75-5-222. State regulation for natural conditions. (1) The department may not apply a standard to a water body for water quality that is more stringent than the nonanthropogenic condition of the water body. For the parameters for which the applicable standards are more stringent than the nonanthropogenic condition, the standard is the nonanthropogenic condition of the parameter in the water body. The department shall implement the standard in a manner that provides for the water quality standards for downstream waters to be attained and maintained.
(2) (a) For water bodies where the standard is more stringent than the condition of the water body but subsection (1) is not applicable, the board shall adopt rules consistent with comparable federal rules and guidelines providing criteria and procedures for the department to issue variances from standards if:
(i) the condition cannot reasonably be expected to be remediated during the permit term for which the application for variance has been received; and
(ii) the discharge to which the variance applies would not materially contribute to the condition.
(b) A variance issued pursuant to subsection (2)(a) must be reviewed every 5 years and may be modified or terminated as a result of the review.