Revisions to Establish the Sixth Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems

Revisions To Establish the Sixth Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems

SUPPLEMENTARY INFORMATION:

I. Executive Summary

A. Purpose of the Regulatory Action

1. What action is the EPA taking?

2. Does this action apply to me?

3. What is the EPA's authority for taking this action?

B. Summary of the Regulatory Action

II. Public Participation

A. Written Comments

B. Participation in Virtual Public Meeting

III. General Background Information

A. How are the Contaminant Candidate List (CCL), the UCMR program, the Regulatory Determination process, and the NCOD interrelated?

B. What public engagement opportunities have been held in preparation for UCMR 6?

C. What notable changes are being proposed for UCMR 6?

D. How did the EPA identify the contaminants being proposed for UCMR 6?

1. 1,2,3-trichloropropane (1,2,3-TCP)

2. Chlorpyrifos and Chlorpyrifos Oxon

E. What other contaminants did the EPA consider for UCMR 6?

1. Microplastics

2. Pharmaceuticals

F. What is the proposed UCMR 6 applicability date?

G. What is the proposed UCMR 6 pre-monitoring reporting date?

H. What is the proposed UCMR 6 timeline of activities?

I. What is the proposed UCMR 6 monitoring design?

1. Sampling, Frequency, and Timing

2. Sampling Locations

J. What are the reporting requirements for UCMR 6?

K. What are the Consumer Confidence Reporting and Public Notice (PN) Reporting requirements for PWSs that are subject to UCMR?

L. How do laboratories become approved to conduct the UCMR 6 analyses?

1. What are UCMR MRLs and how were they determined?

2. Request To Participate

3. Registration

4. Application Package

5. The EPA's Review of Application Package

6. Proficiency Testing

7. Written EPA Approval

M. UCMR 6 Laboratory Capacity

N. What is the state's role in the UCMR?

O. Costs and Benefits

1. What is the estimated cost of this proposed action?

2. What are the costs of alternative approaches to implementing the proposed UCMR 6?

3. What are the benefits of this proposed action?

IV. Supporting Information

A. Economic Analysis

B. How did the EPA consider children's environmental health?

C. What documents are being incorporated by reference?

1. Methods From the U.S. Environmental Protection Agency

V. Statutory and Executive Orders Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

C. Paperwork Reduction Act (PRA)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

H. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use

J. National Technology Transfer and Advancement Act (NTTAA)

VI. References

Abbreviations and Acronyms

µg/L Microgram per Liter

1,2,3-TCP 1,2,3-Trichloropropane

ANCSA Alaska Native Claims Settlement Act

ASDWA Association of State Drinking Water Administrators

ASTM ASTM International

AWIA America's Water Infrastructure Act of 2018

CBI Confidential Business Information

CCL Contaminant Candidate List

CCR Consumer Confidence Report

CFR Code of Federal Regulations

CWS Community Water System

DDVP Dichlorvos

DEET N,N-Diethyl-m-toluamide

DWSRF Drinking Water State Revolving Fund

EPA Environmental Protection Agency

EPTDS Entry Point to the Distribution System

FDA Food and Drug Administration

FR Federal Register

GC/MS Gas Chromatography/Mass Spectrometry

GWRMP Ground Water Representative Monitoring Plan

ICR Information Collection Request

IDC Initial Demonstration of Capability

LC/MS/MS Liquid Chromatography/Tandem Mass Spectrometry

LCMRL Lowest Concentration Minimum Reporting Level

MGK N-octyl bicycloheptene dicarboximide

MRL Minimum Reporting Level

NAICS North American Industry Classification System

NCOD National Contaminant Occurrence Database

NPDWR National Primary Drinking Water Regulation

NTNCWS Non-transient Non-community Water System

NTTAA National Technology Transfer and Advancement Act

OGWDW Office of Ground Water and Drinking Water

OIRA Office of Information and Regulatory Affairs

OMB Office of Management and Budget

PBI Proprietary Business Information

PFAS Per- and Polyfluoroalkyl Substances

PFMOAA Perfluoro-2-methoxyacetic acid

PFOA Perfluorooctanoic acid

PFOS Perfluorooctane sulfonate

PN Public Notice

PRA Paperwork Reduction Act

PT Proficiency Testing

PWS Public Water System

RFA Regulatory Flexibility Act

SBA Small Business Administration

SBREFA Small Business Regulatory Enforcement Fairness Act

SDWA Safe Drinking Water Act

SDWARS Safe Drinking Water Accession and Review System

SDWIS/Fed Safe Drinking Water Information System Federal Reporting Services

SPE Solid Phase Extraction

SRMD Standards and Risk Management Division

TFA Trifluoroacetic Acid

TFMS Trifluoromethanesulfonic Acid

TFSI Bistriflimide

UCMR Unregulated Contaminant Monitoring Rule

UMRA Unfunded Mandates Reform Act of 1995

USDA United States Department of Agriculture

USEPA United States Environmental Protection Agency

USGS United States Geological Survey

VCSB Voluntary Consensus Standard Body

I. Executive Summary

A. Purpose of the Regulatory Action

1. What action is the EPA taking?

The U.S. Environmental Protection Agency (EPA or agency) is proposing the sixth Unregulated Contaminant Monitoring Rule (UCMR 6). Under the Safe Drinking Water Act (SDWA), the UCMR program gathers data about unregulated contaminant occurrence in drinking water. The proposed UCMR 6 would require certain public water systems (PWSs) to collect national occurrence data for 30 unregulated contaminants that are not currently subject to national primary drinking water regulations (NPDWRs). This proposed rulemaking would require all community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) serving 3,300 or more people, and a representative sample of smaller PWSs serving fewer than 3,300 people, to conduct monitoring. The data collected will be publicly available and will inform decisions by the EPA.

Consistent with the " U.S. Environmental Protection Agency Implementation of Gold Standard Science" (USEPA, 2025a) based on Executive Order 14303 (White House, 2025), this proposal identifies four drinking water analytical methods to support PWS monitoring for a total of 30 contaminants. These contaminants consist of seven ultrashort organofluorine compounds (including certain PFAS), three pesticide metabolites, 13 semivolatile organic compounds, and seven purgeable organic compounds. The proposed inclusion of ultrashort organofluorine compounds, which include certain PFAS, ⁽¹⁾ is also consistent with the EPA's priority to address PFAS in drinking water as established in the 2019 PFAS Action Plan (USEPA, 2019). This proposal also describes the EPA's evaluation of alternate contaminants and invites public comment on all aspects of the proposal.

2. Does this action apply to me?

This proposed rule applies to PWSs described in this section. PWSs are systems that provide water for human consumption through pipes, or constructed conveyances, to at least 15 service connections, or that regularly serve an average of at least 25 individuals daily at least 60 days out of the year. A CWS is a PWS that has at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. An NTNCWS is a PWS that is not a CWS and that regularly serves at least 25 of the same people over six months per year. Under this proposal, all large CWSs and NTNCWSs serving more than 10,000 people would be required to monitor. In addition, all small CWSs and NTNCWs serving between 3,300 and 10,000 people and a nationally representative sample of CWSs and NTNCWS serving fewer than 3,300 people would be required to monitor, subject to the availability of appropriations and appropriate laboratory capacity (see discussion of America's Water Infrastructure Act of 2018 (AWIA) in sections I.A.3 and I.B of this document). (For a description of the statistical approach for the nationally representative sample see " Selection of Nationally Representative Public Water Systems for the Unregulated Contaminant Monitoring Rule: 2021 Update" (USEPA, 2021a)). As is generally the case for UCMR sampling, transient non-community water systems (TNCWSs) ( i.e., non-community water systems that do not regularly serve at least 25 of the same people over six months per year) would not be required to monitor under UCMR 6.

States, territories, and tribes with primary enforcement responsibility (primacy) to administer the regulatory program for PWSs under SDWA (hereinafter referred to in this document as "states") can participate in the implementation of UCMR 6 through voluntary Partnership Agreements (see discussion of Partnership Agreements in section III.N in this document). Primacy agencies with Partnership Agreements can choose to be involved in various aspects of the UCMR 6 monitoring for PWSs they oversee; however, the PWS remains responsible for all compliance activities.

Potentially regulated categories and entities are identified in the following table.

This table is not intended to be exhaustive but rather provides a guide for readers regarding entities likely to be regulated by this action. This table includes the types of entities that the EPA is now aware could potentially be regulated by this action. Other types of entities not included could also be regulated. To determine whether your entity is regulated by this action, you should carefully examine the definition of PWS found in sections 141.2 and 141.3, and the applicability criteria found in section 141.40(a)(1) and (2) of Title 40 in the Code of Federal Regulations (CFR). If you have questions regarding the applicability of this action to a particular entity, consult the person listed in the FOR FURTHER INFORMATION CONTACT section.

3. What is the EPA's authority for taking this action?

As part of its authority under SDWA, the EPA implements section 1445(a)(2), Monitoring Program for Unregulated Contaminants. This section, as amended in 1996, requires that once every five years, beginning in August 1999, the EPA issue a list of unregulated contaminants to be monitored by PWSs. SDWA requires that the EPA enter the monitoring data into the agency's publicly available National Contaminant Occurrence Database (NCOD) for drinking water at https://www.epa.gov/sdwa/national-contaminant-occurrence-database-ncod.

The EPA must vary the frequency and schedule for monitoring based on the number of persons served, the source of supply, and the contaminants likely to be found. The EPA is using its SDWA section 1445(a)(2) authority as the basis for requiring covered systems to monitor for the unregulated contaminants proposed under this rulemaking.

SDWA, as amended by the AWIA (Pub. L. 115-270), specifies that, subject to the availability of appropriations for such purpose and appropriate laboratory capacity, the EPA's UCMR program must require all systems serving between 3,300 and 10,000 people to monitor, and ensure that only a nationally representative sample of systems serving fewer than 3,300 people are required to monitor. The program will continue to ensure that all systems serving a population larger than 10,000 people are required to monitor. This AWIA provision became effective October 23, 2021.

B. Summary of the Regulatory Action

The EPA proposes to require certain PWSs to collect occurrence data for 30 contaminants. These contaminants may be present in drinking water but are not yet subject to NPDWRs. More specifically, the UCMR 6 proposal identifies the following: drinking water analytical methods to measure the UCMR contaminants; monitoring timeframe; sampling locations; data elements ( i.e., information required to be collected along with the occurrence data); and conforming and editorial changes, such as those necessary to remove requirements solely related to UCMR 5.

This proposed action, once finalized, will provide the EPA, states, and communities with scientifically valid data on the national occurrence of these contaminants in drinking water. The UCMR data are the primary source of national occurrence data that the EPA uses to inform other SDWA programs and risk management decisions for drinking water contaminants. This proposal identifies four drinking water analytical methods to be used by laboratories analyzing UCMR samples for the unregulated contaminants. In addition, section III.E of this document describes how the EPA evaluated other candidate contaminants.

This proposed rulemaking reflects the monitoring approach defined in the AWIA amendments and describes the UCMR 6 scope as including all systems serving 3,300 or more people, and a representative sample of systems serving fewer than 3,300 people. SDWA section 1445(a)(2)(C)(ii) requires the EPA to "pay the reasonable cost of such testing and laboratory analysis" for all applicable PWSs serving 10,000 or fewer people. Accordingly, the AWIA conditioned the monitoring scope on the availability of appropriations and on the availability of adequate laboratory capacity to analyze the samples.

Based on the EPA's experience implementing the AWIA scope in UCMR 5 and informed by ongoing engagement with the laboratory community, the EPA anticipates that sufficient laboratory capacity will continue to support the scope defined by the AWIA. Regarding the EPA's resources, the agency plans on taking the same approach outlined in UCMR 5 that enables the agency to adjust the number of small PWSs that serve 10,000 or fewer people to monitor based upon the appropriations received each fiscal year. Regardless of whether the EPA is able to carry out the monitoring outlined in the AWIA or reduces the scope of that monitoring due to availability of appropriations, the small PWS data collection, coupled with data collection from all large PWSs serving more than 10,000 people under this action, will provide scientifically valid data on the national occurrence of 30 unregulated contaminants in drinking water. See " Selection of Nationally Representative Public Water Systems for the Unregulated Contaminant Monitoring Rule: 2021 Update " for further details about the nationally representative sample (USEPA, 2021a).

II. Public Participation

A. Written Comments

Submit your comments, identified by Docket ID No. EPA-HQ-OW-2023-0469, at https://www.regulations.gov, (our preferred method), or the other methods identified in the ADDRESSES section of this document. Once submitted, comments cannot be edited or removed from the docket. The EPA may publish any comment received to its public docket. Do not submit to the EPA's docket at https://www.regulations.gov any information you consider to be Confidential Business Information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is restricted by statute. Contact the EPA if you want to submit CBI; see FOR FURTHER INFORMATION CONTACT section of this document. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the web, cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the full EPA public comment policy; information about CBI, PBI, or multimedia submissions; and general guidance on making effective comments.

B. Participation in Virtual Public Meeting

The EPA will hold two identical virtual public meetings during the public comment period on August 11, 2026 and August 12, 2026. Topics will include the proposed UCMR 6 monitoring requirements, contaminant selection and rationale, drinking water analytical methods, and the laboratory approval process. To register to attend the meeting or speak, please use the online registration form available at https://www.epa.gov/dwucmr/unregulated-contaminant-monitoring-rule-ucmr-meetings-and-materials or contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this document. The last day to pre-register to speak at the meeting will be July 31, 2026. On August 10, 2026, the EPA will post a general agenda for the meeting that will list pre-registered speakers in approximate order at https://www.epa.gov/dwucmr/unregulated-contaminant-monitoring-rule-ucmr-meetings-and-materials and will concurrently email registered participants the materials that were posted on the website.

The EPA will make every effort to follow the schedule as closely as possible on the day of the meeting; however, please plan for the identical events to run either ahead of schedule or behind schedule.

Each commenter will have the opportunity to provide oral testimony, and the agency will allocate the time available amongst the commenters who registered to speak ( i.e., not to exceed 10 minutes). We ask that only one person present on behalf of a group or organization. The EPA encourages commenters to provide the EPA with a copy of their oral testimony electronically by emailing it to the person identified in the FOR FURTHER INFORMATION CONTACT section of this document. The EPA also recommends submitting the text of your oral comments as written comments to the rulemaking docket.

The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public meeting.

Please note that any updates made to any aspect of the meeting will be posted online at https://www.epa.gov/dwucmr/unregulated-contaminant-monitoring-rule-ucmr-meetings-and-materials and will be emailed to those who register to attend the meeting. While the EPA expects the meeting to go forward as set forth above, please monitor our website or contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this document to determine if there are any updates. The EPA does not intend to publish a document in the Federal Register announcing updates. The number of connections available for the meeting is limited and will be available on a first-come, first-served basis. If the number of connections becomes limited, the EPA will post additional dates and times online at https://www.epa.gov/dwucmr/unregulated-contaminant-monitoring-rule-ucmr-meetings-and-materials.

The EPA will not provide audiovisual equipment for presentations unless we receive special requests in advance. Commenters should notify the person identified in the FOR FURTHER INFORMATION CONTACT section of this document when they pre-register to speak that they will need specific equipment. If you require the services of an interpreter or special accommodation such as audio description, please pre-register for the webinar with the person identified in the FOR FURTHER INFORMATION CONTACT section of this document and describe your needs by July 30, 2026. The EPA may not be able to arrange accommodations without advance notice.

III. General Background Information

A. How are the Contaminant Candidate List (CCL), the UCMR program, the Regulatory Determination process, and the NCOD interrelated?

Under SDWA, Congress established a multistep, risk-based approach for determining which contaminants would become subject to drinking water standards. Under the first step, the EPA is required to publish a CCL every five years that identifies contaminants that are not subject to any proposed or promulgated drinking water standards, are known or anticipated to occur in PWSs, and may require future action under SDWA. Under the second step, the EPA must require, every five years, monitoring of unregulated contaminants to determine the frequency and level of their occurrence in drinking water systems; this is the UCMR program. Under the third step, the EPA is required to determine, every five years, whether or not to regulate at least five contaminants from the CCL through the regulatory determination process. Under SDWA sections 1412(b)(1)(A), the EPA regulates a contaminant in drinking water if the Administrator determines that:

(1) The contaminant may have an adverse effect on the health of persons;

(2) the contaminant is known to occur or there is substantial likelihood that the contaminant will occur in PWSs with a frequency and at levels of public health concern; and

(3) in the sole judgment of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by PWSs. Where the Administrator determines that a contaminant meets all three criteria, SDWA requires the EPA to propose and publish a NPDWR. Information on the CCL and the regulatory determination process can be found at https://www.epa.gov/ccl.

The data collected through the UCMR program are made available to the public through the NCOD for drinking water. SDWA section 1445(g)(3) requires that the EPA maintain UCMR data in the NCOD and use the data when evaluating the occurrence of contaminants in drinking water at a level of public health concern. The UCMR results can be viewed at https://www.epa.gov/sdwa/ or via the UCMR web page at https://www.epa.gov/dwucmr.

B. What public engagement opportunities have been held in preparation for UCMR 6?

The EPA incorporates public involvement into each UCMR cycle. Specific to the development of UCMR 6, the EPA sought comments on drinking water method development for emerging contaminants, and held a public meeting, state consultation, tribal consultation, and Alaska Native Claims Settlement Act (ANCSA) consultation. A summary of the public comments for each of these meetings is included in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. Additionally, the EPA is announcing another meeting in this proposal (see section II.B of this document).

On February 8, 2024, the EPA published a Federal Register notice that requested public input on the development of drinking water analytical methods for unregulated contaminants (89 FR 8584, (USEPA, 2024a)). The notice focused on contaminants listed on the fifth Contaminant Candidate List (CCL 5), that might support monitoring under the UCMR 6 and/or other future UCMR cycles. The EPA received 12 public comments throughout the 60-day comment period.

The EPA hosted two identical pre-proposal meetings on April 17 and April 18, 2024, to discuss potential approaches for developing UCMR 6, including: the status of drinking water analytical methods and contaminants being considered; possible sampling design; laboratory approval; other potential aspects of the monitoring approach; and included time for public questions and statements (89 FR 8584, (USEPA, 2024a)). Representatives from state agencies, laboratories, PWSs, environmental organizations, and drinking water associations joined the meeting. The presentation materials can be found on the EPA's Unregulated Contaminant Monitoring Program Meetings and Materials webpage at https://www.epa.gov/dwucmr/unregulated-contaminant-monitoring-rule-ucmr-meetings-and-materials.

The EPA hosted the state consultation from May 30 to July 1, 2024, with the meeting on May 29, 2024, to discuss the early development of UCMR 6, and the voluntary options states have in the implementation of the UCMR program. Thirty state representatives attended the meeting and participated in the discussion (USEPA, 2026a).

The EPA hosted the tribal consultation from March 10 to June 20, 2024, with the meeting on May 20, 2024 (USEPA, 2026b), and the ANCSA consultation from December 6, 2024, to February 10, 2025, with the meeting on January 15, 2025 (USEPA, 2026c). More details on tribal and ANCSA consultations can be found in section V.G of this document.

C. What notable changes are being proposed for UCMR 6?

This proposed action updates the existing UCMR ( i.e., UCMR 5), by revising: the list of contaminants for UCMR 6, the drinking water analytical methods for these new contaminants, the data elements for reporting, and the monitoring timeframe. A track-changes version of the rule language, comparing UCMR 5 to the proposed changes for UCMR 6, (" Proposed Revisions to 40 CFR parts 141.35 and 141.40" (USEPA, 2026d)), is included in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The EPA's proposed approach and rationale for changes are described in the following sections.

D. How did the EPA identify the contaminants being proposed for UCMR 6?

In establishing the proposed list of contaminants for UCMR 6, the EPA evaluated unregulated contaminants consistent with the statutory authorities described in section I.A of this document. The UCMR is one of the first steps in the SDWA regulatory process and is used to inform the criteria outlined in SDWA 1412(b) for EPA's regulatory determinations (see section III.A). Consistent with SDWA section 1445(a)(2) as amended by the AWIA, and the process described in this document, the EPA is proposing monitoring for the unregulated contaminants listed in Exhibit 2.

SDWA 1445(a)(2) requires the EPA to establish criteria for a monitoring program for unregulated contaminants. As a starting point, the EPA considered the CCL 5, which includes 66 chemicals, three chemical groups and 12 microbes (87 FR 68060, November 14, 2022 (USEPA, 2022)). The agency also evaluated contaminants nominated by the public for potential inclusion on the sixth CCL (CCL 6) (88 FR 10316, February 17, 2023 (USEPA, 2023)) and considered other priority contaminants beyond the CCL. Further, the EPA considered the opportunity to collect occurrence data for contaminants within the scope of the drinking water analytical methods that already contained a CCL contaminant based on available health and occurrence information to create a more cost-effective design ( i.e., maximize the number of contaminants in each drinking water analytical method, to reduce overall cost and burden). Consistent with the " U.S. Environmental Protection Agency Implementation of Gold Standard Science" (USEPA, 2025a) based on Executive Order 14303 " Restoring Gold Standard Science," (White House, 2025), the EPA evaluated candidate UCMR 6 contaminants using a prioritization process that deprioritized contaminants that were previously monitored under a prior UCMR cycle (unless there was a compelling case to monitor for them again) as well as contaminants not expected to have a completed, validated drinking water method in time for rule proposal. The potential contaminants for the monitoring program were then further evaluated based on health effects information, if available, to inform public health concern, and the occurrence information, if available, to inform the likelihood the contaminant will be found in finished drinking water.

Additional information on this prioritization process, as well as contaminant-specific information ( e.g., source, use, production, release, persistence, mobility, health effects, and occurrence) that the EPA used to evaluate candidate contaminants, is contained in " Information Compendium for Candidate Contaminants for the Proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6)" (USEPA, 2026g), found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The EPA invites comment on the proposed UCMR 6 contaminants (and their associated drinking water analytical methods) identified in Exhibit 2.

PFAS are a diverse group of compounds and the CCL 5 lists PFAS as a group, characterized by a structural definition, which EPA uses as a first step in considering individual compounds. The recently-developed EPA Method 563  ⁽³⁾ can capture certain PFAS, as defined by the CCL 5 ( i.e., PFMOAA, PFPrA, PFPrS, PFEtS). As noted in the 2019 PFAS Action Plan (USEPA, 2019), these PFAS, referred to as short-chain PFAS have been less thoroughly studied, but are a concern due to increase global production and use.

While TFMS, TFSI, and TFA are not defined as PFAS under the CCL 5 structural definition, these ultrashort organofluorine compounds are persistent in the environment, highly mobile, used widely in industry, and have health effects information (USEPA, 2026g). Due to the similarities in chemical structure to the CCL 5 defined PFAS, TFMS, TFSI, and TFA can also be analyzed by EPA Method 563. This allows the EPA to better understand the frequency and occurrence of this suite of contaminants without increased costs, and can inform and prioritize future resource-intensive research. During early stakeholder engagement, the public provided both written comments and discussions in support of monitoring for these contaminants in public drinking water (see section III.B).

Additionally, as a part of the process to identify contaminants for the monitoring program, the agency identified an alternate contaminant in the event that one is needed. The agency identified MGK 264 as the alternate contaminant. MGK 264 is an ingredient used in common insecticides to enhance the potency of pyrethroid ingredients. This contaminant has not been monitored under a previous UCMR cycle, is in a method already proposed for UCMR 6, and has an available health assessment (USEPA, 2021c). If, during the laboratory approval process, the agency determines that laboratories are experiencing analytical difficulties with one of the proposed contaminants, the agency intends to replace that contaminant with MGK 264 a priority alternate from EPA Method 525.3 in the final UCMR 6. The EPA welcomes comments on the potential inclusion of MGK 264 in UCMR 6.

The EPA notes that two contaminants deviate from the prioritization process outlined in this section. 1,2,3-TCP has already been monitored in a previous UCMR cycle and the discussion for that contaminant's inclusion is in section III.D.1 of this document. The parent contaminant to chlorpyrifos oxon, chlorpyrifos, has already been monitored in a previous UCMR cycle and the discussion for that contaminant's inclusion is in section III.D.2 of this document.

1. 1,2,3-Trichloropropane (1,2,3-TCP)

1,2,3-TCP is a likely carcinogenic man-made chemical used as an industrial solvent, cleaning agent, degreasing agent, and synthesis intermediate (USEPA, 2009a, USEPA, 2026g). This contaminant was included on the third, fourth, and fifth CCLs and was monitored during UCMR 3 (USEPA, 2009a, USEPA, 2016a, USEPA, 2022, USEPA, 2012b). The UCMR 3 occurrence data can be found at https://www.epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule#3. The EPA did not make a regulatory determination for 1,2,3-TCP during Regulatory Determination 4 (86 FR 12272, March 3, 2021 (USEPA, 2021b)), and did not make a preliminary determination in Regulatory Determination 5 (90 FR 3830, January 15, 2025 (USEPA, 2025b)), due in part to the drinking water analytical method minimum reporting level (MRL = 0.03 µg/L) being substantially higher than the level of public health concern, which presents uncertainty when characterizing exposure and a potential meaningful opportunity for health risk reduction. To better understand the potential risk of this contaminant in drinking water, the agency developed " Recommended Parameters to Enhance Sensitivity for the Analysis of Select Purgeable Organic Compounds using EPA Method 524.3 in Selected Ion Monitoring (SIM) Mode" (USEPA, 2026e) that can detect 1,2,3-TCP at lower concentrations (0.009 µg/L) than what was feasible in the method " Method 524.3: Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry," (USEPA, 2009b) used during UCMR 3. Monitoring using this optimized method would provide the EPA with occurrence data closer to the levels of public health concern, which will provide the agency with additional information that could inform future regulatory decisions for 1,2,3-TCP through SDWA.

2. Chlorpyrifos and Chlorpyrifos Oxon

Chlorpyrifos and its metabolite, chlorpyrifos oxon, are organophosphate pesticides that are used on crops, animals, in buildings, and in other settings, to kill several pests, including insects and worms (USEPA, 2026g). Chlorpyrifos, which is a neurotoxin (USEPA, 2020), is listed on the CCL 5 (87 FR 68060, November 14, 2022 (USEPA, 2022)), is used across the country on a variety of crops (USGS, 2019), and was monitored during UCMR 4 (MRL = 0.03 µg/L) (81 FR 9266, December 20, 2016 (USEPA, 2016b)). There was limited occurrence of the parent, chlorpyrifos, in UCMR 4 (for data results see https://www.epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule#archival ). However, chlorpyrifos metabolizes into chlorpyrifos oxon during the chlorination of drinking water, which is a treatment commonly used in PWSs (USEPA, 2005). As a result, the metabolite has a higher likelihood of being found in finished drinking water, and occurrence data is critical to characterizing exposure and a potential meaningful opportunity for health risk reduction. Therefore, the EPA proposes to monitor for chlorpyrifos oxon in UCMR 6. Additionally, EPA Method 540 is being considered for UCMR 6 because it includes the pesticide metabolites, phorate sulfone and phorate sulfoxide, which are both tied to the CCL 5 contaminant phorate in EPA Method 525.3.

E. What other contaminants did the EPA consider for UCMR 6?

This notice describes the 30 contaminants that the agency has identified as the highest priorities for UCMR 6 monitoring through the process described in the preceding section of this document. This process prioritizes the unregulated contaminants, for which nationally representative data on the frequency and level of occurrence is critical to characterizing exposure and assessing whether there is a meaningful opportunity for health risk reduction. The EPA considers that the primary utility of the UCMR data is to provide data to the other SDWA programs. SDWA requires that the data collected under the UCMR be used to develop the CCL (see SDWA section 1412(b)(1)(B)(i)(I)) and to make regulatory determinations for CCL contaminants (see SDWA section 1412(b)(1)(B)(ii)(II)). The data collected under the UCMR also provides states and PWSs with information that could be used to protect public health in each state.

In developing this UCMR action, the EPA considered the burden that UCMR places upon PWSs to monitor and, consistent with SDWA sections 1445(j) and 1452(o), the availability of funding to pay the cost of small PWS monitoring, the laboratory capacity to support the analysis of UCMR samples, and the utility of the information to be collected. For further information on these contaminants, see " Information Compendium for Candidate Contaminants for the Proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6)" (USEPA, 2026g), found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469.

The EPA invites comment on the contaminants described in the following sections and any other priority contaminants commenters wish to recommend. In your comments, please identify the following: any new contaminant(s) that you believe should be included in the UCMR 6 monitoring; any contaminant(s) in Exhibit 2 that you believe should be removed from the list; the recommended drinking water analytical method(s) for any new contaminant(s) that you propose; and other relevant details ( e.g., reporting level, sampling location, sampling frequency, analytical cost). Comments that provide supporting data or rationale are especially helpful.

1. Microplastics

On November 26, 2025, the agency received a petition from the Governors of 7 states (Governors' Petition) to include microplastics on UCMR 6. SDWA section 1445(a)(2)(B)(ii) provides that "[t]he Administrator shall include among the list of contaminants for which monitoring is required under this paragraph each contaminant recommended in a petition signed by the Governor of each of 7 or more states, unless the Administrator determines that the action would prevent the listing of other contaminants of a higher public health concern." The EPA also received a petition from the Food and Water Watch group with signatures from other organizations supporting monitoring for microplastics in UCMR 6 (a copy of that petition and response, and the Governors' Petition have been placed in the public Docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469).

The EPA has listed microplastics as a group on the draft Contaminant Candidate List (CCL 6) as a first step toward defining and better understanding potential public health risk from exposure via drinking water (USEPA, 2026h). The EPA will collaborate with other federal agencies to evaluate risks and exposures of microplastics to enable future monitoring for those microplastics that present potential health risks. This approach will also enable the EPA to list microplastics on a future UCMR when national monitoring is scientifically feasible through the availability of a validated drinking water analytical method.

As the Governors' Petition acknowledges, there is no validated EPA or consensus drinking water analytical method with the proper quality control data, accuracy, and precision that could be used for UCMR 6, and it is not feasible to develop a drinking water analytical method within the statutory timeframe ( i.e., December 27, 2026). If microplastics were included on UCMR 6, the PWSs subject to this rulemaking would be unable to successfully monitor for microplastics. Such monitoring is the central purpose of the UCMR as outlined by SDWA section 1445(a)(2). In addition, the agency and the public would lose an opportunity to gain occurrence information on other unregulated contaminants that have a drinking water analytical method available for UCMR 6.

The Governors' Petition asserts that "the variability in methodologies for detecting microplastics poses challenges to data consistency and comparability" and "this variability complicates efforts to standardize findings, underscoring the need for harmonized protocols to ensure reliable data collection and analysis." The agency will continue to evaluate the existing procedures and techniques (ASTM-D8332-20 and D8333-20) (ASTM, 2020a, ASTM, 2020b) to develop robust and validated methods, as well as adequate laboratory capacity, that would support national monitoring for microplastics in a future UCMR.

The agency acknowledges the interest in and concern for microplastics in drinking water, and believes that including these contaminants on the draft CCL 6 as a first step in responding to the petition will prioritize the research that is needed to define and better understand the characteristics of microplastics ( i.e., size, type of plastic, shape, count, etc.) that are associated with the public health risk. This research may inform the development of drinking water analytical methods that can be used to standardize data collection and analysis in the future.

2. Pharmaceuticals

Pharmaceuticals in drinking water have been a public health concern for over a decade. Since 2012, the EPA has led a federal workgroup on pharmaceuticals in water alongside the United States Department of Agriculture (USDA), the United States Food and Drug Administration (FDA), and the United States Geological Survey (USGS) to exchange information on pharmaceuticals in the environment and to support the coordination of joint studies. The agency recently included a pharmaceuticals group on the draft CCL 6 to further prioritize research and information needed to identify which specific pharmaceuticals are occurring in drinking water and may be of greatest public health concern (USEPA, 2026h). The agency also released the " Human Health Benchmarks for Pharmaceuticals (HHB-Rx) in Drinking Water" (USEPA, 2026i). Human health benchmarks are non-enforceable drinking water levels that provide information about adverse health effects from drinking water exposure to contaminants that have no drinking water standards or health advisories. These actions support the agency's approach to prioritize specific pharmaceuticals and develop drinking water analytical methods to support monitoring in a future UCMR.

F. What is the proposed UCMR 6 applicability date?

In CFR 141.40(a), the EPA proposes February 1, 2026, as the date to determine which PWSs are subject to UCMR 6. That is, the determination of whether a PWS is required to monitor under UCMR 6 is based on the type of system ( e.g., CWS, NTNCWS) and its retail population served, as indicated by the Safe Drinking Water Information System Federal Reporting Services (SDWIS/Fed) inventory on February 1, 2026. If a PWS believes its retail population served in SDWIS/Fed is inaccurate, the system should contact their state authority to verify its population as of the specified date and request a correction, if necessary. This applicability date is exactly five years from the last date published in UCMR 5 (86 FR 73131, December 27, 2021 (USEPA, 2021d)), based on the 5-year cycle of the UCMR program.

In CFR 141.35(c)(4), the EPA proposes April 26, 2027, as the date large PWSs must contact the EPA or state if the PWS believes they are subject to UCMR 6 and they have not been contacted by the EPA or the state. This date is also exactly five years from the last date published in UCMR 5 (86 FR 73131, December 27, 2021 (USEPA, 2021d)), based on the 5-year cycle of the UCMR program.

G. What is the proposed UCMR 6 pre-monitoring reporting date?

In five different CFR sections, 141.35 (c)(1), 141.35 (c)(2), 141.35 (c)(5)(i), 141.35 (d)(2) and 141.40 (a)(4)(i), the EPA proposes December 31, 2027, as the reporting and sampling requirements date, by which PWSs are required to report contact information, zip code information, sampling location inventory information, and scheduling and rescheduling notifications. These updated dates are exactly five years from the last dates published in UCMR 5 (86 FR 73131, December 27, 2021 (USEPA, 2021d)), based on the 5-year cycle of the UCMR program.

H. What is the proposed UCMR 6 timeline of activities?

The proposed rule outlines the monitoring period for UCMR 6. From the date of this proposal until January 1, 2028, the EPA will be conducting a number of activities, including reviewing comments and promulgating the final rule, coordinating laboratory approval, selecting representative small PWSs, organizing Partnership Agreements with states, developing State Monitoring Plans (see III.N of this document), establishing monitoring schedules and inventory, and conducting outreach and training. The EPA proposes that PWSs will collect samples between January 1, 2028-December 31, 2030, and PWSs must complete their monitoring by December 31, 2031. Exhibit 3 illustrates the major activities that the EPA expects will take place in preparation for, and during, the implementation of UCMR 6.

I. What is the proposed UCMR 6 monitoring design?

The proposed rule identifies sampling and analysis for UCMR 6 contaminants based on the Assessment Monitoring framework, which provides the best nationally representative monitoring data set for determining if contaminants occur frequently and at levels of public health concern. Further information on this framework, including a description of the statistical approach for the nationally representative sample, can be found in the " Statistical Design and Sample Selection for the Unregulated Contaminant Monitoring Regulation" (USEPA, 2001) in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. With the addition of AWIA in 2018, the " Selection of Nationally Representative Public Water Systems for the Unregulated Contaminant Monitoring Rule: 2021 Update" (USEPA, 2021a) also found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469, expanded the UCMR scope prescribed by AWIA, clarified the monitoring framework, updated the description of the sampling design, and clarified how small PWSs would be selected in the event of insufficient appropriations.

As outlined in SDWA, to minimize the impact of the rule on small PWSs (those serving 10,000 or fewer people), the EPA is responsible for their sample kit preparation, sample shipping fees, and sample analysis. If the EPA concludes that it will not have the appropriations necessary to support the monitoring described by the AWIA, the agency plans to adjust the number of small PWSs that serve 10,000 or fewer people to monitor based upon the available appropriations (see section III.O.2 of this document for more details). Consistent with prior UCMRs, large PWSs serving more than 10,000 people are responsible for any costs associated with their monitoring. Exhibit 4 shows a summary of the estimated number of both small and large PWSs subject to required monitoring.

1. Sampling, Frequency, and Timing

The anticipated number of samples collected by each PWS is consistent with prior UCMR cycles. PWSs would be required to collect samples based on the published UCMR sampling frequency and timeframe as follows: for ground water locations, sampling would take place twice over the course of a single 12-month period (total of two sampling events). Sampling events would occur five to seven months apart. For example, if the first sample is taken in April, the second sample would then occur anytime in September, October, or November. For surface water, ground water under the direct influence of surface water, and mixed locations, sampling would take place for four consecutive quarters over the course of a single 12-month period (total of four sampling events). Sampling events would occur three months apart. For example, if the first sample is taken in January, the second would then occur anytime in April, the third would occur anytime in July, and the fourth would occur anytime in October. The monitoring frequency is designed to be spatially and temporally representative of occurrence. The design ensures that the sample results can be analyzed for temporal, seasonal, and between-system variability on a national level to support future decisions to protect public health. ⁽⁴⁾

The EPA expects to consult with the states and draft schedules for large PWSs. Thereafter, these PWSs would have an opportunity to modify this initial schedule for planning purposes or other reasons ( e.g., to spread costs over multiple years, a sampling location will be closed during the scheduled month of monitoring). The EPA proposes to schedule and coordinate small PWS monitoring by working closely with states and small PWSs. State Monitoring Plans provide an opportunity for states to review and revise the initial sampling schedules that the EPA proposes (see discussion of State Monitoring Plans in section III.N of this document).

2. Sampling Locations

The EPA is proposing that sample collection for the UCMR 6 contaminants would take place at the entry point to the distribution system (EPTDS). The following are two ways for PWSs to reduce the number of EPTDSs at which they must sample: submit a GWRMP and/or utilize representative sampling from wholesaler connection.

One way for large ground water PWSs (or large surface water PWSs with ground water sources) that have multiple ground water EPTDSs to reduce their number of sampling locations, is to submit a GWRMP. GWRMPs approved under prior UCMRs may be used for UCMR 6, presuming no significant changes in the configuration of the ground water EPTDSs since the prior approval. PWSs that intend to use previously approved plans must send the EPA a copy of the approval documents notifying the EPA that they intend on using the approved plan at least six months prior to their scheduled sample collection dates. Large ground water PWSs (and large surface water PWSs with ground water sources) that do not have an approved GWRMP may submit proposals at least six months prior to their scheduled sample collection dates. As for past UCMRs, details are described in CFR section 141.35(c)(3) and are available in the document, " Instructions for Preparing a Ground Water Representative Monitoring Plan for the Unregulated Contaminant Monitoring Rule, " (USEPA, 2021e) found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. Changes to inventory data in the Safe Drinking Water Accession and Review System (SDWARS) that impact a PWS's representative plan before or during the UCMR sampling period must be reported to the EPA within 30 days of the change ( e.g., the representative sampling location closes, and a new representative sampling location needs to be selected).

The second way for PWSs to reduce their number of EPTDSs that they must sample is for PWSs that purchase water with multiple connections from the same wholesaler, to select one representative connection from that wholesaler. As described in CFR section 141.40(a)(3) this representative EPTDS must be a location within the purchaser's water system, after treatment is applied, and represent each non-emergency water source in routine use over the 12-month period of monitoring. The EPTDS sampling location must be representative of the highest annual volume of connections or if the connection selected as the representative EPTDS is not available for sampling, an alternate highest volume representative connection must be sampled.

J. What are the reporting requirements for UCMR 6?

The EPA proposes changes to the reporting requirements currently established for UCMR 6, as detailed in Table 1 of the CFR section 141.35(e), to account for the UCMR 6 contaminants being proposed. These changes include removing data elements related to the specific contaminants from the previous UCMR, adding and updating data elements based on the proposed list of contaminants to be monitored, and improving data reporting from laboratories and PWSs based on experience from the previous UCMR. Recognizing that data elements are updated each monitoring cycle, the EPA invites comment on the proposed data elements and associated definitions, as well as any other data elements that may provide useful information to inform an assessment of the occurrence information and future actions to protect public health.

K. What are the Consumer Confidence Reporting and Public Notice (PN) Reporting requirements for PWSs that are subject to UCMR?

In addition to reporting UCMR monitoring data to the EPA, PWSs are responsible for addressing UCMR results in their Consumer Confidence Reports (CCRs) (40 CFR 141.153), as described in the Federal Register (89 FR 45980, May 24, 2024, (USEPA, 2024b)), and PN requirements (40 CFR 141.207). More details about the CCR and PN requirements can be viewed by the public at https://www.epa.gov/ccr and https://www.epa.gov/dwreginfo/public-notification-rule, respectively.

L. How do laboratories become approved to conduct the UCMR 6 analyses?

Consistent with prior UCMRs, this proposal maintains the requirement that PWSs use laboratories approved by the EPA to analyze UCMR 6 samples. Interested laboratories are encouraged to apply for EPA approval as early as possible, beginning with the publication of this proposal, to ensure national laboratory capacity. This early participation is also necessary, if laboratories are interested in a contract with the EPA to analyze samples from small systems. The contract solicitation will be released prior to the end of the laboratory approval program. The UCMR 6 laboratory approval process is designed to assess whether laboratories possess the required equipment and can meet laboratory-performance and data-reporting criteria described in this action.

The EPA anticipates following its standard approach to approving UCMR laboratories, which would require laboratories seeking approval to: (1) provide the EPA with data that demonstrate a successful completion of an initial demonstration of capability (IDC) as outlined in each method; (2) verify successful performance at or below the MRLs as specified in this action; (3) provide information about laboratory standard operating procedures (SOPs); and (4) participate in an EPA proficiency test (PT) study for the analytes of interest. Audits of laboratories may be conducted by the EPA prior to and/or following approval, and maintaining approval is contingent on timely and accurate reporting. The " UCMR 6 Laboratory Approval Manual" (USEPA, 2026j) provides more specific details on the EPA laboratory approval program and the specific method acceptance criteria. This document can be found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The EPA will also include sample collection procedures that are specific to the methods in the " UCMR 6 Laboratory Approval Manual," and will address this point in the agency's outreach to the PWSs that will be collecting samples.

The structure of the anticipated UCMR 6 laboratory approval program is similar to that employed in the previous UCMRs and would provide an assessment of the ability of laboratories to perform analyses using the methods listed in CFR section 141.40(a)(3), Table 1. PWSs are required to exclusively use laboratories that have been approved under the program. The EPA expects to post a list of approved UCMR 6 laboratories to https://www.epa.gov/dwucmr and will bring this to the attention of the PWSs in the agency's outreach.

1. What are UCMR MRLs and how were they determined?

The EPA establishes MRLs for contaminants under the UCMR to ensure consistency in the quality of the information reported to the agency. As defined in CFR section 141.40(a)(5)(iii), the MRL is the minimum quantitation level that, with 95 percent confidence, can be achieved by capable analysts at 75 percent or more of the laboratories using a specified drinking water analytical method. A more detailed explanation of the MRL calculation is in the " Technical Basis for the Lowest Concentration Minimum Reporting Level (LCMRL) Calculator" (USEPA, 2010), available at https://www.epa.gov/dwanalyticalmethods/lowest-concentration-minimum-reporting-level-lcmrl-calculator and can also be found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469.

The EPA established the proposed MRLs in CFR section 141.40(a)(3), Table 1, for each analyte/method by obtaining data from at least three laboratories that performed "lowest concentration minimum reporting level" (LCMRL) studies. The results from these laboratory LCMRL studies can be found in the " UCMR 6 Laboratory Approval Manual" (USEPA, 2026j) found in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The EPA considers these to be the lowest reporting levels that can practically and consistently be achieved on a national basis (recognizing that individual laboratories may be able to measure at lower levels). The EPA invites comments on the proposed MRLs and will consider scientific information demonstrating that the proposed MRLs are unattainable for laboratories and laboratory capacity would become a concern for the UCMR program.

2. Request To Participate

Laboratories interested in the UCMR 6 laboratory approval program must first email the EPA at [email protected] to request registration materials. The EPA expects to accept such requests beginning with the publication of this proposal in the Federal Register .

3. Registration

Laboratory applicants provide registration information that includes: laboratory name, mailing address, shipping address, contact name, phone number, email address, and a list of the UCMR 6 methods for which the laboratory is seeking approval. This registration step provides the EPA with the necessary contact information and ensures that each laboratory receives a customized application package.

4. Application Package

Laboratory applicants complete and return a customized application package that includes the following: IDC data, including precision, accuracy and results of MRL studies; information regarding analytical equipment and other materials; proof of current drinking water laboratory certification (for select compliance monitoring methods); method specific SOPs; and example chromatograms for each method under review.

5. The EPA's Review of Application Package

The EPA will review the application packages and, if necessary, request follow-up information. Laboratories that successfully complete the application process become eligible to participate in the UCMR 6 PT program. Based on a January 1, 2028, anticipated start date for UCMR 6 sample collection, the EPA anticipates that the final opportunity for a laboratory to complete and submit the necessary registration and application information will be August 1, 2027.

6. Proficiency Testing

A PT sample is a synthetic sample containing a concentration of an analyte or mixture of analytes that is known to the EPA, but unknown to the laboratory. To be approved, a laboratory is expected to meet specific acceptance criteria for the analysis of a UCMR 6 PT sample(s) for each analyte in each method, for which the laboratory is seeking approval. The EPA anticipates offering up to three of these studies prior to the publication of the final rule, and at least two studies after publication of the final rule. This allows laboratories to complete their portion of the laboratory approval process prior to publication of the final rule and receive their approval immediately following the publication of the final rule. Laboratories must pass a PT for every analyte in the method to be approved for that method and may participate in multiple PT studies in order to produce passing results for each analyte. The EPA does not expect to conduct additional PT studies after the start of PWS monitoring; however, laboratory audits will likely be ongoing throughout the implementation of UCMR 6. Initial laboratory approval is expected to be contingent on successful completion of PT studies, which includes properly uploading the PT results to SDWARS. Continued laboratory approval is contingent on successful completion of the audit process and satisfactorily meeting all the other stated conditions.

7. Written EPA Approval

After a laboratory successfully completes steps 1 through 6, the EPA expects to send the laboratory a notification letter listing the methods for which approval is either "pending" ( i.e., pending promulgation of the final rule if the PT studies have been conducted prior to that time), or for which approval is "granted" (if after promulgation of the final rule). Laboratories receiving pending approval are expected to be granted approval without further action following promulgation of the final rule if no changes have been made to the rule that impact the laboratory approval program. The EPA expects to contact the laboratory if changes are made between the proposed and final rules that warrant additional action by the laboratory.

As a condition of receiving and maintaining approval, the laboratory will be expected to promptly post UCMR 6 monitoring results and quality control data that meet method criteria (on behalf of its PWS clients) to the EPA's UCMR electronic data reporting system, SDWARS.

M. UCMR 6 Laboratory Capacity

The EPA believes there will be laboratory capacity for the proposed UCMR 6 contaminants. EPA Method 525.3 and EPA Method 524.3 with enhanced sensitivity, both use the same instrumental technology, SPE GC/MS. Laboratory capacity has been well-established for GC/MS instrumentation based on laboratory participation in previous UCMR cycles. Additionally, the technology is routinely used for compliance with NPDWRs.

The other two methods proposed for UCMR 6, EPA Method 563 and EPA Method 540, utilize LC/MS/MS. Laboratories are familiar with the LC/MS/MS instrumentation that both methods utilize since the LC/MS/MS instrumentation was first introduced to drinking water laboratories under UCMR 2, nearly 20 years prior (72 FR 368, (USEPA, 2007)). Since then, every cycle of the UCMR program has included at least one or more LC/MS/MS method(s), and the UCMR program has not experienced any laboratory capacity issues. EPA Method 563 is easier and quicker to run compared to EPA Methods 533 and 537.1, which were used for UCMR 5, since the sample can be directly injected into the instrumentation with limited preparation. This reduces potential laboratory burden, increases the number of samples that can be analyzed per day, and is ultimately more cost-effective.

The UCMR program engages the drinking water laboratory community early in the action development process and encourages comments regarding proposed methods, contaminants, sampling design, and other aspects of each UCMR cycle. For UCMR 6, laboratories had the opportunity to comment on method development in response to the Federal Register Notice (89 FR 8584, (USEPA, 2024a)), during the public webinars on April 17 and 18, 2024 (see the available summary on the EPA public docket for this proposed rule, under Docket ID No. EPA-HQ-OW-2023-0469), and will have the opportunity to provide input on this proposed action during the public comment period and associated public webinar (see section II of this document for further information).

Another way the EPA has established laboratory capacity is to initiate the UCMR laboratory approval program in concurrence with the proposal, and the agency is committed to this opportunity in the proposal today. This early engagement provides laboratories with more time to receive approval from the EPA prior to the start of monitoring to ensure laboratory capacity. Lastly, the EPA initially schedules PWS monitoring equally over the 3-year monitoring period (2028-2030) to reduce capacity burden on participating laboratories. The EPA welcomes comments regarding laboratory capacity to support the proposed UCMR 6 contaminants, sampling design, and other relevant aspects of the rule.

N. What is the state's role in the UCMR?

UCMR is a direct implementation rule ( i.e., the EPA has primary responsibility for its implementation), and state participation is voluntary. Under the previous UCMR cycles, most states have participated in the UCMR and have agreed to carry out or assist with specific activities that are identified and established exclusively through Partnership Agreements. Through Partnership Agreements, states can help the EPA implement the UCMR and help ensure that the UCMR data are of the highest quality possible to best inform agency decision making. Under UCMR 6, the EPA expects to continue to use the Partnership Agreement process to determine and document the following: the process for review and revision of the State Monitoring Plans; replacing and updating PWS information including inventory; review of proposed GWRMPs; notification and instructions for PWSs; and compliance assistance. The EPA recognizes that primacy agencies often have the best information about their PWSs and encourages them to partner in the UCMR 6 program.

O. Costs and Benefits

1. What is the estimated cost of this proposed action?

The EPA estimates the total annualized national cost of this proposed action in 2025 dollars will be $33.7 million at both a 3 percent and 7 percent discount rate for the years 2027-2031. The EPA has documented the assumptions and data sources used in the preparation of this estimate in the " Draft Economic Analysis of the Sixth Unregulated Contaminant Monitoring Rule" (USEPA, 2026k). Copies of the Draft Economic Analysis may be obtained from the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The agency proposes four drinking water analytical methods to analyze samples for 30 chemical contaminants. The EPA's estimate of the analytical cost for the UCMR 6 contaminants is $1,893 per sample set with field blanks. These costs were calculated by summing the laboratory unit cost of each method, along with the analysis of the quality control samples, and shipping the kits. Exhibit 1 presents a breakdown of the total annualized national costs in 2025 dollars. The EPA invites comment on the proposed UCMR 6 costs identified in Exhibit 5 and throughout this proposal.

The EPA is responsible for the analytical costs for all PWSs serving a population of 10,000 or fewer people. Laboratory analysis and sample shipping account for approximately 77 percent of the total national cost for the implementation of UCMR 6. The EPA estimated laboratory unit costs are based on consultations with multiple commercial drinking water testing laboratories.

State participation in the UCMR program is voluntary; thus, the level of effort is expected to vary among states and would depend on their individual agreements with the EPA. The agency expects that states that choose to participate may incur modest labor costs associated with voluntary assistance with the implementation of UCMR 6. The EPA estimated state costs using the relevant assumptions from the State Resource Model developed by the Association of State Drinking Water Administrators (ASDWA) (ASDWA, 2020) to help states forecast resource needs. Model estimates were adjusted to account for actual levels of state participation under UCMR 5.

The EPA assumes that one-third of the PWSs would monitor during each of the three sample-collection years from January 2028 through December 2030. The total estimated annual costs (labor and non-labor) would be incurred as follows:

2. What are the costs of alternative approaches to implementing the proposed UCMR 6?

As noted in section I.A.3 of this document, the AWIA amendments to SDWA conditioned the UCMR monitoring scope on the availability of appropriations. See SDWA section 1445(j)(1). If the EPA concludes that it will not have the resources necessary to support the full monitoring described by the AWIA, the agency will reduce the number of small PWSs serving 10,000 or fewer people that will be required to monitor. The EPA will determine the number of small PWSs whose monitoring is covered by the appropriations and will notify the included small PWSs of their upcoming requirements at least six months prior to their scheduled monitoring ( i.e., by July 1 of each year preceding sample collection). This notification approach was successfully implemented in the previous UCMR cycle. The number of large PWSs-those serving more than 10,000 people-required to monitor would remain the same, as specified in SDWA.

The EPA has documented the alternative assumptions and data sources used in the preparation of this estimate in the " Draft Economic Analysis of the Sixth Unregulated Contaminant Monitoring Rule" (USEPA, 2026k). The EPA estimates the total annualized national cost of this alternative in 2025 dollars will be $22.1 million at both a 3 percent and 7 percent discount rate for the years 2027-2031. Exhibit 6 presents a breakdown of the estimated annual average national costs.

As outlined in SDWA section 1445, the EPA pays for the analytical costs for all systems serving a population of 10,000 or fewer people. Laboratory analysis and sample shipping account for approximately 77 percent of the total national cost for the implementation of UCMR 6. Under the alternative scenario, this percentage slightly decreases since the number of small PWSs decreases from approximately 6,000 to 800. All other expectations with state participation and years of sampling remain the same. Only the number of small PWSs monitoring will be reduced.

3. What are the benefits of this proposed action?

The UCMR program gathers data about unregulated contaminant occurrence in drinking water. This occurrence information benefits consumers by letting them know whether or not unregulated contaminants are present in their drinking water. If contaminants are not found, consumer confidence in their drinking water will improve. If contaminants are found, PWSs and consumers may be able to take actions to avoid adverse health effects such as treatment optimization or point-of-use filters to reduce or remove those contaminants. While the UCMR program does not result in direct improvements to public health that can be monetized for the purpose of a quantitative benefits analysis, the data gathered under the UCMR program informs other agency actions that could result in quantifiable health risk reduction benefits.

The UCMR program provides a value of information benefit that can be used by federal and state agencies, local governments, water systems, and the public, in their policies and regulatory actions to produce national estimates and quantifiable improvements to public health.

IV. Supporting Information

A. Economic Analysis

The general cost and benefits outlined in the economic analysis for this action are discussed in section III.O of this document. The full analysis is available in the public Docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469.

B. How did the EPA consider children's environmental health?

This action is not subject to the EPA's Children's Health Policy at https://www.epa.gov/children/childrens-health-policy-and-plan, because this is a monitoring rule that does not directly address human health. However, by monitoring for unregulated contaminants that may pose health risks via drinking water, UCMR furthers the protection of public health for all citizens, including children. Children consume more water per unit of body weight compared to adults. Moreover, formula-fed infants drink a large amount of water compared to their body weight. Thus, while children's exposure to contaminants in drinking water may present a disproportionate health risk (USEPA, 2013b), the objective of UCMR 6 is to collect nationally representative drinking water occurrence data on unregulated contaminants. The detailed information on the prioritization process, as well as contaminant-specific information ( e.g., source, use, production, release, persistence, mobility, health effects, and occurrence) that the EPA used to select the proposed analyte list, is contained in " Information Compendium for Candidate Contaminants for the Proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6)" (USEPA, 2026g).

Executive Order 13045 also does not apply to UCMR 6 because the environmental health or safety risks addressed by this action do not present a disproportionate risk to children (See V.H. Executive Order 13045 of this document). However, the EPA's Policy on Evaluating Health Risks to Children, which ensures that the health of infants and children is explicitly considered in the agency's decision making, is applicable, see: https://www.epa.gov/children/epas-policy-evaluating-risk-children.

Using quantitation data from multiple laboratories, the EPA establishes statistically based UCMR reporting levels that are projected to be feasible for the national network of approved drinking water laboratories to quantify accurately. The EPA sets the reporting levels as low as is practical, even if that level is well below concentrations that are currently associated with known or suspected health effects. In doing so, the EPA positions itself to better address contaminant risk information in the future, including that associated with unique risks to children. The EPA requests comments regarding any further steps that may be taken to evaluate and address health risks to children that fall within the scope of UCMR 6.

C. What documents are being incorporated by reference?

The following methods are being incorporated by reference into this section of the document for the UCMR 6 monitoring. All method material is available for inspection electronically at http://www.regulations.gov in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469, or from the sources listed for each method. The EPA has worked to make these methods and documents reasonably available to interested parties. The methods that may be used to support monitoring under this rule are as follows:

1. Methods From the U.S. Environmental Protection Agency

(i) EPA Method 524.3, "Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry," Version 1.0, June 2009, EPA 815-B-09-009. Available at https://www.epa.gov/dwanalyticalmethods. This is an EPA method for analysis of purgeable organic compounds in drinking water using SPE and LC/MS/MS.

(ii) EPA Method 524.3 " Recommended Parameters to Enhance Sensitivity for the Analysis of Select Purgeable Organic Compounds using EPA Method 524.3 (EPA 815-B-09-009) in Selected Ion Monitoring (SIM) Mode," Version 1.0, February 2026, EPA 815-B-26-002. Available at https://www.epa.gov/dwanalyticalmethods. This is an EPA method for the analysis of purgeable organic compounds in drinking water using SPE and LC/MS/MS and is proposed to measure seven purgeable organic compounds during UCMR 6 (1,2,4-Trimethylbenzene, 1,2,3-Trichloropropane (1,2,3-TCP), 1,1,2,2-Tetrachloroethane, Total 1,3-Dichloropropene (cis- & trans-), Naphthalene, 1,1,1,2-Tetrachloroethane, and Hexachlorobutadiene).

(iii) EPA Method 525.3 " Determination of Semivolatile Organic Chemicals in Drinking Water by Solid Phase Extraction (SPE) and Capillary Column Gas Chromatography/Mass Spectrometry (GC/MS)," Version 1.0, February 2012, EPA/600/R-12/01. Available at https://www.epa.gov/dwanalyticalmethods. This is an EPA method for the analysis of semi-volatile organic chemicals in drinking water using SPE and GC/MS and is proposed to measure 13 semi-volatile organic chemicals during UCMR 6 (Phorate, Chlorothalonil, Dichlorvos (DDVP), Metribuzin, N,N-Diethyl-m-toluamide (DEET), Trifluralin, Pyrene, Isophorone, 2,4-Dinitrotoluene, 2,6,-Dinitrotoluene, Stirofos, Anthracene, and Flourene).

(iv) EPA Method 540 " Determination of Selected Organic Chemicals in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)," Version 1.0, September 2013, EPA/600/R-13/119. Available at https://www.epa.gov/dwanalyticalmethods. This is an EPA method for the analysis of selected organic chemicals in drinking water using SPE and LC/MS/MS and is proposed to measure three pesticide metabolites during UCMR 6 (Chlorpyrifos oxon, Phorate sulfone, and Phorate sulfoxide).

(v) EPA Method 563 " Determination of Selected Ultrashort Organofluorine Compounds in Drinking Water by Liquid Chromatography/Tandem Mass Spectrometry," Version 1.0, January, 2026, EPA 815-F-26-002. Available at https://www.epa.gov/dwanalyticalmethods. This is an EPA method for the analysis of ultrashort organofluorine compounds in drinking water using LC/MS/MS and is proposed to measure seven ultrashort organofluorine compounds during UCMR 6 (PFPrS, PFPrA, PFEtS, PFMOAA, TFMS, TFSI, and TFA).

V. Statutory and Executive Orders Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

This action is a significant regulatory action that was submitted to the Office of Management and Budget (OMB) for review defined under Executive Order 12866. Any changes made in response to OMB recommendations have been documented in the docket. The EPA prepared an economic analysis of the potential costs and benefits associated with this action that is briefly summarized in sections III.O and IV.A of this document. This analysis, " Economic Analysis of the Sixth Unregulated Contaminant Monitoring Rule (UCMR 6)" (USEPA, 2026k), is available in the EPA public docket for this proposed rulemaking, under Docket ID No. EPA-HQ-OW-2023-0469. The EPA estimated that the proposed action would result in annualized costs of $33.7 million in 2025 dollars, at both a 3 percent discount rate and a 7 percent discount rate.

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

This action is expected to be an Executive Order 14192 regulatory action. The expected quantified annualized costs of this rule are $7.68 million in 2024 dollars at a 7 percent discount rate and an in-perpetuity time horizon. Details on the estimated costs of this proposed rule can be found in the EPA's analysis of the potential costs and benefits associated with this action.

C. Paperwork Reduction Act (PRA)

The information collection activities in this proposed rule have been submitted for approval to the Office of Management and Budget (OMB) under the PRA. The Information Collection Request (ICR) document that the EPA prepared has been assigned EPA ICR number 7820.01. You can find a copy of the ICR in the docket for this rule, and it is briefly summarized here.

The information that the EPA proposes to collect under this rule fulfills the statutory requirements of SDWA section 1445(a)(2), as amended in 1996, 2018, and 2019. The data will describe the source of the water, location, and test results for samples taken from PWSs as described in 40 CFR 141.35(e). The information collected will inform other SDWA programs and risk management decisions for drinking water contaminants. Reporting is mandatory. The data are not subject to confidentiality protection.

The 5-year UCMR 6 period spans 2027-2031. As proposed, UCMR 6 sample collection begins in 2028 and continues through 2030. Since ICRs cannot be approved by OMB for a period longer than three years pursuant to 5 CFR 1320.10, the primary analysis in the ICR only covers the first three years of the UCMR period (2027-2029). Prior to expiration of the UCMR 6 ICR, the EPA will seek to extend the ICR and thus receive approval to collect information under the PRA in the remaining two years of the UCMR 6 period (2030-2031).

The EPA has reviewed and, as appropriate, revised the cost and burden figures from UCMR 5 for UCMR 6. This includes using updated unit cost estimates for sample analysis. The annual burden and cost estimates described in this section are based on the implementation assumptions described in section III.O.1 of this document, among them the inclusion of all PWSs serving 3,300 to 10,000 people and a representative sample of PWSs serving fewer than 3,300 people. If the EPA does not receive the necessary appropriations in one or more of the collection years-and thus collects data from fewer small PWSs-the actual costs would be lower than those estimated here (USEPA, 2026l).

Respondents/affected entities: The respondents/affected entities are small PWSs (those serving 10,000 or fewer people); large PWSs (those serving more than 10,000 people); and primacy agencies (states, tribes, and territories).

Respondent's obligation to respond: Mandatory (40 CFR 141.35).

Estimated number of respondents: Respondents to UCMR 6, as proposed, include approximately 6,000 small PWSs, approximately 4,600 large PWSs, and the 55 primacy agencies (49 states, one tribal nation, and five territories). There are approximately 10,600 respondents to UCMR 6 during the 5-year program period.

Frequency of response: The frequency of response varies across respondents and years. Across the initial 3-year ICR period for UCMR 6, small PWSs would sample an average of 2.8 times per PWS ( i.e., number of responses per PWS); large PWSs would sample and report and average of 3.2 times per PWS; and very large PWSs would sample and report an average of 3.7 times per PWS.

Total estimated burden: 41,291 hours (per year). Burden is defined at 5 CFR 1320.3(b).

Total estimated cost: $19,670,760, includes $17,451,527 annualized capital or operation & maintenance costs.

An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a currently valid OMB control number. The OMB control numbers for the EPA's regulations in 40 CFR are listed in 40 CFR part 9.

Submit your comments on the agency's need for this information, the accuracy of the provided burden estimates and any suggested methods for minimizing respondent burden to the EPA using the docket identified at the beginning of this rule. The EPA will respond to any ICR-related comments in the final rule. You may also send your ICR-related comments to OMB's Office of Information and Regulatory Affairs using the interface at www.reginfo.gov/public/do/PRAMain. Find this particular information collection by selecting "Currently under Review-Open for Public Comments" or by using the search function. OMB must receive comments no later than July 31, 2026.

D. Regulatory Flexibility Act (RFA)

For purposes of assessing the impacts of this rule on small entities, the EPA considered small entities to be PWSs serving 10,000 or fewer people. As required by the RFA, the EPA proposed using this alternative definition in the Federal Register (63 FR 7607, February 13, 1998 (USEPA, 1998a)), sought public comment, consulted with the Small Business Administration (SBA), and finalized the alternative definition in the Consumer Confidence Reports rulemaking (63 FR 44512, August 19, 1998 (USEPA, 1998b)). As stated in that document, the alternative definition would apply to this regulation.

I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. The small entities subject to the requirements of this action are PWSs serving 10,000 or fewer people. The Agency has determined that up to 5,955 small PWSs would participate in UCMR 6 if the EPA receives the necessary appropriations. Those entities are not expected to experience an impact greater than 0.4% of median revenue because the EPA assumes all costs for analyses of the samples and for shipping the samples from small PWSs to laboratories contracted by the EPA to analyze the UCMR 6 samples (the cost of shipping is included in the cost of each drinking water analytical method). Details of this analysis are in the "Draft Economic Analysis of the Sixth Unregulated Contaminant Monitoring Rule" (USEPA, 2026k). Copies of the Draft Economic Analysis may be obtained from the EPA public docket for this proposed rule, under Docket ID No. EPA-HQ-OW-2023-0469.

The EPA anticipates drawing on the set aside of $12.0 million each year from the Drinking Water State Revolving Fund (DWSRF) consistent with SDWA section 1445(j) and 1452(o) to use DWSRF monies for the purposes of implementing the monitoring program for unregulated contaminants. Thus, the costs to these small PWSs will be modest and limited to the labor associated with collecting a sample and preparing it for shipping. The estimated average annual burden across the 5-year UCMR 6 implementation period is 1.4 hours at $69 per small PWS or approximately $0.4 million in 2025 dollars across all 5,955 small PWSs. We have therefore concluded that this action will not have a significant economic impact on a substantial number of small entities under the RFA.

E. Unfunded Mandates Reform Act (UMRA)

This action does not contain an unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. The action implements mandate(s) specifically and explicitly set forth in SDWA section 1445(a)(2), Monitoring Program for Unregulated Contaminants. The costs involved in this action are estimated not to exceed 100 million in 1995 dollars which is $192.68 million in 2025 dollars (adjusted for inflation using the GDP implicit price deflator) or more in any one year.

F. Executive Order 13132: Federalism

This action does not have federalism implications. The EPA believes, however, that this action may be of significant interest to state governments. Consistent with the EPA's policy to promote communications between the EPA and state and local governments, the EPA consulted with state representatives early in the process of developing the UCMR 6 to permit them to have meaningful and timely input into its development. Please see section II.B of this notice and the summary of the public comments for this meeting included in the EPA public docket for this proposed rule, under Docket ID No. EPA-HQ-OW-2023-0469.

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

This action has tribal implications; however, it will neither impose substantial direct compliance costs on federally recognized tribal governments, nor preempt tribal law. As described previously, this proposed rule requires monitoring by all large PWSs. Information in the SDWIS/Fed water system inventory indicates there are 30 large tribal PWSs (ranging in size from 10,100 to 32,000 people served). The EPA estimates the average annual cost to each of these large PWSs, over the 5-year rule period, to be $3,082. This cost is based on a labor component (associated with the collection of samples) and a non-labor component (associated with shipping and laboratory fees). As planned, UCMR 6 is expected to also require monitoring by all small PWSs serving 3,300 to 10,000 people and a nationally representative sample of small PWSs serving fewer than 3,300 people. Information in the SDWIS/Fed water system inventory indicates there are 77 small tribal PWSs (serving 3,300 to 10,000 people). The EPA estimates that less than 2 percent of small tribal PWSs serving fewer than 3,300 people will be selected as part of the nationally representative sample. The EPA estimates the average annual cost to small tribal PWSs over the 5-year rule period to be $69. Such cost is based on the labor associated with collecting a sample and preparing it for shipping. All other small PWS expenses (associated with shipping and laboratory fees) are paid by the EPA.

The EPA consulted with tribal officials under the EPA Policy on Consultation and Coordination with Indian Tribes early in the process of developing this regulation to permit them to have meaningful and timely input into its development. A summary of that consultation is provided in the EPA public docket for this proposed rule, under Docket ID No. EPA-HQ-OW-2023-0469. The summaries are titled, " Summary of Tribal Consultation and Coordination on the Development of the Sixth Proposed Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems " and " Summary of Alaska Native Claims Settlement Act (ANCSA) Corporations Consultation and Coordination on the Development of the Sixth Proposed Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems" The EPA specifically solicits additional comment on this proposed rule from tribal officials.

H. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks

The EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that the EPA has reason to believe may disproportionately affect children, per the definition of "covered regulatory action" in section 2-202 of the Executive Order.

Therefore, this action is not subject to Executive Order 13045 because this is a monitoring rule, and it does not directly address an environmental health risk or safety risk. Since this action does not directly concern human health, the EPA's Policy on Children's Health also does not apply.

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use

This action is not a "significant energy action" because it is not likely to have a significant adverse effect on the supply, distribution or use of energy. UCMR 6 has not otherwise been designated by the Administrator of the OMB-OIRA as a significant energy action. This is a national drinking water occurrence study that was submitted to OMB for review.

J. National Technology Transfer and Advancement Act (NTTAA)

This action involves technical standards. The EPA proposes to use the following methods developed by the agency to support UCMR 6 monitoring: EPA Method 563, EPA Method 540, EPA Method 525.3, and EPA Method 524.3. While the EPA identified multiple potential voluntary consensus standard body (VCSB) methods from ASTM International (ASTM) and Standard Methods for the Examination of Water as being potentially applicable, the agency does not propose to use them. The use of these VCSB would be impractical because of cost and logistics. Additionally, multiple VCSB methods would need to be used for the analytes included in one EPA method and this increases the overall cost of the analysis. The additional methods would also increase the number of bottles, the weight of the shipping boxes, and the number of boxes that need to be shipped. All of the EPA methods are free for download on the agency's website, and both the ASTM and Standard Methods for the Examination of Water require payment for access to the methods. The EPA welcomes comments on this aspect of the proposed action and specifically invites the public to identify potentially applicable VCSB methods and explain why such standards should be used in this rule.

VI. References

ASDWA. 2020. 2019 Analysis of State Drinking Water Programs' Resources and Needs: Addressing Emerging Issues and State Specificity in Program Implementation. July 2020. Available at https://www.asdwa.org/wp-content/uploads/2020/07/2019-Analysis-of-State-Drinking-Water-Programs-Resources-and-Needs.pdf.

ASTM. 2020a. ASTM D8332-20- Standard Practice for Collection of Water Samples with High, Medium, or Low Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers. ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Approved August 14, 2020. Available for purchase at astm.org.

ASTM. 2020b. ASTM D8333-20- Standard Practice for Preparation of Water Samples with High, Medium, or Low Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers Using Raman Spectroscopy, IR Spectroscopy, or Pyrolysis-GC/MS. ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Approved August 14, 2020. Available for purchase at astm.org.

Governors of New Jersey, Delaware, Illinois, Maryland, Michigan, Wisconsin, and Connecticut. 2025. Re: Request of the Governors of New Jersey, Delaware, Illinois, Maryland, Michigan, Wisconsin, and Connecticut under 42 U.S.C. 300j-4(a)(2)(B)(ii) that EPA Include Microplastics in the Forthcoming Unregulated Contaminant Monitoring Rule 6 List. Submitted to the U.S. Environmental Protection Agency. November 26, 2025.

USEPA. 1998a. National Primary Drinking Water Regulations: Consumer Confidence Reports. Federal Register . Vol. 63, No. 30, p. 7607. February 12, 1998.

USEPA. 1998b. National Primary Drinking Water Regulations: Consumer Confidence Reports. Federal Register . Vol. 63, No. 160, p. 44512. August 19, 1998.

USEPA. 2001. Statistical Design and Sample Selection for the Unregulated Contaminant Monitoring Regulation (1999). EPA 815-R-01-004. Office of Water. August 2001.

USEPA. 2005. Organophosphate Pesticide Degradation Under Drinking Water Treatment Conditions. EPA/600/R-05/103. Office of Research and Development. August 2005.

USEPA. 2007. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water Systems Revisions. Federal Register . Vol. 72, No. 2, p. 368. January 4, 2007.

USEPA. 2009a. Drinking Water Contaminant Candidate List 3-Final. Federal Register . Vol. 74, No. 194, p. 51850. October 8, 2009.

USEPA. 2009b. Method 524.3: Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry. EPA 815-B-09-009. Office of Water. June 2009.

USEPA. 2010. Technical Basis for the Lowest Concentration Minimum Reporting Level (LCMRL) Calculator. EPA 815-R-11-001. Office of Water. December 2010. Available at https://www.epa.gov/dwanalyticalmethods.

USEPA. 2012a. Method 525.3 Determination of Semivolatile Organic Chemicals in Drinking Water by Solid Phase Extraction and Capillary Column Gas Chromatography/Mass Spectrometry (GC/MS). EPA/600/R-12/010. Office of Research and Development. February 2012. Available at https://www.epa.gov/dwanalyticalmethods.

USEPA. 2012b. Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems. Federal Register . Vol. 77, No. 85, p. 26072. May 2, 2012.

USEPA. 2013a. Method 540: Determination of Selected Organic Chemicals in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS). EPA/600/R-13/119. Office of Research and Development. September 2013. Available at https://www.epa.gov/dwanalyticalmethods.

USEPA. 2013b. America's Children and the Environment, Third Edition: Environments and Contaminants: Drinking Water Contaminants. January 2013. Available at: https://www.epa.gov/sites/default/files/2015-06/documents/ace3_2013.pdf

USEPA. 2016a. Drinking Water Contaminant Candidate List 4-Final. Federal Register . Vol. 81, No. 222, p. 81099. November 17, 2016.

USEPA. 2016b. Revisions to the Unregulated Contaminant Monitoring Rule (UCMR 4) for Public Water Systems and Announcement of Public Meeting. Federal Register . Vol. 81, No. 244, p. 92666. December 20, 2016.

USEPA. 2019. EPA's Per- and Polyfluoroalkyl Substances (PFAS) Action Plan. EPA 823R180004. Office of Water. February 2019. Available at https://www.epa.gov/sites/default/files/2019-02/documents/pfas_action_plan_021319_508compliant_1.pdf.

USEPA. 2020. Chlorpyrifos: Third Revised Human Health Risk Assessment for Registration Review. September 21, 2020, memo. Office of Chemical Safety and Pollution Prevention. Available on the internet at: https://www.regulations.gov/document/EPA-HQ-OPP-2008-0850-0944.

USEPA. 2021a. Selection of Nationally Representative Public Water Systems for the Unregulated Contaminant Monitoring Rule: 2021 Update. EPA 815-B-21-012. Office of Water. December 2021.

USEPA. 2021b. Announcement of Final Regulatory Determinations for Contaminants on the Fourth Drinking Water Contaminant Candidate List. Federal Register . Vol. 86, No. 40, p. 12272. March 3, 2021.

USEPA. 2021c. MGK-264: Revised Human Health Risk Assessment in Support of Registration Review. DP No. D460729. Office of Chemical Safety and Pollution Prevention. April 2021.

USEPA. 2021d. Revisions to the Unregulated Contaminant Monitoring Rule (UCMR 5) for Public Water Systems and Announcement of Public Meetings. Federal Register . Vol. 86, No. 245, p. 73131. December 27, 2021.

USEPA. 2021e. Instructions for Preparing a Ground Water Representative Monitoring Plan for the Unregulated Contaminant Monitoring Rule. EPA 815-B-21-013. Office of Water. December 2021.

USEPA. 2022. Drinking Water Contaminant Candidate List 5-Final. Federal Register . Vol. 87, No. 218, p. 68060. November 14, 2022.

USEPA. 2023. Drinking Water Contaminant Candidate List 6 -Nominations. Federal Register . Vol. 88, No. 33, p. 10316. February 17, 2023.

USEPA. 2024a. Unregulated Contaminant Monitoring Rule; Methods Request and Webinar. Federal Register . Vol. 89, No. 27, p. 8584. February 8, 2024.

USEPA. 2024b. National Primary Drinking Water Regulations: Consumer Confidence Reports. Federal Register . Vol. 89, No. 102, p. 45980. May 24, 2024.

USEPA. 2025a. U.S. Environmental Protection Agency Implementation of Gold Standard Science-Based on Executive Order No. 14303 "Restoring Gold Standard Science." August 2025. Available at https://www.epa.gov/system/files/documents/2026-01/final-epa-gss-report.pdf.

USEPA. 2025b. Announcement of Preliminary Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List. Federal Register . Vol. 90, No. 9, p. 3830. January 15, 2025.

USEPA. 2026a. Summary of the State Consultation on the Development of the Sixth Proposed Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems. EPA-815-S-26-006. Office of Water. February 2026.

USEPA. 2026b. Summary of Alaska Native Claims Settlement Act (ANCSA) Corporations Consultation and Coordination on the Development of the Sixth Proposed Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems. EPA 815-S-26-002. Office of Water. February 2026.

USEPA. 2026c. Summary of Tribal Consultation and Coordination on the Development of the Sixth Proposed Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems. EPA-815-S-26-005. Office of Water. February 2026.

USEPA. 2026d. Proposed Revisions to CFR parts 141.35 and 141.40. EPA 815-Z-26-001. Office of Water. February 2026.

USEPA. 2026e. Recommended Parameters to Enhance Sensitivity for the Analysis of Select Purgeable Organic Compounds using EPA Method 524.3 (EPA 815-B-56-002) in Selected Ion Monitoring (SIM) Mode. EPA-815-B-26-002. Office of Water. February 2026.

USEPA. 2026f. Method 563: Determination of Selected Ultrashort Organofluorine Compounds in Drinking Water by Liquid Chromatography/Tandem Mass Spectrometry. EPA 815-F-26-002. Office of Water. January 2026.

USEPA. 2026g. Information Compendium for Candidate Contaminants for the Proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6). EPA 815-R-26-009. Office of Water. February 2026.

USEPA. 2026h. Drinking Water Contaminant Candidate List 6-Draft. Federal Register . Vol. 91, No. 65, p. 17186. April 6, 2026.

USEPA. 2026i. Human Health Benchmarks for Pharmaceuticals (HHB-Rx) in Drinking Water. Updated April 2, 2026. Available at https://www.epa.gov/sdwa/2026-human-health-benchmarks-pharmaceuticals-hhb-rx.

USEPA. 2026j. UCMR 6 Laboratory Approval Manual. EPA 815-B-26-001. Office of Water. February 2026.

USEPA. 2026k. Draft Economic Analysis of the Sixth Unregulated Contaminant Monitoring Rule. EPA 815-R-26-007. Office of Water. February 2026.

USEPA. 2026l. Information Collection Request for the Final Unregulated Contaminant Monitoring Rule (UCMR 6). EPA 815-D-26-001. Office of Water. February 2026.

United States Geological Survey (USGS). 2019. Estimated Annual Agricultural Pesticide Use: Pesticide Use Maps-Chlorpyrifos. United States Geological Survey (UGSS). Updated February 26, 2024. Available at https://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2019&map=CHLORPYRIFOS&hilo=L&disp=Chlorpyrifos.

White House. 2025. Restoring Gold Standard Science. May 2025. Available at https://www.whitehouse.gov/presidential-actions/2025/05/restoring-gold-standard-science/.

[Revisions to the Unregulated Contaminant Monitoring Rule (UCMR 6) for Public Water Systems Page XX of XXX]

For the reasons set forth in the preamble, EPA proposes to amend 40 CFR part 141 as follows:

PART 141-NATIONAL PRIMARY DRINKING WATER REGULATIONS

Subpart D-Reporting and Recordkeeping

The revisions read as follows:

(e) Data elements. Table 1 defines the data elements that must be provided for UCMR monitoring.

Subpart E-Special Regulations, Including Monitoring

The revisions read as follows:

(a) * * *

(3) Analytes to be monitored. Lists 1, 2, and 3 contaminants are provided in table 1 to paragraph (a)(3):

* * * * *

(c) Incorporation by reference. The standards required in this section are incorporated by reference into this section with the approval of the Director of the Federal Register under 5 U.S.C. 552(a) and 1 CFR part 51. All approved material is available for inspection at U.S. Environmental Protection Agency, Water Docket, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave. NW, Washington, DC 20004, (202) 566-1744, email [email protected], or go to https://www.epa.gov/dockets/epa-docket-center-reading-room, and is available from the sources indicated elsewhere in this paragraph. The material is also available for inspection at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, email [email protected], or go to:

(1) U.S. Environmental Protection Agency, EPA West, Room 3334, 1301 Constitution Ave. NW, Washington, DC 20004; telephone: (202) 566-1744.

(i) Method 524.3, " Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry," Version 1.0, June 2009, EPA 815-B-09-009. Available at https://www.epa.gov/dwanalyticalmethods.

(ii) Method 524.3 "Recommended Parameters to Enhance Sensitivity for the Analysis of Select Purgeable Organic Compounds using EPA Method 524.3 (EPA 815-B-09-009) in Selected Ion Monitoring (SIM) Mode," Version 1.0, February 2026, EPA 815-B-26-002. Available at https://www.epa.gov/dwanalyticalmethods.

(iii) Method 525.3, "Determination of Semivolatile Organic Chemicals in Drinking Water by Solid Phase Extraction (SPE) and Capillary Column Gas Chromatography/Mass Spectrometry (GC/MS)," Version 1.0, February 2012, EPA/600/R-12/01. Available at https://www.epa.gov/dwanalyticalmethods.

(iv) Method 540, "Determination of Selected Organic Chemicals in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)," Version 1.0, September 2013, EPA/600/R-13/119. Available at https://www.epa.gov/dwanalyticalmethods.

(v) Method 563 "Determination of Selected Ultrashort Organofluorine Compounds in Drinking Water by Liquid Chromatography/Tandem Mass Spectrometry," Version 1.0, January, 2026, EPA 815-F-26-02. Available at https://www.epa.gov/dwanalyticalmethods.

(2) [Reserved]

[FR Doc. 2026-13263 Filed 6-30-26; 8:45 am]

BILLING CODE 6560-50-P

⁽¹⁾  The fifth Contaminant Candidate List (CCL 5) (87 FR 68060, November 14, 2022 (USEPA. 2022)) defines the structural definition of PFAS to include chemicals that contain at least one of these three structures:

1. R-(CF2)-CF(R′)R″, where both the CF2 and CF moieties are saturated carbons, and none of the R groups can be hydrogen

2. R-CF2OCF2-R′, where both the CF2 moieties are saturated carbons, and none of the R groups can be hydrogen

3. CF3C(CF3)RR′, where all the carbons are saturated, and none of the R groups can be hydrogen.

⁽²⁾  For CCL 5 (USEPA, 2022), the structural definition of PFAS included chemicals that contain at least one of these three structures:

1. R-(CF2)-CF(R′)R″, where both the CF2 and CF moieties are saturated carbons, and none of the R groups can be hydrogen

2. R-CF2OCF2-R′, where both the CF2 moieties are saturated carbons, and none of the R groups can be hydrogen

3. CF3C(CF3)RR′, where all the carbons are saturated, and none of the R groups can be hydrogen.

⁽³⁾  The organofluorine Method 563 was in the early stages of development at the time of the February 2024 Federal Register Notice (89 FR 8584, (USEPA, 2024a)) and did not have a full analyte list. This method has since been finalized and is available in the UCMR 6 docket for public comment.

⁽⁴⁾  The 36-month schedule produces thousands of monthly results per contaminant. These results can be analyzed for seasonal patterns and annual occurrence. The EPA designed the monitoring frequency to ensure that sample results would yield a high level of confidence and a low margin of error. Further information on the statistical approach for the nationally representative sample, can be found in the "Statistical Design and Sample Selection for the Unregulated Contaminant Monitoring Regulation" (USEPA, 2001) found in the docket.