Acid Sulfate Soils Management Plan · OPW19/0205

Gympie Terrace Noosaville Pty Ltd



5.2         Groundwater
Groundwater inflow was encountered between approximately 1.2 m BGL and 1.5 m BGL during our
investigation. Table 2 summarises the groundwater conditions encountered on 14 November 2018.
Table 2: Summary of Groundwater Conditions

  Borehole Location           Groundwater Depth m BGL (~RL m AHD)

            BH1                                   1.5 (0.27)
            BH2                                   1.2 (0.55)
            BH3                                   1.5 (0.20)
            BH4                                   1.5 (0.17)

Groundwater measured in the standpipe in borehole BH1 was 2 m BGL (~RL -0.25 m) on 14 November
2018.
Given the site’s close proximity to the Noosa River, groundwater levels will likely vary with tidal influence and
prevailing weather conditions. Previous experience in the area indicates that the groundwater level can rise
close to the ground surface following periods of heavy or prolonged rainfall.
Provided that the retaining and dewatering system installed to support the basement excavation is able to
‘cut-off’ groundwater flows from the sands, seepage should be limited to flows emanating from sandy
materials in the base of the single level basement excavation. It should be possible to collect such seepage
by shallow gravel filled drains graded to a sump(s) from which the water could be removed from the
excavation to sewer or stormwater by submersible pumps (following treatment if necessary, depending on
the results of groundwater testing).

5.3         Potential Environmental Impacts
Potential environmental impacts associated with ASS disturbance during earthworks and construction for the
proposed development are summarised below in Table 3, along with the level of risk and management
strategies to mitigate the risk.
Table 3: Potential Environmental Impacts

 Activity         Issue                           Level of Risk to the Environment      Mitigation Strategies


                        Acid formation and
                         transport due to                                                Lime neutralisation treatment of
                         disturbance (by           These works present a medium risk.    excavated ASS and verification
                      excavation) of existing                                                       testing.
                       acidity and/or PASS.
 Proposed
 earthworks           Release of acidic and/or
                                                                                         Regular water quality monitoring
 and                   metals impacted waters
                                                         Medium to low level risk       and treatment (if required) prior to
 construction        from within excavations to
                                                                                                discharge off-site.
                          surface waters.
                                                                                          Regular groundwater quality
                   Potential adverse impacts
                                                                                         monitoring and development of
                  to groundwater quality due                   Low level of risk
                                                                                           contingency measures (if
                    to earthworks activities.
                                                                                                   required).

5.3.1        Summary of ASS Management Requirements
Provided the proposed ASS management procedures are effectively implemented and monitored throughout
the construction phase of the development, it is considered that there should be limited internal or external
ASS environmental impacts attributable to soils with existing or potential acidity.
The relevant issues, which are of significance when considering existing and potential acidity management
for the earthworks phase of this development, are:




J000799-003-R-Rev0                                                                                           Page 3