RFI - Attachment D - Geotechnical Investigation Report · MCU25/0053

                                                                                                                                  PTG/01608 – 0001 – Rev0



                                                 Difference in pH following oxidation
                0
               0.5
                1
               1.5
                2
   Depth (m)




               2.5
                3
               3.5
                4
               4.5
                5
                     0           1                   2                  3                  4                   5                  6                   7
                                                                   pH difference (pH units)

Figure 6: Change in pH following oxidisation. The pink area indicates a change in pH of greater than 1.0 pH units.

After receiving the results of the above screening testing, one quarter of the samples were selected for follow up
Chromium Reducible Sulphur (CRS) suite testing. Samples were selected based on screening results that indicated a
large pH difference, a higher reactivity number and/or lower pHFOX results, whilst ensuring a representative spread of
sample depths and boreholes. A summary of the CRS testing is presented in Table 3 below. The detailed laboratory
results are attached in Appendix 3.

Table 3: Summary of Chromium Reducible Sulphur (CRS) test results
                                                                                                                      Acid
                                                                       Actual               Potential
                          Sample                                                                                   Neutralising        Net Acidity
   Borehole ID                                   Material              Acidity               Acidity
                         Depth (m)                                                                                  Capacity            (mol+/ t)
                                                                      (mol+/ t)             (mol+/ t)
                                                                                                                    (mol+/t)
                              0.5                  SAND                     13                    13                    0                     26
                              1.75                 SAND                      2                    11                    0                     13
               BH1            2.75                 SAND                     14                   41                     0                     55
                              3.25                 SAND                      8                   61                     0                    69
                              4.0                  SAND                      8                   77                     0                     85
                               1.5                 SAND                     <2                    11                    0                     11
                              2.25                 SAND                     <2                    11                    0                     11
               BH2             2.5                 SAND                     74                   16                     0                    90
                              3.0                  SAND                      4                    11                    0                     16
                              4.25                 SAND                      8                    51                    0                     58
                              2.25                 SAND                     <2                   14                     0                     14
                              3.75                 SAND                      4                    12                    0                     16
               BH3
                              4.0                  SAND                      6                   121                    0                    128
                              4.5                  SAND                      4                   58                     0                     63
                              1.25                 SAND                      2                    15                    0                     17
                              3.25                 SAND                     <2                   41                   <10                     37
               BH4
                               3.5                 SAND                     <2                   42                    121                   <10
                              4.5                  SAND                     <2                   40                    111                   <10
Note: The highlighted Net Acidity values have exceeded the relevant action criteria as outlined in the National Acid Sulfate Soil Guidelines, assuming less
than 1,000 tonnes of soil are disturbed below RL 5m AHD.




8 ACID SULFATE SOILS COMMENTS
AASS are typically indicated by pHF results below 4.0. None of the samples tested exceeded this criterion. The lowest
pHF result was 4.7 as recorded in the 2.75 m sample from borehole BH2.

Possible PASS are typically indicated by pHF results above 4.0 with a pHFOX result below 3.0 after a reaction to added
peroxide. The following samples tested met this criterion:
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