Deicing Planning Guidelines and Practices for Stormwater Management Systems, second edition (2020)

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6 This chapter provides an overview of technical and regulatory issues, site-specific factors to consider, and a generally applicable methodology for developing an effective deicing runoff control program for airport operators. Aircraft and Airfield Requirements for Deicing Safety Issues Aircraft deicing is required to ensure flight safety. Even small amounts of snow and ice can seriously degrade the aerodynamic performance of an aircraft’s lifting surfaces with poten- tially catastrophic consequences. In addition, ice can impede the operation of control surfaces if it forms on mechanical joints or actuators. Achieving and maintaining safe flight condi- tions requires deicing, possibly followed by anti-icing, which is intended to provide sufficient holdover time to keep the critical aircraft surfaces free of ice-related contamination through taxiing and takeoff. Aircraft deicing is most often conducted by aircraft operators or their contractors, but pilots have the final responsibility regarding the adequacy of deicing relative to flight safety. Similarly, airfield pavement surfaces should provide sufficient friction for safe landing, taxiing, and takeoffs during winter weather conditions. In most instances, deicing is con- ducted to maintain critical friction on the airfield pavement surfaces by keeping them free of snow and ice. Airfield deicing is conducted at the discretion of the airport operator. This discretion extends to closing the airfield if safe operating conditions cannot be maintained. Applicable FAA Regulations Deicing practices are regulated and implemented with an overriding emphasis on safety. No practice or system of practices should degrade or compromise flight safety. The FAA provides guidance on activities related to deicing in the form of ACs, FAA orders, and engineering techni- cal letters. The following key documents provide specific FAA technical and regulatory guidance to airport operators regarding deicing facilities and controls: • AC 150/5300-13, Airport Design. Provides standards and recommendations for the design of civil airports. To ensure aircraft safety, the location and operation of deicing facilities must follow these clearance and separation standards, which involve airspace, aircraft sepa- rations, FAA Technical Operations facilities critical areas, and Airport Traffic Control Tower line-of-sight criteria. • AC 150/5300-14, Design of Aircraft Deicing Facilities. Provides standards, specifications, and guidance for designing aircraft deicing facilities. Airport managers can construct, C H A P T E R 2 Guidelines for Developing Integrated Deicing Runoff Management Systems

Guidelines for Developing Integrated Deicing Runoff Management Systems 7 within FAA standards, deicing facilities at terminals, on apron areas and taxiways, and near departure runways. Aircraft deicing facilities are recommended at airports where icing conditions are expected, including airports that serve aircraft that can develop frost or ice on critical surfaces even if the airport itself does not experience ground-icing conditions. • AC 150/5220-18, Buildings for Storage and Maintenance of Airport Snow and Ice Control Equipment and Materials. Provides guidance for site selection and design of buildings used to store and maintain this equipment, approved materials, and personnel areas required to support the requirements under the airport operator’s winter storm man- agement plan. Specific maintenance buildings with appropriate storage areas are needed to help protect and service the costly pieces of complex and technologically sophisticated equipment for the control of snow, slush, and ice on the nation’s airports. • AC 150/5200-30, Airport Winter Safety and Operations. Provides guidance to assist air- port operators to develop a snow and ice control plan, conduct and report runway friction surveys, and establish snow removal and control procedures. For airports certified under 14 Code of Federal Regulations (CFR) Part 139, Certification of Airports, the Snow and Ice Control Plan is referenced in section 139.313, Snow and Ice Control. This AC also pro- vides guidance on aircraft and airfield deicing source controls and snow clearing operations (deicing activities). Aircraft deicing facilities funded under federal grant assistance programs must follow these guidelines. In addition, FAA provides extensive guidance regarding all aspects of aircraft operations under winter conditions. The following selected ACs are especially relevant to the objectives of this guidance document. • AC 120-60, Ground Deicing and Anti-icing Program. Provides an industrywide stan- dard for obtaining approval of a ground deicing/anti-icing program. In addition, it pro- vides a means for a certificate holder to deice/anti-ice aircraft using another certificate holder’s personnel and procedures or contract personnel who have been trained by the other certificate holder. • AC 135-16, Ground Deicing and Anti-icing Training and Checking. Provides guidance regarding ground deicing and anti-icing training requirements that should be incorpo- rated into an approved training program for certain aircraft operators; ground deicing and anti-icing guidance for those aircraft operators that are not required to have an approved training program; and pre-takeoff contamination aircraft checks required of certain air- craft operators. • AC 120-58, Pilot Guide Large Aircraft Ground Deicing. Provides recommendations for the safe operation of large aircraft during icing conditions and guidelines for the development of adequate procedures for deicing large aircraft. • AC 120-89, Ground Deicing Using Infrared Energy.1 Provides guidelines and recommen- dations for pilots, certificate holders, and operators of deicing facilities regarding the use of infrared technology for deicing aircraft. • AC 150-5070-6, Airport Master Plans. Provides guidelines and recommendations for prepa- ration of master plans for airports including environmental factors like aircraft and pavement deicing. A comprehensive library of ACs may be found on the FAA’s online Advisory Circulars Library: http://rgl.faa.gov/. 1 No airports are known to be actively using infrared deicing technology as of the publication date of ACRP Research Report 14, 2nd edition.

8 Deicing Planning Guidelines and Practices for Stormwater Management Systems SAE International Deicing Standards SAE International’s Technical Standards Development Program publishes the following documents describing specifications, standards, and requirements for virtually every aspect of aircraft and airfield deicing: • AMS1424 Deicing/Anti-Icing Fluid, Aircraft SAE Type 1 • AMS1428 Fluid, Aircraft Deicing/Anti-Icing, Non-Newtonian (Pseudoplastic), SAE Types II, III, and IV • ARP1971 Aircraft Deicing Vehicle – Self-Propelled • ARP5058 Enclosed Operator’s Cabin for Aircraft Ground Deicing Equipment • AS5116 Minimum Operational Performance Specification for Ground Ice Detection Systems • ARP5660 Deicing Facility Operational Procedures • AS5681 Minimum Operational Performance Specification for Remote On-Ground Ice Detection Systems • AS5900 Standard Test Method for Aerodynamic Acceptance of AMS1424 and AMS1428 Aircraft Deicing/Anti-Icing Fluids • AIR6232 Aircraft Surface Coating Interaction with Aircraft Deicing/Anti-Icing Fluids • AIR6284 Forced Air or Forced Air/Fluid Equipment for Removal of Frozen Contaminants • AS6285 Aircraft Ground Deicing/Anti-Icing Processes • AS6286 Training and Qualification Program for Deicing/Anti-icing of Aircraft on the Ground • AS6286/1 Processes Including Methods • AS6286/2 Equipment • AS6286/4 Weather • AS6286/5 Health, Safety and First Aid • AS9968 Laboratory Viscosity Measurement of Thickened Aircraft Deicing/Anti-icing Fluids with the Brookfield LV Viscometer These documents are available from SAE International: www.sae.org. Deicing Products There are a limited number of products that meet SAE standards and are recommended by the FAA for use in aircraft and airfield deicing. For aircraft, the predominant deicing and anti-icing fluids are based on one of two freezing-point depressants (FPDs): propylene glycol (PG) and ethylene glycol (EG). However, there are commercially available aircraft fluids that are based on other FPDs. At the time of this writing, other aircraft deicing products based on propanediol and glycerin are available but have only limited use in U.S. markets. Conversations with various air carriers indicate that available glycerin-based products may lead to smearing on the windshield that interferes with visibility. The most dominant fluids used contain glycols as the main ingredient, along with water and an additives package. The additives package repre- sents a relatively small fraction (less than 2%) of the total fluid volume, and includes corrosion inhibitors, surfactants, dyes, thickeners, pH buffers, and defoamers. The specific constituents vary greatly by product and manufacturer, and are proprietary formulas known only to the manufacturers. PG is the dominant FPD in U.S. markets as EG is considerably more toxic. The National Institute for Occupational Safety and Health (NIOSH) states EG can be rapidly absorbed through the digestive system, and other sources indicate ingestion of approximately three ounces can be fatal. However, as temperatures decrease below 0°F, PG becomes more viscous, which can make it difficult for it to be applied to aircraft. In these situations, EG provides a lower viscosity and better heat transfer and is often used in places like Alaska or Canada.

Guidelines for Developing Integrated Deicing Runoff Management Systems 9 There are several SAE types of aircraft fluid, categorized on the basis of their use and properties: • Type I fluids are typically diluted with water and heated before application to remove frost, ice, and snow from aircraft. Type I fluids are relatively thin-bodied and may provide some nominal anti-icing protection, depending on the ambient weather conditions. These fluids are grouped as aircraft deicing fluids (ADFs). SAE publication AMS 1424, “Deicing/ Anti-Icing Fluid, Aircraft,” contains the specifications for these fluids. • Type II and IV fluids are relatively viscous and are typically applied directly to a clean air- craft surface without dilution. Type IV fluids have improved holdover times and have largely replaced Type II fluids used by commercial aircraft operators. These fluids are grouped as aircraft anti-icing fluids (AAFs). SAE publication AMS 1428, “Fluid, Aircraft Deicing/ Anti-icing, Non-Newtonian (Pseudoplastic), SAE Types II, III, and IV,” contains the speci- fications for these fluids. • Type III fluids are intended for anti-icing protection on aircraft with lower rotation speed at lift off. The use of Type III fluids is relatively limited. SAE publication AMS 1428, “Fluid, Aircraft Deicing/Anti-icing, Non-Newtonian (Pseudoplastic), SAE Types II, III, and IV,” contains the specifications for these fluids. Airfield pavement deicing material (PDM) options are much more varied and include sand as well as liquid and solid-form deicing chemicals. The FPDs in deicing products include EG or PG, polyol, urea, potassium acetate, sodium acetate, sodium formate, and potassium formate. A survey of airports conducted as part of the ACRP Research Report 14, 2nd edition update indicated that potassium acetate-based fluids and sodium formate based solids are the most commonly used PDMs in the North American market. Prior to 1990, glycol and urea products were the primary airfield pavement deicers used at airports. Since then, alternative pavement- deicing products with reduced environmental impact (for example, lower biochemical oxygen demands [BODs] and toxicity) have been introduced to the market. This trend was accelerated by the deicing Effluent Limitation Guidelines, which requires either the elimination of the use of urea-based airfield deicers or compliance with a relatively stringent limitation on ammonia con- centrations in storm water discharges. The reduced environmental impact products are available in both solid (for example, sodium formate and sodium acetate) and liquid (for example, potas- sium acetate) forms. Limited information is available on the contribution of the acetate- and formate-based PDMs to toxicity and BOD in airport stormwater discharges relative to those from aircraft deicers, but research to better define these issues is ongoing. Ongoing research and development of aircraft and airfield deicers is being driven by both environmental considerations and materials compatibility issues. These efforts are resulting in continual improvement of existing products and the introduction of new products. Environmental Concerns Deicing runoff can contribute to adverse environmental impacts from the deicing products used. There also may be environmental impacts from non-deicing-related pollutants that appear in deicing runoff but are unrelated to the deicers themselves. Typical Deicing Runoff Pollutants All chemical formulations currently approved for aircraft and airfield pavement deicing can have environmental implications when they become entrained in stormwater runoff and are dis- charged to receiving waters, such as streams, lakes, or rivers. Environmentally relevant charac- teristics of aircraft deicing and anti-icing products commonly used at North American airports at the time of this writing are listed in Table 2-1. Similar information regarding airfield pavement

10 Deicing Planning Guidelines and Practices for Stormwater Management Systems Table 2-1. Summary of available information regarding the environmental characteristics of aircraft deicing and anti-icing fluids (circa 2018). Brand Name FPD Manufacturer/ Distributor Product No. Specific Gravity COD (mg/L) TOD BOD5 BOD20 (mg/L) Biodegradation or kg O2 /kg fluid 20°C kg/L 20°C 2°C 20°C 2°C Type I Polar Plus ADF Concentrate PG Cyrotech — 1.043 1.57 g O2/g deicer 65% biooxidation — — — — Polar Plus 63/37 Dilute ADF PG Cyrotech — 1.041 0.90 g O2/g deicer — 40% biooxidation — — — — Polar Plus 55/45 Dilute ADF PG Cyrotech — 1.039 0.86 g O2/g deicer — 36% biooxidation — — — — Polar Plus LT ADF Concentrate PG Cyrotech — 1.043 1.61 g O2/g deicer — 57% biooxidation — — — — Polar Plus LT ADF 63/37 Dilute PG Cyrotech — 1.041 1.01 g O2/g deicer — 36% biooxidation — — — — Polar Plus LT ADF 55/45 Dilute PG Cyrotech — 1.039 0.89 g O2/g deicer — 31% biooxidation — — — — Octoflow EF PG Clariant 243150 1.044 — — — — — — — Octoflow EF 55/45 Dilute PG Clariant 243151 1.038 — 1.26 kg O2/kg of fluid 44% biooxidation — — — — Safewing MP I ECO Dilute 55/45 PG Clariant 197564 1.039 — — — — — — — Safewing MP I Eco PG Clariant 190933 1.0452 — — — — — — — E188 EG LNT Solutions — 1.13 – 1.15 g/cm 25°C 1.18 kgO2/kg — 59% biooxidation — — — — P180 PG LNT Solutions — 1.045 1.34 kgO2/kg — 31% biooxidation — — — — UCAR Concentrate EG DOW Chemical Company — 1.1 — 1.29 mg/mg — — — — — UCAR 50/50 EG DOW Chemical Company — 1.1 — 1.29 mg/mg — — — — — UCAR XL 54 EG DOW Chemical Company — 1.073 — 1.29 mg/mg — — — — — UCAR PG Concentrate PG DOW Chemical Company — 1.045 — — — — — — —

Guidelines for Developing Integrated Deicing Runoff Management Systems 11 Aquatic Ecotoxicity Notes Acute Toxicity to Fish Acute Toxicity to Aquatic Inverts Toxicity to Aquatic Plants Toxicity to Microorg. Chronic Toxicity to Fish Chronic Toxicity to Aquatic Inverts Sheepshead Minnow Fathead Minnow Salmon Rainbow Trout Daphnia magna Ceriodaphnia dubia Saltwater Mysid Freshwater Algae Marine Algae — LC50 6,350 mg/l — — LC50 6,825 mg/l — — — — — — — (a) — LC50 6,350 mg/l — — LC50 6,825 mg/l — — — — — — — (a), (b) — LC50 6,350 mg/l — — LC50 6,825 mg/l — — — — — — — (a), (b) — LC50 45,400 mg/l — — LC50 28,000 mg/l LC50 21,800 mg/l — — — — — — — LC50 45,400 mg/l — — LC50 28,000 mg/l LC50 21,800 mg/l — — — — — — (a), (b) — LC50 45,400 mg/l — — LC50 28,000 mg/l LC50 21,800 mg/l — — — — — — (a), (b) — — — LC50/96 HR 40,613 mg/l — — — EC50/96 HR 19,000 mg/l — — 30 DAY 2,500 mg/l NOEC/ 7 DAY 13,020 mg/l (c) — — — LC50/96 HR 40,613 mg/l — — — EC50/96 HR 19,000 mg/l — — 30 DAY 2,500 mg/l NOEC/ 7 DAY 13,020 mg/l (c) — — — LC50/96 HR 40,613 mg/l — — — EC50/96 HR 19,000 mg/l — — 30 DAY 2,500 mg/l NOEC/ 7 DAY 13,020 mg/l (c) — — — LC50/96 HR 40,613 mg/l (c) EC50/48 HR 10,000 mg/l — — EC50/72 HR >10,000 mg/l — — 30 DAY 2,500 mg/l (f) — — LC50/96 HR 10,225 mg/l — — LC50/48 HR 3,650 mg/l — — — — — — — — LC50/96 HR 12,500 mg/l — — LC50/48 HR 10,500 mg/l — — — — — — — — — — — — — — — — — — — — — LC50/96 HR 7,500 mg/l — LC50/96 HR 15,700 mg/l EC50/48 HR 43,4200 mg/l EC50/48 HR 5,700 mg/l — — — — — — — LC50/96 HR 7,500 mg/l — LC50/96 HR 15,700 mg/l EC50/48 HR 43,4200 mg/l EC50/48 HR 5,700 mg/l — — — — — — — LC50/96 HR 6,900 mg/l — LC50/96 HR 20,900 mg/l EC50/48 HR 19,200 mg/l EC50/48 HR 4,300 mg/l — — — — — — (a) (continued on next page)

12 Deicing Planning Guidelines and Practices for Stormwater Management Systems Table 2-1. (Continued). Brand Name FPD Manufacturer/ Distributor Product No. Specific Gravity COD (mg/L) TOD BOD5 BOD20 (mg/L) Biodegradation or kg O2 /kg fluid 20°C kg/L 20°C 2°C 20°C 2°C UCAR PG 55/45 PG DOW Chemical Company — 1.035- 1.055 — — — — — — — Kilfrost DF Plus PG Kilfrost — 1.045 1.39 kgO2/kg — 59% biooxidation — — — — Kilfrost DF Sustain PG Kilfrost — 1.053 1.39 kgO2/kg — — — — — — Type II Kilfrost ADB-K Plus PG Kilfrost — 1.040 0.85 kgO2/kg — 27% biooxidation — — — — Type IV Polar Guard Advance PG Cryotech — 1.038 0.82 g O2/g deicer — 40% biooxidation — — — — Maxflight Type IV PG Clariant 243159 1.041 785,000 mg/l — — 520,000 mg/l — — — Safewing MP IV Launch PG Clariant 233876 1.043 — — — — — — — Kilfrost ABC-S Plus PG Kilfrost — 1.038 0.69 kgO2/kg — 27% biooxidation — — — — Note: Footnoted information provided by manufacturers (a) Toxicological information was based on the undiluted product. (b) Biodegradable information was based on calculation. (c) Specific toxicological information is not available and propylene glycol was used as a surrogate. deicing products is contained in Table 2-2. ACRP Web-Only Document 3: Formulations for Air- craft and Airfield Deicing and Anti-Icings: Aquatic Toxicity and Biochemical Oxygen Demand and ACRP Web-Only Document 8: Alternative Aircraft Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxygen Demand provide more in-depth information on the constitu- ents of deicers, their environmental implications, and the potential for alternative formulations. The FPDs in aircraft and pavement deicing products are highly biodegradable in the environ- ment. Discharges containing deicers may contribute to or result in reduced dissolved oxygen concentrations in receiving waters as a result of the consumption of oxygen by bacteria as they break down the biodegradable matter. Airfield pavement deicers that contain FPDs based on potassium or sodium will contribute to the total dissolved solids (TDS) of airfield deicing runoff. Elevated TDS in airfield deic- ing runoff may have implications to certain treatment technologies or the water quality of receiving waters. Product additives, and to a lesser extent the FPDs required to meet SAE specifications, may result in exposure of aquatic organisms to toxic pollutants. The toxicity of individual products

Guidelines for Developing Integrated Deicing Runoff Management Systems 13 Aquatic Ecotoxicity Notes Acute Toxicity to Fish Acute Toxicity to Aquatic Inverts Toxicity to Aquatic Plants Toxicity to Microorg. Chronic Toxicity to Fish Chronic Toxicity to Aquatic Inverts Sheepshead Minnow Fathead Minnow Salmon Rainbow Trout Daphnia magna Ceriodaphnia dubia Saltwater Mysid Freshwater Algae Marine Algae — LC50/96 HR 6,900 mg/l — LC50/96 HR 20,900 mg/l EC50/48 HR 19,200 mg/l EC50/48 HR 4,300 mg/l — — — — — — (a) — LC50 96 HR 6,250 ml/l — — EC50 48 HR 3,000 mg/l — — — — — — — — LC50 96 HR 26,250 mg/l — LC50 96 HR 27,800 mg/l EC50 48 HR 27,500 mg/l — — — — — — — — — LC50 96 HR 1,425 ml/l — — EC50 48 HR 750 mg/l — — — — — — — — — LC50 707 mg/l — — LC50/ >1,000 mg/l — — — — — — — — LC50/48 HR 1,975 mg/l — LC50/96 HR 40,613 mg/l (f) — — — EC50/96 HR 19,000 mg/l (f) — — 30 DAY 2,500 mg/l (f) NOEC/ 7 DAY 13,020 mg/l (f) — LC50/96 HR 2,443 mg/l — LC50/96 HR 2,443 mg/l EC50/48 HR 976 mg/l — — EC50/96 HR 19,000 mg/l — — 30 DAY 2,500 mg/l (f) NOEC/ 7 DAY 13,020 mg/l (f) — LC50 96 HR 1,725 ml/l — — EC50 48 HR 1,350 mg/l — — — — — — — varies, depending on the proprietary additive packages unique to each formulation. PG and EG can be toxic to aquatic organisms at elevated concentrations, but the toxicity of aircraft deicing runoff is typically driven by the additives in ADF and AAF. The FPDs in acetate- and formate- based PDMs are the primary source of aquatic toxicity in these products.2 Where urea is used for pavement deicing, ammonia toxicity to aquatic organisms is typically a significant concern. Further discussion of the variability in environmental profiles of deicers may be found in the product selection fact sheets (Fact Sheets 1 and 16). Other potential impacts of deicers in runoff can include odor problems and growth of nuisance attached bacteria, typically Sphaerotilus sp. (See ACRP Report 115: Understanding Microbial Bio- films in Receiving Waters Impacted by Airport Deicing Activities). Occasionally, aircraft-deicing runoff has been implicated as contributing to foaming problems at stormwater outfalls. 2 Aquatic Toxicity of Airfield-Pavement Deicer Materials and Implications for Airport Runoff, Corsi, S.R., Geis, S.W., Bowman, G., Failey, G.G. & Rutter, T.W., Environ. Sci. Technol., 2009, 43 (1), pp. 40–46 DOI: 10.1021/es8017732

14 Deicing Planning Guidelines and Practices for Stormwater Management Systems Nondeicing Runoff Pollutants Stormwater runoff from deicing operations is regulated pursuant to federal and state indus- trial stormwater permitting programs. Other airport operations may contribute additional pollutants to these stormwater discharges, including fuels, suspended solids, dissolved solids, and oils/greases. Monitoring Considerations Airport industrial stormwater permits commonly have stormwater monitoring require- ments for deicing materials or other parameters that may be affected by the presence of deicing materials. Monitoring may also be conducted to support operation of stormwater management Table 2-2. Summary of available information regarding the environmental characteristics of airfield pavement deicing products (circa 2018). Note: PA=potassium acetate; SA=sodium acetate; PG=propylene glycol; SF=sodium formate; PF=potassium formate; SP=Susterra propanediol. Brand Name FPD Manufacturer/ Distributor Product No. Specific Gravity/ Relative Density COD (mg/L) TOD BOD5 BOD20 kg O2 /kg fluid, 20°C kg/L, 20°C 2°C kg O2 /kg Fluid 20°C kg O2 /kg Fluid 2°C Safeway KA HOT PA Clariant 198176 1.281 0.3 kg/kg — — — — — — Safeway SF SF Clariant 107966 — 0.24 kg/kg — 58% biooxidation — — — — GEN3 Polyol LNT Solutions — 1.24 – 1.27 g/ml 0.66 kgO2/kg — 30% biooxidation — — — — IceCare SF LNT Solutions — 0.92- 0.95 g/cc 211 mgO2/g — — — — — — Alpine RF-11 PA Nachurs Alpine Solutions I000093, I000115, I000119 1.28 0.35 kg O2/kg 21% biooxidation — — — — Alpine RF-14F PF Nachurs Alpine Solutions I000144 1.33 — — — — — — — Ecoway SF Nachurs Alpine Solutions I000131; I000132 0.9-1.0 211 mgO2/g — — — — — — LC17 PG, PA Cryotech — 1.15 — 0.68 kg O2/ kg 0.24 kg O2/kg — — — — E36 PA Cryotech — 1.28 — 0.34 O2/g 0.25 g O2/g — — — — NAAC SA Cryotech — 1.5 — 0.74 O2/g 0.45 g O2/g — — — — NEWDEAL Blend SF, SA New Deal Deicing — 1.8 — 0.34 O2/g 0.15 O2/g — — — —

Guidelines for Developing Integrated Deicing Runoff Management Systems 15 control measures, including facilitating segregation of stormwater by deicer concentrations, monitoring effluent from control measures to assess performance or identify when maintenance is needed, and metering influent stormwater to treatment system processes. Effective use of moni- toring to support these purposes requires the selection of appropriate monitoring parameters (e.g., chemical oxygen demand [COD], dissolved oxygen [DO], ammonia), moni toring type (handheld, test kit, or online), monitoring methods (e.g., Ultra-violet [UV]/persulfate for online total organic carbon [TOC]), and instruments. ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials includes a step-by-step process for identifying, evaluating, and selecting methods to monitor stormwater containing deicing materials. In addition to monitoring for individual parameters, some airports are required by reg- ulatory agencies to conduct whole effluent toxicity (WET) testing to monitor and limit the Aquatic Ecotoxicity Notes Acute Toxicity to Fish Acute Toxicity to Aquatic Inverts Toxicity to Aquatic Plants Toxicity to Microorg. Chronic Toxicity to Fish Chronic Toxicity to Aquatic Inverts Sheepshead Minnow Fathead Minnow Salmon Rainbow Trout Daphnia magna Ceriodaphnia dubia Saltwater Mysid Freshwater Algae Marine Algae — — — — EC50/48 HR >1,000 mg/l — — EC50/72 HR >100 mg/l — — — — — — — — EC50/48 HR >1,000 mg/l — — EC50/72 HR >100 mg/l — — — — — — LC50 96 HR >11,000 mg/l — EC50/48 HR >12,000 mg/l — — — — — — — — — — — — EC50/48 HR 3.2 g/l — — — — — — — — — — — — LC50/48 HR 2,825 mg/l — — — — — — — — — LC50 96 HR >1,000 mg/l — — EC50/48 HR >1,000 mg/l — — EC50/72 HR >1,000 mg/l — — — — — — — — — EC50/48 HR 3.2 g/l — — — — — — — — — LC50/48 HR 4,225 mg/l — — LC50/48 HR 4,150 mg/l — — — — — — — LC50/48 HR 6,300 mg/l LC50/48 HR 3,000 mg/l — — LC50/48 HR 2,175 mg/l LC50/48 HR 687 mg/l LC50/48 1,414 HR mg/l — — — — — LC50/48 HR >8,000mg/l LC50/48 HR 3,750 mg/l — — LC50/48 HR 3,500 mg/l LC50/48 HR 1,683 mg/l LC50/48 ~8,000 HR mg/l — — — — — — — — — LC50/48 HR 3,950 mg/l — — — — — — —

16 Deicing Planning Guidelines and Practices for Stormwater Management Systems potential for adverse impacts to aquatic organisms. Conducting WET testing at airports can present unique challenges due to the variability in deicer application, stormwater discharge vol- umes, and receiving stream flow and assimilative capacity. ACRP Report 134: Applying Whole Effluent Toxicity Testing to Aircraft Deicing Runoff describes some of the unique characteristics of stormwater WET testing at airports and provides guidance for developing appropriate WET testing programs. Monitoring data may also be used in assessing the effectiveness of existing stormwater control measures or identifying the need for new or enhanced control measures to manage deicing materials in stormwater. Implementation of deicer management control measures may repre- sent a significant investment for an airport and these decisions are often made on the basis of limited monitoring data. Airports must determine if the monitoring data collected as part of routine permit compliance monitoring is sufficient to make decisions about the types and sizes of control measures that are needed. Because deicing chemical loads and stormwater flows are variable, it is important that the data collected represents the variability in discharges that need to be managed so that controls are appropriately selected and sized. If more data are necessary for decision-making, the airport will need to select the appropriate parameters for monitor- ing and the location, extent, and frequency of monitoring to best meet their desired purpose. Data must be reviewed to determine if it is accurate and representative of the discharges and then interpreted using statistics to characterize the stormwater discharges. ACRP Research Report 166: Interpreting the Results of Airport Water Monitoring: A Guidebook provides guidance for acquiring, interpreting, and applying stormwater monitoring data. Green House Gas Considerations The ways in which an airport chooses to manage stormwater containing glycol may affect the amount of greenhouse gas emissions attributable to the airport and how the emissions are accounted for in an Airport Carbon Accreditation (ACA) program greenhouse gas inventory (www.airportcarbonaccreditation.org). Greenhouse gasses attributable to deicer management come from energy use associated with the technologies, vehicles, and emissions from degrada- tion of glycols in biological treatment processes. Many practices described in the technology fact sheets include processes that require energy. For example, some practices include pumps, automated valves, aerators, mixers, heaters, sludge dewatering, or online monitors. Additionally, the glycol recycling technologies are particularly energy-intensive. Energy purchased off-site is considered an ACA Scope 2 indirect emission. Energy produced on-site, such as from solar cells or methane biogas influent water heaters in an anaerobic fluidized bed reactor (AFBR), are considered Scope 1 direct emissions for the ACA pro- gram. The use of glycol recovery vehicles or specialized deicer application trucks (hybrid or blend to temperature) may add to the airport’s fleet. Emissions from these vehicles are also considered a Scope 1 direct emission for the ACA program. Degradation of glycol through biological methods, whether on-site or off-site, produces greenhouse gasses. Aerobic processes, such as in the aerated gravel bed, activated sludge, moving bed biofilm reactor (MBBR), and most municipal wastewater treatment systems produce carbon dioxide as a byproduct. Anaerobic processes such as the AFBR produce a mixture of methane and carbon dioxide as byproducts, although the methane in the AFBR is captured and either burned in a boiler to heat the influent water, or burned in a flare to convert the methane to carbon dioxide. In the end, for a given mass load of glycol, all of the biological processes will produce the same amount of carbon dioxide. Greenhouse gas emissions from onsite biologi- cal treatment would be considered a Scope 1 direct emission for the ACA program, and offsite

Guidelines for Developing Integrated Deicing Runoff Management Systems 17 biological treatment, such as disposal through a municipal wastewater treatment plant, would be considered a Scope 3 indirect emission. The differentiating factor among the biological pro- cesses in terms of volume of greenhouse gas emissions is the energy use. Technologies that include aeration (MBBR, activated sludge, aerated lagoons, aerated gravel bed), significant solids dewatering (activated sludge), or constant mixing (MBBR) are typically more energy intensive. Energy use purchased off-site is a Scope 2 indirect emission. Information regarding energy use is included in the fact sheets and in ACRP Report 99, and may help in comparing technologies. Precise energy needs are very specific to a site, and are highly dependent on the amount of water and glycol load managed and airport layout and grade affecting the distance that water must be pumped. Materials Compatibility Concerns Concerns have been raised regarding the compatibility of the acetate and formate for- mulations with pavement and other airfield infrastructure and certain aircraft materials. The impacts of concern include pavement deterioration due to Alkyli-Silica Reactivity (ASR), dete- rioration of airfield lighting components, accelerated corrosion of cadmium plated aircraft electrical connectors, and evidence of reduced service life of carbon composite brake rotors and stators as the result of catalytic oxidation. Airports have reported anecdotal evidence of concrete deterioration in trench drains, pipes, and storage tanks from long-term exposure to reduced pH conditions resulting from the degradation of deicers. In piping and trench drains this is often associated with locations with frequent standing water (e.g., pipe sections with insufficient slopes). A summary of the issues and available information (as of 2008) is presented in ACRP Syn- thesis 6: Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure. Strategies have been developed to mitigate or avoid most of these issues, but the impacts on carbon brake components remain an active concern in the industry. Carbon Brake Catalytic Oxidation (CBCO). Research has determined that the alkali metals in pavement deicers (i.e., potassium and sodium cations) are a primary factor in accelerated rates of deterioration in aircraft carbon brake components from catalytic oxida- tion. Potassium has been found to have a greater impact on this phenomenon than sodium. Alternative pavement deicer formulations that are typically blends of potassium acetate and another freezing point depressant have been found to exhibit reduced impacts on CBCO, but with higher BOD content, a dilemma that the industry faces. SAE International published AIR5567A Test Method for Catalytic Carbon Brake Disk Oxida- tion to provide a relative assessment of the effect of deicing chemicals on CBCO. This method is referenced in the AMS 1435 and 1431 standards for liquid and solid airfield pavement deicers, respectively. Active collaboration is underway between aircraft manufacturers, aircraft operators, and runway deicer manufacturers to encourage and facilitate the development of environmentally and airplane friendly pavement deicers. The International Air Transport Association’s (IATA’s) CBCO Working Group has been facilitating these collaborations in close coordination with the SAE G-12 Aircraft Ground Deicing Steering Group. Most manufacturers have research and development programs that are aware of the CBCO issue and are actively involved in the aviation industry efforts on this topic. Airports have participated in the industry discussions, providing perspective on environmental sensitivities, including higher BOD content that may come with alternative formulations.

18 Deicing Planning Guidelines and Practices for Stormwater Management Systems Regulatory Drivers This section provides an overview of the environmental regulations and permitting pro- grams that authorize discharges associated with airport deicing and anti-icing operations. Although the emphasis is on regulations that affect U.S. airports, regulations pertaining to Canadian airports are also discussed. Detailed coverage of U.S. regulations is available in ACRP Report Research 169: Clean Water Act Requirements at Airports, and the Deicing Stormwater Permitting page of the ACRP WebResource 3 Airport Stormwater Management Library & Training Materials website. The airport owner generally holds the primary responsibility for compliance with these regulations. However, as new permits are issued, some airport operators are including airlines on their permits. Compliance responsibility also may be shared with aircraft operators and other tenants under facility-specific arrangements that include these parties as co-permittees, or otherwise establish formal responsibilities through lease agreements or mechanisms out- side the scope of any environmental regulation (i.e., that may indemnify the airport owner for activities outside of its control but occurring on airport property). U.S. Federal Acts Effecting Airport Water Quality Regulations The CWA Section 402 creates a permitting system, known as the NPDES program, through which all facilities that discharge pollutants from a point source into waters of the United States must obtain a permit authorizing those discharges. The terms “pollutant,” “point source,” and “waters of the United States” are all very broadly defined. Point source discharges include, for example, those from publicly owned treatment works (POTWs), those from industrial facili- ties, and those associated with stormwater runoff. NPDES permits are issued only to facilities that discharge pollutants directly into receiving water bodies. Airports and individual leaseholders may have NPDES direct discharge permits for stormwater or for discharges of other industrial wastewaters that flow directly to receiving water bodies. Airports that capture deicing operation runoff for treatment or recycling (or that have other onsite operations that generate and capture wastewater and send it to POTWs) may have pretreatment permits or agreements with their local POTW for handling those “indirect” wastewater discharges sent for treatment through the sewer. U.S. Federal Stormwater Program Congress established the current NPDES stormwater program in 1987; EPA implemented it in 1990. EPA now requires that 11 categories of industrial operations obtain NPDES storm- water permits. These categories include Standard Industrial Classification (SIC) code 45, “trans- portation facilities” that conduct vehicle maintenance, equipment cleaning, or airport deicing operations [40 CFR part 122.26(b)(14)(viii)]. The industrial stormwater program regulates only those discharges associated with industrial activity and otherwise unregulated storm- water discharges that are commingled with those industrial stormwater discharges. Types of NPDES Industrial Stormwater Permits. The industrial stormwater program is implemented through two types of NPDES permits. The permitting authority may develop broader permits that allow specified groups of regulated entities to obtain NPDES permit coverage—general permits—or permits can be issued directly to the facility that discharges pollutants to U.S. waters—an individual permit. ACRP Research Report 169: Clean Water Act Requirements at Airports goes into the details of how these permits differ with respect to applica- tion and compliance requirements.

Guidelines for Developing Integrated Deicing Runoff Management Systems 19 Either general permits or individual permits may allow airports to include major tenants as co-permittees. EPA’s Multi-Sector General Permit (MSGP) 2015, which only directly applies to the few states and the District of Columbia where EPA has not delegated NPDES permitting authority, requires all regulated parties at an airport to file for permit coverage, although overall compliance can be shared among the various parties. In most states where permitting authority has been delegated, whether to include such tenants as co-permittees, 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 and manage significant interactions with tenants to ensure that appropriate controls are in place, are functioning, and lead to permit compliance. This may require relatively detailed collaboration with the airport’s stormwater pollution prevention team. Effluent Limitation Guidelines (ELGs). Discharge limits in NPDES permits can be technology-based or water quality-based. Technology-based limits are set by EPA on the basis of a category or type of discharge, and promulgated as ELGs. ELGs establish minimum national technology-based requirements to control discharges from the target industry and may include “new source performance standards” (NSPS) for certain categories of new dischargers. Where ELGs are insufficient to protect the water quality of the receiving water body, site-specific water- quality based limits are developed and applied. In 2012, EPA promulgated ELGs for discharges of stormwater impacted by aircraft and run- way deicing activities (40 CFR Part 449), often referred to as the “Deicing ELG.” For existing airports, the Deicing ELG only addresses controlling ammonia in stormwater discharges asso- ciated with airfield deicing practices. This is accomplished through requirements that either pavement deicers containing urea not be used, or if they are used, limitations on ammonia concentrations in stormwater discharges be implemented in the permit. The NSPS, which only apply to new airports and not new facilities or activities at existing airports, have the same limitations on airfield deicers. In addition, the NSPS add a requirement for collection of “available” applied ADF and numerical limitations on COD concentrations in surface water discharges from onsite facilities that treat collected aircraft deicing runoff. Some airports have encountered confusion about and potential misapplication of the NSPS to exist- ing airports by their permit writers. A clear understanding of the rule by both airports and their regulatory agencies is important to avoid such misunderstandings. Additional detail and information on the Deicing ELG is provided in ACRP Research Report 169: Clean Water Act Requirements at Airports. Other Applicable Regulatory Programs There are specific reporting requirements associated with the use of EG-based deicers. The Comprehensive Environmental Response Compensation and Liability Act (CERCLA or Super- fund) requires that releases of certain chemicals in certain quantities must be reported to the National Response Center (NRC). EG (but not PG) is on the list of chemicals covered by these regulations and has a reporting threshold (called reportable quantity or RQ) of 5,000 pounds. Technically, this means that any release (deicing event) that involves 5,000 pounds of EG during a 24-hour period may be subject to reporting obligations. EPA provides a somewhat stream- lined three-step reporting methodology for facilities (such as airports) that meet a “continuous release” definition. Continuous releases are those that are routine, anticipated, and intermit- tent during normal operations or treatment processes, and that are predictable and regular in amount and rate. Compliance with the reporting requirements is one reason some airports go to PG-based aircraft deicers only. Additional information on the RQ program can be found at http://www.epa.gov/superfund/programs/er/triggers/haztrigs/rqover.htm.

20 Deicing Planning Guidelines and Practices for Stormwater Management Systems Beyond the CWA and CERCLA requirements already discussed, certain projects, including expansion and large capital projects that use federal-funding mechanisms, may trigger compli- ance obligations with other federal environmental laws, including the National Environmental Policy Act (NEPA), the Endangered Species Act (ESA), and the National Historic Preserva- tion Act (NHPA). Activities that have the potential to release pollutants to soil that will reach groundwater also must consider the federal Safe Drinking Water Act (SDWA). All of these statutes could affect an airport’s ability to discharge pollutants to local waters or groundwater. Finally, airports also should check with their state and local authorities to determine if there are state and local environmental or health laws that require authorizations in addition to the federal programs identified earlier. Grant Assurances Deicing projects share many similarities to other airport projects done with federal funding and are subject to sponsor grant assurances. FAA Order 5100.38D, Airport Improvement Pro- gram (AIP) Handbook, provides guidance on the types of deicing projects that may be eligible for federal funding. Although specific eligibility will vary by project, deicing product storage buildings are usually ineligible while weather reporting equipment to be used in supporting deicing decisions or a dedicated deicing pad may be eligible. An eligible deicing pad must be at a commercial service airport, intended exclusively for deicing operations, and eligibility would include the drainage collection, treatment and discharge systems, lighting, and paved access for deicing vehicles and aircraft. The following grant assurance considerations are especially noteworthy in their applicability to planning and constructing federally funded deicing projects: • Sufficient funds must be available for the project and the sponsor (airport) must have legal authority to carry out the proposed project under its governing body. • Design and construction should remain compliant with grant assurances such as 14. Mini- mum Wage Rates, 15. Veteran Preference, and 37. Disadvantaged Business Enterprises. • Because the location of deicing facilities may impact neighboring communities, sponsors should consider grant assurance 19.b Operation and Maintenance, which ensures that spon- sors will continue noise compatibility programs; and 21. Compatible Land Use, because the local zoning ordinance should be compatible with airport use. Operation of the deicing facility once complete also may be responsible to several grant assurances. For instance, if the airport decides to allow a third party to conduct deicing opera- tions, then they should consider grant assurance 22. Economic Nondiscrimination, which requires all fixed based operators (FBOs) to be subject to uniform rules and charges and gives air carriers the right to perform service themselves or make their own selection. Similarly, 23. Exclusive Rights prohibits granting exclusive rights for any singular business or person to provide aeronautical service to the public, although there are some exemptions. It is encouraged for sponsors to be familiar with and consider implications to the FAA grant assurances and other AIP funding eligibility concerns before beginning any deicing project. One such nota- ble AIP consideration includes the Buy American Preferences under 49 USC § 50101, which requires eligible projects to use steel and manufactured goods produced in the United States, although some exceptions are provided. Canadian Federal Acts Regulating Airport Deicing Discharges There are four (4) national Canadian regulations regarding the discharge of airport deicing fluids. The first is the CEPA 1999. This regulation set a total glycol discharge limit of 100 mg/l

Guidelines for Developing Integrated Deicing Runoff Management Systems 21 for discharges to surface waters to protect human health and the environment. The CEPA 1999 requires that the Airport Operator and Aircraft Deicing Service Provider develop a Glycol Management Plan detailing deicing operation and methods used to prevent environmental damage from the deicing operation, and annual monitoring reports be prepared. An Emer- gency Response Plan is also required. The CEPA 1999 applies to all airports owned or operated by the federal government or located on land that is owned by the federal government. The Canadian Council of Ministers of the Environment has prepared surface water quality guidelines that pertain to deicing. Current water quality standards for EG, diethylene glycol, and PG are 3 mg/l, 31 mg/l, and 74 mg/l, respectively. These water quality standards are subject to change and should be checked to ensure the current figures are being used. Guidelines for Effluent Quality and Wastewater Treatment at Federal Establishments (EPS-1-EC-76-1) established a 20 mg/l five-day BOD limit to protect surface waters from oxygen depletion. These guidelines apply to all effluents from land-based establishments under the direct authority of the federal government. The Fisheries Act of 1985 (last amended April 5, 2016) protects the fisheries of Canada by prohibiting activities that could affect fish, fish habitat, or the use of fish. Sections of the Fisheries Act that could affect airport operations deal with the destruction of fish passageways or the altera- tion of fish habitat (Section 35) and the deposit of substances harmful to fish (Section 36). The Fisheries Act is far reaching, and any violation can have serious consequences with the potential to immediately shut down operations. Framework for Planning Deicing Runoff Control Programs This subsection describes a conceptual framework for developing and implementing a deicing runoff management system to comply with environmental regulatory requirements. Some of the elements of this framework coincide with components of a Stormwater Pollution Preven- tion Plan (SWPPP), but by no means should these discussions be considered a comprehensive source of material for developing a fully compliant SWPPP. Also, this framework represents one approach to addressing the component issues and activities. Other approaches may be available and appropriate. (The primary source for information about SWPPP requirements is found in your permit. Additional guidance regarding SWPPP requirements for industrial activity under the NPDES Stormwater Program may be found in the ACRP WebResource 3 Airport Storm- water Management Library & Training Materials website at https://crp.trb.org/acrp0261/). The material in this section is organized according to the steps generally recognized for devel- oping an effective deicing runoff management system for an airport. These steps are depicted in Figure 2-1. This framework is described as an overall process. Some of these steps may not be applicable at an airport with an existing deicing runoff management plan in place. Also, aircraft operators should be represented and involved as active participants in this process. Supplemental information to facilitate understanding and applying this approach is avail- able in the training courses on deicing found in the ACRP WebResource 3 Airport Storm water Management Library & Training Materials website and the ACRP Deicing Runoff Management Planning Decision Support Tool that accompanies this report. Identify Environmental Regulatory Compliance Requirements Compliance with environmental regulatory requirements is a primary objective and metric of success for deicing runoff management, as well as being a legal obligation. Requirements related

22 Deicing Planning Guidelines and Practices for Stormwater Management Systems to permitted deicing discharges will generally fall into the following categories, although these are not necessarily present in every permit: • Narrative/qualitative. These requirements typically involve implementing practices such as handling and storing materials, selecting deicing products (for example, prohibiting urea), and encouraging conservation practices. Commonly, compliance requires that these prac- tices be described in a SWPPP, Deicing Runoff Management Plan, or similar document. • Numerical/quantitative. These requirements establish specific quantitative performance levels that must be achieved. Typically, they are expressed as concentrations or loads in permitted discharges. However, numerical limits may also express the performance of collection efforts in terms of fraction of applied deicers either collected or contained in storm- water discharges. • Reporting. These requirements include routine reporting related to deicing activities and associated stormwater discharges. In some cases, compliance reporting may include some form of demonstration that the practices and other elements of an airport’s SWPPP or Deicing Runoff Management Plan have been implemented and are working. An inventory of all compliance requirements establishes the performance requirements for the deicing runoff management system. Assess Current Compliance with All Applicable Requirements Once all applicable regulatory requirements have been defined, the current status of com- pliance with those requirements can be assessed. If compliance is being achieved with current practices, then normally no further action will be needed. On the other hand, deficiencies in achieving compliance under existing conditions will set the context focus for activities described in subsequent steps. Assess Potential Sources of Deicer Loading to Stormwater This subsection describes the fundamental step of understanding the sources and mecha- nisms that may cause deicers to become entrained in stormwater. The first component is to Figure 2-1. Framework for development and implementation of a deicing runoff management strategy.

Guidelines for Developing Integrated Deicing Runoff Management Systems 23 understand the drainage patterns at the airport. The second is to identify and inventory deicing activities that contribute to runoff. Some of the information presented here addresses runoff control beyond deicing operations. However, it is presented to emphasize the need to integrate deicing into an airport’s overall stormwater management strategy. Assess Airport Drainage System. An airport drainage system is typically a complex com- bination of natural systems and constructed infrastructure covering multiple drainage areas that discharge to different receiving waters. Comprehensive knowledge of the layout and func- tion of the drainage system is needed to understand where runoff originates, how it flows, and what activities may contribute pollutants to stormwater, as it flows towards a receiving water body. At a minimum, understanding the drainage system requires the following information: • Site boundaries and tenant facilities (buildings, roads, access, etc.). • Pervious and impervious surfaces and flow directions. • Layout of the airside and landside storm drain systems including catch basins, pipes, con- nections, and outfalls. • Location, configuration, and design data for all stormwater controls; these would include ponds, collection vaults, oil–water separators, infiltrators, filters, flow splitters, etc. • Receiving water bodies. • Location of materials exposed to precipitation. • Location of deicing activities and support functions that may impact stormwater, such as aircraft deicing or anti-icing, airfield deicing, ground support equipment operations, deicer storage and handling, snow disposal, etc. It is worth noting that atypical deicing practices, such as using aircraft deicers to melt ice on ground service equipment, may affect the risk of non-compliance with discharge permits. These atypical practices may not be well docu- mented or quantified but should be taken into account when designing collection systems and sizing deicer management infrastructure. The inventory of the airport’s drainage system could lead to identifying the possibility of rerouting runoff from deicing areas to avoid discharging to sensitive receiving waters. Pursuing such an opportunity requires site-specific analysis of regulatory, technical, operational, and legal considerations that are beyond the scope of the generalized guidance presented here. Inventory Potential Sources of Deicing Runoff. Potential sources of aircraft and pavement deicing runoff must be identified, quantified, and prioritized. Data on types, volumes, and con- centrations of aircraft deicers and anti-icers used, along with the locations of those uses, should be compiled from all aircraft operators and FBOs that conduct deicing. Attention should be paid to understanding exactly what is represented in the usage data reported by each entity, with a focus on information that reflects the components of the deicers that are of environmental rel- evance. For example, operators may report gallons of applied Type I ADF with no record of the dilution mix (i.e., ratio of ADF concentrate to water) in the applied fluid. If the operators always use the same mixture, then it can be assumed that the glycol concentration in the applied fluid is constant. However, if different mixtures are used under different deicing conditions, having a record of those mixtures will support a more accurate estimate of total glycol used for aircraft deicing. Other elements of the aircraft deicer inventory should include the locations of storage tanks and transfer stations for deicing fluids, and types of equipment used for aircraft deicing. Performance data on existing aircraft-deicing practices also may be helpful. Data that describes the types and amounts of airfield pavement deicers used also should be compiled, along with the areas where they are applied. Pavement deicer storage and handling areas should be identified, along with descriptions of any existing pavement deicing practices that may be in place.

24 Deicing Planning Guidelines and Practices for Stormwater Management Systems Available data on discharges of deicing runoff to stormwater outfalls and treatment systems should be compiled. The critical information here will be flow and volume measurements and associated concentrations of deicing-relevant parameters (glycols, BOD, COD, total organic carbon, ammonia, acetates, formates, etc.). Information regarding deicing season weather conditions (for example, typical conditions and extreme events) also should be developed during this step. ACRP Research Report 166: Interpreting the Results of Airport Water Monitoring: A Guidebook provides guidance on acquiring, interpreting, and applying monitoring data to characterize stormwater quality. The goal of this exercise is to characterize the flow of deicing chemicals through the air- port stormwater system by constructing an approximate material (that is, mass) balance. This analysis will provide an understanding of available data, reveal the spatial distribution of deicing activities and use, and indicate whether the material balance needs to be broken down into distinct areas within the airport. The material balance can be depicted as in Figure 2-2. The material balance is an approximate calculation due to inherent uncertainty in the fate of deicers once they become exposed to wind, soil, and water. Deicer use records are useful to evaluate the maximum amounts that could potentially mix with precipitation and runoff. This information is likely to be the most accurate element of the material balance, provided that good recordkeeping practices are in place. Concentrations and volumes of runoff captured by collection efforts and sent to treatment and recycling can be used as a conservative estimate of how much material was not released to the environment. Outfall-monitoring data can pro- vide an estimate of how much material reaches receiving waters, provided that the data are of sufficient quality and temporal resolution. Outfall monitoring may not be a reliable source of information because of the cost and technical difficulties of obtaining reliable data. In addition to these three quantities, an estimate of fugitive losses is necessary to complete the mass balance. Fugitive losses occur as a result of fluid adhering to aircraft after takeoff, dripping, tracking on the wheels of ground support equipment, being carried off as wind drift, or bio- degrading on pavement surfaces and in soils (Revitt and Worral 2003). These fugitive losses are typically estimated “by difference.” It is not uncommon to see this fugitive fraction consti- tute as much as 20 to 60% of the total deicing materials used (Skjefstad 2005; Williams 2006; Wagoner 2006; Corsi et al. 2006). Despite the uncertainties, a simple material balance establishes a basis for understanding the magnitude of the potential sources of deicing runoff and their geographic distribution. This information can be used to prioritize management measures. Define Runoff Management System A deicing runoff management system is an assemblage of practices that, as an integrated whole, achieves environmental regulatory compliance within the context and constraints of Figure 2-2. Material balance.

Guidelines for Developing Integrated Deicing Runoff Management Systems 25 safety, as well as operational and cost requirements and objectives. As discussed previously, practices for controlling deicing runoff can be arranged in three categories: • Source reduction; • Containment/collection; and • Discharge/treatment/recycling. This step in the framework involves identifying and evaluating different system configura- tions to determine which one will best meet the diverse needs of safety, operational feasibility, regulatory compliance, and cost-effectiveness. The process of formulating a system of runoff controls consists of four steps: 1. Identify potentially suitable practices; 2. Select practices; 3. Identify constraints on system design; and 4. Design and evaluate system alternatives. The Deicing Runoff Management Decision Support Tool is a useful resource in supporting the initial steps in this process. Identify Potentially Suitable Practices. Deicing runoff practices are identified based on their suitability to address an airport’s compliance requirements, usually specified in the NPDES permit (see “Implementation of Regulations in Different Types of Airport Discharge Permits”). Depending on these facility-specific requirements, controls may need to be identified from one or more of the three categories: source controls, containment/collection, and treatment/ recycling. Generally, if source control practices are not going to be adequate for meeting com- pliance, then both containment/collection and treatment/recycling practices will be required. An initial screening of practices will identify those that have potential within the specific con- text of an individual airport. Potentially suitable practices should meet the following criteria: • Meet all applicable safety requirements; • Be applicable to the geographic, operational, and climatic context of the airport; • Be suited to addressing the sources and pollutants of specific concern; and • Have order-of-magnitude costs consistent with the scale of the deicing operations, the nature of compliance requirements, and the economics of the facility. Information that will be useful in evaluating these criteria is provided in Chapter 3 and the individual fact sheets. The resulting list of candidate practices will serve as the basis for a more detailed assessment and selection of practices that can serve as the building blocks of a deicing runoff management system. Select Candidate Practices. Once the subset of potentially applicable practices has been identified, further evaluation will lead to selection of those practices best suited to the facility. This evaluation may reveal the need to subdivide the facility into areas where different prac- tices are appropriate. Chapter 3 provides guidance in the technical aspects of the selection processes of suitable practices. The selection of suitable practices should involve all relevant stakeholders, especially air- craft operators, to ensure that facility-specific issues are thoroughly considered and stake- holders who could be responsible for implementing or operating individual practices have input in the selection process. Many practices are implemented and under the control of aircraft operators, making their participation in the consideration and selection of those practices essential. Similarly, aircraft operators should be consulted regarding any practices

26 Deicing Planning Guidelines and Practices for Stormwater Management Systems that may have a significant and direct impact on aircraft operations. The importance of this involvement applies throughout the process of developing and implementing a deicing run- off management strategy. The resulting list of candidate practices will serve as the basis for subsequent development and evaluation of alternative practice system configurations. Identify Constraints on System Design. Before assemblages of candidate practices can be arranged into runoff control system alternatives, constraints on system design that may not have been apparent when individual controls were being evaluated must be considered. For example: • Maintenance of aircraft/airfield safety, including wildlife hazard concerns. • Assurance of efficient aircraft operations at present and planned demand levels. • Design conditions, such as deicing event size or frequency of system capacity exceedances, associated with compliance requirements. • Available POTW or other existing treatment facility capacity, policies on discharge concen- trations and loads, and discharge fee structures. • Pretreatment requirements. • Airport master plan, airport layout plan, navigation aids, and other constraints on space availability. • Environmental factors (wetlands, floodplains, sensitive ecosystems, nondeicing pollutants of compliance concern, air emissions). • Anticipated growth that may affect deicing activities and controls. • Special flight operations requirements. • Accessibility of candidate practice installations on the airfield. • Funding sources and cost constraints. • System operation complexity. • Acceptance by tenants and other stakeholders. • Constructability. • Utility conflicts. • Aesthetics. These factors may lead to adjustments in the system configuration, but also could require the introduction of practices that were not initially in the list of preferences and that may call for further stakeholder involvement. At this stage in the design process, these factors serve primarily as criteria to evaluate conceptual system alternatives. Assemble and Evaluate Practice System Alternatives. Practices are assembled into con- figurations that are realistically anticipated to meet the regulatory compliance requirements. Potentially applicable source reduction practices are typically defined first to establish a basis for deicer usage expectations, followed by containment/collection and treatment/recycling practices. Generally, the objective will be to take advantage of source reduction opportunities to the extent possible within the requirements of safety and efficient operations and then opti- mize the other two categories of practices to reduce the size and cost of the system. Developing conceptual system alternatives includes the placement of practices. Runoff collection practices may need to be arranged in a configuration that provides containment, diversion controls, conveyance, storage, pretreatment, and onsite or offsite treatment or recy- cling, while also facilitating aircraft operations. It often will be feasible to arrive at more than one system configuration. After the conceptual system is laid out, individual practices may be sized using design param- eters and performance requirements. Sizing for conveyance, storage, and treatment practices requires characterization of the hydrology and deicer loading in runoff to develop peak flows

Guidelines for Developing Integrated Deicing Runoff Management Systems 27 and runoff volumes that the practices must handle. Hydrologic, hydraulic, or water quality models are used to estimate these quantities from data on weather, aircraft, and pavement deicer use, flight operations, basin surface characteristics, and storm sewer system features. The effect of individual practices on deicing runoff is estimated using a variety of tools specific for each control, ranging from empirical equations to separate computer models. In practice, simple computa- tions and rules of thumb may be used to perform preliminary sizing as the system is conceptually designed. The configuration of the system needs to be modified if the estimated performance does not meet compliance criteria; this introduces iterations in the design process. More sophisticated computational tools may be needed to evaluate the range of options related to system sizing and performance under the full range of temporally varying conditions and/or with complex configurations. Such analyses can help avoid over-sizing infrastructure or inadequately address- ing compliance risk. It is important to recognize the sources and impact of sources of uncertainty in sizing collec- tion, storage, and treatment practices. Typically, model estimates of flow and runoff volumes are more accurate than those of deicer application rates and resulting runoff concentrations. In addition, the actual performance of practices often does not reflect ideal conditions, and prac- tice performance may decline with age and with poor maintenance. Models may be used to evaluate the significance of those uncertainties when looking at the range of options and sen- sitivities to a variety of conditions. Engineering judgment needs to be applied in defining the input parameters and interpreting the output of models. Cost estimates for the alternative systems are estimated once the individual components are defined, located, and sized, including ancillary features for access and maintenance. Construc- tion cost elements include engineering design, permitting, and the expenses for installation and startup of the system. Operations and maintenance (O&M) cost elements include operator time (e.g., monitoring, data analysis, system adjustments, reporting), utilities, materials, replacement parts, and repair activities to maintain the performance of the individual controls. Life cycle costs are estimated using a suitable discount rate to enable comparison of systems with different capital and O&M cash flows, and useful lives. The final step in the process is to decide which conceptual deicing runoff management system best meets the diverse requirements of safety, compliance performance, efficient air- craft operations, siting, practicality, reliability, and affordability. The system requirements and constraints identified earlier are used along with the performance and cost to make this decision. Often, as the design progresses, a clear choice becomes apparent. If not, a scoring and ranking process may be applied to assist the decision-making process. Develop Deicing Runoff Management Plan The preferred runoff control system will typically undergo a process of refinement during which configurations, sizes, and cost estimates are refined. A deicing runoff management plan is developed around the selected conceptual system specifying the following: • Purpose and objectives for the system (including compliance criteria); • Identification of responsible parties; • Basis for system and component sizing; • Description of the runoff control system components and configuration; • Schedule and budget for phased implementation; • System operational rules; • Schedule of O&M activities; • Metrics of system performance; • Data collection and analysis to evaluate performance;

28 Deicing Planning Guidelines and Practices for Stormwater Management Systems • Strategies for addressing performance deficiencies; and • Procedures for recordkeeping. These elements can be defined in a stand-alone document or folded into the airport’s SWPPP. Implement Management Plan For implementation, the deicing runoff management plan should be fully integrated with the airport’s SWPPP. Because the plan usually involves significant expenses and resources, imple- mentation is typically achieved in phases. The scheduling of these phases should be vetted by the regulators before it becomes part of the SWPPP. A detailed implementation schedule should be developed to take into account procurement processes, construction activities, commissioning, start-up, and airport operations. Similarly, a detailed annual cash flow needs to be projected. Tenants and other stakeholders must be involved in the development of the implementation schedule so that they can have input and begin planning for and implementing any adjustments in their practices and operations that may be involved. The review process (described in “Revise Deicing Runoff Management Plan”) marks the time to plan the activities for the coming year. Monitor and Evaluate Effectiveness The performance of the deicing runoff management system, as implemented in the plan, should be assessed on a regular basis to allow for adaptive management. Typically, this review will coincide with the end of the deicing season. The metrics used to assess system performance will be specific to the compliance require- ments within the airport’s NPDES permit. The most common NPDES metrics associated with deicing runoff are collection performance and concentrations of pollutants in stormwater discharges associated with deicing. It may be useful to consider additional metrics for each of the practices to provide greater insight into system operation. In addition to concentrations at outfalls, the following are examples of metrics to measure progress toward meeting the goals in the deicing runoff management plan: • Deicer use (correlated to weather); • Deicing runoff treated; • Onsite treatment performance (e.g., influent and effluent BOD concentrations, percent removal of BOD); • Recycled quantities of glycol; • Number of aircraft operators implementing source control practices; and • Estimate of annual BOD removed by the runoff control system. If compliance requirements are not being met, the cause should be investigated. It is possible that one or more deicing practices are not functioning as expected, or that extreme weather con- ditions outside of the conditions assumed when the system was designed have occurred. Exam- ining the metrics may reveal these problems and help isolate underperforming components. Appropriate corrective actions may need to be implemented, as discussed in the next section. It also will be important to assess the performance of the system with respect to nondeicing metrics, such as safety requirements, efficiency of aircraft operations, and compliance with other environmental requirements.

Guidelines for Developing Integrated Deicing Runoff Management Systems 29 Revise Deicing Runoff Management Plan At most airports, the airport’s SWPPP will be reviewed annually as part of compliance with its NPDES industrial stormwater permit. This is an opportunity to review the deicing runoff management plan and identify the infrastructure modifications and maintenance activities that will be accomplished during the coming year. The annual review is also an opportunity to adjust the implementation schedule based on the previous year’s accomplishments and delays, which will affect the current year’s activities. The evaluation described in the previous subsection will indicate whether the deicing run- off management plan is meeting its objectives. If the performance is below the target, correc- tive measures will need to be implemented. These measures may involve maintenance actions, enhancement, or replacement of practices with more-effective controls, or modifications to the overall system. If an upgrade to the system is indicated, the monitoring plan may need to be adjusted to reflect the new configuration. This task completes the cycle shown in Figure 2-1, illustrating the application of principles of adaptive management to deicing stormwater management. It is important that stakeholders be involved as the management program evolves. It is also often advisable to keep regulators informed and appropriately involved in the process. Role and Application of Modeling Tools Computer models are powerful tools for simulating quantity and quality aspects of storm- water pollution, provided that they are appropriately matched to the problem being analyzed and properly constructed and interpreted. A simple materials balance, which is itself a model, may not adequately describe the complexities and dynamics of deicing runoff generation, transport, and discharge to support the characterization of sources of deicing runoff, and the subsequent identification and evaluation of alternative practice system configurations. An example of a situation where this might be the case is a permit that establishes maximum loads to receiving streams, perhaps based on a Total Maximum Daily Load (TMDL) determination. In those instances, the basic materials balance data may be subsequently used to support a variety of computer modeling tools that provide a more sophisticated representation of the airport, deicing activities, and associated runoff. The selection of a model is guided by two basic principles: 1. Choosing a model that fits the problem to be addressed. A model should represent the physical processes critical to the characterization of the problem. The essential nature of the problem should not be modified to meet the capabilities of a particular model—or the expertise of the modeler. 2. Selecting the appropriate level of model complexity consistent with goals and available data. A model should be as simple as possible while addressing the needs of the analysis. It should also be selected to make effective use of the data available, without incorporating complexity that data cannot support. The output from the model only can be as accurate as the input data and parameters used to drive it. Models can be used for characterization of conditions as well as system design. A pollutant- loading model can be used to characterize the loads generated by each of the drainage areas in an airport. A hydraulic model of the stormwater conveyance system that simulates rainfall- runoff processes can be used to size inlets, pipes, treatment facilities, and other stormwater infrastructure.

30 Deicing Planning Guidelines and Practices for Stormwater Management Systems Precipitation-runoff models may be designed to evaluate the response to individual events or simulate long periods of weather. Single-event models are useful in sizing of conveyance and treatment infrastructure under an assumed “design” event condition. On the water quality side, single-event models can provide estimates of pollutant removal under assumed conditions. Continuous simulation models describe the response of a system to a time series of weather conditions. Continuous simulation models tend to be more complex than single-event models but are useful in revealing temporal trends and evaluating risk over a wide range of conditions, and in evaluating cumulative storage volume requirements over the course of one or more seasons. ACRP Report 81: Winter Design Storm Factor Determination for Airports provides guidance on identifying appropriate winter design event conditions based on modeling objec- tives and data availability. Models are approximate (therefore, imperfect) representations of the physical world, and this imperfect knowledge introduces uncertainties in the output. This statement is more criti- cal for water quality modeling efforts than for water quantity. The issue of data availability and data requirements should be carefully considered in determining an appropriate modeling approach. Available data representing critical factors, such as deicer use and associated weather (for example, ice and snow), are often very limited. Without site-specific measurements over a representative range of conditions, extrapolation from other parameters or other facilities may be required, which introduces a potentially significant source of uncertainty. Whenever possible, models should be calibrated using site-specific data, and a sensitivity analysis should be conducted to understand the implications that the variability in model parameters has on the output. At times, the accuracy of model output may not be as important as representativeness when it is used to make management decisions. For example, a modeling effort that compares alter- native management scenarios does not need to focus on the absolute values of output variables but on the relative differences among scenarios under the same set of underlying assumptions and parameter inputs. There are no commercial, off-the-shelf, or public domain models specifically designed for comprehensively modeling all of the processes involved in deicing stormwater flow and quality at airports. Modeling is often performed piecemeal using several separate models, each suited to a particular aspect of the system. Table 2-3 summarizes potential approaches to modeling air- port stormwater processes. Note that many of the processes relevant to deicing runoff manage- ment could be modeled using spreadsheet tools. Also, models range in level of sophistication required for operation, and advanced training in the use of many of the more-sophisticated modeling tools is required for their application.

Guidelines for Developing Integrated Deicing Runoff Management Systems 31 Process Approach Hydrology Runoff generation Several commercial and public-domain models are available to simulate the generation of runoff from rainfall (e.g., SWMM,a TR-55,b HEC-HMSc). These models are useful to size conveyances and treatment facilities for hydrologic control (e.g., peak flow attenuation), and to withstand severe events. However, for deicing, runoff generation typically involves snow or ice melt and many models do not have this capability. SWMM and HEC-HMS can simulate snow processes, but not ice. It should be noted that meteorological measurements of snow, and especially ice, are often sparse or unavailable. Models based on the “curve number” methodology (e.g., TR-55) are appropriate for extreme events but not for the small storms that make up most of the annual runoff. The Rational Method can be used for design of relatively simple drainage configurations, and for pipe sizing for more complex systems. However, a continuous simulation hydrologic and hydraulic model (e.g., SWMM) is recommended to obtain an optimized final design and realize cost savings. Infiltration Infiltration is not a significant component in extreme events. For small events, infiltration can play a major role in reducing runoff volume. For snowmelt flow, infiltration is greatly reduced if the ground is often frozen, if the soil is still saturated, or most of the flow comes from paved areas. There are numerous approaches to simulating infiltration, for instance the Green-Amptd and Hortone empirical formulas. Some of these are included in existing hydrologic models like SWMM and HEC-HMS. Evapotranspiration Similar to infiltration, evapotranspiration can be significant for small rain storms. In the winter months when deicing is required, evapotranspiration is very small. Evapotranspiration data are not widely available and a common method is to derive them from mass or energy budgets such as the Bowen Ratio and Penman methods,f or empirical equations such as the Thornthwaite method.g Hydraulics Conveyance Hydraulic models are the strongest component in the modeling process. At airports, hydraulic modeling addresses flow in pipes and open channels conveying runoff from paved and unpaved surfaces to treatment facilities and outfalls. Suitable models are SWMM for pipe flow and HEC-RASh for open channel flow. Water Quality Pollutant loading There are no standardized models to simulate the uses of aircraft and airfield deicers, and the subsequent generation of BOD loads from de/anti-icing operations. A variety of approaches to modeling the pollutant load associated with aircraft and pavement deicing may be taken. These range from discrete models which attempt to estimate application rates on a per-aircraft basis to empirical/statistical-based models. All approaches require site-specific information regarding historical deicer usage, weather conditions during deicer application, and airport flight schedules. The availability of information for these models will affect model accuracy and validity. Pollutant wash-off Pollutants become mobile when they come in contact with runoff. The hydrodynamic, chemical, and biological processes involved are extremely complex and fraught with uncertainty. Simulation of runoff quality is still an evolving field of science, and credibility of the results depends heavily on accurate field data for calibration and verification. For many applications, simpler, event-based methods can be effective where a finer temporal distribution is not required. One method is to develop a rating curve that relates flow to concentration. A second method uses the concept of Event Mean Concentration (EMC), which is the flow-weighted average concentration of a pollutant during an event. EMCs are typically lognormally distributed (Huber and Dickinson 1992). Regardless of the method, adequate field data are needed to arrive at reliable representations. The SWMM model can be used for this purpose but a custom model can also be programmed in a spreadsheet. Methods have been developed to quantify the fugitive loss mechanisms in a way that would support inclusion in a mechanistic model.i This is an area where much research is still needed. Table 2-3. Modeling approaches for airport runoff quantity and quality processes. (continued on next page)

32 Deicing Planning Guidelines and Practices for Stormwater Management Systems Process Approach Pollutant decay Many pollutants undergo a series of physical, chemical, and biological processes that begin as soon as they come in contact with the environment. The BOD in deicers begins to degrade on pavement surfaces, and degradation continues as deicing runoff travels through the stormwater conveyance system (Revitt and Worrall 2003; Revitt et al. 2002). These processes are very complex and depend on a number of environmental factors, including temperature, which is typically low during deicing events. A common approach to modeling pollutant transformation as it is transported by runoff is to assume a lumped loss factor that includes all fugitive mechanisms, estimated from available mass balance monitoring data. Decay may be important for flow in swales and other natural conveyances, where a more explicit representation may be required. In either case, reliable field data are needed to derive the model parameters. These processes are available in models like SWMM but can also be programmed in a custom spreadsheet. Pollutant removal in runoff controls Both collection and treatment practices reduce the pollutant loads generated by deicing operations and released to the environment. Collection practices may be characterized as a fraction of applied deicers removed by collection activities. Representation of treatment\recycling will depend on the nature of the process and the destination of the effluent stream relative to the objectives of the modeling analysis. Receiving water quality This modeling component may be critical where the need for permit limitations to protect receiving water quality must be determined or discharge limits must be developed in response to that need. Receiving water quality models take the pollutant inputs at outfalls and simulate their fate as they move in natural systems. Besides dilution, the processes in natural streams, lakes, and estuaries are complex and their representation again depends on reliable field data. Simple models, such as the Streeter-Phelps dissolved oxygen model, can be constructed and implemented in spreadsheets. More complex models that have been applied to simulate the impact of deicing discharges on surface waters include the WASPj model, QUAL2Kk and CE- QUAL-W2,l and HSPF.m These are progressively complex programs, and extensive modeling experience is typically required for their application. a Rossman (2004). b USDA (1986). c USACE (2006a). d Mein and Larson (1973). e Bedient and Huber (1989). f Bras (1990). g Singh (1989). h USACE (2006b). i APS Aviation Inc. (2005). j Wool et al. (2001). k Chapra et al. (2007). l Cole and Buchak (1995). m Bicknell et al. (1997). Table 2-3. (Continued).