6. Noosa River DMP Ver0 (Combined)

 Project No. PG-5412                                                                                                             Page | 4
 January, 2023
 Ref: PG-5412, 2022-11-03, GR VER 3
 International Coastal Management – Acid Sulfate Soil Investigation - Noosa River Dredging Program, Noosa River, Noosa




     b) A pHFOX value at least one unit below pHF may indicate a potential ASS. The
        great the difference between the two measurements, the more indicative the
        value is of a potential ASS. The lower the final pHFOX value the better the
        indication of a positive result.

     c) If the pHFOX is less than 3, and the other two conditions apply, then it strongly
        indicates a potential ASS. The more the pHFOX drops below 3, the more positive
        the presence of sulfides.

Chromium Suite Analysis

Chromium suite analysis was undertaken to quantify existing soil acidity and potential
future acid generation from possible ASS. A summary of results is given in Table 1.

TABLE 1                            CHROMIUM SUITE TESTING SUMMARY

                                                      Nett Acidity (incl. AMC)                                     Liming Rate
 BH No.                 Depth (m)
                                                            (mol H+/t)                                            (kg CaCO3/t)
                          0.0-0.2                                <1                                                     Nil
     08
                          0.6-1.2                                <1                                                     Nil
                          0.0-0.3                                <1                                                     Nil
   08.1
                          0.5-1.0                                <1                                                     Nil
                          0.0-0.2                                <1                                                     Nil
   08.2
                          0.6-1.2                                <1                                                     Nil
                          0.0-0.25                               <1                                                     Nil
   0.8.3
                          0.5-1.1                                <1                                                     Nil
                          0.2-0.8                                <1                                                     Nil
   08.4
                          1.0-1.6                                <1                                                     Nil
                          0.0-0.2                                <1                                                     Nil
   08.5
                          0.4-0.8                                <1                                                     Nil


The results of the original testing indicated minimal levels of TAA (actual acidity),
low/minor levels of CRS (potential acidity) and in the main, significant levels of ANC
(soil buffering capacity).

These results were generally consistent with the results of the retesting at the hot spot
identified at BH08.

The results of the earlier laboratory testing have been reviewed. Considering the
proposed dredging methodology (ie. use of a cyclone separator) and the natural
buffering capacity of the sands, treatment for the acid sulfate neutralisation is not
likely to be required. This should be confirmed with validation testing at the time of
the dredging operation. Validation testing should be undertaken at a rate of 1 test
per 250m3 of disturbed material.

If the validation testing indicates the material is providing results above 18molH+/tonne
(ie. above the action criteria) the material should be neutralised at the time of
dredging in accordance with the existing soil management plan.