Winter Design Storm Factor Determination for Airports (2012)

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46 Typically, a winter design storm or event is defined to ensure that the capacity of a facility or system component will ensure compliance at an acceptable service level (i.e., risk) with one or more regulatory requirements. This appendix provides an overview of the relevant FAA and EPA regulations that may apply to deicing runoff management system designs. A.1 FAA Regulatory Drivers The FAA provides guidance on design criteria for airport storm water drainage projects that can include deicing con- trols in the following ACs: 150/5300-14, “Design of Aircraft Deicing Facilities.” This AC discusses the sizing of deicing facilities in terms of the physical configuration of deicing pads and apron deicing areas to accommodate aircraft and in providing enough deic- ing positions to ensure adequate traffic capacity under severe weather conditions. No specific guidance is provided regard- ing the design basis for runoff management systems beyond a discussion of factors that affect sizing and the acknowledge- ment that “the state or local authority having jurisdiction generally sets construction and design standards.” 150/5320-5C/Unified Facilities Criteria 3-230-01, “Surface Drainage Design.” This combined Unified Facilities Criteria document and FAA AC provides comprehensive and practical guidance to engineers, airport managers, and the public for the design of storm drainage systems associated with transpor- tation facilities. Criteria are provided for the design of storm drainage systems that collect, convey, and discharge storm water on and around pavements and other transportation facilities. The updated criteria in this document are considered standard practice and allow users to take advantage of drainage design concepts and methods that are widely understood and accepted throughout the industry today. 150/5300-13, “Airport Design.” This document serves as the foundation of airport project design and establishes the basic criteria the designer must adhere to when design- ing airport deicing facilities. This AC discusses general air- port design practices such as runway and taxiway safety and object-free areas, longitudinal and transverse grading cri- teria, geometric design criteria, and other pertinent criteria that must be considered by the designer when siting and designing an aircraft deicing facility. A.2 Environmental Regulatory Drivers A variety of environmental regulations and permitting programs authorize storm water (or other appropriate) dis- charges associated with airport deicing and anti-icing opera- tions. As noted at the end of this section, federal, state, and local wet-weather permits and regulatory obligations are expanding in scope and complication, and entirely new pro- grams are on the horizon. Therefore, the most current regu- latory requirements must be considered in any evaluation. Federal Acts Affecting Airport Wet-Weather Discharges CWA Section 402 creates the NPDES program, through which all nonexempt facilities that discharge pollutants from a point source directly into a water of the United States must obtain a permit. The terms “pollutant,” “point source,” and “waters of the United States” are very broadly defined. Point-source discharges include, for example, sanitary and industrial wastewater that is treated at POTWs before being discharged to surface waters, treated wastewater from indus- trial facilities that is discharged directly to surface waters (with no POTW involved), and certain designated wet- weather flows that have been identified by Congress or the EPA for treatment prior to their discharge to surface waters. In most cases, storm water that is discharged to the receiv- ing waters via a constructed system (pipe, culvert, channel) is considered a point source necessarily subject to permit. A p p e n d i x A Regulatory Implications of Defining Winter Design Storms

47 Airports (and other regulated entities at airports) may have NPDES direct-discharge permits for storm water or other treated industrial wastewaters that flow directly to receiving water bodies. Airports that capture deicing opera- tion runoff for treatment or recycling (or that have other on- site operations that generate wastewater that is captured and sent to POTWs) may have pretreatment permits or agree- ments with their local POTW for handling those wastewaters sent for treatment through the sewer system. Finally, airports that collect storm water or other wastewater in tanks may truck those wastes to a centralized waste treatment facility for subsequent treatment generally governed by the terms, conditions, and prices set by an agreement with the central- ized waste treatment entity. Federal Storm Water Program Currently, there are three principle storm water regulatory programs in the United States: the industrial storm water permit program regulating discharges from a specific list of industrial operations, the municipal storm water program that controls discharges from most municipal separate storm sewer systems (MS4s), and the construction storm water pro- gram that applies to all active construction that disturbs a threshold quantity of land at a site. An airport could be sub- ject to all three of these programs. Under EPA’s industrial storm water permit program, 11 categories of industrial operations are required to obtain NPDES storm water permits. These categories are denoted by narrative descriptions and industrial classification codes, including Sector S “transportation facilities” that conduct vehicle or aircraft maintenance, equipment cleaning, or air- port deicing operations [see 40 CFR § 122.26(b)(14)(viii)]. The industrial storm water program regulates only those discharges associated with industrial activity and otherwise unregulated storm water discharges that are commingled with those industrial storm water discharges. Purely admin- istrative buildings, administrative parking lots, and storm water discharges from “nonindustrial” areas at the airport may not be covered by the industrial storm water program. The EPA created a municipal storm water program that requires most operators of MS4s to obtain NPDES storm water permits. Under the EPA’s MS4 storm water permit program, MS4 operators are responsible for meeting certain minimum permit requirements and may in turn require those entities that discharge into the MS4 to meet certain conditions or implement practices to minimize the pollutants entering the MS4 system. Typical areas at airports that may not be sub- ject to the industrial program but may otherwise be regulated by the MS4 program include public parking facilities, access roads, and commercial operations accessible by the public (car rental, gas station, food service, etc.). Because these areas generally are designed to drain away from the industrial or active construction areas at an airport (and into the MS4, obviously), the municipal storm water program may not be a significant factor in winter design storm analyses. The EPA also established a storm water permit program for any construction activity that disturbs 1 acre or more of land or is part of a common plan of development that would exceed 1 acre. While applicable to construction operations at airports, the construction storm water program gener- ally would not apply to airport deicing activities, with the exception of initial construction of certain management practices, drainage systems, or other controls. Nevertheless, as described previously, if that construction storm water drained into ponds or other drainage systems dedicated to the industrial storm water program, it would be regulated regardless of its designation as “construction-related storm water.” These overlapping aspects are important consider- ations for appropriately sizing collection and drainage struc- tures and the overall consideration of a design storm. In summary, the CWA requires that airports obtain a NPDES permit for any direct discharges of process waste- water and most storm water. Storm water can be regulated either through the industrial, construction, or municipal storm water programs. Indirect discharges of deicing or other indus- trial wastes sent to a POTW require authorization and often a permit from the POTW’s authority. Finally, any other waste- water may be trucked to a centralized waste treatment site if it cannot be managed in any other way on the airport property. Airport Storm Water Discharge Permits The NPDES program generally is implemented through two types of permits: general permits that reflect the permit- ting authority’s recognition that many similar types of facili- ties and operations may be covered under a more universally applicable permit, and individual permits that are issued spe- cifically to the regulated facility. The following discussions describe these two permitting devices. General industrial storm water permits. Because of the volume of regulated entities subject to the storm water pro- gram, the EPA has used general permits to ease its adminis- trative burden, and states with delegated permitting authority have followed suit. General permits are issued for specific groups of regulated entities and thus must be drafted rather generically to ensure that they are applicable to as many of those entities as possible. General permits go through a notice and comment rulemaking process, and once they are completed, facilities that wish to comply with the general per- mit typically must file a Notice of Intent form that certifies that the permittee will comply with the terms and conditions contained in the permit.

48 Individual industrial storm water permits. Unlike general permits, individual permits are tailored to the actual physical and operational characteristics at the permittee’s facility and require a thorough analysis of site-specific conditions. For this reason, individual permits are preferred by some regulators over general permits for complex facilities or where specific environmental concerns exist. While the EPA and most states have developed general permits that are broadly applicable to industrial storm water discharges, there has been a departure from this trend with airports that are more complex. Several states prohibit complex sites, including some airports, from seeking coverage under the state’s general permit, requiring instead that such sites obtain individual permits. The ratio- nale behind this requirement is that general permits provide limited site-specific controls, and while they may provide suf- ficient environmental protection for small or medium-sized airports, they are unlikely to do so for large airports. There are several fundamental differences in the develop- ment of general versus individual permits. General permits tend to provide more narrative approaches to fundamental permitting issues (for example, compliance with water quality standards and implementation of BMPs). Individual permits require a two-part analysis that first mandates implementa- tion of appropriate technology standards (typically BMPs in storm water permits) and next requires that the permit writer assess receiving waters and determine if additional compli- ance requirements should be imposed to maintain water quality standards. Airports that discharge to smaller, more sensitive water bodies will generate the more stringent analy- ses and requirements. These requirements may be expressed as numeric limits either on the concentrations or mass load- ings associated with the discharges or as performance met- rics associated with the deicing runoff control system (for example, percent of total applied deicers either collected and treated or contained in permitted discharges). Industrial pretreatment permits. Not all deicing runoff is discharged directly to waters of the United States through general or individual storm water permits. Deicer-laden run- off may be collected and then sent to POTWs for treatment. POTWs are allowed to accept industrial waste along with sanitary waste provided they are designed to treat the type of wastewaters entering their systems and that they comply with their own NPDES direct-discharge permits. Industrial users (in this case, airports) must comply with the POTWs’ pretreatment regulations and cannot discharge pollutants that would “pass through” or “interfere” with the POTWs. For the most part, deicing runoff is well suited to treatment at POTWs because it has high BOD, which can serve as food for bacteria used in the biological treatment process. POTWs charge fees to airports to offset the costs of treatment and generate income for the POTW. In many ways, pretreatment permits are similar to NPDES direct-discharge permits. The pretreatment permit may con- tain numeric limits that ensure compliance, or it may rely on BMPs to ensure that waters sent to the POTW are accept- able. As with direct-discharge permits, numeric limits may be expressed as concentration or mass-based limits, and usually both daily maximum and monthly average restrictions are provided. Co-Permittees Either general permits or individual permits may allow airports to include major tenants as co-permittees. Whether to include tenants as such, cover tenant operations through the airport’s permit without co-permittee status, or require tenants to obtain their own permits is an airport-specific decision. In both individual and general permit scenarios, airports may have to engage with tenants and manage sig- nificant interactions with them to ensure that appropriate controls are in place, functioning, and lead to permit com- pliance. This may require relatively detailed collaboration on the airport’s storm water pollution prevention plan, deicing runoff management plan, and other compliance mandates in the permit. A.3 Considering Probability in Permit Compliance There are no regulatory standards for defining the fre- quency of the deicing design event. While the building blocks of NPDES permits described provide the framework, permit- writer discretion fills in many of the specific aspects of the final NPDES permit, including the design event criteria. The probability of design event occurrence is one of the issues that can be discussed and negotiated by an airport dur- ing the permit drafting and negotiation process. Airports can engage permit writers to gain an understanding of the design conditions and other factors that the permit writer may be considering and to offer alternative approaches that might meet the permit writer’s needs while addressing key design storm factors that the airport may desire or that need to be addressed in a final permit. For example, the permit writer may want to apply a storm design criterion of some type but may not necessarily understand how deicing events differ from ordinary precipitation events. That lack of understanding may lead to the permit being developed based on conventional storm water approaches, such as collecting the first ½ in. of precipitation or the 2-year, 24-hour storm event, neither of which may be an appropriate design basis for a system that manages meltwater from snowfall that has accumulated over several days or even weeks of freezing precipitation.

49 Finally, the NPDES permit program provides certain pro- tections for situations that may arise during permit com- pliance, particularly with regard to excessive precipitation or flooding conditions. Standard NPDES permit conditions include two particular safe harbors—one referred to as an “upset,” the other as a “bypass”—each of which may include reference to threshold conditions beyond which system capacity is acknowledged to be exceeded. The negotiation of these conditions should take into consideration the expected frequency of upset and bypass conditions. A.4 Looking Forward A challenge in defining an appropriate design storm event lies in the uncertainty of future environmental standards. NPDES requirements are certain to change, acceptable fre- quency of permit exceedances may change, and permit writ- ers’ level of discretion is an unknown variable. How does the likelihood of more stringent environmental standards and aggressive enforcement affect the effectiveness of a design storm event using current regulatory requirements? There are several programmatic developments ongoing at the EPA that may affect storm water permitting and deter- minations relating to design storm factors for airports in the future. First, the EPA is assessing whether to change its basic storm-water permitting philosophy from a BMP-based approach to one that relies more heavily on end-of-pipe numeric effluent limits. A numerical approach will increase the risk and liability for noncompliance and is likely to require many airports to revisit the design basis for existing controls to confirm that they will comply with NPDES permits. Next, the EPA has initiated a major expansion of the NPDES storm-water permitting program. The EPA has indicated that it will expand the number of MS4s subject to the storm-water permit program as well as place more strict mandates on reg- ulated MS4s regarding controls on discharges into the MS4. This may force MS4s to place greater emphasis on regulating any entity that discharges into the MS4, such as an airport, as opposed to focusing on controlling the discharges at the point where the MS4 discharges into a U.S. water. The EPA also wants to expand the storm water program to control “post- construction” storm water discharges for the life of a building project. As of the date of this report, the EPA has indicated that it may require every developed or redeveloped site to con- trol the first inch of precipitation on site (no discharge) or mandate that the developed site mimic the predevelopment hydrology of that site. While it is not possible to predict what the EPA ultimately may mandate, these issues are critical for factoring into future design storm analyses. The EPA also is proposing to refine its guidance for deter- mining what constitutes a “water of the United States” for permitting purposes. As currently stated, the current draft guidance would significantly expand the scope of regulated water bodies and how the NPDES permits described previ- ously would be implemented and designed. For example, an airport that currently uses naturally created ponds on its property for controlling flows and obtaining on-site treat- ment prior to discharge off site may have to treat those ponds as “waters of the United States” and add new treatment devices before any water can drain into those ponds, even though they are fully contained on airport property and not subject to any public use or enjoyment. The EPA also may regulate drainage ditches that drain to waters of the United States as if those ditches were natural water bodies. No reso- lution is imminent, but these are issues that should be looked into before design storm factors are finalized for an airport.

Abbreviations and acronyms used without definitions in TRB publications: AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation