Tier 3: No Degradation for ONRWs:  Applies only to waters classified as Outstanding National Resource Waters (ONRW).  This classification “overlays” the other designated uses and candidates include, but are not limited to, “waters of National and State parks and wildlife refuges and waters of exceptional recreational or ecological significance.”  Only minor & temporary decreases in water quality are allowed

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Antidegradation Tier 3

Tier 3 states that water quality must be maintained and protected without exception for those waters specially designated by a state, territory, or tribe. EPA regulations refer to such waters as Outstanding National Resource Waters(ONRW). States often use the term Outstanding Resource Waters. The “candidate” water body types (e.g., wild and scenic rivers, waters in national and state parks) are merely suggestions that EPA has provided regarding the kinds of water bodies that states, tribes, and territories might choose to designate for Tier 3 level protection. It is generally recognized that some minor, temporary degradation in ONRWs might occur—for example, during road paving work in a national park. Nevertheless, Tier 3 requires that such degradation be minimized, and that water quality return to the previous level after the activity is completed. The ONRW designation process varies considerably among states. Some states have documented procedures for adding waters to the ONRW list—including those proposed by the public—but others do not.

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Section 26 of 78