ISO/TR 21414:2016

Hydrometry - Groundwater - Surface geophysical surveys for hydrogeological purposes

The application of geophysical methods is an evolving science that can address a variety of objectives in groundwater investigations. However, because the successful application of geophysical methods depends on the available technology, logistics, and expertise of the investigator, there can be no single set of field procedures or approaches prescribed for all cases. ISO/TR 21414:2016 provides guidelines that are useful for conducting geophysical surveys for a variety of objectives (including environmental aspects), within the limits of modern-day instrumentation and interpretive techniques, are provided. The more commonly used field techniques and practices are described, with an emphasis on electrical resistivity, electromagnetic, and seismic refraction techniques as these are widely used in groundwater exploration. Theoretical aspects and details of interpretational procedures are referred to only in a general way. For full details, reference is intended to be made to specialized texts listed in the Bibliography.

Hydrométrie — Eaux souterraines — Relevés géophysiques de surface pour des besoins hydrogéologiques

General Information

• Status: Published
• Publication Date: 16-Feb-2016
• ICS: 07.060 - Geology. Meteorology. Hydrology
• Technical Committee: ISO/TC 113/SC 8 - Ground water
• Drafting Committee: ISO/TC 113/SC 8 - Ground water
• Current Stage: 6060 - International Standard published
• Start Date: 17-Feb-2016
• Completion Date: 13-Dec-2025

Overview

ISO/TR 21414:2016 - Hydrometry: Groundwater - Surface geophysical surveys for hydrogeological purposes provides practical guidance for applying surface geophysical methods in groundwater investigations. It recognizes that geophysical applications vary with technology, logistics and investigator expertise and therefore does not prescribe a single field procedure. Instead, it outlines useful guidelines for planning, data collection, processing and interpretation within the limits of modern instrumentation and techniques. The report emphasizes electrical resistivity, electromagnetic (EM) and seismic refraction methods while also covering self‑potential, VLF, seismic reflection and magnetic surveys.

Key Topics and Requirements

• Scope and terminology: Units, definitions and the purpose of geophysical surveys for hydrogeological objectives.
• Planning and logistics: Access, site/area details, equipment selection, safety and field precautions.
• Quality control: Field QC procedures to ensure reliable data acquisition.
• Technique-specific guidance: For each method the TR summarizes:
  • Purpose and measurement principles
  • Typical instruments and configurations
  • Field procedures for acquisition
  • Data processing and interpretation considerations
  • Advantages, disadvantages and limitations
• Focus areas: Detailed practical coverage of electrical resistivity, frequency-domain and time-domain EM, seismic refraction/reflection, self‑potential, VLF and magnetic surveys.
• Interpretation guidance: General interpretive approaches are discussed; the TR refers readers to specialized texts (listed in its bibliography) for in‑depth theoretical and inversion methodologies.

Applications

ISO/TR 21414:2016 is intended for surface geophysical surveys used in:

• Groundwater exploration and aquifer characterization (depth to water table, lithological boundaries, fracture zones)
• Environmental site assessments (contaminant plume mapping, subsurface heterogeneity)
• Hydrogeological mapping and resource evaluation
• Pre‑drilling reconnaissance and well siting

Practical benefits include improved target definition, reduced drilling risk and cost savings by informing borehole placement and aquifer testing.

Who Should Use This Standard

• Hydrogeologists and geophysicists performing groundwater surveys
• Environmental and engineering consultants conducting site investigations
• Water resource managers and planners evaluating subsurface resources
• Field teams and project managers seeking standardised guidance for survey planning, QC and method selection

Related Standards

ISO/TR 21414 complements other hydrometry and groundwater guidance documents and national survey guidelines. For detailed theory, inversion algorithms and advanced interpretation, consult the specialized texts and references listed in the TR’s bibliography and the ISO catalogue for related hydrometry standards.

Keywords: ISO/TR 21414:2016, hydrometry, groundwater, surface geophysical surveys, electrical resistivity, electromagnetic survey, seismic refraction, hydrogeological investigation.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 21414
First edition
Hydrometry: Ground water —
Surface geophysical surveys for
hydrogeological purposes
Hydrométrie: Eaux souterraines — Relevés géophysiques de surface
pour des besoins hydrogéologiques
PROOF/ÉPREUVE
Reference number
ISO/TR 21414:2015(E)
©
ISO 2015
ISO/TR 21414:2015(E)
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2015 – All rights reserved

ISO/TR 21414:2015(E)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Terms and definitions . 1
3 Units of measurement . 5
4 Purpose of geophysical survey . 5
5 Planning . 6
5.1 General considerations . 6
5.2 Access to the area . 6
5.3 Equipment . 6
5.4 Safety and precautions in operation . 6
5.5 Planning of survey . . 7
5.6 Quality control in field data collection . 7
5.7 Site/area details . 7
6 Electrical resistivity. 7
6.1 Purpose . 7
6.2 Principles of measurement . 8
6.3 Instruments .13
6.4 Field procedures .13
6.5 Processing of data .15
6.6 Interpretation .15
6.7 Advantages .17
6.8 Disadvantages .17
6.9 Limitations .17
7 Self-potential .18
7.1 Purpose .18
7.2 Principles of measurement .18
7.3 Instrument .18
7.4 Field procedures .18
7.5 Processing of data .19
7.6 Interpretation .19
7.7 Advantages .19
7.8 Disadvantages .19
7.9 Limitations .19
8 Frequency domain electromagnetic (horizontal loop) .20
8.1 Purpose .20
8.2 Principles of measurement .20
8.3 Instrument .22
8.4 Field procedures .22
8.5 Processing of data .22
8.6 Interpretations .23
8.7 Advantages .23
8.8 Disadvantages .23
8.9 Limitations .23
9 Transient (time domain) electromagnetic .24
9.1 Purpose .24
9.2 Principles of measurement .24
9.3 Instrument .24
9.4 Field procedures .24
9.5 Processing of data .25
9.6 Interpretation .25
ISO/TR 21414:2015(E)
9.7 Advantages .25
9.8 Disadvantages .25
9.9 Limitations .25
10 Very low frequency (VLF) electromagnetic .25
10.1 Purpose .25
10.2 Principles of measurement .26
10.3 Instrument .26
10.4 Field procedures .26
10.5 Processing of data .27
10.6 Interpretation .27
10.7 Advantages .27
10.8 Disadvantages .27
10.9 Limitations .28
11 Seismic refraction.28
11.1 Purpose .28
11.2 Principles of measurement .28
11.3 Instruments .32
11.4 Field procedure .32
11.5 Processing of data .33
11.6 Interpretation .33
11.7 Advantages .33
11.8 Disadvantages .33
11.9 Limitations .33
12 Seismic reflection .33
12.1 Purpose .33
12.2 Principles of measurement .33
12.3 Instrument .34
12.4 Field procedures .34
12.5 Acquisition and processing of data .35
12.6 Interpretation .35
12.7 Advantages .35
12.8 Disadvantages .35
12.9 Limitations .36
12.10 Comparison of seismic refraction and reflection methods .36
13 Magnetic .36
13.1 Purpose .36
13.2 Principles of measurement .36
13.3 Instrument .37
13.4 Field procedures .37
13.5 Processing of data .38
13.6 Interpretation .39
13.7 Advantages .39
13.8 Disadvantages .39
13.9 Limitations .39
14 Gravity .39
14.1 Purpose .39
14.2 Principles of measurement .39
14.3 Instrument .40
14.4 Field procedure .40
14.5 Processing of data .40
14.6 Micro-gravity measurements .40
14.7 Interpretation .41
14.8 Advantages .41
14.9 Disadvantages .41
14.10 Limitations .41
iv PROOF/ÉPREUVE © ISO 2015 – All rights reserved

ISO/TR 21414:2015(E)
15 Other techniques .41
15.1 Induced polarization .41
15.1.1 Purpose .41
15.1.2 Principles of measurement .41
15.1.3 Instrument .42
15.1.4 Field procedures .42
15.1.5 Processing of data .42
15.1.6 Interpretation .43
15.1.7 Advantages .43
15.1.8 Disadvantages .43
15.1.9 Limitations .43
15.2 Mise-a-la-masse .43
15.2.1 Purpose .43
15.2.2 Principles of measurement .43
15.2.3 Instrument .44
15.2.4 Field procedures .44
15.2.5 Processing of data .44
15.2.6 Interpretation .44
15.2.7 Advantages .45
15.2.8 Disadvantages .45
15.2.9 Limitations .45
15.3 Ground-Penetrating Radar (GPR) .45
15.3.1 Purpose .45
15.3.2 Principles of measurements .45
15.3.3 Field procedures and data acquisition .46
15.3.4 Interpretation .47
15.3.5 Advantages .49
15.3.6 Disadvantages .49
16 Report writing and presentation of results .50
Bibliography .52
ISO/TR 21414:2015(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 113, Hydrometry, Subcommittee SC 8,
Ground water.
vi PROOF/ÉPREUVE © ISO 2015 – All rights reserved

ISO/TR 21414:2015(E)
Introduction
Groundwater is available almost everywhere. Access to clean water is a human right and a basic
requirement for economic development. The safest kind of water supply is the use of groundwater.
However, its distribution is not uniform due to varying hydrogeological, topographical and climatic
conditions. As a result, groundwater is not always available in the required quantity and/or quality,
particularly in hard rock terrains where fractures and weathered zones are the primary conduits
for groundwater storage and flow. Detailed knowledge on the extent, hydraulic properties, and
vulnerability of groundwater reservoirs is necessary to enable a sustainable use of the resources.
Therefore, collection of information on prospective groundwater zones, although costly, is essential.
Geophysical methods are currently recognized as cost-effective techniques useful for collecting ground
water information. Measuring physical properties of the earth and their variation and then associating
these properties with hydrogeological characteristics is the objective of groundwater geophysics.
Of the various geophysical techniques available today, the electrical resistivity method is probably
most commonly used due to its relatively simple and economical field operation, its effective response
to groundwater conditions and the relative ease with which interpretations can be made. This type of
survey is occasionally supplemented by other techniques such as induced polarization, spontaneous
potential, and Mise-a-la-Masse galvanic electrical techniques. Other geophysical methods in order
of preference used for hydrogeological purpose are electromagnetic, refraction seismic, magnetic,
gravity and seismic reflection surveys. More recently developed geophysical techniques include ground
probing radar and nuclear magnetic resonance. Because surface geophysical surveys are carried out
at the surface of the earth, the responses received from different precisional demarcations. Ambiguity
exists in interpreted results and the effective application of these methods often depends on the skill
and experience of the investigator, knowledge of local hydrogeological conditions, and the utility (and
limitations) of the technique(s) themselves. The application of two or more geophysical techniques is a
useful approach to reduce ambiguity. Integration of information from other disciplines, such as remote
sensing, geologic mapping, hydrogeologic characterization, chemical analysis of well water samples,
etc., is also useful for interpreting geophysical field data.
Modern geophysical techniques are highly advanced in terms of instrumentation, field data acquisition,
and interpretation. Field data are digitized to enhance the signal-to-noise ratio and computers are used
to more accurately analyse and interpret the data. However, the present-day potential of geophysical
techniques has probably not been fully realized, not only because such surveys can be expensive, but
also because of the inadequate understanding of the application of relevant techniques in diverse
hydrogeological conditions.
TECHNICAL REPORT ISO/TR 21414:2015(E)
Hydrometry: Ground water — Surface geophysical surveys
for hydrogeological purposes
1 Scope
The application of geophysical methods is an evolving science that can address a variety of objectives
in groundwater investigations. However, because the successful application of geophysical methods
depends on the available technology, logistics, and expertise of the investigator, there can be no
single set of field procedures or approaches prescribed for all cases. This Technical Report provides
guidelines that are useful for conducting geophysical surveys for a variety of objectives (including
environmental aspects), within the limits of modern-day instrumentation and interpretive techniques,
are provided. The more commonly used field techniques and practices are described, with an emphasis
on electrical resistivity, electromagnetic, and seismic refraction techniques as these are widely used in
groundwater exploration. Theoretical aspects and details of interpretational procedures are referred
to only in a general way. For full details, reference is intended to be made to specialized texts listed in
the Bibliography.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
acoustic impedance
product of seismic velocity and density of a layer
2.2
anisotropy
variation in physical property with direction of measurement
2.3
apparent resistivity
ratio of measured voltage to input current multiplied by the geometric factor (2.16) for the electrode
configuration
2.4
blind zone
layer having seismic velocity less than that in the layer overlying it
2.5
Bouguer correction
correction made in observed gravity data to account for the attraction (gravitational) of the rock
between the datum and the plane of measurement
2.6
Bouguer anomaly
anomaly obtained after applying latitude, terrain, and elevation (free air and Bouguer) corrections to
the observed gravity value and finally subtracting it from measured value at some particular station in
the survey area
2.7
contact resistance
electrical resistance developed between an electrode planted in the ground and the ground material
immediately surrounding it
ISO/TR 21414:2015(E)
2.8
Dar Zarrouk parameters
longitudinal unit conductance and transverse unit resistance of a geoelectrical layer
2.9
deconvolution
process of inverse filtering to nullify the undesired effect of an earlier filter operation
2.10
dipole-dipole electrode configuration
configuration in which the spacing between the current electrode pair and that between the potential
electrode pair is considerably small in comparison with the distance between these two pairs
2.11
diurnal correction
correction applied to magnetic data to compensate for daily fluctuations of the geomagnetic field
2.12
drift correction
quantitative adjustment to account for a uniform change in the reference value with time
2.13
eddy current
current induced in a conductive body by the primary electromagnetic (EM) field
2.14
equivalence
function of product or ratio of two parameters (e.g. bed thickness and resistivity) where variation in
the parameters keeping the ratio or product constant can yield almost the same response
2.15
geoelectrical layer
subsurface layer having characteristic of uniform electrical resistivity
2.16
geometric factor
numerical value dependent upon the arrangement of electrodes which, when multiplied by the
measured voltage-to-current ratio, gives the apparent resistivity (2.3)
2.17
geophone
instrument which detects seismic energy and converts it into electrical voltage
2.18
gradient configuration
variation of the Schlumberger configuration (2.38) where the current electrodes are kept at a great
distance from one another and central space is scanned by a small potential dipole
2.19
half–Schlumberger configuration
configuration in which one of the current electrodes is kept at infinity (large distance) and need not be
collinear with the other three electrodes
2.20
homogeneity
characteristic of a formation with uniform physical property or properties
2.21
in-phase
component of a secondary electromagnetic (EM) field with the same phase angle as that of the exciting
primary EM field
2 PROOF/ÉPREUVE © ISO 2015 – All rights reserved

ISO/TR 21414:2015(E)
2.22
Lee-partitioning configuration
variation of the Wenner array where one additional electrode is placed at the centre between the
potential electrodes
2.23
longitudinal conductance
ratio of the thickness of a geoelectric layer to its resistivity
2.24
magnetic permeability
ratio of magnetic induction (flux density) in a body to the strength of the inducing magnetic field
2.25
magnetic susceptibility
ratio of the intensity of magnetization produced in a body to the strength of the magnetic field
2.26
migration
part of processing of seismic reflection data required to plot the dipping reflections at their correct
position
2.27
non-polarizing electrode
electrode which is not affected by electrochemical potential generated between the electrode and
ground material in which it is planted
2.28
normal moveout
effect of variation of shot-geophone distance on time of arrival of seismic reflection
2.29
off-set Wenner configuration
modification in Wenner configuration (2.48) to remove or minimize the effect of lateral inhomogeneities
2.30
overburden
part of the host medium which lies above the target and is usually of no interest in exploration, but has
physical properties that affect the measurements
2.31
phasor diagram
graph obtained by plotting in-phase (2.21) and quadrature (2.35) components of secondary
electromagnetic (EM) field for different frequencies of primary EM field
2.32
polar diagram
method of plotting resistivity sounding data
2.33
porosity
ratio of the volume of pore space in a sample to the bulk volume of that sample
2.34
proton precession magnetometer
instrument to measure the magnetic field normal to the earth’s magnetic field
2.35
quadrature
out-of-phase or imaginary component of secondary electromagnetic (EM) field
ISO/TR 21414:2015(E)
2.36
reflector
interface which separates two layers of contrasting acoustic impedance (2.1) giving rise to reflection
2.37
refractor
layer along which the refracted or head wave travels at a velocity that is higher than that in the
overlying layer
2.38
Schlumberger configuration
collinear four-electrode configuration of current and potential electrodes in which potential electrodes
are kept close to the centre of the configuration
2.39
skin depth
depth of penetration of electromagnetic (EM) field in a medium where the intensity of the EM reduces
to about 37 % of its original value at the surface of the earth
2.40
Snell’s law
laws applied when a seismic wave encounters a boundary between two media having different velocities
2.41
stacking
process of compositing data, for the same parameter, from various data sets for the purpose of
eliminating noise
2.42
suppressed layer
layer lacking a response because of its small thickness and/or contrast in physical property with the
surrounding environment
2.43
terrain correction
correction applied to measured gravity data to nullify the effect of irregular topographic relief in the
immediate vicinity of the station of measurement
2.44
transition
linear or exponential variation of a physical property with depth
2.45
transverse resistance
product of the thickness and resistivity of a geoelectrical layer (2.15)
2.46
two-electrode (pole-pole) configuration
one current and one potential electrode are kept at infinity (more than ten times the distance between
active electrodes) and perpendicular to the profile along which the other two active electrodes are moved
2.47
vibroseis
seismic survey in which a vibrator is used as a non-destructive source, instead of an explosive, to
generate controlled frequency seismic waves in the ground
2.48
Wenner configuration
collinear four-electrode configuration of potential and current electrodes in which all the electrodes
are equidistant
4 PROOF/ÉPREUVE © ISO 2015 – All rights reserved

ISO/TR 21414:2015(E)
3 Units of measurement
Table 1 list the parameters and units of measurement in common use.
Table 1 — List of commonly used geophysical techniques and units of measurement
Physical property in- Unit for parameters
Method Technique
volved measured
Electrical Sounding Resistivity Ohm-m
Resistivity Profiling
Mag. susceptibility
Magnetic
Mag. field intensity Nano Tesla
VLF Conductivity/ Inphase/quadrature
Resistivity Component (%)
HLEM Secondary/primary magnetic
Electromagnetic
field
(%)
TEM Current decay, ohm-m, µs
Refraction Wave velocity m/s
Seismic Reflection Acoustic Ns/m or Pa s/m
(High Res.) Impedance
Induced polarization Chargeability millisecond (ms)
Self-Potential (electro kinetic) Natural potential milliVolt (mV)
Mise-a-la-masse Charged-body Development of Potential milliVolt (mV)
Density
Gravity milliGal (mgal)
(lateral variation)
4 Purpose of geophysical survey
Geophysical surveys play a vital role in groundwater exploration. Surveys can be used to conduct
either shallow subsurface investigation that may be needed for many environmental-related projects
or for deeper investigations that may be required to identify productive aquifers. Also, surveys can
be used to delineate bed rock topography, estimate the thickness of weathered zones, demarcate
fracture geometry, identify the presence of limestone cavities and/or paleochannels, and to assess
quality of groundwater. Furthermore, surveys can be used to assess groundwater contamination and
the movement of plumes, define vadose zone characteristics required for waste disposal or artificial
recharge projects, demarcate sea water intrusion, differentiate between aquifers and aquitards,
monitor the quality and direction of groundwater movement, etc.; geophysical measurements are also
used to estimate hydraulic parameters of aquifers.
Geophysical methods can be grouped into two categories: natural field methods and artificial source
methods. Commonly used natural field methods include gravity, magnetic, and self-potential methods,
which measure variations in the earth’s gravity field, magnetization of rocks and earth’s natural kinetic
potential. Microgravity techniques can detect changes in ground water storage and identify saturated
cavernous limestone features. Artificial source methods measure the response of the subsurface
to artificially induced energy like seismic and electromagnetic waves and electrical currents. These
methods include electrical resistivity, induced polarization, V
...

TECHNICAL ISO/TR
REPORT 21414
First edition
2016-02-15
Hydrometry — Groundwater —
Surface geophysical surveys for
hydrogeological purposes
Hydrométrie — Eaux souterraines — Relevés géophysiques de surface
pour des besoins hydrogéologiques
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2016 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Terms and definitions . 1
3 Units of measurement . 5
4 Purpose of geophysical survey . 5
5 Planning . 6
5.1 General considerations . 6
5.2 Access to the area . 6
5.3 Equipment . 6
5.4 Safety and precautions in operation . 6
5.5 Planning of survey . . 7
5.6 Quality control in field data collection . 7
5.7 Site/area details . 7
6 Electrical resistivity. 7
6.1 Purpose . 7
6.2 Principles of measurement . 8
6.3 Instruments .13
6.4 Field procedures .13
6.5 Processing of data .15
6.6 Interpretation .15
6.7 Advantages .17
6.8 Disadvantages .17
6.9 Limitations .17
7 Self-potential .18
7.1 Purpose .18
7.2 Principles of measurement .18
7.3 Instrument .18
7.4 Field procedures .18
7.5 Processing of data .19
7.6 Interpretation .19
7.7 Advantages .19
7.8 Disadvantages .19
7.9 Limitations .19
8 Frequency domain electromagnetic (horizontal loop) .20
8.1 Purpose .20
8.2 Principles of measurement .20
8.3 Instrument .21
8.4 Field procedures .21
8.5 Processing of data .22
8.6 Interpretations .22
8.7 Advantages .22
8.8 Disadvantages .23
8.9 Limitations .23
9 Transient (time domain) electromagnetic .23
9.1 Purpose .23
9.2 Principles of measurement .23
9.3 Instrument .23
9.4 Field procedures .24
9.5 Processing of data .24
9.6 Interpretation .24
9.7 Advantages .24
9.8 Disadvantages .24
9.9 Limitations .25
10 Very low frequency (VLF) electromagnetic .25
10.1 Purpose .25
10.2 Principles of measurement .25
10.3 Instrument .25
10.4 Field procedures .26
10.5 Processing of data .26
10.6 Interpretation .26
10.7 Advantages .27
10.8 Disadvantages .27
10.9 Limitations .27
11 Seismic refraction.27
11.1 Purpose .27
11.2 Principles of measurement .27
11.3 Instruments .31
11.4 Field procedure .31
11.5 Processing of data .32
11.6 Interpretation .32
11.7 Advantages .32
11.8 Disadvantages .32
11.9 Limitations .32
12 Seismic reflection .32
12.1 Purpose .32
12.2 Principles of measurement .33
12.3 Instrument .33
12.4 Field procedures .33
12.5 Acquisition and processing of data .34
12.6 Interpretation .34
12.7 Advantages .34
12.8 Disadvantages .34
12.9 Limitations .35
12.10 Comparison of seismic refraction and reflection methods .35
13 Magnetic .35
13.1 Purpose .35
13.2 Principles of measurement .35
13.3 Instrument .36
13.4 Field procedures .36
13.5 Processing of data .37
13.6 Interpretation .38
13.7 Advantages .38
13.8 Disadvantages .38
13.9 Limitations .38
14 Gravity .38
14.1 Purpose .38
14.2 Principles of measurement .38
14.3 Instrument .39
14.4 Field procedure .39
14.5 Processing of data .39
14.6 Micro-gravity measurements .39
14.7 Interpretation .40
14.8 Advantages .40
14.9 Disadvantages .40
14.10 Limitations .40
iv © ISO 2016 – All rights reserved

15 Other techniques .40
15.1 Induced polarization .40
15.1.1 Purpose .40
15.1.2 Principles of measurement .41
15.1.3 Instrument .41
15.1.4 Field procedures .41
15.1.5 Processing of data .42
15.1.6 Interpretation .42
15.1.7 Advantages .42
15.1.8 Disadvantages .42
15.1.9 Limitations .42
15.2 Mise-a-la-masse .42
15.2.1 Purpose .42
15.2.2 Principles of measurement .42
15.2.3 Instrument .43
15.2.4 Field procedures .43
15.2.5 Processing of data .43
15.2.6 Interpretation .43
15.2.7 Advantages .44
15.2.8 Disadvantages .44
15.2.9 Limitations .44
15.3 Ground-Penetrating Radar (GPR) .44
15.3.1 Purpose .44
15.3.2 Principles of measurements .44
15.3.3 Field procedures and data acquisition .45
15.3.4 Interpretation .47
15.3.5 Advantages .49
15.3.6 Disadvantages .49
16 Report writing and presentation of results .50
Bibliography .52
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
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Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 113, Hydrometry, Subcommittee SC 8,
Ground water.
vi © ISO 2016 – All rights reserved

Introduction
Groundwater is available almost everywhere. Access to clean water is a human right and a basic
requirement for economic development. The safest kind of water supply is the use of groundwater.
However, its distribution is not uniform due to varying hydrogeological, topographical and climatic
conditions. As a result, groundwater is not always available in the required quantity and/or quality,
particularly in hard rock terrains where fractures and weathered zones are the primary conduits
for groundwater storage and flow. Detailed knowledge on the extent, hydraulic properties, and
vulnerability of groundwater reservoirs is necessary to enable a sustainable use of the resources.
Therefore, collection of information on prospective groundwater zones, although costly, is essential.
Geophysical methods are currently recognized as cost-effective techniques useful for collecting
groundwater information. Measuring physical properties of the earth and their variation and then
associating these properties with hydrogeological characteristics is the objective of groundwater
geophysics.
Of the various geophysical techniques available today, the electrical resistivity method is probably
most commonly used due to its relatively simple and economical field operation, its effective response
to groundwater conditions and the relative ease with which interpretations can be made. This type of
survey is occasionally supplemented by other techniques such as induced polarization, spontaneous
potential, and Mise-a-la-Masse galvanic electrical techniques. Other geophysical methods in order
of preference used for hydrogeological purpose are electromagnetic, seismic refraction, magnetic,
gravity and seismic reflection surveys. More recently developed geophysical techniques include ground
probing radar and nuclear magnetic resonance. Because surface geophysical surveys are carried out
at the surface of the earth, the responses received from different precisional demarcations. Ambiguity
exists in interpreted results and the effective application of these methods often depends on the skill
and experience of the investigator, knowledge of local hydrogeological conditions, and the utility (and
limitations) of the technique(s) themselves. The application of two or more geophysical techniques is a
useful approach to reduce ambiguity. Integration of information from other disciplines, such as remote
sensing, geologic mapping, hydrogeological characterization, chemical analysis of well water samples,
etc., is also useful for interpreting geophysical field data.
Modern geophysical techniques are highly advanced in terms of instrumentation, field data acquisition,
and interpretation. Field data are digitized to enhance the signal-to-noise ratio and computers are used
to more accurately analyse and interpret the data. However, the present-day potential of geophysical
techniques has probably not been fully realized, not only because such surveys can be expensive, but
also because of the inadequate understanding of the application of relevant techniques in diverse
hydrogeological conditions.
TECHNICAL REPORT ISO/TR 21414:2016(E)
Hydrometry — Groundwater — Surface geophysical
surveys for hydrogeological purposes
1 Scope
The application of geophysical methods is an evolving science that can address a variety of objectives
in groundwater investigations. However, because the successful application of geophysical methods
depends on the available technology, logistics, and expertise of the investigator, there can be no
single set of field procedures or approaches prescribed for all cases. This Technical Report provides
guidelines that are useful for conducting geophysical surveys for a variety of objectives (including
environmental aspects), within the limits of modern-day instrumentation and interpretive techniques,
are provided. The more commonly used field techniques and practices are described, with an emphasis
on electrical resistivity, electromagnetic, and seismic refraction techniques as these are widely used in
groundwater exploration. Theoretical aspects and details of interpretational procedures are referred
to only in a general way. For full details, reference is intended to be made to specialized texts listed in
the Bibliography.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
acoustic impedance
product of seismic velocity and density of a layer
2.2
anisotropy
variation in physical property with direction of measurement
2.3
apparent resistivity
ratio of measured voltage to input current multiplied by the geometric factor (2.16) for the electrode
configuration
2.4
blind zone
layer having seismic velocity less than that in the layer overlying it
2.5
Bouguer correction
correction made in observed gravity data to account for the attraction (gravitational) of the rock
between the datum and the plane of measurement
2.6
Bouguer anomaly
anomaly obtained after applying latitude, terrain, and elevation (free air and Bouguer) corrections to
the observed gravity value and finally subtracting it from measured value at some particular station in
the survey area
2.7
contact resistance
electrical resistance developed between an electrode planted in the ground and the ground material
immediately surrounding it
2.8
Dar Zarrouk parameters
longitudinal unit conductance and transverse unit resistance of a geoelectrical layer
2.9
deconvolution
process of inverse filtering to nullify the undesired effect of an earlier filter operation
2.10
dipole-dipole electrode configuration
configuration in which the spacing between the current electrode pair and that between the potential
electrode pair is considerably small in comparison with the distance between these two pairs
2.11
diurnal correction
correction applied to magnetic data to compensate for daily fluctuations of the geomagnetic field
2.12
drift correction
quantitative adjustment to account for a uniform change in the reference value with time
2.13
eddy current
current induced in a conductive body by the primary electromagnetic (EM) field
2.14
equivalence
function of product or ratio of two parameters (e.g. bed thickness and resistivity) where variation in
the parameters keeping the ratio or product constant can yield almost the same response
2.15
geoelectrical layer
subsurface layer having characteristic of uniform electrical resistivity
2.16
geometric factor
numerical value dependent upon the arrangement of electrodes which, when multiplied by the
measured voltage-to-current ratio, gives the apparent resistivity (2.3)
2.17
geophone
instrument which detects seismic energy and converts it into electrical voltage
2.18
gradient configuration
variation of the Schlumberger configuration (2.38) where the current electrodes are kept at a great
distance from one another and central space is scanned by a small potential dipole
2.19
half–Schlumberger configuration
configuration in which one of the current electrodes is kept at infinity (large distance) and need not be
collinear with the other three electrodes
2.20
homogeneity
characteristic of a formation with uniform physical property or properties
2.21
in-phase
component of a secondary electromagnetic (EM) field with the same phase angle as that of the exciting
primary EM field
2 © ISO 2016 – All rights reserved

2.22
Lee-partitioning configuration
variation of the Wenner array where one additional electrode is placed at the centre between the
potential electrodes
2.23
longitudinal conductance
ratio of the thickness of a geoelectrical layer (2.15) to its resistivity
2.24
magnetic permeability
ratio of magnetic induction (flux density) in a body to the strength of the inducing magnetic field
2.25
magnetic susceptibility
ratio of the intensity of magnetization produced in a body to the strength of the magnetic field
2.26
migration
part of processing of seismic reflection data required to plot the dipping reflections at their correct
position
2.27
non-polarizing electrode
electrode which is not affected by electrochemical potential generated between the electrode and
ground material in which it is planted
2.28
normal moveout
effect of variation of shot-geophone distance on time of arrival of seismic reflection
2.29
off-set Wenner configuration
modification in Wenner configuration (2.48) to remove or minimize the effect of lateral inhomogeneities
2.30
overburden
part of the host medium which lies above the target and is usually of no interest in exploration, but has
physical properties that affect the measurements
2.31
phasor diagram
graph obtained by plotting in-phase (2.21) and quadrature (2.35) components of secondary
electromagnetic (EM) field for different frequencies of primary EM field
2.32
polar diagram
method of plotting resistivity sounding data
2.33
porosity
ratio of the volume of pore space in a sample to the bulk volume of that sample
2.34
proton precession magnetometer
instrument to measure the magnetic field normal to the earth’s magnetic field
2.35
quadrature
out-of-phase or imaginary component of secondary electromagnetic (EM) field
2.36
reflector
interface which separates two layers of contrasting acoustic impedance (2.1) giving rise to reflection
2.37
refractor
layer along which the refracted or head wave travels at a velocity that is higher than that in the
overlying layer
2.38
Schlumberger configuration
collinear four-electrode configuration of current and potential electrodes in which potential electrodes
are kept close to the centre of the configuration
2.39
skin depth
depth of penetration of electromagnetic (EM) field in a medium where the intensity of the EM reduces
to about 37 % of its original value at the surface of the earth
2.40
Snell’s law
laws applied when a seismic wave encounters a boundary between two media having different velocities
2.41
stacking
process of compositing data, for the same parameter, from various data sets for the purpose of
eliminating noise
2.42
suppressed layer
layer lacking a response because of its small thickness and/or contrast in physical property with the
surrounding environment
2.43
terrain correction
correction applied to measured gravity data to nullify the effect of irregular topographic relief in the
immediate vicinity of the station of measurement
2.44
transition
linear or exponential variation of a physical property with depth
2.45
transverse resistance
product of the thickness and resistivity of a geoelectrical layer (2.15)
2.46
two-electrode (pole-pole) configuration
one current and one potential electrode are kept at infinity (more than ten times the distance between
active electrodes) and perpendicular to the profile along which the other two active electrodes are moved
2.47
vibroseis
seismic survey in which a vibrator is used as a non-destructive source, instead of an explosive, to
generate controlled frequency seismic waves in the ground
2.48
Wenner configuration
collinear four-electrode configuration of potential and current electrodes in which all the electrodes
are equidistant
4 © ISO 2016 – All rights reserved

3 Units of measurement
Table 1 list the parameters and units of measurement in common use.
Table 1 — List of commonly used geophysical techniques and units of measurement
Physical property in- Unit for parameters
Method Technique
volved measured
Electrical Sounding Resistivity Ohm-m
Resistivity Profiling
Mag. susceptibility
Magnetic
Mag. field intensity NanoTesla
VLF Conductivity/ Inphase/quadrature
Resistivity Component (%)
HLEM Secondary/primary magnetic
Electromagnetic
field
(%)
TEM Current decay, ohm-m, µs
Refraction Wave velocity m/s
Reflection Acoustic 3
Seismic
Ns/m or Pa s/m
(High Res.) Impedance
Induced polarization Chargeability millisecond (ms)
Self-Potential (electro kinetic) Natural potential milliVolt (mV)
Mise-a-la-masse Charged-body Development of Potential milliVolt (mV)
Density
Gravity milligal (mgal)
(lateral variation)
4 Purpose of geophysical survey
Geophysical surveys play a vital role in groundwater exploration. Surveys can be used to conduct
either shallow subsurface investigation that may be needed for many environmental-related projects
or for deeper investigations that may be required to identify productive aquifers. Also, surveys can
be used to delineate bedrock topography, estimate the thickness of weathered zones, demarcate
fracture geometry, identify the presence of limestone cavities and/or paleo-channels, and to assess
quality of groundwater. Furthermore, surveys can be used to assess groundwater contamination and
the movement of plumes, define vadose zone characteristics required for waste disposal or artificial
recharge projects, demarcate sea water intrusion, differentiate between aquifers and aquitards,
monitor the quality and direction of groundwater movement, etc.; geophysical measurements are also
used to estimate hydraulic parameters of aquifers.
Geophysical methods can be grouped into two categories: natural field methods and artificial source
methods. Commonly used natural field methods include gravity, magnetic, and self-potential methods,
which measure variations in the earth’s gravity field, magnetization of rocks and earth’s natural kinetic
potential. Microgravity techniques can detect changes in groundwater storage and identify saturated
cavernous limestone features. Artificial source methods measure the response of the subsurface
to artificially induced energy like seismic and electromagnetic waves and electrical currents. These
methods include electrical resistivity, induced polarization, Very Low Frequency (VLF) electromagnetic,
controlled-source electromagnetic, seismic refraction and, occasion
...