Attachment H - Acid Sulfate Soils Assessment

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                              PROPOSED COMERCIAL & RESIDENTIAL DEVELOPMENT
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Document Review
   Document No.             Revision       Prepared By       Reviewed By             Date Issued

           002                 0           Mark Thomson      Ashley Davey           26 May 2021




Report Distribution
   Revision             Method of Delivery                             Issued To
                                                                     Mr Chris Wright
       0                      Electronic
                                                                ([email protected])
                                                                   Mr Mick Sheppard
       0                      Electronic
                                                          ([email protected])




Prepared By:                                                  Reviewed By:




Mark Thomson BSc, CPESC 7057                                  Ashley Davey RPEQ 8159
Senior Environmental Scientist                                Principal Geotechnical Engineer




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                                             PROPOSED COMERCIAL & RESIDENTIAL DEVELOPMENT
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Table of Contents

1.0     INTRODUCTION ........................................................................................................................................................ 1

2.0     INFORMATION ON ACID SULFATE SOIL ............................................................................................................... 1

3.0     SITE DESCRIPTION .................................................................................................................................................. 1

4.0     PROPOSED DEVELOPMENT ................................................................................................................................... 2

5.0     REGIONAL GEOLOGY ............................................................................................................................................. 4

6.0     GEOTECHNICAL SITE INVESTIGATION ................................................................................................................. 4

7.0     REGIONAL ASS MAPPING ...................................................................................................................................... 5

8.0     APPLICATION TO LOCAL COUNCIL REGULATION .............................................................................................. 6

9.0     RECOMMENDATIONS .............................................................................................................................................. 6

10.0 LIMITATIONS ............................................................................................................................................................ 6



TEXT FIGURES
Text Figure 1: Site Location (courtesy Noosa Council Interactive Mapping) ....................................................................... 2

Text Figure 2: Proposed development layout (Archicology, Project 20531, DWG No. SD01) ............................................. 3

Text Figure 3: Section C through building (Archicology, Project 20531, DWG No. SD13) .................................................. 3

Text Figure 4: Extract from Gympie Special Geology Map.................................................................................................. 4

Text Figure 5: Extract from Department of Environment & Resource Management ASS Risk Map.................................... 5



APPENDICES
APPENDIX A
Limitations




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1.0      INTRODUCTION
Tectonic has undertaken an acid sulfate soil (ASS) assessment for a proposed commercial and residential
development at 30 & 32 Doonella Street, Tewantin. This report summarises the site conditions and
associated ASS hazard posed by the proposed works, to address Items 21 and 22(c) of Noosa Council
(NC) information request (Ref.: MCU21/0013 & OPW21/0031) and presents the results of our assessment
taking into consideration State guidelines and NC requirements pertaining to ASS.

In summary, the local geology, as identified by geotechnical investigation (Tectonic Report No. 18151-001,
dated 22 June 2018), primarily consists of residual soil associated with the Triassic to Jurassic age Myrtle
Creek Sandstone, which is not associated with the formation and occurrence of ASS. This understanding is
supported by published geological and ASS risk mapping.
Proposed site development will not generally involve disturbance of soil below an elevation of RL 5 m AHD,
however some minor disturbances to RL 4.4 m AHD may occur for construction of the lift overrun, water
detention tanks and a bio-retention basin. These works are expected to disturb only residual (non-ASS) soil,
totalling a relatively small total volume (~60 m3), and would therefore present negligible risk of ASS related
impact. Based on the limited extent of excavation below RL 5 m AHD, and presence of residual soils, the
proposed development is deemed to conform with performance outcome PO1 of NC’s ASS Overlay Code
(i.e. development does not disturb ASS). No further site assessment or specific management measures
regarding ASS are warranted for the proposed works.


2.0      INFORMATION ON ACID SULFATE SOIL
ASS is common in low-lying coastal areas of Queensland, typically in Holocene to Pleistocene age alluvial
sediments located below RL 5 m AHD. Such areas are often characterised by the presence of estuaries,
swamps, floodplains, salt marshes and mangroves, primarily occurring in estuarine based alluvial soil.

ASS affected soils contain iron sulfides, most frequently pyrite, which, when exposed to air can oxidise to
form sulfuric acid. Existing acidity attributed to the historic oxidation of iron sulfides may also be present
because of previous exposure of ASS material either by human interference or by natural processes.

When these soils are maintained in their natural setting (generally anaerobic conditions below the
groundwater table or sea level), the iron sulfides are unable to oxidise, therefore the ASS remains in a stable
state, and in equilibrium with the surrounding environment. However, where disturbances such as civil
construction or development expose ASS to aerobic conditions, the iron sulfides are able to oxidise and form
sulfuric acid, resulting in the soil becoming acidic.

The resulting creation of large volumes of acidity can occur rapidly, resulting in significant impacts to local
waterways, sensitive terrestrial environments, or in extreme cases, public health.


3.0      SITE DESCRIPTION
The subject site occupies two parcels of land described as Lot 32 on RP893427 (#30) and Lot 903 on T1631
(#32), situated on the northern side of Doonella Street, Tewantin. The site has an approximate 60 m
frontage to Doonella Street on its southern side and is otherwise bounded by commercial and residential
properties to the north and west and at-grade carparking to the east.
Ground surface elevations across the site range from RL 5 m to RL 9 m AHD and the property is mapped as
ASS Area 2, under NC’s ASS Overlay Code. Topographically, the site is situated on the flank of a gentle
hillslope with the ground surface sloping in a south/south-easterly direction toward Doonella Street.

The site location and general setting are illustrated in Text Figure 1 overpage.




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Text Figure 1: Site Location (courtesy Noosa Council Interactive Mapping)


4.0      PROPOSED DEVELOPMENT
Design drawings prepared by Archicology Pty Ltd (Ref. Project 20531, Drawing Nos. SD01 to SD17, dated
14/05/2021) indicate that the proposed development will comprise a complex of two to three level
commercial and residential buildings, incorporating a partially in-ground carpark level on the ground floor
(Ref. Text Figure 2 overleaf).
The carpark level will extend to within about 2 m to 5 m of site boundaries and will have a finished floor level
of RL 5.7 m AHD, for which bulk excavation and soil disturbance to about RL 5 m AHD is expected for
construction of the slab and footings.

Minor excavations below RL 5 m AHD will be required for construction of the lift overrun pit, water detention
tank and bio-retention basin. These excavations will occur above RL 4.4 m AHD and are expected to total
no more than about 60 m3.

Text Figures 2 and 3 over page show the proposed development layout and a section through the building.




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                              C




Text Figure 2: Proposed development layout (Archicology, Project 20531, DWG No. SD01)




Text Figure 3: Section C through building (Archicology, Project 20531, DWG No. SD13)




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5.0      REGIONAL GEOLOGY
The 1:100,000 scale Gympie Special Geological Map (Sheet 9445 and Part 9545, DME 1999) indicates that
the site is underlain by the late Triassic to Jurassic age Myrtle Creek Sandstone (denoted as RJdm). The
Myrtle Creek Sandstone formation typically comprises quartzose sandstone, siltstone, shale and
conglomerate.
This formation is not associated with the formation or occurrence of ASS.

An extract from the geological map is shown in Text Figure 4 below. Brown stippling indicated on the
geology map is indicative of a deep weathering profile, whereby the rock strata have generally weathered to
soil materials (typically clays for this unit) over geological time.


                                                                          RJdm - Myrtle Creek Sandstone

                                                                          Age         Late Triassic - Early Jurassic

                                                                                      Quartzose sandstone,
                                                                          Lithology   siltstone, shale conglomerate,
                                                                                      coal; weathered

                                                                          Dominant
                                                                                      ARENITE-MUDROCK
                                                                          Rock




Text Figure 4: Extract from Gympie Special Geology Map


6.0      GEOTECHNICAL SITE INVESTIGATION
A geotechnical investigation for the proposed development was completed by Tectonic in June 2018
(Tectonic Report No. 18151-001 Rev0). Site investigation comprised the drilling of five boreholes using a
4WD mounted rotatory drill rig to depths of between 3 m and 6 m below ground level (BGL).
The encountered subsurface conditions typically comprised:

       Fill Material – typically comprising 0.25 m to 0.75 m depth of loose to medium dense silty/clayey
        sands and gravels; overlying

       Inferred Residual Soil – comprising stiff to very stiff, natural silty/sandy/gravelly clays derived from
        weathering of the Myrtle Creek Sandstone to borehole termination.

Standing groundwater and/or seepage was not encountered in any of the boreholes at the time of
investigation.




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7.0      REGIONAL ASS MAPPING
An extract from the Queensland Government’s Redcliffe to Teewah, Acid Sulfate - Sustainable Land
Management Project, Map 2 (NR&M-SEA-I-A0 3261) covering the region is shown in Text Figure 5.
Mapping indicates the site is located above the outer limit of Holocene age/estuarine ASS (i.e. above RL 5 m
AHD). Therefore, the site is characterised as “land with a low probability of acid sulfate soil
occurrence”.
It is noted that land below RL 5 m AHD generally fringing the Noosa River and Doonella Lake to the south is
mapped as SW, being areas associated with Melaleuca wetlands and occasionally Casuarina glauca
communities, commonly a wet, organic rich environment. This is noted to be typical of lower lying land,
located at least 100 m south of the subject site and is not reflective of the site conditions.




                                               Subject Site




Text Figure 5: Extract from Department of Environment & Resource Management ASS Risk Map




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8.0      APPLICATION TO LOCAL COUNCIL REGULATION
Development involving ASS must comply with the requirements of State and Local government regulations
pertaining to ASS. Locally, NC has developed the ASS Overlay Code, and its attendant guidelines, as part
of the Noosa Plan 2020.
The purpose of the ASS overlay code is to ensure that the generation or release of acid and metal
contaminants from disturbance of ASS does not have adverse effects on the natural environment, built
environment, infrastructure or human health.
This is achieved through compliance with the following development outcomes:
    a) development ensures that the release of acid and associated metal contaminants into the
       environment is avoided by either:
           i.    not disturbing ASS when excavating or otherwise removing soil or sediment, extracting
                 groundwater or filling land; or
           ii.   treating and, if required, undertaking ongoing management of any disturbed ASS and
                 associated drainage waters.
Based on our review of the geotechnical investigation results, regional geology, published ASS risk mapping
and proposed development details, it is recognised that the proposed works will not involve disturbance of
soil or groundwater conditions which are likely to contain ASS.
Proposed site development will not generally involve disturbance of soil below an elevation of RL 5 m AHD,
and where excavation below RL 5 m AHD is required, such works would be expected to disturb only residual
(non-ASS) soil of a relatively small total volume (~60 m3), which would present a negligible risk of ASS
disturbance.
Based on the limited extent of excavation below RL 5 m AHD, and presence of residual subsoils from a non-
ASS geological unit, the proposed development is deemed to conform with performance outcome PO1 of
NC’s ASS Overlay Code (i.e. development does not disturb ASS).


9.0      RECOMMENDATIONS
Proposed site development would have a negligible risk of encountering ASS or affecting groundwater
conditions which may impact ASS prone areas. The proposed development may therefore proceed without
need for any further specific ASS management measures. No further site assessment regarding ASS is
warranted for the proposed development.
Should site conditions be encountered during operational works which vary from those described herein,
Tectonic or another suitably qualified ASS specialist should be contacted immediately to inspect the site
conditions, assess the potential ASS risk and provide recommendations as to how works may safely
proceed.


10.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is attached at the end 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.




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APPENDIX A
Limitations




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                                               LIMITATIONS


This document has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is
accepted for the use of this document, in whole or in part, for any other purpose.

The scope of Tectonic’s Services are as described in Tectonic’s proposal, and are subject to restrictions
and limitations. Tectonic did not perform a complete assessment of all possible conditions or
circumstances that may exist at the site referenced in the report. If a service is not expressly indicated, do
not assume it has been provided. If a matter is not addressed, do not assume that any determination has
been made by Tectonic in regards to it.

Conditions may exist which were undetectable given that economic and time constraints limit the practical
extent of geotechnical investigation. Variations in conditions may occur between investigation locations,
and there may be special conditions pertaining to the site which have not been revealed by the
investigation and which have not therefore been taken into account in the document. Where variations exist
on site, additional studies and actions may be required.

Tectonic’s opinions are based upon information that existed at the time that the work was performed. The
passage of time, man-made or natural events, may alter the site conditions. It is understood that the
Services undertaken allowed Tectonic to form an opinion of the actual conditions of the site at the time the
site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the
site, or its surroundings, or any laws or regulations.

Any assessments made in the preparation of this document are based on the conditions indicated from
published sources and the findings of the investigation described. Actual subsurface conditions may differ
from those indicated in the document (e.g. between boreholes or test pits). No warranty is included, either
express or implied, that the actual conditions will conform exactly to the assessments contained in this
document.

Where data supplied by the client or other external sources, including previous site investigation data, have
been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is
accepted by Tectonic for incomplete or inaccurate data supplied by others.

This document is provided for the sole use by the Client and its professional advisers. No responsibility
whatsoever for the contents of this document will be accepted to any person other than the Client. Any use
which a third party makes of this document, or any reliance on or decisions to be made based on it, is the
responsibility of such third parties. Tectonic accepts no responsibility for damages, if any, suffered by any
third party as a result of decisions made or actions based on this document.




Rev 1 (March 2016)