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[Federal Register Volume 90, Number 10 (Thursday, January 16, 2025)]
[Rules and Regulations]
[Pages 4658-4662]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-00464]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 141

[EPA-HQ-OW-2024-0603; FRL-12499-01-OW]

Expedited Approval of Alternative Test Procedures for the 
Analysis of Contaminants Under the Safe Drinking Water Act; Analysis 
and Sampling Procedures

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: This action announces the Environmental Protection Agency's 
(EPA's) approval of alternative testing methods for use in measuring 
the levels of contaminants in drinking water to determine compliance 
with national primary drinking water regulations. The Safe Drinking 
Water Act authorizes EPA to approve the use of alternative testing 
methods through publication in the Federal Register. EPA is using this 
streamlined authority to make two additional methods available for 
analyzing drinking water samples. This expedited approach provides 
public water systems, laboratories, and primacy agencies with more 
timely access to new measurement techniques and greater flexibility in 
the selection of analytical methods, thereby reducing monitoring costs 
while maintaining public health protection.

DATES: This action is effective January 16, 2025.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-HQ-OW-2024-0603. All documents in the docket are listed on the 
https://www.regulations.gov website. Although listed in the index, some 
information is not publicly available, e.g., confidential business 
information (CBI) or other information whose disclosure is restricted 
by statute. Certain other material, such as copyrighted material, is 
not placed on the internet and will be publicly available only in hard 
copy form. Publicly available docket materials are available 
electronically through https://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT: Teresa Wells, Technical Support 
Branch, Standards and Risk Management Division, Office of Ground Water 
and Drinking Water (MS 140), Environmental Protection Agency, 26 West 
Martin Luther King Drive, Cincinnati, OH 45268; telephone number: (513) 
569-7128; email address: [email protected].

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does this action apply to me?

    Public water systems are the regulated entities required to measure 
contaminants in drinking water samples. In addition, EPA Regions as 
well as States and Tribal governments with authority to administer the 
regulatory program for public water systems under the Safe Drinking 
Water Act (SDWA) may measure contaminants in water samples. When EPA 
sets a monitoring requirement in its national primary drinking water 
regulations for a given contaminant, the agency also establishes (in 
the regulations) standardized test procedures for analysis of the 
contaminant. This action makes alternative testing methods available 
for particular drinking water contaminants beyond the testing methods 
currently established in the regulations. EPA is providing public water 
systems, required to test water samples, with a choice of using either 
a test procedure already established in the existing regulations or an 
alternative testing method that has been approved in this action or in 
prior expedited approval actions. Categories and entities that may 
ultimately be affected by this action include:

------------------------------------------------------------------------
                                     Examples of potentially
             Category                   regulated entities     NAICS \1\
------------------------------------------------------------------------
State, local, & Tribal governments  State, local, and Tribal      924110
                                     governments that analyze
                                     water samples on behalf
                                     of public water systems
                                     required to conduct such
                                     analysis; State, local,
                                     and Tribal governments
                                     that directly operate
                                     community and non-
                                     transient non-community
                                     water systems required
                                     to monitor.
Industry..........................  Private operators of          221310
                                     community and non-
                                     transient non-community
                                     water systems required
                                     to monitoras.
Municipalities....................  Municipal operators of        924110
                                     community and non-
                                     transient non-community
                                     water systems required
                                     to monitor.
------------------------------------------------------------------------
\1\ North American Industry Classification System.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be interested in this 
action. Other types of entities not listed in the table could also have 
some interest. To determine whether your facility is affected by this 
action, you should carefully examine the applicability language in the 
Code of Federal Regulations (CFR) at 40 CFR 141.2 (definition of a 
public water system). If you have questions regarding the applicability 
of this action to a particular entity, consult the person listed in the 
preceding FOR FURTHER INFORMATION CONTACT section.

[[Page 4659]]

Abbreviations and Acronyms Used in This Action

AMCD: Automated Micro Chlorine Detection
CFR: Code of Federal Regulations
EPA: United States Environmental Protection Agency
FRB: Field Reagent Blank
LC/MS/MS: Liquid Chromatography/Tandem Mass Spectrometry
NAICS: North American Industry Classification System
PFAS: Per- and Polyfluorinated Alkyl Substances
SDWA: The Safe Drinking Water Act

II. Background

A. What is the purpose of this action?

    In this action, EPA is approving two analytical methods for 
determining contaminant concentrations in drinking water samples 
collected under SDWA. Regulated entities required to sample and monitor 
may use either the testing methods already established in existing 
regulations or the alternative testing methods being approved in this 
action or in prior expedited approval actions. The new methods are 
listed along with other methods similarly approved through previous 
expedited actions in 40 CFR part 141, appendix A to subpart C and on 
EPA's drinking water methods website at https://www.epa.gov/dwanalyticalmethods.

B. What is the basis for this action?

    When EPA determines that an alternative analytical method is 
``equally effective'' (i.e., as effective as a method that has already 
been promulgated in the regulations), SDWA allows EPA to approve the 
use of the alternative testing method through publication in the 
Federal Register (see section 1401(1) of SDWA). EPA is using this 
streamlined approval authority to make two additional methods available 
for determining contaminant concentrations in drinking water samples 
collected under SDWA. EPA has determined that, for each contaminant or 
group of contaminants listed in section III of this preamble, the 
additional testing methods being approved in this action are as 
effective as one or more of the testing methods already approved in the 
regulations for those contaminants. Section 1401(1) of SDWA states that 
the newly approved methods ``shall be treated as an alternative for 
public water systems to the quality control and testing procedures 
listed in the regulation.'' Accordingly, this action makes these 
additional two analytical methods legally available as options for 
meeting EPA's monitoring requirements.
    This action does not add regulatory language, but does, for 
informational purposes, update an appendix to the regulations at 40 CFR 
part 141 that lists all methods approved under section 1401(1) of SDWA. 
Accordingly, while this action is not a rule, it is updating CFR text 
and therefore is being published in the ``Final Rules'' section of the 
Federal Register.

III. Summary of Approvals

    EPA is approving two methods that are equally effective relative to 
methods previously promulgated in the regulations. By means of this 
action, these two methods are added to appendix A to subpart C of 40 
CFR part 141.

A. Methods Developed by EPA

    1. EPA Method 537.1, Version 1.0. Determination of Selected Per- 
and Polyfluorinated Alkyl Substances (PFAS) in Drinking Water by Solid 
Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry 
(LC/MS/MS) (USEPA 2018). The EPA's April 26, 2024, Federal Register 
publication for the PFAS National Primary Drinking Water Regulation (89 
FR 32532) describes EPA Method 533 (``Determination of PFAS in Drinking 
Water by Isotope Dilution Anion Exchange Solid Phase Extraction and LC/
MS/MS,'' November 2019, 815-B-19-020) (USEPA 2019) and EPA Method 
537.1, version 2.0 (``Determination of Selected PFAS in Drinking Water 
by Solid Phase Extraction and LC/MS/MS,'' March 2020, EPA/600/R-20/006) 
(USEPA 2020) as acceptable methods for the analyses specified by the 
National Primary Drinking Water Regulation.
    The primary difference between Method 537.1, version 1.0 and Method 
537.1, version 2.0 is the field reagent blank (FRB) preparation. 
Version 2.0 exposes the FRB to the preservative (Trizma) at the time of 
field sample collection, whereas version 1.0 combines the lab reagent 
water and the preservative together in the FRB prior to field sampling. 
Version 2.0 was created to more-closely mimic the FRB process used in 
Method 533. Additionally, version 2.0 specifies the use of solid phase 
extraction cartridge sorbents containing a styrene divinylbenzene 
polymeric sorbent phase that may not be modified with monomers other 
than SDVB. The method versions are otherwise identical.
    EPA has determined that EPA Method 537.1, version 1.0 is equally 
effective relative to Method 537.1, version 2.0 for the purposes of the 
analyses specified in 40 CFR 141.902(b)(1) [Monitoring requirements for 
PFAS--Initial monitoring]. The basis for this determination is 
discussed in Adams 2024a. Therefore, EPA is approving EPA Method 537.1, 
version 1.0 for determination of selected PFAS in drinking water to 
support initial monitoring required by the PFAS National Primary 
Drinking Water Regulation. EPA Method 537.1, version 1.0 is available 
at the National Service Center for Environmental Publications at 
https://www.epa.gov/nscep.

B. Methods Developed by Vendors

    1. e-sens AMCD Method--e-sens, Inc. Automated Micro Chlorine 
Detection (AMCD) Method for the Determination of Residual Free and 
Total Chlorine in Water (e-sens, Inc. 2023a). e-sens AMCD Method uses a 
three-electrode electrochemical cell, comprised of a reference 
electrode, a platinum micro array working electrode, and a platinum 
counter electrode. The working electrode and the counter electrode are 
batch-produced on a silicon substrate, and the electrical outputs are 
processed by an onboard potentiostat. For free chlorine, after 
electrode conditioning, the embedded microfluidic system adds a precise 
amount of a concentrated phosphate buffer to each sample to adjust its 
ionic strength and pH. A standard voltammetry procedure is then invoked 
on the buffered sample and the faradaic current through the 
electrochemical cell is recorded. The current magnitude is proportional 
to the concentration of free chlorine in the sample. The recorded 
current response is fit to a calibration curve obtained upon 
manufacture of the sensor and the concentration of free chlorine is 
reported. For total chlorine, the free chlorine measurement is 
immediately followed by the total chlorine measurement. A new aliquot 
of sample is mixed with ammonium chloride, which instantly converts 
various chlorine species to monochloramine. A concentrated phosphate 
buffer is then added into the sample to disproportionate monochloramine 
to form dichloramine, which is readily reduced at the surface of the 
platinum working electrode. A standard voltammetry procedure is then 
invoked on the buffered sample and the faradaic current through the 
electrochemical cell is recorded. The current magnitude is proportional 
to the concentration of total chlorine in the sample. The recorded 
current response is fit to a calibration curve obtained upon 
manufacture of the sensor and the concentration of total chlorine is 
reported.
    Approved methods for free and total chlorine are listed at 40 CFR 
141.74(a)(2) and 141.131(c)(1). The

[[Page 4660]]

performance characteristics of e-sens AMCD Method were compared to the 
performance characteristics of the approved Standard Methods 4500-Cl G 
(APHA 2000). The validation study report (e-sens, Inc. 2023b) 
summarizes the results obtained from three different laboratories using 
three different ground water matrixes, and three different surface 
water matrixes collected from six different locations.
    EPA has determined that e-sens AMCD Method is equally effective 
relative to Standard Methods 4500-Cl G. The basis for this 
determination is discussed in Adams 2024b. Therefore, EPA is approving 
the e-sens AMCD Method for determining free and total chlorine in 
drinking water. A copy of the method is available from e-sens, Inc., 
630 Komas Dr., Ste 235, Salt Lake City, Utah 84108.

IV. Statutory and Executive Order Reviews

    As noted in section II of this preamble, under the terms of SDWA 
section 1401(1), this streamlined method approval action is not a rule. 
Accordingly, the Congressional Review Act, 5 U.S.C. 801 et seq., as 
added by the Small Business Regulatory Enforcement Fairness Act of 
1996, does not apply because this action is not a rule for purposes of 
5 U.S.C. 804(3).
    Similarly, this action is not subject to the Regulatory Flexibility 
Act because it is not subject to notice and comment requirements under 
the Administrative Procedure Act or any other statute. In addition, 
because this approval action is not a rule, but simply makes 
alternative testing methods available as options for monitoring under 
SDWA, EPA has concluded that other statutes and executive orders 
generally applicable to rulemaking do not apply to this approval 
action.

V. References

Adams, W. 2024a. Memo to the record describing basis for expedited 
approval of EPA Method 537.1, Version 1.0. December 5, 2024. 
(Available at https://www.regulations.gov; docket ID No. EPA-HQ-OW-
2024-0603.)
Adams, W. 2024b. Memo to the record describing basis for expedited 
approval of e-sens Automated Micro Chlorine Detection Method 
November 26, 2024. (Available at https://www.regulations.gov; docket 
ID No. EPA-HQ-OW-2024-0603.)
American Public Health Association (APHA). 2000. Standard Methods 
4500-Cl D, E, F, G, H, I-00. Chlorine (Residual). D. Amperometric 
Titration Method. E. Low-Level Amperometric Titration Method. F. DPD 
Ferrous Titrimetric Method. G. DPD Colorimetric Method. H. 
Syringaldehyde (FACTS) Method. I. Iodometric Electrode Technique. 
Approved by Standard Methods Committee 2000. Standard Methods Online 
(Available at https://www.standardmethods.org.)
USEPA. 2018. EPA Method 537.1, Version 1.0. Determination of 
Selected Per- and Polyfluorinated Alkyl Substances (PFAS) in 
Drinking Water by Solid Phase Extraction and Liquid Chromatography/
Tandem Mass Spectrometry (LC/MS/MS). EPA/600/R-18/352. November 
2018. (Available at https://www.regulations.gov; docket ID No. EPA-
HQ-OW-2024-0603.)
USEPA. 2019. EPA Method 533. Determination of PFAS in Drinking Water 
by Isotope Dilution Anion Exchange Solid Phase Extraction and LC/MS/
MS. EPA 815-B-19-020. November 2019. (Available at https://www.regulations.gov; docket ID No. EPA-HQ-OW-2024-0603.)
USEPA. 2020. EPA Method 537.1, Version 2.0. Determination of 
Selected Per- and Polyfluorinated Alkyl Substances (PFAS) in 
Drinking Water by Solid Phase Extraction and Liquid Chromatography/
Tandem Mass Spectrometry (LC/MS/MS). EPA/600/R-20/006. March 2020. 
(Available at https://www.regulations.gov; docket ID No. EPA-HQ-OW-
2024-0603.)
e-sens, Inc. 2023a. e-sens AMCD Method. e-sens, Inc. Automated Micro 
Chlorine Detection (AMCD) Method for the Determination of Residual 
Free and Total Chlorine in Water. December 2023. (Available at 
https://www.regulations.gov; docket ID No. EPA-HQ-OW-2024-0603.)
e-sens, Inc. 2023b. Alternate Test Procedure Validation Study Report 
of e-sens, Inc. Automated Micro Chlorine Detection (AMCD) Method for 
the Determination of Residual Free and Total Chlorine in Water. 
December 2023. (Available at https://www.regulations.gov; docket ID 
No. EPA-HQ-OW-2024-0603.)

List of Subjects in 40 CFR Part 141

    Environmental protection, Chemicals, Indians-lands, 
Intergovernmental relations, Reporting and recordkeeping requirements, 
Water supply.

Jennifer L. McLain,
Director, Office of Ground Water and Drinking Water.

    For the reasons stated in the preamble, the Environmental 
Protection Agency amends 40 CFR part 141 as follows:

PART 141--NATIONAL PRIMARY DRINKING WATER REGULATIONS

0
1. The authority citation for part 141 continues to read as follows:

    Authority: 42 U.S.C. 300f, 300g-1, 300g-2, 300g-3, 300g-4, 300g-
5, 300g-6, 300j-4, 300j-9, and 300j-11.

0
2. Amend Appendix A to subpart C of Part 141 by:
0
a. In the table entitled ``Alternative Testing Methods for Contaminants 
Listed at 40 CFR 141.74(a)(2)'' revise the entries for ``Free 
Chlorine'' and ``Total Chlorine'';
0
b. In the table entitled ``Alternative Testing Methods for Contaminants 
Listed at 40 CFR 141.131(c)(1)'' revise the entries for ``Free 
Chlorine'' and ``Total Chlorine'';
0
c. Add the table entitled ``Alternative Testing Methods for 
Contaminants Listed at 40 CFR 141.901(b)(1)'' after the table entitled 
``Alternative Testing Methods for Contaminants Listed at 40 CFR 
141.852(a)(5)'' and before the table entitled ``Alternative Testing 
Methods for Contaminants Listed at 40 CFR 143.4(b)'';
0
d. Add footnotes 69 and 70.
    The revisions and additions read as follows:

Appendix A to Subpart C of Part 141--Alternative Testing Methods 
Approved for Analyses Under the Safe Drinking Water Act

* * * * *

                                  Alternative Testing Methods for Disinfectant Residuals Listed at 40 CFR 141.74(a)(2)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                    SM 22nd
                                                                                                edition,\28\ SM
            Residual                  Methodology         EPA methods       SM 21st edition    23rd Edition,\49\       ASTM \4\              Other
                                                                                  \1\           SM 24th edition
                                                                                                     \66\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Free Chlorine...................  Amperometric        ..................  4500-Cl D.........  4500-Cl D.........  D 1253-08, -14....
                                   Titration.
                                  DPD Ferrous         ..................  4500-Cl F.........  4500-Cl F.........
                                   Titrimetric.
                                  DPD Colorimetric..  ..................  4500-Cl G.........  4500-Cl G.........  ..................  Hach Method
                                                                                                                                       10260.\31\
                                  Indophenol          ..................  ..................  ..................  ..................  Hach Method
                                   Colorimetric.                                                                                       10241.\34\
                                  Syringaldazine      ..................  4500-Cl H.........  4500-Cl H.........
                                   (FACTS).
                                  On-line Chlorine    EPA 334.0 \16\....
                                   Analyzer.

[[Page 4661]]

 
                                  Amperometric        ..................  ..................  ..................  ..................  ChloroSense,\17\
                                   Sensor.                                                                                             ChloroSense, Rev.
                                                                                                                                       1.1,\59\ e-sens
                                                                                                                                       AMCD Method.\69\
Total Chlorine..................  Amperometric        ..................  4500-Cl D.........  4500-Cl D.........  D 1253-08, -14....
                                   Titration.
                                  Amperometric        ..................  4500-Cl E.........  4500-Cl E.........
                                   Titration (Low
                                   level
                                   measurement).
                                  DPD Ferrous         ..................  4500-Cl F.........  4500-Cl F.........
                                   Titrimetric.
                                  DPD Colorimetric..  ..................  4500-Cl G.........  4500-Cl G.........  ..................  Hach Method
                                                                                                                                       10260.\31\
                                  Indophenol          127 \55\..........
                                   Colorimetric.
                                  Iodometric          ..................  4500-Cl I.........  4500-Cl I.........
                                   Electrode.
                                  On-line Chlorine    EPA 334.0 \16\....
                                   Analyzer.
                                  Amperometric        ..................  ..................  ..................  ..................  ChloroSense,\17\
                                   Sensor.                                                                                             ChloroSense, Rev.
                                                                                                                                       1.1,\59\ e-sens
                                                                                                                                       AMCD Method.\69\
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------

                                  Alternative Testing Methods for Disinfectant Residuals Listed at 40 CFR 141.131(c)(1)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                      SM 22nd edition,\28\
              Residual                     Methodology         SM 21st edition \1\    SM 23rd Edition,\49\         ASTM \4\                Other
                                                                                      SM 24th edition \66\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Free Chlorine......................  Amperometric Titration  4500-Cl D.............  4500-Cl D............  D 1253-08, -14.......
                                     DPD Ferrous             4500-Cl F.............  4500-Cl F............
                                      Titrimetric.
                                     DPD Colorimetric......  4500-Cl G.............  4500-Cl G............  .....................  Hach Method
                                                                                                                                    10260.\31\
                                     Indophenol              ......................  .....................  .....................  Hach Method
                                      Colorimetric.                                                                                 10241.\34\
                                     Syringaldazine (FACTS)  4500-Cl H.............  4500-Cl H............
                                     Amperometric Sensor...  ......................  .....................  .....................  ChloroSense,\17\
                                                                                                                                    ChloroSense, Rev.
                                                                                                                                    1.1,\59\ e-sens AMCD
                                                                                                                                    Method.\69\
                                     On-line Chlorine        ......................  .....................  .....................  EPA 334.0.\16\
                                      Analyzer.
 
                                                                      * * * * * * *
Total Chlorine.....................  Amperometric Titration  4500-Cl D.............  4500-Cl D............  D 1253-08, -14.......
                                     Low level Amperometric  4500-Cl E.............  4500-Cl E............
                                      Titration.
                                     DPD Ferrous             4500-Cl F.............  4500-Cl F............
                                      Titrimetric.
                                     DPD Colorimetric......  4500-Cl G.............  4500-Cl G............  .....................  Hach Method
                                                                                                                                    10260.\31\
                                     Iodometric Electrode..  4500-Cl I.............  4500-Cl I............
                                     Amperometric Sensor...  ......................  .....................  .....................  ChloroSense,\17\
                                                                                                                                    ChloroSense, Rev.
                                                                                                                                    1.1,\59\ e-sens AMCD
                                                                                                                                    Method.\69\
                                     On-line Chlorine        ......................  .....................  .....................  EPA 334.0.\16\
                                      Analyzer.
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------

 Alternative Testing Methods for Intial Monitoring Only of Contaminants
                     Listed at 40 CFR 141.901(b)(1)
------------------------------------------------------------------------
           Contaminant                Methodology         EPA method
------------------------------------------------------------------------
Perfluorobutane Sulfonate (PFBS)  SPE LC-MS/MS......  537.1, version
                                                       1.0.\70\
Perfluorohexane Sulfonate         SPE LC-MS/MS......  537.1, version
 (PFHxS).                                              1.0.\70\
Perfluorononanoate (PFNA).......  SPE LC-MS/MS......  537.1, version
                                                       1.0.\70\
Perfluorooctanesulfonic Acid      SPE LC-MS/MS......  537.1, version
 (PFOS).                                               1.0.\70\
Perfluorooctanoic Acid (PFOA)...  SPE LC-MS/MS......  537.1, version
                                                       1.0.\70\
2,3,3,3-Tetrafluoro-2-            SPE LC-MS/MS......  537.1, version
 (heptafluoropropoxy)propanoate                        1.0.\70\
 (HFPO-DA or GenX Chemicals).
------------------------------------------------------------------------
\1\ Standard Methods for the Examination of Water and Wastewater, 21st
  edition (2005). Available from American Public Health Association, 800
  I Street NW, Washington, DC 20001-3710.
 * * * * * * *
\4\ Available from ASTM International, 100 Barr Harbor Drive, West
  Conshohocken, PA 19428-2959 or http://astm.org. The methods listed are
  the only alternative versions that may be used.
 * * * * * * *
\16\ EPA Method 334.0. ``Determination of Residual Chlorine in Drinking
  Water Using an On-line Chlorine Analyzer,'' September 2009. EPA 815-B-
  09-013. Available at https://www.nemi.gov.

[[Page 4662]]

 
\17\ ChloroSense. ``Measurement of Free and Total Chlorine in Drinking
  Water by Palintest ChloroSense,'' August 2009. Available at https://www.nemi.gov or from Palintest Ltd, 1455 Jamike Avenue (Suite 100),
  Erlanger, KY 41018.
 * * * * * * *
\28\ Standard Methods for the Examination of Water and Wastewater, 22nd
  edition (2012). Available from American Public Health Association, 800
  I Street NW, Washington, DC 20001-3710.
 * * * * * * *
\31\ Hach Company. ``Hach Method 10260-Determination of Chlorinated
  Oxidants (Free and Total) in Water Using Disposable Planar Reagent-
  filled Cuvettes and Mesofluidic Channel Colorimetry,'' April 2013.
  5600 Lindbergh Drive, P.O. Box 389, Loveland, CO 80539.
 * * * * * * *
\34\ Hach Company. ``Hach Method 10241-Spectrophotometric Measurement of
  Free Chlorine (Cl2) in Drinking Water,'' November 2015. Revision 1.2.
  5600 Lindbergh Drive, P.O. Box 389, Loveland, CO 80539.
 * * * * * * *
\49\ Standard Methods for the Examination of Water and Wastewater, 23rd
  edition (2017). Available from American Public Health Association, 800
  I Street NW, Washington, DC 20001-3710.
 * * * * * * *
\55\ EPA Method 127. ``Determination of Monochloramine Concentration in
  Drinking Water.'' January 2021. EPA 815-B-21-004. Available at the
  National Service Center for Environmental Publications at https://www.epa.gov/nscep.
 * * * * * * *
\59\ ChloroSense, Rev. 1.1. ``Free and Total Chlorine in Drinking Water
  by Amperometry using Disposable Sensors.'' February 2020. Palintest
  Ltd, 400 Corporate Circle, Suite J, Golden, CO 80401.
 * * * * * * *
\66\ Standard Methods for the Examination of Water and Wastewater, 24th
  edition (2023). Available from American Public Health Association, 800
  I Street NW, Washington, DC 20001-3710.
 * * * * * * *
\69\ e-sens, Inc. ``e-sens, Inc. Automated Micro Chlorine Detection
  (AMCD) Method for the Determination of Residual Free and Total
  Chlorine in Water.'' December 2023. Available from e-sens, Inc., 630
  Komas Dr., Ste 235, Salt Lake City, Utah 84108.
\70\ EPA Method 537.1, Version 1.0. ``Determination of Selected Per- and
  Polyfluorinated Alkyl Substances (PFAS) in Drinking Water by Solid
  Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry
  (LC/MS/MS).'' November 2018. EPA/600/R-18/352. Approved as alternative
  testing method to support initial PFAS monitoring (for monitoring-
  frequency determinations) until April 26, 2027 as described at 40 CFR
  141.902(b)(1) [Monitoring requirements for PFAS--Initial monitoring].
  Available at the National Service Center for Environmental
  Publications at https://www.epa.gov/nscep.

[FR Doc. 2025-00464 Filed 1-15-25; 8:45 am]
BILLING CODE 6560-50-P
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