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Home My WebLink About05-01-26 Correspondence - MT Dept of Environmental Quality - Amending Human Health Standards D E Montana Department of Environmental Quality April 24, 2026 Dear Interested Party, On April 24, 2026,the Montana Department of Environmental Quality(department) initiated rulemaking on rule amendments to update department Circular DEQ-7. Circular DEQ-7 contains numeric water quality standards for surface water and ground water and is incorporated by reference into the Administrative Rules of Montana. The department is proposing several amendments to Circular DEQ-7: • Amend human health standard for cyanide in ground water to express cyanide as free cyanide rather than total cyanide,to add a required reporting value, and to add a nondegradation trigger value; • Amend human health standards for lead in surface water and ground water, lowering the criteria from 15 µg/L to 10 µg/L, and update the reference for the source used to derive the criteria; • Amend human health standards for four pesticides (i.e., 1,2-dibromoethane, nicosulfuron, chlorsulfuron, and imazapic)to correct errors made when calculating their criteria prior to their adoption in 2017; and • Amendments to correct grammatical errors, improve clarity, and remove outdated references. The department also proposes to amend ten rules to replace references to the 2019 edition of Circular DEQ-7 with references to the effective month and year of this rule amendment. On June 8, 2026, at 11:00 a.m., a public hearing will be held in the Wilderness Room on the second floor at 2401 Colonial Drive, Helena, Montana,to consider rule amendments as proposed in MAR 2026-496.1 in the Montana Administrative Register.You may also join the hearing virtually via Zoom. More information is available on the department's website, including a copy of the notice of public hearing on proposed amendments,and instructions on how to attend remotely, at https://deg.mt.gov/public/water-public.The department will make reasonable accommodation for persons with disabilities who wish to participate in this rulemaking process or need an alternative accessible format of this notice (see the MAR notice on the website for details).A copy of the proposed Circular DEQ-7 may be viewed at the department's website using the following web address: https://deg.mt.gov/public/water-public:copies may also be obtained by contacting Katie Makarowski at (406)444-3639 or kmkarowski@mt.gov. You are invited to submit data,views,or arguments concerning the proposed action either orally or in writing at the hearing. Written data, views, or arguments may also be submitted to the Department of Environmental Quality, P.O. Box 200901, Helena, Montana 59620-0901; or e-mailed to DEQMAR496@mt.gov and must be received no later than 5:00 p.m.on June 8, 2026. We thank you for your interest in Montana's water quality. Greg Gianforte,Governor I Sonja Nowakowski,Director I P.O.Box 200901 1 Helena,MT 59620-0901 1(406)444-2544 1 www.deq.mt.gov Sincerely, Katie Makarowski Water Quality Planning Bureau Standards and Modeling Section Supervisor (406)444-3639 kmkarowski@mt.gov o pry MONTANA tf ADMINISTRATIVE REGISTER - �r DEPARTMENT OF ENVIRONMENTAL QUALITY NOTICE OF PROPOSED RULEMAKING MAR NOTICE NO. 2026-496.1 Summary Amendment of Department Circular DEQ-7 pertaining to numeric water quality standards for surface water and ground water Hearing Date and Time Monday,June 8, 2026, at 11:00 a.m. Hearing Information Wilderness Room at 2401 Colonial Drive, Helena, MT 59601. Virtual Hearing Information Interested parties may also attend the hearing electronically in the following ways: Please click the link below to join the webinar: Join Zoom Meeting https://mt-gov.zoom.us/j/83089983448?pwd=H6mhwvZx5ygywmYZybKNaHt6rFtWR4.1 Meeting ID: 830 8998 3448 Password: 047200 Dial by Telephone +1 646 558 8656 Meeting ID: 830 8998 3448 Password: 047200 Issue No. 8 - April 24, 2026 1 Find your local number: https://mt-gov.zoom.us/u/kelEXoKg7 Join by SIP 83089983448@zoomcrc.com Join by H.323 144.195.19.161##83089983448 Comments Comments may be submitted using the contact information below. Comments must be received by Monday, June 8, 2026, at 5:00 p.m. Accommodations The agency will make reasonable accommodations for persons with disabilities who wish to participate in this rulemaking process or need an alternative accessible format of this notice. Requests must be made by Friday, May 29, 2026, at 5:00 p.m. Contact Legal Unit (406) 444-2630 DEQMAR496@mt.gov General Reasonable Necessity Statement Several proposed amendments to Department Circular DEQ-7 (Montana numeric water quality standards) were identified during the department's triennial review of water quality standards; additional amendments were identified to improve clarity and correct clerical errors. The department proposes to amend the human health standard for cyanide in ground water to express the standard as free cyanide rather than total cyanide, to align Montana's standard with federal drinking water regulations; the department is not proposing to change the numeric criteria. Changing the basis of the criteria from total cyanide to free cyanide necessitates addition of a new required reporting value that reflects the laboratory analytical methods approved for measuring free cyanide. A trigger value is also proposed because cyanide is a toxic parameter for which a trigger value was not previously adopted for use when implementing nondegradation rules for toxic parameters. Issue No. 8-April 24, 2026 2 The department proposes to amend the human health standard for lead in surface water and ground water to align Montana's standard with federal drinking water regulations. The department also proposes to correct an erroneous reference to more accurately cite the source used to derive the criteria, that is, to clarify that the standard is based on an action level, not on a maximum contaminant level as there is no maximum contaminant level for lead. The department proposes to amend human health standards for four pesticides in surface water and ground water to correct errors made when the criteria were derived prior to adoption in 2017. Changes are proposed to 1,2-dibromoethane to correct a misplaced decimal, to nicosulfuron to correct a rounding error, and to chlorsulfuron and imazapic to correct an incorrect reference dose used in the calculations. The department also proposes several amendments to correct grammatical errors and improve clarity. The department proposes to amend ten rules to replace citations to the June 2019 edition of Department Circular DEQ-7 with an updated reference to the edition that will be effective following adoption of the proposed amendments. Rulemaking Actions AMEND The rules proposed to be amended are as follows, stricken matter interlined, new matter underlined: 17.24.645 GROUND WATER MONITORING (1)through (5) remain the same. (6) Methods of sample collection, preservation, and sample analysis must be conducted in accordance with 40 CFR Part 136 titled "Guidelines Establishing Test Procedures for the Analysis of Pollutants" (July 2015) and the department's document titled "Department Circular DEQ-7, Montana Numeric Water Quality Standards,"--June-2G44[effective month and year of this rule amendmentl edition. Copies of Department Circular DEQ-7 are available at the Department of Environmental Quality, 1520 E. 6th Ave., P.O. Box 200901, Helena, MT 59620-0901. Sampling and analyses must include a quality assurance program acceptable to the department. (7) and (8) remain the same. Authorizing statute(s): 82-4-205, MCA Issue No. 8 -April 24, 2026 3 Implementing statute(s): 82-4-231, 82-4-232, MCA Reasonable Necessity Statement Section (6) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.24.646 SURFACE WATER MONITORING (1) through (5) remain the same. (6) Methods of sample collection, preservation, and sample analysis must be conducted in accordance with 40 CFR Part 136 titled "Guidelines Establishing Test Procedures for the Analysis of Pollutants" (July 2015) and Part 434 titled "Coal Mining Point Source Category BPT, BAT, BCT Limitations and New Source Performance Standards" (January 2002), and the 1tme-2GI4[effective month and. year of this rule amendmentl edition of the department's document titled "Department Circular DEQ-7, Montana Numeric Water Quality Standards." Copies of 40 CFR Part 136, 40 CFR 434, and Department Circular DEQ-7 are available at the Department of Environmental Quality, 1520 E. 6th Ave., P.O. Box 200901, Helena, MT 59620-0901. Sampling and analyses must include a quality assurance program acceptable to the department. (7) remains the same. Authorizing statute(s): 82-4-205, MCA Implementing statute(s): 82-4-231, 82-4-232, MCA Reasonable Necessity Statement Section (6) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.30.502 DEFINITIONS The following definitions, in addition to those in 75-5-103, MCA, and ARM Title 17, chapter 30, subchapters 6 and 7, apply throughout this subchapter: (1) through (13) remain the same. Issue No. 8 -April 24, 2026 4 (14) The department adopts and incorporates by reference Department Circular DEQ-7, entitled "Montana Numeric Water Quality Standards" (4"e--29+9 [effective month and year of this rule amendmentl edition), which establishes numeric water quality standards for toxic, carcinogenic, bioconcentrating, nutrient, radioactive, and harmful parameters. Copies of Department Circular DEQ-7 are available from the Department of Environmental Quality, P.O. Box 200901, Helena, MT 59620-0901. Authorizing statute(s): 75-5-301, MCA Implementing statute(s): 75-5-301, MCA Reasonable Necessity Statement Section (14) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.30.619 INCORPORATIONS BY REFERENCE (1) The department adopts and incorporates by reference the following state and federal requirements and procedures as part of Montana's surface water quality standards: (a) Department Circular DEQ-7, entitled "Montana Numeric Water Quality Standards" (fttne--9+9 [effective month and year of this rule amendmentl edition), which establishes numeric water quality standards for toxic, carcinogenic, bioconcentrating, radioactive, and harmful parameters and also establishes human health-based water quality standards for the following specific nutrients with toxic effects: (i) through (iii) remain the same. (b) through (f) remain the same. (2) and (3) remain the same. Authorizing statute(s): 75-5-201, 75-5-301, MCA Implementing statute(s): 75-5-301, 75-5-313, MCA Issue No. 8 -April 24, 2026 5 Reasonable Necessity Statement Subsection (1)(a) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.30.702 DEFINITIONS The following definitions, in addition to those in 75-5-103, MCA, apply throughout this subchapter (Note: 75-5-103, MCA, includes definitions for "base numeric nutrient standards," "degradation," "existing uses," "high quality waters," "mixing zone," and "parameter"): (1)through (27) remain the same. (28) The department adopts and incorporates by reference: (a) Department Circular DEQ-7, entitled "Montana Numeric Water Quality Standards" ([tine-2�49 [effective month and year of this rule amendment) edition), which establishes numeric water quality standards for toxic, carcinogenic, bioconcentrating, radioactive, and harmful parameters and also establishes human health-based water quality standards for the following specific nutrients with toxic effects: (i) through (iii) remain the same. (b) through (e) remain the same. Authorizing statute(s): 75-5-301, 75-5-303, MCA Implementing statute(s): 75-5-303, MCA Reasonable Necessity Statement Subsection (28)(a) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.30.1001 DEFINITIONS For the purposes of this subchapter, unless the context clearly indicates otherwise, the following terms have the meanings indicated below and are supplemental to the definitions in 75-5-103, MCA: (1) remains the same. Issue No. 8 -April 24, 2026 6 (2) "DEQ-7" means Department Circular DEQ-7, entitled "Montana Numeric Water Quality Standards" (4tine-29-19 [effective month and year of this rule amendment] edition), which establishes numeric water quality standards for toxic, carcinogenic, radioactive, bioconcentrating, nutrient, and harmful parameters. (a) The department adopts and incorporates by reference Department Circular DEQ-7, entitled "Montana Numeric Water Quality Standards" (4tine 2019 [effective month and year of this rule amendmentl edition), which establishes numeric water quality standards for toxic, carcinogenic, bioconcentrating, nutrient, radioactive, and harmful parameters. (3) through (21) remain the same. Authorizing statute(s): 75-5-201, 75-5-401, MCA Implementing statute(s): 75-5-301, 75-5-401, MCA Reasonable Necessity Statement Section (2) and (2)(a) are amended to update the citations for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.36.126 ADOPTION BY REFERENCE (1) For purposes of this chapter, the department adopts and incorporates by reference the following documents. All references to these documents in this chapter refer to the edition set out below: (a)through (d) remain the same. (e) Department Circular DEQ-7, "Montana Numeric Water Quality Standards" (june-2939 [effective month and year of this rule amendmentl edition); (f)through (m) remain the same. (2) remains the same. Authorizing statute(s): 76-4-104, MCA Implementing statute(s): 76-4-104, MCA Issue No. 8-April 24, 2026 7 Reasonable Necessity Statement Subsection (1)(e) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.55.109 INCORPORATION BY REFERENCE (1) For the purposes of this subchapter, the department adopts and incorporates by reference: (a) Department Circular DEQ-7, "Montana Numeric Water Quality Standards" Nt-ne-29-19 [effective month and year of this rule amendment],edition); (b)through (f) remain the same. (2)through (5) remain the same. Authorizing statute(s): 75-10-702, 75-10-704, MCA Implementing statute(s): 75-10-702, 75-10-704, 75-10-711, MCA Reasonable Necessity Statement Subsection (1)(a) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.56.507 ADOPTION BY REFERENCE (1) For purposes of this subchapter, the department adopts and incorporates by reference: (a) Department Circular DEQ-7, "Montana Numeric Water Quality Standards" 4trne48-9 [effective month and year of this rule amendment] edition); (b) through (e) remain the same. (2) and (3) remain the same. Authorizing statute(s): 75-11-319, 75-11-505, MCA Implementing statute(s): 75-11-309, 75-11-505, MCA Issue No. 8 -April 24, 2026 8 Reasonable Necessity Statement Subsection (1)(a) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. 17.56.608 ADOPTION BY REFERENCE (1) For purposes of this subchapter, the department adopts and incorporates by reference: (a) Department Circular DEQ-7, "Montana Numeric Water Quality Standards" Nuiie-201-9 [effective month and year of this rule amendmentl edition); (b) through (d) remain the same. (2) and (3) remain the same. Authorizing statute(s): 75-11-319, 75-11-505, MCA Implementing statute(s): 75-11-309, 75-11-505, MCA Reasonable Necessity Statement Subsection(1)(a) is amended to update the citation for Circular DEQ-7 from the 2019 edition to the edition dated the effective month and year of this rule amendment. Circular DEQ-7 A copy of the proposed Circular DEQ-7 may be viewed at the department's website using the following web address: https://deq.mt.gov/public/water-public; copies may also be obtained by contacting Katie Makarowski at (406)444-3639 or kmkarowski@mt.gov. Modifications to the circular and reasons for the modifications are as follows: ,Update the form of the cyanide jzround water criterion and add a required reporting value and, a trigger value: The department is proposing to change the form of cyanide upon which the human health criteria for cyanide in ground water is based, from total cyanide to free cyanide; the numeric criteria will remain unchanged. This will align Montana's ground water standard with the maximum contaminant level for drinking water set by the U.S. Environmental Protection Agency (EPA) which is expressed as free cyanide. The department is also proposing to add a required reporting value of 27 µg/L calculated according to the method described in Circular DEQ-7, using method detection limits for free cyanide that were reported to the Issue No. 8-April 24, 2026 9 department by local and regional laboratories, multiplied by a conversion factor of 3.18. The department also proposes to add a trigger value for both free cyanide and total cyanide for use when implementing Montana's nondegradation policy for toxic parameters pursuant to ARM 17.30.715(1)(c). The proposed trigger values reflect published method detection limits for free cyanide and total cyanide. .Update the lead human health criteria:,The department is proposing to amend the human health water quality criteria for lead in surface water and ground water from 15 µg/L to 10 µg/L to align Montana's human health standards with the federal Safe Drinking Water Act Lead and Copper Rule Improvements issued in 2024. The department is also proposing to amend the references to the EPA guidance that the lead human health criteria are based on in both the table and in footnote 17, to clarify that the criteria are based on the Safe Drinking Water Act action level (AL) rather than a maximum contaminant level (MCL). There is no MCL for lead under the Safe Drinking Water Act. Correction of errors for four pesticides:,The department is proposing to amend human health water quality criteria for four pesticides in surface water and ground water: chlorsulfuron, imazapic, 1,2-dibromoethane, and nicosulfuron. These criteria are based on health advisories calculated by the department using methods consistent with the EPA drinking water health advisory calculation methods and current EPA guidance on human health water quality criteria development. The supporting analyses showing human health criteria calculations for these four pesticides may be viewed at the department's website using the following web address: https://deq.mt.gov/public/water-public; copies may also be obtained by contacting Katie Makarowski at(406) 444-3639 or kmkarowski@mt.gov. The following amendments are being proposed to correct errors made in the previous calculation of the human health water quality standards that were adopted in 2017: The department is proposing to amend the human health water quality criteria for chlorsulfuron in surface water and ground water from 100 µg/L to 300 µg/L to correct the reference dose (RfD) used in the previous calculation; the RfD used in the calculation of the proposed criteria is sourced from the 2021 Human Health Benchmarks for Pesticides published by EPA. The RfD is an estimate of the amount of a chemical a person can ingest daily over a lifetime that is unlikely to lead to harmful health effects. The department is proposing to amend the human health water quality criteria for imazapic in surface water and ground water from 3,000 µg/L to 913 µg/L to correct the RfD used in the previous calculation;the RfD used in the calculation of the proposed criteria is sourced from the 2021 Human Health Benchmarks for Pesticides published by EPA. The department is proposing to amend the human health water quality criteria for nicosulfuron in surface water and ground water from 8,500 µg/L to 8,330 µg/L to correct a rounding error made in the previous calculation of these criteria; the criteria should be rounded to three significant figures to align with EPA guidance for the rounding of human health criteria. Issue No. 8-April 24, 2026 10 The department is also proposing to amend the human health water quality criteria for 1,2- dibromoethane in surface and ground water from 0.017 µg/L to 0.2 µg/L to correct an error in decimal placement made during the previous calculation of these criteria; the decimal placement is corrected in the proposed criteria and criteria are rounded to one significant figure to align with EPA guidance for rounding of human health criteria. Grammar, wordsmithing, and technical edits:,The department proposes the following edits to improve the readability and accuracy of Circular DEQ-7: updating the hyperlink to the location on the department's website where Circular DEQ-7 can be found; replacing outdated hyperlinks with current hyperlinks to EPA websites referenced in introduction footnotes; replacing the incorrect usage of the term "toxin" with the correct term "toxic"; adding a hyphen to "risk- based" to be consistent with formatting used throughout the circular; adding commas to improve clarity; clarifying which health effect data is used in human health criteria calculations; removing the word "number" after CASRN to eliminate redundancy as CASRN already abbreviates the word number; correct the hyphen placement in the CASRN for dinitrophenols; remove the word "footnote" from the row containing dioxin in the table to be consistent in referencing footnotes throughout the table; add a zero to the left of the decimal for perfluorooctane sulfonate and perfluorooctanoic acid criteria to be consistent with formatting used throughout the table; fix a typo in the pollutant name propiconazole to remove the extra letter "o"; and clarify references to drinking water regulations in Footnote 17 to specify Safe Drinking Water Act regulations to improve clarity. Small Business Impact With regard to the requirements of 2-4-111, MCA, the department has determined that the amendment of the above-referenced rules and circular will not significantly and directly impact small businesses. Any small business who holds a ground water discharge permit with effluent limits or monitoring requirements for cyanide, or who holds a surface water or ground water discharge permit with effluent limits for lead, 1,2-dibromoethane, chlorsulfuron, nicosulfuron, and/or imazapic, would be affected by the proposed rule amendments. Further, any small business that proposes an activity which may result in a new or increased source (as defined at ARM 17.30.702(17)) which may cause degradation (as defined at 75-5-103, MCA, i.e., a change in water quality that lowers the quality of high-quality waters)for cyanide would be subject to the trigger value proposed for amendment. However, as noted above, no impacts upon small businesses are expected to be significant and direct. The department is not proposing to adopt, increase, or decrease a monetary amount that a person shall pay or will receive. Further documentation of the department's small business impact analysis is available upon request. Issue No. 8-April 24, 2026 11 Bill Sponsor Notification The bill sponsor contact requirements do not apply. Interested Persons The department maintains a list of interested persons who wish to receive notices of rulemaking actions proposed by this agency. Persons who wish to have their name added to the list shall make a written request that includes the name, e-mail, and mailing address of the person to receive notices and specifies for which program the person wishes to receive notices. Notices will be sent by e-mail unless a mailing preference is noted in the request. Such written request may be mailed or delivered to the contact above or may be made by completing a request form at any rules hearing held by the department. Rule Reviewer Jonathan Morgan Approval Sonja Nowakowski, Director Issue No. 8-April 24, 2026 12