Geo-environmental Investigation · MCU25/0020

5.           Investigation Findings
5.1          Regional Geology
The 1:100,000 Series Laguna Bay Surface Geological Map (Sheet 9545, Compiled 11 July 2018) indicates
that the site is immediately underlain by historic reclamation fill, inferred to be associated with the
adjacent canal construction (Ref. extract in Text Figure 7). Natural soils below are indicated to be
Quaternary age, active stream channel and low terrace deposits comprising “sand, gravel, silt and clay”,
which are inferred to be underlain at depth by sedimentary strata (mostly sandstone and siltstone)
associated with the late Triassic to Jurassic age Tiaro Coal Measures.


                                                         Approx. Site location




                        Text Figure 7: Extract from Laguna Bay Surface Geology Map


5.2          Subsurface Conditions
A summary of the subsurface conditions encountered in the boreholes is given below, with more detailed
descriptions provided in the borehole reports in Appendix A.
Relatively consistent subsurface materials were encountered in the boreholes, summarised as follows:
    Existing Fill – mostly loose to medium dense, silty sand, with varying gravel, cobble and deleterious
     material (e.g. metal, organics, cobbles pipe fragments etc.) content to depths between 2.3 m and 3 m
     BGL; then
    Alluvial/Estuarine Materials – mostly medium dense to very dense sands, including indurated sand
     (‘coffee rock’) to depths between 13.2 m and 13.6 m BGL, then mostly stiff clays to the borehole
     termination depths. It is noted that a firm sandy/silty clay layer was intersected in both boreholes
     between about 4.8 m and 5.5 m BGL, with some loose natural sands above. A deeper firm clay layer
     was also encountered in borehole BH1 between about 13.2 m and 14 m BGL.
A summary of the subsurface conditions encountered in the boreholes is given in Table 1 overleaf.




Geo-environmental Investigation Proposed Residence
11 March 2025 | 25040-001-Rev0                                                                             7