Antidegradation

The purpose of the antidegradation policy is to protect existing uses of all waters and maintain the quality of waters with higher quality than the minimum water quality standards. In February 2002, Illinois adopted a comprehensive set of regulations (especially section 302.105) establishing its antidegradation policy. The following is a very simple summary of these regulations designed to assist citizens reviewing NPDES permits.

Existing Uses

ALL existing uses attained on or after November 28, 1975, must be maintained. Such uses might include any recreational use, water supply use, or use by particular aquatic life.

Outstanding Resource Waters

An Outstanding Resource Water (ORW) is a water of "exceptional ecological or recreational significance" that is designated as such by the Illinois Pollution Control Board (IPCB).

ORWs must not be lowered in quality (a few exceptions are described in regulations).

Citizens may submit a petition to designate a water as ORW. Illinois has not yet designated any waters as ORW.

High Quality Waters

Waters that are cleaner than required by the water quality standards must be maintained at high quality unless lowering the quality is necessary to accommodate important economic or social development.

Before Illinois EPA (IEPA) allows increased pollution into any high quality water, through the NPDES program, 401 certification, or other means, it must conduct an antidegradation assessment. The few activities that are not subject to this review are described in the regulations.

Antidegradation Assessments

Permit applications must include information for IEPA's use in making the assessment. This information includes, among other things:

The purpose and anticipated benefits of the proposed activities.

An assessment of alternatives to the proposed discharge that would result in less environmental degradation; these may include additional treatment, discharge to a different location, and changing activities to produce less pollution.

IEPA must use this information to complete an antidegradation assessment. Before issuing the permit, IEPA must assure that:

All water quality standards will be met and all existing uses will be fully protected.

All reasonable measures to avoid or minimize the increased pollution will be taken.

The activity that causes the increased pollution will benefit the community at large.