id-58-0102-2501: Water Quality Standards
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The Idaho Department of Environmental Quality has proposed updates to water quality standards, primarily to ensure alignment with federal regulations from the Environmental Protection Agency. The revisions include removing specific criteria for arsenic and reinstating certain numeric limits for wastewater dischargers that had been previously disapproved by the EPA.
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Dear Senators BURTENSHAW, Hart, Taylor, and Representatives BARBIERI, Furniss, Rubel: The Legislative Services Office, Research and Legislation, has received the enclosed rules of the Department of Environmental Quality: IDAPA 58.01.02 - Water Quality Standards - Proposed Rule (Docket No. 58-0102-2501). Pursuant to Section 67-454, Idaho Code, a meeting on the enclosed rules may be called by the cochairmen or by two (2) or more members of the subcommittee giving oral or written notice to Research and Legislation no later than fourteen (14) days after receipt of the rules' analysis from Legislative Services. The final date to call a meeting on the enclosed rules is no later than 07/25/2025. If a meeting is called, the subcommittee must hold the meeting within forty-two (42) days of receipt of the rules' analysis from Legislative Services. The final date to hold a meeting on the enclosed rules is 08/22/2025. The germane joint subcommittee may request a statement of economic impact with respect to a proposed rule by notifying Research and Legislation. There is no time limit on requesting this statement, and it may be requested whether or not a meeting on the proposed rule is called or after a meeting has been held. To notify Research and Legislation, call 334-4854, or send a written request to the address on the memorandum attached below. Page 1 of 1 Terri Kondeff Director MEMORANDUM TO: Rules Review Subcommittee of the Senate Resources & Environment Committee and the House Environment, Energy & Technology Committee FROM: Legislative Drafting Attorney - Alli Olson DATE: July 07, 2025 SUBJECT: Department of Environmental Quality IDAPA 58.01.02 - Water Quality Standards - Proposed Rule (Docket No. 58-0102-2501) Summary and Stated Reasons for the Rule The Idaho Department of Environmental Quality submits notice of proposed rulemaking for water qual- ity standards, IDAPA 58.01.02. DEQ states that the proposed rulemaking was initiated to make administrative revisions for consistency with the Environmental Protection Agency’s actions on previously submitted water quality standards. The Department also states that the proposed rule is neither broader in scope nor more strin- gent than federal regulations. Negotiated Rulemaking / Fiscal Impact DEQ states that negotiated rulemaking was not conducted due to the simple nature of this rulemaking. The Department also states that there will not be a negative fiscal impact greater than $10,0000 to the general fund. Statutory Authority TheDepartmentappearstohavetheauthoritytopromulgatethisrulepursuanttoSections39-105,39-107, and Chapter 36, Title 39, Idaho Code. cc: Department of Environmental Quality Janeena White *** PLEASE NOTE *** Per the Idaho Constitution, all administrative rules may be reviewed by the Legislature during the next legisla- tive session. The Legislature has 3 options with this rulemaking docket: 1) Approve the docket in its entirety; 2) Reject the docket in its entirety; or 3) Reject the docket in part. Paul Headlee, Deputy DirectMatt Drake, Manager Keith Bybee, ManagerApril Renfro, Manager Norma Clark, Manager Legislative Services OffResearch & Legislation Budget & Policy AnalysLegislative AuditsInformation Technology Statehouse, P.O. Box 83720 Tel: 208–334–2475 Boise, Idaho 83720–0054 legislature.idaho.gov IDAPA 58 – DEPARTMENT OF ENVIRONMENTAL QUALITY 58.01.02 – WATER QUALITY STANDARDS DOCKET NO. 58-0102-2501 NOTICE OF RULEMAKING – PROPOSED RULE AUTHORITY: In compliance with Section 67-5221(1), Idaho Code, notice is hereby given that this agency has initiated proposed rulemaking. This action is authorized by Sections 39-105, 39-107, and Chapter 36, Title 39, Idaho Code. PUBLIC HEARING SCHEDULE: No hearings have been scheduled. Pursuant to Section 67-5222(2), Idaho Code, a public hearing will be held if requested in writing by twenty-five (25) persons, a political subdivision, or an agency. Written requests for a hearing must be received by the undersigned on or before July 18, 2025. If no such written request is received, a public hearing will not be held. DESCRIPTIVE SUMMARY: This rulemaking has been initiated to make administrative revisions. The proposed rule:
1. Deletes arsenic from the table in IDAPA 58.01.02.210.02, Factors for Calculating Hardness Dependent
Metals Criteria, as the calculations no longer apply for arsenic.
2. Includes revisions for consistency with the final actions taken by the U.S. Environmental ProtectionAgency
(EPA) on the rule dockets listed below. These dockets were promulgated by DEQ and submitted to EPA for review under the Clean Water Act (CWA). Pursuant to 40 CFR 131.21, water quality standards adopted and submitted to EPA are not effective for federal CWA purposes until EPA approves them. Notation boxes that had been inserted to explain the status of effectiveness for CWA purposes are no longer necessary and will be deleted. • Docket No. 58-0102-1101: Removal of statewide thermal treatment numeric limits on induced variation for point source wastewater dischargers, submitted to EPA onAugust 7, 2012. EPAAction Letter and Technical Support Document (12/19/24). EPA disapproved the removal of IDAPA 58.01.02.401.01.c. – e., statewide thermal treatment numeric limits on induced variation for point source wastewater dischargers. This proposed rule reinstates 401.01.c. – e. as currently published in the 2011 IdahoAdministrative Code. • Docket No. 58-0102-1803: Addition of a de minimis temperature allowance of up to 0.3 degrees Celsius above applicable temperature criteria, submitted to EPA onApril 15, 2019. EPAAction Letter and Technical Support Document (12/19/24). EPA disapproved this docket except that the non-substantive revision in current rule 401.01.c., “above the natural background conditions” was approved. In this proposed rule, the remaining version of current rule 401.01.c. now takes the place of deleted 401.01.c., and current rule 401.01.d. is deleted. • Docket No. 58-0102-2201 (Negotiated under Docket No. 58-0102-1801): Revisions to Idaho’s Surface Water Quality Standards for Arsenic Human Health Criteria, submitted to EPA on July 6, 2023. EPAAction Letter and Technical Support Document (9/29/23). EPA approved this docket except that the provision, in IDAPA 58.01.02.210.03.e.v.(4), to calculate bioaccumulation factors using “… other scientifically defensible method for deriving protective BAF” was disapproved. This proposed rule deletes the disapproved phrase. The proposed rule text is in legislative format. Language the agency proposes to add is underlined. Language the agency proposes to remove is struck out. It is these additions and deletions to which public comment should be addressed. If adopted by the Idaho Board of Environmental Quality and approved by concurrent resolution of the 2026 Idaho State Legislature, the rule will become effective on July 1, 2026, unless otherwise specified in the concurrent resolution. FISCAL IMPACT: The following is a specific description, if applicable, of any negative fiscal impact on the state general fund greater than ten thousand dollars ($10,000) during the fiscal year resulting from this rulemaking: Not applicable. NEGOTIATED RULEMAKING: Negotiated rulemaking was not conducted. DEQ determined that negotiated rulemaking is not feasible due to the simple nature of this rulemaking. This rulemaking makes the necessary IdahoAdministrative Bulletin Page 130 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking administrative revisions to IDAPA 58.01.02, Water Quality Standards, for consistency with EPA actions on previously adopted water quality standards submitted to EPAfor review. INCORPORATION BY REFERENCE: Pursuant to Section 67-5229(2)(a), Idaho Code, the following is a brief synopsis of why the materials cited are being incorporated by reference into this rule: Not applicable. IDAHO CODE SECTION 39-107D STATEMENT: This proposed rule does not regulate an activity not regulated by the federal government, nor is it broader in scope or more stringent than federal regulations. ASSISTANCE ON TECHNICAL QUESTIONS: For assistance on questions concerning this proposed rulemaking, contact Elizabeth Spelsberg at elizabeth.spelsberg@deq.idaho.gov or (208) 373-0158. SUBMISSION OF WRITTEN COMMENTS: Anyone may submit written comments regarding this proposed rule. The Department will consider all written comments received on or before August 1, 2025. Submit written comments to: Elizabeth Spelsberg Department of Environmental Quality 1410 N. Hilton, Boise, ID 83706 elizabeth.spelsberg@deq.idaho.gov Dated this 2nd day of July, 2025. Diane Cutler, Rules and PlanningAnalyst Department of Environmental Quality 1410 N. Hilton Street Boise, Idaho 83706 208-373-0165 diane.cutler@deq.idaho.gov THE FOLLOWING IS THE PROPOSED TEXT OF DOCKET NO. 58-0102-2501 (Only Those Sections With Amendments Are Shown.) 58.01.02 – WATER QUALITY STANDARDS 210. NUMERIC CRITERIA FOR TOXIC SUBSTANCES FOR WATERS DESIGNATED FOR AQUATIC LIFE, RECREATION, OR DOMESTIC WATER SUPPLY USE.
01. Criteria for Toxic Substances. The criteria of Section 210 apply to surface waters of the state as
provided in Tables 1 and 2. Criteria for metals (arsenic through zinc) listed in Tables 1 and 2 are expressed as a dissolved fraction (i.e., passes through a forty-five hundredths (0.45) micron filter) unless otherwise noted. (4-6-23) a. Table 1 contains criteria to protect aquatic life. (4-6-23) IdahoAdministrative Bulletin Page 131 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 1. Criteria for Protection of Aquatic Life a b b Compound CAS Number CMC CCC (µg/L) (µg/L) Inorganic Compounds/Metals Arsenic 7440382 340 c 150 c Cadmium 7440439 1.3 f 0.6 f Chromium III 16065831 570 f 74 f Chromium VI 18540299 16 c 11 c Copper 7440508 12.3 k 7.6 k Lead 7439921 65 f 2.5 f Mercury 7439976 e e Note: In 2005, Idaho adopted EPA's recommended methylmercury fish tissue criterion for protection of human health (docket 58-0102-0302). The decision was made to remove the old tissue-based aquatic life criteria and rely on the fish tissue criterion to provide protection for aquatic life as well as human health. Thus, current Idaho water quality stan- dards do not have mercury water column criteria for the protection of aquatic life. While EPA approved Idaho's adop- tion of the fish tissue criterion in September 2005, it had withheld judgment on Idaho's removal of aquatic life criteria. On December 12, 2008, EPAdisapproved Idaho's removal of the old aquatic life criteria. The water column criteria for total recoverable mercury published 2004 IdahoAdministrative Code continue to apply and are effective for CWA purposes. For more information go tottp://www.deq.idaho.gov/epa-actions-on-proposed-standar.s Nickel 7440020 470 f 52 f Selenium 7782492 m l Silver 7440224 3.4 f Zinc 7440666 120 f 120 f Inorganic Compounds/Non-Metals Chlorine 19 h 11 h Cyanide 57125 22 g 5.2 g Organic Compounds --1 -- Acrolein 107028 -------------- -------------- 2 2 3 3 1Effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102- 2802 have been approved. Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58- 0102-1802 have been approved. Aldrin 39002 3 gamma-BHC (Lindane) 58899 2 0.08 IdahoAdministrative Bulletin Page 132 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 1. Criteria for Protection of Aquatic Life a b b Compound CAS Number CMC CCC (µg/L) (µg/L) -- --1 Carbaryl 63252 -------------- -------------- 2 2 2.1 2.1 1 Effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102- 1802 have been approved. 2Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58- 0102-1802 have been approved. Chlordane 57749 2.4 0.0043 4,4’-DDT 50293 1.1 0.001 1 1 -- -- Diazinon 333415 -------------- -------------- 0.17 2 0.172 1 Effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102- 1802 have been approved. 2Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58- 0102-1802 have been approved. Dieldrin 60571 2.5 0.0019 alpha-Endosulfan 959988 0.22 0.056 beta-Endosulfan 33213659 0.22 0.056 Endrin 72208 0.18 0.0023 Heptachlor 76448 0.52 0.0038 Heptachlor Epoxide 1024573 0.52 0.0038 Pentachlorophenol 87865 20 i 13 i Polychlorinated Biphenyls PCBs j 0.014 j Toxaphene 8001352 0.73 0.0002 Footnotes for Table 1. Criteria for Protection of Aquatic Life a. Chemical Abstracts Service (CAS) registry numbers which provide a unique identification for each chemical. b. See definitions of Acute Criteria (CMC) and Chronic Criteria (CCC), Section 010 of these rules. c. Criteria for these metals are expressed as a function of the water effect ratio, WER, as defined in Subsection 210.03.c.iii. CMC = CMC column value X WER. CCC = CCC column value X WER. d. Criterion expressed as total recoverable (unfiltered) concentrations. e. No aquatic life criterion is adopted for inorganic mercury. However, the narrative criteria for toxics in Section 200 of these rules applies. The Department believes application of the human health criterion for methylmercury will be protective of aquatic life in most situations. IdahoAdministrative Bulletin Page 133 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 1. Criteria for Protection of Aquatic Life a b b Compound CAS Number CMC CCC (µg/L) (µg/L) f. Aquatic life criteria for these metals are a function of total hardness (mg/L as calcium carbonate), the pollutant’s water effect ratio (WER) as defined in Subsection 210.03.c.iii. and multiplied by an appropriate dissolved conversion factor as defined in Subsection 210.02. For comparative purposes only, the example values displayed in this table are shown as dissolved metal and correspond to a total hardness of one hundred (100) mg/L and a water effect ratio of one (1.0). g. Criteria are expressed as weak acid dissociable (WAD) cyanide. h. Total chlorine residual concentrations. i. Aquatic life criteria for pentachlorophenol are expressed as a function of pH, and are calculated as follows. Values displayed above in the table correspond to a pH of seven and eight tenths (7.8). CMC = exp(1.005(pH)-4.830) CCC = exp(1.005(pH)-5.290) j. PCBs are a class of chemicals which include Aroclors, 1242, 1254, 1221, 1232, 1248, 1260, and 1016, CAS numbers 53469219, 11097691, 11104282, 11141165, 12672296, 11096825 and 12674112 respectively. The aquatic life criteria apply to this set of PCBs. k. Aquatic life criteria for copper shall be derived in accordance with Subsection 210.03.c.v. For comparative pur- poses only, the example values displayed in this table correspond to the Biotic Ligand Model output based on the fol- lowing inputs: temperature = 14.9°C, pH = 8.16, dissolved organic carbon = 1.4 mg/L, humic acid fraction = 10%, calcium = 44.6 mg/L, magnesium = 11.0 mg/L, sodium = 11.7 mg/L, potassiu-8= 2.12 mg/L, sulfate = 46.2 mg/L, chlo- ride = 12.7 mg/L, alkalinity = 123 mg/L CaCO3, and sulfide = 1.00 x 10 mg/L. l. Chronic Short-term Egg-Ovary (mg/kg dw) Fish Tissue (mg/kg dw) Water Column (µg/L) Water Column (µg/L) Egg-Ovary Whole-Body Muscle Water Lentic Water Lotic Water 1.5 (30 day 3.1 (30 day Intermittent Exposure 15.1 1 8.5 2 11.3 2 3 3 3.4 average) average) Equation mg/kg dw – milligrams per kilogram dry weight, µg/L – micrograms per liter
1. Egg-ovary supersedes any whole-body, muscle, or water column element when fish egg-ovary concentrations
are measured. Single measurement of an average or composite sample of at least five (5) individuals of the same species. Not to be exceeded; DEQ will evaluate all representative egg-ovary data to determine compliance with this criterion element.
2. Fish whole-body or muscle tissue supersedes water column element when both fish tissue and water concen-
trations are measured. Single measurement of an average or composite sample of at least five (5) individuals of the same species where the smallest individual is no less than seventy-five percent (75%) of the total length (size) of the largest individual. Not to be exceeded; DEQ will evaluate all representative whole body or muscle data to determine compliance with this criterion element.
3. Water column values are based on dissolved total selenium in water and are derived from fish tissue values via
bioaccumulation modeling. Water column values are the applicable criterion element in the absence of steady-state condition fish tissue data. In fishless waters, selenium concentrations in fish from the nearest downstream waters may be used to assess compliance using methods provided in Aquatic Life Ambient Water Quality Criterion for Sele- nium – Freshwater, EPA-822-R-16-006,Appendix K: Translation of a Selenium Fish Tissue Criterion Element to a Site-Specific Water Column Value (June 2016) . IdahoAdministrative Bulletin Page 134 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 1. Criteria for Protection of Aquatic Life a b b Compound CAS Number CMC CCC (µg/L) (µg/L)
4. Intermittent Exposure Equation=
where WQC is the applicable water column element, for either lentic or lotic waters; Crage background bkgrnd selenium concentration, aintf the fraction of any 30-day period during which elevated selenium concentrations occur, witintassigned a value ≥ 0.033 (corresponding to one day). m. There is no specific acute criterion for aquatic life; however, the aquatic life criterion is based on chronic effects of the selenium on aquatic life and is expected to adequately protect against acute effects. (3-31-22) b. Table 2 contains criteria to protect human health. The Water & Fish criteria apply to waters designated for domestic water supply use. The Fish Only criteria apply to waters designated for primary or secondary contact recreation use. (4-6-23) Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) Inorganic Compounds/Metals Antimony 7440360 5.2 b 190 b 4.3; Arsenic 7440382 Y 10 cdj 8.0 µg/kg ck fish tissue Beryllium 7440417 e e Cadmium 7440439 e e Chromium III 16065831 e e Chromium VI 18540299 e e Copper 7440508 1300 j Lead 7439921 e e Methylmercury 22967926 0.3mg/kg i Nickel 7440020 58 b 100 b Selenium 7782492 29 b 250 b Thallium 7440280 0.017 b 0.023 b Zinc 7440666 870 b 1,500 b IdahoAdministrative Bulletin Page 135 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) Inorganic Compounds/Non-Metals Cyanide 57125 3.9 b 140 b 7,000,000 Asbestos 1332214 Fibers/L j Organic Compounds Acenaphthene 83329 26 b 28 b Acenaphthylene 208968 e e Acrolein 107028 3.2 b 120 b Acrylonitrile 107131 Y 0.60 bf 22 bf Aldrin 309002 Y 2.5E-06 bf 2.5E-06 bf Anthracene 120127 110 b 120 b alpha-BHC 319846 Y 0.0012 bf 0.0013 bf beta-BHC 319857 Y 0.036 bf 0.045 bf gamma-BHC (Lindane) 58899 1.4 b 1.4 b delta-BHC 319868 e e Benzene 71432 3.0 bf 28 b Benzidine 92875 Y 0.0014 bf 0.033 bf Benzo(a)Anthracene 56553 Y 0.0042 bf 0.0042 bf Benzo(b)Fluoranthene 205992 Y 0.0042 bf 0.0042 bf Benzo(k)Fluoranthene 207089 Y 0.042 bf 0.042 bf Benzo(ghi)Perylene 191242 e e Benzo(a)Pyrene 50328 Y 0.00042 bf 0.00042 bf Bis(2-Chloroethoxy) Methane 111911 e e Bis(2-Chloroethyl) Ether 111444 Y 0.29 bf 6.8 bf Bis(2-Chloroisopropyl) 108601 220 b 1,200 b Ether Bis(Chloromethyl) Ether 542881 Y 0.0015 bf 0.055 bf Bis(2-Ethylhexyl) 117817 Y 1.2 bf 1.2 bf Phthalate Bromoform 75252 Y 62 bf 380 bf IdahoAdministrative Bulletin Page 136 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) 4-Bromophenyl Phenyl Ether 101553 e e Butylbenzyl Phthalate 85687 0.33 b 0.33 b Carbon Tetrachloride 56235 Y 3.6 bf 15 bf Chlorobenzene 108907 89 b 270 b Chlordane 57749 Y 0.0010 bf 0.0010 bf Chlorodibromomethane 124481 Y 7.4 bf 67 bf Chloroethane 75003 e e 2-Chloroethylvinyl Ether 110758 e e Chloroform 67663 61 b 730 b 2-Chloronaphthalene 91587 330 b 380 b 2-Chlorophenol 95578 30 b 260 b Chlorophenoxy Herbicide 94757 1,000 b 3,900 b (2,4-D) Chlorophenoxy Herbicide 93721 82 b 130 b (2,4,5-TP) [Silvex] 4-Chlorophenyl Phenyl 7005723 e e Ether Chrysene 218019 Y 0.42 bf 0.42 bf 4,4'-DDD 72548 Y 0.00042 bf 0.00042 bf 4,4'-DDE 72559 Y 5.5E-05 bf 5.5E-05 bf 4,4'-DDT 50293 Y 9.8E-05 bf 9.8E-05 bf Di-n-Butyl Phthalate 84742 8.2 b 8.3 b Di-n-Octyl Phthalate 117840 e e Dibenzo (a,h) Anthracene 53703 Y 0.00042 bf 0.00042 bf 1,2-Dichlorobenzene 95501 700 b 1,100 b 1,3-Dichlorobenzene 541731 3.5 b 4.8 b 1,4-Dichlorobenzene 106467 180 b 300 b 3,3'-Dichlorobenzidine 91941 Y 0.29 bf 0.48 bf Dichlorobromomethane 75274 Y 8.8 bf 86 bf 1,1-Dichloroethane 75343 e e 1,2-Dichloroethane 107062 Y 96 bf 2,000 bf IdahoAdministrative Bulletin Page 137 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) 1,1-Dichloroethylene 75354 310 b 5,200 b 2,4-Dichlorophenol 120832 9.6 b 19 b 1,2-Dichloropropane 78875 Y 8.5 bf 98 bf 1,3-Dichloropropene 542756 Y 2.5 bf 38 bf Dieldrin 60571 Y 4.2E-06 bf 4.2E-06 bf Diethyl Phthalate 84662 200 b 210 b 2,4-Dimethylphenol 105679 110 b 820 b Dimethyl Phthalate 131113 600 b 600 b Dinitrophenols 25550587 13 b 320 b 2,4-Dinitrophenol 51285 12 b 110 b 2,4-Dinitrotoluene 121142 Y 0.46 bf 5.5 bf 2,6-Dinitrotoluene 606202 e e 1,2-Diphenylhydrazine 122667 Y 0.25 bf 0.65 bf 2, 3, 7, 8-TCDD Dioxin 1746016 Y 1.8E-08 bf 1.9E-08 bf alpha-Endosulfan 959988 7.0 b 8.5 b beta-Endosulfan 33213659 11 b 14 b Endosulfan Sulfate 1031078 9.9 b 13 b Endrin 72208 0.011 b 0.011 b Endrin Aldehyde 7421934 0.38 b 0.40 b Ethylbenzene 100414 32 b 41 b Fluoranthene 206440 6.3 b 6.4 b Fluorene 86737 21 b 22 b Heptachlor 76448 Y 2.0E-05 bf 2.0E-05 bf Heptachlor Epoxide 1024573 Y 0.00010 bf 0.00010 bf Hexachlorobenzene 118741 Y 0.00026 bf 0.00026 bf Hexachlorobutadiene 87683 Y 0.031 bf 0.031 bf Hexachlorocyclohexane 608731 Y 0.027 bf 0.032 bf (HCH)-Technical Hexachloro- 77474 1.3 b 1.3 b cyclopentadiene Hexachloroethane 67721 0.23 b 0.24 b Ideno (1,2,3-cd) Pyrene 193395 Y 0.0042 bf 0.0042 bf IdahoAdministrative Bulletin Page 138 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) Isophorone 78591 Y 330 bf 6,000 bf Methoxychlor 72435 0.0054 b 0.0055 b Methyl Bromide 74839 130 b 3,700 b Methyl Chloride 74873 e e 3-Methyl-4-Chlorophenol 59507 350 b 750 b 2-Methyl-4,6-Dinitrophenol 534521 1.6 b 8.6 b Methylene Chloride 75092 38 b 960 b Naphthalene 91203 e e Nitrobenzene 98953 12 b 180 b 2-Nitrophenol 88755 e e 4-Nitrophenol 100027 e e N-Nitrosodimethylamine 62759 Y 0.0065 bf 9.1 bf N-Nitrosodi-n-Propylamine 621647 Y 0.046 bf 1.5 bf N-Nitrosodiphenylamine 86306 Y 3.14 bf 18 bf Pentachlorobenzene 608935 0.035 b 0.036 b Pentachlorophenol 87865 Y 0.11 bf 0.12 bf Phenanthrene 85018 e e Phenol 108952 3,800 b 85,000 b Polychlorinated Biphenyls g Y 0.00019 bfh 0.00019 bfh PCBs Pyrene 129000 8.1 b 8.4 b 1,2,4,5- 95943 0.0093 b 0.0094 b Tetrachlorobenzene 1,1,2,2-Tetrachloroethane 79345 Y 1.4 bf 8.6 bf Tetrachloroethylene 127184 15 b 23 b Toluene 108883 47 b 170 b Toxaphene 8001352 Y 0.0023 bf 0.0023 bf 1,2-Trans- 156605 120 b 1,200 b Dichloroethylene 1,2,4-Trichlorobenzene 120821 0.24 b 0.24 b 1,1,1-Trichloroethane 71556 11,000 b 56,000 b 1,1,2-Trichloroethane 79005 Y 4.9 bf 29 bf IdahoAdministrative Bulletin Page 139 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) a Water & Fish Fish Only (µg/L unless (µg/L unless Compound CAS Number Carcinogen? otherwise otherwise specified) specified) Trichloroethylene 79016 2.6 b 11 b 2,4,5-Trichlorophenol 95954 140 b 190 b 2,4,6-Trichlorophenol 88062 1.5 b 2.0 b Vinyl Chloride 75014 Y 0.21 bf 5.0 bf Footnotes for Table 2. Criteria for Protection of Human Health a. Chemical Abstracts Service (CAS) registry numbers which provide a unique identification for each chemical. b. This criterion is based on input values to human health criteria calculation specifIdaho's Technical Sup- port Document (TSD) for Human Health Criteria Calculations - 2015 . Criteria for non-carcinogens are calculated using the formula: BW AWQC = RfD * RSC * (-----------------)----- DI + (FI * BAF) and criteria for carcinogens are calculated using the formula: BW AWQC = RSD * ( ----------------)------ DI + (FI * BAF) Where: AWQC = Ambient water quality criterion (mg/L) BW = Human Body Weight (kg), 80 is used in these criteria DI = Drinking Water Intake, (L/day), 2.4 is used in these criteria FI = Fish Intake, (kg/day), 0.0665 is used in these criteria BAF = Bioaccumualtion Factor, L/kg, chemical specific value, see TSD RfD = Reference dose (mg/kg-day), chemical specific value, see TSD RSD = ---------------------------------------------- (mg/kg-day), chemical specific value, see TSD Cancer Potency Factor RSC = Relative Source Contribution, chemical specific value, see TSD c. Inorganic forms only. d. Criterion expressed as total recoverable (unfiltered) concentrations. IdahoAdministrative Bulletin Page 140 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Table 2. Criteria for Protection of Human Health (based on consumption of:) Water & Fish Fish Only a Compound CAS Number Carcinogen? (µg/L unless (µg/L unless otherwise otherwise specified) specified) e. No numeric human health criteria has been established for this contaminant. However, permit authorities should address this contaminant in NPDES permit actions using the narrative criteria for toxics from Section 200 of these rules. f. EPA guidance allows states to choose from a range of 10 to 10 for the incremental increase in cancer risk used in human health criteria calculation. Idaho has chosen to base this criterion on carcinogenicity of 10isk. g. PCBs are a class of chemicals which include Aroclors, 1242, 1254, 1221, 1232, 1248, 1260, and 1016, CAS numbers 53469219, 11097691, 11104282, 11141165, 12672296, 11096825 and 12674112 respectively. The aquatic life criteria apply to this set of PCBs. h. This criterion applies to total PCBs, (e.g. the sum of all congener, isomer, or Aroclor analyses). i. This fish tissue residue criterion (TRC) for methylmercury is based on a human health reference dose (RfD) of 0.0001 mg/kg body weight-day; a relative source contribution (RSC) estimated to be 27% of the RfD; a human body weight (BW) of 70 kg (for adults); and a total fish consumption rate of 0.0175 kg/day for the general population, summed from trophic level (TL) breakdown of TL2 = 0.0038 kg fish/day + TL3 = 0.0080 kg fish/day + TL4 = 0.0057 kg fish/day. This is a criterion that is protective of the general population. A site-specific criterion or a criterion for a par- ticular subpopulation may be calculated by using local or regional data, rather than the above default values, in the formula: TRC = [BW x {RfD – (RSCxRfD)}] / Σ TL. In waters inhabited by species listed as threatened or endangered under the Endangered Species Act or designated as their critical habitat, the Department will apply the human health fish tissue residue criterion for methylmercury to the highest trophic level available for sampling and analysis. j. This criterion is based on the drinking water Maximum Contaminant Level (MCL). k. For Fish Only exposure to inorganic arsenic, the human health criterion is: Fish Tissue (µg/kg wet-weight) Water Column (µg/L) 8.01 4.32 1Fish tissue element is based on total recoverable inorganic arsenic in muscle or fillet. The fish tissue element super- sedes the water column element provided at least ninety (90) days have passed since any new activity or discharge has occurred within the water body. Fish tissue element will be applied in accordance with Subsection 210.03.e. 2 Water column element is based on dissolved inorganic arsenic in water. (4-6-23) 02. Factors for Calculating Hardness Dependent Metals Criteria. Hardness dependent metals criteria are calculated using values from the following table in the equations: (3-31-22) a. CMC=WER exp{mA[ln(hardness)]+bA} XAcute Conversion Factor. (3-31-22) b. CCC=WER exp{mc[ln(hardness)]+bc} X Chronic Conversion Factor. aAcute Conversion aChronic Conversion Metal mA bA mc bc Factor Factor IdahoAdministrative Bulletin Page 141 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking Arsenic b b b b 1.0 1.0 0.944 Cadmium 0.8367 -3.560 0.6247 -3.344 0.909 see footnote a Chromium (III) 0.819 3.7256 0.8190 0.6848 0.316 0.860 Chromium (VI) b b b b 0.982 0.962 Lead 1.273 -1.460 1.273 -4.705 0.791 0.791 Mercury b b b b 0.85 0.85 Nickel 0.846 2.255 0.8460 0.0584 0.998 0.997 Silver 1.72 -6.52 c c 0.85 c Zinc 0.8473 0.884 0.8473 0.884 0.978 0.986 Note to table: The term “exp” represents the base e exponential function. Footnotes to table: a. Conversion factors (CF) are from “Stephan, C. E. 1995. Derivation of conversion factors for the calculation of dissolved freshwater aquatic life criteria for metals. U.S. Environmental Protection Agency, Environmental Research Laboratory – Duluth.” The conversion factors for cadmium and lead are hardness-dependent and can be calculated for any hardness (see limitations in Subsection 210.03.b.i.) using the following equations. For comparative purposes, the conversion factors for a total hardness of one hundred (100) mg/L are shown in the table. The conversion factor shall not exceed one (1). Cadmium Acute: CF=1.136672–[(ln hardness)(0.041838)] NOTE: The cadmium acute criterion equation was derived from dissolved metals toxicity data and thus requires no conversion; this conversion factor may be used to back calculate an equivalent total recoverable concentration. Chronic: CF=1.101672–[(ln hardness)(0.041838)] Lead (Acute and Chronic): CF=1.46203–[(ln hardness)(0.145712) b. Not applicable c. No chronic criteria are available for silver. (3-31-22)( ) 03. Applicability. The criteria established in Section 210 are subject to the general rules of applicability in the same way and to the same extent as are the other numeric chemical criteria when applied to the same use classifications. Mixing zones may be applied to toxic substance criteria subject to the limitations set forth in Section 060 and set out below. (3-31-22) a. For all waters for which the Department has determined mixing zones to be applicable, the toxic substance criteria apply at the boundary of the mixing zone(s) and beyond. Absent an authorized mixing zone, the toxic substance criteria apply throughout the waterbody including at the end of any discharge pipe, canal or other discharge point. (3-31-22) b. Low flow design conditions. Water quality-based effluent limits and mixing zones for toxic substances shall be based on the following low flows in perennial receiving streams. Numeric chemical criteria may be exceeded in perennial streams outside any applicable mixing zone only when flows are less than these values: Aquatic Life Human Health CMC (“acute” criteria) 1Q10 or 1B3 Non-carcinogens Harmonic mean flow CCC (“chronic” criteria) 7Q10 or 4B3 Carcinogens Harmonic mean flow IdahoAdministrative Bulletin Page 142 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking (3-31-22) i. Where “1Q10” is the lowest one-day flow with an average recurrence frequency of once in ten (10) years determined hydrologically; (3-31-22) ii. Where “1B3” is biologically based and indicates an allowable exceedance of once every three (3) years. It may be determined by EPA’s computerized method (DFLOW model); (3-31-22) iii. Where “7Q10” is the lowest average seven (7) consecutive day low flow with an average recurrence frequency of once in ten (10) years determined hydrologically; (3-31-22) iv. Where “4B3” is biologically based and indicates an allowable exceedance for four (4) consecutive days once every three (3) years. It may be determined by EPA’s computerized method (DFLOW model); (3-31-22) v. Where the harmonic mean flow is a long term mean flow value calculated by dividing the number of daily flows analyzed by the sum of the reciprocals of those daily flows. (3-31-22) c. Application of aquatic life metals criteria. (3-31-22) i. For metals other than cadmium, for purposes of calculating hardness dependent aquatic life criteria from the equations in Subsection 210.02, the minimum hardness allowed for use in those equations shall not be less than twenty-five (25) mg/l, as calcium carbonate, even if the actual ambient hardness is less than twenty-five (25) mg/ l as calcium carbonate. For cadmium, the minimum hardness for use in those equations shall not be less than ten (10) mg/l, as calcium carbonate. The maximum hardness allowed for use in those equations shall not be greater than four hundred (400) mg/l, as calcium carbonate, except as specified in Subsections 210.03.c.ii. and 210.03.c.iii., even if the actual ambient hardness is greater than four hundred (400) mg/l as calcium carbonate. (3-31-22) ii. The hardness values used for calculating aquatic life criteria for metals at design discharge conditions shall be representative of the ambient hardnesses for a receiving water that occur at the design discharge conditions given in Subsection 210.03.b. (3-31-22) iii. Except as otherwise noted, the aquatic life criteria for metals (arsenic through zinc in Table 1 in Subsection 210.01) are expressed as dissolved metal concentrations. Unless otherwise specified by the Department, dissolved concentrations are considered to be concentrations recovered from a sample which has passed through a forty-five hundredths (0.45) micron filter. For the purposes of calculating aquatic life criteria for metals from the equations in footnotes c. and f. in Table 1 in Subsection 210.01, the water effect ratio is computed as a specific pollutant’s acute or chronic toxicity values measured in water from the site covered by the standard, divided by the respective acute or chronic toxicity value in laboratory dilution water. The water-effect ratio shall be assigned a value of one (1.0), except where the Department assigns a different value that protects the designated uses of the water body from the toxic effects of the pollutant, and is derived from suitable tests on sampled water representative of conditions in the affected water body, consistent with the design discharge conditions established in Subsection 210.03.b. For purposes of calculating water effects ratios, the term acute toxicity value is the toxicity test results, such as the concentration lethal one-half (1/2) of the test organisms (i.e., LC5O) after ninety-six (96) hours of exposure (e.g., fish toxicity tests) or the effect concentration to one-half of the test organisms, (i.e., EC5O) after forty-eight (48) hours of exposure (e.g., daphnia toxicity tests). For purposes of calculating water effects ratios, the term chronic value is the result from appropriate hypothesis testing or regression analysis of measurements of growth, reproduction, or survival from life cycle, partial life cycle, or early life stage tests. The determination of acute and chronic values shall be according to current standard protocols (e.g., those published by the American Society for Testing and Materials (ASTM)) or other comparable methods. For calculation of criteria using site-specific values for both the hardness and the water effect ratio, the hardness used in the equations in Subsection 210.02 shall be as required in Subsection 210.03.c.ii. Water hardness shall be calculated from the measured calcium and magnesium ions present, and the ratio of calcium to magnesium shall be approximately the same in laboratory toxicity testing water as in the site water, or be similar to average ratios of laboratory waters used to derive the criteria. (3-31-22) iv. Implementation Guidance for the Idaho Mercury Water Quality Criteria. (3-31-22) IdahoAdministrative Bulletin Page 143 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking (1) The “Implementation Guidance for the Idaho Mercury Water Quality Criteria” describes in detail suggested methods for discharge related monitoring requirements, calculation of reasonable potential to exceed (RPTE) water quality criteria in determining need for mercury effluent limits, and use of fish tissue mercury data in calculating mercury load reductions. This guidance, or its updates, will provide assistance to the Department and the public when implementing the methylmercury criterion. The “Implementation Guidance for the Idaho Mercury Water Quality Criteria” also provides basic background information on mercury in the environment, the novelty of a fish tissue criterion for water quality, the connection between human health and aquatic life protection, and the relation of environmental programs outside of Clean Water Act programs to reducing mercury contamination of the environment. The “Implementation Guidance for the Idaho Mercury Water Quality Criteria” is available at the Department of Environmental Quality, 1410 N. Hilton, Boise, Idaho 83706, and on the DEQ website at https:// www.deq.idaho.gov. (3-31-22) (2) The implementation of a fish tissue criterion in NPDES permits and TMDLs requires a non- traditional approach, as the basic criterion is not a concentration in water. In applying the methylmercury fish tissue criterion in the context of NPDES effluent limits and TMDL load reductions, the Department will assume change in fish tissue concentrations of methylmercury are proportional to change in water body loading of total mercury. Reasonable potential to exceed (RPTE) the fish tissue criterion for existing NPDES sources will be based on measured fish tissue concentrations potentially affected by the discharge exceeding a specified threshold value, based on uncertainty due to measurement variability. This threshold value is also used for TMDL decisions. Because measured fish tissue concentrations do not reflect the effect of proposed new or increased discharge of mercury, RPTE in these cases will be based upon an estimated fish tissue methylmercury concentration, using projected changes in waterbody loading of total mercury and a proportional response in fish tissue mercury. For the above purposes, mercury will be measured in the skinless filets of sport fish using techniques capable of detecting tissue concentrations down to point zero five (0.05) mg/kg. Total mercury analysis may be used, but will be assumed to be all methylmercury for purposes of implementing the criterion. (3-31-22) v. Copper Criteria forAquatic Life. (3-31-22) (1) Aquatic life criteria for copper shall be derived using: (3-31-22) (a) Biotic Ligand Model (BLM) software that calculates criteria consistent with the “Aquatic Life Ambient Freshwater Quality Criteria – Copper”: EPA-822-R-07-001 (February 2007); or (3-31-22) (b) An estimate derived from BLM outputs that is based on a scientifically sound method and protective of the designated aquatic life use. (3-31-22) (2) To calculate copper criteria using the BLM, the following parameters from each site shall be used: temperature, pH, dissolved organic carbon (DOC), calcium, magnesium, sodium, potassium, sulfate, chloride, and alkalinity. The BLM inputs for humic acid (HA) as a proportion of DOC and sulfide shall be based on either measured values or the following default values: 10% HA as a proportion of DOC, 1.00 x 10 -8 mg/L sulfide. Measured values shall supersede any estimate or default input. (3-31-22) (3) BLM input measurements shall be planned to capture the most bioavailable conditions for copper. (3-31-22) (4) A criterion derived under Subsection 210.03.c.v.(1)(a) shall supersede any criterion derived under Subsection 210.03.c.v.(1)(b). Acceptable BLM software includes the “US EPA WQC Calculation” for copper in BLM Version 3.1.2.37 (October 2015). (3-31-22) (5) Implementation Guidance for the Idaho Copper Criteria for Aquatic Life. The “Implementation Guidance for the Idaho Copper Criteria forAquatic Life: Using the Biotic Ligand Model” describes in detail methods for implementing the aquatic life criteria for copper using the BLM. This guidance, or its updates, will provide assistance to the Department and the public for determining minimum data requirements for BLM inputs and how to estimate criteria when data are incomplete or unavailable. The “Implementation Guidance for the Idaho Copper Criteria for Aquatic Life: Using the Biotic Ligand Model” is available at the Department of Environmental Quality, 1410 N. Hilton, Boise, Idaho 83706, and on the DEQ website at https://www.deq.idaho.gov. (3-31-22) IdahoAdministrative Bulletin Page 144 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking d. Application of toxics criteria. (3-31-22) i. Frequency and duration for aquatic life toxics criteria. CMC column criteria in Table 1 in Subsection 210.01 are concentrations not to be exceeded for a one-hour average more than once in three (3) years unless otherwise specified. CCC column criteria in Table 1 in Subsection 210.01 are concentrations not to be exceeded for a four-day average more than once in three (3) years unless otherwise specified. (3-31-22) ii. Frequency and duration for human health toxics criteria. Criteria in Table 2, Subsection 210.01, are not to be exceeded based on an annual arithmetic mean concentration. (4-6-23) e. Application of the fish tissue element of the arsenic criterion for human health. (4-6-23) i. The fish tissue element for total recoverable inorganic arsenic is based on a single measurement using sufficiently sensitive methods. (4-6-23) ii. The single measurement must be made on a sample that is an average or composite of a minimum of five (5) individual fish of the same species collected from the same water body within the same calendar year. When available, game fish species representative of the size and species that may be legally harvested within the waterbody are preferred. Results from multiple sample events may be averaged or composited provided they represent the same species collected from the same water body within the same calendar year. (4-6-23) iii. Not to be exceeded; the Department will evaluate all representative fish tissue data to determine compliance with this criterion element. (4-6-23) iv. For purposes of determining water column targets for the development of effluent limits, TMDL targets, or water column targets for fishless waters, the fish tissue element may be translated to a water column value using a site-specific bioaccumulation factor (BAF) based on the ratio of total recoverable inorganic arsenic in fish muscle or fillet tissue to dissolved inorganic arsenic in the water column using the following equation: Where: WC (Tg/L) is the translated water column value; and BAF L/kg is the site specific BAF calculated consistent with 210.03.e.v. In fishless waters, surface water and fish tissue from the immediate downstream waters may be used for bioaccumulation modeling. In the absence of sufficient fish tissue data, the water column element is the applicable criterion element in fishless waters. (4-6-23) v. When translating the fish tissue element to a water column value, the following procedures will be followed. (4-6-23) (1) Data used to translate the fish tissue element must be based on current conditions and consistent with Subsections 210.03.e.i. and ii. (4-6-23) (2) Whenever practical, fish tissue samples must be representative of the game fish species present within the waterbody and include game fish of legally harvestable size. In the absence of suitable game fish species, other resident fish species may be used. (4-6-23) (3) Water column samples must be representative of the annual average concentration of dissolved inorganic arsenic at the site. (4-6-23) (4) BAFs are calculated as a trophic-level weighted BAF or other scientifically defensible method for deriving protective BAF. (4-6-23)( ) IdahoAdministrative Bulletin Page 145 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking EPA approved Docket No. 58-0102-2201 with exception of disapproving the provision, in IDAPA 58.01.02.210.03.e.v.(4), to calculate bioaccumulation factors using “… other scientifically defensible method for deriving protective BAF.” The EPA Action Letter and Technical Support Document were received on September 29, 2023. The remainder of IDAPA 58.01.02.210.03.e.v.(4) was approved by EPA and is effective for CWA purposes: “BAFs are calculated as a trophic-level weighted BAF.” 04. National Pollutant Discharge Elimination System Permitting. For the purposes of NPDES permitting, interpretation and implementation of metals criteria listed in Subsection 210.02 should be governed by the following standards, that are hereby incorporated by reference, in addition to other scientifically defensible methods deemed appropriate by the Department; provided, however, any identified conversion factors within these documents are not incorporated by reference. Metals criteria conversion factors are identified in Subsection 210.02 of this rule. (3-31-22) a. “Guidance Document on Dissolved Criteria -- Expression of Aquatic Life Criteria,” EPA, October 1993. (3-31-22) b. “Guidance Document on Dynamic Modeling and Translators,” EPA,August 1993. (3-31-22) c. “Guidance Document on CleanAnalytical Techniques and Monitoring,” EPA, October 1993. (3-31-22) d. “Interim Guidance on Determination and Use of Water-Effect Ratios for Metals,” EPA, February 1994. (3-31-22) e. “Technical Support Document for Water Quality-Based Toxics Control.” EPA, March 1991. (3-31-22)
05. Development of Toxic Substance Criteria. (3-31-22)
a. Aquatic Life Communities Criteria. Numeric criteria for the protection of aquatic life uses not identified in these rules for toxic substances, may be derived by the Department from the following information: (3-31-22) i. Site-specific criteria developed pursuant to Section 275; (3-31-22) ii. Effluent biomonitoring, toxicity testing and whole-effluent toxicity determinations; (3-31-22) iii. The most recent recommended criteria defined in EPA's ECOTOX database. When using EPA recommended criteria to derive water quality criteria to protect aquatic life uses, the lowest observed effect concentrations (LOECs) shall be considered; or (3-31-22) iv. Scientific studies including, but not limited to, instream benthic assessment or rapid bioassessment. (3-31-22) b. Human Health Criteria. (3-31-22) i. When numeric criteria for the protection of human health are not identified in these rules for toxic substances, quantifiable criteria may be derived by the Department using best available science on toxicity thresholds (i.e. reference dose or cancer slope factor), such as defined in EPA's Integrated Risk Information System (IRIS) or other peer-reviewed source acceptable to the Department. (3-31-22) ii. When using toxicity thresholds to derive water quality criteria to protect human health, a fish consumption rate representative of the population to be protected, a mean adult body weight, an adult 90th percentile water ingestion rate, -5trophic level weighted BAF or BCF, and a hazard quotient of one (1) for non-carcinogens or a cancer risk level of 10 for carcinogens will be utilized for any compound not listed in Subsection 210.05.b.iii. IdahoAdministrative Bulletin Page 146 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking (4-6-23) iii. Subsection 210.05.b.ii. does not apply to the fish tissue element for inorganic arsenic. (4-6-23) (BREAK IN CONTINUITY OF SECTIONS) 401. POINT SOURCE WASTEWATER TREATMENT REQUIREMENTS. Unless more stringent limitations are necessary to meet the applicable requirements of Sections 200 through 300, or unless specific exemptions are made pursuant to Subsection 080.02, wastewaters discharged into surface waters of the state must have the following characteristics: (3-31-22)
01. Temperature. The wastewater must not affect the receiving water outside the mixing zone so that:
(3-31-22) a. The temperature of the receiving water or of downstream waters will interfere with designated beneficial uses. (3-31-22) b. Daily and seasonal temperature cycles characteristic of the water body are not maintained. (3-31-22) c. If temperature criteria for the designated aquatic life use are exceeded in the receiving waters upstream of the discharge due to natural background conditions, then wastewater must not raise the receiving water temperatures by more than three tenths (0.3) degrees C. (3-31-22) Note: Submitted to EPA as a temporary rule on July 20, 2011, and as a final rule on August 7, 2012 (docket 58-0102-1101). This revision removed the numeric limits on point source induced changes in receiving water temperature. Until EPA approves this revision, the previous treatment requirements published in 2011 IdahoAdministrative Code continue to apply and are effective for CWA purposes. For more information, go to http://www.deq.idaho.gov/epa-actions-on-proposed- standards. The previous treatment requirements published in 2011 IdahoAdministrative Code are effective for CWA purposes until the date EPA issues written notification that the revisions in Docket Nos. 58-0102-1101 or 58-0102-1803 have been approved. c. If the water is designated for warm water aquatic life, the induced variation is more than plus two (+2) degrees C. ( ) d. If the water is designated for cold water aquatic life, seasonal cold water aquatic life, or salmonid spawning, the induced variation is more than plus one (+1) degree C. ( ) ce. If temperature criteria for the designated aquatic life use are exceeded in the receiving waters upstream of the discharge due to natural background conditions, then Subsections 401.01.c. and 401.01.d. do not apply and instead wastewater must not raise the receiving water temperatures by more than three tenths (0.3) degrees C above the natural background conditions. (3-31-22)( ) Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102- 1803 have been approved. d. If temperature criteria for the designated aquatic life use are exceeded in the receiving waters upstream of the discharge, then wastewater must not raise the receiving water temperatures by more than three tenths IdahoAdministrative Bulletin Page 147 July 2, 2025 – Vol. 25-7 DEPARTMENT OF ENVIRONMENTAL QUALITY Docket No. 58-0102-2501 Water Quality Standards Proposed Rulemaking (0.3) degrees C above applicable numeric criteria. (3-31-22) Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102- 1803 have been approved.
02. Turbidity. The wastewater must not increase the turbidity of the receiving water outside the mixing
zone by: (3-31-22) a. More than five (5) NTU (Nephelometric Turbidity Units) over background turbidity, when background turbidity is fifty (50) NTU or less; or (3-31-22) b. More than ten percent (10%) increase in turbidity when background turbidity is more than fifty (50) NTU, not to exceed a maximum increase of twenty-five (25) NTU. (3-31-22) IdahoAdministrative Bulletin Page 148 July 2, 2025 – Vol. 25-7
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