ISO 21413:2005

INTERNATIONAL ISO
STANDARD 21413
First edition
2005-10-15
Manual methods for the measurement
of a groundwater level in a well
Méthodes manuelles pour le mesurage du niveau de l'eau souterraine
dans un puits
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope.1
2 Terms and definitions .1
3 Water-level measurement using a graduated steel tape .2
3.1 Purpose.2
3.2 Materials and instruments .2
3.3 Data accuracy and limitations.2
3.4 Advantages and disadvantages.3
3.5 Assumptions .3
3.6 Procedures.3
4 Water-level measurement using an electric tape .6
4.1 Purpose.6
4.2 Materials and instruments .6
4.3 Data accuracy and limitations.6
4.4 Advantages and disadvantages.7
4.5 Assumptions .7
4.6 Procedures.7
5 Water-level measurement using an air line.10
5.1 Purpose.10
5.2 Materials and instruments .10
5.3 Data accuracy and limitations.10
5.4 Advantages and disadvantages.11
5.5 Assumptions .11
5.6 Procedures.11
6 Water-level measurement in a flowing well .13
6.1 Purpose.13
6.2 Materials and instruments .13
6.3 Data accuracy and limitations.14
6.4 Advantages and disadvantages.15
6.5 Assumptions .15
6.6 Procedures.15
6.6.1 Low-pressure head measurement (direct measurement) .15
6.6.2 High-pressure head measurement (indirect measurement) .15
7 Establishing a permanent measuring point.16
7.1 Purpose.16
7.2 Materials and instruments .16
7.3 Data accuracy and limitations.17
7.4 Assumptions .17
7.5 Procedure.17
Annex A (informative) Corrections for water levels measured in deep wells by steel tapes subject
to temperature changes and tape stretch .26
Annex B (informative) Corrections for water levels measured in wells with the air-line method.28
Bibliography .30

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 21413 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 8, Ground
water.
iv © ISO 2005 – All rights reserved

Introduction
The measurement of a water level in a well constitutes a data-collection process that provides fundamental
information about the status of a groundwater system. Accordingly, measured water levels should be
sufficiently accurate and reproducible to meet the needs of most data-collection and monitoring programs.
Several manual methods commonly used to collect water-level data in wells employ relatively simple
measuring devices such as graduated steel tapes, electric tapes, and air lines. In some cases, water-level
measurements are required in flowing wells. The procedures associated with each of these methods are
intrinsically different and subject to varying limitations and accuracies. Standardization of these methods
would ensure that the procedures and associated equipment used by the international community to collect
water-level data in a well are consistent, and that the results can be compared with minimal concern about the
relative accuracies and/or the procedures use in collecting the data.

INTERNATIONAL STANDARD ISO 21413:2005(E)

Manual methods for the measurement of a groundwater level in
a well
1 Scope
This International Standard develops procedures and prescribes the minimum accuracy required of water-
level measurements made in wells using graduated steel tapes, electric tapes and air lines. Procedures and
accuracy requirements for measuring water levels in a flowing well are also included, as are procedures
required to establish a permanent measuring point. This International Standard discusses the advantages and
limitations of each method and requirements for recording the data. This International Standard does not
include methods that use automated electrical or mechanical means to measure and record water levels.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply:
2.1
air line
water-level measuring device consisting of a small diameter open-ended tube fixed in position that is
accessible from the top of the casing and extends to below the water level in a well where pressurized air
measurements can be used to determine the depth to water
2.2
casing (well casing)
tubular retaining structure, which is installed in a drilled borehole or excavated well, to maintain the borehole
opening. Plain (unscreened) casing prevents the entry of water and fine material into the well, while open
(screened) casing allows water ingress but should exclude fines
2.3
electric tape
water-level measuring device that uses an electrical signal, sent through a cable with fixed distance marks, to
determine the water level relative to a fixed reference point. The electrical signal, which is induced when the
sensor makes contact with the water surface, activates an indicator (typically a light, buzzer or needle)
2.4
flowing well (or overflowing well)
well from which groundwater is discharged at the ground surface without the aid of pumping
NOTE A deprecated term for this definition is an artesian well.
2.5
graduated steel tape
water-level measuring device consisting of a flat measuring tape with permanently fixed distance marks that
can be wound on a reel
2.6
groundwater
water within the saturated zone
2.7
land surface datum
average altitude of land surface at a referenced well
2.8
measuring point
permanent reference marked on well casing
2.9
static water level (or static head)
height, relative to an arbitrary reference level, of a column of water that can be supported by the static
pressure at a given point
2.10
well
hole sunk into the ground for abstraction of water or for observation purposes
3 Water-level measurement using a graduated steel tape
3.1 Purpose
The purpose of this method is to measure the depth to the water surface (level) below a measuring point using
the graduated steel tape (wetted-tape) method.
3.2 Materials and instruments
The following materials and instruments are required.
3.2.1 Steel tape graduated in metres and centimetres.
A black tape is preferred to a chromium-plated tape because the wetted chalk mark is easier to read against a
black tape. A break-away weight should be attached to the ring on the end of the tape with wire strong enough
to hold the weight, but not as strong as the tape, so that if the weight becomes lodged in the well, the tape can
still be pulled free. The weight should be made of brass, stainless steel or iron.
3.2.2 Coloured chalk.
3.2.3 Clean cloth.
3.2.4 Pencil and eraser.
3.2.5 Steel tape calibration and maintenance equipment log book.
3.2.6 Water-level measurement field form (see the example in Figure 6).
3.2.7 Equipment to gain access to the well (wrenches, crow bars, manhole keys, etc.).
3.2.8 Common household chlorine bleach or other suitable disinfect
...