Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. of
Sub-Agency 0011 - Water Quality
Chapter 1 - WYOMING SURFACE WATER QUALITY STANDARDS
Appendix B - Water Quality Criteria[1]

Current through September 21, 2024

(a) Priority Pollutants.

(b) Non-Priority Pollutants.

(1)Except for the aquatic life values for metals and where otherwise indicated, the values given in Appendix B refer to the total recoverable (dissolved plus suspended) amount of each substance. For the aquatic life values for metals, the values refer to dissolved amount.

(2)Except where otherwise indicated, these values are based on EPA Section 304(a) criteria recommendations assuming consumption of 2 liters of water and 17.5 grams of aquatic organisms per day.

(3)Except for arsenic, the substance is classified as a carcinogen with the value based on an incremental risk of one additional instance of cancer in one million persons. Arsenic is classified as a carcinogen, however, the value is not based on an additional 1:1,000,000 cancer risk.

(4)Hardness dependent criterion. Value given is an example only and is based on a CaCO3 hardness of 100 mg/L. Criteria for hardness concentrations other than 100 mg/L as CaCO3 must be calculated using the formulas in Appendix F.

(5)pH dependent criterion. Value given is an example only and is based on a pH of 7.8. Criteria for pH values other than 7.8 must be calculated using the formulas in Appendix G.

(6)Criterion expressed as total cyanide, even though the method used to derive the criterion is based on free cyanide. If a substantial fraction of the cyanide present in a water body is present in a complexed form (e.g. Fe4[Fe(CN)6]3), this criterion may be overly conservative.

(7)Criterion is based on organoleptic (taste and odor) effects and is more stringent than if based solely on toxic or carcinogenic effects.

(8)EPA Section 304(a) human health criteria recommendation assuming consumption of contaminated aquatic organisms at a rate of 17.5 grams per day.

(9)Criterion is based on an EPA drinking water standard (maximum contaminant level or MCL).

(10)This value is expressed in terms of total recoverable metal in the water column. It is scientifically acceptable to use a conversion factor (0.996 for the acute and 0.922 for the chronic) to convert this number to a value that is expressed in terms of a dissolved metal. Using these conversion factors, the aquatic life acute value for selenium is 19.92 µg/L as a dissolved metal and the aquatic life chronic value for selenium is 4.61 µg/L as a dissolved metal.

(11) Criterion is based on Safe Drinking Water Act secondary standards and is intended to prevent undesirable cosmetic or aesthetic effects. Value represents the dissolved amount of each substance rather than the total amount. Criterion only applies where drinking water is an actual use.

(12)Value is based on the dissolved amount which is the amount that will pass through a 0.45 µm membrane filter prior to acidification to pH 1.5-2.0 with nitric acid.

(13)This criterion applies to total PCBs (i.e. the sum of all congener or all isomer or homolog or Aroclor analyses).

(14)The 87 µg/L chronic criterion for aluminum is based on information showing chronic effects on brook trout and striped bass. The studies underlying the 87 µg/L chronic value, however, were conducted at low pH (6.5-6.6) and low hardness (< 10 mg/L CaCO3), conditions uncommon in Wyoming surface waters. A water effect ratio toxicity study in West Virginia indicated that aluminum is substantially less toxic at higher pH and hardness (although the relationship is not well quantified at this time). EPA is also aware of field data indicating that many high quality waters in the U.S. contain more than 87 µg/L when either total recoverable or dissolved aluminum is measured. Based on this information and considering the available toxicological information in Tables 1 and 2 of EPAs Aluminum Criteria Document (EPA 440/5-86-008), the department will implement the 87 µg/L chronic criterion for aluminum as follows: the 87 µg/L chronic criterion will apply except where the receiving water after mixing has a pH greater than or equal to 7.0 and a hardness (as CaCO3) greater than or equal to 50 mg/L. Where the receiving stream after mixing has a pH greater than or equal to 7.0 and a hardness (as CaCO3) greater than or equal to 50 mg/L, the 750 µg/L acute criterion will apply. In situations where the 87 µg/L chronic criterion applies, a discharger may request development of and provide the basis for a site-specific chronic criterion based on a water-effect ratio.

(15)Criterion applies on Class 1, 2AB, 2B and 2C waters only.

(16)Criterion has been divided by two to be comparable with other acute values derived using an averaging period. Value can be multiplied by two if criterion is to be used as an instantaneous maximum or end of pipe value, as the original criterion was derived using EPA's 1980 guidelines as a not to be exceeded instantaneous maximum.

(c) Site-Specific Criteria. The criteria in this section are applicable only to the waters and/or locations specified and replaces similar criteria expressed elsewhere in these regulations.

(i) Belle Fourche Drainage

(A) The numeric human health criteria for iron and manganese shall not apply to Class 2 waters in the Belle Fourche River Drainage above the confluence of Donkey Creek and the main stem of the Belle Fourche River;

(B) The numeric human health criteria for iron and manganese shall not apply to main stem of the Belle Fourche River below the confluence of Donkey Creek.

(ii) Big Horn River Drainage

(A) Cottonwood Creek (near Hamilton Dome): The aquatic life criterion for chloride shall be 860 mg/L and the aquatic life criterion for selenium shall be 43 µg/L. These values represent instantaneous maximum values, not to be exceeded at any time.

(iii) Cheyenne River Drainage

(A) The numeric human health criteria for iron and manganese shall not apply to Class 2 tributaries of Antelope Creek;

(B) The numeric human health criteria for iron and manganese shall not apply to Little Thunder Creek and all of its Class 2 tributaries below the confluence of North Prong.

(iv) Little Powder River Drainage

(A) The numeric human health criteria for iron and manganese shall not apply to Class 2 waters in the Little Powder River Drainage.

(v) North Platte River Drainage

(A) Poison Spider Creek: The aquatic life criterion for chloride shall be 531 mg/L. This value represents an instantaneous maximum value, not to be exceeded at any time.

(vi) Powder River Drainage

(A) The numeric human health criteria for iron and manganese shall not apply to Class 2 waters in the Powder River Drainage except on the following waters:

(I) The main stem of Clear Creek and its Class 2 tributaries upstream of Clearmont, Wyoming;

(II) The main stem of Crazy Woman Creek and its Class 2 tributaries;

(III) The North Fork of the Powder River and all its Class 2 tributaries; and

(IV) The Middle Fork of the Powder River and all its Class 2 tributaries.

(B) Salt Creek: The aquatic life criterion for chloride shall be 1600 mg/L. This value represents an instantaneous maximum value, not to be exceeded at any time.

(C) Meadow Creek (tributary to Salt Creek): The aquatic life criterion for chloride shall be 1600 mg/L. This value represents an instantaneous maximum value, not to be exceeded at any time.

(D) Powder River below Salt Creek: The aquatic life criterion for chloride shall be 984 mg/L. This value represents an instantaneous maximum value, not to be exceeded at any time.