RFI - Attachment F - Engineering Report

15 May 2019


Issue – Acid Sulfate Soils

O1 of the Water Sensitive Design Code requires downstream ecosystems, properties and
infrastructure are not adversely impacted by either changes to flow, water quality or ecosystem
health caused by development; and

O25 of the Natural Hazards and Natural Resources Overlay Code requires Works do not disturb
acid sulfate soils or are managed to avoid the release of acid or associated metal contaminants.

The Stormwater Management Plan states:

The runoff from the basement subsurface drainage pump out sump will be treated to neutralise any pH
increases due to the acid sulfate soils prior to discharge from site. This system will be separate to the
treatment of the stormwater runoff from the exposed surfaces of the site which will be treated by the
filtration cartridges.

This comment implies that the development will require continual dewatering of groundwater. It is
unclear if the cone of depression that will be caused as a result of the dewatering will extend into
and convert Potential Acid Sulfate Soils into Actual Acid Sulfate soils and consequently release
metals to the receiving environment. Simply neutralising waters pumped from the basement does
not act to prevent release of metal contaminants from conversion of PASS to ASS, additionally,
neutralising of the water does not necessarily mean the pH and other chemistry requirements of
the receiving environment will remain unaffected.

Information Required

27.     Demonstrate how construction and operation of the development will be managed to
        prevent, or manage all the impacts associated with conversion of Potential Acid Sulfate Soils
        to Actual Sulfate soils as a result if dewatering required for the basement. The response must
        have regard to the ecological needs of the environment receiving any discharge waters or
        likely to be impacted by chemistry changes within the soil. The response must also have
        regard to the impacts of any changes in soil chemistry on the surrounding built environment
        as a result impacts to acid sulfate soil from dewatering.

28.     The response must be supported by an Acid Sulfate Soils Investigation prepared in
        accordance with the Queensland Acid Sulfate Soils technical manual: soil management
        guidelines and the Guidelines for sampling and analysis of lowland acid sulfate soils.

Response

An acid sulfate soils investigation has been completed on site with a report prepared. The report has been
appended to this response.

The Stormwater Management Plan has been amended to suit the outcomes of the Acid Sulfate Soils
investigation.




Excellence with Economy in Engineering                                                                       2
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