INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 1 of 28

To:

Tristan Jónsson Menzies (Golder Associates)

From:

Lee Tasker (Draig Geoscience Pty. Ltd.)

Subject:

Geophysical Investigation – Ground Penetrating Radar (GPR), Fremantle Prison, Fremantle,
WA

1. Introduction & Objectives
Golder Associates (Golder) approached Draig Geoscience (Draig) to provide a quote for a ground
penetrating radar (GPR) survey to assist with assessing the underlying ground for an historical sewerline within areas of interest inside the Fremantle Prison property grounds and also outside theFremantle Prison property grounds (tel. comms. Tristan Menzies, Senior Engineering Geologist,
Golder, 23/03/2022). A quotation was provided to Golder on 23/02/2022 (Draig quote ref.
DG1747GLD_1.0) and a purchase order to proceed was provided by Tristan Menzies on 12/04/2022.
General site maps of the Fremantle Prison historical main sewer line areas of interest were provided
by Golder as part of the quotation submission (see Figure 1 and Figure 2).

Figure 1. A general site map of the Fremantle Prison historical main sewer line within the Fremantle
Prison grounds area of interest (red arrow) (image source: Golder).

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 2 of 28

Figure 2. A general site map of the Fremantle Prison historical main sewer line area of interest outside
the Fremantle Prison buildings (white rectangle and red circle) (image source: Golder).

Draig proposed utilising a GPR antenna to cover a depth of coverage of ~5 m within the areas ofinterest (e.g. 250 MHz antenna). Draig also proposed an approximate 1 m parallel GPR profile
spacing, where possible within the areas of interest.

2. Data Acquisition
2.1 Geographical Location and Fieldwork Dates
Data acquisition was conducted along the western flank on the outside of main Fremantle Prison
outer walls on Wednesday 20/04/2022 and the GPR survey was completed on the same day.

2.2 Equipment Details and Data Acquisition Parameters
Approximately 1,000 line-m of GPR profile data were acquired across the investigation site over
51 GPR profiles, labelled DAT_0001 to DAT_0051. GPR data were acquired using a Mala GPR
250 MHz antenna with the GPR antenna coupled to a rough terrain cart and calibrated wheel
encoder. The 250 MHz antenna provided a depth of coverage to ~5 m.

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 3 of 28

GPR profile start and end positions were recorded with a GPS survey using a Juniper Systems
Geode DGPS unit, acquired through EffiGIS EZTag software and post-processed using EffiGIS
EZSurv software.
The GPR survey was split into 6 areas of interest as dictated by the ground conditions encounteredat the site. The survey area consisted of grass, concrete and asphalt surfaces. The areas were as
follows:•

Area 1 ran under the verandah of a building out onto the grass, and contained 4 profiles(DAT_0001 to DAT_0004);•

Area 2 was located predominantly on grass, but also crossing a concrete footpath, andcontained 9 profiles (DAT_0005 to DAT_0013);•

Area 3 was located on the road and contained 13 profiles (DAT_0014 to DAT_0026);•

Area 4 was located on the grass west of the road, with lines split around a tree and light post.
The area contained 8 profiles (DAT_0027 to DAT_0034);•

Area 5 was located on a sloped ramp and contained 8 profiles (DAT_0035 to DAT_0042);•

Area 6 was located in a carpark and contained 9 profiles (DAT_0043 to DAT_0051).

GPR profiles were acquired as close as possible parallel to one another at a profile separation of~0.5 m. A site plan of the approximate GPR profile locations is shown in Appendix A, Figure A1 andphotographs of the general site conditions are shown in Figure 3.

(a)

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

(c)

(d)

(e)

(f)

(g)

(h)

Issue date:
06/05/2022

Page 4 of 28

Figure 3. General site conditions (a) Area 1, facing south; (b) Area 2, facing north; (c) Area 3 facing
north; (d) Area 4, facing north; (e) Area 5, facing north; (f) Area 6, facing east; (g) site features in Area
5 including a square rock in wall, and metal pipe extruding from wall; and (h) site features in Area 4
such as concrete service cover, subsidence in grass, light pole and metal drainage grate (image
source: Draig Geoscience).
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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 5 of 28

3. Results and Interpretation
3.1. GPR Data Processing Steps
GPR data processing was conducted in the GPR data processing software ‘GPR-Slice’(https://www.gpr-survey.com/). GPR depth-slices were created from combining the 2D radargramsin a 3D data volume and these depth-slices were exported as Surfer .grd files from GPR-Slice.
Depth-slice data grids are provided as an electronic deliverable to this report in ERMapper (.ers)
format (and also displayed in Appendix B, Figures B1-B6). A general processing flow for the GPR
data processing is listed below:➢ Import raw radar data into GPR-Slice;➢ Post-process GPR with GPS data (QC data, check GPS points);➢ Time-zero and truncate samples;➢ Filter data;o

Estimated dielectric constant (9) and background electromagnetic velocity (0.1 m/ns)(a depth of coverage ~5 m has been achieved with the 250 MHz GPR antenna using
these values), apply background filter, apply amplitude gain, apply bandpass filter(250 MHz data: low-cut = 32 MHz, high-cut = 709 MHz);➢ Combine the 2D radargrams into a 3D volume of data and slice through the volume of
combined data at a specified depth interval;oNumber of slices for volume = 41;oThickness of slices = 25 samples, 4.94 nanosec (~0.25 m);oOverlap in slices = 50%;

➢ Grid depth-slices;o

Grid cell size = 0.1 m;oX-search radius = 1.0 m, Y-search radius = 1.0 m, Blanking radius = 1.0 m;➢ Display and export gridded depth-slices to Surfer .GRD files for interpretation in DiscoverPA;➢ Assess for presence of GPR features in depth-slices and compare with 2D radargrams in 3D
space and pick feature location if present;
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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 6 of 28➢ Export Shapefile format depth-slice interpretation features (if applicable).
➢ Export ASCII format radargram section interpretation point features (if applicable).

3.2. GPR Data Analysis
Draig interpretated the processed GPR data in two manners; interpreting regions of high amplitude
response across the radar depth-slices and also high amplitude features of interest along theradargram section data. Maps presenting depth-slice interpretation linework and radargram section
interpretation point features are presented in Appendix C, Figures C1-C6.
3.2.1. Depth-Slice Interpretation
To aid with interpretation, Draig applied a colour-clip to the average GPR amplitude intensity maps
to highlight regions of high amplitude response (red-coloured “hot spots”).
A linear (increasing) transform (rainbow colour-scale) was applied to each individual average GPR
amplitude intensity map with a bandpass cut-off/clip of 1-97/98%. (The linear transform stretches thecolour-scale from the lowest value data value to lowest mapped colour, to highest value mapped tohighest mapped colour.) Figure 4 shows an example of an unclipped and clipped average GPR
amplitude intensity map. Once colour-clipped, high amplitude response targets were interpreted andtraced. Figure 5 shows an example of the interpretation linework to outline a zone of high amplitude(hot spot).

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 7 of 28

(a)

(b)
Figure 4. (a) An average GPR amplitude intensity map for site Area 03 (Depth-Slice 25) showing nocolour clip (full colour-scale) and (b) showing a 1-97% clipped colour-scale. The clipped colour-scale
was the colour-scale used for data interpretation.

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 8 of 28

(a)

(b)
Figure 5. Example of interpretation of average GPR amplitude intensity map for high amplitude zones(hot spot). (a) An average GPR amplitude intensity map at site 03 (Depth-Slice 25) with 1-97% clippedcolour-scale applied and interpretation drawn (magenta line), (b) interpretation linework only (magentaline).

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 9 of 28

These high amplitude zones were grouped into designated depth intervals and coloured as shownin Figure 6.

Figure 6. High amplitude zone (depth-slice interpretation) designated depth intervals and colour
coding.

3.2.2. Radargram Section Interpretation
Draig initially interpreted the radargram sections for high amplitude responses that appeared
anomalous to the reflections surrounding the feature. Examples of high amplitude response featuresare shown in Figure 7 and Figure 8 (black dots/magenta arrows – top of high amplitude responsefeatures). These features may be associated with underground tunnels, buried infrastructure,lithological changes with the geological material and regions of possible fracturing/voiding. Theinterpreted radargram point features were then grouped into 0.0-0.99 m, 1.0-1.99 m, 2.0-2.99 m,
3.0-3.99 m and 4+m depth brackets (see Appendix C, Figure C1-C6).

Figure 7. Radargram DAT_0027 interpreted high amplitude response features (black dots/magenta
arrows – top of high amplitude response feature).

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 10 of 28

Figure 8. Radargram DAT_0041 interpreted high amplitude response features (black dots/magenta
arrows – top of high amplitude response feature).

3.2.3. Estimated Tunnel Alignment of Interest
The top of the historical sewer line is interpreted to occur at a depth of ~2.05 m, as observed in the
GPR response. E.g. The feature observed in Figure 9 (DAT_0010 radargram) at ~382240.8 mE,
6452841.5 mN and ~2.1 m depth is interpreted as likely to be caused by the top of the historicalsewer line/tunnel.

Figure 9. Radargram DAT_0010 interpreted high amplitude response features (black dots/magenta
arrows – top of high amplitude response feature). Interpreted historical sewer location circled in cyan.

Following this feature through the GPR data and images, the location of the historical sewer line isinterpreted to extend ~E-W from the SW corner of the building’s verandah (~ 382243.0 mE,
6452841.7 mN, 2.4 m depth, DAT_0006) to approximately 2 m into the road west of the building’s
western gated fenceline (~ 382235.0 mE, 6452842.4 mN, 2.2 m depth, DAT_0018). At this point, ahigh amplitude GPR response is observed extending approximately northwards, parallel to the road
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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 11 of 28

direction, to ~382234 mE, 6452847 mN, a distance of ~6 m. This area when viewed in the 2D
radargram images displays what appears to be a subsurface ground disturbance (see Figure 10 foran example). Where this subsurface change is observed in the 2D radargrams also coincides with asudden decrease in GPR amplitude response for the historical sewer line feature, making it difficult
to interpret the sewer line’s location westwards beyond that point.

Figure 10. Radargram DAT_0017 with zone of ground disturbance highlighted (circled in cyan).

4. Conclusions
Draig were able to successfully identify the location of the historical sewer line within the area ofinvestigation utilising the GPR method.
The sewer line is located at ~2.1-2.4 m depth (top of the sewer). It is interpretable for a length of~9 m, between the SW corner of the building extending westwards to ~2 m into the adjacent road.
The GPR results also revealed an area of subsurface ground disturbance underneath the road,coinciding with the location of where the historical sewer line ceases to be interpretable, extending~6 m north in the direction of the road.
It is not clear whether the historical sewer tunnel terminated at the western-most interpreted location,
where a subsurface disturbance is located beneath the road, or whether it exists west of that location
but has collapsed or been infilled with host/local material. In either of the latter two cases, this may
have decreased the material contrast and resulted in an indiscernible GPR response.
Three other shallow linear features were also identified in the 0-1 m depth range – two south of thehistorical sewer line extending ~E-W from the eastern edge of the surveyed area (Area 1) to thewestern edge of Area 4 (grassed area west of the road), and a third extending ~E-W beneath theramped walkway (Area 5). These are likely associated with utilities.
DG1747GLD_2.0

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INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 12 of 28

APPENDIX A – SITE PLAN

DG1747GLD_2.0

12Easting (m)LegendGPR survey line
Area 1 - Verandah
Area 2 - Grass
Area 3 - Road
Area 4 - Grass
Area 5 - Ramp
Area 6 - Carpark

Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
GPR Survey - Site Plan

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: A1

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendGPR survey line
Area 1 - Verandah
Area 2 - Grass
Area 3 - Road
Area 4 - Grass
Area 5 - Ramp
Area 6 - Carpark

Northing (m)Northing (m)Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
GPR Survey - Site Plan
with Site Features

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: A2

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 15 of 28

APPENDIX B – GPR DATA DEPTH-SLICES

DG1747GLD_2.0

15

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 0.25 - 0.49 m (Slice 03)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B1

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 1.49 - 1.74 m (Slice 13)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B2

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 2.60 - 2.85 m (Slice 22)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B3

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 3.10 - 3.35 m (Slice 26)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B4

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 4.09 - 4.34 m (Slice 34)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B5

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendLocations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 4.96 - 5.09 m (Slice 41)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: B6

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

INTERPRETATION REPORT:

DG1747GLD

Rep. No. 2.0

GEOPHYSICAL INVESTIGATIONGROUND PENETRATING RADAR (GPR)
FREMANTLE PRISON, FREMANTLE, WA

Issue date:
06/05/2022

Page 22 of 28

APPENDIX C – GPR FEATURE INTERPRETATION PLOTS

DG1747GLD_2.0

22Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 0.00 - 0.99 m (slices 01 - 07)
Depth 1.00 - 1.99 m (slices 10 - 15)
Depth 2.00 - 2.99 m (slices 18 - 23)
Depth 3.00 - 3.99 m (slices 26 - 31)
Depth 4.00 - 5.09 m (slices 34 - 41)
Location of Interpreted Points ofHigh Amplitude
Depth 0.00 - 0.99 m
Depth 1.00 - 1.99 m
Depth 2.00 - 2.99 m
Depth 3.00 - 3.99 m
Depth 4.00 m and greater

Northing (m)Northing (m)Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C1

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 0.00 - 0.99 m (slices 01 - 07)
Location of Interpreted Points ofHigh Amplitude
Depth 0.00 - 0.99 m
Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Northing (m)Northing (m)Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude (Depths 0.00 - 0.99 m)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C2

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 1.00 - 1.99 m (slices 10 - 15)
Location of Interpreted Points ofHigh Amplitude
Depth 1.00 - 1.99 m
Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Northing (m)Northing (m)Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude (Depths 1.00 - 1.99 m)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C3

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 2.00 - 2.99 m (slices 18 - 23)
Location of Interpreted Points ofHigh Amplitude
Depth 2.00 - 2.99 m
Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Northing (m)Northing (m)Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude (Depths 2.00 - 2.99 m)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C4

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 3.00 - 3.99 m (slices 26 - 31)
Location of Interpreted Points ofHigh Amplitude
Depth 3.00 - 3.99 m
Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Northing (m)Northing (m)Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude (Depths 3.00 - 3.99 m)

Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C5

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300

Easting (m)LegendOutline of Interpreted Zones ofHigh Amplitude
Depth 4.00 - 5.09 m (slices 34 - 41)
Location of Interpreted Points ofHigh Amplitude
Depth 4.00 m and greater
Locations of site features
Large square rock in wall
Metal pipe extruding from wall
Subsidence in grass
Light Pole
Service Cover - Concrete/Metal
Northing (m)Northing (m)Metal Drainage Grate
Tunnel - 1898 Map

Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
Combined Interpretation of GPR Data Images andGPR Amplitude Intensity Maps for Points andZones of High Amplitude (Depths 4.00 m and over)Easting (m)Author: M McMahon
Drawn: M McMahon

Date: 3 May 2022

Plan No: C6

Report No: DG1747GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:300