Compiled Reference Document - MCU25/0020 (As Published)

4.           Method of Investigation
4.1          Fieldwork
Two boreholes (designated BH1 and BH2) were drilled across the site using a tracked vehicle mounted
rotary drill rig owned and operated by MK Drilling. Boreholes were drilled using a combination of solid
flight augering and cased washboring to target depths of 15 m and 16.5 m below ground level (BGL).
To enable an assessment of in situ soil strength, standard penetration tests (SPTs) were conducted at
regular intervals. SPTs were substituted for undisturbed (U50 tube) samples in firm clays. Shear vane
and pocket penetrometer testing were undertaken in undisturbed samples. Soil samples for ASS testing
were collected at 0.25 m depth intervals from both boreholes to depths of 4 m BGL.
A Class 18 PVC-U standpipe with factory slotted screen for the lower 1.5 m was installed in borehole BH1,
to a depth of 4 m BGL, encased in sand to about 1 m BGL, then sealed with bentonite above. Following
installation, the standpipe was purged of drilling fluid. At the completion of fieldwork the groundwater
level was measured, with samples collected to conduct field and laboratory testing. Results of the
groundwater monitoring are discussed in Section 5.3.
Borehole BH2 was capped near the surface using an ‘octo-plug’ and backfilled using compact drilling
spoil. Excess drilling fluid was spread across nearby site areas.
Investigation fieldwork was completed by experienced geotechnical engineers from Tectonic on
18 February 2025. The engineers were responsible for logging subsurface profiles in accordance with
AS1726 Geotechnical site investigations, supervising in situ testing, and recovering samples.
The positions of the boreholes were recorded using a handheld GPS, with a typical reported accuracy of
±3 m. Reports of the boreholes, along with explanatory notes, are presented in Appendix A.


4.2          Environmental Laboratory Testing
A total of 32 soil samples returned from the field investigation were dispatched to Eurofins MGT
(Eurofins), a NATA accredited environmental laboratory located in Murrarrie, Brisbane. All samples were
screened for ASS potential by measurement of field pH (pHF) and pH after oxidation (pHFOX) using 30 %
hydrogen solution.
Six samples also underwent quantitative analysis by the Total Actual Acidity (TAA) and Chromium
Reducible Sulfur (CRS) suite in accordance with ASS Method 23F (TAA) and 22B (CRS) laboratory
procedures. The pH was measured in KCl suspension by the analytical laboratory on samples submitted
for testing. ASS laboratory test results are discussed in Section 7.
One groundwater sample, recovered from the standpipe in borehole BH1, was tested for a range of
parameters relevant to design of the construction dewatering system. Groundwater test results are
discussed in Section 5.3.
Two soil samples were also tested for aggressivity towards concrete and steel structures. Aggressivity
test results are discussed in Section 5.4.
Environmental test certificates are attached in Appendix B.




Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                              6