Green Stormwater Infrastructure - Volume 2: Guidebook (2017)

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3 Background Conventional stormwater infrastructure (or “gray infrastructure”) relies on catch basins, pipes, and ditches to remove stormwater from sites using storage or treatment prior to discharge to a natural receiving water (e.g., lake or river). In contrast, GSI is a stormwater management approach that attempts to maintain, mimic, or restore the natural response of the landscape to a storm. Runoff is managed as close as possible to the point of origin, generally through the use of various structural management practices that promote infiltration and evapotranspiration. An effective stormwater management system can include both GSI and gray infrastructure BMPs to manage stormwater runoff. Applicability of Green Stormwater Infrastructure at Airports GSI strategies can provide effective stormwater management as well as deliver a variety of benefits to airports, such as: • Environmental benefits (e.g., improved water quality, groundwater recharge); • Aesthetic benefits (e.g., landscape improvements); • Economic benefits (e.g., potentially lower capital and O&M costs, reduction in the airport’s energy and other operational costs); and • Social benefits (e.g., demonstration of stewardship to communities and stakeholders). GSI strategies have been implemented at a number of airports, ranging in size from general aviation to large commercial airports. For example, the Florida Department of Transportation (DOT) has developed an airport stormwater management program that supports airports of all sizes (Florida DOT 2016). However, the use of GSI at airports has been limited due to a combination of actual and per- ceived barriers. These barriers include the potential to attract hazardous wildlife and the com- mon misperception that GSI increases O&M costs, among others. Regulatory Support The U.S. Environmental Protection Agency (EPA) and delegated state water management authorities allow and encourage the use of GSI to comply with National Pollutant Discharge Elimination System (NPDES) permit requirements at airports. U.S. EPA has worked with state and local governments to incorporate green infrastructure into stormwater permitting programs. For example, since 2009, regional water quality boards in California have developed nine U.S. EPA-approved municipal stormwater permits that require For more information on stormwater permits, see Volume 1: Primer and U.S. EPA’s website (https://www. epa.gov/npdes/npdes- stormwater-program). S t e p 1 Understanding Green Stormwater Infrastructure

4 Green Stormwater Infrastructure GSI BMPs (Stoner 2011a). Also, many states (e.g., Kentucky, Florida, and North Carolina) have written general stormwater permits for general aviation (GA) airports that encourage the use of GSI BMPs such as bioswales and vegetated filter strips. Over the last several years, U.S. EPA has actively encouraged the incorporation of green infra- structure into stormwater management “to the maximum extent practicable” and is a key member of the Green Infrastructure Collaborative (Stoner 2011b; U.S. EPA 2017). Since 2007, U.S. EPA has released a series of memoranda encouraging green infrastructure as a means to comply with NPDES and state permit requirements (U.S. EPA 2016). For example, U.S. EPA’s 2011 memo to U.S. EPA Regional Administrators notes that, “. . . EPA strongly encourages the use of green infra- structure and technologies, approaches, and practices to manage stormwater as a resource, reduce sewer overflows, enhance environmental quality, and achieve other economic and community benefits” (Stoner 2011c). In 2013, U.S. EPA released its green infrastructure strategy to outline its overall approach to encouraging the implementation of GSI (U.S. EPA 2013). Advantages of GSI Efficient Use of Land At many airports, space is at a premium, and any development with features that serve mul- tiple functions or provide several benefits is desirable. GSI BMPs can often serve more than one purpose (e.g., provide drainage, treat runoff, and improve aesthetics) and can be constructed within the existing landscape without occupying valuable property. For example, bioswales are often installed in locations normally occupied by flower beds or other landscaping features. Similarly, vegetated filter strips (Figure 1) along runways and taxiways are incorporated into the existing landscape, which otherwise cannot be used. GSI Design Criteria GSI is typically designed to capture and treat stormwater runoff generated from frequent, smaller storm events. The specific design storm (i.e., the rainfall amount and storm frequency that is used to calculate the stormwater runoff volume) for GSI is generally provided by local regula- tory requirements (e.g., municipal ordinances and design guidelines). The typical design storm for GSI is generally based on a storm event generating one inch or less of rainfall. GSI is typically Source: R. Duffner (© 2015). Figure 1. Vegetated filter strip, Seattle–Tacoma International Airport.

Understanding Green Stormwater Infrastructure 5 not intended to address flood control mitigation requirements common in new development and redevelopment projects. However, GSI may provide conveyance and infiltration of stormwater runoff that will contribute to mitigating flooding. In contrast, conventional stormwater infrastruc- ture is often designed for flood control alone and is based on less frequent, larger storm events. Drivers that Promote Green Stormwater Infrastructure Airports participating in the study to support development of this guidebook overwhelmingly cited regulations (e.g., NPDES) as the primary driver for considering or implementing GSI. Some airports, however, have also suggested that environmental sustainability is an important incentive to implementing GSI. Regulations Stormwater Regulations Federal, state, and local stormwater regulations, in addition to FAA requirements, remain critical for the future implementation of GSI at airports. The NPDES programs include general permits that address stormwater discharges from industrial and construction activities, as well as municipal separate storm sewer systems (MS4s), and provide the baseline regulatory framework for stormwater management at airports. Since the inception of NPDES stormwater industrial permitting in 1990, airport and tenant activities have been subject to its stormwater per- mitting program either under individual permits or under multi-sector general permits (MSGPs). Specific airports categorized as MS4s are per- mitted directly under the NPDES municipal stormwater permit pro- gram. Airports may also be subject to the MS4 requirements indirectly if their stormwater discharges to the municipal storm sewer system. Activities subject to the MSGP at airports include but are not limited to: 1. Servicing, repairing, or maintaining aircraft and ground vehicles; 2. Cleaning and maintaining equipment (including vehicle and equipment rehabilitation, mechanical repairs, painting, fueling, lubrication); and 3. Deicing/anti-icing operations. Under the industrial, municipal, and construction programs, airports must implement a storm- water pollution prevention plan (SWPPP) that includes standard stormwater treatment BMPs and must conduct quarterly visual monitoring and, in some cases, monthly water quality moni- toring and reporting. In addition, airports are subject to the stormwater construction program. The construction program requires a SWPPP that implements construction BMPs and an erosion and sediment control plan. At the local level, ordinances promulgated by municipalities and other local governments typi- cally regulate stormwater management. These ordinances often incorporate additional require- ments from the NPDES program. For example, in Los Angeles County, state and local regulations and ordinances, some of which were developed to comply with the programs issuing MS4 permits, have required the airport to implement a combination of conventional infrastructure and GSI pro- grams to manage its stormwater. Similarly, compliance with the state and federal regulations as well as the influence of local non-government organizations (NGOs), prompted Seattle–Tacoma International Airport to implement GSI and to monitor effectiveness at stormwater outfalls. Regulatory Drivers Regulatory considerations were consis- tently mentioned as a primary driver by the airports that participated in the focus groups and interviews for this project. Local regulations were also cited as drivers as they often mandate the implementation of GSI during development or redevelopment of airport property.

6 Green Stormwater Infrastructure National Environmental Policy Act Mitigation Because many projects at airports are considered federal actions, projects involving GSI may be subject to the National Environmental Policy Act (NEPA). Airport projects may trigger a NEPA review and compliance if the proposed GSI implementation: 1. Results in a change in the Airport Layout Plan (ALP) or 2. Uses federal funds (grants and passenger facility charge funds). Changes in the ALP are often required for major airport development projects like terminal expansion or runway extension, which by their nature include stormwater management. These projects would normally require NEPA review of the proposed infrastructure. The other trigger, funding from federal grants, would also result in NEPA review of airport development projects. For smaller, stand-alone infrastructure projects, like implementing a GSI BMP, a NEPA review may also be required if either of the triggers is involved. It is recommended that the project coor- dinator contact the local environmental protection officer at the FAA area district office to discuss such projects to ensure that NEPA compliance is met. NEPA compliance can take one of several forms: • Categorical exclusion (CatEx), • Environmental Assessment (EA), or • Environmental Impact Statement (EIS). The FAA has a list of projects that, if no extraordinary circumstances are triggered, are potentially eligible for a CatEx. The CatEx list represents projects that are not expected to produce significant environmental effects or generate controversy. If a CatEx is obtained, then no further mitigation is required. FAA allows airport sponsors to prepare the impact analysis underlying a CatEx. An EA is prepared for a small subset of projects and can be undertaken for projects that are not CatEx eligible to determine if impacts would be significant. When it is determined in the EA that the projects will have a significant environmental impact, then the project must undergo an EIS. FAA allows airport sponsors to prepare the impact analysis underlying an EA, but only the FAA prepares an EIS. The completion of an EA or EIS may result in development of mitiga- tion measures, which could simply require compliance with local, state, or federal stormwater regulations or, in exceptional cases, specify implementation of GSI. Airport Sustainability Programs Policies on sustainability practices have been adopted by certain airports; these may be devel- oped in response to state and local environmental concerns, including pressure from local stake- holders (e.g., NGOs). Seattle–Tacoma International Airport, San Diego International Airport, O’Hare International Airport, Gulfport–Biloxi Airport, and Hartsfield–Jackson Atlanta Inter- national Airport have sustainability goals that drive GSI implementation. Implementation Issues for GSI Best Management Practices at Airports The challenges associated with implementing GSI at airports include: 1. The perceived barrier of higher capital and O&M costs associated with all GSI strategies, 2. Compatibility with the varying landscape and other characteristics at airports (e.g., climate, topography, site hydrology, facility experience with stormwater management),

Understanding Green Stormwater Infrastructure 7 3. Limited data on soil characteristics and detailed, activity-specific stormwater characteristics, 4. Understanding and acceptance of GSI practices by local and state permitting authorities and practitioners, 5. Creation of hazardous wildlife habitat (attractant), 6. Compatibility with FAA design guidelines, and 7. Predicting and verifying GSI performance. In addition, regional differences in the definition of GSI, variability in review processes, and knowledge and experience of design and GSI performance make guidance on application of GSI approaches on a national level challenging. Finally, documented examples of the application of GSI at airports are limited. Exam- ples of airports using GSI practices in areas that are not unique to airports (e.g., parking lots, landscaped areas, rooftops) are more common. Two airports, Seattle–Tacoma Inter- national Airport and Austin–Bergstrom International Airport, have installed vegetated filter strips for treating and dispersing runway runoff. However these airports originally installed these filter strips without considering them GSI BMPs (Parametrix 2000; Nye and Carpenter 2013). Environmental Drivers Seattle–Tacoma International Airport Seattle–Tacoma International Airport included in its strategic plan its commit- ment to GSI: “Strategy 3, Objective 6: Water Quality: Contribute to the restoration of Puget Sound and local receiving waters by providing water quality treatment, flow control, and using green stormwater infrastructure (where feasible) for airport industrial stormwater.” (Port of Seattle 2015) Hartsfield–Jackson Atlanta International Airport Located at the source of the water-stressed Flint River basin, Hartsfield–Jackson Atlanta International Airport set the ambitious goal of becoming the “greenest” airport in the world (American Rivers 2015). The airport’s focus is to reduce peak runoff volume by infiltration rather than detention. Throughout its campus, ATL has replaced impervious surfaces with permeable pavement, constructed bioswales, implemented rainwater harvesting practices, and is planning to implement bioretention systems. Furthermore, the airport has conducted a thorough land suitability analysis which identified 38 percent of the airport land as highly suitable for GSI implementation (American Rivers 2015). Gulfport–Biloxi International Airport In 2013, Gulfport–Biloxi International Airport received a $150,000 FAA grant to develop a sustainability management plan, which works toward ultimately reducing the airport’s environmental footprint. Because the airport is located within the environmentally sensitive Turkey Creek Watershed, protecting water quality is a priority in environmental stewardship.

8 Green Stormwater Infrastructure Addressing Potential Conflicts Wildlife Hazard Management The airports participating in the study supporting the development of this guidebook noted that FAA regulations regarding wildlife hazards are a major consideration when evaluating the feasibility of GSI. The use of vegetation appears to conflict with FAA guidance to control wild- life attractants at airport facilities. The FAA Advisory Circular (AC) 150/5200-33B, Hazardous Wildlife Attractants On or Near Airports: • Recommends that “All vegetation in or around detention basins that provide food or cover for hazardous wildlife should be eliminated.” • Advises the elimination of ponding or open water. However, it recommends the use of stormwater infiltration systems when possible. This recommendation is consistent with the use of GSI. • Prohibits wildlife attractants within: – 5,000 feet of aircraft movement areas for piston-powered aircraft, or – 10,000 feet of aircraft movement areas for turbine-powered aircraft, and – 5 miles from the edge of the Air Operations Area if it results in wildlife movement across the approach or departure airspace (depending on control/ownership of this area). Given concerns over wildlife hazards, airports can work to minimize these risks by: • Carefully incorporating wildlife hazard management measures into the design of airport development projects and stormwater management systems (Allerton et al. 2015), • Using vegetation as a deterrent (e.g., dense planting, non-food source vegetation) (WSDOT 2007), • Carefully maintaining drainage infrastructure (Cleary and Dickey 2010; McGormley et al. 2011), and • Judiciously implementing wildlife hazard management controls (FAA AC 150/5200-33B; Cleary and Dickey 2010; McGormley et al. 2011). See Figure 2 for an example of management controls. There may be regional climatic (e.g., high rainfall) or hydrogeological (e.g., high water table) considerations as well. These regional considerations are best addressed by developing and implementing a holistic and adaptive wildlife hazard management plan that addresses factors Source: Michael Baker International (© 2016). Figure 2. Bird balls in detention pond.

Understanding Green Stormwater Infrastructure 9 such as the airport’s location and the surrounding environmental, political, and social climates. This guidebook describes some general wildlife hazard management strategies for GSI that have been used by airports and can be tailored to an airport’s specific needs through a more compre- hensive wildlife hazard management plan. Helpful Resources • Cleary, E. C. and R. A. Dolbeer. 2005. Wildlife Hazard Management at Airports: A Manual for Airport Personnel. FAA. http://www.faa.gov/airports/airport_safety/wildlife/resources/ media/2005_FAA_Manual_complete.pdf. • Herrera Environmental Consultants, Inc. 2007. Technical Memorandum: Guidance for Devel- oping a Stormwater Management Manual in Washington State: Mitigating Hazards due to Wild- life Attractants and Airports. Washington State DOT (WSDOT). http://www.wsdot.wa.gov/NR/ rdonlyres/D806B7C5-48C6-41D5-BB4E-058A2B9CD370/0/TechMemoMitigationHazards DuetoWildlifeAttractants71207.pdf • WSDOT. 2008. Aviation Stormwater Design Manual: Managing Wildlife Hazards near Airports, Chapter 3: Stormwater and Wildlife Planning and Appendix A: Vegetation Recommendations for Airport Settings. http://www.wsdot.wa.gov/aviation/AirportStormwaterGuidanceManual.htm • Florida DOT. 2013. Statewide Airport Stormwater Best Management Practices Manual. Additional Airport Safety and Operational Requirements As summarized in Table 1, the FAA-designated areas described in the FAA AC 150/5300-13A, Airport Design, can limit the design and installation of stormwater BMPs. GSI installation is primarily limited in the runway safety area and stopway, as the BMP must support the weight of GSI Best Management Practices and Managing Wildlife Hazards A number of airports have successfully managed wildlife hazards at their conven- tional stormwater BMPs as well as at their GSI BMPs: • Seattle–Tacoma International Airport plants dense stands of species that do not attract nuisance birds in its wetlands. As a result, the birds are not attracted to the standing water. These strategies can also be used for GSI where vegetation or open water is inherent to the BMP. • Minneapolis–Saint Paul International Airport uses liners and nets at its conven- tional stormwater detention ponds (per AC 150/5200-33B). • Cleveland Hopkins International Airport plants tall, non-spreading reeds to obscure the banks of ponds and uses Mylar strips in large quantities around the terminal to deter wildlife. • San Diego International Airport has bioswales and bioinfiltration systems installed at its cell phone lot and rental car center. • Austin–Bergstrom International Airport has installed vegetated filter strips (which are mowed for maintenance) in the runway and taxiway areas to mini- mize vegetation that attracts wildlife. • Los Angeles International Airport has installed porous pavement in parking areas and access roads. These airports have proven that modifications can be made to stormwater BMPs to manage and prevent wildlife hazards.

10 Green Stormwater Infrastructure aircraft. Other operational areas, including the clearway and runway protection zone, provide fewer constraints, as the BMPs do not have to support the weight of aircraft. As a result, potential GSI such as infiltration systems and vegetated filter strips could be designed to be installed in these operational areas. Pavement Design / Compaction Restrictions. Design requirements for paved areas (e.g., structural strength) and unpaved areas (e.g., compaction) limit the use of GSI in the active air- side areas. Due to airfield pavement strength requirements, porous pavement should not be used in areas with heavy vehicle traffic, including any commercial airplane traffic. Porous pavement may be structurally feasible on the airside at smaller airports where only lightweight GA aircraft (less than 12,500 pounds) operate. Further studies would be necessary to determine if a porous pavement could be constructed to support lightweight aircraft loading and withstand 20 years of traffic. Compaction requirements to prevent rutting, and to support aircraft, in the operational areas noted in Table 1 can prevent or severely limit the installation of GSI in these areas (e.g., in the runway safety area or the stopway). Anti-icing/Deicing Operations. Anti-icing and deicing of aircraft and pavement can be performed at the gate area or in designated deicing areas. Glycol recovery vehicles are used at approximately one-third of airports in the United States [40 Code of Federal Regulations (CFR) Parts 9 and 449] to collect fluids and contaminated runoff before they enter the storm sewer system. In some cases, the stormwater collection system is equipped with a valve system to divert fluid-laden stormwater to a wastewater treatment system when the contaminant level reaches a threshold concentration during deicing operations. At these airports, the collected fluids and fluid-laden stormwater are treated in local wastewater treatment plants or fluid recovery/ recycling systems. Not all fluid-laden stormwater runoff will be captured by these systems (i.e., glycol recovery vehicles or diversions). Uncollected runoff with dilute concentrations of fluid FAA Operational Area General Location/Definition Stormwater BMP Restriction Runway safety area (RSA) Area surrounding the runway prepared to reduce damage to aircraft in the event of an undershoot, overshoot, or excursion from the runway BMPs must be located outside of the RSA unless they are subsurface facilities and can be driven over without damage to vehicles, or aircraft. BMPs must not prevent rescue and firefighting vehicles from accessing the entire RSA. Clearway (CWY) Rectangular area beyond the end of a runway cleared or suitable for use in lieu of runway to satisfy takeoff distance requirements BMPs are allowed on the ground under the CWY. Object-free area (OFA) An area on the ground centered on a runway, taxiway, or taxi lane centerline BMPs within the OFA must not protrude above the RSA edge elevation. Restrictions would limit O&M of BMPs in OFA. Runway protection zone (RPZ) An area off the end of a runway that enhances the protection of people and property BMPs are allowed as long as they do not attract wildlife and are located outside of the OFA. Stopway (SWY) Rectangular surface beyond the end of a runway prepared to support an aircraft during an aborted takeoff BMPs within the SWY need to be subsurface and capable of supporting aircraft. Taxiway safety area (TSA) Area along the taxiway suitable for reducing damage to an aircraft unintentionally leaving the taxiway BMPs must be located outside of the TSA unless they are subsurface facilities and can be driven over without damage to vehicles, or aircraft. Source: WSDOT (2008). Table 1. Stormwater BMP restrictions in FAA operational areas.

Understanding Green Stormwater Infrastructure 11 could enter GSI BMPs, which could provide limited incidental treatment; however, GSI BMPs do not always include mechanisms or features to mitigate or treat anti-icing or deicing fluids. Therefore it is recommended that GSI not be the primary means to capture and treat deicing fluids and fluid-laden runoff without specific design elements that target these fluids. Foreign Object Debris Restrictions. FAA defines foreign object debris (FOD) as “any object, live or not, located in an inappropriate location in the airport environment that has the capacity to injure airport or air carrier personnel and damage aircraft.” Porous pavement is the GSI BMP that could be subject to FOD restrictions. Potentially a piece of pavement could break away from the pavement structure and be ingested in an aircraft engine or damage aircraft sys- tems. Porous pavement materials may be at an increased risk to produce FOD due to the open- ness of the material and potential for dislodging of the aggregate. Though the FOD risk from porous pavement has been noted in interviews with airports, several airports—including San Diego International Airport and Los Angeles International Airport—have used porous pave- ment extensively in parking lots adjacent to the airfield. Understanding the Cost of Green Stormwater Infrastructure The cost of using GSI in any setting has been assessed in detail across the country by advocates and detractors with a range of results and outcomes. The specific perspective of the evaluator often has more influence on the significance of costs than the actual findings. Consequently, GSI capital, replacement, and O&M costs in total should be evaluated at a specific site, and compli- ance risk used as a driving factor for comparison. In general, when the appropriate application of GSI is used, most GSI approaches are “self-selecting,” which means the selected approach would be the preferred and appropriate method that considers all aspects of the selection process and performance to achieve compliance. Cost comparisons should be made on different methods of stormwater control, not on con- trolled and not controlled stormwater. Land cost and constraints tend to be the most signifi- cant and highly variable factor in capital costs, followed by differences in treatment technology, usually when considering passive versus active treatment systems, the notable exception being pervious pavements. The other major cost consideration is conveyance, which is the cost to deliver stormwater to and from BMPs; cost of conveyance is very site specific and should be an important factor in evaluating the capital costs of GSI. Concerns that capital, O&M, and replacement costs may be higher for GSI than for con- ventional stormwater management approaches can be a barrier to implementation of GSI at airports. Information gathered during the study to support development of this guidebook sug- gests that this perception is more common among airports that are less familiar with GSI imple- mentation. Often, it is the uncertainty of the review process, acceptance by review agencies, and the familiarity and skill of the designer and reviewer, as well as the lack of contracting familiarity that lead to concerns over delays and failures, not necessarily costs. Although GSI may involve higher upfront costs in some cases, there may be advantages to GSI for O&M and other costs. Through small-scale analyses of various GSI BMPs, the University of New Hampshire’s Stormwater Center (UNHSC) found that GSI BMPs have lower O&M costs compared to conventional stormwater BMPs (UNHSC 2012). Due to the potential reduction in runoff, GSI can reduce the compliance risk of water quality discharges. This results in other potential savings not available to conventional treat-and-discharge-type BMPs. Planning tools are available to help airports estimate the cost of inspection and O&M for stormwater GSI BMPs. For example, U.S. EPA maintains Green Infrastructure Modeling Tools, a website that offers resources to help generate cost and performance estimates as well as applica- tions to estimate stormwater runoff and land use changes based on GSI measures.

12 Green Stormwater Infrastructure O&M costs of GSI BMPs are often based on a combination of data from actual operations and standard cost estimating tools (e.g., RSMeans). For example, Table 2 shows unit costs for estimating BMP maintenance costs that were developed by the Urban Drainage and Flood Con- trol District (UDFCD) in Denver, Colorado (UDFCD 2013). These cost estimates are by their nature dependent on the regional labor and material rates; thus, the data shown in Table 2 is for illustrative purposes only. Similarly, DOT manuals and highway industry guidance include extensive guidance on the relative capital and O&M costs of stormwater GSI BMPs (Taylor et al. 2014). For those airports that have implemented GSI, the capital and O&M costs have been manage- able. Table 3 provides bioswale capital costs incurred at three airports and includes the approxi- mate size of the bioswale and the loading rate of stormwater runoff. Source: UDFCD (2013). Table 2. Example table of BMP maintenance unit costs developed for an effectiveness and cost analysis model. Airport Hartsfield–Jackson Atlanta International Airport San Diego International Airport Seattle–Tacoma International Airport Seattle–Tacoma International Airport Total Cost* $416,000 $650,000 $580,000 $257,000 Approximate Bioswale Size (sf) 18,531 226,512 (Four bioswales) 7550 (Two 25–50 feet wide bioswales) 1700 (Two 5–10 feet wide bioswales) Loading Rate of Runoff (gpm/sf) Not available Not available 0.25 to 0.35 0.015 to 0.175 Airport Location Landside (parking area) Landside (rental car center) Landside (commercial) Landside (commercial) *In some cases, it appears that the capital costs for GSI have been effectively incorporated into larger capital improvement projects. Similarly, the O&M costs for GSI at these airports have been incorporated into the normal operating costs of either the airport or its tenants and are not seen as expensive or as an additional cost. Table 3. Summary of capital costs for bioswales from airports participating in the study to support development of this guidebook.

Understanding Green Stormwater Infrastructure 13 Helpful Resources • University of New Hampshire Stormwater Center. 2012 Biennial Report, pp. 28–29. http:// www.unh.edu/unhsc/sites/unh.edu.unhsc/files/docs/UNHSC.2012Report.10.10.12.pdf. • Water Environment & Reuse Foundation. 2009. Best Management Practices and LID Whole Life Cost Models. www.werf.org/bmpcost. • UDFCD. – BMP sizing tool. http://udfcd.org/software. – 2013. BMP-REALCOST (Rational Estimation of Actual Likely Costs of Stormwater Treat- ment) software. www.udfcd.org/downloads/software/BMP-REALCOST_v1.0.zip. • EPA. 2016. National Stormwater Calculator. https://www.epa.gov/water-research/national- stormwater-calculator. Identification of Solutions Engaging Local Jurisdictions to Identify Solutions to Challenges When an airport approaches the local planning and zoning officials with a potential GSI project, it may be appropriate to discuss the unique status and needs of airports (e.g., compli- ance with FAA regulations). These outreach discussions not only provide a forum for alterna- tive solutions to the challenges of implementing GSI at airports, but can also improve existing relationships with local jurisdictions. In addition, these discussions can provide a platform for potential future negotiations around stormwater management. The objectives of the discussion with local officials will depend on the phase of the GSI project. The basis of each discussion should be that both the local jurisdiction and the airport have the same goal: to implement a solution that provides the critical features of GSI while preventing O&M: Who’s in Charge? O&M costs need to be projected during the initial planning of GSI. These costs will vary among airports and for different BMPs. In some cases, O&M for GSI may be readily included in existing O&M practices. For example, mowing in filter strips in a runway area and maintaining bioretention cells are O&M activities that are performed in existing landscaped areas at the airport. In some cases, O&M of GSI may require more coordination and planning if tenants are responsible for each GSI BMP. For example, LAX has reported that maintenance for their vegetated swales requires additional coordination. The airport is currently developing an inventory of BMPs, including the owners and those responsible for maintenance. Ideally, O&M organization would consist of a list of BMPs, a person associated with each BMP, and a regular report on maintenance. At many airports, airport personnel are responsible for O&M associated with GSI, but at others, contractors are responsible. For SEA, contractors are responsible for landscaping and grounds maintenance related to GSI. Its vegetated swales were installed with plants known to have low long-term maintenance. At LAX, O&M of the porous pavement parking lot is the responsibility of an airline tenant. The tenant vacuums the parking lot two times per year to ensure that the pavement pores are not clogged.

14 Green Stormwater Infrastructure downstream negative effects. Airports should have discussions with local officials during the following phases of a GSI project: 1. Preliminary planning phase of new capital improvement project, 2. Environmental review in the EA scoping phase of the NEPA process, 3. Construction/installation phase of GSI, and 4. Ongoing O&M phase. Verification of Performance Given the uncertainty of the performance of particular innovative measures, pilot testing the proposed BMPs during design, and potentially after installation, may also be an appropriate strategy at airports considering GSI. Confirming the performance of a proposed BMP prior to implementation of GSI at the airport would be ideal if the airport has sufficient time and space to do so. In some cases, the local stormwater management ordinance provides compliance credit for a select list of approved BMPs. Testing and piloting these BMPs at the airport could provide both the airport and the local officials with critical data needed to confirm BMP performance and obtain credits on existing or future projects. Helpful Resources • The National Cooperative Highway Research Program (NCHRP) has extensive guidance doc- uments (Oregon State University et al. 2006, Taylor et al. 2014, and Geosyntec Consultants et al. 2011) on controlling highway runoff via GSI BMP installation that include in-depth reviews of the various methodologies in which GSI BMP effectiveness and efficiency may be evaluated. • The International Stormwater BMP Database provides guidance on protocols for monitoring and evaluation of BMPs. – Monitoring and Performance Evaluation Guidance. http://www.bmpdatabase.org/monitoring- guidance.html. – Geosyntec Consultants and Wright Water Engineers, Inc. 2009. Urban Stormwater BMP Performance Monitoring Manual, Chapters 8: Low Impact Development Monitoring, 9: Data Interpretation and Performance Evaluation of LID Monitoring Studies, and 10: LID Monitoring Case Studies. Water Environment Research Foundation. http://www.bmp database.org/Docs/2009%20Stormwater%20BMP%20Monitoring%20Manual.pdf.