHfox between 3 and 4 indicates the possibility of PASS material and a pHfox between 4 and 5
     may indicate the presence of small amounts of sulfide or fine carbonates. The remaining samples
     tested return returned a pHfox of between 3 and 3.6.

To provide confirmation of the above qualitative testing, quantitative analytical testing was carried out
on selected samples, generally with the greatest difference in pHf and pHfox readings and strongest
reaction using the Chromium Suite method.
    The chromium reducible sulfur values (SCR) 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 QASSIT guideline value. None of the samples tested returned SCR values greater
     than 0.03 %S.
    Where the total actual acidity (TAA) value exceeds 18 mol/t then the soil has an acidity level
     exceeding the QASSIT guideline value. All of the samples tested returned TAA values greater
     than 18 mol/t indicating the presence of acidity.

Where the sulfur in KCl extract values (SKCl) is less than 0.01 %S, then the soil has little or no history
of sulfide oxidation. A low SKCl combined with a low SCR indicates the soil is not an acid sulfate soil and
further development of acid is likely to be low. All of the fill samples tested, except one at the fill/natural
interface in Bore 4, returned SKCl values of less than 0.01 %S.

       7.2.3 Management and Treatment

Generally, the action criterion from the chromium suite of tests, which triggers a requirement for ASS
disturbance to be managed, derived from the QASSIT and Soil Management Guidelines 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.




Acid Sulfate Soils Investigation, Proposed Medical Centre                                   94967.00.R.001.docx
36 & 40 Hofmann Drive, Noosaville                                                                     May 2019