The CWA Framework

Water Quality Prot​ection Implementation Process

Tier II Background Information

Although a Tier II antidegradation review is not required when a WRE is adopted by a local government, understanding the review is essential to understanding how future development envisioned within the local land use plan could be affected, and whether the proposed land use plan approach, along with any associated water protection strategies, would be sufficient to protect the Tier II waters. Generally, the land use plan should avoid new development within Tier II watersheds (and in watersheds of other types of high quality waters - see the Water Quality Protection Process section for a list of these) and the WRE should include strategies for ensuring the implementation of BMPs and other environmental protection measures recommended by MDE within Tier II watersheds.

A Tier II antidegradation review is required for new or modified National Pollutant Discharge Elimination System permit applications, Nontidal Wetlands and Waterways permits, and activities requiring a 401 Water Quality Certification (also issued by MDE). Additionally, the review is required for new or proposed amendments to local water and sewer plans. Other MDE environmental reviews that may result in future permitting, for example Interagency Clearinghouse Reviews administered by Planning, may also identify related projects that 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.

Maryland’s Tier II streams​ are designated based on biological community scores for benthic macroinvertebrates (e.g., aquatic insects, crayfish, worms), and fish. MDE bases its decision on data collection and analysis procedures that strictly follow the Maryland Biological Stream Survey protocols developed by DNR. The analysis protocol generates index of biotic integrity (IBI) scores for benthic and fish data. Any stream where both IBI scores are 4.00 or greater are designated Tier II.

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.

The Tier II review must be completed with all special conditions satisfied, prior to an applicant receiving final permits from MDE, including coverage under the general construction permit for stormwater discharges.

The Tier II review implementation process can contain gaps or limitations and the process is subject to regular updates and refinements. For example, the Tier II review during the local water and sewer plan amendment review process is less about individual project reviews, but rather as an early warning system to inform the long-term planning process and better prepare for future Tier II reviews for projects generally covered under each amendment. Future improvements will include guidance for counties navigating public projects through the Tier II review, and providing notification to individuals with private projects covered under each water and sewer plan amendment.

Counties are provided the following comments during local water and sewer plan amendment reviews:

  • “Tier II streams are high quality waters that require, under regulation, additional consideration to protect their water quality. Any new or expanded discharge to these Tier II watersheds would require an Anti-degradation Review. All possible considerations should be implemented to protect high quality waters from water quality degradation. This primarily consists of rigorous watershed planning, with consideration of the extra provisions necessary to protect high quality waters.”
  • “The Department recommends that the County consider the following measures in an effort to maintain these high quality waters when approving new growth in the watersheds of these stream segments: 1) implement restrictive zoning or ordinances to protect environmental features; 2) redirect planned growth out of the watersheds of these stream segments; 3) retrofit existing stormwater infrastructure; 4) incorporate ESD and other low-impact development practices into new development; 5) maintain and expand existing forest cover; and 6) provide riparian buffers of 100-230 feet (depending upon soil types and slopes). The county should be aware that future plans facilitated by this Amendment may incur an additional Anti-degradation Review at later stages, on a project-by-project basis.”

Tier II Review Process


Step 1: Identify Impacts

Impacts vary depending upon the proposed activity requiring MDE permits or approvals. When evaluating potential Tier II impacts consider: (1) all MDE permits or approvals necessary and how each may affect in-stream water quality or (2) how implementing the proposed activity may affect resources that support in-stream water quality. MDE has posted information that describes the Tier II review process and provides links to checklists on the common impacts for several permit types that commonly receive Tier II reviews (e.g., Nontidal Wetlands and Waterways, General Permit for Stormwater associated with Construction Activity). This information can be found HERE​.

Permit renewals, with no change in treatment process, flow capacity, or no increased impacts to Tier II or to other regulated resources, generally do not undergo Tier II review unless there is an ongoing compliance issue or other special concern.

There are several common situations related to landscape changes that generally do not require Tier II review. Such situations include emergency work and repairs, habitat restoration, rehabilitation, and stabilization, and minor activities like road resurfacing. While MDE permits or approvals may be required for such activities, there may be little to no Tier II resource impacts. Therefore, applicants are given the opportunity to provide adequate documentation to support a determination that no Tier II review is necessary.

Step 2: Avoidance Alternatives Analysis

The avoidance, or ‘no-discharge’ alternatives analysis determines whether or not an applicant can implement the permitted activity without impacting Tier II waters. This may be achieved by modifying wastewater treatment, relocating outfalls to places outside of Tier II watersheds, rerouting other support infrastructure such as roads, pipelines, powerlines, etc. to avoid intersecting Tier II watersheds, and evaluating alternative sites. If a reasonable alternative is identified, it is then required as a condition of the permit or approval, and the Tier II review ends. If not, the next step is minimization. As the first and best measure to protect high quality waters, local jurisdictions should avoid planning new growth and development in Tier II watersheds.

There are several instances where there are no options for avoidance, including restrictions due to site specific repairs or restoration, funding incentives, financing limitations, phased projects, certain military projects, or other special cases. During the no-discharge alternatives analysis, applicants are given the opportunity to provide adequate documentation to support an exemption from the no-discharge alternatives analysis.

Step 3: Minimization Alternatives Analysis

The minimization alternatives analysis identifies options that when implemented, minimize impacts to Tier II waters. These options can include treatment modification, design modification to reduce impacts, and mitigation to offset unavoidable impacts. MDE may also identify other project, site-specific, or compliance concerns that may require the development of management or action plans, stream monitoring, biological monitoring, or studies, as special conditions.

Impacts to Tier II streams, stream buffers, forest cover, and changes in impervious cover area, are considered. All identified impacts are classified as either avoidable or unavoidable. Unavoidable impacts are due to existing infrastructure, buildings, SW, or other requirements for construction to meet standards and regulations, such as those pertaining to minimum right-of-way or design standards. All other impacts should be minimized to the greatest extent feasible. Any actions related to design, siting, treatment configuration, etc. previously incorporated into the activity to reduce water quality impacts can be accounted for in this portion of the review. If an applicant has done a thorough feasibility and impact analysis prior to submitting the permit application for MDE review, much of this can be considered during the course of the Tier II review.

Mitigation is an integral part of the minimization process. While certain losses are unavoidable, those losses could be mitigated either on-site or elsewhere within the Tier II watershed impacted by the activity. For land disturbing activities, the preferred mitigation method is ‘in-kind’. This means, for example, that the amount of forest restored within the Tier II watershed should equal the amount of net forest lost due to the permitted activity. This also holds true if an area is permanently converted to impervious cover, but is not managed with ESD. Buffer impacts can be mitigated on-site by increasing widths where possible to account for permanent changes within the minimum 100-foot targeted stream buffer. Areas identified for Tier II mitigation should be protected in perpetuity. Conservation at a 2:1 ratio for net loss can also be considered if there are no other options available for reforestation/afforestation.

If there is no assimilative capacity (AC) in the Tier II water, i.e., MDE has determined that the stream has degraded below Tier II standards, then a more substantial justification for remaining impacts is required before the Tier II review is satisfied. The process for determining AC can be found in (Code of Maryland Regulations (COMAR)

Step 4: Social and Economic Justification (SEJ) for Unavoidable Impacts

If impacts cannot be fully avoided, minimized, or mitigated, the applicant may have to provide MDE with an SEJ. The SEJ must demonstrate that an economic hardship and/or public benefit overrides the value of the ecological services or water quality benefit that the Tier II water segment provides. B​efore MDE can consider the SEJ in a decision, the applicant must first provide documentation to show that all reasonable avoidance, minimization, and mitigation alternatives have been considered, and where economically feasible, implemented. The SEJ is usually required when the Tier II stream affected has no remaining AC.

However, if the impacts associated with the project are widespread, or are likely to cause substantial impacts due to significant clearing, grading, hydrologic modification, temperature, etc., MDE may require an SEJ even when there is remaining AC. At a minimum, each SEJ should include the economic contributions of the project such as job creation, tax revenue, as well as other social benefits gained by the affected community located in the watershed of the Tier II water. The SEJ should also discuss the loss in value of the Tier II water as well as the economics of restoration of lost water quality. Different aspects of economic information are required for public vs private entities.

Click here to download the SEJ (Public Entities) Outline.

Click here to download the SEJ (Private Entities) Outline.

Additional Tier II Forms and Resources:

Tier II Fact Sheet - 2 page summary of basic Tier II information.

Tier II Story Map - Interactive application using photos, diagrams, narrative, and maps, to introduce Tier II information and data.

List of Tier II Waters - Tabular version of Tier II data contained within the Searchable Tier II Web Map.

Tier II No-Discharge Analysis Form​ - This form assists the applicant with the avoidance analysis.

Tier II Minimization Alternative Analysis Form V1.1​ - This form helps the applicant comprehensively identify water quality impacts to minimize, mitigate, and justify.

Construction Stormwater Antidegradation Checklist​ - This form includes BMP considerations for erosion and sediment controls.

Tier II Frequently Asked Questions

Tier II GIS files: Click here​ to download a zip file containing Tier II stream segments and Tier II watersheds.

Human Trafficking GET HELP

National Human Trafficking Hotline - 24/7 Confidential

1-888-373-7888 233733 More Information on human trafficking in Maryland

Customer Service Promise

The State of Maryland pledges to provide constituents, businesses, customers, and stakeholders with friendly and courteous, timely and responsive, accurate and consistent, accessible and convenient, and truthful and transparent services.

Take Our Survey

Help Stop Fraud in State Government

The Maryland General Assembly’s Office of Legislative Audits operates a toll-free fraud hotline to receive allegations of fraud and/or abuse of State government resources. Information reported to the hotline in the past has helped to eliminate certain fraudulent activities and protect State resources.

More Information