MS4s that are designated may be eligible for a waiver from coverage under 327 IAC 15-13. Waivers allowed under this Rule are conditional, and are only allowed for two population-based categories of MS4 entities.
- For MS4 entities within a mapped Urbanized Area (UA) that have an MS4 conveyance serving a population of less than 1,000 people, a waiver is granted automatically unless the MS4 conveyance is substantially contributing to the pollutant loadings of a regulated, physically interconnected MS4 entity or a department determination is made that requires storm water controls.
- For the second conditional waiver1 to be allowed, the following conditions must be met:
- The MS4 entity’s conveyance system serves a population of less than 10,000;
- The MS4 entity’s conveyance system is not contributing substantially to the pollutant loadings of a physically interconnected MS4 entity that is regulated by this rule;
- An evaluation of all waters that receive a discharge from the MS4 entity’s conveyance system has been conducted by the department or another approved entity;
- For all evaluated waters, the department has determined that storm water controls are not needed based on waste load allocations that are part of a United States Environmental Protection Agency approved or established total maximum daily load or equivalent process, and are reflective of pollutants identified as sources of impairment; and
- The department has determined that future discharges from the MS4 entity’s conveyance system do not have the potential to result in exceedances of water quality standards, including impairment of designated uses, or other significant water quality impacts, including habitat and biological impacts.
1 The waiver is contingent on currently unavailable receiving water quality data evaluations. IDEM does not expect that an MS4 entity will be able to adequately meet all five of the required conditions for a waiver to be allowed in 2003.