1. (a)

   1. (1) Toxic substances shall not be present in receiving waters, after mixing, in such quantities as to be toxic to human, animal, plant, or aquatic life or to interfere with the normal propagation, growth, and survival of the aquatic biota.
   2. (2) Acute toxicity standards apply outside the zone of initial dilution. Within the zone of initial dilution acute toxicity standards may be exceeded but acute toxicity may not occur.
   3. (3) Chronic toxicity and chronic numeric toxicity standards apply at, or beyond, the edge of the mixing zone.
2. (b) Permitting of all toxic substances shall be in accordance with the toxic implementation strategy found in the State of Arkansas Continuing Planning Process.
3. (c) For nonpermit issues and as a guideline for evaluating toxic substances not listed in the following tables, the Division of Environmental Quality may consider No Observed Effect Concentrations or other literature values as appropriate.
4. (d) For the substances listed below, the following standards shall apply:

5. (e)

   1. (1) (e)(1) The permittee shall have the option to develop site-specific numerical standards for toxic substances using United States Environmental Protection Agency approved bioassay methodology and guidance.
   2. (2) Such guidance may include but may not be limited to Water Quality Standards (EPA-823-B-94-005, August, 1994); Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms (EPA-821-R-02- 012. 5th ed. December 2002); Short Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms (EPA/600/4-91/002, 4th ed. October 2002) or most recent update thereof.
6. (f) Only ambient water quality data for dissolved metals generated or approved by the division after March 1, 1993 will be considered in the documentation of background concentrations for the purpose of developing permit limitations.

Codification Notes: This section contains the following footnotes: Footnote 5 provides as follows: "Total of all isomers." Footnote 6 provides as follows: "These values may be adjusted by a site specific Water Effects Ratio (WER) as defined in 40 C.F.R. § 131.36 (c)." Footnote 7 provides as follows: "Mercury based on bioaccumulation of residues in aquatic organisms." Footnote 8 provides as follows: "Expressed as total recoverable." Footnote 9 provides as follows: "Mercury based on bioaccumulation of residues in aquatic organisms." Footnote 10 provides as follows: "Criteria based on a lifetime risk factor of 10-5." Footnote 11 provides as follows: "Criteria based on a lifetime risk factor of 10-6 and cancer slope factor of 0.015 unless otherwise noted." Footnote 12 provides as follows: "The maximum contaminant level under the Safe Drinking Water Act, 42 U.S.C.§ 300f et seq." Footnote 13 provides as follows: "Total of all isomers." Footnote 14 provides as follows: "10000 ug/L is also represented as 10 mg/L, which is the maximum contaminant level under the Safe Drinking Water Act, 42 U.S.C. 300f et seq."