Attachment 4 - Geotech Report · MCU23/0030

                                   50 NOOSA PARADE, NOOSA HEADS
                                   PROPOSED RESIDENCE

        4.0, then an ASS specialist should be engaged to determine whether there has been any significant
        environmental impact, why the pH has dropped and how the works may progress without undue
        environmental risk.
Once basement excavation has achieved the final design level a reinforced concrete structural slab and
perimeter walls will be constructed to seal the basement and achieve a ‘tanked structure’, whereby no
permanent dewatering will be required (during operation).

8.4       Water Quality Management
Erosion and sediment control measures are expected to be applied in accordance with current industry
practice to contain and control site runoff waters during construction. Runoff generated from the ASS
treatment area(s), including excavation activities, will be contained, tested and treated (if necessary) prior to
discharge or re-use onsite. Uncontrolled discharge of water from excavation areas, ASS treatment areas or
exposed works areas will not be allowed to occur.
If discharge from the site is required, performance criteria detailed in Table 5 must be met prior to release.
The Contractor shall be responsible for ensuring relevant water quality criteria are met prior to discharge.

Table 5: Water Quality Release Criteria

                       Indicator                                             Release Limit

                            pH                                                  6.5 - 8.5

               Total Suspended Solids                                          < 50 mg/L

                      Aluminium                                                < 0.2 mg/L

                            Iron                                               < 0.3 mg/L
                                                         No visible litter sheen or odour washed from the site
                Litter/Gross Pollutants
                                                         or deposited in waters downstream of any discharge

Groundwater extracted internally would be expected to require quality adjustment prior to off-site release to
stormwater. At a minimum, this is expected to involve buffering (increasing) of the pH to within the range 6.5
to 8.5 by the addition of a suitable agent, followed by the addition of a flocculant to reduce turbidity and
subsequent metal loads. Effective treatment of groundwater to achieve suitable release criteria requires
reasonable spatial and temporal consideration. Where required, a suitable dewatering sub-contractor should
be consulted to ensure appropriate outcomes can be achieved.
For basement excavations in similar conditions, groundwater treatment is normally carried out using a staged
process. The first stage involves adjustment of the pH, typically by mixing caustic soda solution within an
enclosed tank. As dissolved metals (mostly iron) typically ‘come out’ of solution as the pH is raised, thereby
increasing turbidity, a second stage of treatment is normally required. This involves reduction of the turbidity
by the addition of a flocculant.


9.0      LIMITATIONS
Your attention is drawn to the document Limitations, which is included in Appendix D of this report. The
statements presented in this document are intended to advise you of what your realistic expectations of this
report should be, and to present you with recommendations on how to minimise the risks associated with the
services provided by Tectonic for this project.




2 February 2023
Report No. 22500-001-Rev0                               18