Dewatering Management Plan

                                                                                      ADG Consulting Pty Ltd


5    Dewatering methodology
5.1 Basement excavation and shoring
     It is understood that the excavation/basement perimeter will be stabilised along the perimeter of the
     basement excavations using anchored interlocking steel sheet piles and/or contiguous soldier pile wall.
     Excavations to facilitate the basement construction will extend to a maximum of approximately 3.8 m
     below ground level (bgl) to approximately RL‐1.4 m Australian Height Datum (AHD; assuming local
     existing surface levels of around 2.4 m AHD and a basement slab in the order of 0.35 to 0.4 m thickness).
     Localised deeper excavations may be required for the construction of the car stacker overrun pit and
     other structural elements (i.e. footings and pile caps), where required.

     Groundwater seepage was historically recorded at a depth of approximately 2.1 mbgl (equating to an
     approximate elevation of approximately 0.3 m AHD), during preliminary geotechnical investigations on
     the site (Global 2016). No further recent data has been supplied for review in preparing this DMP,
     however based on ADG’s experience on nearby sites in the locality in recent years, it is anticipated that
     groundwater should be expected at or around 1.0 m AHD, +/‐ 0.5 m, depending on tidal and seasonal
     rainfall conditions. Dewatering will therefore be necessary to allow the basement to be constructed in
     dry conditions.

     It is expected that the development will include a ‘tanked’ basement to prevent the requirement for a
     permanent dewatering facility at the site.
5.2 Groundwater extraction
     Dewatering is anticipated to be undertaken using a series of 6.0 m length, 40 mm diameter PVC spears
     installed to 6.0 m in depth at 1.5 m intervals around the internal and external perimeter of the basement
     excavation.

     The basement excavation must be dewatered to a minimum of approximately 1.0 m below the deepest
     point of excavation to allow construction to be undertaken in dry conditions. The water table is therefore
     expected to be lowered by a minimum of approximately 2.7 m to around ‐2.4 m AHD. It is expected that
     the cone of depression in the standing groundwater table will be predominantly limited to within the site
     boundaries.

     It is proposed that the development will include a ‘tanked’ basement to prevent the requirement for a
     permanent dewatering facility at the site. Similarly, no permanent groundwater dewatering is proposed
     or likely to occur as a result of the development, with all services and pipework proposed to be situated
     above standing groundwater elevations (that is, at elevations above 0.3 mAHD) and subject to the
     nominated hold points at Section 5.7. Where any deviation is proposed from this arrangement, all
     pipework within the saturated zone, that outlets direct to waterways must be fitted with buried
     headstocks at suitable intervals to prevent ongoing dewatering of groundwater along pipework bedding.
5.3 Extraction/discharge rates and volume
5.3.1 Dewatering extraction calculation based on subsurface soil profile
     The dewatering extraction rate, area of influence and cone of depression has been estimated using the
     Western Australian Department of Water and Environmental Regulation Cone of Depression Calculator.

     The calculation results are based on the following parameters (as provided by SCG) and known site‐
     specific conditions. The following is applicable to the basement excavations spanning across the lot:

           Approximate length of excavation = 23 m
           Approximate width of excavation = 17 m
           Reduction in depth of groundwater across the basement footprint/excavation = 2.7 m
           Approximate depth of saturated aquifer = 10 m (standardised conservative value applied)



ADG1786.25 Dewatering Management Plan_Rev0_20.02.25                                                      Page 9