Green Stormwater Infrastructure - Volume 2: Guidebook (2017)

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76 A p p e n d i x A The following case studies and lessons learned are from airports that have implemented GSI management strategies: • San Diego International Airport (SAN) • Austin–Bergstrom International Airport (AUS) • Seattle–Tacoma International Airport (SEA) Case Studies of GSI Strategies at Airports

Case Studies of GSi Strategies at Airports 77 Case Study of San Diego International Airport (SAN) November 24, 2015 Characteristics: Climate Zone: Hot-Dry FAA Region: Western-Pacific FAA Category: Primary Large Highlights: 1) Artificial turf infiltration area. 2) Porous pavement areas at rental car center, general aviation parking, south public parking area. 3) Bioswales at rental car center. 4) Pervious pavers in public parking area at Terminal 2. Lessons Learned: 1) Capital costs for green stormwater infrastructure (GSI) are not major challenge. 2) Deterioration of porous pavement does not appear to be a major operational issue. 3) Wildlife attractants are not a major issue as open water is minimized, and endangered species habitat maintained adjacent to the runway and taxiway. 4) Local regulatory climate is increasing current and future use of GSI. Description of Existing and Planned Green Stormwater Infrastructure While SAN’s previous Phase I municipal separate storm sewer systems (MS4) stormwater permit did contain GSI requirements, most GSI was implemented to comply with requirements added in 2007. In 2008, SAN began planning for The Green Build Expansion Project. The Green Build added 10 new gates to Terminal 2 West, created an elevated dual-level roadway system to separate arrivals from departures, reconfigured the terminal parking lot, and added approxi- mately 30 acres of new tarmac to the airside of Terminal 2. The Green Build was constructed between 2010 and 2013. Reconfiguration of the Terminal 2 parking lot during the Green Build incorporated sustain- able low-impact design features to manage stormwater runoff. The design team made every effort to capture and infiltrate stormwater into the ground rather than direct runoff into the storm drain system. Stormwater runoff from rooftops and roadway surfaces is directed into swales, where the water can infiltrate into the ground. The swales feature native, drought-tolerant vegetation that is watered by the runoff. To reduce the volume of stormwater runoff from the parking lot, permeable pavers are incorporated throughout the site and along the perimeter to allow water to infiltrate into the ground. Artificial Turf Infiltration Area – West Side: At the west side of the airport, as part of the Green Build project, a 1.75-acre stormwater infiltration system was installed. Nearly one-third of the 30 acres of new airfield tarmac has been designed to drain into the infiltration system. The system is constructed of FAA-approved artificial turf installed at the surface with a layer of reservoir stone below. A 2-inch layer of sand has been placed on the turf to hold it in place. The infiltration system includes the 3- to 4-inch reservoir stone that captures and infiltrates approximately 18,000 cubic feet of stormwater runoff (meeting the MS4 permit requirement to treat the volume of water from the 85th percentile of 2-year storm event). The infiltration basin is another low-impact develop- ment (LID) feature that allows stormwater runoff to infiltrate into the ground.

78 Green Stormwater infrastructure Source: J. Jolley (© 2015). Figure A1. West side artificial turf infiltration area. Source: J. Jolley (© 2015). Figure A2. West side artificial turf infiltration area. Source: J. Jolley (© 2015). Figure A3. West side artificial turf infiltration area – exposed area during construction showing reservoir stone below turf.

Case Studies of GSi Strategies at Airports 79 Porous Pavement – Landmark Aviation Fixed Base Operator (FBO)/General Aviation: At the general aviation area, completed in August 2014, porous pavement has been installed along access roads and in parking areas. The porous pavement has been installed in the parking spots alone (Figure A5). Rental Car Center – Bioswales: SAN is currently constructing a rental car center (scheduled to open in January 2016) on a 25-acre parcel. Along the entire perimeter of the new rental car center, four large, engineered bioswales have been installed (totaling 5.2 acres; see Figures A6–A8). The engineered bioswales capture runoff from storms with an intensity of approximately 1 inch per hour (100 percent capture for a 50-year storm event). The bioswale design includes a layer of engineered soil as shown in Figure A8. Permeable pavement was generally not considered feasible for the site, given the heavy volume of traffic expected. However, the project did incorporate a permeable surface on the access road for fire rescue vehicles. Approximately $650,000 was spent on the bioswales and landscaping for this facility. Public Parking Lot – South: Porous Pavement Areas: The parking lots installed by SAN between 2008 and 2010 have permeable pavement strips featuring underdrains, which discharge to below-ground, high-rate media filters. SAN has installed porous pavement along the previous drainage swales in the public parking area. The entire paving area was installed in 2008 over a pre-existing lot (Figures A9 and A10). The porous pavement is generally located along the low point of the parking area. Storm drain inlets are located in the center to provide for overflow Figure A5. Landmark FBO parking lot area – view of porous pavement in the parking spots. Source: J. Jolley (© 2015). Source: J. Jolley (© 2015). Figure A4. Landmark FBO parking lot area – view of entrance, with rain garden.

Figure A6. Rental car center bioswales. Source: J. Jolley (© 2015). Figure A7. Rental car center bioswales. Source: J. Jolley (© 2015). Figure A8. Rental car center bioswale – design cross section. Source: Parsons Brinckerhoff – 10-24-14 San Diego International Airport Authority – Rental Car Center Drawings – Package 1, Rev 4: Civil.

Case Studies of GSi Strategies at Airports 81 during large storm events. The high-rate media filters are similar to sand filters but are aug- mented with compost, zeolite, and other media. Green Build Landside Parking Areas – Porous Pavers/Porous Paving: As part of the Green Build project, porous pavers were installed in the public parking areas at strategic areas (Fig- ure A11). In addition, rain gardens (Figure A12) were incorporated into the medians (with curb cuts to allow drainage to enter). Operation and Maintenance (O&M) Requirements of the GSI SAN has faced minimal challenges with the O&M of its GSI best management practices (BMPs). Since the BMPs were recently built, they have not yet required extensive maintenance. Airport maintenance staff will be responsible for most O&M. Permeable pavers and permeable asphalt function as BMPs and will need to be maintained, and staff have expressed concern about the longevity and effectiveness of the permeable pavement. Source: J. Jolley (© 2015). Figure A9. South public parking lot area – view of porous pavement along the center, low point, of the parking area. Source: J. Jolley. Figure A10. South public parking lot area – close up view of strip of porous pavement.

82 Green Stormwater infrastructure Figure A11. Green build landside parking lot area – view of porous pavers in parking spots. Source: J. Jolley. Figure A12. Green build landside parking lot area – view of rain garden. Source: J. Jolley.

Case Studies of GSi Strategies at Airports 83 Except for the rental car center, all property is managed by airport staff. The 12-acre rental car center includes a recently installed engineered bioswale system. The facility operator is respon- sible for O&M of this BMP. There is no requirement to replace the engineered soil in this BMP, though SAN is developing an O&M plan to remove trash and loosen the soil. SAN has provided O&M operational procedures as required by local regulations. Regulatory Constraints and Flexibility The primary driver at SAN for GSI is compliance with the Phase I MS4 stormwater permit that applies to the airport and 20 other jurisdictions in the county. This permit requires treatment of the pollutants of the 85th percentile of a 2-year storm. SAN is most concerned with the heavy metal criteria (for copper and zinc). One potential source of these metals is the 3 miles of galva- nized fencing at the airport perimeter. The airport is also subject to a general industrial National Pollutant Discharge Elimination System (NPDES) permit. The BMP design standards generally come from California Stormwater Quality Association and other regional standards. The airport landscape design aims for a “campus pallet” and is expected to include many drought-tolerant landscapes, incorporating more GSI features such as swales. While not currently a design standard, swales will help with xeriscaping and reducing the amount of water used for irrigation. In response to worsening droughts, the state is promoting the capture/reuse of stormwater to aid long-term water management. SAN is considering capture and reuse of runoff collected from the new 12-acre parking structure (for use in its adjacent Central Utility Plant). Subsurface conditions at the proposed parking plaza location provide an opportunity to build a vault below the parking area to capture water. Construction begins in August 2016. SAN is beginning the development of a holistic sustainability management plan that will inte- grate strategies for energy conservation, water efficiency, waste diversion, emissions reductions, and climate preparedness. Costs: Capital and O&M SAN provided capital costs for the bioswales at the rental car center. As noted above, the approximate costs for the bioswale system at the rental car center is $650,000 out of a total cost of $316 million. The costs for O&M are covered under the umbrella contract for landscaping. Important Implementation Issues for GSI Strategies The airport is developing an overall master plan concerning water management, to identify how much water to capture and how to use the collected water, taking into account the cost of water treatment. Once the plan is completed, SAN will be able to determine how each project at the airport will contribute to the overall goal. Unfortunately, one opportunity to implement concepts envisioned in the master plan – the construction of a new parking plaza – is moving too quickly to wait for completion of the master plan. Nonetheless, SAN is looking to incorporate rainwater capture and reuse into the design of the parking plaza. SAN does not encounter wildlife attractant issues. Standing water is avoided and no deten- tion/retention basins are located at the airport. SAN lacks space that other airports might have to expand or add other GSI BMPs. Its property spans 660 acres (one-sixth the size of Tampa International Airport), and it has only one runway.

84 Green Stormwater infrastructure Case Study of Austin–Bergstrom International Airport October 12, 2015 Characteristics: Climate Zone: Hot-Humid FAA Region: Southwest FAA Category: Primary Medium Highlights: 1) Vegetated filter strips utilized within runway safety area (RSA). 2) Bioretention systems installed in the median of access roads. 3) Rainwater harvesting installed at roofs in taxi cab parking area. Lessons Learned: 1) RSA requirements (i.e., compaction) may limit the effectiveness of vegetated filter strips. 2) FAA wildlife attractant requirements limit installation of GSI. 3) LEED certification drives installation of rainwater harvesting. 4) Maintenance appears to be limited to normal airport mowing and landscaping. 5) Vegetated filter strips utilization requires an approved Integrated Pest Management Plan. Green Stormwater Infrastructure: Austin–Bergstrom International Airport (AUS) has a variety of GSI practices including vege- tated filter strips, bioretention system, and rainwater harvesting. These are in addition to numer- ous sedimentation/filtration systems (Austin sand filters) that provide the primary treatment for stormwater runoff for much of the airport. A primary concern when selecting stormwater BMPs is to ensure that they do not attract wildlife. Vegetated Filter Strips: AUS uses vegetated filter strips along its runways and taxiways. Veg- etated filter strips are a natural choice for providing runoff management along runways and taxiways, because of the substantial vegetated area typically found adjacent to these surfaces, a configuration generated by the need to provide an RSA.1 The required RSA width is more than wide enough to provide substantial stormwater treatment; however, the required compaction of soils within the RSA may limit the stormwater volume reduction typical of vegetated filter strips. The City of Austin credits vegetated filter strips for water quality treatment at the airport when a ratio of 1 foot of pervious area to 0.33 of vegetated area exists. Maintenance for the vegetated filter strips mainly includes mowing as to not attract wildlife. Bioretention/Rain Garden Systems: AUS has installed a series of bioretention/rain garden sys- tems in the median of Spirit of Austin Lane (Figures A14 and A15) as a part of a project to convert the taxi cab waiting area to a cell phone lot. Part of the objective of this retrofit was to decrease the road width and provide a measure of traffic calming. The maintenance is completed as part 1 An RSA is defined as “the surface surrounding the runway prepared or suitable for reducing the risk of damage to airplanes in the event of an excursion from the runway.” In the United States, the recommended RSA should extend to 250 feet in each direction from the centerline of the runway. This area has to be capable, under normal (dry) conditions, of supporting air- planes without causing structural damage to the airplanes or injury to their occupants, which requires that the soil be highly compacted.

Source: M. Barrett (© 2015). Figure A14. Rain garden/bioretention facility at AUS. Source: M. Barrett (© 2015). Figure A15. Cross section of rain garden. Source: © Google Earth. Figure A13. Vegetated filter strips along runways at AUS.

86 Green Stormwater infrastructure of regular landscape maintenance. The bioretention systems have not been in place long enough to require major maintenance or any activities related to maintaining the water quality function. Rainwater Harvesting: AUS has installed rainwater harvesting systems at the taxi cab wait- ing area (Figure A16). The harvested rainwater is used for landscape irrigation. This system is a relatively new measure that was installed when the original taxi waiting area was converted to a cell phone lot. It appears that the major driver for this installation was to achieve a LEED rating for the facility. Lessons Learned from Installed GSI The lessons learned from the installed systems have been generally positive. It was especially important for the airport and the regulators to recognize the water quality benefits of the veg- etated filter strips located adjacent to the runways and taxiways. When the airport was first con- structed, these areas were not credited for any stormwater quality or volume reduction. It was only after the airport had been in operation for more than 10 years that the City of Austin was convinced of its benefits. Because of the large area occupied by the vegetated filter strips, the City now considers the runways to be “over-treated,” which provides a credit to offset stormwater treatment requirements for future additions to the airport. The bioretention systems/rain gardens installed as a traffic calming/separation feature appear to be working well. They are attractive and are indistinguishable from conventional landscaping in the general public’s eye. The rainwater harvesting was successful in that it helped the facility where it is installed achieve LEED Gold status. From an actual functional standpoint, it is likely not cost effective, since reclaimed water was already available on the airport property when the system was constructed. Operation and Maintenance (O&M) Requirements of the GSI The maintenance of the vegetated filter strips consists almost exclusively of mowing with the primary objective being to manage wildlife on the site. At AUS, the concern is rodents in the grass attracting predatory birds, which are a risk to aircraft. Consequently, the grass is mowed Figure A16. Rainwater harvesting at AUS taxi waiting area. Source: M. Barrett (© 2015).

Case Studies of GSi Strategies at Airports 87 frequently to a height of 6 inches to reduce cover and discourage rodents. There does not appear to be any maintenance exclusively done for water quality reasons, but vegetated filter strips do require the development and implementation of an Integrated Pest Management Plan. The maintenance of the rain garden/bioretention system is done by regular landscape crew as part of regular landscape maintenance. In effect, the rain gardens are treated like another flower bed on the site. The bioretention systems have not been in place long enough to require major maintenance or any activities related to maintaining the water quality function. Costs: Capital and O&M The vegetated filter strips were originally constructed to act as runway safety areas as required by FAA, and it was only afterward that their water quality benefit was recognized. Consequently, there is no capital cost associated strictly with their environmental benefit. This situation is analo- gous to the clear zones used on highways that intrinsically also function as vegetated filter strips. As mentioned previously, maintenance of the vegetated filter strips consists solely of mowing, which is done to discourage wildlife. This is an FAA requirement for safety areas, so there is no maintenance cost associated with the water quality element. Operation and maintenance costs have not been broken down for the rain gardens constructed near the cell phone waiting lot or for the rainwater harvesting system. The costs appear to be minimal and similar to costs incurred by other flower beds on the site. This may change in the future, should major rehabilitation be required to restore permeability of the filtration media. Regulatory Constraints and Flexibility Design of stormwater management facilities at AUS is primarily driven by the City of Austin requirements related to both quality and volume. In the conversion from an Air Force base to the airport, the amount of impervious cover at the site actually decreased, so no water quality controls were required at the time. Nevertheless, runoff treatment was provided for all the areas developed in the 1990s at the airport with the exception of the taxiways and runways. In 2012, an ordinance was adopted by the City that includes a “constrained development area” that includes the terminal, ramp, and most of the facility parking. This ordinance allows an alternative method for the purpose of meeting water quality volume requirements, as com- pared to the standard method specified in code. Design of the stormwater controls, except for the vegetated filter strips, appear to come directly from the City of Austin Environmental Criteria Manual (https://www.municode.com/library/tx/austin/codes/environmental_criteria_ manual). It is important to note that the City of Austin Land Development Code requires that water quality volume receives treatment equivalent to that provided by a sedimentation/filtration system. The City does not recognize some GSI treatment options as effective. These include vegetated swales and green roofs. The City design manual specifies capture volume as a function of the level of impervious cover. For sites with up to 20 percent impervious cover, the capture volume is 0.5 inch, which then increases by 0.1 inch for each 10 percent increase in impervious cover up to the maximum of 1.3 inches. The ordinance adopted by the City of Austin for the airport only requires 0.5-inch capture volume for all development within the “constrained development area”; however, this is compensated by over-treatment at other areas of the airport. The City of Austin credits vegetated filter strips for water quality treatment at the airport when a ratio of 1 foot of pervious area to 0.33 feet of vegetated area exists. Vegetated controls tend not to provide very good bacteria reduction, so all the sizing for systems in the Austin area is

88 Green Stormwater infrastructure done so that all runoff is assumed to be infiltrated, which makes them very large compared to the design guidelines used in many other jurisdictions. AUS has a detailed stormwater management plan that includes delineated drainage areas for all outfalls, as well as hydrologic (MIKE-SWMM) and hydraulic (HEC-HMS) models. The Imagine Austin Plan adopted by the City contains goals for sustainability for all municipal operations. Central goals of this priority program are to conserve water resources and improve watershed health. It also requires that all new facilities be at least LEED Silver. This guidance directs the airport staff to consider sustainability and environmental protection when making decisions regarding stormwater treatment, which helps promote the use of GSI where feasible. Airport staff play a role in determining type of stormwater treatment, but the options on the air- side especially are constrained. A sedimentation/filtration system will provide treatment for a new addition planned for the terminal and expansion of the ramp area. It is unlikely that bioretention would be acceptable, given a concern that the vegetation in such a system would provide habitat for rodents, which attract predatory birds. An existing vegetated filter strip did provide required water quality treatment for an extension of one of the taxiways. Another constraint for using GSI on the site arises from the airport’s previous use as an Air Force base. At that time, solvents (particularly tetrachloroethylene (TCE)) were routinely used for cleaning aircraft; consequently, there are areas of groundwater contamination on the site. In these areas, infiltration of runoff must be avoided to minimize mobilization of the groundwater. AUS operates under a Texas Industrial Multi-sector General Permit and has a SWPPP. The permit requires quarterly visual monitoring of outfalls and annual quantitative monitoring for heavy metals from representative outfalls. The monitoring is accomplished with grab samples. There has been no monitoring specifically related to determining BMP performance. The airport has extensive stormwater analytical data characterizing the terminal ramp’s runoff. This area of the airport has the highest potential for impacting stormwater. This analytical data is available for review and illustrates that AUS’s extensive stormwater management program, including BMPs, is functioning well. Airlines at AUS use propylene glycol for deicing. Planes are deiced at the gate, and runoff is col- lected in a trench drain on the ramp. The water and deicing chemical are collected in a concrete- lined basin. When the chemical oxygen demand is elevated, the mixture is pumped to a nearby Austin wastewater treatment plant, otherwise it is filtered, via the sand filter, and discharged to the storm drain system. A planned ramp expansion will include an expanded and improved concrete- lined pond system to accommodate increased operations, and provide better operational control over runoff. Typical deice events which result in low- to medium-strength contaminated storm- water will be managed primarily in the new pond system. In addition, the airport plans to construct an on-site land application treatment system to manage higher-strength stormwater impacted by aircraft deicing fluids. The land application system will be authorized by the Texas Commission on Environmental Quality (TCEQ) and City of Austin. The TCEQ and City requirements for land application are designed to ensure no stormwater runoff or groundwater are impacted by the land application area. Land application of higher-strength material will provide relief to the City of Austin waste- water treatment plant, which in the past has not been able to accept the large volume of higher- strength material. Land application will provide an alternative for the airport in instances where the treatment plant cannot accept the material, which in turn will help prevent operational and environmental concerns for the airport. All stormwater runoff from the airport is discharged to Onion Creek or one of its tributaries. The airport is not subject to any total maximum daily load (TMDL) requirements regarding

Case Studies of GSi Strategies at Airports 89 specific pollutants. As mentioned previously, any GSI practice installed at the airport must provide sand filter equivalent treatment for the following constituents: total suspended solids (20.62 mg/L), total nitrogen (1.07 mg/L), total phosphorus (0.099 mg/L), zinc (0.023 mg/L), lead (0.005 mg/L), chemical oxygen demand (22.4 mg/L), and E. coli (4895 CFU/100mL). Important Implementation Issues for GSI Strategies The two main issues associated with the implementation of GSI are wildlife management and groundwater contamination. Wildlife management on the airside is a particular concern with a desire to avoid either standing water or tall vegetation. Neither of these is an inherent issue with the use of bioretention/rain gardens, since they should drain fairly rapidly and low-growing turf- like vegetation could be selected instead of the larger plants often seen in these systems. There is more flexibility on the landside, but standing water is still a concern for attracting birds. At AUS, a potential issue is groundwater contamination from the time this was an Air Force base. Consequently, any facilities constructed in those areas must have an impermeable liner, which would preclude most of the expected volume reduction associated with infiltration. AUS went through a costly and time-consuming alternative compliance process allowed by City code, so that alternative design standards could be used. Furthermore, there are several addi- tional factors that were considered in the development of AUS’s ordinance, including (1) AUS has an industrial SWPPP and spill response plan that requires paved areas to be maintained so that they are clean and free of debris and chemicals and (2) AUS has an Integrated Pest Management Plan to manage pesticides and herbicides in order to reduce stormwater pollution. Alternative design standards include using sand filtration ponds in combination with vegetative filter strips to meet water quality volume requirements for the constrained development area. In addition, AUS has a site-specific vegetated filter strip treatment ratio that differs from the standard City of Austin code ratio. It would also fall on the Watershed Protection Department to verify or test alternative GSI practices before they could be routinely used at the airport. On the whole, it appears that the airport has successfully engaged the City departments that regulate stormwater runoff.

90 Green Stormwater infrastructure Case Study of Seattle–Tacoma International Airport October 7, 2015 Characteristics: Climate Zone: Marine FAA Region: Northwest Mountain FAA Category: Primary Large Highlights: 1) Bioswales receiving stormwater directly from streets and parking areas. 2) Vegetated filter strips installed along runways at 10 locations. 3) Enhanced bioswales polishing discharge from upstream detention ponds. 4) Installation of “Ecology Embankment” BMP. Lessons Learned: 1) Open water associated with GSI can be minimized by preventing access by wildlife (e.g., netting) or discouraging access by wildlife (e.g., overplanting for high-density growth of less desirable vegetation). 2) Capital costs for GSI are not a major challenge. 3) Minimize GSI operation and maintenance (O&M) costs by: a. Considering O&M requirements during design and b. Including O&M personnel during planning and design of BMPs. 4) Complete upstream pollutant source control as much as possible prior to installation of new BMPs. 5) Airports should consider installation of GSI BMPs at “end of pipe” rather than near the source (i.e., only vegetated filter strips can be used along runways). 6) Identify and reserve land for future GSI BMPs (potentially at end of runways in RSAs). Background: Seattle–Tacoma International Airport (SEA) is operated by the Port of Seattle as a primary large hub airport (2014 total air passengers: 37,497,941; total enplanements: 14,632,137). SEA has two runways. SEA contains approximately 2600 acres.2 The stormwater drainage system (SDS) collects over 900 acres of area, half of which is impervious. The normal average yearly precipitation for Seattle is approximately 38 inches.3 The weather in the Seattle–Tacoma area can be characterized as having a relatively high number of days per year with recorded precipitation (158 days) in comparison to other cities such as New York and Nashville at 119 days. Stormwater from the airport is collected in the stormwater collection system and, depending on the drainage area and water quality, is discharged either to the airport’s Industrial Wastewater System (IWS) for the biochemical oxygen demand (BOD) waste streams or to the Des Moines and Miller Creeks, for non-BOD waste streams. The SDS receives runoff from the subwatershed, 2 Washington State DOT Airport Facilities and Services Report; SEA, http://wsdot.wa.gov/aviation/planning/systemplan/ conditionassessment/ReportViewer.aspx. 3 Western Regional Climate Center, http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?wa7473.

Case Studies of GSi Strategies at Airports 91 with less potential for industrial activity on the west side of the airport. Industrial stormwater from the subwatershed on the east side of the airport is treated within the IWS for fuel spills by dissolved air floatation and discharged, depending on whether it is low- or high-strength BOD wastewater, to Puget Sound via the Midway Sewer District outfall pipe (low strength) or prior to transmission to King County’s Renton Treatment Plant (high strength). All stormwater dis- charges are subject to the requirements of the SEA NPDES permit (#WA-002465-1). Existing Green Stormwater Infrastructure: SEA has implemented examples of low-impact development (LID) and green stormwater infrastructure (GSI) strategies in three categories of BMPs: bioswales, vegetated filter strips, and enhanced swales. As of 2008,4 approximately 33 bioswales, 5 infiltration facilities (including the SDS2 biofiltration swale), and 10 runway filter strips had been installed at the airport. In the future, additional BMPs will be designed and installed based on the pending 2016 SEA storm- water management manual.5 Bioswales: The bioswales receive stormwater directly from the drainage areas associated with streets and parking lots and act like typical LID BMPs. These bioswales have been applied at two locations at SEA: 1. At the cell phone lot 2. Along the expressway. The bioswale located adjacent to the cell phone lot (Figure A17) was installed in approxi- mately October 2014 and was vegetated in March 2016. 4 RW Beck, Inspection, Maintenance, and Operation Procedures Manual, Seattle–Tacoma International Airport, February 2008, amended August 2013, Appendix C, Tables 3-1, 3-4 and 3-5. 5 RW Beck, Stormwater Management Manual for Port Aviation Division Property, October 2008, Port of Seattle, Aviation Division. Source: J. Jolley (© 2015). Figure A17. Cell phone lot bioswale.

92 Green Stormwater infrastructure The “ecology embankment” bioswale, installed in 2008–2009 adjacent to the expressway, was designed to follow the Washington State Department of Transportation (WSDOT) “ecology embankment system” (see Figures A18 to A20). It is an engineered filter strip containing four primary elements: the gravel (unvegetated) strip, the vegetated filter strip, an “ecology-mix” bed, and the gravel-lined underdrain.6 The bioswale has shown positive results in pollutant removal at WSDOT roadway projects in western Washington.7 The ecology embankment includes an underdrain which limits the amount of infiltration and is typically not included in LID bio- swales. SEA installed the underdrain as a precautionary measure to ensure standing water does not occur in compliance with FAA guidelines. The underdrain has since been found to be not necessary to prevent standing water and will be abandoned in order to increase infiltration. Vegetated Filter Strips: SEA has installed vegetated filter strips along the airfield in pre-existing grassy infield areas along all runways and taxiways (see Figures A21 through A24). Conventional grass filter strips were originally constructed at SEA to provide basic water quality treatment. As part of the new runway construction and other runway reconstruction, the filter strips were enhanced to encourage greater dispersion, water retention, and infiltration. Filter strip widths were extended by installing catch basins at locations farther from the edge of the tarmac during the runway retrofit. In most cases distance between the tarmac edge and the catch basin now exceeds 100 feet, as compared to the approximate 30 feet required for basic treatment. In addition, soil 6 Herrera Environmental Consultants, Inc., Technology Evaluation and Engineering Report: WSDOT Ecology Embankment; July 2006, http://www.wsdot.wa.gov/NR/rdonlyres/3D73CD62-6F99-45DD-B004-D7B7B4796C2E/0/EcologyEmbankment TEER.pdf. 7 RW Beck, Stormwater Management Manual for Port Aviation Division Property, October 2008, Port of Seattle, Aviation Division, page 111, Table 4-2, “Treatment BMPs Considered Reasonable for Use at STIA.” Figure A18. Expressway “ecology embankment” bioswale – cross section view. Source: WSDOT (2005) in Herrera Environmental Consultants, Inc., Technology Evaluation and Engineering Report: WSDOT Ecology Embankment; July 2006, http://www.wsdot.wa.gov/NR/rdonlyres/3D73CD62-6F99-45DD-B004-D7B7B4796C2E/0/ EcologyEmbankmentTEER.pdf.

Case Studies of GSi Strategies at Airports 93 Source: J. Jolley (© 2015). Figure A19. “Ecology embankment” bioswale. Figure A20. “Ecology embankment” along expressway, and cell phone lot bioretention swale on aerial photo of airport. Source: Port of Seattle (© 2013).

94 Green Stormwater infrastructure Source: Port of Seattle (© 2015). Figure A22. SEA filter strips configuration with catch basin and conveyance pipe layout. Source: B. Duffner (© 2015). Figure A21. Vegetated filter strip along SEA runway. within the filter strips’ upper 4 inches has been amended with compost to achieve an organic content of at least 10 percent. Enhanced (Bioretention/Media Filter) Swales: SEA has installed enhanced swales, which do not drain directly from impervious areas. These swales typically provide treatment polishing of discharge from upstream detention ponds (drained or pumped from dead storage in pond). Typi- cal designs of these swales have the cross section shown in Figure A25. GSI bioretention swale designs normally do not include underdrains in order to maximize infiltration. As shown below,

Case Studies of GSi Strategies at Airports 95 Source: B. Duffner (© 2015). Figure A23. Vegetated filter strip – storm drain in center of the strip. Source: B. Duffner (© 2015). Figure A24. Vegetated filter strip – view towards storm drain. SEA has added underdrains to its bioretention swales. However a valve is added at the underdrain discharge which is closed throughout most of the year. This modification allows SEA to drain the swale during the periods when the existence of standing water is expected to exceed 48 hours. These swales are primarily of two basic configurations—the bioretention swale or the media filter swales—which have been used alone or in combination. The bioretention swale is grass lined and composed of the following elements: (1) the fore bay unit containing quarry spalls or oyster shells to increase hardness (to enhance removal of dissolved zinc and copper) and (2) the 2-foot layer of amended soils of relatively high hydraulic conductivity, between 1 to 4 inches per hour. Infiltration may be limited below the amended soil by native materials.

96 Green Stormwater infrastructure The media filter swale is composed of layers of highly permeable, highly reactive sands to reduce zinc levels in the stormwater runoff including: • Planting topsoil: 50 to 70 percent sand, 15 to 25 percent compost, and 10 to 20 percent clean topsoil; • Media: 50 percent rhyolite sand, 30 percent zeolite, and 20 percent granular activated carbon; and • Coarse sand/pea gravel mix between media and underdrain. An example of a system combining the bioretention swale with the polishing media filter swale is shown in Figures A26 through A28. This system serves the upstream stormwater deten- tion basin SDN1/SDE4 at SEA. Operation and Maintenance (O&M) Requirements At SEA, operation and maintenance of GSI does not appear to be a major issue. Typical land- scaping O&M tasks associated with GSI at SEA include: • Watering – use drought-tolerant species, no watering required. • Erosion control – despite proper design, erosion may occur, inspect and replace soil, plant, and mulch in areas where erosion has occurred. • Sediment removal, which includes: – Occasionally pruning and removing dead material; – Removing nuisance or invasive plants through weeding (SEA does not use herbicides); – Selecting soil mix and plants for optimum fertility to ensure that nutrients and pesticides should not be required; Figure A25. Enhanced swale – typical design. Source: Adapted from Oregon State University Extension, Green Girl LDS, 2012. http://extension.oregonstate.edu/stormwater/standard- details#rgd. (CC BY-SA 3.0, https://creativecommons.org/licenses/by-sa/3.0/).

Case Studies of GSi Strategies at Airports 97 Figure A26. Location of SDE4/SDS1 bioswale and media filter (shown as lime green strips S1-8, and E4-15). Source: Port of Seattle (© 2013). Source: J. Jolley (© 2015). Figure A27. SDS1 infiltration filter.

98 Green Stormwater infrastructure – Replacing mulch annually where heavy metal deposition could occur (high traffic areas), or every 3 to 5 years for residential areas to maintain 2- to 3-inch depth; and – Replacing soil every 20 years and conducting tests to ensure soil removes heavy metals. Examples of SEA O&M procedures for GSI are included in the attachment to this case study. Capital and O&M Costs At SEA, capital costs do not appear to have been a major challenge to implementing its strate- gies. Though final cost estimates for GSI BMPs at SEA are not available, the illustrative costs at the 60 percent design stage for some BMPs were provided. The costs for enhanced bioswales are listed below (based on 60 percent design stage). • SDS1 = $192,725 (retrofit, 25 ft by 110 ft, media swale only) • SDE4 = $104,834 (5 ft by 160 ft grass swale and 5 ft by 150 ft media swale) • SDS4 = $386,799 (30 ft by 160 ft media swale only) • SDN1 = $151,889 (10 ft by 85 ft grass swale and 10 ft by 90 ft media swale) These costs are illustrative only and depend on the size and design of the system in addition to the local costs of labor and material in the Seattle area. Attachment: Example O&M Procedures for GSI at SEA8 Bioswale • Remove trash and debris accumulated in the bioswale or blocking inlet/outlet piping. • Mow vegetation or remove nuisance vegetation so that flow is not impeded. When grass becomes excessively tall (greater than 10 inches), it should be mowed to a height of 3 to 4 inches. Remove grass clippings. • When the depth of sediment accumulation on the grass exceeds 2 inches, remove sediment deposits on grass treatment area of the bioswale. There should be no areas of standing water once inflow has ceased. 8 RW Beck, Inspection, Maintenance, and Operation Procedures Manual, Seattle–Tacoma International Airport, February 2008, amended August 2013, Section 4, pp. 4-2 to 4-3. Source: J. Jolley (© 2015). Figure A28. SDS1 media filter swale.

Case Studies of GSi Strategies at Airports 99 • Regrade and reseed to design specifications where the bioswale has been eroded or scoured due to high flows or flow channelization. Filter Strips • Remove trash and debris accumulated in the filter strip. • Remove sediment deposits when they exceed 2 inches in depth or when edge dams prevent even flow through the filter strip. Re-level so slope is even and flows pass evenly through the strip. • Mow vegetation or remove nuisance vegetation so that flow is not impeded. When grass becomes excessively tall (greater than 10 inches), it should be mowed to a height of 3 to 4 inches. Remove grass clippings. • Repair eroded or scoured areas due to flow channelization, or higher flows. For ruts or bare areas less than 12 inches wide, repair the damaged area by filling with crushed gravel. The grass will creep in over the rock in time. If bare areas are large, generally greater than 12 inches wide, the filter strip should be re-graded and re-seeded. For smaller bare areas, overseed when bare spots are evident. Infiltration Facilities • Remove trash and debris from the top of the trench and surrounding area so runoff freely flows into the infiltration trench. • When depth of sediment accumulation on infiltration area exceeds 2 inches, remove sediment. • When infiltration rate is significantly decreased, remove sediment that forms a cover or fills void space so that the infiltration rate is similar (number of inches or millimeters per hour) to previous measurements.