Recent changes in Maryland’s Tier II Antidegradation Review policies are impacting an increasing number of development projects, and in many cases are causing significant delays in permit approvals from Maryland Department of the Environment (MDE). Maryland has been regulating impacts to Tier II (high-quality) watersheds for nearly 20 years in accordance with Code of Maryland Wetland Studies and Solutions, Inc. (WSSI) has been monitoring the situation and continues to work with clients to identify Tier II waters in the project planning stages so project teams can avoid or minimize impacts, secure mitigation credits for unavoidable impacts, and avoid delays.

What Is a Tier II Water?

Tier II waters are streams and rivers where water quality exceeds the state minimum standards and biological communities are healthy, robust, and diverse. MDE has designated 263 Tier II Watersheds across Maryland (per MDE at time of publication). MDE divvies up Tier II waters according to their ability to maintain ecological integrity.

• Waters with “assimilative capacity remaining” can withstand proposed landcover changes.
• Those classified as “no assimilative capacity remaining” require a more in-depth analysis of the potential impacts from proposed landcover changes and may need impact mitigation.

What Is Under Review?

MDE staff look for any impacts within watersheds that are mapped as Tier II waters. These impacts may include:

  1. Any impacts to streams and 100′ stream buffers,
  2. One acre of more of forest clearing,
  3. Any increases to untreated impervious cover.

When Does the Review Cycle Start?

MDE ‘s review process is triggered when a project is under MDE review for any of these development project stages:

  1. Joint State/Federal (JS/F) permit application review (for projects with impacts to wetlands, waterways, or floodplains);
  2. Requests for JS/F permit reauthorizations or to cover new phases of an existing project;
  3. NPDES1 permit application review. Note, if a project does not have wetland and stream impacts, it can reach the NPDES permitting stage (i.e., the 11th hour) before the need for Tier II Antidegradation review is identified at the agency level; or,
  4. Water and sewer amendments.

Why Are There So Many Delays?

Three changes over the last four years have resulted in an increased backlog in MDE’s Tier II Antidegradation Review process. These changes have increased the number of projects eligible for review, and made if more difficult for projects to be released from review.


MDE began requiring Tier II approval for all projects undergoing NPDES permit processing.


MDE reassessed watershed assimilative capacity, and the number of watersheds with “no assimilative capacity remaining” increased from 24% to 44% of Tier II watersheds.


The Maryland Attorney General’s office implemented new policies that have significantly changed the Tier II Approval process and extended the review approval timeline. This new policy stipulates that no approval may be granted until all mitigation documentation has been submitted and deemed complete, including restrictive covenants, easements, and bank purchases. (enacted to ensure compliance with the CP20, see our related Field Notes article.

The AG’s office implemented this change to address the failure of permittees to consistently follow through on reforestation and forest conservation permit requirements. The inadequate forest mitigation was deemed to be a threat to Maryland’s success in protecting high quality waters, as required by federal law.

How Can I Avoid Delays?

WSSI’s Maryland-based staff are experts in identifying Tier II watersheds, preparing Tier II analyses, and coordinating Wetlands and Waterways permitting and Tier II approvals with MDE (under all the aforementioned review scenarios). WSSI works with our clients to identify Tier II waters early in project planning, so the need for the Antidegradation review can be managed proactively. The goal is to prevent projects from making significant progress through the design and local permit process before the Tier II issues are identified and addressed.

Early coordination is key. MDE’s Wetlands and Waterways permits and NPDES permits cannot be authorized until the Tier II Review is complete. The MDE Tier II Antidegradation review team aims to provide initial comments within 30 and 45 days of receiving applications2, although, this timeframe may be longer for complex projects. Applicants should anticipate multiple rounds of comments for complex projects and expect to have lengthy review times of up to six months or more.

If your project requires a Nontidal Wetlands and Waterways permit from MDE or NPDES permit, it is subject to a Tier II Antidegradation review. If you have proposed impacts to these specially protected waters, your project may need plan changes or you may need to purchase mitigation credits to offset proposed impacts. Many projects have not identified these critical waters ahead of time, missing an opportunity to reduce the potential impact on Tier II waters and the cascading effect on a project. Managing the impacts with plan changes at the NPDES permitting stage can be prohibitively expensive, and mitigation credits can be costly and difficult to secure due to scarcity and land management issues.

Contact the WSSI staff listed below to discuss how we can navigate the Tier II Antidegradation Review process for your projects.

Interested in Learning More About the Tier II Antidegradation Review Process? Keep Reading.

For projects requiring Tier II review, there are three possible approval paths.

  1. No Additional Review Exemption: This exemption applies to projects with minimal forest clearing (less than 1 acre) and minor impacts to streams and 100’ stream buffers. To qualify, all proposed impervious surfaces must be treated by Environmental Site Design (ESD) stormwater management practices with capacity remaining in some or all of the ESD features. Additionally, projects must be exempt from the Alternative Site Analysis requirements (see #2, below).
  2. Alternative Site Analysis Exemption: This exemption covers one portion of the Tier II Antidegradation Review Process. To be eligible for this exemption, a project must have a site-specific limitation (e.g. expanding an existing school campus), be in a federal, state, or local economic incentive zone (e.g. State Priority Funding Area), deal with matters of military or national security, have little to no resource impacts (repairs, replacements, ecosystem restoration, etc.), or be grandfathered under the 2010 Maryland Stormwater Management Manual. Projects that are eligible for this exemption are still required to complete an impact analysis and justification for stream buffer disturbance, forest cover loss, and untreated impervious surface cover; detailed Avoidance and Minimization Measures; and a completed mitigation package.
  3. Full Tier II Antidegradation Review: A full Tier II review is a lengthy process that includes site planning and engineering, environmental, and fiscal project information. The full review requires a detailed Alternative Site Analysis; impact exhibits and justification for stream buffer disturbance, forest cover loss, and untreated impervious surface cover; detailed Avoidance and Minimization Measures; and a completed mitigation package.

Additional review and approval considerations include:

  1. Project impact on social justice in the watershed: In Watersheds with No Assimilative Capacity (click here for map), applicants must also complete a Social and Economic Justice Analysis if impacts cannot be entirely avoided or mitigated for. Per Step 4 on MDE’s Tier II Review webpage, applicants must demonstrate that the “economic hardship and/or public benefit overrides the value of the ecological services or water quality benefit that the Tier II Water Segment provides.” This analysis includes the project budget, economic benefits of the project (including potential job creation and tax revenue), social benefits of the project, and any contributions to the environment. This is balanced against an accounting of the economic and social benefits provided by high-quality waters and the costs associated with mitigation.
  1. Water quality benefit of proffered impact mitigation: The mitigation proffered is an important piece of the approval process. Mitigation options include on-site forest buffer expansion, on-site reforestation, and off-site reforestation. Any off-site reforestation must be located within the same Tier II Watershed. A protection mechanism, usually in the form of a Forest Conservation Easement, is required for all mitigation involving tree planting; easements must be recorded prior to Tier II Approval. MDE may also consider other forms of mitigation as “out-of-kind” if the activity provides a water quality benefit, such as stream restoration, wetland creation, or removal of untreated impervious surfaces.


1 NPDES: National Pollutant Discharge Elimination System
2 WSSI understanding based on communication with MDE staff.


  • Haley Kelly, PWS, CSE, ISA Certified Arborist MA-6567A

    Senior Environmental Scientist

    Millersville, Maryland

  • Mike Klebasko, PWS, QFP

    Manager - Maryland Environmental Science

    Millersville, Maryland

  • Joshua Howard, CESSWI, CPESC

    Environmental Compliance Specialist

    Millersville, Maryland