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Permittee-Responsible Mitigation

Photo of ducks in a wetland


Mitigation Overview: What is Wetland Mitigation?

When a transportation project is planned,a wetland biologist must identify, delineate, and assess all wetlands that could be impacted by the project, before it progresses. The wetland biologist then prepares a Wetland and Stream Assessment Report (doc 457 kb). This report guides project designers in their efforts to avoid and/or minimize impacts to wetlands along the project corridor.

If the project will unavoidably and adversely impact wetland resources, WSDOT is required under federal, state, and local laws to provide mitigation for those impacts. The mitigation sequence includes: avoidance, minimization, restoration, preservation, and compensation.

Why do we mitigate?

Regulations guiding wetland protection include: Section 401 and Section 404 of the Clean Water Act, the Governor's Executive Orders 89-10 & 90-04, and local Critical Areas Ordinances. More information on wetland-specific policy can be found at the WSDOT Wetland Mitigation Toolbox WebPage.

Under the state's Growth Management Act, local governments are required to use Best Available Science when reviewing and revising their policies and regulations on wetlands.

What are the different types of wetland mitigation?

WSDOT staff consider many mitigation options to deliver projects. Permittee-responsible mitigation is done concurrently with project impacts, and may include on-site, off-site, in-kind, out-of-kind mitigation, or any combination of these.

WSDOT's Mitigation Options Webpage describes other alternatives including wetland banking, out-of-kind or structural mitigation, in-lieu fee, and other nontraditional compensatory mitigation approaches. These options employ methods that can result in lowered costs and increased environmental benefits.

Regulations often focus on compensatory mitigation, though as illustrated on the Mitigation Sequence page, it is the final step in the process. Compensatory wetland mitigation types (pdf 27 kb) include: wetland establishment, wetland restoration (which includes re-establishment and rehabilitation), wetland enhancement, and wetland preservation (pdf 229 kb).

Project Impacts: How does the project negatively affect wetlands?

WSDOT is required by federal and state law and local Critical Areas Ordinances (CAO) to provide adequate mitigation for impacts to wetlands. Impact assessment is the first step in the mitigation process and incorrect impact assessment can result in inappropriate, inadequate, or excessive mitigation.

The final Federal Rule on Compensatory Mitigation for Losses of Aquatic Resources (2008) (pdf 567 kb), developed by the USACE and the EPA, clarifies how to provide compensatory mitigation for wetland impacts.

The WSDOT Mitigation Process (pdf 131 kb) provides an overview of the wetland mitigation process. Please contact the region biologist to identify any regional or project specific variations to this process.

The WSDOT Wetland Mitigation Timeline (pdf 64 kb) provides a timeframe for the entire mitigation process for typical projects. Please contact the region biologist to identify any regional or project specific variations to this timeline.

The Generic Scope of Work for Mitigation Consultant Contracts (pdf 84 kb) contains the WSDOT template for developing consultant contracts that involve mitigation work. Please contact the region biologist to identify any regional or project specific variations to this scope of work.

Wetland and Buffer Impact Characterization

For permitting purposes:

  • Wetland impacts are characterized as permanent, temporary, or indirect.
  • Buffer impacts are characterized as permanent or temporary.

Wetland and Buffer Impact Calculation

The WSDOT Wetland and Buffer Impact Assessment Guidance (pdf 465 kb) describes the process WSDOT uses to determine wetland and buffer impacts. This guidance provides a process and checklist for impact assessment.

Mitigation Requirements and Ratios: How much mitigation is needed?


Wetland and Buffer Mitigation Calculation

Federal, state, and local agencies may have different mitigation requirements and ratios. WSDOT satisfies the most stringent level of these regulatory requirements.

WSDOT Mitigation Area Calculation Guidance (pdf 70 kb) provides information on determining the acreage required to mitigate for wetland and buffer impacts, using the information below.

Mitigation Ratios: The Department of Ecology's guidance, Wetland Mitigation in Washington State: Part 1 - Agency Policies and Guidance, includes proposed mitigation ratios for Western and Eastern Washington, shown in the links below. These mitigation ratios only apply to projects in Washington that do not alter the hydrogeomorphic (HGM) setting of the site used for mitigation.

Buffer Width: The Department of Ecology's guidance also provides information on widths of buffers in Western (pdf 180 kb) and Eastern (pdf 176 kb) Washington. In addition, buffer width recommendations can be found in local Critical Areas Ordinances (CAO), and should be included in all mitigation design packages.

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Wetland Mitigation Site Selection: Which is the best mitigation site?

The first step in the site selection process is the calculation of the amount of mitigation area required and identification of the wetland functions to be provided. Mitigation sites must provide enough acreage of the correct wetland type to replace lost wetland functions. The mitigation site must also possess appropriate buffers as identified by the local CAO.

Where can the mitigation site be located?

  • Potential properties must typically be in the same basin or sub-basin as the impacted wetlands, though it varies by jurisdiction. Refer to the local CAO to determine their recommendations. If no properties are available within the area, local agencies may approve expanding the site search to the requested area.
  • Refer to WSDOT Wetlands Guidance on Cultural Resources (pdf 9 kb) to minimize the risk of potential problems with cultural resources sites. This process identifies recorded potential cultural resources adjacent to or within the proposed mitigation site, and evaluates the probability of encountering undiscovered cultural resources during site development.
  • Public lands can be used for wetland mitigation, however a Section 4(f) Evaluation may be required. Refer to the Environmental Manual.

How does WSDOT select a mitigation site?

The WSDOT Preliminary Wetland Mitigation Site Selection Process (pdf 20 kb) helps determine which potential properties are suitable for a mitigation site. The preliminary process is modified to comply with RCW 47.01.305 if potentially suitable properties include protected agricultural lands.

Using this guidance, a list of properties can be assembled. Sites that clearly posses the appropriate characteristics and are available for sale can then be evaluated using:

Following site evaluation, A Site Feasibility Memo/Report is usually drafted discussing the attributes, amenities, risks, and relative construction costs of the evaluated sites. Once a mitigation site has been selected, the property acquisition process may be initiated.

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Permitting & Reporting: What is the regulatory permit application process?

Permits must be secured before any existing wetland can be impacted. Discussions of the proposed wetland impacts and mitigation begin early in the permitting process. At the Environmental Impact Statement (EIS), Environmental Assessment (EA), or Documented Categorical Exclusion (DCE) stage, some form of Conceptual Wetland and Stream Mitigation Report is prepared for submittal.

Environmental Impact Statement Reports

  • Evaluation of wetland impacts
  • NEPA/SEPA Mitigation Memo

An evaluation of wetland impacts is required for EIS, EA and DCE projects. The evaluation provides a summary of potential wetland impacts for each alternative being considered. This evaluation is the basis for developing the proposed conceptual mitigation.

The NEPA/SEPA Mitigation Memorandum (38 kb) is used to identify potential wetland impacts and required wetland mitigation. This report provides enough information for WSDOT and resource agency personnel to agree upon or reject a mitigation proposal before a detailed analysis is done. The NEPA/SEPA Mitigation Memorandum is used either as an internal WSDOT document, or to coordinate with other agencies at an early stage of project development.

    Wetland and Stream Mitigation Reports for Project Permit Submittal


    Report Preparation

    WSDOT must first obtain permits from regulatory agencies before constructing a project that impacts wetlands. WSDOT must collect enough data to show the proposed mitigation site design will be successful and will provide the required wetland acreage and functions. This information is submitted to the review agencies in a Wetland and Stream Mitigation Report.

    Hydrologic, vegetation, soils, and survey data must be collected to complete the mitigation site design. Hydrologic data collection may require the installation of groundwater piezometers.

    Mitigation Site Wetland Technical Memo must be prepared if wetlands are present on the mitigation site. The Memo requires data from a wetland delineation and rating. See Example 1 (pdf 3.5 mb) and Example 2 (pdf 61 kb) for guidance.

    The WSDOT Wetland and Stream Mitigation Report Template (doc 1.2 mb) and Example Wetland and Stream Mitigation Report provides the basis for the three drafts of a Wetland and Stream Mitigation Report.

    • Conceptual Wetland (and Stream) Mitigation Report
    • Draft Wetland and Stream Mitigation Report
    • Final Wetland and Stream Mitigation Report

    The Conceptual Wetland (and Stream) Mitigation Report is used when a mitigation site has been selected, but there isn't enough site data to complete a detailed wetland mitigation site design. This report includes information quantifying project impacts, wetland impact avoidance and minimization, and general conceptual information on the mitigation site design. Once sufficient site data has been collected, a Draft Wetland and Stream Mitigation Report can be prepared.

    The Draft Wetland and Stream Mitigation Report is submitted with permit applications. It includes information on project impacts, wetland impact avoidance and minimization, compensatory mitigation, detailed mitigation site design, and performance criteria.

    • Use WSDOT's Mitigation Design Evaluation (pdf 35 kb) to determine if the design makes sense and contains all the information needed for agency review.
    • After WSDOT internal review and comment, regulatory and resource agency staff review the project proposal and the Draft Wetland and Stream Mitigation Report. The Draft Wetland and Stream Mitigation Report is submitted to all parties concerned.
    • Regulatory agencies should provide written conditional approval of the Draft Wetland and Stream Mitigation Report before work proceeds any further. Coordination and clear communication at this stage speed up the permit review process. An on-site review of the project and discussion of proposed wetland mitigation is also advisable to determine if the design makes sense and contains all the information needed for agency review.

    The Final Wetland and Stream Mitigation Report is prepared after incorporating negotiated conditions and receiving written conditional approval of the Draft Wetland and Stream Mitigation Report from review agencies. After the completed Final Wetland Mitigation Report is submitted, permits are received from regulatory agencies.

    Wildlife Habitat Structures

    WSDOT Guidance on Wildlife Habitat Structures in Mitigation Sites (pdf 1.3 mb) provides assistance on habitat structure type, selection, quantity and location for mitigation sites in Western Washington with suggestions for experimental designs based on best professional judgment.

    Performance Criteria

    WSDOT Performance Criteria Guidance includes the following guidance on specific performance criteria:

    Plans Specifications & Estimates Mitigation Plan

    The design plans submitted with the Final Wetland and Stream Mitigation Report provide sufficient detail for permitting. After permits are received, the design plans are reviewed internally; put into Plans, Specifications, and Estimates format; refined 20% more to be complete for contractual purposes. The PS&E plans will reflect WSDOT's environmental commitments and comply with permitted plans.

    Plan sheets for wetland mitigation sites may include but are not limited to the following:

    • Temporary Erosion and Sedimentation Control (TESC);
    • Clearing and Grubbing; Grading Plan; Planting Plan;
    • Plant Materials List; Planting Details; and
    • Habitat Structures Details.