ASTM G200-20

Standard Test Method for Measurement of Oxidation-Reduction Potential (ORP) of Soil

SIGNIFICANCE AND USE
5.1 Soil ORP, in conjunction with other soil characteristics such as pH (see Test Method G51), and electrical resistivity (see Test Methods G57 and G187), is used to predict corrosion tendencies of buried metallic structures (for example, pipelines and culverts). The ORP of the soil is one of many factors that influence structure service life. Its measurement is used in the design of new buried structures and in the evaluation of existing buried structures.  
5.2 Soil ORP is a time-sensitive measurement. For an accurate indication of soil corrosivity, the measurement should be made in-situ in the field or as soon as practicable after removal of the soil sample from the ground.  
5.3 The user of this test method is responsible for determining the significance of reported ORP measurements. ORP alone should typically not be used in characterizing the corrosivity of a particular soil. ORP measurements are appropriate when evaluating oxygen related reactions.  
5.4 ORP measurements can sometimes be quite variable and non-reproducible. This is related, in part, to the general heterogeneity of a given soil. It is also related to the introduction of increased oxygen into the sample after extraction. The interpretation of soil ORP should be considered in terms of its general range rather than as an absolute measurement.  
5.5 ORP measurements can be used to determine if a particular soil has the propensity to support microbiologically influenced corrosion (MIC) attack. These measurements can also be used to provide an indication of whether soil conditions will be aerobic or anaerobic. Appendix X1 provides reference guidelines for general interpretation of ORP data.
SCOPE
1.1 This test method covers a procedure and related test equipment for measuring oxidation-reduction potential (ORP) of soil samples in-situ or removed from the ground.  
1.2 The procedure in Section 9 is appropriate for field and laboratory measurements.  
1.3 Accurate measurement of oxidation-reduction potential aids in the analysis of soil corrosivity and its impact on buried metallic structure corrosion rates.  
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 13.080.30 - Biological properties of soils
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.10 - Corrosion in Soils

Relations

• Refers: ASTM G187-23 - Standard Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
• Effective Date: 01-Nov-2023
• Refers: ASTM G51-23 - Standard Test Method for Measuring pH of Soil for Use in Corrosion Evaluations
• Effective Date: 01-Nov-2023
• Refers: ASTM G3-14(2019) - Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
• Effective Date: 01-May-2019
• Refers: ASTM G187-18 - Standard Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
• Effective Date: 01-May-2018
• Refers: ASTM G215-17 - Standard Guide for Electrode Potential Measurement
• Effective Date: 01-Jan-2017
• Refers: ASTM G215-16 - Standard Guide for Electrode Potential Measurement
• Effective Date: 01-May-2016
• Refers: ASTM G3-14 - Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
• Effective Date: 15-Dec-2014
• Refers: ASTM G3-13 - Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
• Effective Date: 01-Dec-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM G187-12a - Standard Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
• Effective Date: 01-Nov-2012
• Refers: ASTM G187-12 - Standard Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
• Effective Date: 01-May-2012
• Refers: ASTM G51-95(2012) - Standard Test Method for Measuring pH of Soil for Use in Corrosion Testing
• Effective Date: 01-May-2012
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM G3-89(2010) - Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
• Effective Date: 01-May-2010
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008

Overview

ASTM G200-20: Standard Test Method for Measurement of Oxidation-Reduction Potential (ORP) of Soil provides a comprehensive procedure for determining the ORP of soil samples, either in-situ (field) or following removal from the ground. Developed by ASTM International, this standard outlines the significance of soil ORP measurements, especially in relation to the assessment of corrosion risks for buried metallic structures such as pipelines and culverts.

The oxidation-reduction potential of soil is a critical parameter when evaluating corrosion processes, as it helps identify soil conditions that may accelerate or inhibit the rate of metal degradation. This standard is essential for engineers, corrosion specialists, and soil scientists who require reliable data on soil environments affecting infrastructure longevity.

Key Topics

• Test Method Coverage: Outlines equipment and procedures for measuring soil ORP in both field and laboratory settings.
• Significance of ORP: Discusses the importance of ORP measurement in tandem with other soil analyses such as pH and resistivity to predict corrosion tendencies of buried structures.
• Time Sensitivity: Emphasizes that ORP measurements should be conducted as soon as possible after sampling to ensure accuracy, as values can change due to exposure to oxygen and other environmental factors.
• Data Interpretation: Advises that ORP is one of several factors in soil corrosivity assessment. Interpretation should consider the general range, as soil heterogeneity and handling can introduce variability.
• Microbiologically Influenced Corrosion (MIC): Explains how ORP data can indicate the potential for MIC, differentiating between aerobic and anaerobic soil conditions.
• Precision and Reproducibility: Provides guidelines for repeatability and reproducibility of measurements, ensuring consistency across different operators and locations.

Applications

The procedures described in ASTM G200-20 are vital for:

• Corrosion Risk Assessment: Used by engineers and corrosion professionals to determine the likelihood of degradation in buried metallic structures, including pipelines, tanks, and culverts.
• Design of New Installations: Supports the design process for underground infrastructure, enabling selection of materials and protective measures based on anticipated soil conditions.
• Evaluation of Existing Structures: Assists in maintenance and inspection activities, providing data that inform remediation or replacement decisions.
• Environmental and Soil Characterization: Helps soil scientists and environmental consultants analyze redox conditions, contributing to broader environmental assessments.
• MIC Prevention: Offers insight into the microbiologically influenced corrosion potential, guiding mitigation strategies for at-risk environments.

Related Standards

ASTM G200-20 refers to and complements several other standards in corrosion testing:

• ASTM G51: Test Method for Measuring pH of Soil for Use in Corrosion Testing
• ASTM G57: Test Method for Measurement of Soil Resistivity Using the Wenner Four-Electrode Method
• ASTM G187: Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
• ASTM D1498: Test Method for Oxidation-Reduction Potential of Water (for aqueous samples)
• ASTM G3: Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
• ASTM G193: Terminology and Acronyms Relating to Corrosion
• ASTM G215: Guide for Electrode Potential Measurement

Practical Value

Implementing ASTM G200-20 ensures standardized, reliable ORP measurement practices, leading to:

• Accurate Corrosion Predictions: Superior data for risk management of buried assets.
• Consistent Testing Protocols: Facilitates comparison of results across projects and organizations.
• Enhanced Asset Lifespan: Informed decisions on material selection and protective strategies.
• Regulatory Compliance: Alignment with internationally recognized standardization practices.

Keywords: oxidation-reduction potential, soil ORP measurement, buried metallic structures, corrosion, ASTM G200-20, field testing, laboratory soil analysis, microbiologically influenced corrosion.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G200 − 20
Standard Test Method for
Measurement of Oxidation-Reduction Potential (ORP) of
Soil
This standard is issued under the fixed designation G200; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G3 Practice for Conventions Applicable to Electrochemical
Measurements in Corrosion Testing
1.1 This test method covers a procedure and related test
G51 Test Method for Measuring pH of Soil for Use in
equipment for measuring oxidation-reduction potential (ORP)
Corrosion Testing
of soil samples in-situ or removed from the ground.
G57 Test Method for Field Measurement of Soil Resistivity
1.2 The procedure in Section 9 is appropriate for field and
Using the Wenner Four-Electrode Method
laboratory measurements.
G187 Test Method for Measurement of Soil Resistivity
Using the Two-Electrode Soil Box Method
1.3 Accurate measurement of oxidation-reduction potential
aids in the analysis of soil corrosivity and its impact on buried G193 Terminology and Acronyms Relating to Corrosion
G215 Guide for Electrode Potential Measurement
metallic structure corrosion rates.
1.4 The values stated in inch-pound units are to be regarded
3. Terminology
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
3.1 The terminology used in this test method, if not specifi-
and are not considered standard. cally defined otherwise, shall be in accordance with Terminol-
ogy G193.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.2.1 calibration solution, n—commercially available solu-
priate safety, health, and environmental practices and deter-
tion with a stable ORP used for calibrating an ORP measuring
mine the applicability of regulatory limitations prior to use.
system (meter and probe).
1.6 This international standard was developed in accor-
3.2.2 ORP—abbreviation for oxidation-reduction potential.
dance with internationally recognized principles on standard-
3.2.3 ORP electrode (probe), n—commercially available
ization established in the Decision on Principles for the
combination two-element electrode (probe) specifically de-
Development of International Standards, Guides and Recom-
signed for the measurement of ORP when used in conjunction
mendations issued by the World Trade Organization Technical
with a compatible ORP meter.
Barriers to Trade (TBT) Committee.
3.2.3.1 Discussion—The combination probe consists of a
2. Referenced Documents platinum electrode and a reference electrode, which are gen-
2 erally silver/silver chloride. For soil measurements, the probe
2.1 ASTM Standards:
must be sufficiently robust to withstand the rigors of the
D1498 Test Method for Oxidation-Reduction Potential of
measurement. Regardless, the often fragile probe should be
Water
used with caution to avoid damage and maintain measurement
E691 Practice for Conducting an Interlaboratory Study to
reliability.
Determine the Precision of a Test Method
3.2.4 ORP meter, n—commercially available electrical me-
ter specifically designed for the measurement of ORP with
This test method is under the jurisdiction of ASTM Committee G01 on internal impedance greater than 10 megohms. Often, the meter
Corrosion of Metals and is the direct responsibility of Subcommittee G01.10 on
is capable of measuring ORPand pH when used in conjunction
Corrosion in Soils.
with the appropriate electrode.
Current edition approved Nov. 1, 2020. Published December 2020. Originally
3.2.4.1 Discussion—Standard voltmeters or multimeters
approvedin2009.Lastpreviouseditionapprovedin2014asG200-09(2014).DOI:
10.1520/G0200-20.
with internal impedances typically less than 10 megohms are
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
not suitable for soil ORP measurements. Pocket style meters
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
where the electrode is an integral part of the meter housing are
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. also not suitable.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G200 − 20
3.2.5 oxidation-reduction potential (soil), n—electrical po- 5.5 ORP measurements can be used to determine if a
tential measurement to determine the tendency of a soil to particular soil has the propensity to support microbiologically
transfer electrons between its chemical species. It is the influenced corrosion (MIC) attack. These measurements can
measured potential of an inert metal electrode (generally alsobeusedtoprovideanindicationofwhethersoilconditions
platinum) with respect to a reference electrode such as silver/ will be aerobic or anaerobic. Appendix X1 provides reference
silver chloride. guidelines for general interpretation of ORP data.
3.2.5.1 Discussion—A soil with a higher, more positive
6. Apparatus
potential has an increased tendency to acquire electrons and be
reduced (aerobic soil conditions). A soil with a lower positive
6.1 The equipment required for the measurement of soil
or negative potential has an increased tendency to lose elec-
ORP, either in the field or in the laboratory, consists of:
trons and be oxidized (anaerobic soil conditions). Soil
6.1.1 ORP Meter.
oxidation-reduction potential is typically reported in units of
6.1.2 Compatible Two-Electrode Combination ORP Elec-
millivolts (mV) or volts (1 volt = 1000 mV). Sign convention
trode (Probe)—A main probe and a backup probe are recom-
and reference electrodes conform to Practice G3.
mended.
3.2.6 redox potential, n—synonym for oxidation-reduction
NOTE 1—This test method calls for soil ORPmeasurements to utilize a
potential.
commercially available combination electrode (inert metal and reference
combined in one probe). Commercially available ORP combination
3.2.7 soil sample, n—sample of soil to be tested. The
electrodes are generally platinum (inert metal) with silver/silver chloride
minimum (typical) sample size is 1 qt.
(reference) in a 3.5 M to 4 M KCl electrolyte. (Refer to Guide G215.)
6.1.3 Operating Instructions—For ORP meter and ORP
4. Summary of Test Method
electrode.
4.1 The measurement procedure, as described in Section 9 6.1.4 Calibration Solution(s)—For verification of measur-
of this test method for determining the ORP of a soil sample,
ing system accuracy within the range of expected ORPvalues.
aids in determining the corrosivity of that sample. Calibration solutions should remain uncontaminated. They
typically have a published shelf life of no more than 1 year and
4.2 Soil ORP can be measured in a field or laboratory
should not be used once the shelf life is exceeded. Calibration
setting.
solutionscanbeobtainedcommerciallyormaybemixedinthe
4.3 While the primary purpose of this test method is
laboratory using standard pH buffers (4 and 7) and quinhy-
measuring soil ORP, it may also be used as a general indicator
drone.
of ORP in groundwater. Test Method D1498 was specifically
NOTE 2—Commercially available ORP calibration solution values
developed for accurate ORP measurements of aqueous
should be appropriate for the combination electrode (platinum and
samples.
silver/silver chloride) used. Calibration kits utilizing pH buffers and
quinhydronesolutionsaregenerallyusedfortheplatinumandsilver/silver
chloride combination electrode.
5. Significance and Use
6.1.5 Clear Plastic or Polyethylene Bags—1 gal (3.785 L)
5.1 Soil ORP, in conjunction with other soil characteristics
size is typical, or other convenient means to collect the soil
such as pH (see Test Method G51), and electrical resistivity
sampleandtocompressthesamplewhileundertest.Oneclean
(see Test Methods G57 and G187), is used to predict corrosion
and dry bag should be used for each sample. Do not reuse.
tendencies of buried metallic structures (for example, pipelines
6.1.6 Squirt Bottle and Soft Toothbrush—Bottle with goose-
and culverts). The ORP of the soil is one of many factors that
neck (or similar) filled with distilled or deionized water and
influence structure service life. Its measurement is used in the
soft toothbrush (or similar) for cleaning ORP electrode after
design of new buried structures and in the evaluation of
each measurement. Cleaning procedures should be in accor-
existing buried structures.
dance with the probe manufacturer’s written instructions and
5.2 Soil ORP is a time-sensitive measurement. For an
should in no way damage the probe or otherwise compromise
accurate indication of soil corrosivity, the measurement should
the ORP measurement.
be made in-situ in the field or as soon as practicable after
removal of the soil sample from the ground.
7. Sampling
5.3 The user of this test method is responsible for determin-
7.1 Generally, collected soil samples to be tested in the
ingthesignificanceofreportedORPmeasurements.ORPalone
laboratory shall be placed in an appropriate sealable container
shouldtypicallynotbeusedincharacterizingthecorrosivityof
or polyethylene type bag. This allows containers to be identi-
a particular soil. ORP measurements are appropriate when
fied by location, date/time sample was collected, etc.
evaluating oxygen related reactions.
7.2 Soil samples shall be representative of the area of
5.4 ORPmeasurementscansometimesbequitevariableand interest.Where the stratum of interest contains a variety of soil
non-reproducible. This is related, in part, to the general types, it is desirable to sample each type separately. Soil
heterogeneity of a given soil. It is also related to the introduc- samples to be tested in the laboratory shall be allowed to reach
tion of increased oxygen into the sample after extraction. The room temperature, approximately 68 °F (20 °C), prior to the
interpretation of soil ORP should be considered in terms of its ORP measurement. Field measurements shall reflect the soil’s
general range rather than as an absolute measurement. temperature during testing.
G200 − 20
8. Calibration and Standardization samples taken for laboratory analysis, remove all stones,
pebbles, gravel, roots, twigs and other deleterious material
8.1 Turn on the ORP meter in accordance with the meter
from t
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G200 − 09 (Reapproved 2014) G200 − 20
Standard Test Method for
Measurement of Oxidation-Reduction Potential (ORP) of
Soil
This standard is issued under the fixed designation G200; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers a procedure and related test equipment for measuring oxidation-reduction potential (ORP) of soil
samples in-situ or removed from the ground.
1.2 The procedure in Section 9 is appropriate for field and laboratory measurements.
1.3 Accurate measurement of oxidation-reduction potential aids in the analysis of soil corrosivity and its impact on buried metallic
structure corrosion rates.
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1498 Test Method for Oxidation-Reduction Potential of Water
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
G15G51 Terminology Relating to Corrosion and Corrosion Test Method for Measuring pH of Soil for Use in Corrosion Testing
(Withdrawn 2010)
G57 Test Method for Measurement of Soil Resistivity Using the Wenner Four-Electrode Method
G187 Test Method for Measurement of Soil Resistivity Using the Two-Electrode Soil Box Method
G193 Terminology and Acronyms Relating to Corrosion
G215 Guide for Electrode Potential Measurement
This test method is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.10 on Corrosion in
Soils.
Current edition approved May 1, 2014Nov. 1, 2020. Published May 2014December 2020. Originally approved in 2009. Last previous edition approved in 20092014 as
G200 - 09.09(2014). DOI: 10.1520/G0200-09R14.10.1520/G0200-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G200 − 20
3. Terminology
3.1 The terminology used in this test method, if not specifically defined otherwise, shall be in accordance with Terminology
G15G193.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration solution, n—commercially available solution with a stable ORP used for calibrating an ORP measuring system
(meter and probe).
3.2.2 ORP—abbreviation for oxidation-reduction potential.
3.2.3 ORP electrode (probe), n—commercially available combination two-element electrode (probe) specifically designed for the
measurement of ORP when used in conjunction with a compatible ORP meter.
3.2.3.1 Discussion—
The combination probe consists of a platinum electrode and a reference electrode, which are generally silver/silver chloride. For
soil measurements, the probe must be sufficiently robust to withstand the rigors of the measurement. Regardless, the often fragile
probe should be used with caution to avoid damage and maintain measurement reliability.
3.2.4 ORP meter, n—commercially available electrical meter specifically designed for the measurement of ORP with internal
impedance greater than 10 Ω.megohms. Often, the meter is capable of measuring ORP and pH when used in conjunction with the
appropriate electrode.
3.2.4.1 Discussion—
Standard voltmeters or multimeters with internal impedances typically less than 10 Ωmegohms are not suitable for soil ORP
measurements. Pocket style meters where the electrode is an integral part of the meter housing are also not suitable.
3.2.5 oxidation-reduction potential (soil), n—electrical potential measurement to determine the tendency of a soil to transfer
electrons between its chemical species. It is the measured potential of an inert metal electrode (generally platinum) with respect
to a reference electrode such as silver/silver chloride.
3.2.5.1 Discussion—
A soil with a higher, more positive potential has an increased tendency to acquire electrons and be reduced (aerobic soil
conditions). A soil with a lower positive or negative potential has an increased tendency to lose electrons and be oxidized
(anaerobic soil conditions). Soil oxidation-reduction potential is typically reported in units of millivolts (mV) or volts (1 volt =
1000 mV). Sign convention and reference electrodes conform to Practice G3.
3.2.6 redox potential, n—synonym for oxidation-reduction potential.
3.2.7 soil sample, n—sample of soil to be tested. The minimum (typical) sample size is 1 qt.
4. Summary of Test Method
4.1 The measurement procedure, as described in Section 9 of this test method for determining the ORP of a soil sample, aids in
determining the corrosivity of that sample.
4.2 Soil ORP can be measured in a field or laboratory setting.
4.3 While the primary purpose of this test method is measuring soil ORP, it may also be used as a general indicator of ORP in
groundwater. Test Method D1498 was specifically developed for accurate ORP measurements of aqueous samples.
5. Significance and Use
5.1 Soil ORP, in conjunction with other soil characteristics such as pH (see Test Method G51), and electrical resistivity (see Test
Methods G57 and G187), is used to predict corrosion tendencies of buried metallic structures (for example, pipelines and
culverts.culverts). The ORP of the soil is one of many factors that influence structure service life. Its measurement is used in the
design of new buried structures and in the evaluation of existing buried structures.
G200 − 20
5.2 Soil ORP is a time-sensitive measurement. For an accurate indication of soil corrosivity, the measurement should be made
in-situ in the field or as soon as practicable after removal of the soil sample from the ground.
5.3 The user of this test method is responsible for determining the significance of reported ORP measurements. ORP alone should
typically not be used in characterizing the corrosivity of a particular soil. ORP measurements are appropriate when evaluating
oxygen related reactions.
5.4 ORP measurements can sometimes be quite variable and non-reproducible. This is related, in part, to the general heterogeneity
of a given soil. It is also related to the introduction of increased oxygen into the sample after extraction. The interpretation of soil
ORP should be considered in terms of its general range rather than as an absolute measurement.
5.5 ORP measurements can be used to determine if a particular soil has the propensity to support microbiologically influenced
corrosion (MIC) attack. These measurements can also be used to provide an indication of whether soil conditions will be aerobic
or anaerobic. Appendix X1 provides reference guidelines for general interpretation of ORP data.
6. Apparatus
6.1 The equipment required for the measurement of soil ORP, either in the field or in the laboratory, consists of:
6.1.1 ORP Meter. ORP Meter.
6.1.2 Compatible Two-Electrode Combination ORP Electrode (Probe)—A main probe and a backup probe are recommended.
NOTE 1—This test method calls for soil ORP measurements to utilize a commercially available combination electrode (inert metal and reference combined
in one probe). Commercially available ORP combination electrodes are generally platinum (inert metal) with silver/silver chloride (reference) in a
3.53.5 M to 4 M 4 M KCl electrolyte. (Refer to Guide G215.)
6.1.3 Operating Instructions—For ORP meter and ORP electrode.
6.1.4 Calibration Solution(s)—For verification of measuring system accuracy within the range of expected ORP values.
Calibration solutions should remain uncontaminated. They typically have a published shelf life of no more than 1 year and should
not be used once the shelf life is exceeded. Calibration solutions can be obtained commercially or may be mixed in the laboratory
using standard pH buffers (4 and 7) and quinhydrone.
NOTE 2—Commercially available ORP calibration solution values should be appropriate for the combination electrode (platinum and silver/silver
chloride) used. Calibration kits utilizing pH buffers and quinhydrone solutions are generally used for the platinum and silver/silver chloride combination
electrode.
6.1.5 Clear Plastic or Polyethylene Bags—1 gal (3.785 L) size is typical, or other convenient means to collect the soil sample and
to compress the sample while under test. One clean and dry bag should be used for each sample. Do not reuse.
6.1.6 Squirt Bottle and Soft Toothbrush—Bottle with gooseneck (or similar) filled with distilled or deionized water and soft
toothbrush (or similar) for cleaning ORP electrode after each measurement. Cleaning procedures should be in accordance with the
probe manufacturer’s written instructions and should in no way damage the probe or otherwise compromise the ORP measurement.
7. Sampling
7.1 Generally, collected soil samples to be tested in the laboratory shall be placed in an appropriate sealable container or
polyethylene type bag. This allows containers to be identified by location, date/time sample was collected, etc.
7.2 Soil samples shall be representative of the area of interest. Where the stratum of interest contains a variety of soil types, it is
desirable to sample each type separately. Soil samples to be tested in the laboratory shall be allowed to reach room temperature,
approximately 68°F (20°C),68 °F (20 °C), prior to the ORP measurement. Field measurements shall reflect the soil’s temperature
during testing.
G200 − 20
8. Calibration and Standardization
8.1 Turn on the ORP meter in accordance with the meter manufacturer’s written instructions. Allow sufficient warm-up/
stabilization time as specified by the manufacturer.
8.2 Check the meter “zero” by shorting the input connection Calibrate ORP meter in accordance with the manufacturer’s
instructions. For a BNC type connection and probe cable, a paper clip between the me
...