Guidance for Treatment of Airport Stormwater Containing Deicers (2013)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

11 Deicer treatment systems are implemented primarily because the pollutants contained in the deicer-affected runoff are greater than the allowable pollutant in discharges to surface waters or groundwater. When assessing what deicer treatment is needed (see Figure 8), the following must be determined by the airport: • The type of deicer treatment technology(s). • The capacity or size of treatment required. • The role of treatment in the deicer management system. To determine the specific deicer treatment needs, the following must first be defined: 1. Allowable pollutant discharges based on regulatory requirements (Section 2.1). 2. Characteristics of the stormwater affected by excess pollutants from deicing (Section 2.2). 3. Constraints to implementing treatment at the airport based on site characteristics and opera- tional needs (Section 2.3). In Section 2.4, example tables for documenting the results of this assessment are provided. 2.1 Allowable Pollutant Discharges Almost all applications of deicer treatment technologies and their supporting systems are driven by the need to comply with environmental-based regulatory requirements. Typically, numeric limitations for commonly regulated deicing-related pollutants (e.g., BOD, PG) have the largest effect on treatment. Occasionally, other regulatory conditions can affect treatment tech- nology implementation, including numeric limits for less common parameters, numeric ambient or receiving system conditions, narrative conditions, and receiving waters capacity limitations. An analysis is necessary to find the limiting conditions for the existing permits and agreements that will govern the treatment requirements for a specific airport facility. Such an analysis may also need to incorporate assessment of potential new limits that will be imposed on the airport. An overview of the process for determining the governing limits is presented in Figure 9 and discussed in the following sections. 2.1.1 Identify Applicable Regulations and Agreements Obtaining an understanding of the applicable regulations, permits, and agreements is the first step toward determining the allowable discharges that govern the basis of design for a treat- ment system. The criteria defining the allowable discharge could apply to untreated effluent discharged to an off-site location or treated effluent from a future on-site treatment system. C H A P T E R 2 Defining Deicer Treatment Needs and Implementation Constraints Stormwater with Excess Pollutants from Deicing Pollutants Removed by Treatment Allowable Pollutant Discharges Figure 8. Quantifying treatment needs.

12 Guidance for Treatment of Airport Stormwater Containing Deicers 2.1.1.1 Overview of Applicable U.S. Regulations The federal Water Pollution Control Act amendments of 1972 and subsequent amendments, commonly known as the Clean Water Act (CWA), established the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. Through Section 402 of the CWA, the National Pollutant Discharge Elimination System (NPDES) was created as a system for permitting point-source discharges to the waters of the United States. Point sources include treated wastewater from domestic, commercial, and industrial sources as well as stormwater contaminated with pollutants. The NPDES permit pro- gram generally requires that point-source dischargers of pollutants to waters of the United States (i.e., direct dischargers) obtain an NPDES permit or their state equivalent. The U.S. Environ- mental Protection Agency (EPA) has authorized regulatory agencies in most states to administer their NPDES programs, but there are four states1 and the District of Columbia for which EPA retains this authority and issues NPDES permits to all direct dischargers. Point sources may also discharge into collection (sewer) systems of other treatment facilities (instead of direct discharge under an NPDES permit). Such point sources are indirect discharg- ers. Airports may discharge either directly or indirectly—with appropriate regulatory permits in either case. Airports that directly discharge deicer-affected stormwater runoff into surface waters are required to have one of two types of NPDES permit: either coverage under an applicable general NPDES permit, or an individual NPDES permit issued specifically for their facility. General NPDES permits cover many facilities that have similar operations or similar types of discharges, whereas individual NPDES permits are issued based on site-specific activities or discharges. General NPDES permits typically have requirements to implement BMPs to minimize pollution and may or may not have specific numeric effluent limitations. Individual NPDES permits typi- cally have specific numeric effluent limitations for one or more pollutants, and they are usually required by the state agency or EPA based upon relative concern for potential violations of water quality standards. The agency will determine whether an airport will be required to obtain a general or individual NPDES permit. 1 Idaho, Massachusetts, New Hampshire, New Mexico, and the District of Columbia do not have approved state NPDES permit programs. NPDES permits in these states are issued by the respective EPA region. Identify applicable regulations and permits Document all numeric effluent limits from all permits Determine the governing parameters, numeric limits, and conditions from the permits and agreements Determine the most restrictive limitations that the discharges must meet Figure 9. Steps in determining the discharge limitations that govern treatment needs.

Defining Deicer Treatment Needs and Implementation Constraints 13 Under the CWA, the effluent limits in NPDES permits are based on two principles: (1) all wastewater discharges must be treated with the best treatment technology economically achiev- able, regardless of the condition of the receiving water (which results in technology-based lim- its); and (2) more stringent effluent limits may be imposed if the technology-based limits do not prevent violations of water quality standards in the receiving water (which results in water- quality–based limits). 2.1.1.2 General NPDES Permits General NPDES permits cover multiple facilities within a specific category, are issued by a state agency or the EPA, and are applicable only to dischargers within one state. Multiple facilities may be authorized to discharge under a single general permit. Many states have adapted general permits modeled after the EPA Multi-Sector General Permit.2 Some states have their own version of a general permit applicable to industrial stormwater discharge, which, in general, has similar provisions and requirements. General permits for stormwater discharges include requirements to implement BMPs, to prepare and implement a stormwater pollution prevention plan (SWPPP), and to perform monitoring of stormwater discharges, and may include effluent limitations or discharge benchmarks. The Multi- Sector General Permit has a section with sector-specific requirements that apply to air transportation facilities and, specifically, to discharges from airfield and aircraft deicing activities. Included in this permit are effluent monitoring benchmark concentrations for 5-day bio chemical oxygen demand (BOD5) (30 mg/L), COD (120 mg/L), ammonia (2.14 mg/L), and pH [6.0 – 9.0 s.u.(standard units)]. If benchmarks are exceeded, it is not a permit violation, although the airport would be required to implement additional practices to prevent further exceedances. In some states, failure to meet benchmarks results in the issuance of an individual NPDES permit. 2.1.1.3 Individual NPDES Permits and Effluent Limits Individual NPDES permits are typically required when the state agency believes there is a reasonable potential for violation of water quality standards in the receiving water body as a result of the airport’s stormwater discharges. As do general permits, a typical individual NPDES permit for an airport will include requirements that appropriate BMPs be implemented and that an SWPPP be prepared and implemented. An individual permit for an airport will also have effluent limits that are developed based on water quality considerations and may also include technology-based effluent limits. Effluent limits in individual NPDES permits are either water-quality–based limits (based on the water quality criteria and conditions of water bodies receiving the discharges) or technology-based limits (based on a treatment technology that is considered appropriate for dischargers in the same industrial category), as further described in the following. Water-Quality–Based Limits: Water-quality–based effluent limits are developed to ensure that the permitted discharge will not result in an exceedance of water quality criteria in the receiving water body. The limits are derived from existing upstream pollutant concentrations and the corresponding water quality criteria applicable downstream of the discharge. If water quality for one or more pollutants is not currently in attainment, then a total maximum daily load (TMDL) assessment for the entire watershed (or a portion) will be performed. The TMDL for each pollutant will determine an allowable allocation of pollutant loads to each point source (including the airport) and all nonpoint sources, and these load allocations will be used to derive the specific permit limit. Technology-Based Limits: Regulations under the CWA direct the EPA to develop treatment-technology– based effluent limits for groups of industrial facilities (“categories”) that are similar in their activi- ties or the nature of wastewater generated and that apply to all industries within the same category 2 “Multi-Sector General Permit for Stormwater Discharges Associated with Industrial Activity,” U.S. EPA, 2008. http://cfpub. epa.gov/npdes/stormwater/msgp.cfm.

14 Guidance for Treatment of Airport Stormwater Containing Deicers regardless of their location in the United States. In 2012, the EPA published final technology-based effluent limitations guidelines (ELGs) and new source performance standards to control discharges of pollutants from airport deicing operations.3 The requirements generally apply to wastewater associ- ated with the deicing of airfield pavement at primary existing airports. The rule also establishes New Source Performance Standards (NSPSs) for wastewater discharges associated with aircraft deicing for a subset of new airports. The rule does not establish uniform, national requirements for aircraft deicing discharges at existing airports. Requirements will continue to be established in general permits, or for individual permits on a site-specific, best professional judgment basis by EPA or state permit writers, as appropriate. Existing and new primary airports with 1,000 or more annual jet departures (non- propeller aircraft) that generate wastewater associated with airfield pavement deicing are to use non– urea-containing deicers or, alternatively, meet a numeric effluent limitation for ammonia (14.7 mg/L) prior to any dilution or commingling with any non-deicing discharge. New airports, excluding air- ports in Alaska, with 10,000 annual departures located in cold climate zones are required to collect 60% of aircraft deicing fluid available for capture. Airports that discharge the collected aircraft deicing fluid directly to waters of the United States must also meet numeric discharge requirements for COD (271 mg/L daily maximum, 154 mg/L weekly average). These limits are based on the anaerobic fluid- ized bed reactor (AFBR) treatment technology representing best available technology economically achievable for deicer-runoff treatment, although an airport subject to these may use any alternative treatment technology. Technology-based limits applicable to an airport are integrated into the facility’s NPDES permit by the governing agency’s permit writer. If both technology-based limits and water-quality–based limits are applicable for a given parameter, the most restrictive of the limits is incorporated into the permit. 2.1.1.4 MS4 Permits Some airports, or portions of airports, may be regulated under rules for municipal separate storm sewer systems (MS4s). An MS4 is a conveyance or system of conveyances (including roads, catch basins, curbs, gutters, ditches, man-made channels, and storm drains) that is owned or operated by a public body, designed and used for collecting stormwater, is not a combined sewer, and is not part of a POTW. An entity designated as an MS4, such as a local municipality, may impose certain conditions on airport stormwater discharges within the municipality’s MS4 ser- vice area, typically through conditions in the municipality’s stormwater management plan. This may result in the need for additional monitoring and control of pollutants within the airport’s drainage area. Some airports may also be classified as MS4s themselves, which can result in the need to develop targets for reducing the quantities of particular pollutants in their discharges. Those pol- lutant reduction targets may result in the need for the airport to control deicer discharges beyond, or differently from, what is required in its individual or general industrial NPDES permit. 2.1.1.5 Industrial User Discharge Permits from POTWs POTWs collect and treat wastewater from residential, commercial, and industrial sources. Generally, POTWs are designed to treat only domestic sewage and biodegradable commercial and industrial wastewater. POTWs are not necessarily capable of treating all pollutants dis- charged by industries. They are also not always capable of treating the full load of biodegradable wastes from industries. The undesirable effects of discharges from industries can be prevented by various management practices or treatment at the industrial facility (referred to as “pretreat- ment”). In order to protect the POTWs and avoid adverse impacts from industrial wastewater that could prevent full compliance with the POTW’s NPDES permits, the EPA established the National Pretreatment Program [regulations are published in 40 Code of Federal Regulations (CFR) 403]. These regulations require that POTWs receiving industrial wastewater must develop and implement their own industrial pretreatment program. The POTW is established as the 3 “Effluent Limitations Guidelines and New Source Performance Standards for the Airport Deicing Category,” 40 CFR Part 449, May 16, 2012.

Defining Deicer Treatment Needs and Implementation Constraints 15 control authority for implementation of its pretreatment program, much as a state agency is the control authority for its NPDES permit program. A central requirement of pretreatment programs is the development of local limits appli- cable to discharges from industries, which will prevent interference with operation of the treatment processes or sludge use or disposal, and which will prevent pass-through of pol- lutants that could result in violation of NPDES permit limits or water quality criteria in the receiving water body. An airport is considered an industrial discharger by POTWs in the United States, and the airport stormwater discharges to the sanitary sewers are viewed simi- larly to wastewater discharges from manufacturing industrial facilities in terms of pollutant discharges. POTWs may also have concerns about the stormwater aspect of the discharges— specifically the volumes of stormwater that are processed by the POTW, and in some cases, POTW regulatory requirements regarding receipt of stormwater discharges may affect their ability to accept airport discharges of stormwater. With respect to the pollutant content of airport deicer-affected stormwater discharges, during development of local limits, the POTW treatment BOD capacity must be assessed, and loading or concentration discharge limits for BOD or COD may be established. Under the POTW pretreatment program, all significant industrial dischargers, called indus- trial users (IUs), must obtain permits (or equivalent control mechanisms) to discharge to the POTW. These IU discharge permits include the local limits developed by the POTW, as well as effluent monitoring and reporting requirements. Each IU is responsible for determination of what level of pretreatment may be necessary to comply with the limits, and must design, install, and operate its pretreatment system in order to comply. IU discharge permits may also include other conditions and requirements relating to the discharge. The discharge limits and other conditions in the IU permits are necessary to allow POTWs to comply with their own NPDES permit requirements. Each POTW (municipality, county, or local authority) establishes its own local sewer use ordinance that defines requirements for obtaining a user permit and appropriate discharge requirements and conditions. As discussed in Chapter 6, the entity issuing IU permits will establish a cost structure for the allowable discharges. The cost structure might include fees based on flow volume, as well as surcharge fees for parameters such as BOD, COD, total suspended solids (TSS), and ammonia-nitrogen (NH3-N). The surcharges are applied when discharge concentrations exceed a predetermined threshold concentration or mass load amount. Treatment Tips Impact of Deicing ELG on Treatment Requirements The U.S. EPA ELG for airport deicing operations did not establish uniform, national requirements for aircraft deicing discharges for existing U.S. airports. For new airports exceeding a specified number of flight operations, effluent limits for COD are established for discharge directly to receiving waters. The ELG does not specifically require that deicer-affected stormwater be treated or that any specific type of treatment technology be used. Site-specific water-quality–based effluent limits will continue to be the primary regulatory drivers for deicer treatment in the United States.

16 Guidance for Treatment of Airport Stormwater Containing Deicers 2.1.1.6 Applying for Discharge Permits The airport must submit an application for the appropriate discharge permit to the control authority: either the state agency or EPA for an NPDES permit, or the local POTW for an IU discharge permit. In some cases, the application will be for modification of an existing permit. Each control authority has specific application procedures and permit application forms. These are often available from the control authority’s website, although it is highly recommended that the airport call or meet with the appropriate contact person(s) to discuss application require- ments and verify understanding of specific information required. Both NPDES permits and IU discharge permits are issued with an effective duration of not more than 5 years and must be renewed prior to expiration. The permitting control author- ity (either state agency/EPA or the POTW) establishes procedures and application forms for renewal of the discharge permit. NPDES permits (both individual and general) require that the permit holder submit the permit renewal application at least 180 days prior to the permit expiration date. Local IU discharge permit renewal requirements and procedures vary from one POTW pretreatment program to another, and the program contact should be consulted for specific details. 2.1.1.7 Agreements with Private Entities For some airports, deicer-affected stormwater is conveyed or trucked to privately owned off-site facilities for processing. Typically, the off-site facilities are glycol recycling operations, but some airports also use private wastewater treatment facilities. The airports, or entities representing the airports, will establish agreements with these facilities that establish the terms of the disposal. These terms could place restrictions on the quantities, lower or upper concentrations, or timing of the material transfer, which could in turn affect pretreatment or storage needs at the airport. In a typical arrangement with a private entity, stormwater containing aircraft deicing fluid (ADF) is collected at the airport, temporarily held in storage tanks, and transported to the off-site, privately owned treatment facility. In some cases, the airport can transport the collected fluid without any on-site treatment. In other situations, some partial treatment of the collected ADF at the airport is necessary to reduce water content so that overall volume can be reduced. The airport, as gen- erator of the collected ADF, must ensure that proper chain of custody is completed, and it also assumes liability for the waste not being treated in accordance with all local, state, and federal requirements. Treatment Tips Regulatory Considerations for Airports Discharging to POTWs When establishing limits for potential airport deicer-impacted stormwater discharges to sanitary sewers, the POTW’s primary consideration is the measures necessary to protect the POTW from violating its own NPDES permit limits or exceeding receiving stream water-quality criteria. Industrial user permit limits are therefore set to ensure that the airport discharges: 1. Do not exceed the POTW hydraulic capacity, BOD load treatment capacity, or solids handling capacity. 2. Do not compromise POTW treatment operations.

Defining Deicer Treatment Needs and Implementation Constraints 17 2.1.2 Documenting All Applicable Limits and Conditions from Permits and Agreements NPDES permits regulating discharges to surface waters, IU permits regulating discharges to sanitary sewers, and other permits may trigger the need for an airport to monitor stormwater discharges and to meet effluent limitations. Privately run facilities that accept deicer-affected stormwater for treatment or recycling may establish limits on the characteristics and quantity of the stormwater. In addition, the regulatory permits and agreements with private entities may place restrictions on the timing or conditions under which discharges can occur. The limits contained in the permits and agreements provide airport operators with their initial drivers for considering treatment. As a first step in understanding the governing limits for treated effluent, the parameters from the various permits that potentially govern discharges to on-site treatment systems or off-site entities should be documented. The many limits, timescale of applicability (e.g., daily maximum, monthly average), points of compliance, monitoring requirements, and associated conditions should be documented in a comprehensive matrix covering all applicable permits and agreements. This will serve as the basis for determining which of the conditions from the permits govern compliance, as discussed in Section 2.1.3. 2.1.3 Determining the Governing Conditions from Permits and Agreements Not all limits contained in the permits directly affect the selection of treatment technology and the design of the treatment system. Analysis of the permits and agreements is needed to define the parameters and limits that will govern design conditions. The governing conditions are essentially the most restrictive effective limits and the limits that help define the extent of the required treat- ment. A variety of permit features may affect the governing conditions for treatment, including: • Limits for the same parameters may be found in multiple permits, causing issues with conflicts and overlaps. • A given parameter may be limited in multiple ways. A common example is having BOD5 limits for both concentration and mass loading. Common Limiting Parameters Driving Treatment Performance Needs Treated effluent BOD, COD, PG concentrations Treated effluent BOD and COD loads Treated effluent nutrient concentrations (N, P) Stormwater flow rates Stormwater volume Less-Common Limiting Parameters Driving Treatment Performance Needs Effluent total suspended solids Effluent total dissolved solids Effluent temperature Stream or groundwater temperature Groundwater depth Receiving stream flow rate Time of day or year POTW short-term capacity Presence of nuisance growth pH

18 Guidance for Treatment of Airport Stormwater Containing Deicers • Parameters might be limited on multiple timescales (e.g., maximum and monthly average). • A permit may contain limits for related parameters, such as BOD5, COD, and PG. Frequently, only one of the related parameters provides the governing limits. It is also necessary to consider the circumstances and ambient conditions under which NPDES limits apply. For example: • The point of compliance for a treated effluent may not be at treatment facility discharge, but at a downstream point where the treated effluent has mixed with other stormwater discharges. • In addition to other permitting requirements, new outfalls necessary for discharge of treated effluent to surface waters could trigger waste-load allocation and anti-degradation analyses requirements, with the result being newly regulated parameters or outfall-specific effluent limits. • Discharges to surface waters might be restricted during dry weather conditions. • The permit monitoring requirements may not align with the monitoring needed for treat- ment system process control. • Limits for summertime discharges may be more restrictive than wintertime discharges. This can affect airports that treat down stored loads well past the end of the deicing season. Conditions in IU permits from POTWs, such as those in the following, must be assessed: • Allowable loadings for BOD5 may vary with time or condition. • Restrictions can be placed on discharges to the sanitary sewer during wet weather conditions. • The monitoring performed by the POTW may not synchronize well with the monitoring per- formed by the airport for the type of sample, type of analyses, location, or number of samples used to calculate allowable discharges and fees. • The POTW may impose restrictions on flow rates because of POTW treatment plant or sani- tary sewer capacity limitations. Some examples of specific types of restrictions from actual POTW IU discharge permits are shown in the “Examples of Types of Airport Discharge Limitations in POTW Discharge Permits” text box. The specific combination of discharge restrictions and limits will be unique to each airport and POTW. Potential considerations in establishing limiting conditions in agreements with private entities for off-site recycling are listed in the following bullets. These conditions may be Examples of Types of Airport Discharge Limitations in POTW Discharge Permits • Daily maximum BOD5 (or COD) load ..............................pounds per day (lbs/day) • Daily maximum BOD5 increase from prior day ........................................... lbs/day • Daily maximum BOD5 (or COD) concentration ........... milligrams per liter (mg/L) • Daily maximum flow ...............................................million gallons per day (mgd) • Daily flow rate ........................................distributed uniformly over 24-hr period • Discharge not permitted when POTW influent (or specified sewer) flow rate is greater than ................................................ mgd • Acclimation period (start of discharge season) – Maximum initial discharge ................................................................... lbs/day – Maximum daily increase ....................................................................... lbs/day

Defining Deicer Treatment Needs and Implementation Constraints 19 integrated into the contracts between the airport and the firm managing recycling operations at the airport. • Minimum glycol concentration requirements. • Treatment and storage capacities at the off-site facility that dictate the volumes that can be shipped and treated per day, per week, or per month. • Requirements associated with non-glycol constituents. The analyses for determining the governing limits associated with permits and agreements specific to treatment have to be site-specific and are an important part of the technology selec- tion and system design process. Calculations may be needed to assess the governing limits under various conditions. An example is provided in the “Example for Establishing Governing Limits from Permits and Agreements” text box. 2.2 Characterizing Stormwater to be Treated Prior to selecting a deicer treatment technology, the questions of what to treat and how much to treat have to be answered. This requires characterizing the stormwater to be treated on-site or discharged off-site for treatment. This section provides information and guidance on the stormwater characterization process. 2.2.1 Water Quality and Quantity Parameters Water quality of both the deicer-affected runoff and the receiving streams is largely described in terms of the laboratory analyses used to quantify potential pollutants. As illustrated in Figure 10, water quality analyses associated with deicing typically fall into four major categories: organics, solids, nutrients, and physical properties. The most typical deicing-related water quality analysis parameters associated with each category are also shown in the figure. Many of the water quality issues created by deicing are associated with the presence of the primary deicer constituents in stormwater. In this guidebook, the term primary deicer constituents refers to the chemicals in aircraft and airfield deicers that serve as freezing-point depressants. The most common primary deicer constituents are propylene glycol, ethylene glycol, glycerin, sodium acetate, sodium formate, potassium acetate, and urea. While the deicer-affected runoff contains other constituents (most typically, deicing fluid chemical additives and non-deicing pollutants), the primary deicer constituents, especially in aircraft Treatment Tips Establishing Governing Conditions Affecting Treatment 1. Not all effluent limits affect treatment technology selection and design. 2. Establishing the governing limits that drive treatment may require consider- ation of multiple deicing conditions, receiving waters conditions, and inter- active effects of multiple regulated parameters. 3. Potential changes in permit conditions that may occur during the life cycle of the treatment system or discharge should be considered, to the extent possible.

20 Guidance for Treatment of Airport Stormwater Containing Deicers Example for Establishing Governing Limits from Permits and Agreements An airport has an NPDES permit with concentration and mass loading limits for BOD5 and concentration limits for PG (shown below). The treated effluent will potentially mix with stormwater runoff from other areas of the airport prior to the NPDES compliance point. The average flow rate discharged from the poten- tial treatment system is 100 gpm. The airport must assess the question: What are the governing limitations for the treatment facility effluent? Parameter Permit Concentration Limit Permit Mass Loading Limit Is Treated Effluent Mixed with Other Stormwater? BOD5 100 mg/L 50 lbs/day Yes PG 30 mg/L No No At first glance, the limiting conditions for concentration, flow, and load may seem straightforward. Further examination reveals more information about the effective limiting conditions that will govern the treatment design: 1. The potential mixing of the treated effluent with stormwater from other sources prior to the compliance point could result in higher BOD5 and PG concentration targets for the treated effluent than are indicated by the permit limits. However, the stormwater flows from other areas are likely to be variable and potentially could be zero (e.g., in an extended dry period). The airport will need to decide if the mixing can be relied upon for dilution. If not, no benefits to the allowable effluent concentrations from mixing should be assumed in treatment system design. 2. At a flow rate of 100 gpm for a treated discharge, the maximum BOD5 concentration that could be discharged is only 41 mg/L without exceeding the 50-lbs/day mass loading limit (mass loading rate/flow rate * conversion factor = concentration). Hence, at that flow rate, the BOD loading rate is the governing limit, which translates into an effective maximum BOD5 con- centration of 41 mg/L. This concentration is lower than the 100-mg/L limit in the permit, and 41 mg/L becomes the effective concentration limit at high flow rates. At lower flow rates, the effective BOD5 limit would be higher until the point where the 100-mg/L limit becomes most restrictive. As a result of the effective BOD concentration limit being affected by the mass loading limit, the treatment plant in this example would need to be designed to reach a much lower target for treated effluent concentration. 3. Since 1 mg/L of PG is approximately 1 mg/L of BOD5, and the PG limit is lower than the BOD5 limit, PG could be the governing limit, depending on the technology that is used. 4. The governing limits are not necessarily the design points—to account for unknowns in measurement error, equipment functioning, response times, and so forth, the design points are typically set to a more restrictive value to provide a margin of safety.

Defining Deicer Treatment Needs and Implementation Constraints 21 deicers, are most often the principal drivers for selecting, sizing, and operating deicer treatment technologies and systems. The primary deicer constituents can directly contribute to the presence of organics, nutrients, solids, and physical properties, as shown in Figure 11. The water quality parameters shown in Figure 10 and Figure 11 and the associated analyses are described in detail in ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. A summary of the parameters most commonly associated with deicer treatment is provided in the following. Propylene Glycol, Ethylene Glycol, and Glycerin PG is the freezing-point depressant most frequently used in aircraft deicers in the United States, while EG is widely used in Canada. Aircraft deicing fluids that include glycerin as a contribut- ing freezing-point depressant are now available, although their use is not currently widespread. Both PG and EG can be isolated in on-site and off-site deicer recycling technologies and reused in other products, providing some potential payback to offset processing costs. No known glycerin recycling operations exist for deicing operations. Many airports that use recycling tech- nologies have moved toward arrangements where those applying deicer at the airport use only EG- or PG-based aircraft deicers to maximize the value that can be obtained from the recycling operation. Higher concentrations of both EG and PG result in a more cost-effective overall recy- cling process, and there is no known limitation on the maximum EG or PG concentration that can be recycled. No technological limitations exist for the minimum EG or PG concentration that Organics BOD, COD, TOC, PG, EG Physical Properties Temperature, pH, Odor Nutrients NH3-N, PO -P4 Solids TSS, TDS Figure 10. Primary analysis-based water quality parameters associated with deicer treatment. Glycols, Glycerin in Aircraft Deicers Formate, Acetate, Glycols in Pavement Deicers Urea in Pavement Deicers Organics BOD, COD, TOC, PG, EG Solids TSS, TDS Physical Properties pH, Odor, Foam Nutrients NH3-N, PO -P4 Figure 11. Relationships between deicer constituents and water quality parameters.

22 Guidance for Treatment of Airport Stormwater Containing Deicers can be recycled by the typically used recycling technologies; however, the economics of recycling are affected at lower concentrations because of the increased volumes of water that need to be processed. A general rule of thumb is that minimum EG or PG concentrations of 1% are needed to make recycling economical. From a biological treatment perspective, EG, PG, and glycerin are all similar chemical com- pounds and are highly biodegradable. All commonly used biological treatment technologies should successfully treat each chemical if designed and operated properly. The oxygen demands of the chemicals do differ. PG and glycerin carry similar oxygen demands and both have oxygen demands that are higher than that of EG. As a result, biological systems that treat PG and glycerin require larger capacities than systems that treat the equivalent volume of EG. Biological treat- ment systems can treat a mix of PG, EG, and glycerin without great difficulty, although bacterial populations that are acclimated predominantly to one or the other may take time to acclimate to a new mixture. This may result in short-term decreases in treatment efficiency when the relative concentrations of the constituents change. In most biological treatment systems, the potential toxic effects of PG, EG, and glycerin on the bacteria are not a limiting factor in treatment. While potential toxic effects of these chemi- cals to a biological treatment system cannot be ruled out, from a practical sense, it is far more likely that limitations from factors such as oxygen supply, temperature, nutrient supply, extent of bacterial population, and operational variability will affect treatment before toxicity has an effect. In practice, biological treatment systems have demonstrated the ability to treat PG-based runoff with concentrations as high as 50,000 mg/L for anaerobic conditions and 15,000 mg/L for aerobic conditions. The laboratory testing associated with this guidebook did not reveal any inhibitory impacts for aerobic or anaerobic treatment at concentrations less than 7,000 mg/L (the maximum concentration tested). Field performance data on EG-only biological treatment systems are not readily available, but it is likely the maximum toxicity-based EG concentrations are somewhat less than the maximum PG or glycerin toxicity-based concentrations. If toxicity from PG, EG, or glycerin is a concern for the feasibility of biological treatment in unique cases, a pilot study to assess the toxicity is recommended. Acetates and Formates from Pavement Deicing Materials The organic portions of potassium acetate, sodium formate, and potassium formate are the acetates and formates. These organics carry an oxygen demand that may be high enough to require treatment. Like the glycols and glycerin in aircraft deicers, the acetates and formates are relatively simple organic molecules and are readily biodegradable. There are no known operations for recycling acetates and formates. If these chemicals are contained in runoff to be proposed for recycling of glycols, the acetates and formates will typi- cally be separated into the dilute stream and contribute to the BOD that needs to be removed. If treatment for pavement deicers is necessary, it will be biological in nature. The BOD, COD, and TOC associated with these organics are generally lower than for the aircraft deicers, and often the pavement deicers are applied less frequently. As such, the impact of the pavement deic- ers to the sizing of biological deicer treatment systems is typically less significant than the impact from aircraft deicers. While the acetates and formates in pavement deicer materials are biodegradable, their degra- dation rates can differ from glycols and glycerin. As a result, in treatment systems with biology that is not acclimated to acetates or formates, differences in treatment efficiency can be observed if there are spikes in the presence of these compounds. The performance changes are not typi- cally significant enough to completely disrupt operations, but some adjustments to operational parameters, including potentially short-term reductions in throughput, may be necessary until the bacterial population can acclimate to the different chemicals.

Defining Deicer Treatment Needs and Implementation Constraints 23 Biochemical Oxygen Demand: BOD is the quantity of oxygen required when organic and nitrogen-based compounds in stormwater are biologically oxidized by bacteria. The BOD con- centration is used as a measure of the total concentrations of biodegradable compounds in the sample. Most often, when the term BOD is used in the aviation industry, it is in reference to the 5-day BOD laboratory test (BOD5), which is often a required monitoring parameter in NPDES per- mits. A total BOD analysis will measure both the carbonaceous and nitrogenous contributors to the oxygen demand. The carbonaceous aspect of BOD (CBOD) in deicer-affected stormwater is primarily associated with the organics from glycols, glycerin, acetate, and formate. In addi- tion, those organic compounds may biodegrade in the stormwater during collection and storage and result in breakdown products that also contribute to BOD. For example, PG can anaerobi- cally degrade in storage tanks to produce compounds such as propionates. Propionate compounds derived from PG will not be measured as PG in a lab test, but they will be measured as BOD. The nitrogenous aspect of the BOD in deicer-affected stormwater is associated with nitrogen com- pounds in urea. With urea mostly taken out of use for deic- ing, for all practical purposes, the total BOD of a typical airport stormwater sample equals the CBOD. Since BOD is a measure of the organics that are biode- gradable in deicer-affected stormwater, BOD is also the most direct measure of the extent of biological treatment that is necessary. Biological treatment systems are often sized based on BOD load. The mix of constituents contributing to the BOD can also be a factor in biological treatment system perfor- mance if the bacterial population becomes predominantly acclimated to a particular chemical. Many NPDES permits have BOD5 limits, necessitating BOD measurement in the treated efflu- ent for both biological- and recycling-based systems. (The dilute streams from evaporation and membrane filtration processes for recycling contain concentrations of BOD that may trigger the need for additional treatment to meet compliance criteria.) Chemical Oxygen Demand: COD is the quantity of oxygen required when an organic com- pound is chemically oxidized to its ultimate breakdown products (usually carbon dioxide and water). It is a measurement of all the chemicals in the stormwater that can be oxidized. The COD concentration is used as a surrogate measure of the total concentration of all organic compounds in the sample, whether they are biodegradable or not. COD analyses usually result in higher laboratory concentrations than BOD5 analyses because (a) more stormwater constituents can be chemically oxidized than biologically oxidized, and (b) the BOD5 test may not completely measure all of the biodegradable compounds in the sample because the test is limited to 5 days. However, because deicer-affected stormwater samples tend to be dominated by the primary deicer constituent in aircraft deicers (e.g., propylene glycol), there is often a strong correlation between COD and BOD5 in untreated deicer-affected stormwater. This may not be the case if there is a significant impact from pavement deicers in the mix. The correlation between COD and BOD5 in treated deicer-affected stormwater effluent may not be as strong because the nonbiodegradable compounds in treated effluent are a higher percentage of the total organics remaining after treatment. Typically, the COD-to-BOD5 ratio in treated efflu- ent is significantly higher than the COD-to-BOD5 ratio in the untreated influent. COD is an attractive and frequently used alternative to BOD5 for process control in many air- port deicer treatment systems because COD analyses results can be obtained in less than 3 hours, as opposed to at least a 5-day wait time for the BOD5 analysis. BOD5 analyses are also subject to Treatment Tips Parameters Driving Treatment Most often, it is the quantities of BOD, PG, or EG in aircraft deicers and the volume of water to process that drive the selection of treatment technology and capacity of the treatment system.

24 Guidance for Treatment of Airport Stormwater Containing Deicers inaccuracies from factors such as interfering constituents, non-acclimated biological seed, and improper test dilutions. COD analyses are not affected by these conditions. Total Organic Carbon: TOC monitoring methods measure the amount of carbon dioxide pro- duced when the organic carbon in a water sample is oxidized (thermally, chemically, or by ultraviolet light). TOC concentration is a measure of the total concentra- tion of organic carbon compounds in a sample. TOC is used by some airports in lieu of using COD or BOD to characterize the total concentration or load of deicer constituents to be treated. Most often, TOC is used when online TOC monitors are used to take real-time measurements from flowing storm- water samples. Online monitors can reduce the time to obtain an analytical result to a range of 5 to 10 min. Like COD, TOC generally correlates well to BOD5 in untreated deicer-affected stormwater that is dominated by aircraft deicers. In casual discussions on treatment, the terms BOD, COD, and TOC are sometimes used interchangeably. While rela- tionships between the parameters can be established, the correlations can vary considerably based on multiple factors, including those identified in the “Treatment Tips – Correla- tions” text box. When sizing and operating treatment systems, it is therefore critical to establish site-specific relationships and understand that those relationships can vary with conditions. Ammonia: Ammonia-nitrogen exerts an oxygen demand that has a similar impact on receiving surface waters as do biodegradable organic compounds. This is defined as nitrogenous oxygen demand (NOD). The analytical parameter of total BOD is equal to the sum of CBOD and NOD. Ammonia is also toxic to aquatic life, and accordingly, water quality criteria are established at very low concentrations. Although most deicers do not include ammonia, urea used to deice pavement readily biodegrades in the environment to release ammonia. Many NPDES permits for municipal and industrial treatment plants include effluent limitations for ammonia. The ELG established by U.S.EPA requires that non–urea-containing deicers be used for pavement deicing, or that any discharge must meet an ammonia limitation. Because of water quality concerns about ammonia, most airports have replaced urea with use of alternative pavement deicers. Nutrients: Nutrients are the typically inorganic stormwater constituents that can affect sur- face waters through formation of algal blooms, decreases in in-stream dissolved oxygen, addi- tion of turbidity, and potentially toxic impacts on aquatic life. The nutrients of concern are certain forms of nitrogen and phosphorus. The NPDES permits of airports located near surface waters where excessive nutrients are a concern may contain limits or monitoring requirements for nutrients, most typically for total nitrogen (TN), total inorganic nitrogen (TIN), total phos- phorus (TP), or orthophosphate (PO4-P). Inorganic nitrogen in three forms can be a nutrient: ammonia-nitrogen (the same form that is both toxic to aquatic life and has an oxygen demand), nitrate nitrogen (NO3), and nitrate (NO2). Nutrient contributions from untreated deicer-affected stormwater are not typically a significant issue today because most airports have shifted away from urea use. However, nutrients are needed to support the functioning of biological treatment systems. Airport stormwater runoff typically does not contain significant nutrient concentra- tions because of the lack of nutrients present on airport surfaces and the lack of nutrient content in deicers. As a result, unlike municipal wastewater, airports operating deicer biological treat- ment systems need to add nutrients to the stormwater at treatment to support bacterial growth. Solids: The pavement deicers used at airports are primarily chemical salts (inorganic cations and organic anions) and can contribute to high concentrations of total dissolved solids (TDS). Treatment Tips Correlations The correlations among BOD5, COD, TOC, PG, and EG measurements may vary significantly with: 1. Relative contributions of aircraft and pavement deicers, 2. Concentration range, 3. Treated versus untreated runoff, 4. Relative presence of solids, and 5. Characteristics of the measuring instruments. Understanding the basis and errors in correlations assumed in treatment system sizing and operations is critical for managing cost and compliance risk.

Defining Deicer Treatment Needs and Implementation Constraints 25 Excessive concentrations of TDS can potentially inhibit biological activity and could lead to scaling in physical treatment systems. Biological treatment systems will not remove TDS. The physical treatment systems used primarily for recycling may result in larger quantities of TDS segregated into the concentrate streams and less TDS in the dilute streams. Total Suspended Solids: TSS associated with deicer-affected stormwater can arise from a variety of sources, and treatment support systems may need to be implemented to remove TSS. NPDES permits or user permits for sanitary discharges may limit TSS contained in stormwater discharges. TSS can be inorganic (e.g., sand, sediment) or organic (e.g., biomass, vegetative mat- ter) in nature. The TSS contained in deicer-affected stormwater can lead to clogging in some bio- logical treatment systems and can potentially damage equipment. TSS in the inflows to physical treatment systems such as membrane filtration and evaporation-based systems can cause fouling or damage to equipment. Biological treatment systems produce biological solids (measured as TSS) that may need to be wasted (sometimes referred to as biosolids or sludge). If the TSS need to be removed for compliance purposes or for protection of the deicer treat- ment system, support systems for removing TSS before or after deicer treatment may be neces- sary. The removed solids are typically disposed of off-site. It may be economically beneficial to dewater the solids prior to transport. pH: Deicer can affect pH in stormwater, but typically not enough to result in water quality issues. However, if deicer-affected stormwater is stored in tanks for long periods of time, espe- cially in warm conditions, the pH may decrease to as low as 3 to 5. Some biological treatment systems, especially anaerobic systems, require integral pH control because of acids produced during the biodegradation of the organics. Typically, however, pH control for deicer-affected stormwater is not a significant consideration. Temperature: While cold temperatures are not typically a water quality issue for deicer- affected stormwater discharges, low water temperatures have a significant impact on most bio- logical treatment systems. Low temperatures can also affect the pressures needed in membrane filtration (reverse osmosis) systems and also lead to additional energy input for evaporation- based treatment systems. Cold temperatures have resulted in the need to adapt treatment system implementation through heating of the water, insulating systems from heat losses, storing storm- water until temperatures warm, or slowing down the throughput in treatment systems. Some NPDES permits for protected waters place limits on the maximum temperatures, and there may be a few select circumstances where operators need to observe the effluent temperature and manage discharges if treatment extends into warm months. 2.2.2 Water Quality and Quantity Characterization Methods One of the critical yet challenging aspects of selecting treatment technologies and imple- menting deicer treatment systems is characterizing the stormwater quality and quantities to be treated. The nature of deicing, driven by variable weather conditions and airport operations, results in significant fluctuations in the flow rates, concentrations, and pollutant mass loadings over the course of time. That variability must be understood not only for the design of the treat- ment elements, but also to assess if control of the stormwater entering treatment is needed to attenuate peaks. A detailed assessment of the methods for characterizing deicer-affected stormwater is beyond the scope of this document. Several other ACRP documents can be referenced to provide guidance, including: ACRP Report 14: Deicing Planning Guidelines and Practices for Stormwater Management Systems ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials ACRP Report 81: Winter Design Storm Factor Determination for Airports

26 Guidance for Treatment of Airport Stormwater Containing Deicers Although detailed guidance on stormwater characterization analyses cannot be presented here, an overview of the stormwater characterization needs is provided because it is critical to effective selection and implementation of deicer treatment systems. 2.2.2.1 Defining the Water Quality and Quantity Parameters An important step in characterizing stormwater for assessment of deicer treatment needs is to identify the water quality and quantity parameters applicable to your treatment situation. The parameter list will be partially driven by the applicable permit and agreement criteria, but other parameters that affect the ability of a treatment system to function may also be characterized. Typi- cal characterizations that may be required for treatment-related assessments are shown in Table 2. 2.2.2.2 Considerations for Quantifying Stormwater Parameters The process of quantifying the characteristics of deicer-affected stormwater is unique among wastewaters to be treated because of the variation in flow rates, deicer application quantities, and airport operations. Considerations when developing a characterization of the stormwater for implementing treatment include: • Range of weather and deicing conditions assessed; • Time-step for characterization of parameters (annual, monthly, daily, hourly); • Timeframe for airport/deicing operations (current, future); • Assumptions on flight schedule, fleet mix, and deicing locations; • Handling of snow piling and snow melt processes; • Data/assumptions on precipitation conditions; and • Information/assumptions on stormwater conveyance infrastructure. 2.2.2.3 Methods for Quantifying Stormwater Parameters The method by which the stormwater characteristics are quantified can have a significant impact on the results. Quantification methods are rooted in (1) sampling and analysis or (2) modeling. Simplified methods using few deicing events, large time periods between sam- ples, and significant assumptions are less costly to use initially but often lack data on the critical conditions that often drive treatment sizing. Treatment Tips Determining the Parameters to Measure When Characterizing Deicer Treatment Needs When determining the stormwater parameters to characterize, consider the following criteria: • Parameters identified in permit limits and monitoring requirements. • Parameters the potential treatment technologies typically use to define capacity and operations. • Ability to collect sufficient samples at the appropriate runoff conditions. • Time and cost to perform lab analyses. • Feasibility and cost of collecting real-time data with portable and fixed online monitoring instruments. • Ability to simulate the parameters in models instead of sampling and characterization. • Risks associated with insufficient characterization.

Defining Deicer Treatment Needs and Implementation Constraints 27 More sophisticated modeling methods or extensive sampling requires additional up-front cost but can significantly reduce the risk that treatment is oversized (resulting in unnecessary cost) or undersized (resulting in more compliance risk). Each airport must decide the level of risk that it is able and willing to tolerate. As discussed in ACRP Report 14, the selected method should fit the situation being addressed and be consistent with the project goals and level of available data. As with any calculation method or model, the output from the model can only be as accurate as the input data and parameters used to drive it. When making treatment decisions, stakeholders should be aware of how the characterization data were acquired. The extent that the data represent the variety of conditions, as well as the assumptions and errors implicit in the data, can affect the choice of treatment technology and the success of its long-term operation. For example, conservative assumptions necessitated by a lack of characterization data could result in significantly overestimating the concentration of PG that will be sent to an evaporation-based recycling treatment system. This could change the economics of recycling if the water to be evaporated is vastly different from what was assumed in design. As another example, if the BOD load to be treated in a biological system is underesti- mated, the system may be undersized. In an undersized system, an operator may be forced to load the system higher than its capacity under heavy deicing conditions, leading to higher effluent BOD concentrations or inhibition of the biological activity. 2.3 Evaluating the Airport Site Conditions and Constraints Individual airports have specific site and operational characteristics that affect the feasibility and cost of implementing particular deicer treatment technologies. Evaluating those conditions and constraints prior to the evaluation of the technologies can streamline the deicer treatment technology selection process. Table 2. Most common stormwater characterization parameters in deicer treatment. Parameter Characteristic Treatment Technologies Where Parameter Is Important BOD, COD, or TOC Average loading rate Maximum concentration Biological systems POTW discharges PG or EG Average and maximum concentrations Biological systems Minimum concentration Evaporation systems Membrane filtration systems Private recycling systems NH3-N Average and maximum concentrations Biological systems POTW discharge TSS Average and peak concentrations Average and peak loading rates Evaporation systems Membrane filtration systems Private recycling systems TDS Average and peak concentrations Biological systems Membrane filtration systems Evaporation systems Flow rate Average and peak flow rates Biological systems Evaporation systems Membrane filtration systems Private recycling systems POTW discharges Stormwater volume Total per day and season Evaporation systems Membrane filtration systems Private recycling systems POTW discharges Water temperature Minimum and average Biological systems Membrane filtration systems Evaporation systems

28 Guidance for Treatment of Airport Stormwater Containing Deicers 2.3.1 Siting Constraints As part of the constraints analysis, an assessment of potential treatment system sites should be conducted. Siting considerations include: • Proximity to collected and stored stormwater; • Proximity to outfalls and sanitary sewers; • Proximity to utilities, including power, water, and natural gas; • Proximity to restricted airfield areas; • Clashes with existing utilities; • Presence of protected water resource land uses, such as wetlands; • Stormwater management requirements; • Geotechnical and hydrogeological characteristics; • Presence of environmental contamination; • Planned land uses such as may be found in the airport master plan; and • Accessibility. Considerations on potential site constraints are described in the following. Available Land Land is almost always at a premium at an airport. Deicer treatment systems typically require between 0.25 acres and 10 acres of land. Most treatment technologies have flexible configura- tions to allow adaptation to site features. From a siting analysis performed prior to selecting a treatment technology, the available area for a treatment system (and other deicer management features like storage) can be determined for use in the treatment technology screening analysis. Height and Location Restrictions A siting analysis should be incorporated into selecting an appropriate treatment technology and siting the treatment system for an airport. Each treatment system has unique operations that require a specific footprint or height that may exclude it from practical application based on various factors at an airport. Treatment Tips Understanding the Reliability of Your Stormwater Data Airports report that insufficient or inaccurate characterization often has led directly to unanticipated treatment costs and noncompliance from overloaded treatment systems. Steps to take in understanding the reliability of your data include: • Understand the method used to collect the data (sampling/analyses, real-time monitoring, model simulations); • Verify that sample locations are representative; • Document the accuracy of analytical methods; • Verify the occurrence and potential errors of instrument calibration; • Ensure that accurate correlations are used when relating parameters (e.g., BOD and PG); • Review collected field data to exclude data affected by instrument malfunctions; and • Understand timescales, limitations of applicability, assumptions, calibration, and accuracy of site representation in models—test model sensitivity if possible.

Defining Deicer Treatment Needs and Implementation Constraints 29 In addition to local construction regulations, construction at an airport is regulated by the FAA, primarily to mitigate hazards to aircraft operations. To reduce obstructions to airport operations, the FAA regulations generally specify minimum distances and maximum allowable heights for objects at or near an airport. FAA Advisory Circular (AC) 150/5370-2F states that any construc- tion or alteration of objects that affects “navigable airspace” requires notification to the FAA. The FAA defines navigable airspace in Federal Aviation Regulation (FAR) 77 with various imaginary surfaces. These imaginary surfaces are regions of space offset and sloped upwards from various airport features such as runways. The offsets and slopes are defined by the run- way approach controls. Permanent structures or activities located outside the areas described by FAR 77 will not require notification to the FAA. However, FAR 77 states that a permanent structure or activity that breaks the imaginary surface defined within the regulation will require notification to the FAA and subsequent FAA approval. Typically notification is provided by sub- mitting FAA Form 7460-1, “Notice of Proposed Construction or Alteration,” to the appropri- ate FAA Airports Regional or District Office. Although the FAA may permit some objects and operations within the imaginary surfaces defined by FAR 77, there are areas in which FAA design criteria prohibit structures or activities. FAA AC 150/5300-13A (Airport Design) indicates the minimum offsets and maximum allowable heights that are permitted adjacent to airports for operations and permanent structures. While these sources of information (AC 150/5370-2F, FAR 77, AC 150-5300-13A) provide sufficient information for determining siting criteria for a treatment system, it is important to coordinate with the appropriate FAA regulators throughout the selection and design processes of a treatment system. As the airport considers treatment technology selection, the specific location, footprint, and height constraints driven by these FAA criteria for potential treatment system sites should be documented. If a structure or operation necessary for a treatment system penetrates imaginary surfaces defined by FAR 77 or AC 150/5300-13A, then consider the following options: 1. Lower the height of the structure or operation. 2. Move the structure further away from the airport. 3. Use Airspace OMS software to determine a new location that is ideal for your needs. 4. Consider alternate treatment methods. Environmental Conditions Environmental conditions at potential treatment sites could affect the treatment technol- ogy selection process. An inventory of potentially affected environmental conditions should be performed, including evaluation of environmental resources, conditions, and permits (beyond those directly affecting the treated discharge), and should encompass the following: • Potential water resource impacts (wetlands, streams, floodplains, groundwater, buffer zones), • Limitations on air emissions, • Restrictions on stormwater discharges associated with development, • Presence of environmental contamination, and • Willingness to go through the National Environmental Policy Act (NEPA) process (which may be triggered by some, but not all, treatment solutions). It is possible that particular environmental restrictions may affect the viability of some deicer treatment technologies more than others. For example, significant environmental issues may eliminate any kind of on-site treatment. For additional information on potential water resources impacts, see ACRP Report 53: A Handbook for Addressing Water Resource Issues Affecting Airport Development Planning.

30 Guidance for Treatment of Airport Stormwater Containing Deicers 2.3.2 Operational Constraints Limitations on Open-Water Surfaces Some deicer treatment technologies, like activated sludge or aerated lagoons, are typically designed with open-water surfaces. Open-water surfaces can be wildlife attractants and provide reflectivity issues. Other treatment technologies, such as subsurface wetland treatment systems, may not have open-water surfaces but could attract wildlife. FAA AC 150/5200-33, “Hazardous Wildlife Attractants on or near Airports,” defines minimum separation criteria between an air- port’s air operations area (AOA) and potential hazardous wildlife attractants, which would include stormwater management facilities with open-water surfaces. For facilities with open-water surfaces that do not comply with the proposed separation criteria, the FAA strongly recommends that these facilities be designed to eliminate permanent open-water surfaces and limit temporary ponding to a 48-hour period after the design storm. The AC also recommends additional design criteria for the BMPs to reduce their attractiveness to wildlife, including steep sides, rip-rap, narrow and linear shape, and no attractive vegetation. While modifications can sometimes be made in the design process to address the open-water surfaces or other wildlife attractant features in a deicer treat- ment system, the modifications can add cost. The airport and airline position on the acceptability of open water should be made clear prior to the treatment technology screening process. Construction Interferences In most cases, airports have found ways to work around the interferences with operations that could occur with construction of a treatment system. However, the airport should provide the treatment technology selection team with potentially constraining conditions, such as limita- tions on when runways can be closed, early in the project. These constraints could potentially rule out certain technologies in the screening process. 2.3.3 Other Constraints Airport Policies and Management Interests Airport policies on considerations such as staffing, reliance on outside agencies, taking on deicer treatment operations, and capital versus operating costs may play a role in deicer treat- ment selection. Some airports have clearly stated that they do not wish their deicer treatment operations to be dependent on the decisions and functions of outside entities like POTWs or private recycling firms. Understanding the airport’s position on these issues helps to streamline the technology selection process. Another frequently discussed factor is whether the airport wants to take on operational respon- sibilities for a potential treatment plant, contract out the operation, or have no responsibility for operations. This decision may be affected by the ease of obtaining maintenance support. The allowable design and construction schedule can be a constraint. Many times, deicer treat- ment systems must be constructed within a compliance schedule within an individual permit. The time required to design and construct various treatment technologies varies. The airport should identify the timeframe available for design and construction early in the project. During the treatment technology screening phase, the times required for design and construction of the individual technologies can be determined and compared to the available schedule. The ability to fund a treatment system’s implementation is site-specific and often time-specific. Understanding what the available funds are for capital and operating expenses can be a factor that eliminates certain technologies. Also, the preference for expenditures of capital versus operating funds should be considered. Some treatment technologies (e.g., recycling) are more dependent on annual funding, while others (e.g., biological treatment systems) are more dependent on capital funds. Finally, available funding can limit the maximum treatment capacity that can be con- structed. A lower capacity can result in increased risk resulting from extreme deicing conditions and in the need to expand the system sooner.

Defining Deicer Treatment Needs and Implementation Constraints 31 Aesthetics can sometimes play a factor in treatment technology decisions. Most often, accommo- dations for aesthetic preferences can be made in the design phases, but occasionally, aesthetic issues can be a cause for elimination of certain technologies during the technology screening phases. The airport’s position on these items should be identified in this phase of the work. Stakeholder Buy-In While the level of involvement varies from project to project, stakeholders such as private citizens, public interest groups, other local entities, regulatory agencies, airlines, and other tenants may have voices in the decisions on treatment technologies. Airports should identify potentially interested parties and assess the impact of their perspectives on the technology selection, cost, sizing, and siting. 2.4 Worksheets for Documenting Treatment Needs and Constraints This section provides example worksheets for documenting the findings from the analysis of treatment needs and constraints. The worksheets are: • Criteria Worksheet for Allowable Pollutant Discharges (Section 2.4.1), • Criteria Worksheet for Characteristics of Stormwater to be Treated (Section 2.4.2), and • Criteria Worksheet for Airport Site and Operational Constraints (Section 2.4.3). The criteria worksheets are intended as guidance for the parameters to be considered. When considering treatment technologies, a more detailed and nuanced consideration of allowable pollutant discharges, stormwater characteristics, site constraints, and operational constraints will also be needed to support the decision-making process. 2.4.1 Criteria Worksheet for Allowable Pollutant Discharges The site-specific criteria governing the allowable pollutant discharges can be documented in a matrix or table similar to what is shown in Worksheet 1. The criteria worksheet should include: 1. Documentation of all limiting parameters, numeric limits, and conditions explicitly stated in the applicable permits, and Worksheet 1. Example of criteria table of potential and governing limits for discharges. Limiting Criteria Limit Value and Units from Permit Example Applicable Conditions Is It a Governing Limit? (Yes/No) Governing Criteria Value for Treatment Technology Basis of Selection COD _____mg/L Daily maximum _____mg/L COD _____lbs/day Monthly average _____lbs/day BOD5 _____mg/L Daily maximum _____mg/L BOD5 _____lbs/day Monthly average _____lbs/day PG _____mg/L Daily maximum _____mg/L EG _____mg/L Daily maximum _____mg/L NH3-N _____mg/L Daily maximum _____mg/L Phosphorus _____mg/L Daily maximum _____mg/L Flow Rate _____gpm Monitor _____gpm pH _____s.u. Range _____s.u. Dissolved Oxygen _____mg/L Minimum _____mg/L TSS _____mg/L Maximum _____mg/L TDS _____mg/L Maximum _____mg/L Temperature _____°F Maximum at any time _____°F

32 Guidance for Treatment of Airport Stormwater Containing Deicers 2. Documentation of the governing parameters, numeric limits, and conditions obtained from a comprehensive analysis. A criteria worksheet for potential and governing discharge limits associated with allowable pollutant discharges provides the following value: 1. A portion of the data necessary to calculate the required treatment capacity, and 2. Definition of the treated effluent quality that the selected treatment technologies will need to meet. 2.4.2 Criteria Worksheet for Characteristics of Stormwater to be Treated The characteristics of the stormwater that requires treatment can be summarized in a criteria table similar to the one shown in Worksheet 2. A criteria worksheet for untreated stormwater characteristics provides the following value: 1. Provides data necessary to calculate the required treatment capacity, and 2. Defines the range of influent characteristics that the selected treatment technologies will have to process. A criteria worksheet will need to be supplemented with an understanding of how these param- eter values change over time, the basis for how the information was derived, the frequency of occurrence, the assumptions underlying the analysis, and the limitations of the methods used to derive the information. 2.4.3 Criteria Worksheet for Airport Site and Operational Constraints Assessing the potential site and operational constraint criteria associated with implementing a treatment technology is somewhat of an iterative process. Some constraints may be abso- lute. Other constraints are preferences that can be overcome with adequate design and funding. Worksheet 3 presents an example of a matrix that documents site and operational constraints that may affect treatment technology selection, sizing, and siting. Worksheet 2. Example of criteria table of stormwater characteristics to be treated. Criteria Description Example Criteria Value Flow rate Average, maximum, minimum _____ gpm BOD, COD mass loading rates Average, maximum, minimum _____ lbs/day Maximum BOD, COD, EG, or PG concentration Identify frequency of maximum condition _____ mg/L Minimum PG, EG, BOD concentration Primarily a concern from an operating cost perspective _____ mg/L Stormwater temperature Range _____°F TSS concentration Identify range and form of TSS (sediment, sand, organic) _____ mg/L TDS concentration Could be a factor if proportion of pavement deicers is high _____ mg/L Presence of fuel Associated with the likelihood of a spill Specify Presence of metals Associated with typical stormwater runoff Specify Presence of fouling and clogging materials Specific materials that could cause fouling or precipitation on treatment system equipment, such as silica, inorganics with high hardness Specify

Defining Deicer Treatment Needs and Implementation Constraints 33 A criteria worksheet for airport site and operational constraints provides the following value: 1. A list of potential siting and operational considerations to promote discussion by stakeholders, 2. The data necessary to supporting the siting process, and 3. Characterization of the potential operating burden and constraints. Worksheet 3. Example criteria table of limiting site and operational conditions. Criteria Limiting Criteria Value (Complete for Multiple Sites if Applicable) Land available for on-site treatment 1. Available 2. Not available Maximum available footprint Specify Maximum height Specify Open water 1. Allowed 2. Not allowed NEPA process 1. Willing to go through NEPA process 2. Not willing to go through NEPA process Water resource impacts 1. No impacts allowed 2. Willing to allow impacts for treatment system construction with appropriate permits Site contamination 1. No contamination that limits on-site treatment facility construction 2. Contamination that eliminates on-site treatment construction 3. Contamination, but willing to remediate Air emissions restrictions 1. No restrictions 2. Known restrictions (identify parameters and values) Odors 1. Typically no odors 2. Potential for odors Utility availability 3. Water, power, natural gas available 4. Specify utilities not available 5. Utilities available with significant added cost Availability of surface water discharge 1. Receiving waters discharge point accessible 2. Receiving waters discharge point inaccessible 3. Receiving waters discharge point accessible with significant added cost Availability of sanitary sewer for POTW discharge 1. Sanitary discharge point accessible 2. Sanitary discharge point inaccessible 3. Sanitary discharge point accessible with significant added cost Groundwater conditions 1. Groundwater depth below surface Treatment plant operations 1. Airport willing to operate on-site system 2. Airport willing to subcontract on-site system 3. Airport not willing to operate or subcontract on-site operation Reliance on POTW to accept discharge 1. Airport willing to rely 2. Airport not willing to rely Reliance on off-site recycling and market for recycled glycol 1. Airport willing to rely 2. Airport not willing to rely Time available for design and construction Specify Maximum capital funding Specify Maximum annual operations and maintenance (O&M) funding Specify Preference to funding and capital or operating cost 1. Capital 2. Operating Accessibility 1. Sites accessible to land-side vehicle traffic, including trucks 2. Sites not accessible Ability to get regulatory approval 1. No concerns with eventual approval of technology 2. Potential concerns with eventual approval of technology Aesthetic criteria Specify Construction constraints Specify Miscellaneous constraints Specify