Geophysical investigations for the due diligence study of dismissed urban and industrial sites

1. Geophysical survey methods: How To Manage
the Due Diligence Risk

2. One of the primary reasons for conducting a due diligence assessment on a property that
will either be purchased or sold is to understand the potential hazards and liabilities
associated with the past and present activities conducted on-site. In summary, the goal is
to “manage risk”.
The main issue is the clear understanding of what operations occurred and what the
subsurface holds.
MANAGING RISK AND UNCERTAINTY
Georadar section on an area nearby
a river with location of old bridge
arcades
10 m
1 m

3. LOCATION OF THE POTENTIAL RISKS
UXO (unexploded ordnance) location with
Magnetometer – CIRPARK Prj – Turin, 2014
In many instances, a geophysical
investigation can be part of the
solution to the problem. These non-
invasive exploratory methods can
greatly reduce the risk of missing
critical subsurface problems or
encountering a buried hazard by
providing a screening tool and
strategy for proposed follow-up
subsurface investigations.
How to identify an unknown buried
object (potential risk and hazard)
on a property?
Invasive investigations (borehole
drilling, excavations, etc.) are:
• Sometime not permitted by the
current site owner or facility
operations
• Limited at a single point and
without any certainty to locate
buried object
• location of buried utilities or
other subsurface hazards may
render invasive methods as
unsafe or impossible

4. • Non-invasive collection of data
• Cost-effective
• Quick mobilization
• Fast on-site set-up and breakdown
• Identification of hazardous prior to subsurface work
• Permitting generally not required
• Wide and comprehensive area of coverage
• No generation of impacted media
BENEFITS OF GEOPHYSICAL ASSESSMENTS
EM survey for location of waste disposal
Sacmi Prj – Scandiano (Italy), 2014

5. There are several types of geophysical methods available, all of which can be used independently or in
tandem with each other. Fr the due diligence risk assessment we can consider two different geophysical
survey: LARGE SCALE SURVEY AND (IF NECESSARY) SMALL SCALE SURVEY
Large-scale geophysical survey (surface mapping of the underground properties) –
MAGNETIC ELECTROMAGNETIC MAPPING
GEOPHYSICAL METHODS
Location of the main targets (buried tanks,
underground pipes, unknown waste disposals, any
underground anomalies)
satisfying detail NOYES
small-scale geophysical survey (anomalies
characterization) GROUND PROBING
RADAR, ELECTRICAL TOMOGRAPHY
Direct ground
investigation/remediation
FIRST PHASE
SECOND PHASE

6. Frequency Domain Electro Magnetic induction (FDEM) involves generating
an electromagnetic field (primary field) which induces current in the earth
which in turn causes the subsurface to create a secondary magnetic field.
By measuring this secondary magnetic field and the difference with the
primary field, subsurface soil properties and the main features (buried
objects) can be detected. This method measures the magnitude and phase
of induced electromagnetic currents, which are related to the subsurface
electrical conductivity. Electrical conductivity is different for soil types, ad it is
a function of the soil and rock matrix, percentage of saturation, and the
conductivity of the pore fluids. EM instruments provide two measurements
simultaneously, the electrical conductivity data and the in-phase component,
which responds to magnetic susceptibility and metal.
FDEM has distinct advantages over many other techniques. Because no
contact with the ground is required, FDEM can cover a large area quickly
and therefore with cost saving.
LARGE-SCALE GEOPHYSICAL SURVEY
Common applications of FDEM include
• the mapping of buried wastes, metal drums, UST tanks, and metal utilities
• Detect archeological remnants
• Locate UXO (unexploded Ordnance)
FD EM Survey
The survey area is divided in regular grid. The spacing
between line is usually 1 or 2 m
a
Transmitter
Receiver
target
Primary EM Field
Secondary EM Field

7. Example 1 - EM SURVEY TO LOCATE ILLEGAL UNDERGROUND DUMPING
FDEM Survey
Electrical conductivity
FDEM Survey
Magnetic susceptibility
Gas pipe
Illegal landfill
Natural soil
Foundry waste
Detection and location of an illegal waste disposal - Brescia (ITALY)
The ground conductivity maps obtained with electromagnetic survey can easily locate buried waste or
contaminated areas. The magnetic susceptivity is particularly suitable for the detection of metals and helps a
lot in the detection of buried drums or, for example, to recognize different waste type (in the example below,
foundry wastes from ferrous foundries)
REMARKS: THE EM METHOD INVOLVE A GROUND THICKNESS OF 5-6 M

8. Example 2 - EM SURVEY TO LOCATE ILLEGAL UNDERGROUND DUMPING
0 50 100 150 200
Distanza [m]
0 50 100 150 200
-120
-90
-60
-30
0
Distanza[m]
143500
145500
147500
149500
151500
Illegal disposal 1
Tyre waste illegal disposal – Old trench excavation filled with
tyre wire waste (HIGH CONDUCTIVITY)
Illegal disposal 2
Old gravel pit excavation filled with rubber waste (LOW
CONDUCTIVITY)
Mapping of an illegal waste disposal - Cuneo (ITALY)

9. SMALL-SCALE GEOPHYSICAL SURVEY
Small-scale geophysical survey has the main
objective of better defining the ground
characteristics (soil profiling, waste disposal
thickess and geometry, shape of the buried
structure, etc)
There are two main methodologies:
• ELECTRICAL RESISTIVITY
TOMOGRAPHY (ERT)
• GROUND PROBING RADAR
0m 50m 100m 150m 200m
-150
-100
-50
0
Resistivity Map
Resistivity section
Mapping of an illegal waste
disposal - Cuneo (ITALY)
Thickness of the waste
disposal = 10-11 m

10. The electrical resistivity tomography (ERT) is used to map the
subsurface distribution of electrical resistivity by means of injection of
DC current in the ground and by measuring the voltage on the ground
surface or inside boreholes. The characteristics of electric resistivity
are tightly correlated to the chemical-physics characteristics of the
ground materials and, for this reason, ERT provide a very precise
vision of the subsurface
Electrical resistivity survey are
applied to evaluate:
1. Presence of groundwater
2. Depth of bedrock
3. Mapping of contaminant plumes
4. Location of faults and rock
fractures
5. Detection of buried landfill cells
6. Location of clayey zones that
may form aquitards
7. Zones of buried constructions
debris
8. Void spaces, such as large
culverts, pipelines, caves, or
abandoned mine adits
Electrical resistivity values are
digitally recorded on a multi-
electrodes georesistivimeter and
processed using inversion software
(RES2DINV) to create 2D sections
or a three-dimensional model of the
underground. Depth of penetration:
1/3 of the length of the line
ELECTRICAL RESISTIVITY TOMOGRAPHY

11. 0 5 10 15 20 25 30 35 40 45
Distance [m]
-7
-6
-5
-4
-3
-2
-1
0
Profondità[m]
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
The plume of contamination usually show a strong
contrast with the natural soil or groundwater. The oil (and
all hydrocarbons) have a high electrical resistivity, and
can be easily recognized with the geoelectrical survey
LNAPL
MW3
Linea ERT7
GWL
DNAPL
Underground pipe
Floating oil
Polluted water
3 3.2 3.4 3.6 3.8 4 4.2 4.4
<3
(log-resistivity)
Natural soil
Oil tak
Source of the contamination
LNAPL
Example 3 – ERT SECTION TO LOCATE THE CONTAMINATION PLUME OF
PLASTIFICANT OIL IN THE GROUNDWATER TABLE
Mapping of the pollution plume due to a leakage
from an oil storage tank (project not citable)

12. GPR (GROUND PROBING RADAR) SURVEY METHOD
The ground penetrating radar (GPR - Ground Probing Radar) is a geophysical method used to investigate the near
surface underground. Thanks to its high degree of resolution, the GPR is the most effective method for locating
cavities, underground tanks or utilities, and buried artifacts, archaeological remains and structures in general. In
addition, the GPR can be used to identify geologic contacts, substrates and surface geological features of various
kinds (fractures, groundwater levels, etc..).
The GPR method can detect underground storage
tanks and pipes, underground utilities of any type
(metal, plastic and concrete). A typical GPR survey
requires the acquisition of a series of lines arranged
in a regular grid, in order to investigate the entire
site. When a radar profile crosses a cylindrical
shape (pipe or tank) across its axis, the
electromagnetic signal undergoes a reflection effect
that results in a typical hyperbolic shape .

13. For any kind of work involving excavation of the ground, the exact knowledge of the location of
underground structures is a key element for proper execution of the work. In this perspective, the use
of GPR is an excellent tool to obtain all the information needed to perform the actions provided for in an
effective way, safe and without damage to the infrastructure.
Georadar section
3D reconstruction of the buried structures
UST
Underground
tank
utilities
B
A
UST
GPR SURVEY METHOD

14. Example 4 – GPR SURVEY FOR LOCATE THE FOUNDATIONS OF SOME RADIO
TRANSMITTER TOWERS
Sistema di
dispersione a
lisca di pesce
TRANSMITTER TOWER
GPR SECTION – GEOMETRY RECONSTRUCTION OF THE
FOUNDATION
ACQUISIZIONE DATI
SKETCH MAP AND SECTION
RADAR ANTENNA
CIVIL WORKS IN THE RIGHT POSITION
Transmitter tower replacement and restoration - Pisa airport (ITALY)

15. 3
4
GPR section 3
Sketch map
GPR section 4
Site: restoration of a warehouse (Novara, 2010)
The purpose of the survey: The survey was conducted to assess the characteristics of the pavement of an old industrial building to converted in a storage warehouse. More in
detail, we detected the potential weakness zones, which may cause differential settlement or structural collapses due to concentrated loads .
Design Survey: The survey methodology was conducted with GPR (400 MHz antenna) on the whole area of the building (2000 m2): The operation required the use of
two technicians for about half a day of site acquisition.
Results: The investigation showed the presence of several underground old pipes (concrete and fiber-concrete), 15 hidden metal plates (basement of industrial machines) and
the mapping of the reinforced concrete pavement.
Example 4 –CONCRETE FLOOR ASSESSMENT OF A CONVERTED INDUSTRIAL
BUILDING
pipesReinforced concrete pavement
Small tunnel
Small tunnel
Concrete rebars
Reinforced concrete