ISO/TR 23211:2009
(Main)Hydrometry — Measuring the water level in a well using automated pressure transducer methods
Hydrometry — Measuring the water level in a well using automated pressure transducer methods
ISO/TR 23211:2009 provides information about the functional requirements of instrumentation for measuring the water level in a well using automated pressure transducer methods. ISO/TR 23211:2009 provides guidance for the proper selection, installation and operation of submersible pressure transducers and data loggers for the collection of hydrologic data, primarily for the collection of water-level data from wells. Basic principles, measurement needs and considerations for operating submersible pressure transducers are described and the systematic errors inherent in their use are discussed. Standard operational procedures for data collection and data processing, as well as applications of transducers for specific types of hydrologic investigations are included. Basic concepts regarding the physics of pressure and the mechanics of measuring pressure are presented, along with information on the electronics used to make and record these measurements. Guidelines for transducer calibration, proper use and quality assurance of data also are presented. Ground water field applications of pressure transducer systems are discussed, as are common problems that may corrupt data, along with suggestions for field repairs. An informative annex provides guidance on the types of pressure transducers commonly used for water-level measurement and the measurement uncertainty associated with them.
Hydrométrie — Méthodes automatisées, utilisant des transducteurs de pression, pour mesurer le niveau d'eau dans un puits
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 23211
First edition
2009-07-01
Hydrometry — Measuring the water level
in a well using automated pressure
transducer methods
Hydrométrie — Méthodes automatisées, utilisant des transducteurs de
pression, pour mesurer le niveau d'eau dans un puits
Reference number
ISO/TR 23211:2009(E)
©
ISO 2009
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ISO/TR 23211:2009(E)
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ii © ISO 2009 – All rights reserved
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ISO/TR 23211:2009(E)
Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Applications of the use of pressure transducers to ground-water resource investigations .1
4.1 Ground-water monitoring .1
4.2 Long-term monitoring.2
4.3 Short-term monitoring .4
4.4 Reducing well-bore storage .4
5 Planning considerations for sensor systems.8
5.1 General .8
5.2 Study duration and system reliability .8
5.3 Required accuracy .8
5.4 Installation location and site accessibility.9
5.5 System components and compatibility.9
5.6 Water quality .9
5.7 Number of wells.9
5.8 Well location, diameter and depth .10
5.9 Data-collection frequency.10
5.10 Data transfer .11
5.11 Cost.11
6 Assembly, calibration and testing .11
6.1 General .11
6.2 Familiarization with transducer performance.11
6.3 Linear transducer calibration.13
6.4 Sources of error in linear calibrations .14
6.5 Temperature-corrected transducer calibration .14
7 Installation.16
7.1 General .16
7.2 Care and handling .17
7.3 Shelter.18
7.4 Power requirements .19
7.5 Hanging transducers in wells .20
7.6 Measuring system drift .22
7.7 Desiccation systems .23
7.8 Transducer field calibration .23
7.9 Optimizing measurement-system performance.26
8 Data collection .27
8.1 General .27
8.2 Frequency of visits.27
8.3 Field checks .27
8.4 Data recording and retrieval.28
8.5 Verification .30
8.6 Use with data loggers .30
8.7 Field documentation .30
8.8 Maintenance.30
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ISO/TR 23211:2009(E)
9 Data processing.31
9.1 General.31
9.2 Adjustments .31
9.3 Documentation.31
Annex A (informative) Pressure transducers — Characterization, common problems and
solutions .33
A.1 Pressure transducer characterization .33
A.1.1 General.33
A.1.2 Types of pressure measurements .33
A.1.3 Common pressure units used in hydrology .34
A.1.4 Basic types of transducers for measuring pressure .35
A.1.5 Understanding pressure-transducer specifications .47
A.2 Common problems and solutions.53
A.2.1 General.53
A.2.2 Leakage.53
A.2.3 Open and short circuits .55
A.2.4 Grounding problems .56
A.2.5 Diaphragm failure .56
A.2.6 Power-supply failure .56
A.2.7 Data logger channel failure.56
A.2.8 Voltage surges .57
A.2.9 Faulty shielding.57
A.2.10 Over-range problems .57
Bibliography .58
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ISO/TR 23211:2009(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.
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.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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/TR 23211 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 8, Ground
water.
[8]
This Technical Report is based on, and much of the material is from, Freeman and others . It complements
ISO 4373, Hydrometry — Water level measuring devices.
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ISO/TR 23211:2009(E)
Introduction
Submersible pressure transducers, developed in the early 1960s, have made the collection of water-level and
pressure data much more convenient than former methods. Submersible pressure transducers, when
combined with electronic data recorders have made it possible to collect continuous or nearly continuous
water-level or pressure data from wells, piezometers, soil-moisture tensiometers, and surface water gages.
These more frequent measurements have led to an improved understanding of the hydraulic processes in
streams, soils, and aquifers.
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TECHNICAL REPORT ISO/TR 23211:2009(E)
Hydrometry — Measuring the water level in a well using
automated pressure transducer methods
1 Scope
This Technical Report provides information about the functional requirements of instrumentation for measuring
the water level in a well using automated pressure transducer methods.
This Technical Report provides guidance for the proper selection, installation and operation of submersible
pressure transducers and data loggers for the collection of hydrologic data, primarily for the collection of
water-level data from wells. Basic principles, measurement needs and considerations for operating
submersible pressure transducers are described and the systematic errors inherent in their use are discussed.
Standard operational procedures for data collection and data processing, as well as applications of
transducers for specific types of hydrologic investigations are included. Basic concepts regarding the physics
of pressure and the mechanics of measuring pressure are presented, along with information on the electronics
used to make and record these measurements. Guidelines for transducer calibration, proper use and quality
assurance of data also are presented. Ground water field applications of pressure transducer systems are
discussed, as are common problems that may corrupt data, along with suggestions for field repairs.
Annex A provides guidance on the types of pressure transducers commonly used for water-level
measurement and the measurement uncertainty associated with them.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 apply.
4 Applications of the use of pressure transducers to ground-water resource
investigations
4.1 Ground-water monitoring
Submersible pressure transducers can be used for long-term and short-term applications. This clause
discusses both applications. In addition, in 4.4, information is provided on the technique of reducing well-bore
storage so that the user can apply this technique to reduce the effective diameter of wells during slug tests or
aquifer tests.
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ISO/TR 23211:2009(E)
4.2 Long-term monitoring
4.2.1 General
Many hydrologic investigations require continual monitoring (over periods of weeks to years) of water levels in
wells. Examples of such studies include monitoring water levels for
[10], [16]
⎯ indication of earth tides ,
[6], [26]
⎯ indication of earthquakes ,
[11], [28]
⎯ determination of temporal variation in vertical or horizontal hydraulic gradients ,
[23], [28]
⎯ determination of timing and magnitude of recharge to ground water following precipitation events ,
and
⎯ monitoring of pump-and-treat operations at ground-water reclamation sites.
For many studies, even if continual data collection is not necessary, it is cost effective to monitor water-level
fluctuations in wells with a sensor rather than using human resources to collect discrete measurements.
[11], [29]
Submersible pressure transducers have long been used for monitoring water-level fluctuations in wells .
Buried in the soil, these devices also have been used for decades to monitor pressure heads. Sensors used in
this way have historically been called the “Casagrande type” pressure transducers, and are commonly used to
monitor pressure heads in and around dams. While other automated water-level sensor systems also can
provide continual water-level data in wells, submersible pressure transducers are particularly well suited for
some applications. Typically small, and requiring little maintenance because they are immersed in water, their
environmental conditions are relatively stable. Some examples of applications in which submersible pressure
transducers are particularly well suited are listed below.
4.2.2 Pressure range considerations
Submersible pressure transducers can be selected to monitor a small or large range of expected water-level
conditions. Transducers designed to measure a small pressure range can monitor stage changes of 3 m
(10 ft) or less with a very high degree of resolution and accuracy. However, higher range pressure transducers
can monitor water level changes on the order of 100 m (300 ft) with little loss of resolution or accuracy.
Pressure transducers are well suited when large and sometimes rapid stage changes are expected, such as
monitoring head changes in karst terrain, production wells, or pressure pulses associated with earthquakes.
4.2.3 Non-vertical or irregular situations
Submersible pressure transducers can be used in non-vertical or irregular wells when other systems cannot
operate effectively. For a non-vertical well, a properly calibrated pressure transducer will indicate changes in
vertical head in the well, requiring no adjustment to the data, whereas data from a float installed in the same
well would require adjustment to compensate for the well’s non-vertical orientation. Also, severe irregularities
or deviations in the bore of a well could render acoustic-velocity devices or float mechanisms inoperative,
while data from a pressure transducer would not be affected.
4.2.4 Severe environments
Submersible pressure transducers are well suited for data collection in severe environmental conditions, such
as arctic or low-latitude desert climates. The relative stability of ground-water temperature provides a much
more suitable environment for submersible pressure transducers than for sensors that are mounted above
ground or inside a well but above the water table. During freezing conditions, other types of sensors mounted
[28]
to the top of a well can be disabled by freezing of water that has condensed on the sensor . Not only is the
submersible pressure transducer usually not exposed to such extreme temperatures, if the water level in the
well is shallow enough to freeze, the pressure transducer can continue to register pressure fluctuations below
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ISO/TR 23211:2009(E)
the ice lens. If ice were present in the well, an acoustic-velocity system or a float would indicate a constant
water level. Relic ice lenses still frozen to the side of a well can hinder the operation of sensors.
4.2.5 Flowing wells
In flowing artesian wells (wells with potentiometric heads above land surface), a submersible pressure
transducer can provide potentiometric-head data. This transducer is especially well suited to provide data
when the potentiometric head fluctuates both above and below land surface. If potentiometric head rises to
the point where a standpipe is impractical, or if heads frequently drop below land surface, a submersible
pressure transducer may be the only practical option for providing continuous potentiometric-head data.
4.2.6 Large depth-to-water considerations
Wells with a depth to water greater than 100 m (300 ft) present special problems for most submersible
pressure transducers. Cable or line stretch, thermal expansion, vent-tube blockage, and signal loss can
[24]
introduce significant errors in deep wells or where sensors are located far from a logging device. O'Brien
noted that voltage problems caused by lead lengths of up to 1 500 m (5 000 ft), and blocked vent tubes, led to
problems when monitoring water-level fluctuations in deep wells. Well-bore deviation, a problem common to
deep wells, is magnified by the depth to water. Submersible pressure transducer models capable of making
an analogue to digital conversion before transmitting the signal up the well to the data logger can overcome
many of these problems.
4.2.7 Small diameter situations
To mitigate problems associated with hydraulic lag time, small-diameter piezometers commonly are installed
in wells drilled in geologic materials with low hydraulic conductivity. Although other types of sensors have
[21]
been used for monitoring water-level fluctuations in small-diameter wells , most sensors are too large to fit
inside wells with a diameter much smaller than about 2,54 cm (1 in). Vibrating wire pressure transducers small
enough to fit inside wells as small as 1,27 cm (0,5 in) can provide reliable data when some other sensor types
cannot.
4.2.8 Marsh installations
Water levels in wells installed in easily compressed materials, such as those in a salt marsh or a fen, can be
altered by a person walking on the surface so that the water levels recorded during site visits are not
representative of a site’s long-term conditions. Frequently, these wells are of small diameter to minimize
hydraulic lag time associated with low hydraulic conductivity materials. Submersible pressure transducers
[28]
have been used to provide unaltered hydraulic-head data during intervals between site visits .
4.2.9 Buried installation
Submersible pressure transducers have been used to monitor pore pressure at earth-filled dams and in slope-
stability studies. Buried transducers can provide pore-pressure data without the aid of a well. Carpenter and
[3]
others buried submersible pressure transducers in sandbars to monitor pore-pressure fluctuations in
response to significant stage changes of a river. The sensors were installed in areas where wells would not
have been feasible because the river periodically inundated the sandbar.
4.2.10 Multiple zone measurements
Submersible pressure transducers are convenient when making multiple-zone pressure-head measurements
in open boreholes containing packers that isolate intervals of the borehole. Transducers can be connected to
threaded tubes that pass through the packers and register pressure head of isolated intervals without
[15][25]
requiring the transducer to be located in those intervals . This type of connection can reduce complexity,
borehole clutter and cost.
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ISO/TR 23211:2009(E)
4.2.11 Conclusion
As shown in the previous discussion, submersible pressure transducers are well suited for many hydrologic
applications; however, their use for long-term monitoring of water levels occasionally can lead to errors if data
are not corroborated. The convenience and low maintenance of submersible pressure transducers can lead to
long intervals between calibration checks and overconfidence in the reliability of the sensor’s data. If checks
on the calibration of sensors are not made, data may be erroneous to the point of leading to incorrect
hydrologic interpretations. A study of vertical hydraulic head gradients at a well nest showed that uncorrected
data from submersible pressure transducers resulted in an interpretation of reversals in vertical hydraulic-head
[28]
gradients when none actually occurred . Linear adjustment of data based on monthly check measurements
would have led to the conclusion that additional water-table fluctuations of up to 0,052 m (0,17 ft) occurred
when weekly check measurements indicated that sensor drift actually was responsible for those interpreted
water-level fluctuations.
Gage pressure transducers usually are used to measure pressure in a water body open to the atmosphere,
whereas absolute transducers usually are used as barometers and in sealed environments such as below
packers. The user may wish to substitute absolute transducers for gage transducers to eliminate the need for
vented cable, especially to multiple transducers in close proximity, connected to one data logger. A barometer,
which can be an identical inexpensive absolute transducer, also must be operated. When using an absolute
transducer in a gage transducer application, subtract the barometric record from the water-level record to get
submergence. Three redundant barometers can be used in conjunction with many absolute transducers
measuring water levels. Because the adjusted record is the difference between two records, noise and drift
that are not common to both transducers may increase by as much as a factor of two.
An absolute transducer can also be used instead of a gage transducer to measure changes in wells in
aquifers with barometric efficiencies close to 100 %. After verifying that the barometric efficiency is indeed
close to 100 %, the original record from the absolute transducer is acceptable as the “barometrically adjusted”
record.
4.3 Short-term monitoring
Submersible pressure transducers have been used extensively for monitoring water-level fluctuations during
single-well and multiple-well aquifer and slug tests. Before the use of automated sensors, aquifer tests were
labour intensive, and early drawdown in the pumped well was not easily observed. Similarly, for single-well
slug tests in sandy material, the early portion of the recovery commonly went unrecorded simply because it
was not possible to get water-level measurements that were only seconds apart. Using submersible pressure
transducers has reduced labour costs and has provided the opportunity to collect data frequently during the
early portion of aquifer and slug tests. When combined with a programmable data logger, the pressure
transducer can supply data frequently during the early portion of the test and less frequently as the test
progresses and the recovery rate slows. For clean, coarse sand, when the recovery of a slug test can be
completed in less than half a minute, the fast response of many types of submersible pressure transducers
can allow measurement with a sampling interval of half a second or less.
The pressure transducer used for aquifer tests should be capable of reliably measuring the expected range of
water-level fluctuations. For example, for an aquifer test, the pressure transducer in the pumped well should
be capable of monitoring head changes much larger than is necessary for transducers installed in observation
wells, where changes in water level are smaller and where
...
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