The purpose of the Tier II antidegradation review is to protect and maintain Tier II high quality waters from degradation. The Tier II review is required for new or modified National Pollutant Discharge Elimination System (NPDES) permit applications, Nontidal Wetlands and Waterways permits, and activities requiring a 401 Water Quality Certification (also issued by the MDE Nontidal Wetlands and Waterways Program). Additionally, the review is required for Water and Sewer Plan Amendment reviews. Other MDE environmental reviews that may result in future permitting, for example Interagency Clearinghouse Reviews, may also identify related projects that may need to undergo a Tier II review, and potentially require Tier II review information at that time. The Tier II review is applicable to applications and approvals for local, state, and federal entities and projects.
The Tier II review is implemented on a watershed basis using an upstream approach intended to protect downstream water quality. This means that regulated activities occurring anywhere within a Tier II watershed area may require a Tier II review. Using a science-based implementation strategy, the review identifies common impacts associated with a given regulated activity, and provides where appropriate, comments to help address those impacts. Permits and approvals may include special conditions and requirements to address antidegradation issues
In the diagram, the vertical arrow on left represents Tier II water quality. The midline value of “0” represents no net change in water quality. The horizontal arrow represents the progression of the Tier II review for each project.
No net change is the overarching goal of the Tier II review. This is achieved by reducing environmental water quality impacts (the dark purple box) as much as is possible. If mitigation is not possible, remaining impacts should be justified before being permitted. This process is called a ‘social and economic justification’.
Overall Review Process
All analyses described below are applicable to all areas of the whole and complete project within a Tier II watershed. It is recommended that applicants provide MDE with a final “Tier II Review Antidegradation” Report that organizes responses to questions, forms, and other supporting documentation used to support the final review determination. Once the Tier II review is complete for the project, this report documentation can be used for other related MDE permits and approvals related to that project. If the permitted activity is modified, then at that time MDE may initiate further review to determine if changes will impact Tier II water quality.