Idaho Administrative Code
Title IDAPA 58 - Environmental Quality, Department of
Rule 58.01.02 - WATER QUALITY STANDARDS
Section 58.01.02.210 - NUMERIC CRITERIA FOR TOXIC SUBSTANCES FOR WATERS DESIGNATED FOR AQUATIC LIFE, RECREATION, OR DOMESTIC WATER SUPPLY USE

Universal Citation: ID Admin Code 58.01.02.210

Current through August 31, 2023

01. Criteria for Toxic Substances. The criteria of Section 210 apply to surface waters of the state as provided in Tables 1 and 2. (3-31-22)

a. Table 1 contains criteria set for protection of aquatic life. Criteria for metals (arsenic through zinc) are expressed as dissolved fraction unless otherwise noted. For purposes of these criteria, dissolved fraction means that which passes through a forty-five hundredths (0.45) micron filter. (3-31-22)

Subsections 210.01 and 210.01.a. are effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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)

Subsections 210.01 and 210.01.a. are not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

Table 1. Criteria for Protection of Aquatic Life

Compound

a CAS Number

b CMC (µg/L)

b CCC (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, EPA disapproved Idaho's removal of the old aquatic life criteria. The water column criteria for total recoverable mercury published in 2004 Idaho Administrative 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.

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

Acrolein

107028

--1 -------------- 32

--1 -------------- 32

1Effective 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.

Aldrin

39002

3

gamma-BHC (Lindane)

58899

2

0.08

Carbaryl

63252

--1 -------------- 2.12

--1 -------------- 2.12

1Effective 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

Diazinon

333415

--1 -------------- 0.172

--1 -------------- 0.172

1Effective 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

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.

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, potassium = 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 10-8 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

15.11

8.52

11. 32

1.5 (30 day average)3

3.1 (30 day average)3

Intermittent Exposure Equation3.4

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 Selenium - 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).

4. Intermittent Exposure Equation=

Click here to view image

where WQC is the applicable water column element, for either lentic or lotic waters; Cbkgrnd is the average back-ground selenium concentration, and fint is the fraction of any 30-day period during which elevated selenium concentra-tions occur, with fint assigned a value [GREATER THAN EQUAL TOO] 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:)

Compound

a CAS Number

Carcinogen?

Water & Fish (µg/L unless otherwise specified)

Fish Only (µg/L unless otherwise specified)

Inorganic Compounds/Metals

Antimony

7440360

5.2

b

190

b

Arsenic1

7440382

Y

10

cdj

10

cdj

Note: In 2008, Idaho adopted 10 µg/L as its CWA arsenic criterion for both exposure through fish consumption only and exposure through drinking water+fish consumption, choosing the SDWA MCL due to concerns about background levels that exceed EPA's 304(a) criteria (docket 58-0102-0801). EPA approved this action in 2010. In June 2015, Northwest Environmental Advocates challenged EPA's 2010 approval. Court remanded action back to EPA. On September 15, 2016, EPA disapproved Idaho's adoption of 10 µg/L. Neither EPA nor the state of Idaho has promulgated replacement criteria. For more information, go to http://www.deq.idaho.gov/epa-actions-on-proposed-standards.

1Effective for CWA purposes. Water & Fish value, Fish Only value, and footnotes continue to be effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved. See Arsenic2 immediately below.

Arsenic2

7440382

Y

10

cdj

4.3; 8.0 µg/kg fish tissue

ck

2Not yet effective for CWA purposes. Fish Only value and footnote k are not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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

Inorganic Compounds/Non-Metals

Cyanide

57125

3.9

b

140

b

Asbestos

1332214

7,000,000 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) Ether

108601

220

b

1,200

b

Bis(Chloromethyl) Ether

542881

Y

0.0015

bf

0.055

bf

Bis(2-Ethylhexyl) Phthalate

117817

Y

1.2

bf

1.2

bf

Bromoform

75252

Y

62

bf

380

bf

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 (2,4-D)

94757

1,000

b

3,900

b

Chlorophenoxy Herbicide (2,4,5-TP) [Silvex]

93721

82

b

130

b

4-Chlorophenyl Phenyl Ether

7005723

e

e

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

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 (HCH)-Technical

608731

Y

0.027

bf

0.032

bf

Hexachloro-cyclopentadiene

77474

1.3

b

1.3

b

Hexachloroethane

67721

0.23

b

0.24

b

Ideno (1,2,3-cd) Pyrene

193395

Y

0.0042

bf

0.0042

bf

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 PCBs

g

Y

0.00019

bfh

0.00019

bfh

Pyrene

129000

8.1

b

8.4

b

1,2,4,5-Tetrachlorobenzene

95943

0.0093

b

0.0094

b

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-Dichloroethylene

156605

120

b

1,200

b

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

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 specified in Idaho's Technical Sup-port Document (TSD) for Human Health Criteria Calculations - 2015. Criteria for non-carcinogens are calculated using the formula:

Click here to view image

and criteria for carcinogens are calculated using the formula:

Click here to view image

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

Click here to view image

RSC = Relative Source Contribution, chemical specific value, see TSD

c. Inorganic forms only.

d. Criterion expressed as total recoverable (unfiltered) concentrations.

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 10-4 to 10-6 for the incremental increase in cancer risk used in human health criteria calculation. Idaho has chosen to base this criterion on carcinogenicity of 10-5 risk.

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)}] / [SIGMA]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.

2Water column element is based on dissolved inorganic arsenic in water.

Footnote k is not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

(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} X Acute Conversion Factor. (3-31-22)

b. CCC=WER exp{mc[ln(hardness)]+bc} X Chronic Conversion Factor.

Metal

mA

bA

mc

bc

aAcute Conversion Factor

aChronic Conversion Factor

Arsenic

b

b

b

b

1.0

1.0

Cadmium

0.8367

-3.560

0.6247

-3.344

0.944 see footnote a

0.909

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

(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)
(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 for Aquatic 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 for Aquatic 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)

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 in Subsection 210.0 1 are not to be exceeded based on an annual harmonic mean. (3-31-22)

Effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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)

Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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:

Click here to view image

Where:

WCT (µg/L) is the translated water column value; and

BAFSS 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)

Subsection 210.03.e. is not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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 Clean Analytical 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, a trophic level weighted BAF or BCF, and a hazard quotient of one (1) for non-carcinogens or a cancer risk level of 10-5 for carcinogens shall be utilized. (3-31-22)

Effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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, a trophic level weighted BAF or BCF, and a hazard quotient of one (1) for non-carcinogens or a cancer risk level of 10-5 for carcinogens will be utilized for any compound not listed in Subsection 210.05.b.iii. (4-6-23)

Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

iii. Subsection 210.05.b.ii. does not apply to the fish tissue element for inorganic arsenic. (4-6-23)

Not effective for CWA purposes until the date EPA issues written notification that the revisions in Docket No. 58-0102-2201 have been approved.

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