Watershed Approach to Mitigating Hydrologic Impacts of Transportation Projects: Conduct of Research Report (2022)

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124 Chapter 6. Stormwater Banking Opportunities This chapter explores opportunities that stormwater banking may offer to State DOTs in the context of a watershed approach to mitigation of transportation stormwater quantity impacts. First, the potential for using wetland mitigation banking as a potential model for stormwater banking is described. The next section describes the regulatory environment for banking and its compatibility with the stormwater mitigation banking concept. These two sections lead into a description of a model for stormwater banking using the 12 components required for wetland mitigation banking. Two different models of stormwater banking are considered: • A mitigation bank with the combined purpose of providing both wetland mitigation and stormwater mitigation by providing credits for both goals. (When feasible, this model could provide cost savings because one facility is provided rather than two.) • A single objective stormwater mitigation bank that could feature wetlands, forest restoration, stream restoration, or other landscape modifications through which stormwater credits are established. Finally, a summary of the topic concludes the chapter. Further investigation of models for stormwater mitigation banking is recommended but is beyond the scope of this research. 6.1. Wetland Banking as a Potential Model for Stormwater Banking In 2008 the USACE and USEPA published the Compensatory Mitigation for Losses of Aquatic Resources; Final Rule (U.S. Department of Defense and USEPA 2008, at 33 CFR Parts 325 and 332 and 40 CFR Part 230). This rule expanded the Section 404(b)(1) guidelines to include comprehensive standards for compensatory mitigation and established a standardized mitigation rule to regulate wetland compensatory mitigation. To offset unavoidable impacts to wetlands and other waters of the U.S., options for compensatory wetland mitigation are tiered with established permitted wetland mitigation banks being the preferred option when available in the watershed. According to the USACE Regulatory In-Lieu Fee and Bank Tracking System (RIBITS), there are over 1,800 approved mitigation banks as of 2019 (USACE 2019). Mitigation banks have been established by a wide range of entities including local and state governments, nongovernmental agencies, private individuals, and for-profit corporations. Each permitted wetland mitigation bank has a defined “service area” in which wetland functional losses (impacts) can be offset. Service areas might be coincident with a watershed defined in one or more of the ways described in Section 4.1. Wetland mitigation bank credits can be derived from a wide range of activities, including wetland habitat preservation, wetland enhancement, and/ or wetland creation. The current wetland mitigation banking program is framed by an assortment of federal, state, and local government wetland regulatory programs that require replacement of wetland functions lost by development impacts. The evaluation of wetland functions, for both impact and mitigation, is undertaken through many different functional assessment tools throughout the U.S. These assessment tools generally provide for an evaluation of how wetland habitat types support fish and wildlife utilization. The focus on habitat is driven by regulatory requirements such as the USACE mitigation rule that states: “restoration and establishment entail manipulation of physical, biological, and chemical characteristics of a compensatory mitigation site to produce a desired

125 habitat type.” However, other ecological co-benefits may occur including those listed in Table 5.3. Distinct from wetland mitigation regulations, stormwater regulations at the federal, state, and local government levels are designed to prevent adverse hydrologic and pollutant concentration impacts associated with runoff generated from development. Regulations that identify and limit stormwater hydrologic impacts (peak and volume) are largely enforced at the local and regional level. These regulations frequently require compensatory storage of runoff from new impervious surfaces to manage or prevent increases in off-site stormwater peaks and/or volumes. Land scarcity and development constraints in urban areas have reduced the ability to provide on- site compensatory stormwater storage in existing transportation corridors. To provide solutions to compensatory storage challenges, local government entities across the U.S. that operate NPDES permitted stormwater systems are beginning to explore ways to develop off-site stormwater storage banking programs. Using wetland mitigation banking as a model, stormwater bank credits, using ratios or scoring mechanisms, could be developed and applied to stormwater BMPs, as well as to landscape mitigation techniques such as forest or stream restoration. Some of the more common “green” stormwater quantity landscape modifications used in transportation projects include rain gardens, floodplain enhancement and restoration, vegetated swales, infiltration basins, wetland treatment/storage areas, and uplands buffer/green space vegetative enhancement. Installation of vegetation in stormwater storage and conveyance features provides several benefits including nutrient uptake, flow velocity reduction, and runoff reduction through increased evapotranspiration. Because some of these stormwater landscape modification BMPs appear similar to activities routinely undertaken in wetland mitigation banks wetland mitigation banking credits may be a model for stormwater banking credits. While the goals of stormwater mitigation banks and wetland habitat mitigation banks may be different, there are some similarities between the two that could make them compatible. Wetlands and surface water features, whether natural or man-made, store and release water over the surface or through infiltration. Currently, most rules and criteria along with the regulatory agencies that administer them with respect to wetland and stormwater activities are not highly collaborative. Coordination with federal, state, and local regulatory partners will be required to combine the two types of mitigation banks and establish a mechanism for combined stormwater and wetland habitat bank credits. One approach for coordinating stormwater banking between agencies has been the implementation of a Memorandum of Agreement (MOA) between regulatory agencies. For example, in 1996 the Delaware Department of Transportation (DelDOT) formalized an MOA with the Delaware Department of Natural Resources and Environmental Control (DNREC). This MOA was for stormwater banking credits only, but it established criteria that allowed the DelDOT to consider regional stormwater solutions instead of on-site solutions outlined in their State Statutes (DelDOT MOA 1996). One of the surface water quality control measures allowed in their inter-agency MOA included creation of wetlands.

126 6.2. Compatibility of Stormwater Banking with Existing Regulations Most transportation projects undergo a range of coordinated federal reviews pursuant to the NEPA which are outlined in the FHWA 2015 Redbook. These reviews are designed to ensure project compliance with federal laws including the Clean Water Act (CWA), Title 33 of the U.S. Code (Bridges), the Endangered Species Act (ESA), the Magnuson-Stevens Act, and Section 4(4) of the USDOT Act (Parks and Recreational Lands). States have a role within the federal review process under Section 401 of the CWA providing the authority to certify compliance with existing water quality requirements or to waive the need for certification. Similarly, under the Coastal Zone Management Act, coastal states may adopt, develop, and implement federally-approved coastal management programs to achieve wise use of land and water resources. Within this regulatory context, there are several key regulatory differences between stormwater banking for hydrologic benefits and mitigation banking for wetland habitat benefits. While the level of fish and wildlife support for wetland mitigation banks is tied to habitat values, this evaluation methodology does not overlap with criteria used to evaluate the benefits which are intended to be provided by stormwater mitigation banks. Due to existing wetland regulations, it is difficult to use existing wetlands for stormwater quality or quantity treatment. A primary objective of the CWA is to restore and maintain the chemical, physical and biological integrity of the Nation’s waters. Federal regulations state that wetland mitigation bank performance standards may be based on variables or measures of functional capacity described in functional assessment methodologies, measurements of hydrology or other aquatic resource characteristics, and/or comparisons to reference aquatic resources of similar type and landscape position (33 CFR Parts 325 and 332, 40 CFR Part 230). While many wetland mitigation bank performance standard variables include monitoring for healthy hydrologic regimes which could translate into stormwater mitigation credit variables for stage and volume, assessing pollutant loads / concentrations is generally not considered in existing wetland functional assessment methodologies, and therefore would not be a compatible benefit to both banking mechanisms. For the most part, wetland regulatory programs discourage the use of existing wetlands for stormwater storage or treatment because of the possibility of adversely affecting the wetland hydrology or increasing pollutant loads. Pre-treatment of stormwater flows before entering a wetland may partially address this concern so that the wetland mitigation site does not become a contaminant sink. With or without pre-treatment, constructed and restored wetlands could potentially be used for both wetland habitat and stormwater mitigation if conditions are favorable. There are two scenarios under which a combined wetland mitigation and stormwater mitigation bank could be established within the current regulatory framework. First, if a wetland created for habitat mitigation purposes receives stormwater runoff from a transportation project assignment of stormwater credits could potentially be negotiated for the stormwater storage capacity in the created wetland. Second, and somewhat less likely from a regulatory standpoint, would be to derive wetland habitat mitigation credits for wetlands created for stormwater management. In this scenario, inter-agency coordination would be required for dual credit assignment as wetland habitat mitigation management and maintenance techniques are tied to established performance standards that must be met to ensure credit releases. Regular site maintenance and often perpetual monitoring are regularly required by resource agencies to ensure that performance standards are documented and met.

127 Wetland habitat mitigation bank credits are tied to wildlife utilization and ecological functions. Qualitative and quantitative measurements that evaluate these functions usually require the collection of vegetation cover, hydroperiod, and/or wildlife utilization data. Wetland mitigation monitoring is usually carried out during a multi-year process to determine success of habitat establishment. Typical wetland mitigation bank monitoring includes the establishment of fixed transects within each wetland, and quantitative vegetative surveys of the fixed transects for up to 5 years followed by annual qualitative surveys that may be required in perpetuity Stormwater storage and treatment features generally do not require vegetative or wildlife monitoring to determine their success or effectiveness. One exception is vegetated littoral shelves that can be required for nutrient uptake. Frequently, the only requirement for littoral shelves is that vegetation not be removed. According to some case studies of stormwater banking two different types of data have been used to determine stormwater banking credit availability (Cappiella et al. 2014). One is the use of nutrient loading data for watersheds that is evaluated to determine load reduction estimates for TMDL credits. The other is data collected on potential volume calculations for BMPs and other storage mechanisms to assign stormwater volume credits as part of a bank. 6.3. A Framework for Stormwater Mitigation Banking Stormwater mitigation banking is a largely untested concept. However, the national experience with wetland mitigation banking provides insight into possible frameworks for either combining stormwater mitigation and wetland mitigation into a single banking concept or developing single objective stormwater mitigation banks based on a model from wetland mitigation banks. For the combined approach where stormwater mitigation banks also provide joint compensatory wetland mitigation, the jurisdictional regulatory requirements of the U.S. Environmental Protection Agency (USEPA) and USACE must be maintained unless there are changes in statutes or regulations. Many local and state regulatory agencies have additional wetland mitigation banking regulatory requirements making it more difficult to create a national framework for a combined stormwater/wetland mitigation banking approach. Another challenge for a combined approach is that federal regulations define waters of the U.S. and stormwater-related facilities differently. For example, federal regulations explicitly consider traditional stormwater features (e.g., detention ponds) and GI practices (e.g., bioretention facilities) distinct from waters of the U.S. by exempting such waters from regulatory requirements for waters of the U.S. Similarly, 33CFR Part 328 states that “Waste treatment systems, including treatment ponds or lagoons designed to meet the requirements of CWA (other than cooling ponds as defined in 40 CFR 423.11(m) are not waters of the United States.” For the single objective approach where stormwater mitigation banks are created for the sole purpose of banking and trading credits there is no national, state, or regional framework. A single objective stormwater mitigation bank could take several landscape forms including wetlands, forestlands, stream restoration, and uplands. Significant effort would be needed to create a framework, but there are few regulatory or statutory barriers. Although wetland mitigation would not be part of the purpose of a single objective stormwater mitigation bank, the approach to wetland mitigation banking can provide a template.

128 The 2008 Compensatory Mitigation for Losses of Aquatic Resources; Final Rule (U.S. Department of Defense and USEPA 2008, at 33 CFR Parts 325 and 332 and 40 CFR Part 230) expanded the Section 404(b)(1) Guidelines contains 12 required components for proposed compensatory wetland mitigation plans including proposed wetland mitigation banks. These required components are summarized in the following sections regarding the applicability and challenges associated with establishing a combined stormwater/wetland mitigation bank. An important challenge is that adding functionality for stormwater considerations may diminish functionality for wetland banking credits. The following sections also include observations regarding use of the 12 required components for wetland mitigation banking as a framework for a single objective stormwater mitigation bank. Differences between the goals, objectives, and constraints of wetland mitigation and stormwater mitigation banking are highlighted. Each section begins with a statement of the required component from the 2008 wetland mitigation rule. 6.3.1. Objectives “A description of the resource type(s) and amount(s) that will be provided, the method of compensation (restoration, establishment, preservation etc.), and how the anticipated functions of the mitigation project will address watershed needs.” The objectives of a stormwater mitigation bank diverge from a wetland habitat mitigation bank in several areas. The objectives of a wetland mitigation bank contain specific, measurable outcomes tied into the overall goal of improving fish and wildlife habitat use/connectivity and the overall integrity of the ecological communities within a designated watershed. In a stormwater mitigation bank, the primary objectives would likely be to provide storage capacity, attenuation, and/or water quality treatment within the watershed. While it is anticipated that wetland mitigation banks can provide storage and treatment functions, these are usually not quantified or stated goals of wetland mitigation banks. One mutual aspect of both wetland and stormwater banks is that their credit assignments will both be tied to the service areas in which they are located. A single objective stormwater mitigation banking program would have fewer constraints because there would not be a requirement to measure and track ecological outcomes that would be required in a wetland mitigation bank. 6.3.2. Site Selection “A description of the factors considered during the site selection process. This should include consideration of watershed needs, on-site alternatives where applicable, and practicability of accomplishing ecologically self-sustaining aquatic resource restoration, establishment, enhancement, and/or preservation at the mitigation project site.” Selection of a wetland mitigation bank site involves assessment of wildlife functions, which usually benefits from large-scale corridor connectivity and greater distances from development. These factors might not be specific requirements to provide for stormwater mitigation banking and could be detrimental when factoring in construction, maintenance, and infrastructure costs in situations where large regional stormwater facilities are considered. Alternative, low intensity stormwater mitigation landscape modifications, such as reforestation and wetland creation, could benefit from these site selection criteria but might not be reliant on them for success.

129 The site selection process for a single objective stormwater mitigation bank program should be less complex than a combined approach because accomplishing an ecologically self-sustaining aquatic resource is not a critical consideration for defining success. A single objective stormwater mitigation bank program may also benefit from additional site selection flexibility if ecological criteria are not applicable. It is likely that more urban and developed sites could be considered to provide storage and/or attenuation functions. From an ecological perspective, sites such as these would not be practical or desirable for establishing ecologically self-sustaining aquatic resources required for wetland mitigation. 6.3.3. Site Protection Instrument “A description of the legal arrangements and instrument including site ownership, that will be used to ensure the long-term protection of the mitigation project site.” Stormwater management infrastructure can require intensive periodic maintenance, such as dredging to remove silt or contaminants, to ensure operation of the system in accordance with engineering design goals. Stormwater management facilities may also require frequent vegetation removal to prevent clogging and maintain permitted storage volume or flows rates. Landscape approaches to stormwater management would likely require less maintenance because of their reliance on natural processes. Wetland mitigation banks require long-term protection through mechanisms such as conservation easements, which generally prohibit disturbances, particularly to vegetative communities. While it may be possible to find an overlapping protection measure that satisfies the goals of both types of mitigation banks, additional wetland regulatory agency coordination would likely be needed. Maintenance of the stormwater bank infrastructure would need to be accomplished in a manner that is not detrimental to the protection of long-term ecological functions of a wetland mitigation bank. A single objective stormwater mitigation bank program will also require legal arrangements that address ownership and operation of bank sites. Without the need to ensure long-term protection of ecological functions of a wetland mitigation site, protection mechanism complexity would likely be reduced for stormwater banks. Many local and state regulatory programs have requirements for stormwater management facility operation, including periodic inspection and operational detail review. 6.3.4. Baseline Information “A description of the ecological characteristics of the proposed mitigation project site, in the case of an application for a [Department of the Army] DA permit, the impact site. This may include descriptions of historic and existing plant communities, historic and existing hydrology, soil conditions, a map showing the locations of the impact and mitigation site(s) or the geographic coordinates for those site(s), and other characteristics appropriate to the type of resource proposed as compensation. The baseline information should include a delineation of waters of the United States on the proposed mitigation project site. A prospective permittee planning to secure credits from an approved mitigation bank or in-lieu fee program only needs to provide baseline information about the impact site.” When comparing wetland mitigation banks and stormwater mitigation banks, this element is perhaps where the two would require divergent data collection information. Stormwater storage, attenuation, and/or treatment is currently evaluated independently of habitat types. One possible

130 way to address this element as part of dual-use mitigation bank scenario might be to collect additional engineering stormwater data as part of the wetland hydrology information used for habitat baseline evaluation. Currently, wetland mitigation banks, particularly at the federal level, do not routinely evaluate existing/proposed stormwater storage, treatment, or attenuation potential. It is reasonable to anticipate that most wetland creation projects provide at least minimal attenuation and perhaps some other functions. Collection of baseline stormwater engineering data may add permitting costs; however, this information could be used to document stormwater bank co-benefits associated with proposed wetland mitigation The waters of the U.S. exemptions for stormwater systems would still need to be considered, however. If a mitigation area is determined not to be waters of the U.S., it is possible that the proposed wetland mitigation bank may be deemed inappropriate by the USACE. The collection of baseline ecological data for wetland mitigation banks requires extensive vegetative surveys to characterize the habitat types which will provide credits. It is anticipated that credits yielded by a single objective stormwater mitigation banking program could be determined without any context or review of the proposed impacts that they will offset because both attenuation and/or storage for a single objective stormwater mitigation bank can be determined up front, through engineering analysis and mapping exercises. For this reason, baseline data collection effort for such a bank should be substantially less than a combination wetland and stormwater bank. However, federal wetland regulations do not require or account for stormwater management facilities or treatment and they contain no mechanisms for collection or review of stormwater baseline data. 6.3.5. Determination of Credits “A description of the number of credits to be provided including a brief explanation of the rationale for this determination. • For permittee-responsible mitigation, this should include an explanation of how the mitigation project will provide the required compensation for unavoidable impacts to aquatic resources resulting from the permitted activity. • For permittees intending to secure credits from an approved mitigation bank or in-lieu fee program, it should include the number and resource type of credits to be secured and how these were determined.” The methods for determination of credits for stormwater mitigation banks and wetland mitigation banks differ greatly. Wetland habitat mitigation credits are primarily determined through habitat analysis such as the Wetland Rapid Assessment Program (WRAP) or at the state level through methods like the Uniform Mitigation Assessment Method (UMAM) in Florida. Stormwater credits might likely be determined by volume or peak flow rates. In a combined stormwater/wetland mitigation bank credits for the two would likely be determined and tracked separately. This scenario is not unprecedented in wetland mitigation banking as some of the older wetland banks have different credit ledgers utilizing different assessment methodologies (e.g., WRAP vs. UMAM). Credit yields for a single objective stormwater mitigation bank program will be simpler to determine than ecologically-based wetland mitigation credits. It is likely that credits for a single objective stormwater mitigation bank can be awarded up front, or at least upon completion of system construction. A single objective stormwater bank would be less constrained by the

131 incremental credit releases which are often associated with wetland mitigation banking. From a cost and time perspective this could be beneficial if an entity such as a local government or DOT wanted to provide stormwater mitigation on a project-by-project basis. Quite often, wetland mitigation bank credit release timing does not coincide with impacts. A single objective stormwater mitigation bank could be designed and implemented concurrently with a group of regional projects, either large or small scale, without timing issues associated with wetland banking ecological variables. 6.3.6. Mitigation Work Plan “Detailed written specifications and work descriptions for the mitigation project, including: the geographic boundaries of the project; construction methods, timing, and sequence; source(s) of water; methods for establishing the desired plant community; plans to control invasive plant species; proposed grading plan; soil management; and erosion control measures. For stream mitigation projects, the mitigation work plan may also include other relevant information, such as planform geometry, channel form (e.g., typical channel cross-sections), watershed size, design discharge, and riparian area plantings.” This element can be shared between stormwater and wetland mitigation banks. It is reasonable to anticipate that one workplan could be developed for use by both types of banks. Aside from the vegetative component, all the mitigation work plan requirements outlined in this element would need to be considered for a single objective stormwater mitigation bank. 6.3.7. Maintenance Plan “A description and schedule of maintenance requirements to ensure the continued viability of the resource once initial construction is completed.” A wetland mitigation bank maintenance plan will need to include many activities which are not likely to be a requirement for a stormwater mitigation bank. These can include activities such as nuisance vegetation management, tree canopy thinning, and prescribed burns. It will be important to demonstrate that any stormwater bank maintenance plan does not interfere with the continued viability of the wetland habitats in the bank. A single objective stormwater mitigation banking program would involve substantially less maintenance than a wetland mitigation bank. Since the performance metrics of a stormwater mitigation bank will likely only include demonstration that proposed flow and volume parameters are met, the level of work required to maintain it will be lower. A single objective stormwater mitigation bank would need still need to be maintained and operated in perpetuity, however maintenance could be as simple as periodic engineering inspections to certify continued operational capability. 6.3.8. Performance Standards “Ecologically-based standards that will be used to determine whether the mitigation project is achieving its objectives.” Like the baseline information requirement above, the performance standards of a stormwater mitigation bank have the potential to differ greatly from those of a wetland mitigation bank. It is unlikely that standard ecological wetland performance standards will be sufficient to demonstrate

132 stormwater bank success or vice versa. However, some of the wetland bank hydrologic standards could potentially be interwoven in the case of wetland creation, restoration, or enhancement. Hydrologic benchmarks could potentially be augmented to satisfy the objectives of both types of banks. Additional regulatory agency coordination would be recommended to ensure stakeholder concurrence of any dual performance standards. A single objective stormwater mitigation bank could have additional performance flexibility if it is not constrained by ecologically-based standards. Most regulatory stormwater criteria simply require that volume and/or flow metrics be met for any given project. For the most part, the methodology and standards used to demonstrate attenuation volume and flow parameters are being met are already well-established. For this reason, it is reasonable to anticipate that proving successful achievement of proposed stormwater mitigation bank objectives should take less time and require less work than a wetland mitigation bank would. 6.3.9. Monitoring Requirements “A description of parameters monitored to determine whether the mitigation project is on track to meet performance standards and if adaptive management is needed. A schedule for monitoring and reporting monitoring results to the District Engineer must be included.” As with credit determination, the monitoring requirements for the two types of mitigation banks diverge greatly. Tasks associated with monitoring of wetland mitigation bank performance will be largely ecological and biological. Stormwater bank performance monitoring will entail mostly engineering evaluation. It is not likely that these independent monitoring requirements can be interwoven. While it may cost more to undertake two different monitoring programs, this is not expected to create a barrier to the establishment of a combined wetland and stormwater mitigation bank. Ecological and biological monitoring and stormwater performance monitoring would likely be undertaken as two distinct tasks in any dual-use mitigation bank. The monitoring plan for single objective stormwater mitigation bank would most likely be far less labor and time-intensive than for a wetland mitigation bank. The addition of wetland mitigation monitoring could prove to be cost prohibitive for smaller mitigation projects, eliminating the feasibility of wetland mitigation banking in those situations. 6.3.10. Long-Term Management Plan “A description of how the mitigation project will be managed after performance standards have been achieved to ensure the long-term sustainability of the resource, including long-term financing mechanisms and the party responsible for long-term management.” The long-term management plan for any combined stormwater and wetland mitigation bank will need to provide details to ensure that long-term sustainability of the wetland mitigation bank will not be jeopardized. It is reasonable to anticipate that a single long-term financial assurance mechanism could be developed to encompass management of both bank types. In most cases, demonstrating the sustainability of a single objective stormwater mitigation bank will be easier to accomplish than a wetland mitigation bank. The owner of a single objective stormwater mitigation bank would be responsible for its continued operation; however,

133 maintenance and management requirements are likely to be minimal compared to wetland mitigation standards. 6.3.11. Adaptive Management Plan “A management strategy to address unforeseen changes in site conditions or other components of the mitigation project, including the party or parties responsible for implementing adaptive management measures.” It is not likely that development of an adaptive management plan suitable for both stormwater and wetland mitigation will be considered a constraint to establishment of a joint use mitigation bank. A single objective stormwater mitigation bank would require minimal adaptive management strategy. 6.3.12. Financial Assurances “A description of financial assurances that will be provided and how they are sufficient to ensure a high level of confidence that the mitigation project will be successfully completed, in accordance with its performance standards.” A combined wetland and stormwater mitigation bank will likely cost more to permit, construct, and maintain than either type of mitigation bank alone. However, aside from the added costs, it should be possible to providing a method of financial assurance that will ensure success of the project. Financial assurance requirements for a single objective stormwater mitigation bank would be substantially less than a wetland mitigation bank. 6.4. Summary The 12 components of the 2008 Compensatory Mitigation for Losses of Aquatic Resources; Final Rule can be used to outline the types of considerations appropriate for planning and implementing stormwater mitigation banking either combined with wetland mitigation banking or as a single objective stormwater mitigation bank based on wetlands, forest creation or restoration, or another landscape approach. For a combined approach, there may be some components where stormwater mitigation and wetland mitigation bank requirements may overlap. However, there are several components where additional inter-agency coordination will likely be required. These include baseline conditions documentation, site selection, and monitoring/maintenance requirements. A significant constraint to establishing a combined wetland and stormwater mitigation bank could be federal wetland jurisdictional criteria and permitting requirements. As noted above, facilities associated with traditional stormwater management, such as regional ponds, may not meet the jurisdictional requirements of the USACE. Therefore, these facilities could be deemed inappropriate as a wetland mitigation banks. Additional coordination with stormwater regulatory agencies such as the USEPA and/or states with the NPDES delegation might be beneficial to explore ways to utilize the components in the 2008 Rule to establish combined stormwater mitigation and wetland mitigation banking. The Delaware DOT has shown that it is possible to establish cooperation through implementation of a MOA between transportation departments and NPDES administrators (McCleary 1999, DelDOT/DNREC 2019). An MOA to co-establish wetland mitigation and stormwater mitigation

134 banks could potentially be implemented between the USACE and the USEPA utilizing components of the 2008 Mitigation Rule. Although not required as part of the 12 components, market research to determine the financial feasibility of a combined mitigation bank or a single objective stormwater bank, as well as the potential market for credits is generally an important step in planning a mitigation credit bank. Wetland mitigation banking provides valuable ecological functions on a landscape level, and it may be anticipated that combined stormwater mitigation and wetland mitigation banks could provide long-term stormwater management cost savings for transportation projects even though up-front costs (permitting, infrastructure, land acquisition) could be higher. Public entities may also have more options for demonstrating financial surety than private-sector bankers. As such the potential local, regional, and landscape-level ecological and financial benefits to combined banking may outweigh the inherent regulatory and financial challenges. Further research and implementation of this concept should remain a priority among stakeholders.