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Appendix E - Wastewater Report
Attached to the e-mail RAL20/0014 - Response to Council's Information Request - 9A Jirrima Cres, Cooroibah - Email 02 of 02.
ON-SITE WASTEWATER TREATMENT
AND DISPOSAL ASSESSMENT
Proposed Residential Subdivision
9A Jirrima Crescent, Cooroibah
Report for: Maud Cazot
C/- Murray & Associates (Qld) Pty Ltd
20333-001-Rev0
4 November 2020
Tectonic Geotechnical Pty Ltd
PO Box 899, Buderim QLD 4556
Office: 07 5478 9016
Email: [email protected]
www.tectonicgeo.com.au
A.B.N. 83 165 727 828
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Page 2
PROPOSED RESIDENTIAL SUBDIVISION
9A JIRRIMA CRESCENT, COOROIBAH
Document Review
Document No. Revision Prepared By Reviewed By Date Issued
001 0 Mark Thomson Ashley Davey 4 November 2020
Report Distribution
Revision Method of Delivery Issued To
Maud Cazot
0 Electronic
([email protected])
Callan Lowrie
0 Electronic
([email protected])
Prepared By: Reviewed By:
Mark Thomson Ashley Davey RPEQ 8159
Senior Environmental Scientist Principal Geotechnical Engineer
4 November 2020
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PROPOSED RESIDENTIAL SUBDIVISION
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Executive Summary
This report details the results of a geo-environmental investigation undertaken to address the feasibility of
on-site effluent disposal for a proposed 1 into 2 lot residential subdivision of Lot 101 on SP168341, located at
9A Jirrama Crescent, Cooroibah. The investigation was performed by Tectonic for Maud Cazot. Murray &
Associates (Qld) Pty Ltd are the town planners for the project.
The existing property covers an area of approximately 4.5 ha and is zoned rural residential under the Noosa
Plan 2020. Proposed development will comprise the separation of the existing house and land situated on
the eastern half of the site from vacant land in the western half of the site to form two new land parcels
(numbered Lots 1 and 2).
Site investigation comprised a walk-over by an experienced environmental scientist and drilling of one hand
augured borehole at the proposed wastewater land application area. Subsurface conditions encountered in
HA1 comprised stiff clayey silt to 0.3 m below ground level (BGL), overlying very stiff silty clay to borehole
termination at 1.5 m BGL. Groundwater was not encountered.
Topography across the site is consistent with relatively flat and gentle slopes, where present. Available
areas for effluent disposal have been categorised as Linear Planar, with a subsurface soil profile equivalent
to Medium to Heavy Clays (Soil Category 6).
Having consideration for the terrain-soil assessment and environmental constraints of the site it is
recommended that wastewater from the proposed lots be directed to suitably sized Household Sewage
Treatment Plants (HSTPs) connected to a shallow subsurface or surface irrigation systems. The
HSTPs must be licensed to produce at least Secondary standard effluent.
Considering the site and soil conditions across the proposed development areas, a surface or shallow
subsurface irrigation area of about 360 m² would be required for proposed Lot 1. Sufficient room to site the
wastewater irrigation areas with the necessary setbacks is available for both proposed lots. Final irrigation
area and detailed wastewater system design will be dependent upon individual site assessment at the building
stage.
An existing wastewater treatment system and surface irrigated land application area was identified on the
southern side of the existing residence on Lot 2. No evidence of malfunction or failure was noted during site
inspection. As there are no alterations to the existing dwelling proposed, and both the existing dwelling and
associated wastewater treatment system are entirely located within the bounds of proposed Lot 2, this
system is considered suitable to continue to service the existing dwelling.
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Table of Contents
1.0 INTRODUCTION ........................................................................................................................................................ 1
2.0 SITE DESCRIPTION .................................................................................................................................................. 1
3.0 PROPOSED DEVELOPMENT ................................................................................................................................... 2
4.0 EXISTING WASTEWATER INFRASTRUCTURE ..................................................................................................... 3
5.0 AIMS & METHOD OF INVESTIGATION ................................................................................................................... 4
6.0 SUBSURFACE INVESTIGATION FINDINGS ........................................................................................................... 5
6.1 Regional Geology ......................................................................................................................................... 5
6.2 Subsurface Conditions.................................................................................................................................. 5
7.0 WASTEWATER TREATMENT AND DISPOSAL ...................................................................................................... 6
7.1 Wastewater Flow Design Allowance ............................................................................................................. 6
7.2 Terrain-Soil Assessment............................................................................................................................... 6
7.3 Recommendations ........................................................................................................................................ 7
7.3.1 System Type ........................................................................................................................................... 7
7.3.2 System Positioning.................................................................................................................................. 7
7.3.3 System Construction ............................................................................................................................... 9
7.3.4 Maintenance and Inspection ................................................................................................................... 9
8.0 LIMITATIONS ............................................................................................................................................................ 9
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PROPOSED RESIDENTIAL SUBDIVISION
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TABLES
Table 1: Setbacks for subsurface land application area for on-site sewage treatment plant ............................................... 7
Table 2: Setbacks for surface irrigated land application area for on-site sewage treatment plant ....................................... 8
Table 3: Setback distances for on-site sewerage facilities (Protection of surface and groundwater) .................................. 8
TEXT FIGURES
Text Figure 1: Site location (courtesy Google Earth)........................................................................................................... 1
Text Figure 2: Looking east across proposed Lot 2 ............................................................................................................ 2
Text Figure 3: Looking west across proposed Lot 1 building envelope ............................................................................... 2
Text Figure 4: Proposed layout (Job No.: 62805/A, dated 8/06/2020) ................................................................................ 3
Text Figure 5: Current wastewater treatment system (aerated HSTP)................................................................................ 3
Text Figure 6: Looking west across current application area (surface irrigation) for Lot 2................................................... 4
Text Figure 7: Extract of Geology Map with Annotations by Tectonic ................................................................................. 5
FIGURES
Figure 1: Site Plan
APPENDICES
APPENDIX A
Borehole Report & Explanatory Notes
APPENDIX B
Limitations
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1.0 INTRODUCTION
This report details the results of a geo-environmental investigation undertaken to address the feasibility of
on-site effluent disposal for a proposed residential subdivision at 9A Jirrima Crescent, Cooroibah. The
investigation was performed by Tectonic for Maud Cazot in accordance with proposal P20475-Rev0, dated
7 October 2020. Murray & Associates (Qld) Pty Ltd (Murray) are the town planners for the project.
Site investigation comprised a walk-over by an experienced environmental scientist and drilling of one hand
augured borehole in the vicinity of open space expected to be utilised for on-site land application on
proposed Lot 1. This report summarises the results of the investigation and includes a site-and-soil
evaluation for on-site land application of treated sewage. Recommendations are provided regarding the
construction, sizing and positioning of required sewerage treatment plant and effluent disposal areas,
confirming the feasibility of onsite wastewater treatment for the proposed lot reconfiguration.
2.0 SITE DESCRIPTION
The existing property is legally described as Lot 101 on SP168041 and covers an area of approximately
4.5 ha. The existing allotment is generally trapezoidal in shape, with an approximate 200 m handle access
driveway to Jirrima Crescent extending eastward from the sites north-east corner. The site is otherwise
surrounded by neighbouring rural residential land.
An existing residence is situated in the north-eastern corner of the site, which is expected to be fully retained
within proposed Lot 2.
Most of the site is likely to have been previously cleared, with some remnant native vegetation present near
the site’s western boundary. Site vegetation across the central and eastern side of the site consists of low
grass cover with sporadically distributed eucalypt and melaleuca trees.
Existing ground elevation across the site ranges from RL 6 m to RL 10 m AHD. The site is relatively flat, with
some gentle ground slopes (< 5%) sloping inward toward a central creek line which exits the site at the
northern boundary.
Text Figure 1 below illustrates to subject site location and surroundings. Text Figures 2 and 3 over page
show the site general site conditions at the time of investigation.
Subject Site
Text Figure 1: Site location (courtesy Google Earth)
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PROPOSED RESIDENTIAL SUBDIVISION
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Text Figure 2: Looking east across proposed Lot 2
Text Figure 3: Looking west across proposed Lot 1 building envelope
3.0 PROPOSED DEVELOPMENT
A plan of development prepared by Murray & Associates has been provided to Tectonic (Job No.: 62805/A,
dated 8/06/2020) which indicates that the development will comprise the subdivision of the existing allotment
into two new lots (numbered Lots 1 and 2).
The local area is not currently connected to reticulated town water or sewerage networks, therefore the
existing residence and the new lot will be serviced by rainwater tank supply and on-site wastewater
treatment and disposal. As the site is currently unsewered, an assessment of on-site effluent treatment and
disposal is required to identify the wastewater system requirements and to provide recommendations on
construction, sizing and suitable positioning of the effluent treatment and disposal infrastructure.
No significant alterations to the existing dwelling are proposed as a result of site subdivision, with both the
existing dwelling and existing wastewater treatment system to be entirely located within the bounds of
proposed Lot 2. A second allotment (Lot 1) will be created on the western half of the site. A proposed
building envelope is located on the eastern side of Lot 1.
Text Figure 4 over page illustrates the proposed subdivision layout.
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PROPOSED RESIDENTIAL SUBDIVISION
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Text Figure 4: Proposed layout (Job No.: 62805/A, dated 8/06/2020)
4.0 EXISTING WASTEWATER INFRASTRUCTURE
The existing residence is serviced by an operational aerated wastewater treatment system, which is located
approximately 20 m south of the existing house. It is understood that the system is regularly serviced, with
onsite service tags indicating that the system produces Advanced Secondary standard effluent.
Treated effluent from the system is piped to a surface irrigation area (approximate 300 m²) located south of
the residence, adjacent to the eastern boundary. At the time of inspection there were no indications of
inadequate operation or failure of the system observed (e.g. wet, soft ground; irregular grass growth).
Text Figures 5 and 6 show the existing wastewater treatment infrastructure observed on site.
Text Figure 5: Current wastewater treatment system (aerated HSTP)
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Application Area
(Approx. 300m2)
HSTP
Text Figure 6: Looking west across current application area (surface irrigation) for Lot 2
5.0 AIMS & METHOD OF INVESTIGATION
The main aim of the investigation was to confirm feasibility of on-site wastewater management for the
proposed lot reconfiguration. It is understood that this report will be submitted to Noosa Council to support a
Development Application for Reconfiguration of a Lot. The investigation and report have therefore been
designed to address the requirements of the relevant Noosa Council codes and policies, together with
Australian Standard AS1547-2012 On-site Domestic Wastewater Management.
An experienced geo-environmental scientist from Tectonic undertook a site walk-over to visually assess
possible constraints to on-site wastewater management on 27 October 2020. The walk-over included
assessment of soil and rock outcrops (if any), surface drainage conditions, topography, evidence of erosion,
and vegetation coverage/condition.
This was incorporated with a subsurface investigation comprising the hand augered drilling of one borehole
(designated HA1) to a depth of 1.5 m below ground level (BGL), in the area likely to be used for onsite
effluent disposal.
The environmental scientist undertook logging of soil profiles in accordance with AS1726 Geotechnical Site
Investigations. The borehole was positioned within the area likely to be utilised for on-site effluent disposal
on proposed Lot 1 based on the layout plan provided. The borehole was backfilled with drilling spoil and
compacted to the ground surface level upon completion.
The borehole log together with notes explaining the terms and symbols used are presented in Appendix A.
The borehole location is shown in Figure 1 (at end of text).
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6.0 SUBSURFACE INVESTIGATION FINDINGS
6.1 Regional Geology
Published geological information 1 indicates that the soil profile at the subject site consists of predominantly
residual soil derived from the Triassic to Jurassic aged, Tiaro Coal Measures (Jdt (w)). This formation
typically comprises weathered lithofeldspathic labile and sublabile to quartzose sandstone, siltstone, shale,
coal, ferruginous oolite marker quartzose sandstone, siltstone, shale conglomerate, coal. Alluvial clay, silt
sand and gravel may also overly the western end of the site. An extract of the geology map is shown in Text
Figure 7 below.
Jdt (w) - Tiaro Coal Measures
Qa-SEQ Age Triassic - Jurassic
Weathered lithofeldspathic labile
and sublabile to quartzose
Lithology
sandstone, siltstone, shale, coal,
ferruginous oolite marker
Dominant
ARENITE-MUDROCK
Rock
Jdt (w)
Qa-SEQ – Tertiary Basalt
Age Quaternary
Clay, silt, sand, gravel; flood plain
Lithology
alluvium
Dominant
ALLUVIUM
Rock
Text Figure 7: Extract of Geology Map with Annotations by Tectonic
6.2 Subsurface Conditions
Subsurface conditions encountered in the borehole generally supports the mapped geology for the site,
comprising:
Stiff clayey silt with some organic fines (topsoils) to depth of 0.3 m BGL; overlying
Very stiff to hard silty clays to borehole termination at 1.5 m BGL.
The soil profile is considered primarily residual soil, derived by the weathering of the parent formation (Tiaro
Coal Measures).
Groundwater was not encountered in the completed borehole. It should be noted that ‘perched’ groundwater
seepage may develop at the interface between upper silts and underlying clays (0.3 m BGL) following
periods of heavy or prolonged rainfall.
For detailed descriptions of the soils encountered in the borehole, refer to the borehole report and
explanatory notes attached in Appendix A.
1
State of Queensland, Queensland Globe Geology Map, 2017
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7.0 WASTEWATER TREATMENT AND DISPOSAL
An assessment of the type and configuration of wastewater system(s) that may be suitable for a proposed
development requires:
Assumptions to be made regarding the typical building/visitor configuration and probable
wastewater flow; and
Evaluation of the terrain-soil combinations to identify distinct units.
7.1 Wastewater Flow Design Allowance
For a typical four bedroom house (or three bedrooms plus study), we have estimated a peak occupancy of
six persons. This assumption is consistent with current Council development standards and has been used
to demonstrate feasibility of onsite effluent disposal. Should the proposed residence exceed this size, it is
the owner’s responsibility to demonstrate feasibility of the design, meeting all relevant regulations.
For each occupant, a typical wastewater flow allowance of 120 L/person/day has been taken from
Appendix H of AS1547:2012. This represents the flow allowance for households with standard water
reduction fixtures (including duel flush toilets, shower flow restrictors, aerator faucets and water conserving
automatic washing machines) with on-site roof water tank supply.
We therefore estimate a typical daily household wastewater flow rate of 720 L/day (6 x 120 L/person/day).
This gives a weekly flow rate of 5,040 L/week.
It should be noted that wastewater flow rates may be further reduced by the adoption of full water reduction
facilities (e.g. reduced flush 6/3 L toilets, shower flow restrictors, aerator faucets, front-load washing
machines and flow/pressure control valves on all water-use outlets, etc.). Conversely, the use of extra
wastewater producing fixtures (e.g. spa baths) has the potential to increase the household wastewater flow
rate.
Final wastewater flow rates must be calculated at the time of detailed design of the wastewater system, at
building stage once the house design is known.
7.2 Terrain-Soil Assessment
The terrain-soil combination(s) encountered at a site are assessed so that an Expected Available Area (EAA)
can be delineated for suitable methods of wastewater treatment and land application.
The terrain across the potential effluent disposal areas is relatively consistent and has been categorised as
Linear Planar in accordance with the slope configurations described in Figure C2 of AS1547:2012, which
also describes the relationship between the shape of the slope and surface drainage. Such slopes have less
effective natural drainage as distance from the crest increases, with no spreading or acceleration of run-off
as it moves down slope.
It has been assessed from the results of the investigation that the soil profile across likely effluent disposal
area on Lot 1 characterised by the borehole is equivalent to Medium to Heavy Clay (Soil Category 6). This
categorisation has been derived via the method described in Table M1 of AS1547:2012.
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PROPOSED RESIDENTIAL SUBDIVISION
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7.3 Recommendations
7.3.1 System Type
It is recommended that wastewater from the future residence on Lot 1 be directed to a suitably sized
Household Sewage Treatment Plant (HSTP) connected to a shallow subsurface or surface irrigation system.
The HSTP must be licensed to produce at least Secondary standard effluent, with Chief Executive approval
from the Department of Housing and Public Works. To maximise available residential space, by limiting
setback requirements, it may also be desirable to use an Advanced Secondary treatment system on the new
allotment.
The HSTP and land application area currently servicing the existing residence located within proposed Lot 2
would be adequate to continue to service the existing dwelling. Relocation or retrofitting of the existing
system is not expected to be necessary, but if required, should be completed by a suitably qualified and
licensed plumber, experienced with on-site effluent systems.
Table M1 of AS1547:2012 recommends a Design Irrigation Rate (DIR) of 2 mm/day for Category 6 soil.
Therefore, a minimum irrigation area of about 360 m² (720 L/day / 2 mm/day) will be required for each lot.
Sufficient wastewater irrigation areas for both proposed lots are available and are shown in Figure 1, where it
can be seen that there is sufficient room to site the wastewater irrigation areas with the necessary setbacks.
7.3.2 System Positioning
Positioning (‘setbacks’) of the land application systems must be in accordance with the horizontal and
vertical setback distances recommended in Tables T2, T3 and T5 of the Queensland Plumbing and
Wastewater Code 2019, as summarised in Tables 1, 2 and 3 below and over page.
Table 1: Setbacks for subsurface land application area for on-site sewage treatment plant
Horizontal separation distance
Site Feature
Upslope Downslope Level
Property boundaries, pedestrian paths, walkways, recreation areas,
2m 4m 2m
retaining wall, and footings for buildings and other structures.
Inground swimming pools. 6m
Inground potable water tank.
6m
(Secondary standard effluent or better)
Note: Distances measured from the edge of trench/bed excavation or subsurface irrigation distribution
pipework to the nearest point of the feature.
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Table 2: Setbacks for surface irrigated land application area for on-site sewage treatment plant
Site Feature Horizontal separation distance
Property boundaries, pedestrian paths and walkways 2m
Water edge of a swimming pool 6m
Dwellings, recreation areas 10 m
Note: Distances measured from the edge of the irrigated wetted area to any point of the feature.
Table 3: Setback distances for on-site sewerage facilities (Protection of surface and groundwater)
Separation Distance
Site Feature
Advanced Secondary Secondary Effluent
Effluent
Surface Waters:
Top of bank of permanent or intermittent water course, lake,
bay or estuary;
Top water level of a surface water source used for agriculture, 10 m 30 m
aquaculture or stock purposes;
Open stormwater drainage channel or drain;
Bore or a dam.
Unsaturated soil depth to a permanent water table (vertically) 0.3 m 0.6 m
Note: Distances measured from the edge of the irrigated wetted area to any point of the feature.
Unsaturated soil depths of 0.6 m (i.e. depth to rock or wet soil) and 0.3 m are recommended for Secondary
and Advanced Secondary effluent, respectively. Boreholes indicate adequate unsaturated soil depths are
available across all proposed effluent disposal areas.
A conceptual wastewater treatment plan has been prepared which demonstrates that a suitably sized
effluent disposal area can be positioned within each proposed allotment. The conceptual wastewater
treatment plan is attached as Figure 1. It is noted that this plan demonstrates conceptual layout only for the
purpose of demonstrating feasibility. Individual site layout shall be decided at building stage.
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PROPOSED RESIDENTIAL SUBDIVISION
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7.3.3 System Construction
Construction of the wastewater land application areas should be carried out in accordance with Appendix K2
of AS1547:2012 and Council requirements. In order to minimise potential deleterious environmental impacts
associated with wastewater application at the site, the following practices should be employed:
Any sandy topsoil material won from stripping works associated with residential construction may be
used to supplement the soil within the respective disposal fields.
Install surface diversion drainage (e.g. grassed swale) on the up-slope side of the land application
area to divert stormwater flows away from the land application area.
Install earthen bunding (e.g. mounded garden bed) along the down slope side of the effluent disposal
area to retain effluent run-off and promote sheet flow.
Plant and maintain vegetation on the down slope side of the land application area. Preference
should be given to native plant species endemic to the local area, which are suitable for mostly wet
soils and are tolerant of high nutrient loads.
To evenly distribute wastewater throughout the irrigation area, a pressure equalisation system
should be installed.
Where trickle irrigation pipework is installed, construct irrigation laterals parallel with the natural
ground surface contours.
Erect signage at the boundaries of the area in at least two places in accordance with Council
requirements to warn people regarding the presence of wastewater pipes (e.g. “Sewage Effluent
Pipework Installed Below – DO NOT DIG” or “Recycled Water – Avoid Contact - DO NOT DRINK”).
Detailed design of the effluent disposal systems must be carried out by a Registered Evaluator to
accompany the plumbing application at the building stage, once the building designs are finalised.
7.3.4 Maintenance and Inspection
Operation and maintenance of a HSTP system is the responsibility of the property owner. A licensed service
agent must be appointed to undertake routine servicing works in line with regulatory authority approval
conditions. To comply with Council requirements, the following management and inspection shall be
implemented once the effluent disposal systems are established:
Continuous monitoring by the property owner for any signs of system failure such as septic odour,
seepage, soil and/or plant discoloration.
Should any signs of system failure be observed by the property owner, including the in-built HSTP
failure alarm, the manufacturer shall be contacted immediately to arrange for the necessary repairs.
Quarterly inspection, testing and repair (if necessary) to the HSTP and irrigation area by a Licensed
Inspector (normally a service provided by the HSTP manufacturer).
8.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is included in Appendix B 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.
4 November 2020
Report No. 20333-001-Rev0 9
Page 15
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Ph: 07 5478 9016
PROJECT:
GEO-ENVIRONMENTAL
INVESTIGATION
9A JIRRIMA CRESCENT,
Existing Advanced
COOROIBAH
Secondary HSTP
TITLE:
SITE PLAN
CLIENT:
MAUD CAZOT
Existing Land C/- MURRAY ASSOCIATES PTY LTD
Application Area
> 360 m2 Available
DRAWN: DATE:
MT 3/11/2020
CHECKED: DATE:
ACD 3/11/2020
SCALE:
AS SHOWN
LEGEND:
Proposed Building Envelope
Investigation Borehole
HA1
360 m2 Land-application Area
(Secondary or Adv. Secondary
Standard Effluent)
Existing Aerated Treatment System
Existing Land-application Area
(Adv. Secondary Standard Effluent
Surface Irrigated)
PROJECT NO.: FIGURE: REV:
20333 1 0
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PROPOSED RESIDENTIAL SUBDIVISION
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APPENDIX A
Borehole Logs and Explanatory Notes
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Report No. 20333-001-Rev0
Page 17
Borehole No.
HA1
Page 1 of 1
Engineering Log - Borehole Project No.: 20333
Client: Murray & Associates Commenced: 27/10/2020
Project Name: Completed: 27/10/2020
Hole Location: 9A Jirrima Crescent, Cooroibah Logged By: MT
Hole Position: 499598.0 m E 7084737.0 m N MGA94 Zone 56 Checked By: MT
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 80 mm Bearing: 360° Datum: AHD Operator: Tectonic
Drilling Information Soil Description Observations
Relative Density
Classification
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer Structure and
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Additional Observations
Symbol
Method
secondary and minor components, colour
Water
Remarks RL Depth (kPa)
(m) (m)
100
200
300
400
500
ML Clayey SILT, low liquid limit, brown, low
plasticity clay fines, trace of fine to medium
grained sand
D to
St
M
CH Silty CLAY, high plasticity, brown grey and red
to orange, trace of fine to medium grained
sand
0.5
Not Encountered
TECTONIC 2.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 20333.GPJ <<DrawingFile>> 03/11/2020 10:47 10.00.01.07 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 2.00.2 2016-10-13 Prj: Tectonic 2.00 2016-02-16
HA
M VSt
1.0
becoming pale grey and red to orange
1.5
Hole Terminated at 1.50 m
Target depth
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AD/T-Auger Drilling TC Bit No resistance Level (Date) U - Undisturbed Sample D - Dry VS - Very Soft
RR - Rock Roller ranging to D - Disturbed Sample M - Moist S - Soft
RD - Rotary Drilling refusal Inflow SPT - Standard Penetration Test W - Wet F - Firm
NMLC -Rock Core Partial Loss VSt - Very Stiff
HA - Hand Auger Complete Loss H - Hard
Plastic Limit VL - Very Loose
Graphic Log/Core Loss L - Loose
Classification Symbols < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System
Page 18
METHOD OF SOIL DESCRIPTION
USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Soil is classified and described in borehole and test pit logs using the preferred method given in AS1726 – 2017.
The material properties are assessed in the field by visual/tactile methods.
Particle Size Plasticity Properties
Major Sub Division Particle Size
Division
BOULDERS > 200 mm
COBBLES 63 to 200 mm
Coarse 19 to 63 mm
GRAVEL Medium 6.7 to 19 mm
Fine 2.36 to 6.7 mm
Coarse 0.6 to 2.36 mm
SAND Medium 0.21 to 0.6 mm
Fine 0.075 to 0.21
SILT 0.002 to 0.075
CLAY < 0.002 mm
NOTE: The U line is an approximate upper bound for most materials.
Data which plot above the U line may represent unusual/problem soil
behavior, or unreliable data and should be considered carefully.
MOISTURE CONDITION AS1726 - 2017
Symbol Term Description
D Dry Sands and gravels are free flowing. Clays & Silts may be brittle or friable and powdery.
M Moist Soils are darker than in the dry condition & may feel cool. Sands and gravels tend to cohere.
W Wet Soils exude free water. Sands and gravels tend to cohere.
CONSISTENCY AND DENSITY AS1726 - 2017
Symbol Term Undrained Shear Symbol Term Density Index % SPT “N” #
Strength
VS Very Soft 0 to 12 kPa VL Very Loose Less than 15 0 to 4
S Soft 12 to 25 kPa L Loose 15 to 35 4 to 10
F Firm 25 to 50 kPa MD Medium Dense 35 to 65 10 to 30
St Stiff 50 to 100 kPa D Dense 65 to 85 30 to 50
VSt Very Stiff 100 to 200 kPa VD Very Dense Above 85 Above 50
H Hard Above 200 kPa
In the absence of test results, consistency and density may be assessed from correlations with the observed behaviour of
the material.
# SPT correlations are not stated in AS1726 – 2017, and may be subject to corrections for overburden pressure and
equipment type.
Rev1
October 2017
Page 19
PROPOSED RESIDENTIAL SUBDIVISION
9A JIRRIMA CRESCENT, COOROIBAH
APPENDIX B
Limitations
4 November 2020
Report No. 20333-001-Rev0
Page 20
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)