RFI - Attachment G - Acid Sulfate Soils Investigation

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The laboratory test results indicate that the samples tested are acidic. However, the measured acidity
from the upper fill is not likely attributed to sulfides (based on the SKCl results), but rather naturally
occurring acidity. Only the levels of acidity measured for the samples of the lower natural sands and
clays tested are likely to be attributed to sulfides (ie. AASS).

The acidity found naturally in non-ASS soils (ie. existing fill material) is not typically damaging to the
environment and indeed the ecology. Some environments are naturally acidic and support ecologies
adapted to those acidic conditions. Therefore, the complete treatment and neutralisation of the
naturally occurring acidic soils is considered not necessary. While these naturally acidic non-ASS soils
do not require specific treatment, appropriate management of the natural acidity should however be
carried out to reduce the risks of environmental impact in order to comply with the general
environmental duty of care where appropriate (ie. neutralisation of any acidic leachate).

It is recommended that a guard layer of neutralising agent (eg. aglime) be spread under and also over
the top of stockpiles of acidic soils (ie. existing fill material) to limit the generation of acidity from the
surface of the stockpile and any leachate emerging near the base. A nominal guard layer rate of
          2
2.5 kg/m is recommended. Reapplication of the guard layer will be necessary under areas of
repeated temporary stockpiling.

As for the AASS soils (ie. natural sands and clays), while any further changes to soil pH which can
occur upon sulfide oxidation which is often what leads to adverse environmental impacts is considered
to be low, these materials will require neutralisation treatment if they are to be disturbed.

‘Ag lime’ should be used as the preferred neutralisation material for the management of ASS as it is
usually the cheapest and most readily available product for soil neutralisation. This material is mildly
alkaline (pH of 8.5 to 9), of low solubility, and does not present any handling problems. The ‘ag lime’
comprises calcium carbonate typically made from limestone that has been finely grounded and sieved
to a fine powder.

Table 1 provides indicative liming rates for neutralisation of the AASS material likely to be disturbed.

Table 1: Indicative Liming Rates
                                                                                                  3
                    Material                            Lime Application Rate for Treatment (kg/m )
           Natural sands and clays                                         14.5
                                                                   3
Notes: Assumes a bulking up factor of approximately 1.5 tonnes/m


It is generally preferable if an ‘ag lime’ with a purity of 95% or better is used (ie. NV >95, where NV is
the neutralising value, a term used to rate the neutralising power of different forms of materials relative
to pure, fine calcium carbonate which is designated NV = 100). The above lime dosing rates should be
adjusted by a factor of 100/NV.




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