RFI - Appendix 6 - Ground Water Response · MCU19/0117

Groundwater Dependant Ecology Preliminary Impact Assessment v1                         NCES REF: J000538
90 Beach Road, Noosa North Shore




4    ANTICIPATED WAVE POOL DISCHARGE IMPACTS

No information has been provided to NCES regarding the proposed water quality of the overflow
waters to be discharged from the wave pool holding tanks. It is unknown whether the wave pool
will host natural freshwater or whether it will host ionised water from salt or chlorine additives. The
TOD Water Management Plan presented with the application proposes that the discharge waters
will be treated to remove either salt or chlorine additives but offers no further details regarding
treatment methods and final water chemistry.

To avoid potential impact to the underlying groundwater and adjacent NP groundwater dependant
ecosystems, it will be imperative that the discharge waters are treated to a standard which
replicates natural rainfall water chemistry, or very close to same (i.e. freshwater). It is envisaged
the wave pool water will need to meet the QLD Water Quality Guidelines and or ANZECC Water
Quality Guidelines for recreational use for freshwater lakes hence will be of a reasonable freshwater
quality standard. Nonetheless the waters may require a degree of treatment to control bacterial
and fungal contaminants and this is normally achieved in pools via chlorine or salt dosing. Aerators
are typically employed in freshwater lakes and lagoons to maintain suitable dissolved oxygen levels
hence limit algal blooms and water quality deterioration.

Sustained release of salinized (from salt or chlorine additives) discharge water would represent
potential to influence local water chemistry which in turn may impact the composition and
abundance of local groundwater organisms as well as floras dependent upon the groundwater.
Given the sandy soils beneath the site the release of salinized discharge water may bear little
influence on the underlying upper soil structure itself but may impact the deeper underlying sandy
clay horizon from approximately 1.6m depth.

The proposed overflow dispersal method of direct soil infiltration from the holding tanks would be
expected to result in negligible surface run-off and upper soil profile through flow toward the wetland
given the inherently high permeability of the in-situ sandy soils present on Lot 500. Direct vertical
infiltration would be expected until approximately 1.6m depth upon interception of the sandy clay
horizon. The overflow infiltration may then be expected to be redirected down slope toward the
wetland as a source of groundwater recharge, as a result of the influence of the underlying sandy
clay horizon. Given the prevalence of dry open forest floristics (i.e. RE 12.9-10.4 – refer Section
3.4.1) in the far east of Lot 500 it can be inferred that the semi-impermeable layer at 1.6m depth is
of insufficient influence to foster the development of an overlying GDE.

Consequently, the wave pool over flow discharge would not be expected to significantly influence
the existing dry open forest floristics within Lot 500 on its migratory pathway toward the underlying
groundwater table.

Assuming the discharge water quality reflects natural rainfall water chemistry, or very close to it,
then the only perceivable impact to the adjacent groundwater dependant ecosystem would relate
to an increase in groundwater recharge volume on the fringe of the NP interface with the site. The
mostly likely case where such recharge may influence the overlaying vegetation would be where a
localised concentrated plume of throughflow intercepts the underlying groundwater table on the
fringe of the NP and subsequently raises the groundwater level beneath the vegetation for a
temporary period of time. Over time such impacts may influence the floristic composition of the
overlying vegetation, facilitating habitat conditions suited to more moisture tolerant species (i.e. wet
heath as compared to dry heath).

Given the sheer size of the local alluvial plain hence high capacity for through flow / recharge
dissipation across a broad groundwater table, and the in-situ wetland flora’s evolution in association
with a naturally fluctuating groundwater table over thousands of years, it is considered unlikely that
the minor number of overflow discharge days proposed in combination with the volumes proposed,
would tangibly influence the sustainability of the existing groundwater dependant ecosystem and
its constituents in the adjacent NP.




                                                            9                                       2020