Key Concepts

Variances: When Allowed

States/Tribes must use one of the six factors listed below (listed in 40 CFR 131.10(g)) to demonstrate that the designated use is not feasible to attain in the short term.

• Factors for Establishing the Basis for Granting a Variance
  1. Naturally occurring pollutant concentrations.
  2. Dams or other hydrologic modifications.
  3. Natural, ephemeral intermittent low-flow.
  4. Natural physical conditions preclude attainment of aquatic life uses.
  5. Human-caused conditions or pollutant sources that cannot be remedied or would cause more environmental damage to correct than to leave in place.
  6. Substantial and widespread economic and social impact.

Question. Can you guess which of the six factors is most commonly used to justify a variance?

Answer. While any of the six factors can be used, in practice, the "substantial and widespread economic impact" factor is most commonly used to justify a variance.