RFI - Revised Geo-Environmental Investigation · MCU25/0020

Testing indicates that the groundwater is alkaline and brackish. The unusually alkaline result for the
groundwater may be due to previous lime treatment of the fill materials (Ref. Section 7.4).
Chloride and sulfate levels are consistent with an estuarine groundwater system, however, the titratable
acidity levels were lower than expected which may be due to previous lime treatment as outlined above.
The filtered (dissolved) alluvium and iron concentrations of 7.5 mg/L and 1.1 mg/L, respectively, are well
above the acceptance criteria for release of water into the environment (Ref. Section 7.6). During
dewatering for the basement excavation, appropriate water quality treatment will be required to bring
iron and aluminium levels down to acceptable limits prior to discharge, and also manage pH and
turbidity. The advice of an experienced dewatering (and water quality treatment) sub-contractor should
be sought.


5.4          Aggressivity Laboratory Test Results
Table 3 below summarises the results of aggressivity laboratory testing conducted on two selected soil
samples recovered from the boreholes. The aggressivity laboratory certificates are presented in
Appendix B, with the ASS certificates.

Table 3: Summary of Aggressivity Laboratory Results

    Location &                                               Aggressive Soil Suite
      Depth             Material                                   Chloride       Sulphate      Resistivity
                                        EC (µS/cm)     pH
      (m BGL)                                                      (mg/kg)        (mg/kg)       (ohm.cm)
        BH1
                       Silty SAND          1100        6.3           1400            220            900
      7 – 7.45
         BH2
                       Silty SAND           94         6.8            6.8            31           11,000
      3.25 – 3.5

Soil aggressiveness test results have been assessed against Table 6.4.2(C) and Table 6.5.2(C) of AS 2159
2009 Piling Design and Installation. The results generally indicate ‘mild’ classifications for concrete
structures based on the samples tested for soils conditions ‘A’, with a ‘non-aggressive’ classification for
steel structures based on the sample tested from borehole BH2. Due to the low resistivity value, the
sample tested from borehole BH1 indicated a ‘severe’ exposure classification for steel structures.
Due to the proximity to the tidal Noosa River, ‘severe’ and ‘very severe’ classifications would be expected
for concrete and steel elements subjected to the ‘splash zone’ (e.g. revetment structures), respectively.




Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                                  9