R18-11-210. Site Specific Standards

A. The Director shall adopt a site-specific standard by rule. B. The Director may adopt a site-specific standard based upon a request or upon the Director’s initiative for any of the following reasons: 1. Local physical, chemical, or hydrological conditions of a non-WOTUS protected surface water such as pH, hardness, fate and transport, or temperature alters the biological availability or toxicity of a pollutant; 2. The sensitivity of resident aquatic organisms that occur in a non-WOTUS protected surface water to a pollutant differs from the sensitivity of the species used to derive the numeric water quality standards to protect aquatic life in R18-11-215; 3. Resident aquatic organisms that occur in a non-WOTUS protected surface water represent a narrower mix of species than those in the dataset used by ADEQ to derive numeric water quality standards to protect aquatic life in R18-11-215; 4. The natural background concentration of a pollutant is greater than the numeric water quality standard to protect aquatic life prescribed in R18-11-215. “Natural background” means the concentration of a pollutant in a non- WOTUS protected surface water due only to non-anthropogenic sources; or 5. Other factors or combination of factors that upon review by the Director warrant changing a numeric water quality standard for a non-WOTUS protected surface water. C. Site-specific standard by request. To request that the Director adopt a site-specific standard, a person must conduct a study to support the development of a site-specific standard using a scientifically defensible procedure. Before conducting the study, a person shall submit a study outline to the Director for approval that contains the following elements: 1. Identifies the pollutant; 2. Describes the reach’s boundaries; 3. Describes the hydrologic regime of the waterbody; 4. Describes the scientifically defensible procedure, which can include relevant aquatic life studies, ecological studies, laboratory tests, biological translators, fate and transport models, and risk analyses; 5. Describes and compares the taxonomic composition, distribution and density of the aquatic biota within the reach to a reference reach and describes the basis of any major taxonomic differences; 6. Describes the pollutant’s effect on the affected species or appropriate surrogate species and on the other designated uses listed for the reach; 7. Demonstrates that all designated usesare protected; and 8. A person seeking to develop a site-specific standard based on natural background may use statistical or modeling approaches to determine natural background concentration.