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GEOPHYSICAL SURVEY REPORT
Project
Geophysical survey to map former
foundations and obstructions
Location
Harbourside development, Port Talbot
Client
WPS OPUS
Unit 1 Link Trade Park Penarth Road Cardiff CF11 8TQ United Kingdom Tel: +44 (0)2920 700127 Fax: +44 (0)8707 303051 Web: www.terradat.co.uk
Job reference: 5906 Date: March 2018 Version: 2
Geophysical Survey Report – 5906/2
Harbourside, Port Talbot March 2018 2
GEOPHYSICAL SURVEY REPORT
Project
Geophysical survey to map former foundations and
obstructions
Location
Harbourside development, Port Talbot
Client
WPS OPUS
Project Geophysicist: J Thomas BSc PhD FGS _____________
Reviewer: M Bottomley BSc MSC _____________
Job Reference: 5906
Date: March 2018
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CONTENTS
1 ....... EXECUTIVE SUMMARY .......................................................................................... 5
2 ....... INTRODUCTION ...................................................................................................... 6
2.1 Site description ................................................................................................ 6
2.2 Geological setting ............................................................................................ 7
2.3 Survey objectives ............................................................................................ 7
2.4 Survey design .................................................................................................. 7
2.5 Quality control ................................................................................................. 8
3 ....... SURVEY DESCRIPTION ......................................................................................... 8
3.1 Survey layout and topographic survey ............................................................. 9
3.2 Metal detection survey (EM-61) ....................................................................... 9
3.2.1 ..... Metal detection survey (EM-61) - field activity 9
3.2.2 ..... Metal detection survey (EM-61) - data processing 10
3.3 Magnetic survey (G-858) ................................................................................. 10
3.3.1 ..... Magnetic survey - field activity 10
3.3.2 ..... Magnetic survey - data processing 11
3.4 Electromagnetic (GEM-2) ................................................................................ 11
3.4.1 ..... Electromagnetic - field activity 12
3.4.2 ..... Electromagnetic - data processing 12
3.5 Ground penetrating radar (GPR) survey (Trivue) ............................................. 12
3.5.1 ..... GPR survey - field activity 13
3.5.2 ..... GPR survey - data processing 13
4 ....... RESULTS AND DISCUSSION ................................................................................. 14
4.1 Summary discussion ....................................................................................... 16
5 ....... CONCLUSIONS ....................................................................................................... 20
Figures
Figure 1 – Location plan
Figure 2 – EM61 – Metal Detection
Figure 3 – Magnetic – Total Field
Figure 4 – GEM-2 – Quadrature phase Figure 5 - Interpretation Plan
Figure 6 – Ground Radar – Selected sections
Figure 7 – Ground Radar – Selected sections
Figure 8 – Ground Radar – Selected sections
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Appendices EM-61 metal detection
Magnetics
GEM-2
Ground Radar
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1 EXECUTIVE SUMMARY
A geophysical survey was carried out at the Harbourside development site, Port Talbot. The
survey was commissioned by WSP OPUS (the Client) on behalf of Neath Port Talbot County
Council and took place between the 31st January and 2nd February 2018. The primary
objective of the survey was to map any former foundation structures and buried obstructions.
The survey area was approximately 3.2Ha and mainly consisted of areas of hardstanding,
remnant floor slabs and other residual surface structures following demolition work.
Historically the site has been occupied by steel works, chemical plant and some light industrial
units.
Based on the survey brief, an integrated geophysical survey was carried out consisting of
metal detection, magnetic, electromagnetic and ground radar techniques. The results of the
metal detection (EM-61) and electromagnetic (GEM-2) surveys were very good. However,
both the magnetic and radar techniques were limited by interference from the slag content
and variability within the made ground.
The resulting plots display a wide range of responses across the survey area which is typical
for this type of site. These include broad zones, lineations, localised anomalies and isolated
features. The most significant features have been highlighted on the corresponding plots and
tabulated. The most notable features include the large circular response (believed to be a
former gas holder) and the numerous rectilinear zones (remnant floor slabs/buried structures).
There are also several smaller zones, which could either be buried structures or discarded
debris within the made ground. There are also several lineations, some of which seem to
correspond with the perimeter of some of the historical buildings, while others are likely to be
buried services.
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2 INTRODUCTION
This report describes a geophysical survey that was carried out at the Harbourside
development site, Port Talbot. The survey was commissioned by WSP OPUS (the Client) on
behalf of Neath Port Talbot County Council and took place between the 31st January and 2nd
February 2018. The primary objective of the survey was to map any former foundation
structures and buried obstructions.
2.1 Site description
The Harbourside site is located approximately 500m south of Port Talbot town centre and is
centred on OS National Grid Reference 276580E, 189520N. The survey area was
approximately 3.2Ha and mainly consisted of areas of hardstanding, remnant floor slabs and
other residual surface structures following demolition work. For the purpose of this report, the
survey area has been divided into 6 zones as illustrated in Figure 1 and detailed below:
Zone A: Raised plateau region along the western edge of the survey area which appears to
have been partially landscaped.
Zone B: Small fenced off area containing some former floor slabs, manholes and other
structures.
Zone C: Small area with circular concrete feature and raised structure.
Zone D: Small fenced off gravel covered area, relatively flat with remnant floor slab.
Zone E: Main area with a mixture of demolition rubble hardstanding, remnant floor slabs, large
circular base and other residual structures.
Zone F: Tarmac road section.
Based on information provided by the Client and historical maps, the western portion of the
site was largely developed with buildings and railway for industrial use (Port Talbot Steel
Works). Reconfiguration of the buildings occurred around 1964 when they were then mostly
replaced by roadways in the western area and the eastern portion of the site was developed
as a chemical works. The works buildings were demolished and the site generally levelled at
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an undetermined date between 1997 and 2007. A selection of historical maps is included in
Figure 9.
2.2 Geological setting
Previous and more recent ground investigations on site have revealed the ground conditions
to comprise:
Made Ground: encountered across the site and was predominately granular and coarse in
nature, comprising a mixture of ash, slag, brick, concrete and stone with various inclusions of
deleterious material including metal, glass and wood. The thickness of the Made Ground
ranged from 1.0m bgl to 3.4m bgl, with an average thickness of 2.1m.
Superficial Deposits: In most of the exploratory holes that encountered natural strata,
variable granular and cohesive superficial deposits were encountered beneath the Made
Ground materials. The Made Ground, Alluvial Clay and Alluvial Sand deposits were underlain
by Alluvial Gravels and were proven to depths >10.0m bgl and indicated to be dense to very
dense granular strata.
Bedrock: Interbedded strong Sandstone and weathered Mudstone.
2.3 Survey objectives
The primary objectives of the survey were to:
Map the extent of residual foundation structures and buried obstructions.
2.4 Survey design
To map the location of the target structure, it was decided to adopt an integrated survey
approach comprising the following techniques:
Metal detection survey (Geonics EM-61) – to map variations in the metal (ferrous and
non-ferrous) content of the subsurface.
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Magnetic survey (Geometrics G-858) – to map the presence of ferrous objects and
disturbed material in the near surface.
Electromagnetic (Geophex GEM-2) – to map variations in electrical properties
(clay/water/metal content) of the subsurface.
Ground Penetrating Radar (GPR) survey (Utsi Trivue) – To provide detailed cross-
sectional images and depth plans that would be used to identify anomalous shallow
features.
2.5 Quality control
The geophysical data were collected in line with normal operating procedures as outlined by
the instrument manufacturer and TerraDat company policy. On completion of the survey, the
data was downloaded from the survey instrument onto a computer and backed up
appropriately. The acquired data set was initially checked for errors that may be caused by
instrument noise; low batteries, positional discrepancies, etc. and any field notes were either
written up or incorporated in the initial data processing stage. The data set is then processed
using the standard processing routines and once completed; the resulting plots are subject to
peer review to ensure the integrity of the interpretation. Our quality control standards are BS
EN ISO 9001: 2008 certified.
3 SURVEY DESCRIPTION
The geophysical survey was carried out using the following techniques:
Metal detection survey (EM-61)
Magnetic survey (G-858)
Electromagnetic survey (GEM-2)
Ground Penetrating Radar (GPR) survey (Utsi Trivue)
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The results of the surveys are presented in the form of interpreted data plans and sections
indicating the location and physical characteristics of identified anomalous features, together
with a description.
Background information for each of the survey methods is provided in the appendices and
descriptions of the actual survey work carried out on site are provided in the sections below.
3.1 Survey layout and topographic survey
A Network RTK dGPS system was used to set out a local survey grid that was preferentially
aligned approximately southeast-northwest to suit the alignment of the survey area. The
geophysical data sets were then acquired under both dGPS and local grid control.
The base map was supplied by the Client and contains a combination of both existing and
historical features. However, as the site has undergone more recent changes, there are some
discrepancies. Some additional topographical points were recorded during the geophysical
survey and these have been added to the original plan.
3.2 Metal detection survey (EM-61)
A metal detection survey is based on measuring the response of the ground due to the
propagation of an electromagnetic field. In contrast to other electromagnetic techniques, the
EM-61 is a time domain instrument, which means that measurements are made at set time
intervals following the cessation of the primary field. The magnitude of the response depends
on the quantity and distribution of metallic (ferrous and non-ferrous) materials within the
shallow subsurface (<3m deep).
3.2.1 Metal detection survey (EM-61) - field activity
The metal detection data were acquired using a Geonics EM-61 instrument (Plate 1). The
dataset was acquired at a nominal 0.2m interval along a series of 3m spaced parallel survey
lines.
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Plate 1: EM-61 instrument
3.2.2 Metal detection survey (EM-61) - data processing
The dataset is downloaded from the data logger and compiled using dedicated software
DAT61. Initial editing was carried out to remove positional errors and rogue values. The data
is then exported as an ‘XYZ’ file and translated into the appropriate coordinate system. The
next step is to bring the data into OASIS MONTAJ, where it can be edited and manipulated to
enhance any features of interest. The colour contour plots are then integrated with the base
plan information, and the resulting plans are exported to CORELDRAW for final annotation.
3.3 Magnetic survey (G-858)
A magnetic survey is a passive technique that measures local perturbations in the Earth’s
wider magnetic field, caused by the presence of magnetically susceptible objects in the
subsurface. These subtle perturbations are mainly a result of the presence of ferrous metals,
but some ferrous-bearing materials, such as fired red brick, slags, and ash can also give a
measurable response.
3.3.1 Magnetic survey - field activity
The magnetic survey was conducted using a Geometrics G-858 instrument which was
mounted on a bespoke hand cart (Plate 2). The data were recorded uni-directionally along 3m
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spaced survey lines in a near-continuous walking mode. The magnetic dataset was acquired
under EGNOS corrected GPS control (EZ-Guide) to an accuracy of +/- 0.5m.
3.3.2 Magnetic survey - data processing
The dataset is downloaded from the data logger and compiled using dedicated software
MAGMAP2000. Initial editing is then carried out to remove positional errors and rogue values.
The data is then exported as an ‘XYZ’ file and translated into the appropriate coordinate
system. The next step is to bring the data into OASIS MONTAJ, where it can be edited and
manipulated to enhance any features of interest. The colour contour plots are then integrated
with the base plan information, and the resulting plans are exported to CORELDRAW for final
annotation.
Plate 2: G-858 instrument
3.4 Electromagnetic (GEM-2)
An electromagnetic survey is based on measuring the response of the ground due to the
propagation of an electromagnetic field. The magnitude of this response depends on the type
and distribution of conductive material in the subsurface and can be broken into two
components, namely the quadrature and in-phase components. The quadrature is usually
converted to ground conductivity, which reflects the electrical properties of the subsurface (i.e.
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clay, water, ash, metal), while the in-phase component is dependent on the magnetic
susceptibility of the subsurface.
3.4.1 Electromagnetic - field activity
The conductivity data were acquired using a multi-frequency GEOPHEX GEM-2 instrument
that was mounted on a bespoke hand cart (Plate 2). The dataset was acquired at a nominal
0.5m interval along a series of 3m spaced parallel survey lines. For this particular survey, the
instrument was primarily configured to investigate depths of 3 to 5m below ground level. The
GEM-2 dataset was acquired under EGNOS corrected GPS control (EZ-Guide) to an accuracy
of +/- 0.5m.
3.4.2 Electromagnetic - data processing
The dataset is downloaded from the data logger and compiled using dedicated software
WINGEM-3. Initial editing was carried out to remove positional errors and rogue values. The
data is then exported as an ‘XYZ’ file and translated into the appropriate coordinate system.
The next step is to bring the data into OASIS MONTAJ, where it can be edited and
manipulated to enhance any features of interest. The colour contour plots are then integrated
with the base plan information, and the resulting plans are exported to CORELDRAW for final
annotation.
3.5 Ground penetrating radar (GPR) survey (Trivue)
A ground penetrating radar (GPR) survey involves the transmission and subsequent recording
of high frequency pulsed electromagnetic (radio) waves. The transmitted waves are focused
into the ground and can penetrate soils, sediment, rock, concrete, water and air. When this
energy wave encounters a buried object or a boundary between materials having different
permittivities, it may be reflected or refracted or scattered back to the surface. Given a
sufficient contrast, reflection events from geological or hydrological boundaries can be
observed together with ‘point’ sources such as buried services, rebar, voids and large
boulders. Readings are taken at small intervals as the radar unit is pushed along the survey
line.
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3.5.1 GPR survey - field activity
A Utsi Trivue radar system (Plate 3) using shielded 250MHz, 500MHz and 1000MHz antenna
were used to collect data continuously along a series of profile lines across the survey area
(Figure 1). The combination of these frequencies offers a balance between high-resolution
and increased levels of penetration.
Given the higher frequency (i.e. shortest wavelength), the 1000MHz (1GHz) antenna should
provide the greatest target resolution and in good ground conditions (i.e. homogenous/dry/clay
deficient sediment) has typical penetration depths of between 0.5 to 1.0m. This is in contrast
to the 250MHz antenna, which even though it can achieve greater depths (typically up to 5m),
it’s target resolution is significantly lower (i.e. suited to larger features).
Plate 3: GPR Utsi Trivue
3.5.2 GPR survey - data processing
The data processing was carried out using GPR-SLICE software, and the first stage involves
the compilation of each separate 2D profile line. A series of editing and gain functions are then
applied to enhance features of interest and the resulting sections/time slices are converted to
depth using a nominal velocity correction. Additional processing routines (e.g. bandpass
filtering, background removal, migration, etc.) may be applied to improve the coherency of the
radar events and remove any unwanted noise such as multiple reflections, diffractions, etc.
The end product is a series of depth corrected radar sections, which emphasise the key
features/responses.
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4 RESULTS AND DISCUSSION
The results of the geophysical survey are presented as a series of colour contour plots and
sections in Figures 2 to 8 and an interpretation plan in Figure 5 (and Figure 9). A general
description of the interpretation process for each technique is given below, and a summary
discussion of the results is provided in Section 4.1
Metal detection Survey (EM-61)
The results are presented as a colour contoured plot of the response by the bottom coil in
Figure 2. The interpretation of the bottom coil response is based on the principle that metal
objects within the range of the instrument (~3m) will produce a proportional response, i.e. a
relative increase in the amplitude of the response will reflect an increase in the amount of
metal present at a given depth.
Magnetic (G-858)
The results of the magnetic survey are presented as a total field plot in Figure 3. The
interpretation of a magnetic anomaly is normally based on observing the type (pole/dipole),
amplitude and wavelength of the anomalous feature. Unfortunately, the results of the magnetic
survey are disappointing when compared to the other techniques. Even though a small
number of features are observed, the chaotic nature of the magnetic response has masked
many of the others. It is likely that the presence of slag in the made ground has caused
distortions in the local magnetic field which has affected the magnetic dataset.
Electromagnetic (GEM-2)
Normally, the results of a GEM-2 survey are presented as a colour contoured plot of ground
conductivity and In-phase response. However, following a review of the data, it was decided to
only present the quadrature-phase data (i.e. primary response) from the 30,925 MHz
frequency channel, as this seemed to be the optimum dataset in terms of representing the
underlying ground conditions (Figure 4). A relative increase in quadrature values usually
indicates a localised increase in the clay/ash/water content, which for example could signify
either a lateral change in lithology or groundwater. However, it can also represent interference
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from adjacent metallic features (both above and below ground). Extreme fluctuations in
quadrature-phase values are usually indicative of instrument ‘overload’ due to high metal
content.
Ground Penetrating Radar
The results of the radar survey are presented in Figures 5 to 8 as a series of selected cross-
sectional images. Even though all three frequency datasets were considered, it was found that
the 500MHz data set was the most coherent for the shallow near-surface.
The quality of the radar data across the site was generally mixed. There was some correlation
with the other techniques and there were obvious responses over the visible structures.
However, the variable/disturbed nature of the made ground over most of the site has limited
the consistency of the interpretation. Therefore the radar results are primarily considered as a
supplement to the metal detection and electromagnetic survey. Conversely, for the adjacent
road areas (Zone F), the quality of the data was much more consistent and it was possible to
observe a number of different features.
In cross-section (i.e. radargram), the interpretation of the radar data is based on recognising
certain responses and characteristics as detailed below in Table 1. These include reflection
boundaries, diffraction hyperbolae and changes in signal character/penetration. With regards
to signal penetration, the key factor is the relative conductivity of the ground: for example, an
increase in clay or water content would attenuate the radar signal and result in a decrease in
the signal penetration.
Buried structures in cross-section are typically identified either by a large single diffraction
event, cluster of diffractions or changes in the signal character/penetration. Depending on
ground conditions and the nature of the specific buried structure, the radar can either directly
map the target structure or identify indirect attributes associated with the target structure, i.e.
disturbed ground, fill material, etc. Regarding target detectability, the main issues include the
depth of target structure, size, nature of host material (i.e. homogeneous/heterogeneous),
moisture content and the contrast between target/host materials.
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Table 1: Responses and characteristics of GPR sectional data
4.1 Summary discussion
The interpretation of the geophysical survey is primarily based on the results of the metal
detection (EM-61) and electromagnetic (GEM-2) surveys (Figure 5). The resulting plots
display a wide range of responses across the survey area which is typical for this type of site.
These include broad zones, lineations, localised anomalies and isolated features. To discuss
each anomaly/response would be exhaustive, so it was decided to highlight the most
significant and these are revealed in the corresponding figures and tabulated in Table 2 below.
Some of the responses relate to observed or recorded metallic features/structures, but many
originate from unknown buried features. Depth estimates have been provided based on the
collective response of the EM-61 and GPR.
In addition to the historical features shown on the supplied base map, a selection of historical
maps are also included and these have also been overlaid with the interpretation plan (Figure
9).
The most notable features include the large circular response (believed to be a former gas
holder) and the numerous rectilinear zones (remnant floor slabs/buried structures). There are
also several smaller zones, which could either be buried structures or discarded debris within
the made ground. The other significant responses include a number of linear features, many
of which seem to correspond to the perimeter of some of the historical buildings. It is unsure if
these are associated with the foundations or adjacent services. Many of the other linear
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features are more likely to represent buried services, e.g., the GEM-2 survey has mapped two
curved services running north-south across Zone E.
With reference to identifying the extent of hydrocarbon contamination within the vicinity of
TP05, then this is not possible due to the variable ground conditions. There is a slightly
elevated response in the GEM-2 results, but this is likely to be due to the buried structures
rather than changes in electrical properties associated with biodegradation of hydrocarbon.
The response/anomalies/features prefixed with an F are primarily associated with metal
detection and GEM-2 survey. There are some magnetic anomalies, but generally, these are
quite limited. The additional response/anomalies/features prefixed with an R relate to the radar
survey along the adjacent roadways. Even though some of these radar responses are
indicative of buried services, there is not sufficient detail/coverage to link these features and
include them on to a plan.
Feature
Eastings/ Northings
Depth range (bgl)
Metal Detection
GEM-2 Description
F1 276639.8 189482.7
0 – 1m X X
Circular zone coinciding with the former gas holder base. The GPR suggests that the reinforced concrete slab is 0.2-0.3m thick.
F2 276606.5 189493.4
0 – 1m X X
Localised rectilinear zone suggesting metallic structure. Appears to correspond with corner of historical building.
F3 276602.7 189449.3
0 – 1m X X Linear feature that correlates with buried metal pipeline.
F4 276581.1 189423.4
0 – 1m X X Localised metallic response – buried structure at corner of historical building.
F5 276535.6 189436.2
0 – 1m X X
Rectilinear response associated with floor slab in Zone D. There may be an additional buried structure to the south of the slab.
F6 276540.3 189465.6
0 – 1m X X Rectilinear response from buried feature. Seems to be associated with historical structure.
F7 276557.9 189497.3
0 – 1m X X Rectilinear response from concrete base.
Table 2: Interpreted feature description
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F8 276535.5 189488.4
0 – 1m X X Localised response from buried structure.
F9 276542.0 189516.4
0 – 1m X X Rectilinear response associated with historical building. Correlates with ‘obstruction’ during the GI.
F10 276552.9 189543.3
0 – 1m X X Rectilinear response associated with historical building.
F11 F11a
276511.5 189504.6
0 – 1m X X Linear features corresponding to the edge of historical building.
F12 276519.9 189555.2
0 – 1m X X
Localised zone within Zone A – possible discarded debris. Correlates with ‘obstruction’ during the GI.
F13 276499.2 189558.2
0 – 1m X X
Localised zone within Zone A. Seems to be associated with historical structure. Correlates with ‘obstruction’ during the GI.
F13a 276508.3 189582.9
0 – 1m X
Localised zone within Zone A. Seems to be associated with historical structure. No metallic response.
F14 276534.9 189595.5
0 – 1m X X Rectilinear response adjacent to existing floor slab.
F15 276561.1 189572.1
0 – 1m X X Localised zone within Zone B. Seems to be associated with historical structure.
F16 276587.6 189546.4
0 – 1m X X Rectilinear response that seems to lie between some historical buildings
F17 276605.0 189558.9
0 – 1m X X Localised zone within Zone E – possibly discarded debris
F18 F18a
276603.7 189519.3
0 – 1m X X Linear feature corresponding to the edge of historical building.
F19 276615.5 189517.1
0 – 3m X X Linear feature suspected to be a buried service
F19a 276601.9 189509.9
0 – 3m X Linear feature suspected to be a buried service
F20 276593.4 189536.0
0 – 1m X Linear feature suspected to be a buried service
F21 276645.8 189520.8
0 – 1m X Linear feature corresponding to the edge and centreline of historical building.
F22 276580.5 189478.3
0 – 1m X Linear feature corresponding to the edge and centre of historical building.
Table 2: Interpreted feature description (continued)
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Feature
Eastings/ Northings
Depth range (bgl
GPR EM-61 Description
R1 276669.3 189529.0
0 – 1m X Isolated diffraction - possible buried service.
R2 276674.0 189488.6
0 – 1m X Shallow reflection event– geological boundary or buried feature.
R3 276678.9 189464.8
1 – 3m X Isolated diffraction - possible buried service.
R4 276680.1 189456.4
0 – 1m X Cluster of shallow diffractions – buried service, structure or disturbed ground.
R5 276660.0 189433.3
1 – 3m X Isolated diffraction - possible buried service.
R6 276630.3 189426.2
0 – 1m X X Isolated diffraction - possible buried service. Correlation with EM-61 response.
R7 276588.3 189413.1
0 – 1m X Localised diffractions and increased penetration - buried service, structure or disturbed ground.
R8 276575.0 189407.8
0 – 1m X
Localised zone with increased penetration, diffractions & reflections. - buried service, structure or disturbed ground.
R9 276556.6 189410.0
0 – 1m X
Localised diffractions and increased penetration - buried service, structure or disturbed ground
R10 276538.9 189404.6
0 – 1m X
Localised zone with increased penetration, diffractions & reflections. - buried service, structure or disturbed ground
Table 2: Interpreted feature description (continued)
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5 CONCLUSIONS
The geophysical survey has provided a non-invasive means for investigating the
subsurface with a high degree of spatial coverage. By considering a number of
geophysical methods, it has significantly enhanced the ability to characterise the
subsurface as the techniques are based on different physical principles and provide
complementary information for interpretation.
The interpretation of the geophysical survey is primarily based on the results of the
metal detection (EM-61) and electromagnetic (GEM-2) survey. Unfortunately, the
magnetic survey seemed to be influenced by the slag material within the made ground
and thereby masking the response from the target structures. As far as the ground
radar is concerned, the variable/disturbed nature of the made ground over most of the
site has limited the consistency of the interpretation.
The resulting plots display a wide range of responses across the survey area which is
typical for this type of site. These include broad zones, lineations, localised anomalies
and isolated features. The most significant features have been highlighted on the
corresponding plots and tabulated. The most notable features include the large circular
response (believed to be a former gas holder) and the numerous rectilinear zones
(remnant floor slabs/buried structures). There are also several smaller zones, which
could either be buried structures or discarded debris within the made ground. There
are also several lineations, some of which seem to correspond to the perimeter of
some of the historical buildings, while others are likely to be buried services.
We would normally recommend some follow up invasive work to ground-truth the main
anomalies identified by the geophysical survey. However as the ground investigation
work has already been done, then it may not be necessary. If any additional
information becomes available, then it may be possible to extend the interpretation
further and calibrate the datasets
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Disclaimer
This report represents an opinionated interpretation of the geophysical data. It is intended for guidance
purposes only. Features that do not produce measurable geophysical anomalies or are hidden by other
features may remain undetected. Geophysical surveys compliment invasive/destructive methods and
provide a tool for investigating the subsurface; they do not produce data that can be taken to represent
all of the ground conditions found within the surveyed area. Areas that have not been surveyed due to
obstructed access or any other reason are excluded from the interpretation.
FIGURES
Scale:
FIGURE 11:500 at A4
LOCATION PLAN
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref:
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
KEY NOTES/OBSERVATIONS
Club
HARBOURSIDE DEVELOPMENT
PORT TALBOT
JT/5906/1
Survey area
Radar Profiles
1: Base topographic map supplied by Client
Zone A
Zone F
Zone BZone E
Zone D
Zone C
Scale:
FIGURE 21:1000 at A3
EM61 - BOTTOM COIL
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/2
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
KEY
COLOUR SCALE
Metal response
(mV)
NOTES
1: Base topographic map supplied by Client
F1
F2
F3
F4
F5
F6
F7
F8
F9
F10
F15
F12
F13
F14
F16
F17
F18
F19
F11
Survey area
Feature #(please refer to Table for full description)
F7
Scale:
FIGURE 31:1000 at A3
MAGNETIC - TOTAL FIELD
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/3
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
KEY
COLOUR SCALE
Total Field
(nT)
NOTES
1: Base topographic map supplied by Client
F1
F4
F5
F6
F9
F14
F11
F13
F17
F10
Survey area
Feature #(please refer to Table for full description)
F7
Scale:
FIGURE 41:1000 at A3
GEM2 - QUAD PHASE
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/4
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
KEY
COLOUR SCALE
Quadrature Phase
(ppm)
NOTES
1: Base topographic map supplied by Client
F1
F2
F3
F4
F5
F6
F7F8
F9
F10
F15
F14
F16
F17
F18
F19
F11
F20
F19a
F21
F22
F11a
F18a
Survey area
Feature #(please refer to Table for full description)
F7
Club
Scale:
FIGURE 51:1000 at A3
INTERPRETATION PLAN
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 13 MAR 2018
Drawn by/Ref: JT/5906/5
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
Survey area
Not surveyed due toobstructions/fences
Feature #
Feature # (radar)
Obstruction encountered during GI
(please refer to Table for full description)
(taken from Exploratory hole location plan - OPUS)
KEY
NOTES
1: Base topographic map supplied by Client
F1
F2
F3
F4
F5
F6
F7
F8
F9
F10
F15
F14
F16
F17
F18
F19
F11
F20
F19a
F21
F22
F11a
F18a
F7
F12
F13
Note: The geophysical anomalies eitherrepresent the peak or increased response ofa given feature. The shape and lateral extentof a feature is based on the limitations of thetechnique. Any response thought to originatefrom a mapped buried service or surfacestructures have not been included on theinterpretive plan.
Linear feature - may representburied services, foundations, tracks
EM-61 (metal response)
Magnetic Survey
GEM-2 (Quad-phase)
Feature classificiation
Survey Technique
- may representdisturbed ground, buried structureor service trench
Broad feature
- may representLocalised feature
disturbed ground or buried feature/debris
R10
R9
R8
R7
R6
R4
R3
R2
R1
R7
F13a
R5
Scale:
FIGURE 6NTS at A3
SELECTED GPR PROFILES
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/6
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
Survey area
KEY
NOTES
1: Base topographic map supplied by Client
a) View 1 - Looking northeast across Zone A
b) View 2 - Looking east across Zone B
Location plan of selective radar profiles
Linear feature - may representburied services, foundations, tracks
EM-61 (metal response)
Magnetic Survey
GEM-2 (Quad-phase)
Feature classificiation
Survey Technique
- may representdisturbed ground, buried structureor service trench
Broad feature
- may representLocalised feature
disturbed ground or buried feature/debris
F16
F13
F14
F12
F11a
F11
F10
F15
F13a
F15
F10 F11a
F7
F18 F18a
F6
F17
Scale:
FIGURE 7NTS at A3
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/7
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
Survey area
Feature #(please refer to Table for full description)
KEY
NOTES
1: Base topographic map supplied by Client
F7
a) View 3 - Looking north across Zone E
b) View 4 - Looking west across Zone E and F
Location plan of selective radar profiles
SELECTED GPR PROFILES
Linear feature - may representburied services, foundations, tracks
EM-61 (metal response)
Magnetic Survey
GEM-2 (Quad-phase)
Feature classificiation
Survey Technique
- may representdisturbed ground, buried structureor service trench
Broad feature
- may representLocalised feature
disturbed ground or buried feature/debris
F1
F3
F22F7
F18a
F19
F2
F19a
R4
R3
R1
R2
Scale:
FIGURE 8NTS at A3
GROUND RADAR EXAMPLES
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 13 MAR 2018
Drawn by/Ref: JT/5906/8
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
Survey area
Not surveyed due toobstructions/fences
Feature #(please refer to Table for full description)
KEY
NOTES
1: Base topographic map supplied by Client
F7
a) View 5 - Looking north across Zone F
b) View 6 - Looking north across Zone F
Location plan of selective radar profiles
EM-61 (metal response)
Magnetic Survey
GEM-2 (Quad-phase)
Ground radar
Survey Technique
R10
R8F7
R6R9
R8F7
R6
R5
Scale:
FIGURE 9NTS at A3
HISTORICAL MAPS
HARBOURSIDE DEVELOPMENT
PORT TALBOT
Title:
Project:
Date: 26 FEB 2018
Drawn by/Ref: JT/5906/9
Tel: +44 (0) 2920 700127
Web:www.terradat.co.uk
Email: [email protected]
Survey area
KEY
NOTES
1: Base topographic map supplied by Client
Note: The geophysical anomalies eitherrepresent the peak or increased response ofa given feature. The shape and lateral extentof a feature is based on the limitations of thetechnique. Any response thought to originatefrom a mapped buried service or surfacestructures have not been included on theinterpretive plan.
Linear feature - may representburied services, foundations, tracks
EM-61 (metal response)
Magnetic Survey
GEM-2 (Quad-phase)
Feature classificiation
Survey Technique
- may representdisturbed ground, buried structureor service trench
Broad feature
- may representLocalised feature
disturbed ground or buried feature/debris
c) Historical map c. 1968
a) Historical map c. 1952
b) Historical map c. 1958
Website © Copyright and data base rights Old-Maps.co.uk 2018
Website © Copyright and data base rights Old-Maps.co.uk 2018
Website © Copyright and data base rights Old-Maps.co.uk 2018
APPENDICES
Appendix - EM-61 Metal Detection Survey
Towed EM-61 with dGPS
GPS antennalinear buried
services
linear feature
Metal Response (top coil)
subtle response from former building
transmitter/
receiver coils
Constraints
Surface metal objects or structures (fences, rebar, vehicles, debris etc.) produce a strong signal that canmask more subtle response from any underlying target structures.
EM-61 survey
isolated
anomalies
The EM-61 is a time-domain metal detector that can detect both ferrous and non-ferrous metals. Theinstrument was initially designed to map buried ordnance but is now used for general site characterisationespecially in the mapping of former foundation structures. The EM-61 is either towed by hand or mountedbehind a quad bike. Readings are usually taken on a regular grid or along selected traverse lines andpositional control can be provided by dGPS if there is sufficient satellite coverage.
The instrument functions by inducing current into the ground via a transmitter coil which causes thegeneration of secondary electromagnetic fields in any ground conductors present within the depth rangeof the instrument. By taking the measurement at a relatively long time after the start of the decay, thecurrent induced in the ground has fully dissipated and only the current in the metal is still producing asecondary field. The responses are recorded and displayed by an integrated data logger.
At the end of each survey, the data are downloaded to a field computer and corrected for instrument,diurnal and positional shifts. Additional editing may be carried out to remove any 'noisy' datavalues/positions.
The results are presented as a colour contoured plot based on the responses (mV) from the receiver coilsof the instrument. The interpretation of the data is based on the principle that metal objects within therange of the instrument (~3m) will produce a response that is proportional to the amount of metal presentat a given depth. By considering the response between the top and bottom receiver coils, it is possible toderive an estimate of source depth for a given anomaly.
General principle of EM-61 surveying
data logger
power
unit
transmitter/
receiver coils
data logger and
GPS controller
Bottom Tx/Rx
Top Rx
Secondary
FieldModified
Primary Field
metal target
Transmitting mode Receiving mode
Bottom Tx/Rx
Top Rx
linear buried
services
Eddy currentsEddy currents
metal target
50m
Appendix - Magnetic Survey
Towed gradiometer with dGPS
GPS antennatop sensor
cluster of
anomalies
influence of
metal fence
Analytical signal plot
linear
feature
bottom sensor
The magnetic survey technique is based on mapping localised variations in the Earth’s magnetic field causedsub-surface magnetic materials, which range from naturally occurring magnetic minerals to man-madeferrous objects. This leads to a wide range of applications from small-scale archeology and engineeringsurveys to detect buried metallic objects, to large-scale surveys carried out to investigate regional geologicaltrends or mineralisation.
Magnetic surveys are carried out using a man-portable instrument with readings taken on a regular grid oralong selected traverse lines. The equipment functions by measuring the Earth's magnetic field to a very highprecision at each survey station. Ferrous materials in the subsurface have an induced magnetic field that issuperimposed on the Earth's field at that location creating a magnetic anomaly. The spacing of survey stationsdepends on the width of the expected anomaly, which broadens with the size, and depth of burial of thetargeted feature. Continuous profiling methods may be used for a high-resolution dataset.
Magnetometer data are stored digitally by the survey instrument and down loaded to a field computer at theend of each day. The magnetic data are then processed to enhance any identifiable anomalies and presentedon colour-contoured plots overlain with site maps (when available).
The results of the magnetic survey are usually presented as total field and analytical signal plots . The totalfield data may be used to observe the general character of the magnetic field across the survey area while thepeak values (pink) displayed on the analytical signal plot indicate the source positions for dipole type magneticanomalies. In general terms, the interpretation of a magnetic anomaly is based on observing the type(pole/dipole), amplitude and wavelength of the anomalous features.
Constraints
Metal objects or structures close to the survey area (fences, vehicles, debris etc.) produce a strong signalthat can overshadow more subtle effects of sub-surface anomalies.
Gradiometer survey
isolated
anomalies
top sensor
bottom sensor1 4 6 8 102
10
100
50
200
300
400500
1kg
of
iron
control unit/
data logger
Depth (m from sensor)
Mag
neti
cfi
eld
(nTesla
)
100kg
ofiro
n
1000kg
ofiro
n
6”
iron
pip
e
12”
iron
pip
e
Mag
neti
cfi
eld
Deeper target
Surface
Shallow target+ -
short wavelengthhigh amplitude
longer wavelengthlower amplitude
+ -
Surface
Mag
neti
cfi
eld
Magnetic anomalies Guide to anomaly size
Constraints
Power lines, buildings, metal structures (fences, rebar, vehicles, debris etc.) and buried services can interferewith the electro-magnetic measurements.
Appendix - Ground conductivity (EM) survey
Scintrex CG-3M
gravitymeter
EDM survey
instrument
General principle of EM surveyingTowed EM-38 with dGPS
Mounted EM-31 with dGPS
EM-31
GPS antenna
line marking system
transmitter receiverprimary EM field
modified
primary field
secondary
field
conductor
surface
eddy currents
shallow
limestone
bedrock
clay-rich
sediments
Ground conductivity data plot
linear feature
A nvolves the generation of an EM field at the surface andsubsequent measuring of the response as it propagates through the subsurface. The main components of the
a transmitter coil (to generate the primary EM field) and receiver coil (to measure the inducedsecondary EM field). The amplitude and phase-shift of the secondary field are recorded and are thenconverted into values for
ground conductivity or electromagnetic (EM) survey i
instrument are
ground conductivity and in-phase component (metal indicator).
The ground conductivity (EM) instruments are either hand carried or mounted/towed behind a quad bike.Readings are usually taken on a regular grid or along selected traverse lines and positional control can beprovided by dGPS if there is sufficient satellite coverage.
The selection of the particular EM instrument (EM-38/EM-31/GEM-2) is primarily based on the requiredpenetration depth of the survey. However for most conductivity surveys the GEM-2 has replaced the moreconventional EM-31 instrument due to its ability to simultaneously acquire data at different frequencies (i.e.different depth levels) and a greater depth of penetration.
The results from the EM survey can be presented as colour contoured plots of conductivity and inphase (metalresponse) data. In general terms, a relative increase in conductivity values usually indicates a local increase inclay content or water saturation. However, if there is a corresponding increase in the inphase response, theinfluence of some artificial source is likely (i.e. metal).
At the end of each survey, the survey data isdownloaded to a field computer and corrected for instrument, diurnal and positional shifts. Additional editingmay be carried out to remove any 'noisy' data values/positions.
EM-38
Single frequencyExploration depth ~1.5m
EM-31
Single frequencyExploration depth ~3 to 5m
GEM-2
Multi-frequencyExploration depth up to 10m
GPS antenna
EM-38 mounted
within trailer
A Ground Penetrating Radar (GPR) survey involves one or two people either continuously towing a radar
system or taking readings at very closely spaced intervals along selected traverse lines. GPR systems use a
pulsed electromagnetic (radio wave) transmitted via a tuned frequency antenna that can penetrate soils, rock,
concrete, and many other natural and man-made materials. Reflection events from geological or hydrological
boundaries between sufficiently contrasting materials are recorded via a receiver antenna. A time-depth
cross-section (radargram) of the shallow subsurface is constructed as the radar system is moved along a
survey line. The radargram can be depth calibrated to enable detailed interpretation given known or measured
velocities for the materials being investigated. While viewing relatively raw radar data can prove useful in the
field there are numerous processing routines that can be employed to significantly improve the results. Final
sections are presented showing annotated features of interest with apparent depth calibration.
In order to improve the quality of the recorded radar data, a number of processing routines can be applied to the
data using dedicated software (REFLEX). The final radar sections are converted to depth by applying a
conversion velocity, which is usually based on an average velocity value for the local sediments. Without any
additional calibration the measured depth to a particular feature is likely to be resolved within a 20% error
margin depending on the local velocity structure.
The main limitations affecting radar surveys are the presence of conductive materials near surface (e.g., clay
and water) which reduce penetration, and blocky material which scatters signal.
Constraints:
Metal Electrode
Multi-core Cable
Iris Resistivity
Meter
0
Distance (m)
Depth
(m)
10
5
0
50
Dipping beds withinsand dune
Water table reflection
Diffraction curvesdue to gravel zone
Lack of radar signal penetration due to clay-rich material
Ground Radar profile over a parabolic sand dune (100MHz)
Horizon 2
Horizon 1
Horizon 3
Service
Tx
Rx
Antenna
ControlUnit
Observed diffraction curves over asub-surface cavity within limestone
10.0
5.0
0.0
16
De
pth
(m)
0Distance (m)
Appendix - Ground Penetrating Radar (GPR)
General principle of Ground Radar GPR Survey in progress