INTERPRETATION REPORT:

DG1732GLD

Rep. No. 2.0

HISTORICAL DATA REVIEW
Issue date:
GROUND PENETRATING RADAR (GPR)

Page 1 of 31

09/02/2022
FREMANTLE PRISON, FREMANTLE, WA

To:

Tristan Jónsson Menzies (Golder Associates)

From:

Lee Tasker (Draig Geoscience Pty. Ltd.)

Subject:

Historical Data Review – Ground Penetrating Radar (GPR), Fremantle Prison, Fremantle, WA

1. Introduction & Objectives
Golder Associates (Golder) approached Draig Geoscience Pty. Ltd. (Draig) to review historical GPR
data from a GPR survey carried out by the University of Western Australia (UWA) in April 2016 (emailcomms. Tristan Menzies, Golder, 13/12/2021). The objectives for the historical GPR data review
were to assist with locating a possible buried well location within the area of interest. A general mapof the GPR survey area and GPR profiles was provided by Golder1 (see Figure 1).

Figure 1. A general site map of the April 2016 GPR survey profile lines (red lines) and key area ofinterest (green square) (image source: Golder).

1

Shragge, J. (2016) “Geophysical Investigation at the Fremantle Prison – Summary from the UWA GEOP4002 Class
Unit Findings”. University of Western Australia / Centre for Energy Geoscience.
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2. Data Acquisition
2.1 Geographical Location and Fieldwork Dates
Data acquisition was conducted by a volunteer student team from UWA geophysics department at
Fremantle Prison, in the interior parade grounds between 23/02/2016-25/02/2016. Draig
georeferenced the historical GPR profile map in relation to surface features in the satellite imagery
and also the alignment of those surface feature with surface responses observed in the GPR data.
The georeferenced location map is shown in Appendix A, Figure A1.

2.2 Equipment Details and Data Acquisition Parameters
Approximately 2,250 line-m of GPR profile data were acquired across the investigation site over
96 GPR profiles. Y-orientated GPR profiles (“east-west”) were labelled A_001y to A_041y.
X-orientated GPR profiles (“north-south”) were labelled A_001x to A_055x.
GPR data were acquired using a Mala GPR 500 MHz antenna and calibrated wheel encoder. A
sample frequency ~6800 MHz and a trace record length ~107 nanosec were utilised for the data
recording parameters. With these parameters the 500 MHz antenna provided a depth of coverage
to ~5-6 m.

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/).
2D raw GPR data were processed to produce “data section images” ready for interpretation (these
vertical section-view data images are also known as radargrams). These processed 2D radargrams
were also combined into a 3D data volume, creating a 3D volume of GPR amplitude intensity.
Multiple overlapping horizontal blocks of this 3D data volume, of a specified thickness at incremental
depth intervals, were gridded and exported to produce a set of 2D plan-view “average GPR
amplitude intensity map” images ready for interpretation (also known as depth slice images). (Adiagram of this concept is shown in Figure 2) These average GPR amplitude intensity maps were
exported as Surfer grid (.grd) files from GPR-Slice, and were both presented as ERMapper (.ers)
images and provided as an electronic deliverable to this report (and also displayed in Appendix B,
Figures B1-B7).

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Figure 2. Conceptual diagram of the production of depth slice images from a 3D GPR data volume.

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

Estimate dielectric constant (7.44) and background electromagnetic velocity(0.11 m/ns) (a depth of coverage ~6 m has been achieved with the 500 MHz GPR
antenna using these values), apply background filter, apply amplitude gain, apply
bandpass filter (250 MHz data: low-cut = 87 MHz, high-cut = 485 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 = 36;oThickness of slices = 38 samples, 5.58 nanosec (~0.31 m);oOverlap in slices = 50%;

➢ Grid these data slices to produce average GPR amplitude intensity maps;oGrid cell size = 0.1 m;oX-search radius = 0.8 m, Y-search radius = 0.8 m, Blanking radius = 0.8 m;

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FREMANTLE PRISON, FREMANTLE, WA➢ Display and export gridded average GPR amplitude intensity maps from GPR-Slice to Surfer
grids (.grd) format;➢ Assess for presence of GPR features in amplitude intensity maps and compare with 2D
radargram data sections in 3D space and pick interpretable feature location (if present);➢ Export Shapefile format interpretation features from average GPR amplitude intensity maps
(where applicable);➢ Export ASCII format interpretation features from radargram section images (whereapplicable).

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/hyperbola features of interest along
the radargram section data. Maps presenting depth-slice interpretation linework and radargram
section interpretation point features are presented in Appendix C, Figures C1-C8.
3.2.1. Radargram Section Interpretation
Draig initially interpreted the radargram sections for high amplitude responses (red-coloured “hotspots”) and hyperbola responses that appeared anomalous to the surrounding data. Examples ofradargram 2D data section images with high amplitude/hyperbola response features are shown in
Figure 3 and Figure 4 (black dots/red arrows indicate the top of high amplitude/hyperbola responsefeatures).

Figure 3. Radargram A_001y interpreted high amplitude/hyperbola response features (black dots/red
arrows – top of high amplitude/hyperbola response feature).

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Figure 4. Radargram A_004y interpreted high amplitude/hyperbola response features (black dots/red
arrows – top of high amplitude/hyperbola response feature).

1,706 GPR radargram point features were interpreted across the dataset. These radargram featurepoints were grouped into designated depth intervals and coloured as shown in Figure 5.

Figure 5. Radargram point feature interpretation designated depth intervals and colour coding.

3.2.2. Average GPR Amplitude Intensity Map (Depth-Slice) Interpretation
Figures presenting a representative seven of the average GPR amplitude intensity maps are shownin Appendix B – Figure B1-B7.
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%. (The linear transform stretches thecolour-scale from the lowest value data value to lowest mapped colour, to highest value mapped tohighest mapped colour.) Figure 6 shows an example of an unclipped and clipped average GPR
amplitude intensity map.

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Figure 6. (a) An average GPR amplitude intensity map (Depth-Slice 02) showing no colour clip (fullcolour-scale) and (b) showing a 1-97% clipped colour-scale. The clipped colour-scale was the colourscale used for data interpretation.

Once colour-clipped, high amplitude response targets were interpreted and traced. Figure 7 shows
an example of the interpretation linework to outline a zone of high amplitude (hot spot).

Figure 7. Example of interpretation of average GPR amplitude intensity map for high amplitude zones(hot spot). (a) An average GPR amplitude intensity map (Depth-Slice 02) with 1-97% clipped colourscale applied and interpretation drawn (magenta line), (b) interpretation linework only (magenta line).

756 high amplitude zones were interpreted over the 36 average GPR amplitude intensity maps
(depth-slices). These high amplitude zones were grouped into designated depth intervals andcoloured as shown in Figure 8.

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Figure 8. High amplitude zone (depth-slice interpretation) designated depth intervals and colour
coding.

3.2.3. Comparison of estimated location of the historical well with 2016 GPR interpretation
features
Comparing the area within which the historical well is estimated to exist, from the site plans illustrated
in the UWA geophysical report (see previous footnote 1 for reference), it can be seen that there aresome GPR interpretation features observed at multiple depths orientated approximately east-west
through the northern section of this area (length ~ 25 m, from 382297 mE / 6452729 mN to382322 mE / 6452732 mN) (see Figure 9). There is a “gap” in this east-west feature, where theobserved GPR amplitude intensity is relatively lower. To the west of the “gap” are high amplitude
zones observed over multiple depth-slices. This area has been labelled as W1 and could possibly
be an historical well feature (centre coordinate ~382313 mE, 6452731 mN).

Figure 9. Radargram point feature interpretation and high amplitude zones (depth-slice interpretation)
in relation to the area estimated to contain the historical well of interest (black dashed line). “W1”indicates possible location of historical well (satellite image source: ESRI World Map Online).
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Following the observation of a gap in the high amplitude east-west feature, Draig proceeded to
examine historical photos to correlate any GPR features with observed surface features. In doingso, Draig found some interesting correlations, many of which likely represent historical foundation
remanence from previous site infrastructure (see Figure 10 to Figure 15). A summary table of an
estimated description of the observed historical aerial photographs and the GPR interpretation
features is shown in Table 1.

Figure 10. Common features highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 1983) (satellite image source: Landgate Imagery Online).

Figure 11. Common feature highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 1985) (satellite image source: Landgate Imagery Online).
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Figure 12. Common feature highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 1989) (satellite image source: Landgate Imagery Online).

Figure 13. Common feature highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 2005) (satellite image source: Landgate Imagery Online).

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Figure 14. Common feature highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 2008) (satellite image source: Landgate Imagery Online).

Figure 15. Common features highlighted (red outline) between (a) GPR interpretation (showing area
estimated to contain the historical well of interest (black dashed line)) and (b) historical satellite image(circa. 2014) (satellite image source: Landgate Imagery Online).

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Table 1. Brief description summary table of correlated historical aerial photograph features and GPRinterpretation features.
Historical Aerial Photograph Feature ID

Brief Description

A1

Building foundation footprint

A2

Buried pipe / concreted or paved pathway

A3

Building foundation footprint

A4

Building foundation footprint

A5

Building foundation footprint

A6

Moisture catchment zone / topographic depression

A7

Trench

A8

Buried pipe

A9

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4. Conclusions
In summary, 1,706 GPR radargram point features were interpreted across the dataset. In general,
1,623 points (95% of points) were found within the top 2 m. Many of these shallow features are likely
associated with buried/surface infrastructure.
756 high amplitude zones were interpreted over the 36 average GPR amplitude intensity maps
(depth-slices).
1 feature (W1) was interpreted as a possible historical well site for future investigation within theestimated boundary of the historical well location.
9 features (A1-A9) were interpreted as possible buried structures or remnants associated withevidence observed in historical aerial photography. The estimates of possible buried structures
ranged from building foundation footprints to trenches and buried pipelines / pathways.

5. Recommendations
Following a review of the UWA 2016 electrical resistivity, magnetic and shallow electromagnetic(EM) datasets, Draig recommends a repeat data acquisition of the shallow EM dataset to improveon the dataset and provide greater clarity on the EM conductivity response in the top 1-2 m. Draig
also recommends a repeat of the data acquisition of the electrical resistivity dataset to improve on
the dataset and provide greater clarity on the electrical resistivity response in the top 5 m of the soilcolumn.

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APPENDIX A – SITE PLAN

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Easting (m)LegendGPR Survey - April 2016
10m x 10m area
Area A1 GPR survey line

GPR survey - October 2021
GPR survey line

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: 28 January 2022

Plan No: A1

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

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APPENDIX B – MAPS OF AVERAGE GPR AMPLITUDE INTENSITY(DEPTH-SLICES)DG1732GLD_2.0

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Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 01: 0.0 - 0.31 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 01: 0.0 - 0.41 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 0.0 - 0.31 m (Slice 01)

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

Date: 4 February 2022

Plan No: B1

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 05: 0.61- 0.92 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 04: 0.62 - 1.04 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 0.61 - 0.92 m (Slice 05)

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

Date: 4 February 2022

Plan No: B2

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 10: 1.38 - 1.69 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 07: 1.25 - 1.66 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 1.38 - 1.69 m (Slice 10)

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

Date: 4 February 2022

Plan No: B3

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 14: 2.00 - 2.30 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 11: 2.08 - 2.49 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 2.00 - 2.30 m (Slice 14)

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

Date: 4 February 2022

Plan No: B4

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 22: 3.23 - 3.53 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 16: 3.11 - 3.53 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 3.23 - 3.53 m (Slice 22)

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

Date: 4 February 2022

Plan No: B5

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 30: 4.45 - 4.76 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 22: 4.36 - 4.77 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 4.45 - 4.76 m (Slice 30)

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

Date: 4 February 2022

Plan No: B6

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendGPR Survey - April 2016
GPR Survey Extent(Slice 36: 5.38 - 5.53 m)

GPR Survey - October 2021
GPR Survey Extent(Slice 27: 5.4 - 5.61 m)

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

Fremantle Prison, Fremantle, WA
Average GPR amplitude intensity for
depth range 5.38 - 5.53 m (Slice 36)

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

Date: 4 February 2022

Plan No: B7

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

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APPENDIX C – COMBINED INTERPRETATION OF GPR DATAIMAGES AND MAPS FOR POINTS AND ZONES OF HIGHAMPLITUDE

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Easting (m)LegendRadargram Interpreted Points
Depth 0 to 0.9 m
Depth 1.0 to 1.9 m
Depth 2.0 to 2.9 m
Depth 3.0 to 3.9 m
Depth 4.0 to 4.9 m
Depth >= 5.0 m

GPR Survey Extent
April 2016
October 2021
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
GPR - Radargram Interpreted
Point Features

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

Date: 4 February 2022

Plan No: C1

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendDepth Slice Interpreted Linework
Depth 0 to 0.99 m
Depth 1.0 to 1.99 m
Depth 2.0 to 2.99 m
Depth 3.0 to 3.99 m
Depth 4.0 to 4.99 m
Depth >= 5 m

GPR Survey Extent
April 2016
October 2021
Northing (m)Northing (m)Image source: Landgate Satellite

Fremantle Prison, Fremantle, WA
GPR - Radargram Interpreted
Point Features

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

Date: 4 February 2022

Plan No: C2

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth 0 to 0.9 m

Depth Slice Interpreted Linework
Depth 0 to 0.92 m

GPR Survey Extent
April 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 0 - 0.99 m)

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

Date: 4 February 2022

Plan No: C3

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth 1.0 to 1.9 m

Depth Slice Interpreted Linework
Depth 1.04 to 1.87 m

GPR Group Extent
April 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 1.0 - 1.99 m)

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

Date: 4 February 2022

Plan No: C4

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth 2.0 to 2.9 m

Depth Slice Interpreted Linework
Depth 2.00 to 2.92 m

GPR Survey Extent
April 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 2.0 - 2.99 m)

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

Date: 4 February 2022

Plan No: C5

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth 3.0 to 3.9 m

Depth Slice Interpreted Linework
Depth 3.07 to 3.99 m

GPR Survey Extent
April 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 3.0 - 3.99 m)

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

Date: 4 February 2022

Plan No: C6

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth 4.0 to 4.9 m

Depth Slice Interpreted Linework
Depth 4.15 to 4.98 m

GroupApril 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 4.0 - 4.99 m)

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

Date: 4 February 2022

Plan No: C7

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250

Easting (m)LegendRadargram Interpreted Points
Depth >= 5.0 m

Depth Slice Interpreted Linework
Depth 5.07 to 5.61 m

GPR Survey Extent
April 2016
October 2021

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

Fremantle Prison, Fremantle, WA
GPR Feature Interpretation(Depths 5.0 m and greater)

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

Date: 4 February 2022

Plan No: C8

Report No: DG1732GLD_2.0

Revised:

Projection: GDA94 MGA Z50S Scale: 1:250