Reference Document - Dewatering Management Plan (For Stamping) MCU25/0053 & OPW25/0074

                                                                                                                   ADG Consulting Pty Ltd

                              The calculation results are based on the following parameters and known site‐specific conditions:
                                  Approximate length of excavation = 36 m
                                  Approximate width of excavation = 17 m
                                  Reduction in depth of groundwater across the excavation = 2.6 m (based on an approximate
                                   groundwater depth of 0.5 m AHD)
                                  Approximate depth of saturated thickness of unconfined aquifer = 10 m (conservative standardised
                                   approximation)

                              A conservative soil profile of fine to medium grained sands, has a hydraulic conductivity of approximately
                              8.2 m/day, or equivalent 0.0000949 m/sec (WA Calculator). The results of the calculation are shown in
                              Table 4 below, and provided in Appendix D.

                             Table 4 Dewatering extraction rate results

                                                           Output                                           Result

                                  Effective radius of pumping well (m)                                        14
                                  Dewatering radius of influence (m)                                          76
                                  Discharge rate (L/sec)                                                       8
                                  Discharge rate (L/hr)                                                     28,600
                                  Establishment of cone of depression (hours)                                102


                              Based on the above inputs, a groundwater flow rate of approximately 480 L/min or 28,600 L/hr has been
                              predicted for the development. Flow rates are predicted to be highest during initial drawdown of the
                              groundwater table within the basement excavation footprint and reducing to approximately 5 – 6 L/sec
                              following establishment of the cone of depression within the excavation. Flow rates may fluctuate due
                              to tidal variations, generally approximately ± 0.5 m, and will also be influenced by rainfall and surface
                              water collection within the basement excavation footprint noting the underlying predominantly sand
                              profile encountered during geotechnical investigations.

                              Regardless of the contractor employed, groundwater treatment systems should be installed with
                              capability for treating flow rates of up to 8 to 10 L/sec, as a contingency against higher than anticipated
                              flow rates exceeding the estimated 7 L/sec as a result of varying ground conditions across the extent of
                              excavation.

                              However, it should be noted that the WA Calculator provides a conservative assessment of inflows to an
                              excavation footprint based on area and depth but does not take account of the shoring wall, which will
                              inhibit lateral inflows to some extent. Also note that the cone of depression radius measure includes
                              water table depressions of 1 mm depth or more, so any significant depression of the water table is limited
                              to much closer to the dewatering spears or wells (generally within 3 to 10 m from the shoring wall in fine‐
                              medium grained sands, depending on density of the strata).
                      5.4     Dewatering duration
                              Dewatering will be necessary throughout the basement construction phase, which is expected to require
                              continual dewatering for approximately eight to twelve weeks. To minimise the potential impacts during
                              construction of short‐term dewatering, periods of active dewatering will be minimised as much as
                              possible. However, ADG notes that once active dewatering has commenced, dewatering will not be able
                              to be ceased until both: a) the basement hydrostatic uplift forces have been compensated to the
                              satisfaction of the consulting RPEQ engineer; and b) potential hydraulic loading on the external face of
                              the shoring system has been compensated to the satisfaction of the consulting RPEQ engineer and
                              shoring contractor.
                      5.5     Groundwater drawdown
                              Groundwater drawdown caused by dewatering has the potential to create settlement in unconsolidated
                              sediments and loose sands. It is noted that dilapidation reports for surrounding structures and services

                        ADG1777.25 Dewatering Management Plan_Rev0_01.05.25                                                       Page 11




Document Set ID: 23735664
Version: 1, Version Date: 12/05/2025