Attachment 4 - Geotech Report · MCU23/0030

                                 50 NOOSA PARADE, NOOSA HEADS
                                 PROPOSED RESIDENCE

5.3        Groundwater
Groundwater seepage and saturated sand indicating the presence of groundwater inflow was encountered
during drilling between 1.8 m and 2.0 m BGL (~ RL 0.4 m to RL 0.6 m AHD). Standing groundwater was
recorded at a depth of 1.8 m BGL (measured during mid tide) in the borehole BH1 standpipe at completion of
drilling works. A groundwater sample was collected (following bore purging) and basic field water quality
parameters measured, prior to dispatch to Eurofins MGT for analysis of ASS related water quality
parameters. Results of the field and laboratory testing conducted on the groundwater sample from borehole
BH1 are given in Table 1.

Table 1: Summary of Groundwater Physio-chemical Parameters and Laboratory Testing

                   Parameter                                 Units                             BH1

                      SWL*                                  m BGL                               1.8

                        pH                                    pH                               6.52

                  Conductivity                              mS/cm                             0.626

                     REDOX                                    mV                               -227

               Acidity (as CaCO3)                            mg/L                              310

                    Sulphate                                 mg/L                               55

                     Chloride                                mg/L                              120

                Total Aluminium                              mg/L                               7.6

              Aluminium (Soluble)                            mg/L                              0.78

                    Total Iron                               mg/L                               9.0

                      Iron
                                                             mg/L                              0.49
                    (Soluble)
 Note: SWL denotes standing water level.


Test results indicate that the groundwater conditions are fresh (EC >1.5 mS/cm), and neutral (pH 6.5 - 8.5).
This is not uncommon for groundwater within such a setting near a tidal river.
Levels of chloride and sulphate are typical of estuarine groundwater conditions and do not indicate an added
source of sulphate from past oxidation of ASS.
Levels of total aluminium and iron are relatively high when compared to guideline levels for recreational
surface waters. It is noted that levels of total aluminium and total iron are likely to be mostly present as
suspended and colloidal sediment within the groundwater. Where dewatering takes place, appropriate water
treatment will be required to adjust pH and reduce total suspended sediment loads, thereby also reducing
iron and aluminium levels prior to discharge or release.
Groundwater is expected to be generally encountered during excavation of the lower half of the proposed
basement excavation, below about RL 1 m AHD. As the site is located directly adjacent to Noosa River, a
relatively consistent phreatic groundwater level is likely to be present which will rise and fall in sympathy with
tidal surface water movements. Groundwater is expected to be well recharged based on proximity to the
river and rates of infiltration into excavations below the water table would likely be high given the sandy
nature of the soil profile.




2 February 2023
Report No. 22500-001-Rev0                               6