OPW16-0020 information request · OPW16/0020

                                                                                OPW16/0020



Information Required
2      Demonstrate whether any design amendment is possible to limit necessary
       excavations to be shallower than 2m below the existing ground level, and therefore
       avoid the identified medium acid sulphate soil risks.

Issue
Specific Outcome O6 of the Water Sensitive Design Code requires that:
Run-off that leaves the site is treated so as not to adversely impact on the ecology and
hydrology of downstream environmental flows.

And Specific Outcome O22 of the Natural Hazards and Natural Resources Overlay Code
outlines that:
Works do not disturb acid sulfate soils or are managed to avoid the release of acid or
associated metal contaminants

Common metal contaminants released from oxidation of Acid Sulfate Soil via drawdown
from dewatering are Iron and Aluminium. Table 3.4.1 of the ANZECC guidelines outlines
that in order to protect 80% of aquatic species, Aluminium and Iron should not be able to be
detected in the receiving waters.

The application outlines that waters will continually need to be pumped until such time as
the house is properly settled. There is no indication of the maximum depth of excavation for
foundations and pipework , the depth groundwater’s will need to be pumped, or how far the
cone of depression of the groundwater drawdown will extend. This information is necessary
to determine the full extent where oxidation and therefore new metal release into ground
water is possible.

There is no information regarding the existing concentration of metals in the groundwater
from previous acid sulphate soil disturbance and whether there is an associated possibility
for release of those metal contaminants, existing or potential, from groundwater into the
receiving waters.

Additionally, there is no detail provided whether there will be continual dewatering along
bedding material surrounding pipework after pumping for settlement of the house ceases.

Information Required
3      Provide longitudinal section plans showing the maximum depth of excavations
       needed in relation to the medium risk acid sulphate soil horizon and groundwater
       fluctuation zone and detail the expected cone of depression.
4      Detail management measures to prevent any continual dewatering via the bedding
       material surrounding the house and pipework.
5      Demonstrate how the development will not increase oxidation of Potential Acid
       Sulfate soils within the expected cone of depression via dewatering for house
       settlement, or continual dewaters due to bedding material surrounding the building
       and pipework.
6      Demonstrate how there will be no release of metals within groundwater that will
       affect Aquatic Ecosystem Environmental Values in the receiving waters.

Issue
The Acid Sulfate Soil Investigation by Core Consultants recommends for an Acid Sulfate
Soils Management Plan.




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