SUPERSEDED Reference Document

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The action criterion was exceeded in the natural sand samples tested from Bore 1 and in the
clayey sand fill from Bore 2, thus management of ASS disturbance will be required.

       6.6.3    Management and Treatment of ASS

Based on the laboratory test results the clayey sand fill and the natural sand are considered to
contain PASS, having the potential to generate sulfuric acid when disturbed and exposed to
oxygen. The sand if disturbed will require neutralisation treatment in order to reduce the risk of
oxidation and consequent reduction of pH to produce acidic conditions potentially damaging to
the environment and to buried steel and concrete.

Neutralisation treatment of ASS generally involves the application and mixing of lime to ASS
material either placed on a treatment pad, or as part of the excavation process.

‘Ag lime’ should be used as the preferred neutralisation agent 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. ‘Ag
lime’ comprises calcium carbonate typically made from limestone that has been finely grounded
and sieved to a fine powder.

Table 6 provides an indicative liming rate for neutralisation of the ASS material likely to be
disturbed.

Table 6: Indicative Liming Rates
 Material                                           Lime Application Rate for Treatment
                                                    (kg/m3)
 Clayey sand fill                                   2
 Natural sand                                       5.5

A guard layer of ‘ag lime’ should also be applied over the base of the basement excavation. This
guard layer of lime should be applied at a rate of 2 kg/m2.

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.

Temporary dewatering for basement excavation will result in the localised lowering of the water
table. How the groundwater will be extracted and treated will depend on the groundwater
dewatering contractor at the time of construction. It is assumed dewatering will probably
comprise a ring of dewatering spears around the outside of the sheetpiles.

It should be anticipated that for a properly designed and constructed retention and dewatering
system would result in minimal drawdown of the groundwater outside of the excavation and
mitigate the extent of aeration of permanently saturated potential acid sulfate soils. The
dewatering contractor would need to develop their own dewatering management plan to ensure
negligible environmental impact.




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