ASTM D7315-17(2023)

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: D7315 − 17 (Reapproved 2023)
Standard Test Method for
Determination of Turbidity Above 1 Turbidity Unit (TU) in
Static Mode
This standard is issued under the fixed designation D7315; 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 to measure. In these cases, and alternative measurement
method such as the process monitoring method can be consid-
1.1 This test method covers the static determination of
ered.
turbidity in water. Static refers to a sample that is removed
1.7 This standard does not purport to address all of the
from its source and tested in an isolated instrument. (See
safety concerns, if any, associated with its use. It is the
Section 4.)
responsibility of the user of this standard to establish appro-
1.2 This test method is applicable to the measurement of
priate safety, health, and environmental practices and deter-
turbidities greater than 1.0 turbidity unit (TU). The upper end
mine the applicability of regulatory limitations prior to use.
of the measurement range was left undefined because different
Refer to the MSDSs for all chemicals used in this procedure.
technologies described in this test method can cover very
1.8 This international standard was developed in accor-
different ranges. The round robin study covered the range of 0
dance with internationally recognized principles on standard-
to 4000 turbidity units because instrument verification in this
ization established in the Decision on Principles for the
range can typically be covered by standards that can be
Development of International Standards, Guides and Recom-
consistently reproduced.
mendations issued by the World Trade Organization Technical
1.3 Many of the turbidity units and instrument designs
Barriers to Trade (TBT) Committee.
covered in this test method are numerically equivalent in
calibration when a common calibration standard is applied 2. Referenced Documents
across those designs listed in Table 1. Measurement of a
2.1 ASTM Standards:
common calibration standard of a defined value will also
D1129 Terminology Relating to Water
produce equivalent results across these technologies.
D1193 Specification for Reagent Water
1.3.1 In this test method calibration standards are often
D2777 Practice for Determination of Precision and Bias of
defined in NTU values, but the other assigned turbidity units,
Applicable Test Methods of Committee D19 on Water
such as those in Table 1 are equivalent. For example, a 1 NTU
D4411 Guide for Sampling Fluvial Sediment in Motion
formazin standard is also a 1 FNU, a 1 FAU, a 1 BU, and so
D5847 Practice for Writing Quality Control Specifications
forth.
for Standard Test Methods for Water Analysis
1.4 This test method does not purport to cover all available D6855 Test Method for Determination of Turbidity Below 5
NTU in Static Mode
technologies for high-level turbidity measurement.
E691 Practice for Conducting an Interlaboratory Study to
1.5 This test method was tested on different natural waters
Determine the Precision of a Test Method
and wastewater, and with standards that will serve as surro-
2.2 Other Referenced Standards:
gates to samples. It is the user’s responsibility to ensure the
U.S. EPA Method 180.1 Methods for Chemical Analysis of
validity of this test method for waters of untested matrices.
Water and Wastes, Turbidity
1.6 Depending on the constituents within a high-level
ISO 7027 Water Quality—Determination of Turbidity
sample, the proposed sample preparation and measurement
methods may or may not be applicable. Those samples with the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
highest particle densities typically prove to be the most difficult
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This test method is under the jurisdiction of ASTM Committee D19 on Water Available from United States Environmental Protection Agency (EPA), William
and is the direct responsibility of Subcommittee D19.07 on Sediments, Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
Geomorphology, and Open-Channel Flow. http://www.epa.gov.
Current edition approved Nov. 1, 2023. Published December 2023. Originally Available from International Organization for Standardization (ISO), ISO
approved in 2007. Last previous edition approved in 2017 as D7315 – 17. DOI: Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
10.1520/D7315-17R23. Geneva, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7315 − 17 (2023)
TABLE 1 Summary of Known Instrument Designs, Applications, Ranges, and Reporting Units
Design and Typical Suggested
Prominent Application Key Design Features
Reporting Unit Instrument Range Application Ranges
Nephelometric non-ratio White light turbidimeters. Comply Detector centered at 90° relative 0.0–40 0.0–40 Regulatory
(NTU) with U.S. EPA Method 180.1 for to the incident light beam. Uses
low level turbidity monitoring. a white light spectral source.
Ratio White Light turbidime- Complies with ISWTR regulations Used a white light spectral 0–10 000 0–40 Regulatory
ters (NTRU) and Standard Method 2130B. source. Primary detector cen- 0–10 000 other
Can be used for both low and tered at 90°. Other detectors
high level measurement. located at other angles. An in-
strument algorithm uses a com-
bination of detector readings to
generate the turbidity reading.
Nephelometric, near-IR Complies with ISO 7027. The Detector centered at 90° relative 0–1000 0–40 Regulatory (non-
turbidimeters, non- wavelength is less susceptible to the incident light beam. Uses US)
ratiometric (FNU) to color interferences. Appli- a near-IR (780 nm–900 nm) 0–1000 other
cable for samples with color monochromatic light source.
and good for low level monitor-
ing.
Nephelometric near-IR Complies with ISO 7027. Appli- Uses a near-IR monochromatic 0–10 000 0–40 Regulatory
turbidimeters, ratio metric cable for samples with high lev- light source (780 nm–900 nm). 0–10 000 other
(FNRU) els of color and for monitoring Primary detector centered at
to high turbidity levels. 90°. Other detectors located at
other angles. An instrument al-
gorithm uses a combination of
detector readings to generate
the turbidity reading.
Surface Scatter Turbidimeters Turbidity is determined through Detector centered at 90° relative 10–10 000 10–10 000
(NTU) light scatter from or near the to the incident light beam. Uses
surface of a sample. a white light spectral source.
Formazin Back Scatter (FBU) Not applicable for regulatory pur- Uses a near-IR monochromatic 100–10 000+ 100–10 000
poses. Best applied to high tur- light source in the 780 nm–900
bidity samples. Backscatter is nm range. Detector geometry is
common with but not all only between 90° and 180° relative
probe technology and is best to the incident light beam.
applied in higher turbidity
samples.
Backscatter Unit (BU) Not applicable for regulatory pur- Uses a white light spectral source 10–10 000+ 100–10 000+
poses. Best applied for samples (400 nm–680 nm range). Detec-
with high level turbidity. tor geometry is between 90°
and 180° relative to the incident
light beam.
Formazin attenuation unit May be applicable for some regu- Detector is geometrically centered 20–1000 20–1000 Regulatory
(FAU) latory purposes. This is com- at 0° relative to incident beam
monly applied with spectropho- (attenuation). Wavelength is
tometers. Best applied for 780 nm–900 nm.
samples with high level turbid-
ity.
Light attenuation unit (AU) Not applicable for some regulatory Detector is geometrically centered 20–1000 20–1000
purposes. This is commonly at 0° relative to incident beam
applied with spectrophotom- (attenuation). Wavelength is
eters. 400 nm–680 nm.
Nephelometric Turbidity Multi- Is applicable to EPA regulatory Detectors are geometrically cen- 0.02–4000 0–40 Regulatory
beam Unit (NTMU) method GLI Method 2. Appli- tered at 0° and 90°. An instru- 0–4000 other
cable to drinking water and ment algorithm uses a combina-
wastewater monitoring applica- tion of detector readings, which
tions. may differ for turbidities varying
magnitude.
USGS National Field Manual for the Collection of Water 3.2.1 attenuation, v—the amount of incident light that is
Quality Data scattered and absorbed before reaching a detector, which is
geometrically centered at 0° relative to the centerline of the
3. Terminology
incident light beam.
3.1 Definitions:
3.2.1.1 Discussion—Attenuation is inversely proportional to
3.1.1 For definitions of terms used in this standard, refer to
transmitted signal.
Terminology D1129.
Attenuated Turbidity 5 Absorbed Light1Scattered Light
3.2 Definitions of Terms Specific to This Standard:
The application of attenuation in this test method is as a dis-
tinct means of measuring turbidity. When measuring in the
FAU or AU mode, the turbidity value is a combination of
Available from United Stated Geological Survey (USGS), 12201 Sunrise Valley
Drive, Reston, VA 20192, http://www.usgs.gov. scattered (attenuated) plus absorbed light. The scattered light
D7315 − 17 (2023)
is affected by particle size and is a positive response. The
3.2.10 turbidimeter, n—an instrument that measures light
absorption due to color is a negative. The sum of these two
scatter, caused by particulates within a sample and converts the
entities results in the turbidity value in the respective units.
measurement to a turbidity value.
3.2.2 calibration turbidity standard, n—a turbidity standard 3.2.10.1 Discussion—The detected light is quantitatively
that is traceable and equivalent to the reference turbidity converted to a numeric value that is traced to a light-scatter
standard to within statistical errors; calibration turbidity stan- standard. See Table 1 for examples of designs.
dards include commercially prepared 4000 NTU Formazin,
3.2.11 turbidity, n—an expression of the optical properties
stabilized formazin (see 9.2.3), and styrenedivinylbenzene
of a sample that causes light rays to be scattered and absorbed
(SDVB) (see 9.2.4).
rather than transmitted in straight lines through the sample.
3.2.2.1 Discussion—These standards may be used to cali-
3.2.11.1 Discussion—Turbidity of water is caused by the
brate the instrument. Calibration standards may be instrument
presence of matter such as clay, silt, finely divided organic
design specific. Calibration standards that exceed 10 000
matter, plankton, other microscopic organisms, organic acids,
turbidity units are commercially available.
and dyes.
3.2.3 calibration verification standards, n—defined stan-
4. Summary of Test Method
dards used to verify the accuracy of a calibration in the
measurement range of interest. 4.1 The optical property expressed as turbidity is measured
by the scattering effect that constituents within a sample have
3.2.3.1 Discussion—These standards may not be used to
on light; the higher the quantity of scattered or attenuated
perform calibrations, only calibration verifications. Included
incident light, the higher the turbidity. In samples containing
standards are opto-mechanical light scatter devices, gel-like
particulate material, light scatter and attenuation will vary (1)
standards, or any other type of stable liquid standard. Calibra-
due to size, shape and composition of the particles in the water,
tion verification standards may be instrument design specific.
and (2) the wavelength of the incident light.
3.2.4 nephelometric turbidity measurement, n—The mea-
4.2 This test method is based upon a comparison of the
surement of light scatter from a sample in a direction that is at
amount of light scattered or attenuated by the sample with the
90° with respect to the centerline of the incident light path.
amount of light scattered or attenuated by a reference suspen-
3.2.4.1 Discussion—Units are NTU (Nephelometric Turbid-
sion. Lower turbidity values are typically determined by a
ity Units). When ISO 7027 technology is employed units are in
nephelometer, which measures light scatter from a sample in a
FNU (Formazin Nephelometric Units).
direction that is at 90° with respect to the centerline of the
3.2.5 ratio turbidity measurement, n—the measurement de-
incident light path. High-level turbidity determination can be
rived through the use of a nephelometric detector that serves as
performed using many different technologies. It is critical
the primary detector and one or more other detectors used to
when reporting the measurement, traceability to the type of
compensate for variation in incident light fluctuation, stray
technology be used. Turbidity measurements are not often
light, instrument noise, or sample color.
consistent among differing technologies.
3.2.6 reference turbidity standard, n—a standard that is
5. Significance and Use
synthesized reproducibly from traceable raw materials by the
user.
5.1 Turbidity at the levels defined in the scope of this test
3.2.6.1 Discussion—All other standards are traced back to method are often monitored to help control processes, monitor
this standard. The reference standard for turbidity is formazin the health and biology of water environments and determine
(see 9.2.2). the impact of changes in response to environmental events
(weather events, floods, etc.). Turbidity is often undesirable in
3.2.7 seasoning, v—the process of conditioning labware
drinking water, plant effluent waters, water for food and
with the standard to be diluted to a lower value.
beverage processing, and for a large number of other water-
3.2.7.1 Discussion—The process reduces contamination and
dependent manufacturing processes. Removal is often accom-
dilution errors.
plished by coagulation, sedimentation, and various levels of
3.2.8 stray light, n—all light reaching the detector other than filtration. Measurement of turbidity provides an indicator of
that which is scattered by the sample. contamination, and is a vital measurement for monitoring the
characteristics and or quality within the sample’s source or
3.2.8.1 Discussion—For example: ambient light leakage,
process.
internal reflections and divergent light in optical systems. For
this test method, stray light is like
...