Wetland Mitigation, Volume 2, A Guidebook for Airports (2019)

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60 6.1 Introduction Mitigation projects can vary significantly depending on the type and quantity of impacts to the wetland, as well as the engineering and design elements. This chapter focuses on the plan- ning and engineering/design issues associated with permittee-responsible on-site and off-site restoration, creation, and enhancement. Preservation, which is also an option for permittee- responsible mitigation, is not included in this chapter as it does not involve engineering and/or design, although it may require effort to identify and possibly acquire land for preservation, if not already under airport ownership. The discussion will cover selecting appropriate sites for both on-site and off-site mitigation, acquiring sites (if needed), and long-term management and stewardship. This chapter is not applicable to airports that choose to use an established wetland mitigation bank or participate in an in-lieu-fee program. When developing permittee-responsible mitigation, the following critical factors must be con- sidered during the early planning and design phases: • Operational safety (the potential for creating or increasing wildlife attractants), • Local or regional geology, • Geography, • Hydrology, • Climate, • Soil type, • Historical impacts, and • Land use. A wetland mitigation design must first implement all practicable efforts to avoid and mini- mize wetland impacts, and then, to the extent possible, replace any lost wetland functions and values. The pros and cons of alternative mitigation strategies and their suitability for application to airport projects were discussed in Chapter 4. Mitigation for wetland impacts associated with an airport project is typically addressed in the NEPA process. During the NEPA process, a preferred alternative is analyzed, and the environmental documentation (EIS, EA, or CatEx) that deals with the environmental consequences of the preferred alternative describes the mitigation for wetland impacts. At this stage, the description is conceptual and based on consultation with project sponsors, the FAA, and the regulatory agencies. This usually involves the decision as to whether miti- gation will be provided by wetland banking, payment of in-lieu-fees, or construction of a permittee-responsible (project-specific) wetland mitigation site if initial indications appear there is a feasible alternative for this type of mitigation. Chapter 4 describes these various types of mitigation. C H A P T E R 6 Engineering and Design Issues

Engineering and Design Issues 61 For permittee-responsible mitigation, the mitigation plan should be developed with the assistance of environmental professionals to maximize the chances of hydrologic and eco- logical success. For use of non-airport–owned lands for mitigation, real estate services are also usually required and may become a critical-path effort to secure a site within a time frame that does not compromise project objectives. 6.2 Mitigation Within Separation Distances (On-site) Aviation safety is paramount, and conflicts between wildlife and aviation are well docu- mented. The FAA has identified recommended separation distances in AC 150/5200-33B that consider potential conflicts between wildlife and aircraft operations. Figure 6-1 illustrates the separation distance between the AOA and features that are attractive to hazardous wildlife. Since most wetlands provide habitat attractive to wildlife, the FAA advises aircraft operators to avoid mitigation within these separation distances. Since sepa- ration distances often include land that is outside of the airport property boundary, the FAA promulgated the following policy in AC 150/5200-33B to assist airport operators, devel- opers, and local jurisdictions when considering locating mitigation on or near airports. The policy considers any proposed mitigation within the separation distance as on-site mitigation. (1) Onsite mitigation of wetland functions. The FAA may consider exceptions to locating mitigation activities outside the separations identified in Sections 1-2 through 1-4 if the affected wetlands provide unique ecological functions, such as critical habitat for threatened or endangered species or ground water recharge, which cannot be replicated when moved to a different location. Using existing airport prop- erty is sometimes the only feasible way to achieve the mitigation ratios mandated in regulatory orders and/or settlement agreements with the resource agencies. Conservation easements are an additional means of providing mitigation for project impacts. Typically, the airport operator continues to own the property, and an easement is created stipulating that the property will be maintained as habitat for state or federally listed species. Mitigation must not inhibit the airport operator’s ability to effectively control hazardous wildlife on or near the mitigation site or effectively maintain other aspects of safe airport operations. Enhancing such mitigation areas to attract hazardous wildlife must be avoided. The FAA will review any onsite mitigation proposals to determine compatibility with safe airport operations. A wildlife damage management biolo- gist should evaluate any wetland mitigation projects that are needed to protect unique wetland functions and that must be located in the separation criteria in Sections 1-2 through 1-4 before the mitigation is implemented. A WHMP [Wildlife Hazard Management Plan] should be developed to reduce the wildlife hazards. (FAA 2007, Sec. 2-4, c.1) When mitigation is necessary but cannot comply with FAA’s separation criteria, close coor- dination with multiple agencies is required. Interagency coordination is essential during miti- gation planning and design, as it provides an opportunity to identify and avoid possible design features that could attract potentially hazardous wildlife while fulfilling functional values. Figure 6-2 identifies the many agencies who may need to be consulted. 6.3 Off-site Mitigation or Mitigation Outside Separation Distances Off-site mitigation work, for this guidebook and for consistency with FAA AC 150/5200-33B, is considered any project outside the separation distances identified in FAA AC 150/5200-33B: 5,000 feet for airports limited to piston-powered aircraft, and 10,000 feet for airports serv- ing jets and shown previously in Figure 6-1. The FAA considers ponds, water bodies, and wildlife habitat outside these distances to have minimal potential for wildlife uses hazardous to aircraft.

62 Wetland Mitigation, Volume 2: A Guidebook for Airports Source: FAA Advisory Circular 150/5200-33B, Hazardous Wildlife Attractants On or Near Airports Figure 6-1. FAA-identified separation distances from an AOA.

Engineering and Design Issues 63 6.4 Site Selection and Real Estate Acquisition The elements that usually exert the most control over a mitigation schedule are site selec- tion and real estate acquisition. Timely acquisition is the key to moving forward with any mitigation site outside the current airport boundary. Resource agencies sometimes iden- tify sites that could be eligible to meet this need in their watershed planning documents. These sites often have been prioritized for further study. The United States Geological Survey (USGS) categorizes watersheds with a hydrologic unit code (HUC). Mitigation within the same USGS HUC-8 level watershed is almost always preferred by the agencies. HUC-8 maps the subbasin level and is analogous to medium-sized river basins (USEPA 2018). The average size of such watersheds is about 700 square miles, and there are approximately 2,200 HUC-8 watersheds in the United States. Other local or regional criteria, such as proximity to a criti- cal habitat for migratory birds, may arise via the input of federal, state, and local regulators. Candidate mitigation sites for restoration and enhancement must have former wetland areas that have been converted by filling or construction of drainage features that have affected wetland hydrology to the extent that wetland functions are substan- tially absent. As described in Chapter 4, “Restoration involves returning historic functions to a degraded wetland site. Enhancement involves improving the functions of an existing aquatic resource. Enhancement does not result in an increase in wetland area but results in a gain of a specific function or functions. Establishment/creation involves the development of a new aquatic resource in an upland area, resulting in both a gain in wetland area and functions.” Some airports have landholdings that meet separation distances to allow off-site mitigation with land acquisition. Regardless, a can- didate site study that evaluates the status and wetland restoration or creation potential of each site is almost always necessary at the NEPA-documentation stage if permittee-responsible mitigation is determined to be necessary. Such studies assure the sponsor, the FAA, and regulatory agencies that the potential wetland yield of any site is sufficient for project purposes. Figure 6-2. Coordinating agencies for on-site mitigation/ mitigation within separation distances. As described in Chapter 4, “Restoration involves returning historic functions to a degraded wetland site. Enhancement involves improving the functions of an existing aquatic resource. Enhancement does not result in an increase in wetland area, but results in a gain of a specific function or functions. Establishment/ creation involves the development of a new aquatic resource in an upland area, resulting in both a gain in wetland area and functions.”

64 Wetland Mitigation, Volume 2: A Guidebook for Airports Water rights are important to consider in parts of the country, particularly the West and Southwest. If proposed mitigation requires use of water (including storing, exposing ground- water table, etc.) in an area with water rights, implementing mitigation may require conveyance of water rights from the original owner if available. The need to consider water rights is critical to determine early in the site selection process. Another element to consider in site selection is how accessible the site is for construction, monitoring, and maintenance. Both construction (temporary) and long-term easements may need to be considered as part of the land acquisition. These may require coordinating with pri- vate land owners, as well as road and rail. The agencies nearly always prefer in-kind replacement of wetland impacts to assure that lost wetland functions are adequately replaced. This always places a premium on securing a site with a landscape position and hydric soil type comparable to that of the impacted wetlands. If other types of wetlands are provided, perhaps because of the ecological characteristics of the available real estate, the permitting agencies may increase wetland mitigation ratios. This factors into the size of mitigation site required. 6.4.1 Site Investigation Once a project-specific mitigation site is secured, a much more detailed site investigation is necessary to support project design and construction. If the site was not included and evaluated in the NEPA document for the project, the more detailed investigation also verifies regulatory com- pliance. Archaeological and historic investigations are needed to comply with Section 106 of the NHPA. The presence or absence of hazardous materials must be assessed under the Federal Resource Conservation and Recovery Act. Both investigations require the services of qualified spe- cialists to assure receiving agencies that they were performed properly. Other site investigations help determine the ecological condition and potential wetland yield of the site under various restoration, enhance- ment, or creation scenarios. Such studies should always have the input and overall supervision of qualified specialists such as a certified pro- fessional wetland scientist (PWS); in fact, some states require these specialized services as a condition of any wetland mitigation project. These investigations include a topographic survey. The survey should tie to a known benchmark with set horizontal coordinates and verti- cal elevation. Since restoration sites typically have very low relief, such surveys must contain great enough detail to provide the level of contour to inform the design. Wetland delineation is usually needed to verify remnant wetland bound- aries as well as potential yield of the site based on hydric soil coverage. Soil borings may also be needed to confirm soil profiles, if fill or modern alluvium is to be removed to re-establish wetland hydrology, or if the groundwater contribution to post-restoration hydrology is to be determined. Ecological assessments of overall site condition, including the presence of problem- atic invasive species, are also needed. Often, historical aerial photographs can help determine the nature and extent of modern impacts and the means to reverse them. 6.4.2 Hydrologic Studies Hydrologic data collection and/or studies of some level are generally necessary. These studies establish how effective restoration and creation efforts may be and measure in what amounts Types of possible necessary site investigations • Section 106 • Archaeological • Historic • Hazardous materials • Ecological condition • Topographic survey • Wetland delineation Qualified Specialists for Investigations • Archaeologist • Cultural Resources Specialist • Professional Wetland Scientist • Registered Land Surveyor

Engineering and Design Issues 65 local water sources contribute to the hydrology of a site, also critical if creation is being considered. These local sources range from run- off to over-bank flooding from nearby streams to groundwater, etc. Floods from streams or waterways can be modelled using accepted one- dimensional models such as HEC-RAS, while runoff contributions can be derived using any number of TR55-based watershed mod- els, with off-site topography provided by USGS mapping. Often a simple, uncalibrated seasonal water budget model may be sufficient to demonstrate the hydrologic feasibility of replacement wetlands. If the groundwater contributions are to be a significant portion of post- restoration hydrology, perhaps because of the existence of tile drainage systems, a full growing season of water table monitoring with a well net- work may be necessary. More in-depth analyses of groundwater effects are only useful if a model is fully calibrated to field conditions through extensive data collection. 6.4.3 Other Considerations Other factors affect the functional performance and viability of a mitigation site. Environmental corridor features, the quality and extent of remnant habitat (including uplands), and options for long-term stewardship must be considered as part of the effort. Options for long- term stewardship are especially important for sponsors that do not want to retain ownership and responsibility for a site past the permit compliance period (usually 5 years). When sites are adjacent to resource agency land holdings, especially those that plug gaps in wildlife habitat, ultimately accepting the title can be very attractive for those agencies. Most public conservation areas have long-term acquisition boundaries included within their long-range planning documents. Any drained wetland areas within these boundaries could be priority mitigation sites. Non-profit environmental organizations, especially federally recog- nized land trusts, are also potential long-term owners. The national Land Trust Alliance keeps a current list of land trusts active in each state. Regardless of the ultimate owner, each wetland mitigation site will have to be protected in perpetuity by a permanent Conservation Easement or restriction that runs with the land and is irrevocable. State and federal wetland regulatory agencies have model easements that can be used outright or tailored to the special circumstances of each site. Such easements are usually placed after all wetland mitigation performance standards have been met and there is no need for further construction or other disturbance. 6.5 Preliminary Design Field data collection, such as topographic survey, well, and boring data, and modeling of existing hydrologic conditions should precede preliminary design of the mitigation site. After data collection and modeling is finished, preliminary designs are usually completed in col- laboration with the agencies. At this stage, project wetland losses (impacts that are being mitigated for) help to determine overall wetland habitat objectives. These objectives allow the habitat potential of the mitigation site and restoration alternatives to be examined further to advance the mitigation plan. At this stage, the design is advanced by analyzing two or more alternatives for restoration or creation of wetland hydrology. Options may include reversing historic impacts through the removal of tile systems, filling of ditches, levee breaches, and the removal of historic fill or Professional Wetland Scientist The Society of Wetland Scientists (SWS) has a professional certification program. The SWS website states, “Certification signifies that the academic and work experience of a Professional Wetland Scientist (PWS) meets the standards expected by his or her peers of a practic- ing wetland professional and provides acknowledgment to his or her peers of adherence to standards of professional ethics with regard to the conduct and practice of wetland science. Certification will enhance recognition of wetland science within other disciplines, especially in multi-disciplinary work environments.” Search by state to find a PWS in your project area at http://www.wetlandcert.org/search.html.

66 Wetland Mitigation, Volume 2: A Guidebook for Airports sediment. Generally, the long-term viability of the site is greater if the use of artificial structures that produce backwater effects such as dikes, impoundment berms, and flash board weirs are avoided. Such structures nearly always increase construction and maintenance costs and impose artificially high water levels on hydric soil areas. They should be used only if no other apparent means of restoration is available, or if select wildlife functions, such as colonial waterbird habitat, is an objective of the permit. The outcome of preliminary design should be a statement of wetland and upland habitat objectives and measurable performance standards for wetland hydrology and wetland and upland vegetation, a construction plan showing existing and proposed grades, a planting plan, and any special provisions needed, including any native seed mixes or plantings. Special provi- sions may also include procedural measures and equipment requirements, such as equipment cleaning to prevent introduction of invasive species and the use of low ground pressure (LGP) earth movers, wildflower seed drills, or other specialized equipment and supplies. A sequence of general notes or plan of prosecution and progress, with milestone dates and the overall project timeline, is also needed. This plan should be presented for agency review at or before project construction plans reach a comparable level of completeness. These plans will typically be required as part of the wetland permit application. During preliminary design preliminary cost estimates are also prepared. During the design phase, the project proponent also must consider construction phasing, bid packages, and how construction activities will coincide with funding programs, while minimiz- ing impacts to airport operations and the environment. The project team should also evaluate procurement methods during this phase. The mitigation plan is submitted with the wetland permit application. The extent of mitiga- tion design required for the permit application varies with the mitigation complexity, but suffi- ciently detailed narrative, analysis, and design needs to be provided to clearly demonstrate how it will function and what its objectives are. The wetland permit application can be submitted once sufficient project design of the airport project has been completed and has been developed to a degree that regulators can agree it will meet mitigation requirements as proposed. The time it takes to receive wetland permits varies depending on its type, regulatory staffing, and other issues. Working with regulators during the entire process is critical to the timely processing of the wetland mitigation approvals. 6.6 Final Design Only after agency review and approval of the preliminary plan should final construction plans with quantities and construction cost estimates be developed. The final plan should also include an erosion control plan and any necessary monitoring stations or project- dedicated installations for monitoring permit compliance. Additionally, mitigation site design may require special provisions to supplement or modify the standard specifications to ensure the construction is completed to meet project objectives. Bid documents that address the unique features associated with mitigation projects, such as plantings, are key to successful mitigation projects. The final plan should be supplemented with a monitoring plan that includes seasonal data col- lection measures designed to show yearly progress toward attainment of the wetland permit per- formance standards arrived at during preliminary design. The specific data collection metrics, time frames, reporting standards, formats, and dates should all be included in the monitoring plan. Because the success of a mitigation project is dependent on hydrology during its establish- ment period, plans should address how this will be provided.

Engineering and Design Issues 67 6.7 Construction Wetland mitigation projects require qualified professionals during both design and construc- tion. On-site airport representatives must have a clear understanding of the mitigation design and ultimate function. Construction supervision and engineering must include a project scientist or PWS, ideally the one who determined project objectives and performance standards and supervised or was otherwise involved in the detailed design, the planting plan, and the formulation of any special provisions or procedures. Inspection and approval of all native plant materials by such personnel aids in success, as is their involvement in review and approval of final grades, topsoil materials, and performance of all planting and seeding operations. Some states require the involvement of a certified PWS as a condition of any wetland mitigation project. Care should be taken in the selection of the contractors to make sure they are qualified to perform the work. Sometimes mitigation projects are bid separately from an airport development project, which provides an opportunity for the airport operator to select a contractor with greater expertise in mitigation or ecological restoration to bid. 6.8 Monitoring The wetland permit will include monitoring requirements to confirm that the mitigation project meets performance objectives established. Typically, this period is 5 years or can be less if performance objectives are met sooner. Monitoring specifics are tailored to the type of mitiga- tion and developed in coordination with resource agencies. It can consist of monitoring wells, vegetative transects, and other field data collection. An annual report is typically submitted to regulatory agencies for their review. 6.9 Summary Chapter 4 presented the different types of mitigation options: banking, in-lieu-fee, and per- mittee-responsible. This chapter focused on the engineering and design elements of permit- tee-responsible mitigation. The chief difference is that implementation of the first two types is more an administrative effort with regulatory agencies and wetland administrators. Banking and in-lieu-fee do not have an engineering and design component besides that associated with sequencing (avoid, minimize, and mitigate) to determine the wetland impact during the project design itself. As explained in Chapter 4, permittee-responsible site-specific mitigation is typi- cally only pursued if other options aren’t available, or there is a specific resource that requires specific mitigation be developed. This chapter identified the engineering and design considerations for mitigation site selection, which include up-front field investigations, such as hydrologic studies and wetland delinea- tions. A key element to a successful mitigation project is finding a suitable mitigation site. This can be a considerable undertaking in terms of effort and time. The chapter explained that it is important to determine early in the site selection process how the site will be managed long- term (after post-project monitoring is complete) as agencies will require documentation of this as part of the wetland permitting process. In this chapter, an overview of the design process from site selection through post-project construction monitoring was presented, emphasizing that wetland mitigation design varies considerably by site conditions and requires the partici- pation of wetland professionals throughout the process, from inception and planning through monitoring.