ASTM D6764-02(2019)

Standard Guide for Collection of Water Temperature, Dissolved-Oxygen Concentrations, Specific Electrical Conductance, and pH Data from Open Channels

SIGNIFICANCE AND USE
5.1 This guide describes stabilization criteria for recording field measurements of temperature, DO, SC, and pH.  
5.2 This guide describes the procedures used to calibrate and check meters to be used in the field to records these measurements and the procedures to be use in the field to obtain these data.  
5.3 This guide describes quality assurance procedures to be followed when obtaining cross-sectional means of temperature, DO, SC, and pH of water flowing in open channels.  
5.4 Field measurement must accurately represent the water flowing in the open channel being measured. Methods need to be used that will result in an accurate representation of the mean of the parameter of interest. Procedures must be used that will take into consideration the variation in the parameter across the sections and with depth.  
5.5 Temperature and DO must be measured directly in the water in the open channel. SC and pH are often measured in situ, but also may be measured in a subsample of a composite sample collected using discharge-weighted methods.
SCOPE
1.1 This guide describes procedures to collect cross-sectional means of temperature, dissolved oxygen (DO), specific electrical conductance (SC), and pH of water flowing in open channels.  
1.2 This guide provides guidelines for preparation and calibration of the equipment to collect cross-sectional means of temperature, DO, SC, and pH of water flowing in open channels.  
1.3 This guide describes what equipment should be used to collect cross-sectional means of temperature, DO, SC, and pH of water flowing in open channels.  
1.4 This guide covers the cross-sectional means of temperature, DO, SC, and pH of fresh water flowing in open channels.  
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-2019
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.07 - Sediments, Geomorphology, and Open-Channel Flow

Relations

• Replaces: ASTM D6764-02(2013) - Standard Guide for Collection of Water Temperature, Dissolved-Oxygen Concentrations, Specific Electrical Conductance, and pH Data from Open Channels
• Effective Date: 01-Nov-2019
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D4411-03(2019) - Standard Guide for Sampling Fluvial Sediment in Motion
• Effective Date: 01-Nov-2019
• Refers: ASTM D4410-16 - Terminology for Fluvial Sediment
• Effective Date: 01-Jan-2016
• Refers: ASTM D4411-03(2014) - Standard Guide for Sampling Fluvial Sediment in Motion
• Effective Date: 01-Jan-2014
• Refers: ASTM D4411-03(2014)e1 - Standard Guide for Sampling Fluvial Sediment in Motion
• Effective Date: 01-Jan-2014
• Refers: ASTM D888-12e1 - Standard Test Methods for Dissolved Oxygen in Water
• Effective Date: 01-Mar-2012
• Refers: ASTM D888-12 - Standard Test Methods for Dissolved Oxygen in Water
• Effective Date: 01-Mar-2012
• Refers: ASTM D1293-12 - Standard Test Methods for pH of Water
• Effective Date: 01-Jan-2012
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D4410-10 - Terminology for Fluvial Sediment
• Effective Date: 01-Feb-2010
• Refers: ASTM D4411-03(2008) - Standard Guide for Sampling Fluvial Sediment in Motion
• Effective Date: 01-Oct-2008
• Refers: ASTM D5464-07 - Standard Test Method for pH Measurement of Water of Low Conductivity
• Effective Date: 01-Aug-2007
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006

Overview

ASTM D6764-02(2019) provides comprehensive guidelines for the accurate collection of cross-sectional means of water temperature, dissolved-oxygen (DO) concentration, specific electrical conductance (SC), and pH in open channels. Published by ASTM International, this standard ensures that water quality data gathered in rivers, streams, and other open channels are scientifically robust and representative of actual conditions. It addresses both the preparation and calibration of measurement equipment, stipulates best practices for field data collection, and highlights essential quality assurance procedures.

Key Topics

• Measurement Stabilization and Representation:
  The standard outlines stabilization criteria for recording field measurements of temperature, DO, SC, and pH. Field readings must stabilize within prescribed variability thresholds to ensure accuracy.

• Equipment Calibration and Verification:
  Procedures for the preparation, calibration, and field verification of meters and sensors are covered, emphasizing the use of calibrated instruments and the review of logbooks for each device.

• Data Collection Procedures:
  Detailed techniques are provided for collecting representative cross-sectional data, including methods like Equal-Discharge-Increment (EDI) and Equal-Width-Increment (EWI), in-situ and subsample measurements, and field profiles.

• Quality Assurance Measures:
  The guide discusses rigorous quality assurance practices, such as regular calibration checks, use of backup instruments, and proper documentation. It stresses the importance of adapting measurement practices to field conditions.

• Safety and Compliance:
  Users are reminded that all safety, health, and environmental concerns must be addressed by the practitioner, according to relevant regulations.

Applications

• Environmental Monitoring and Water Quality Assessment:
  This standard is essential for environmental scientists and technicians responsible for monitoring and reporting on the health of freshwater systems. Consistent, accurate temperature, DO, conductivity, and pH measurements support ecological research, regulatory compliance, and environmental remediation activities.

• Hydrological and Water Resource Studies:
  Reliable field data are vital for hydrologists and engineers modeling water flow, pollutant transport, and aquatic habitat conditions in open channel systems.

• Regulatory Compliance and Reporting:
  Agencies and consultants use this standard to fulfill requirements for water quality monitoring programs, particularly where data integrity and comparability are critical for decision-making and public reporting.

• Instrument Manufacturers and Field Technicians:
  The standard guides the selection, calibration, and operation of portable meters and sensors, ensuring that product development and maintenance align with field requirements.

Related Standards

• ASTM D888: Test Methods for Dissolved Oxygen in Water
  Provides detailed procedures for measuring DO, complementing the approaches outlined in D6764.

• ASTM D1125: Test Methods for Electrical Conductivity and Resistivity of Water
  Focuses on measuring water’s electrical properties, an integral parameter in D6764.

• ASTM D1293: Test Methods for pH of Water
  Describes laboratory and field methods for determining water pH.

• ASTM D4410 / D4411: Terminology and guide for sampling fluvial sediment in motion
  Provides context for sediment-related measurements taken alongside water quality sampling in open channels.

Conclusion

ASTM D6764-02(2019) is a critical international standard for practitioners involved in surface water data collection. By providing robust methodologies for measuring temperature, dissolved oxygen, specific conductance, and pH, it underpins environmental monitoring efforts and supports regulatory, scientific, and engineering objectives. Adhering to this guide enhances the quality, reliability, and comparability of open channel water quality data.

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:D6764 −02 (Reapproved 2019)
Standard Guide for
Collection of Water Temperature, Dissolved-Oxygen
Concentrations, Specific Electrical Conductance, and pH
Data from Open Channels
This standard is issued under the fixed designation D6764; 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 D1125 Test Methods for Electrical Conductivity and Resis-
tivity of Water
1.1 This guide describes procedures to collect cross-
D1129 Terminology Relating to Water
sectional means of temperature, dissolved oxygen (DO), spe-
D1293 Test Methods for pH of Water
cific electrical conductance (SC), and pH of water flowing in
D4410 Terminology for Fluvial Sediment
open channels.
D4411 Guide for Sampling Fluvial Sediment in Motion
1.2 This guide provides guidelines for preparation and
D5464 Test Method for pH Measurement of Water of Low
calibrationoftheequipmenttocollectcross-sectionalmeansof
Conductivity
temperature, DO, SC, and pH of water flowing in open
3. Terminology
channels.
3.1 Definitions:
1.3 This guide describes what equipment should be used to
3.1.1 For definitions of terms used in this standard, refer to
collect cross-sectional means of temperature, DO, SC, and pH
Terminologies D1129 and D4410.
of water flowing in open channels.
3.2 Definitions of Terms Specific to This Standard:
1.4 This guide covers the cross-sectional means of
3.2.1 electronic temperature sensor, n—an electrical device
temperature, DO, SC, and pH of fresh water flowing in open
that converts changes in resistance to a readout calibrated in
channels.
temperature units. Thermistors and resistance temperature
1.5 This standard does not purport to address all of the
detectors are examples of electronic temperature sensors.
safety concerns, if any, associated with its use. It is the
3.2.2 thermometer, n—any device used to measure
responsibility of the user of this standard to establish appro-
temperature, consisting of a temperature sensor and some type
priate safety, health, and environmental practices and deter-
of calibrated scale or readout device.
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
4. Summary of Guide
dance with internationally recognized principles on standard-
4.1 This guide establishes criteria and describes procedures
ization established in the Decision on Principles for the
for the collection of cross-sectional means of temperature, DO,
Development of International Standards, Guides and Recom-
SC, and pH of water flowing in open channels.
mendations issued by the World Trade Organization Technical
4.2 This guide provides only generic guidelines for equip-
Barriers to Trade (TBT) Committee.
ment use and maintenance. Field personnel must be familiar
2. Referenced Documents with the instructions provided by equipment manufacturers.
2 Therearealargevarietyofavailablefieldinstrumentsandfield
2.1 ASTM Standards:
instruments are being continuously updated or replaced using
D888 Test Methods for Dissolved Oxygen in Water
newer technology. Field personnel are encouraged to contact
equipment manufacturers for answers to technical questions.
This guide is under the jurisdiction ofASTM Committee D19 on Water and is
5. Significance and Use
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
and Open-Channel Flow.
5.1 This guide describes stabilization criteria for recording
Current edition approved Nov. 1, 2019. Published December 2019. Originally
field measurements of temperature, DO, SC, and pH.
approved in 2002. Last previous edition approved in 2013 as D6764 – 02 (2013).
DOI: 10.1520/D6764-02R19.
5.2 This guide describes the procedures used to calibrate
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and check meters to be used in the field to records these
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
measurements and the procedures to be use in the field to
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. obtain these data.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6764−02 (2019)
5.3 This guide describes quality assurance procedures to be 6.1.1.4 Have backup instruments readily available and in
followedwhenobtainingcross-sectionalmeansoftemperature, good working condition.
DO, SC, and pH of water flowing in open channels.
6.1.2 Before making field measurements, sensors must be
allowed to equilibrate to the temperature of the water being
5.4 Field measurement must accurately represent the water
monitored. Sensors have equilibrated adequately when instru-
flowing in the open channel being measured. Methods need to
ment readings have “stabilized,” that is, when the variability
be used that will result in an accurate representation of the
among measurements does not exceed an established criterion.
meanoftheparameterofinterest.Proceduresmustbeusedthat
The criteria for stabilized field readings are defined operation-
will take into consideration the variation in the parameter
ally in Table 1, for a set of three or more sequential measure-
across the sections and with depth.
ments. The natural variability inherent in surface water at the
5.5 Temperature and DO must be measured directly in the
time of sampling generally falls within these stability criteria
water in the open channel. SC and pH are often measured in
and reflects the accuracy that should be attainable with a
situ, but also may be measured in a subsample of a composite
calibrated instrument.
sample collected using discharge-weighted methods.
6.1.3 Allow at least 60 s (or follow the manufacturer’s
guidelines) for sensors to equilibrate with sample water. Take
6. Procedure
instrumentreadingsuntilthestabilizationcriteriainTable1are
met. Record the median of the final three or more readings as
GENERAL COMMENTS
the value to be reported for that measurement point.
6.1 Field measurements should represent, as closely as
possible, the natural condition of the surface-water system at 6.2 Locating Points of Measurement in Cross-Section:
the time of sampling. Field teams must determine if the 6.2.1 The location and the number of field measurements
instruments and method to be used will produce data of the depend on study objectives. Generally, a single set of field-
type and quality required to fulfill study needs. Experience and measurement data is used to represent an entire stream cross
knowledge of field conditions often are indispensable for section at a sampling site and can be useful when calculating
determining the most accurate field-measurement value. chemical loads.
6.1.1 To ensure the quality of the data collected (1):
6.2.2 To obtain data representative of the section, the
6.1.1.1 Calibration is required at the field site for most variability of discharge and field measurements across the
instruments. Make field measurements only with calibrated
stream must be known. This information is used to determine
instruments. if the equal-discharge-increment (EDI) or equal-width-
6.1.1.2 Each field instrument must have a permanent log-
increment (EWI) method of locating field-measurement points
book for recording calibrations and repairs. Review the log- should be used. See Terminology D4410 for definitions of
book before leaving for the field.
these terms.
6.1.1.3 Test each instrument (meters and sensors) before
6.2.2.1 Check the cross-sectional profile data of the stream
leaving for the field. Practice your measurement technique if
site to determine the variability of discharge per unit width of
the instrument or measurement is new to you.
the stream and of field-measurement values across the section.
Make individual measurements at a number of equally-
spaced verticals along the cross section and at multiple depths
within each vertical; or, consult previous records for the site.
The boldface numbers in parentheses refer to a list of references at the end of
Make in situ (see 6.2.3.3) field measurements for the
this standard.
profile.
Field-measurement profiles of stream variability are
TABLE 1 Stabilization Criteria for Recording Field
needed for low- and high-flow conditions and should be
Measurements (1)
verified at least every 2 years or as study objectives dictate.
NOTE 1—[±, plus or minus value shown; °C, degrees Celsius; ≤ less
6.2.2.2 Select the EDI or EWI method to locate points of
than or equal to values shown; µS/cm microsiemens at 25°C, >, greater
measurement (see Ref (2) for information on EDI and EWI
than value shown; unit, standard pH unit; mg/L milligram per litre].
methods) to select and execute the appropriate method.
Stabilization Criteria for Mea-
Standard Direct surements
If stream depth and velocities along the cross section are
Field Measurement (Variability Should Be Within
relatively uniform, use the EWI method.
the Value Shown)
If stream depth and velocities along the cross section are
Temperature:
highly variable, use the EDI method.
Electronic temperature sensor ±0.2°C
Liquid-in-glass thermometer ±0.5°C
In a small and well-mixed stream, a single point at the
centroidofflowmaybeusedtorepresentthecrosssection.The
Specific Electrical Conductance:
centroid of flow is defined as the point in the increment at
when#100 mS/cm ±5 %
when >100 mS/cm ±5 %
which discharge in that increment is equal on both sides of the
point.
pH:
6.2.3 Use the following procedure when making a field
Meter displays to 0.01 ±0.1 unit
measurement using the EDI method.
Dissolved Oxygen:
6.2.3.1 Divide the cross section into equal increments of
Amperometric method ±0.3 mg/L
discharge (see Ref (1) for details on how to properly do this.)
D6764−02 (2019)
6.2.3.2 Select either the in situ or subsample method and collected using an isokinetic sample and isokinetic depth-
follow the instructions in 6.3 or 6.4. integrating method. The volume of the isokinetic sample must
6.2.3.3 In Situ Method—Go to the centroid of the first be proportional to the amount of discharge in each increment
equal-discharge increment. Using submersible sensors, mea- and measurements in subsamples taken from the compositing
sure at mid-depth (or multiple depths) in the vertical. Repeat at device result in discharge-weighted values.
eachvertical.Thevaluerecordedateachverticalrepresentsthe
6.2.4.4 Select either the in situ or subsample method and
median of values observed within approximately 60 s after
follow the instructions in 6.3 or 6.4.
sensor(s) have equilibrated with stream water.
6.2.4.5 In Situ Method—Measure at the midpoint of each
6.2.3.4 Subsample Method—Collect an isokinetic depth-
equal-width increment. Using submersible sensors, measure at
integrated sample at the centroid of each equal-discharge
mid-depth in the vertical.
increment, emptying the increment sample into a compositing
6.2.4.6 Subsample Method—Collect an isokinetic depth-
device. Measure field parameters either in the sample collected
integrated sample at the midpoint of each equal-width
at each increment or in a subsample taken from the composite
increment, emptying each sample into a compositing device.
of all the increment samples.
Useofthecorrectsamplingequipmentiscriticaltoexecutethis
6.2.3.5 The final field-measurement value is the mean of the
method successfully: standard samplers cannot meet isokinetic
in situ or individual increment-sample value for all the EDI
requirements when stream velocity is less than 1.5 ft/s.
verticals in the section (the composite subsample yields a
6.2.4.7 Record a value for each field measurement for each
single value). Note for pH it is necessary to calculate the mean
vertical. The value recorded represents the stabilized values
by (1) converting each pH measurement to its antilogarithm
observed within approximately 60 s after the sensor(s) have
–(pH)
times minus one (10 ), (2) using these transformed values
equilibrated with the stream or subsample water.
to calculate the mean, and (3) converting the mean value to a
6.2.4.8 Example—Table 3 provides an example of an area-
logarithm multiplied by minus one (refer to 6.8.4.5).
weighted median measurement for conductivity measured in
6.2.3.6 Enter data on a field form.
situ. In the example, the area-weighted median conductivity
6.2.3.7 Example—Table 2 is an example of how mean
equals 130 µS/cm. To calculate an area-weighted median,
conductivity measured in situ is calculated using the EDI
multiply the area of each increment by its corresponding field
method.
measurement, sum the products of all the increments, and
6.2.3.8 In the example, the correct value for the discharge-
divide by total cross-sectional area. Note that if the conductiv-
weightedmeanconductivityis163µS/cm,calculatedfrom815
ity reported was selected at mid-depth of the vertical of
dividedby5(thesumoftherecordedmedianvaluesdividedby
centroid of flow (Section 10), it would have been reported as
the number of median measurements). Note that at the mid-
125 µS/cm; if the conductivity reported was near the left edge
point of the center centroid of flow (increment 3) the median
of water, it would have been reported as 150 µS/cm.
conductivity would have been reported as 155 µS/cm; if
6.2.4.9 The final field-measurement value normally is cal-
conductivity had been measured near the left edge of the water
culated as the mean of the values recorded at all EWI
(Increment 1), the conductivity would have been reported as
increments, resulting in an area-weighted mean (for pH it is
185 µS/cm.
necessary to calculate the mean by (1) converting each pH
6.2.4 Use the following procedure when making a field
–(pH)
measurementtoitsantilogarithmtimesminusone(10 ),(2)
measurement using the EWI method.
using these transformed values to calculate the mean, and (3)
6.2.4.1 Divide the cross section into equal increments of
converting the mean value to a logarithm multiplied by minus
width (see Ref (1) for details on how to properly do this.)
one.)
6.2.4.2 Insitufieldmeasurementsaremadeatthemidpoints
6.3 In Situ Measurement Procedures:
of each increment. Area-weighted concentrations can be com-
puted from these measurements (Table 3). 6.3.1 In situ measurement (Fig. 1), made by immersing a
6.2.4.3 Subsample field measurements are made in discrete field-measurement sensor directly in the water body, is used to
samples that usually are withdrawn from a composite sample determineaprofileofvariabilityacrossastreamsection.Insitu
TABLE 2 Example of Field Notes for a Discharge-Weighted Conductivity Measurement
2 3
NOTE 1—[ft/sec, feet per second; ft, feet; ft , square feet; ft /s, cubic feet per second; µS/cm, microsiemens per centimetre at 25°C; LEW, left edge
of water; —, not available; REW, right edge of water].
NOTE 2—Calculation of conductivity: mean of median conductivity measurements (815 divided by 5) = 163 µS/cm.
Mean Width of Depth of Area of
Equal Discharge Percent of Flow Increment Discharge, Median Conductivity,
Velocity, Increment, Increment, Increment,
Increment in Increment in ft /s in µS/cm
in ft/s in ft in ft in ft
LEW 0 — — — — — —
1 20 2.0 22 5.7 125 250 185
2 20 2.2 11 10.4 114 250 170
3 20 2.3 9 12.0 109 250 155
4 20 3.9 5 12.8 64 250 155
5 20 3.4 10 7.4 74 250 150
REW 0 — — — — — —
D6764−02 (2019)
TABLE 3 Example of Field Notes for an Area-Weighted Conductivity Measurement
NOTE 1—[ft, feet; LEW, left edge of water; ft , square feet; µS/cm, microsiemens per centimetre at 25°C; —, not available; REW, right edge of water].
NOTE 2—Calculation of conductivity: sum of values in last column divided by the total cross-sectional area 27 836⁄214 = 130 µS/cm.
Section Cumulative Percent of Vertical Location, Width of Section, Depth of Vertical, Area of Section, Median Conductivity, Product of Median
Number Flow in Section in ft from LEW in ft in ft in ft in µS/cm Conductivity and Area
LEW 0 0 — — — — —
1 2 2 4 1.0 4.0 150 600
2 4 6 4 2.0 8.0 145 1160
3 6 10 4 2.6 10.4 145 1508
4 10 14 4 3.2 12.8 140 1792
5 16 18 4 3.5 14.0 135 1890
6 22 22 4 4.0 16.0 130 2080
7 28 26 4 4.5 18.0 130 2340
8 34 30 4 5.4 21.6 125 2700
9 42 34 4 6.0 24.0 125 3000
10 50 38 4 5.7 22.8 125 2850
11 62 42 4 5.1 20.4 125 2550
12 76 46 4 4.6 18.4 125 2300
13 88 50 4 3.5 14.0 12 1750
14 96 54 4 1.4 5.6 135 756
15 99 58 4 1.0 4.0 140 560
REW 100 60 — — — — —
measurement can be repeated if stream discharge is highly 6.5.2 Equipment:
variable and measurement points need to be located at incre- 6.5.2.1 Liquid-in-glass thermometers and electronic tem-
ments of equal discharge. However, in situ measurements are perature sensors are most commonly used to measure water
point samples, and, thus, are not depth integrated. temperature.
6.5.2.2 Recommended liquid-in-glass thermometers are
6.3.2 Measurements made directly (in situ) in the surface-
total-immersion thermometers filled with alcohol. Before mea-
water body are preferable in order to avoid changes that result
suring temperature, check the type of liquid-filled thermometer
from removing a water sample from its source. In situ
being used. (Partial-immersion thermometers are not recom-
measurement is necessary to avoid changes in chemical prop-
mended: these have a ring or other mark to indicate the
erties of anoxic water.
immersion depth required.)
6.3.2.1 In situ measurement is mandatory for determination
6.5.2.3 Thermometers can easily become damaged or out of
of temperature and dissolved-oxygen concentration.
calibration. Take care to:
6.3.2.2 In situ measurement also can be used for pH and
Keep thermometers clean (follow manufacturer’s recom-
conductivity.
mendations).
6.4 Subsample Measurement:
Carry thermometers in protective cases; thermometers and
6.4.1 Depth- and width-integrating sampling methods are
cases must be free of sand and debris.
used to collect and composite samples that can be subsampled
Store liquid-filled thermometers in a bulb-down position
for some field measurements. The same field measurements
and in a cool place away from direct sunlight.
can be performed on discrete samples collected with thief,
6.5.2.4 As an additional precaution on field trips, carry
bailer, or grab samplers. Subsamples or discrete samples that
extra-calibrated thermometers as spares, and a supply of
have been withdrawn from a sample-compositing device or
batteries for instrument systems.
point sampler can yield good data for conductivity and pH as
6.5.3 Calibration:
long as correct procedures are followed and the water is not
6.5.3.1 To calibrate a thermometer, instrument readings are
anoxic (Fig. 2).
checked across a range of temperatures against those of a
6.4.2 Before using a sample-compositing/splitting device,
thermometerofcertifiedaccuracy.Calibrateliquid-in-glassand
precleanandfieldrinsethedeviceinaccordancewithapproved
electronic temperature sensors in the office at regularly sched-
procedures such as described in Horowitz and others, 1994 (3).
uled intervals. Tag acceptable thermometers with date of
6.4.3 When compositing and splitting a sample, follow
calibration.
instructions for the clean hands/dirty hands technique such as 6.5.3.2 Calibrate a liquid-in-glass thermometer every 3 to 6
those detailed in Horowitz and others (3), as required.
months, using a 2-point calibration, and annually, using a
3-point calibration.
6.5 Temperature:
6.5.3.3 Calibrate an electronic temperature sensor annually
6.5.1 Measurements of water and air temperatures at the
using a 5-point calibration check and every 3 to 4 months
fieldsiteareessentialforwater-datacollection.Determinations
check several reading against reading form a NIST-certified
of dissolved-oxygen concentrations, conductivity, pH, rate and
thermometer.
equilibria of chemical reactions, biological activity, and fluid
6.5.3.4 For further information and instructions on calibra-
properties rely on accurate temperature measurements.
tions see Ref (1).
D6764−02 (2019)
FIG. 1In Situ Field-Measurement Procedures (1)
6.5.4 Measurement: Measure temperature in those sections of the stream that
6.5.4.1 Before measuring temperature:
represent most of the water flowing in a reach. Do not make
Inspect liquid-in-glass thermometers to be certain liquid
temperature measurements in or directly below stream sections
columns have not separated.
with turbulent flow or from the stream bank (unless this
Inspect bulbs to be sure they are clean.
represents the condition to be monitored).
Inspect protective cases to be sure they are free of sand or
6.5.4.4 Use either a liquid-in-glass thermometer tagged as
debris.
“certified” within the past 12 months, or an electronic tempera-
6.5.4.2 The reported surface-water temperature must be
ture sensor tagged “certified” within the past 4 months.
measured in situ. Do not measure temperature on subsamples
6.5.4.5 Record on field forms the temperature variation
from a sample compositing device.
from the cross-sectional profile, and the sampling method
6.5.4.3 To measure the temperature of surface water:
selected.
Make a cross-sectional temperature profile to determine
Flowing, shallow stream—wade to the location(s) where
temperaturevariability;anelectronictemperaturesensorworks
temperature is to be measured. To prevent erroneous readings
best for purpose.
caused by direct solar radiation, stand so that a shadow is cast
Determine from the cross-sectional profile and from study
objectives which sampling method to use (see 6.2). on the site for temperature measurement.
D6764−02 (2019)
FIG. 2Subsample Field-Measurement Procedures for Conductivity and pH (1)
Streamtoodeeporswifttowade—measuretemperatureby 6.5.4.6 Immerse the sensor in the water to the correct depth
lowering from a bridge, cableway, or boat an electronic and hold it there for no less than 60 s until the sensor
temperature sensor attached to a weighted cable. Do not attach equilibrates thermally. The sensor must be immersed properly
a weight to the sensor or sensor cable. while reading the temperature; this might require attaching the
Still-water conditions—measure temperature at multiple thermistor to a weighted cable. (Technical Note: For in situ
depths at several points in the cross section. measurement with liquid-filled thermometers; the water depth
D6764−02 (2019)
must be no greater than twice the length of the liquid column 6.6.2.3 All built-in electronic temperature sensors must be
of the thermometer in order to make an accurate measurement. calibrated and field checked before use.
6.6.2.4 Equipment and supplies used for amperometric
6.5.4.7 Read the temperature to the nearest 0.5°C (0.2°C for
method of dissolved-oxygen determination are listed in Table
thermistor readings). Do not remove the sensor from the water.
4.
Using a liquid-in-glass thermometer, check the reading
6.6.2.5 Follow the manufacturer’s recommendations for
three times and record all values on field forms and note the
short-term (field) and long-term (office) storage of sensors and
median of these values.
for performance checks. Protect instruments and sensors from
Using an electronic temperature sensor, wait until the
being jostled during transportation, from sudden impacts,
readings stabilize to within 0.2°C, then record the median of
sudden temperature changes, and extremes of heat and cold.
approximately the last 5 values.
6.6.2.6 Before each field trip:
6.5.4.8 Removethetemperaturesensorfromthewater,rinse
(1) Check the temperature-display thermistor in the DO
it thoroughly with deionized water (DIW), and store it.
sensor against a certified thermometer over the normal operat-
6.5.5 Record the stream temperature on field forms:
ing range of the instrument. If a thermistor reading is incorrect,
In still water—median of three or more sequential values.
apply a correction or return the instrument to the manufacturer
EDI—mean value of subsections measured (use median if
for adjustment.
measuring one vertical at the centroid of flow).
(2) Recondition the DO sensor if it fails a performance
EWI—mean or median value of subsections measured.
check.
6.6 Dissolved Oxygen (DO):
(3) Check the instrument batteries and all electrical con-
6.6.1 Accurate data on concentrations of DO in water are
nections.
essential for documenting changes to the environment caused
(4) Test the instrument to ensure that it will read zero in a
by natural phenomena and human activities. Many chemical
DO-free solution.
and biological reactions in surface water depend directly or
(a) If the instrument reading exceeds 0.2 mg/L, then the
indirectly on the amount of oxygen present. DO is necessary in
sensor membrane and electrolyte (if present) need to be
aquatic systems for the survival and growth of many aquatic
replaced or the sensor needs to be repaired.
organisms.
(b) Before repairing or replacing the sensor, check zero
6.6.1.1 There are several field methods for determining DO again with a freshly prepared zero DO solution.
concentrations of DO in surface. The more common ones are (5) On analog instruments:
amperometric method, spectrophotometric method and the (a) Check mechanical zero (if applicable) before turning
iodometric (Winkler) method. the instrument on; adjust it if necessary.
(b) Check redline and zero readings (if applicable) and
6.6.1.2 The most commonly used field method for measur-
adjust as needed.
ing DO in water is the amperometric method, in which DO
concentration is determined with a temperature-compensating
instrument or meter that works with a polarographic
membrane-type sensor. Because it is the most commonly used
TABLE 4 Equipment and Supplies Used for Amperometric
A
Method of Dissolved-Oxygen Determination
field DO method, the discussion in this guide will assume that
it is the method that is being used. (1)
NOTE 1—[DO, dissolved oxygen; YSI, Yellow Springs Instrument
Company; mm, millimetre; g, gram; mL, millilitre; L, litre; DIW,
6.6.1.3 The spectrophotometric method such as the one that
deionized water].
uses Rhodazine-D is recommended for determining concentra-
DO instrument and DO sensor or multiparameter instrument with DO capability
tions of DO less than 1.0 mg/L.
Temperature readout display, analog or digital
6.6.1.4 The iodometric (Winkler) method generally is not
Temperature and pressure compensated
Operating range at least -5°C to +45°C
recommended for field determination of DO because the
Measure concentrations$1to20mg/L
accuracy and reproducibility achieved depend largely on the
Minimum scale readability, preferably 0.05 mg/L DO
experience and technique of the data collector. (1)
Calibrated accuracy within 5 % or ±0.3 mg/L DO, whichever is less
DO sensor membrane replacement kit: membranes, O-rings, filling solution
6.6.1.5 See Test Method D888 for more information on the
Stirrer attachment for DO sensor
measurement of DO in water.
Calibration chamber: YSI model 5075A sensor, or equivalent
Pocket altimeter-barometer, calibrated; measures to nearest 2 mm, Thommen
6.6.2 Equipment:
model 2000
6.6.2.1 The instrument system used to measure DO must be
Thermometer, calibrated (see 6.1 for selection and calibration criteria)
B
tested before each field trip and cleaned soon after each use. Zero DO calibration solution : dissolve 1 g sodium sulfite and a few crystals of
cobalt chloride in 1 L DIW
Battery-powered instruments are recommended. A variety of
Flowthrough chamber for determining DO in ground water
DO meters and sensors are available. Read thoroughly the
Oxygen solubility table (Table 6.2-6)
Waste disposal container or equivalent
instructions provided by the manufacturer. Every DO instru-
Spare batteries, filing solution, and membranes
ment and the barometer must have a log book in which repairs
Log books for DO instrument and barometer for recording all calibrations,
and calibrations are recorded, along with the manufacturer maintenance, and repairs
A
makeandmodeldescription,andtheserialorpropertynumber.
Modify this list to meet specific needs of the field effort. See (1) Table 6.2-3 for
equipment list for iodometric DO determination and Table 6.2-5 for equipment list
6.6.2.2 Dissolved-oxygen sensors must be temperature
for Rhodazine-D DO determination.
compensating:thepermeabilityofthemembraneandsolubility B
Prepare fresh zero DO solution before each field trip.
of oxygen in water change as a function of temperature.
D6764−02 (2019)
(c) If the instrument cannot be adjusted, recharge or (3) Immerse the DO and temperature sensors directly into
replace the batteries. the water body and allow the sensors to equilibrate to the water
(6) Calibrate the pocket altimeter-barometer according to
temperature (no less than 60 s). If the water velocity at the
manufactures specifications.
point of measurement is less than about 1 ft/s, use a stirring
6.6.3 Calibration: device or stir by hand to increase the velocity (to hand stir,
raise and lower the sensor at a rate of about 1 ft/s, but do not
6.6.3.1 Calibration and operation procedures for the am-
break the surface of the water). Very high velocities can cause
perometric method differ among instrument types and makes.
Refer to manufacturer’s instructions. Record all calibration erroneous DO measurements.
information in instrument logbooks and copy calibration data (4) Record the temperature without removing the sensors
onto field forms at the time of calibration. See Ref (1) for from the water. Turn the operation switch to the range that was
instructions on calibration.
used during instrument calibration.
6.6.3.2 Calibration must be done for atmospheric pressure, (5) After the instrument reading has stabilized (allow 1 to
salinity, and for the instrument readings. Although the salinity 2 min and 60.3 mg/L), record the median DO concentration.
correction can be made either during calibration or after (6) For EWI or EDI measurements, proceed to the next
measurement, the preferred USGS method is to apply salinity station in the cross section and repeat steps 3 through 5. When
correctionfactorsaftercalibrationandmeasurement(recalibra-
measurements for the stream have been completed, remove the
tion is necessary for each field variation in salinity and
sensor from the water, rinse it with DIW, and store it according
temperature if the correction is made during calibration) (1)
to the manufacturer’s instructions.
6.6.3.3 There are four procedures for calibrating a DO (7) Record DO concentrations on the field forms:
system: (1) air-calibration chamber in water, (2) calibration
(a) In still water—median of three or more sequential
with air-saturated water, (3) air-calibration chamber in air, and
values.
(4) iodometric (Winkler) titration. When using an analog
(b) EDI—mean value of all subsections measured (use
instrument: Do not change scales without either recalibrating
the median if measuring one vertical at the centroid of flow).
or verifying that identical readings are obtained on both scales;
(c) EWI—mean (or median) of all subsections measured.
Place an analog instrument in its operating position—either
6.7 Specific Electrical Conductance (SC):
vertical, tilted, or on its back—before calibration. More read-
6.7.1 Electrical conductance is a measure of the capacity of
justments may be necessary if the operating position is
water (or other media) to conduct an electrical current. Elec-
changed, so do not change the position of the meter until DO
trical conductance of water is a function of the types and
measurement is complete.
quantities of dissolved substances in water, but there is no
6.6.4 Measurement:
universallinearrelationbetweentotaldissolvedsubstancesand
6.6.4.1 Standard DO determination for surface water repre-
conductivity.
sents the cross-sectional median or mean concentration of DO
6.7.1.1 See Test Methods D1125 for more information on
at the time of observation. Measuring DO concentration at one
distinct spot in a cross section is valid only for flowing water the measurement of SC in water.
with a cross-sectional DO variation of less than 0.5 mg/L (1).
6.7.2 Equipment and Supplies:
Determining DO in a single vertical at the centroid of flow at
6.7.2.1 The instrument system used to measure conductivity
the midpoint of the vertical is only representative of the cross
mustbetestedbeforeeachfieldtripandcleanedsoonafteruse.
section under ideal mixing conditions.
Every conductivity instrument must have a logbook in which
6.6.4.2 Do not measure DO in or directly below sections
repairs and calibrations are recorded, along with manufacturer
with turbulent flow, in still water, or from the bank, unless
make and model description and serial or property number.
these conditions represent most of the reach or are required by
6.7.2.2 Table 5 contains a list of equipment and supplies
the study objectives.
used for measuring conductivity.
6.6.4.3 Follow the 7 steps below to measure DO in surface
6.7.2.3 Many conductivity instruments are available; the
water (1):
specifications and instructions provided here are general. Users
(1) Calibrate the DO instrument system at the field site and
must be familiar with the instructions provided by the manu-
check that the temperature thermistor has been District-
facturer.
certified within the past 4 months (within 12 months if a
6.7.2.4 Conductivity sensors are either contacting-type sen-
liquid-in-glass thermometer is used).
sors with electrodes or electrodeless-type sensors.
(2) Record the DO variation from the cross-sectional pro-
Contacting-Type Sensors With Electrodes—Three types of
file and select the sampling method:
cells are available: (1) a dip cell that can be suspended in the
(a) Flowing, shallow stream—Wade to the location(s)
sample, (2) a cup cell that contains the sample, or (3) a flow
where DO is to be measured.
cell that is connected to a fluid line.
(b) Stream too deep or swift to wade—Lower a weighted
Electrodeless-Type Sensors—These operate by inducing an
DO sensor with calibrated temperature sensor from a bridge,
alternating current in a closed loop of solution, and they
cableway, or boat. (Do not attach the weight to the sensors or
sensor cables.) measure the magnitude of the current. Electrodeless sensors
avoid errors caused by electrode polarization or electrode
(c) Still-water conditions—Measure DO at multiple
depths at several points in the cross section. fouling.
D6764−02 (2019)
TABLE 5 Equipment and Supplies Used for Measuring
Clean carbon and stainless steel sensors with a soft brush.
A
Conductivity
Never use a brush on platinum-coated sensors.
NOTE 1—[°C, degrees Celsius; L, litre; µS/cm, microsiemens per
6.7.2.8 Refer to the manufacturer’s recommendations on
centimetre at 25°C]
sensor storage. Sensors may be temporarily stored in DIW
Conductivity instrument and conductivity sensor
between measurements and when the system is in daily use.
Battery powered Wheatstone bridge
For long-term storage, store sensors clean and dry.
Direct readout
Temperature range at least -5 to +45°C
6.7.3 Calibration:
Temperature compensating (25°C)
6.7.3.1 Conductivity systems must be calibrated before
Accuracy: Conductivity = 100 µS/cm, within 5 % of full scale
Conductivity > 100 µS/cm, within 3 % of full scale
every water-quality field trip and again at each site before
Electronic Temperature Sensor sensor (for automatic temperature-compensating
samples are measured. Calibration readings are recorded in the
models)
instrument logbook and on field forms at the time the instru-
Thermometer, liquid-in-glass or thermistor
Extra sensors (if possible) and batteries, or backup instrument
ment is calibrated. Remember, the temperature sensor on the
Conductivity standards at conductivities that approximate and bracket field val-
conductivity sensor must be calibrated and certified within the
ues
past 4 months.
Compositing and splitting device for surface-water samples
Flowthrough chamber or downhole instrument for ground-water measurements
6.7.3.2 Calibration and operating procedures differ, depend-
Plastic beakers (assorted sizes)
ing on instrument and sensor type.
Soap solution, nonphosphate (1 L)
Hydrochloric acid solution, 5 % volume-to-volume (1 L)
Some conductivity sensors may need to be soaked over-
Deionized water, 1 L, maximum conductivity of 1 mS/cm
night in DIW before use. Check the manufacturer’s instruc-
Paper tissues, disposable, soft, and lint free
tions.
Brush (small, soft)
Waste disposal container
Someanaloginstrumentsrequireaninitialmechanicalzero
Minnow bucket with tether (or equivalent) for equilibrating buffer solutions to
adjustment of the indicator needle.
sample temperature
For a cup-type cell, calibration and measurement proce-
Instrument log book for recording calibrations, maintenance, and repairs
A
dures described for the dip-type cell apply; the only difference
Modify this list to meet the specific needs of the field effort.
is that standards are poured directly into the cup-type cell.
When using a dip-type cell, do not let the cell rest on the
bottom or sides of the measuring container.
6.7.2.5 Quality-controlled conductivity standards be or-
dered from suppliers of chemical reagents. Conductivity stan- 6.7.3.3 Conductivitysystemsnormallyarecalibratedwithat
dards usually consist of potassium chloride dissolved in least two standards. Calibrate sensors against a standard that
reagent-grade water. They are readily available from 50 to approximates sample conductivity and use the second standard
50,000 µS/cm at 25°C. Values outside of this range can be as a calibration check. The general procedures described in
prepared or special ordered.As soon as possible after delivery steps 1-15 below apply to most instruments used for field
to the office, label conductivity standards with the date of measurements-check the instrument manual for specific in-
expiration. Discard standards that have expired, been frozen, structions.
have begun to evaporate, or that were decanted from the (1) Inspect the instrument and the conductivity sensor for
storage container. damage. Check the battery voltage. Make sure that all cables
6.7.2.6 Maintenance of conductivity equipment includes are clean and connected properly.
periodic office checks of instrument operation. To help keep (2) Turn the instrument on and allow sufficient time for
equipment in good operating condition: electronic stabilization.
Protect the conductivity system from dust and excessive (3) Select the correct instrument calibration scale for ex-
heat and cold.
pected conductivity.
Keep all cable connectors dry and free of dirt and extra- (4) Select the sensor type and the cell constant that will
neous matter.
most accurately measure expected conductivity.
Protect connector ends in a clean plastic bag when not in (5) Select two conductivity standards that will bracket the
use. expected sample conductivity. Verify that the date on the
6.7.2.7 Conductivity sensors must be clean to produce standards has not expired.
accurate results; residues from previous samples can coat (6) Equilibrate the standards and the conductivity sensor to
surfaces of sensors and cause erroneous readings. the temperature of the sample.
Clean sensors thoroughly with DIW before and after (a) Putbottlesofstandardsinaminnowbucket,cooler,or
making a measurement (this is sufficient cleaning in most large water bath that is being filled with ambient water.
cases). (b) Allow 15 to 30 min for thermal equilibration. Do not
Removeoilyresidueorotherchemicalresidues(salts)with allow water to dilute the standard.
a detergent solution. Sensors can soak in detergent solution for (7) Rinsetheconductivitysensor,thethermometer(liquid-
many hours without damage. in-glassorthermistor),andacontainerlargeenoughtoholdthe
If oil or other residues persist, dip the sensor in a dilute dip-type sensor and the thermometer.
hydrochloric acid solution. Never leave the sensor in contact (a) First, rinse the sensor, the thermometer, and the
with acid solution for more than a few minutes. Check the container three times with DIW.
manufacturer’s recommendations before using acid solution on (b) Next, rinse the sensor, the thermometer, and the
sensors. container three times with the standard to be used.
D6764−02 (2019)
(8) Put the sensor and the thermometer into the rinsed positing device. Filtered samples may be needed if the con-
container and pour in fresh calibration standard. centrations of suspended material interfere with obtaining a
(9) Measure water temperature. Accurate conductivity
stable measurement. Be alert to the following problems if
measurements depend on accurate temperature measurements conductivity is measured in an isolated (discrete) sample or
or accurate temperature compensation.
subsample:
(a) If the sensor contains a calibrated thermistor, use this
The conductivity of water can change over time as a result
thermistor to measure water temperature.
of chemical and physical processes such as precipitation,
(b) If using a manual instrument without a temperature
adsorption, ion exchange, oxidation, and reduction. Do not
display or temperature compensation, adjust the instrument to
delay making conductivity measurements.
the temperature of the standard using a calibrated liquid-in-
Field conditions (rain, wind, cold, dust, direct sunlight) can
glass or an electronic temperature sensor.
cause measurement problems. Shield the instrument to the
(10) Agitate a submersible-type conductivity sensor up
extent possible and perform measurements in a collection
and down under the solution surface to expel air trapped in the
chamber in an enclosed vehicle or an on-site laboratory.
sensor. Read the instrument display. Agitate the sensor up and
For waters susceptible to significant gain and loss of
down under the solution surface again, and read the display.
dissolved gases, make the measurement within a gas-
Repeat the procedure until consecutive readings are the same.
impermeable container (Berzelius flask) fitted with a stopper.
(11) Record the instrument reading and adjust the instru-
Place the sensor through the stopper and work quickly to
ment to the known standard value.
maintain the sample at ambient water temperature.
(a) For nontemperature-compensating conductivity
AvoidcontaminationfromthepHelectrodefillingsolution.
instruments, apply a temperature-correction factor to convert
Measure conductivity on a separate discrete sample from the
the instrument reading to conductivity at 25°C.
one used for measuring pH.
(b) The correction factor depends to some degree on the
6.7.4.1 In Situ Measurement—Conductivity measurements
specific instrument used-use the temperature-correction factor
in flowing surface water should represent the cross-sectional
recommended by the manufacturer. If this is not available, use
mean or median conductivity at the time of observation (see
correction factors from Table 6.3–3 (1) or Table 3 in Test
step 7, below). Any deviation from this convention should be
Methods D1125.
documented in the data base and with the published data. First:
(c) If an instrument cannot be adjusted to a known
Take a cross-sectional conductivity profile to determine the
calibration standard value, develop a calibration curve. After
degree of system variability. A submersible sensor works best
temperature compensation, if the percentage difference from
for this purpose. Refer to 6.1 for criteria to help decide which
the standard exceeds 5 %, refer to the manufactures guide or
sampling method to use. Next, follow the 7 steps listed below:
troubleshooting guide (section 6.3.4) (1).
(1) Calibratetheconductivityinstrumentsystematthefield
(12) Record in the instrument logbook and on field forms:
site after equilibrating the buffers with stream temperature.
(a) The temperature of the standard solution.
(2) Record the conductivity variation from a cross-
(b) The known and the measured conductivity of the
sectional profile on a field form and select the sampling
standard solution (including 6 variation).
method.
(c) The temperature-correction factor (if necessary).
(a) Flowing, shallow stream—wade to the location(s)
(13) Discard the used standard into a waste container.
...