Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials (2017)

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5 2.1 Parameter Screening Stormwater parameters may be monitored using traditional off-site methods where samples are collected at sample locations by automatic or manual means and sent to an off-site laboratory for analytical test- ing. Most often, and where they exist, the laboratory analyses use meth- ods that have been specifically approved by regulatory agencies such as the EPA. Off-site monitoring data are characterized by fewer samples of higher quality data but have potential for long delays between sampling and acquisition of analytical results. Stormwater parameters can also be monitored using on-site monitor- ing methods. On-site monitoring methods involve various combinations of sampling and analysis that all occur on the airport site. Some on- site monitoring methods are approved by regulatory agencies for use in compliance reporting, but many are not. On-site monitoring of data is characterized by the ability to collect a greater number of samples with a shorter delay between sampling and acquisition of analytical results. This chapter describes a parameter screening process to guide users through the selection of parameters that will be monitored at their airport. Once parameters have been identified, air- port personnel can use the parameter list to facilitate the identification of applicable monitoring types. The parameter screening process considers the potential sample requirements that exist at the airport for each parameter. A parameter screening form to aid in the selection process is included at the end of this chapter. The screening for parameters to be monitored is performed by considering each reason that monitoring may be required (i.e., the drivers for monitoring). Each monitoring driver may result in a list of multiple parameters at multiple sampling locations. For example, an airport’s National Pollutant Discharge Elimination System (NPDES) permit may list several outfalls, each with dif- ferent monitoring parameters. In addition, there may be deicer management system processes that use monitoring to facilitate actions such as stormwater diversion. At each location, the critical function of each parameter should be considered to determine which monitoring method is appropriate for that parameter. The primary criteria for considering appropriate monitoring methods are the monitoring driver and the action that will be performed as a result of the measurement. Monitoring drivers with actions that will be performed immedi- ately (e.g., stormwater diversion) will require immediate monitoring results. Monitoring drivers with actions that can be delayed (e.g., percent deicer capture estimates) can be performed with Identify Applicable Monitoring Parameters C h a p t e r 2

6 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials delayed monitoring results. If a monitoring method for one parameter is to be performed on-site, it may be convenient for airport personnel to perform the analyses for the parameter from other sampling locations on-site as well. 2.2 Drivers for Monitoring The need to monitor the characteristics of stormwater discharges affected by airport and air- craft deicing materials is frequently driven by one of the following factors: • Regulatory drivers based on compliance requirements in permits authorizing discharge of stormwater, • Process control drivers based on the need to direct and convey stormwater to specific areas in a deicer management system, and • Tracking and accounting drivers based on the desire to quantify the constituents and charac- teristics of stormwater. These drivers provide the information necessary to determine the parameters to be monitored, sampling types, analyses to be conducted, monitoring locations, and frequency of monitoring. 2.2.1 Regulatory Drivers The Federal Water Pollution Control Act (FWPCA) of 1972, 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 Sec- tion 402 of the CWA, NPDES was created as a system for permitting point source discharges to the waters of the United States. The NPDES permit program generally requires that dischargers of pollutants to waters of the United States (i.e., direct dischargers) obtain an NPDES permit or their state equivalent. Airports are generally regulated under the Industrial Storm Water Program element of NPDES, although regulation through other aspects of the program is possible, especially if the airport is regulated as a municipal entity or if an airport discharges into a municipal storm sewer system. The CWA also established a regulatory program to address indirect discharges from industries, including airports, to POTWs through the National Pretreatment Program, a component of the NPDES Permit Program. The National Pretreatment Program requires industrial and commer- cial dischargers, called industrial users (IUs), to obtain permits or other control mechanisms to discharge to the POTW. Details on the CWA and NPDES program and associated permitting and compliance requirements may be found in ACRP Research Report 169: Clean Water Act Require- ments for Airports. Both NPDES stormwater discharge permits and IU permits from POTWs may incorporate effluent limitations or benchmarks and require periodic monitoring of discharges. The per- mits may also specify the acceptable laboratory analysis methods and provide requirements for monitoring type, monitoring frequency, and reporting. The conditions in NPDES, IU, and other permits typically provide airport operators with their initial drivers to consider for the need for and benefits of on-site monitoring of deicer-affected stormwater. In many cases, use of conventional off-site monitoring methods (grab or automatic sample collection plus laboratory analysis) will be sufficient to meet the parameter and sampling fre- quency requirements in NPDES and IU permits. Potential circumstances where use of on-site monitoring methods for regulatory compliance purposes may be beneficial are listed in the “Reasons On-Site Monitoring May Be Used for Permit Compliance” sidebar. Whatever the rea-

Identify applicable Monitoring parameters 7 son for using on-site monitoring for compliance purposes, it is critical to determine whether use of the on-site method needs to be approved by the applicable regulatory agencies. 2.2.2 Stormwater or Deicer Management System Process Control Drivers Airports may find that it is beneficial or cost-effective to use on-site monitoring as part of control systems for stormwater or deicer management, even if that on-site monitoring is not used for compliance purposes. Poten- tial uses for on-site monitors in stormwater and deicer management systems include: • Segregating or diverting stormwater based on pollutant concentration (e.g., concentrations higher than a permit effluent limitation or concentrations that are internal control set points for further processing), • Blending stormwater streams of different concentrations together to facilitate more efficient treatment and reduc- tion of peak concentrations in discharges, and • Controlling flow or mass loadings into treatment systems or to POTWs. Online monitors can be used as part of an automatic diversion or control system for storm- water and deicer management. With an automatically controlled diversion system, measure- ments of particular stormwater parameters made by the online monitor are sent to a control panel/computer that subsequently triggers a change to system equipment positions or rates (e.g., gate, valve, or pump) that affects the stormwater flow. This results in the ability to create separate streams of stormwater runoff that can be managed according to their characteristics. Use of an automatically controlled diversion system frequently results in the need to convey, treat, and discharge smaller volumes of water than would be required if all stormwater during the deicing season was collected and/or processed. The installation of an online monitor often allows for a reduction in storage capacity, pump capacity, pipe sizes, and treatment capacity, resulting in overall reductions in both capital and operating costs. 2.2.3 Tracking and Accounting Deicer In some cases, airport operators may find that they are required to track and account for the quantity of deicer-related parameters in stormwater. Typically tracked values may be flow rates, pollutant concentrations, or mass loadings for various parameters. A need to track discharge quantities could be driven by: • Tracking loads to a POTW, • Tracking loads or flows to surface waters, • Tracking loads or flows in and out of on-site deicer treatment facilities, • Calculating percent capture of applied deicer, or • Calculating fees for flows or loads to surface waters or a POTW. An airport operator may need to track mass loads of pollutants to a POTW or surface waters to comply with discharge monitoring requirements. Similarly, an airport operator may need to track loads in the influent to an on-site treatment system or a POTW as a means of managing Reasons On-Site Monitoring May Be Used for Permit Compliance • The frequency of monitoring is high (e.g., more than once per day). • The monitored location is remote and/or difficult to get to. • Compliance points also serve as stormwater diversion points. • Compliance parameters are in terms of mass loadings, where frequent measurements of flow and concentration are used to calculate load. • There is significant variation in concentrations that must be understood for compliance purposes. • Fast response time to track changes in discharge characteristics is required or desired. • If the permits require the airport to determine and report the percent of applied deicer that is collected.

8 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials the flow rates. As flows and loads change in the stormwater, the airport would have to measure both the flow and the concentrations to accurately determine the load rates, or it may have to cease discharge if a maximum total has been reached. Since flow rate and concentration can change quickly, a large number of sample data points may be required to monitor the cumula- tive loading. An airport may choose to determine the percent of applied deicer that is captured by a deicer management system. Total deicer applied could be determined from application records, with a factor applied for the percent of deicer available for capture, and then sampling results would be used to estimate the amount of deicer captured in the stormwater collection system. Use of on-site monitoring (especially online) for deicer-related pollutants would be a good means of capturing the inherent variability in concentrations, thus providing a more accurate calculation of the deicer captured. In addition, if decisions based on the results require quick actions, such as stormwater capture or adjustment to the sampling plan frequency or locations, then on-site methods may be performed to quickly determine the monitoring results. Airports that discharge deicer to POTWs are billed for the load that they discharge. The load- ing is typically based on a unit price per pound of pollutant discharged. The amount is usually called a surcharge for wastewater concentrations that exceed the concentration typical of sanitary wastewater. The amount of deicer discharged to a POTW must be monitored for billing pur- poses. On-site or off-site monitoring may be performed to determine the stormwater concentra- tion for billing purposes. Deicers in the Environment The chemicals in deicers are regulated primarily because of their potential effects on aquatic life in receiving streams. These chemicals include the primary deicer constituent (typically propylene glycol) and the various additives. Potential nega- tive effects on aquatic life can occur if the chemicals in deicers reach threshold concentrations and/or loadings under certain environmental conditions. The water quality standards can be based on potential toxic effects of individual constituents or on the cumulative effects of multiple constituents. The most common effect of the primary deicer constituents in the environment and the most common reason for the regulation of deicer discharges are the effects that they have on the oxygen content in the receiving waters. When the primary deicer constituents are discharged, they can become a food source for bacteria in the environment. Bacteria also use oxygen when degrading primary deicer constituents. Primary deicer constituent concentrations can range into thousands of mg/L, leading to oxygen demands in a similar range. The saturation concentration of oxygen in surface water is between 6.6 mg/L (100°F) and 14 mg/L (32°F) (American Public Health Association et al., 2005, p. 4–139). As a result, far more oxygen can be consumed to degrade primary deicer constituents than is available in the water. When the temperatures and nutrients allow bacterial activity to occur in streams with deicer, oxygen concentrations can be depleted, negatively affecting aquatic life. Cold temperatures and nutrient limi- tation will limit the amount of bacterial growth, and reaeration of the stream will add in oxygen removed by the bacterial degradation of deicer.

Identify applicable Monitoring parameters 9 2.3 Potential Monitoring Parameters The potential monitoring parameters applicable to each airport are unique to the airport’s permit conditions, deicer types, and deicer man- agement requirements. The term “deicer” as used in this guidebook refers to either aircraft deicing fluids (ADFs), aircraft anti-icing fluids (AAFs), or airfield pavement deicer materials (PDMs). The organic freezing point depressants that are the primary deicer constituents are propylene glycol, ethylene glycol, formates, acetates, and glycerin. Urea has historically been used as a pavement deicer and may still be used at some airports. When considering the methods for monitoring these deicer con- stituents, it is critical to understand that there is no on-site monitoring method that directly measures the primary deicer constituents (e.g., glycol, formate, or acetate) in stormwater. Instead, on-site monitoring of surrogate constituents for these constituents is conducted. Common surrogates for the pri- mary deicer constituents include biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC). Urea readily breaks down to ammonia in stormwater and ammonia–nitrogen is typically used as the surrogate constituent for urea. These surrogates are discussed further in the following sections. Commonly required monitoring parameters applicable to monitoring of general stormwater quality include pH, dissolved oxygen, temperature, total suspended solids, and flow. A description of the most commonly encountered monitoring parameters is provided in the following sections; however, some airport permits may require additional monitoring for spe- cific parameters not discussed in this guidebook such as deicer additives, total dissolved solids, or phosphorous. The user is reminded to confirm all permit requirements when selecting analytical parameters. 2.3.1 Glycols Glycols, especially propylene glycol and ethylene glycol (EG), are the primary deicer constitu- ents serving as freezing point depressants in ADFs/AAFs and some PDMs. Glycols are frequently included in airports’ monitoring programs as indicators of deicers in stormwater discharges. Glycols are also monitored at some airports with deicer treatment or recycling systems for the purpose of deicer management. Glycols are typically analyzed by collecting samples and ship- ping them to a laboratory. Because glycols are expensive to analyze at a laboratory and there is a significant delay for the results, the concentration of glycol in airport stormwater is often determined by measuring concentrations of surrogate parameters and developing correlations to glycols, as discussed in Sections 2.3.3 and 2.4. 2.3.2 Formates and Acetates Airfield pavement deicers containing urea or glycols have become less popular owing to their adverse environmental impacts (i.e., elevated concentrations of ammonia and oxygen demand). Other PDMs containing acetate or formate as the freezing point depressant were developed as alternatives that do not contribute to ammonia and have significantly lower oxygen demand. Acetate and formate concentrations are determined by laboratory analysis of water samples. Percentage of Surveyed Airports That Perform Monitoring for a Parameter Glycols or surrogates (BOD, COD, or TOC) 67% Ammonia 8% pH 67% DO 54% Temperature 54% TSS 4% Flow 29%

10 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials 2.3.3 Surrogates for Primary Deicer Constituents Primary deicer constituent concentrations in stormwater can also be determined using a sur- rogate parameter. A surrogate parameter is a parameter that is measured instead of the desired parameter. The decision or need to use a surrogate parameter is often driven by the absence of direct means of measuring the parameter of interest or the ability to get better information when a surrogate is used. The specific surrogate parameter selected is typically chosen based on the data needs, ability to correlate results to deicer concentrations, frequency of data collection, time to complete the analysis, and cost. The most common surrogate parameters for the primary deicer constituents are listed in the following subsections. 2.3.3.1 Biochemical Oxygen Demand When biodegradable compounds degrade, dissolved oxygen in the water is consumed, and there is a resulting oxygen demand. Biodegradable compounds in deicers include propylene glycol, ethylene glycol, glycerin, formates, and acetates. The EPA-approved method for measuring BOD that is used by certified analytical laboratories places a sample in a closed jar with bacteria and nutrients and measures the decrease in dissolved oxygen that occurs as the bacteria consume the pollutants. This biological degradation in the laboratory BOD test is similar to what can happen in the environment, and as a result BOD is often chosen by regulatory agencies as a monitoring and limited parameter in discharge permits. BOD limits and monitoring requirements are typically included in discharge permits when there is known potential for discharge of compounds to decrease the dissolved oxygen concentration in the receiving waters. Permits for industrial discharges to POTWs also often use BOD for monitoring and limits because those facilities have BOD limits in their own NPDES permits. The standard laboratory method for measuring BOD is performed over a 5-day period and is designated BOD5. The BOD5 analysis has several issues that may affect the ability to accurately measure the oxygen demand, including: • The bacteria seed used may not be conditioned to the chemical(s) being tested, • Toxicity in the sample may inhibit degradation and yield a false low result, • There is often high variability in the sample results (Liptak, 2003, p. 1226), • Airport samples may contain samples with higher and more variable BOD concentrations than are typically seen from other industries, which requires sample dilution that introduces the possibility of error in the test results, and • Five days are required to get a result. The laboratory results for BOD5 typically represent a conservatively higher oxygen demand than the oxygen demand in surface waters. The actual oxygen demand in surface waters will be limited because of in-stream conditions for nutrient availability, temperature, and bacteria avail- ability. Low water temperatures typical of streams during deicing events typically inhibit biologi- cal activity and reduce the biological oxygen demand. However, some BOD analyses may result in low values if the laboratory uses a bacterial seed that is unconditioned to the deicer chemicals. Carbonaceous BOD is a subset of the BOD analysis. Denoted as CBOD, it is the BOD caused only by the conversion of carbon to carbon dioxide. Therefore, measuring CBOD does not measure the oxygen demand from non-carbon sources such as ammonia. There are no on-site monitoring methods that measure only CBOD. These analyses are typically performed in off- site laboratories. 2.3.3.2 Chemical Oxygen Demand To avoid the issues with the BOD5 method, the COD parameter is sometimes used as a measure of oxygen demand. Rather than using bacteria, a COD test uses chemicals reacting with organic

Identify applicable Monitoring parameters 11 compounds to determine the oxygen demand. The chemicals completely oxidize the organic com- pounds. As a result, COD values are typically higher than actual in-stream oxygen demand from biodegradation because COD reflects compounds that may not all be biologically reactive. If both BOD5 and COD are measured, the COD value should always be larger than the BOD5 value. This relationship can be used as a quick quality control check of the sample results. In deicing monitoring, it is typically assumed that all of the COD contribution is attributed to deicers. However, there is generally a low, background contribution from other sources in stormwater collection systems. The typical background concentration range can be determined by monitoring outside of the deicing season. 2.3.3.3 Total Organic Carbon Another surrogate parameter for primary deicer constituents is TOC. The TOC method con- verts all of the organic carbon in a sample to carbon dioxide and measures the amount of carbon dioxide produced. Because the conversion of organic compounds to carbon dioxide is essentially complete in a TOC analysis, TOC represents a more conservative reflection of the potential oxy- gen demand. TOC correlates well with the concentration of organic compounds and to COD in water samples dominated by a single constituent (e.g., propylene glycol). In samples that contain a mixture of constituents such as glycols, acetates, and formates, the correlations among TOC, COD, and BOD become less accurate. 2.3.4 Ammonia–Nitrogen Ammonia–nitrogen is defined as the concentration of nitrogen contained in the compound ammonia in a water sample. Ammonia–nitrogen frequently appears in airport NPDES permits because most entities regulating water quality have numeric standards for the ammonia concen- trations acceptable in surface waters. The standards exist because ammonia can be toxic to some kinds of aquatic life, depending on temperature and pH (Levelton Consultants, Limited, 2007, p. 40). The young life stages of some aquatic species are more susceptible to ammonia toxicity. Historically, ammonia has been a significant consideration in airport NPDES permits stem- ming from the use of urea as a pavement deicer. Urea degrades in the environment into ammonia– nitrogen. With the conversion of much of the aviation industry to non-urea pavement deicers, the issues surrounding ammonia monitoring are less significant. However, ammonia–nitrogen can be present in current stormwater discharges as a result of historical urea use. In addition, ammonia– nitrogen may be present in biological deicer treatment system discharges where nitrogen-based compounds are added as a nutrient from the biomass and in stormwater runoff from areas where fertilizers have been used for landscaping or farm applications. Whether an airport has an effluent limit for ammonia–nitrogen or simply monitoring require- ments is dependent on a mathematical analysis of the reasonable potential that airport discharges will exceed the regulatory in-stream water quality criteria. 2.3.5 pH The pH value is a measure of the acidity or alkalinity of a water sample. The pH scale uses values between 0 and 14, with values decreasing from 7 to 0 indicating strength of an acid and values increasing from 7 to 14 indicating strength of a base. Strictly speaking, pH is the mea- sure of hydrogen ion concentration in water. Streams are typically near neutral, or have a pH of approximately 7. Surface water pH values further away from neutral will inhibit aquatic life. Water discharges with a pH value of less than 2 or greater than 12 are defined by the EPA as hazardous waste.

12 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials The pH values of stormwater runoff can be affected by multiple conditions, including break- down of primary deicer constituents on the airfield. Acidic conditions can occur when primary deicer constituents are exposed to warm temperatures, resulting in partial degradation of deicer by bacteria, which results in the byproduct formation of acids. 2.3.6 Dissolved Oxygen Dissolved oxygen (DO) is a requirement for most aquatic life. Because of DO’s importance to aquatic life, virtually all surface waters have DO numeric water quality standards for minimum in-stream concentrations. For some airports, outfall discharges are required to meet minimum DO concentrations. The DO of a stream can be reduced as oxygen is consumed during biological breakdown of degradable chemicals. This is described in Section 2.3.3.1. 2.3.7 Water Temperature Some surface waters have water quality standards for maximum temperature of discharges based on the type of aquatic life found in the area. If discharges have sufficient potential for high temperatures, NPDES permits may contain monitoring requirements and/or limits for maximum temperatures at various times of the year. The temperature of streams can also be important for airports because natural stream temperatures typically fluctuate with the seasons and reduce or accelerate the biological oxygen demands occurring in a stream. Discharges with temperatures above permitted levels can inhibit aquatic life. Temperature of stormwater runoff from airports is typically not an issue; however, discharges from processes such as treatment or heating and cooling processes could be outside of the normal surface water ranges for a season. This may necessitate the need for monitoring and control of the temperature of the discharges. 2.3.8 Total Suspended Solids Suspended solids in stormwater runoff may pose threats to the environment because they can (1) cause sedimentation in a stream and harm benthic life, and (2) block light and inhibit aquatic life. Total suspended solids (TSS) are the class of solids that are associated with particulates from inorganic solids (e.g., silt, sand) or organic solids (e.g., biosolids or decaying vegetation). Inorganic solids in discharges from airports may be the result of particulates from paved and unpaved surfaces as well as sand application to the ramp areas for traction. Although sand is not strictly defined as a deicer, it is applied at the same time as deicing chemicals. Organic solids may be present in airport discharges from deicer treatment systems or stormwater storage sys- tems as a result of the biological activities in those systems. Organic solids may also be present in stormwater discharges from biological growths on airfield surfaces, soils, and infrastructure. When these growths occur in surface waters, they are often characterized as nuisance growths. Deposition of biological solids in a stream and their breakdown by bacteria can decrease the DO concentration as the bacteria in the stream degrade and consume oxygen in the water. If the airport is required to determine whether the solids in surface water samples are inorganic or organic suspended solids, a specialized analysis of solids called volatile suspended solids will measure only the suspended solids associated with the organic solids. Instruments that measure solids in the field will only determine the TSS. The volatile fraction must be determined using off-site laboratory methods.

Identify applicable Monitoring parameters 13 TSS limits and monitoring requirements in IU permits from POTWs are common. Many stormwater NPDES permits contain monitoring requirements but not TSS limits. NPDES per- mits involving construction discharges or discharges from biological treatment systems are more likely to have TSS limits. 2.3.9 Flow Monitoring or estimation of flow rates discharged from airport outfalls into surface waters is often required in discharge permits. Monitored flow rates and volumes can be used in calculation of stormwater discharge fees, for consideration of downstream erosion and flooding impacts, and in support of stormwater runoff modeling. Flow rates are also often used for calculation of mass loading rates (mass of pounds of the parameter in a time period). Calculated mass loads are generally required for deicer discharges to treatment systems or POTWs or for discharges to receiving waters with total maximum daily loads (TMDLs). Loads in stormwater can be compared to applied deicer usage records to deter- mine the percentage of deicer collected. Mass loading rates are calculated by multiplying the flow rate (volume per unit time) by the concentration of a given parameter (mass per unit volume). The loading is calculated by: Loading lbs day flow gpm concentration mg L( ) = ( ) ∗ ( ) ∗0 0120. Or for metric units: Loading kg day flow m day concentration mg L( ) = ( ) ∗ ( ) ∗0 00100. Mass loads (mass of a parameter) are the loading rates multiplied by the time period of interest. 2.4 Correlation Between BOD/COD/TOC/Glycol As discussed in Section 2.3.1, glycol analyses typically require off-site laboratory analyses and are expensive. Surrogate parameters that can be measured by on-site analyses are sometimes used to estimate the glycol or other primary deicer constituent concentrations in stormwater based on correlations. Propylene glycol concentrations can be correlated to COD and TOC because of the oxidation reaction used in the monitoring methods. Correlation is defined as the mathematical relationship between the parameter values derived from different test methods. The oxidation reaction of propylene glycol shown in the following equation is used as a basis for understanding the relationships of the parameters. C H O 4 O 3 CO 4 H O3 8 2 2 2 2 PROPYLENE GLYCOL MW 76.09 g mol OXYGEN MOLECULE MW 32.00 g mol CARBON DIOXIDE MW 44.01 g mol MW carbon12.01 g mol WATER + → + Where MW = molecular weight. In the reaction, for every molecule of propylene glycol oxidized (chemically or biologically), four molecules of oxygen are consumed and three molecules of carbon dioxide are produced.

14 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials The amount of oxygen required in a complete oxidation is known as the theoretical oxygen demand. Using the molecular weights, the following relationships can be found: Propylene glycol concentration: 1 76.09∗ = 76 0. 9 128 mg L Theoretical oxygen demand: 4 32.00∗ = .00mg L Organic carbon from carbon dioxide produced : 3 12.01 mg L( ) ∗ = 36 03. For propylene glycol, the theoretical oxygen demand is essentially the same as the COD (Johnson, Varney, and Switzenbaum, 2001, p. 17) because the COD test oxidizes virtually all of the propylene glycol in the sample. Using the theoretical oxidation relationship, the correlations are: Propylene glycol concentration 128.00 76.09∗ = COD concentration or Propylene glycol concentration 1.69 COD con∗ = centration and Propylene glycol concentration 36.03 76.09 T∗ = OC concentration or Propylene glycol concentration 0.474 TOC co∗ = ncentration Correlations for other primary deicer constituents (i.e., ethylene glycol, glycerin, acetates, and formates) can be estimated using oxidation reactions in a similar manner. The relationships listed previously are for propylene glycol, and if other compounds are in the sample in significant con- centrations, the correlation will change based on the oxidation reaction for the other compounds. Therefore, it is difficult to get good correlations to COD, BOD, or TOC for stormwater samples if the primary deicing compound concentration is not significantly greater than concentrations of the other compounds in the sample. The relationships listed previously are for propylene glycol as a pure compound. Correlation of a pure compound sample will result in a near-perfect linear relationship because only one compound is oxidizing and causing the oxygen demand and the carbon dioxide production. Correlation testing using a calibration solution will result in this type of relationship. The cor- relation to stormwater samples will generally be good for high deicer concentrations but will become less accurate as the deicer concentration approaches the background concentration for COD or TOC. A correlation for a calibration solution will give an incorrect assessment of the accuracy of the correlation for actual stormwater samples—especially at low concentration. In stormwater sam- ples, other compounds may be present, including organics from deicer additives, contaminants, and breakdown products of the primary deicer constituents. These other organic compounds will have different correlations to the oxygen demand or the carbon dioxide production, causing deviations from the ideal, single-compound correlation. Determining the correlation accuracy of deicer to COD or TOC at low concentration requires both the propylene glycol concentration and the COD or TOC concentration to determine the variability. Variability at low concentrations will be site-specific and will be caused by the indi- vidual sample stream water quality. Many measurements will be required to determine the vari- ability. Measurements at higher deicer concentrations are not as critical because the oxygen

Identify applicable Monitoring parameters 15 demand (for COD) or carbon dioxide production (for TOC) will be almost completely from propylene glycol and will therefore approximate the ideal correlation. Measurements of both parameters (propylene glycol and either COD or TOC) for the correlation should be weighted to the lower concentrations to accurately determine the range where significant deviations from ideal correlation begin to occur. It is recommended that correlations below approximately 300 mg/L propylene glycol be checked for significant deviations. Correlation of deicer to BOD5 is performed by laboratory testing because there is no math- ematical model to accurately estimate theoretical BOD5. To develop the correlation to propylene glycol, for example, the ratio of BOD5 to COD is determined through laboratory testing. The ratio is then inserted into the theoretical correlation between propylene glycol and COD. Litera- ture values indicate that the ratio of BOD5 to COD for a propylene glycol solution is approxi- mately 0.55 (Johnson, Varney, and Switzenbaum, 2001, p. 2). Using the relationship between BOD5 and COD and the correlation between propylene glycol concentration and COD from before gives the correlation between propylene glycol and BOD5 (0.55 * 1.69 = 0.93): Propylene glycol concentration 0.93 BOD co5∗ = ncentration 2.5 Using the Parameter Screening Worksheet A parameter screening worksheet (see Figure 2.1) was developed for this guidebook to facili- tate the screening of potential drivers for monitoring and to determine the parameters an airport needs to monitor. As each monitoring driver (i.e., NPDES permit discharge or stormwater diver- sion) is reviewed for each required monitoring location, the worksheet can be used to document the findings for each required location. The monitoring drivers for each parameter can be indi- cated with check marks under the monitoring driver heading on the worksheet. The worksheet is used to organize the monitoring requirements for the airport. The data from the worksheet can be used as the baseline documentation for the remainder of the on-site monitoring screening process described in the next chapters. 2.6 Reasons On-Site Monitoring May Be Used for Permit Compliance On-site monitoring may be used for permit compliance if: • The frequency of monitoring is high (e.g., more than once per day), • The monitored location is remote or difficult to get to, • Compliance points also serve as stormwater diversion points, • Compliance parameters are in terms of mass loadings, where frequent measurements of flow and concentration are used to calculate load, • There is significant variation in concentrations that must be understood for compliance purposes, • Fast response time to track changes in discharge characteristics is required or desired, or • If the permits require the airport to determine and report the percent of applied deicer that is collected. 2.7 Deicers in the Environment The chemicals in deicers are regulated primarily because of their potential effects on aquatic life in receiving streams. These chemicals include the primary deicer constituent (typically pro- pylene glycol) and various additives. Potential negative effects on aquatic life can occur if the

16 Guidebook for Selecting Methods to Monitor airport and aircraft Deicing Materials Figure 2.1. Parameter screening worksheet.

Identify applicable Monitoring parameters 17 chemicals in deicers reach threshold concentrations or loadings under certain environmental conditions. The water quality standards can be based on potential toxic effects of individual constituents or on the cumulative effects of multiple constituents. The most common effect of the primary deicer constituents in the environment is the effect that they have on the oxygen content in receiving waters, and this is the main reason for the regula- tion of deicer discharges. When the primary deicer constituents are discharged, they can become a food source for bacteria in the environment. Bacteria also use oxygen when degrading primary deicer constituents. Primary deicer constituent concentrations can range into thousands of mg/L, leading to oxygen demands in a similar range. The saturation concentration of oxygen in surface water is between 6.6 mg/L (at 100°F) and 14 mg/L (at 32°F) (American Public Health Associa- tion, American Water Works Association, and Water Environment Federation, 2005, pp. 4–139). As a result, far more oxygen could be consumed to degrade primary deicer constituents than is available in the water. When the temperatures and nutrients allow bacterial activity to occur in streams with deicer, oxygen concentrations can be depleted, negatively affecting aquatic life. Cold temperatures and nutrient limitation will limit the amount of bacterial growth, and reaeration of the stream will add in oxygen removed by the bacterial degradation of deicer.