Appendix 5. Geotechnical Engineering Report [As Published] · 132007.2399

October 2007                                  - 10 -                          077682076(AB)


Liming rates calculated from the laboratory analyses are summarised in Table C1, Appendix
C, along with a summary of the soil type. As shown in Table C1, calculation of liming rates
required for full neutralisation of combined actual and potential acidity indicates a range in
treatment rates from <1 kg.CaCO3/m³ to 99 kg.CaCO3/m³. These rates have been calculated
by using the net acidity values, without ANC, for the various depth intervals, include a factor
of safety of 1.5 and a bulk density of 1.8 tonne/m³.

Liming rates of less than 10 kg.CaCO3/m³ should be anticipated for fill materials and pale
coloured residual soils, whilst rates in the order of 50 kg.CaCO3/m³ and 100 kg.CaCO3/m³
could be expected for dark coloured natural clayey sands and silty ‘marine’ clays.

Delineation of the various layers in the field during excavation, and corresponding required
lime treatment rates, would be based upon visual observations and pH testing. As an
example, the ‘marine’ clays that are high level ASS would be identified by their dark colour
and soft consistency, together with pHFOX values of generally less than 2. Field pHFOX
screening would be a relatively simple procedure during construction earthworks.

5.6     Preliminary Recommendations

As there are likely to be significant earthworks in areas of ASS, and such works will also
likely disturb existing groundwater, there will be a requirement for detailed management of
these issues. The volume of disturbance and the level of treatment required indicates that
management of ASS at this site could be classified as Category XH (extra high level)
treatment in accordance with SPP2/02 Guideline - Table 4.

SPP2/02 Guideline requires that for Category XH treatment an environmental management
plan (EMP) must be provided. Furthermore, Section 9.15 of SP2/02 Guideline stipulates that
“this plan should provide for ongoing management and monitoring of the effects of
disturbance of ASS through the construction and operation of the project and describe the
construction schedules and environmental management procedures. The project should also
be staged so that the potential effects on any area disturbed at anyone time is limited and
easily managed.”

Preliminary recommendations on strategies to be included in the EMP are discussed as
follows.

5.6.1    Treatment of Excavated Soil

It is anticipated that most soils excavated from the site below RL 5 m AHD will be used as fill
above the water table and must therefore be managed by full neutralisation of existing plus
potential acidity. It is proposed that fine agricultural lime thoroughly mixed with the soil is
used as the neutralising agent. Lime treatment should be carried out in accordance with
Queensland Acid Sulfate Soil Technical Manual, Soil Management Guidelines (Ver 3.8 Nov.
2002).




                                     Golder Associates