Attachment 4 - Geotech Report · MCU23/0030

                             50 NOOSA PARADE, NOOSA HEADS
                             PROPOSED RESIDENCE

4.0      METHOD OF INVESTIGATION

4.1      Fieldwork
Fieldwork was carried out on 13 January 2023 by an experienced environmental consultant from Tectonic.
Two boreholes, designated boreholes BH1 and BH2, were drilled within the site footprint. Borehole BH1
was drilled on the southern side of the property using a tracked vehicle mounted Hanjin DB8 rotary drill rig,
by a combination of solid flight augering and rotary wash boring techniques, to a depth of about 22 m below
ground level (BGL). In situ soil strength was assessed in BH1 by conducting standard penetration tests
(SPTs) at regular intervals. Pocket penetrometer (PP) testing was also undertaken on relatively
undisturbed auger cuttings and SPT samples of clay where appropriate.
Machinery access to the rear of the site was limited by the existing residence, therefore, borehole BH2 was
drilled on the northern side of the property using hand auger equipment, extending to a depth of 3.5 m BGL.
The hand augered borehole was unable to achieve full target depth (4 m BGL) due to borehole collapse in
wet sand at around 3 m BGL. Dynamic cone penetrometer (DCP) testing was completed adjacent BH2 for
assessment of the density/consistency of the soil profile to a depth of 4.5 m BGL.
All boreholes were logged in accordance with the AS1726-2017 Geotechnical Site Investigations.
Samples for ASS laboratory analysis were recovered at 0.25 m depth intervals to 4.0 m BGL in borehole
BH1 and to 3.5 m BGL in borehole BH2. ASS sampling protocols in the field were observed in order to
minimise potential for oxidation prior to laboratory testing and followed the National Acid Sulfate Soil
Guidance; National acid sulfate soils sampling and identification manual (2018).
A PVC standpipe was installed in borehole BH1 to a depth of 4.5 m BGL to enable measurement of
standing groundwater level and sampling. The groundwater level in the standpipe was measured after the
completion of the drilling works and prior to environmental sampling. Borehole BH2 was backfilled with
cuttings and slightly mounded at ground surface.
Borehole locations are illustrated in the Site Plan attached as Figure 1. Borehole logs (including SPT and
DCP results) together with explanation sheets describing the terms and symbols used are attached in
Appendix A.

4.2      Geotechnical Laboratory Testing
Selected soil samples were dispatched to a NATA accredited laboratory for geotechnical testing. Laboratory
testing was undertaken in accordance with Australian Standard AS1289 Method for Testing Soils for
Engineering Purposes and comprised one particle size distribution (PSD) analyses and Atterberg Limits to
assess material properties. Geotechnical laboratory test results are summarised in Section 5.4, and test
certificates are attached in Appendix B.

4.3      Environmental Laboratory Testing
Collected ASS and groundwater samples were dispatched to Eurofins MGT, a NATA accredited analytical
laboratory located in Brisbane. A total of 30 ASS samples were screened to assess field pH (pHF) and pH
after oxidation (pHFOX). Following the screen testing, 8 samples were selected to undergo quantitative
analysis by the Total Actual Acidity (TAA) and Chromium Reducible Sulfur (CRS) suite in accordance with
ASS Methods 23F (TAA) and 22B (CRS) laboratory procedures. ASS laboratory test results are discussed
in Section 7. ASS results are summarised in Table C1 attached in Appendix C, together with the
environmental laboratory test certificates.
Groundwater field and laboratory testing was also undertaken on a sample recovered from the borehole BH1
standpipe. Field quality parameters, including pH, electrical conductivity and REDOX were measured, and
the sample dispatched to Eurofins for analysis of dissolved and total aluminium and iron, chloride, sulfate,
and titratable acidity. Groundwater test results are summarised in Section 5.3. Groundwater test certificates
are attached in Appendix C.


2 February 2023
Report No. 22500-001-Rev0                             4