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

Chapter: Chapter 4 - Identify Applicable Monitoring Methods

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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
×
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
×
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Suggested Citation:"Chapter 4 - Identify Applicable Monitoring Methods." National Academies of Sciences, Engineering, and Medicine. 2017. Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. Washington, DC: The National Academies Press. doi: 10.17226/22749.
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23 4.1 Screening of Monitoring Methods Once the monitor type required for each parameter has been deter- mined, the next step is selecting the monitoring methods. For on-site monitoring, the method is the specific process by which the parameter is analyzed by the instrument. Each parameter may have several methods by which it can be analyzed. For example, temperature can be analyzed by infrared, thermocouple, glass-bulb, or other handheld methods. For off-site monitoring, the method is the specific test-method pro- tocols the laboratory will follow to analyze the water sample. For some analyses, there are multiple analytical methods that could be used to analyze a particular parameter. For others, very specialized methods have been developed by individual laboratories. Typical analytical methods for deicing constituents are provided in Table 3.1. In order to choose the correct method, the following information should be considered: • Purpose of monitoring – permit compliance versus characterization, • Regulatory requirements – specific methods may be identified by stormwater permits or regulatory agencies, • The analytical sensitivity needed, and • What sample containers and preservation will be used and what holding times may apply. Selection of the proper monitoring method will allow for the desired monitoring approach while minimizing the maintenance needs of the system. For each parameter, general background information and common monitoring method issues are presented in Section 4.3. 4.2 Use of the Criteria Tables and Fact Sheets Because of the complexity of choices for on-site methods and instruments, criteria tables and fact sheets were developed for this guidebook to organize the on-site monitoring method selection process. Criteria tables are provided in Appendix A as a tool for comparing moni- toring methods for each parameter. The fact sheets (available at http://www.trb.org/Main/ Blurbs/167504.aspx) offer detailed information on each of the on-site monitoring methods. 4.2.1 How to Use the Criteria Tables The criteria tables are designed as a screening tool to narrow down the potential on-site moni- toring methods applicable for a particular parameter and sampling location. Handheld and test Identify Applicable Monitoring Methods C H A P T E R 4

24 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials kit method criteria tables are separate from online methods. Critical features of the monitoring methods are compared head-to-head so that features important for the airport’s specific needs can be weighted for the selection process. The site-specific requirements can then be weighted by airport personnel to aid in determining the best monitoring methods for the situation. The criteria tables are divided into three parts: (1) method and use status, (2) implementation considerations, and (3) typical costs. Table 4.1 through Table 4.3 provide the definitions and further information regarding the criteria used. The first section of each criteria table describes methods and typical uses (see Table 4.1). The second section of each criteria table presents implementation considerations (see Table 4.2). Finally, the third section of each criteria table discusses typical costs, including capital and operating cost ranges (see Table 4.3). 4.2.2 How to Use the Fact Sheets The fact sheets (available at http://www.trb.org/Main/Blurbs/167504.aspx) are information sheets that summarize the technical capabilities and applicability of each on-site monitoring Criterion Description Reason It Is Important Regulatory - a pproved m ethod Does the method have a federal or local regulatory approval ? Significant consideration for NPDES discharge or compliance monitoring . Not important for internal monitoring. Measurement r ange Range in which method can accurately measure Compare to the expected stormwater range . Accuracy Measurement accuracy as a percentage of measurement Provided by manufacturers . Other factors may influence the actual accuracy . Siting constraints/needs ( online only) Utility or other needs for implementation Getting utilities to the sampling point may be a significant cost . Flow and stream constraints Requirements for the sample collection Sample stream may need continuous wate r supply, or filtering may be required . Interferences Parameters that can cause a measurement malfunction Determine if these are present in the stormwater at critical concentrations. Staff time requirements Provides information on expected labor needs Significant consideration for airports with limited environmental staff for installations in remote locations . Level of staff knowledge Provides information on complexity of method Consideration for potential staff training requirement . O&M i ssues Pro vides information on expected operation (including calibration) and maintenance labor needs Significant consideration for airports with limited maintenance staff . Table 4.2. Criteria tables’ implementation consideration criteria. Criterion Description Reason I t I s Important Method Short description of the analytical method used to make the measurement Some manufacturers ’ literature is ambiguous as to which method is used . Confirm with manufacturer when selecting equipment that the selected method is used. Type ( handheld and t est kit only) Method type Differentiates between the two types of methods ( handheld or test kit) . Demonstrated technology for airport stormwater? Defined as successful implementation at one airport for one entire season Demonstration provides reason to believe the method can work at other a irports, but is not a guarantee. General availability of technology Provides informa tion on number of manufacturers supplying equipment using this method Limited number of vendors may indicate that spare part s are difficult to get or method is not well used . Table 4.1. Criteria tables’ method and use criteria.

Identify Applicable Monitoring Methods 25 method. The information in the fact sheets was derived from manufacturers’ information and field operating experience gained from airports. The objective of the fact sheets is to present data on a monitoring method in sufficient detail to support final selection of a method. The fact sheets also provide information addressing implementation considerations. The first section of each fact sheet summarizes the method and typical uses (see Table 4.4). The second section of each fact sheet describes implementation considerations (see Table 4.5). Finally, the third section of each fact sheet presents typical costs, including capital and operating cost ranges (see Table 4.6). 4.2.3 Typical Installation Location Criteria for Online Monitors Deicing monitoring is typically performed to measure the parameter of concern in one sample stream. The sample collection method or online monitor should be selected and optimized to work within the expected characteristics of the sample stream. Characteristics of sample streams Criterion Description Notes Capital c osts Estimated range for cost of the equipment and installation for online equipment Costs are in ranges so that qualitative comparisons can be made . Costs should be confirmed with suppliers during detailed comparisons . Typical additional capital costs ( online only) Estimated range for capital cost for other recommended system equipment Cost for utility connection and small shelter are not included . Annual operation and maintenance costs Estimated range for annual operating and maintenance costs Contract maintenance costs typical for airport s are included , but O&M labor by airport personnel is not included . The typical range listed under “Staff Time Requirements” should be used with the airport’s labor rate to estimate the airport’s labor cost. Table 4.3. Criteria tables’ typical costs criteria. Criterion Description Reason It Is Important Parameter Parameter applicable to method Note that the reported value may be correlated to the parameter rather than being a direct measurement of the parameter. See Chapter 5 for discussion. Type Method type Differentiates between the three types of methods. Method description Short description of the analytical method used to make the measurement Some manufacturers’ literature is ambiguous as to which method is used. Confirm with manufacturer when selecting equipment that the selected method is used. Level of technology development Defines the range of years the technology has been in general use Methods that are emergent (i.e., 1 to 5 years of general use) are more likely to have unknown issues than well- established methods. Demonstrated technology for airport stormwater? Defined as successful implementation at one airport for one entire season Demonstration provides reason to believe the method can work at other airports, but is not a guarantee. General availability of technology Provides information on number of manufacturers supplying equipment using this method Limited number of vendors may indicate that spare parts are difficult to get or method is not widely used/researched. Table 4.4. Fact sheets’ method and use criteria.

26 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials associated with typical stormwater drivers (see Section 2.2) can be used as criteria for identifying monitoring locations. The criteria are also summarized in the on-site monitor fact sheets under “Typical Installation Locations.” 4.2.3.1 Outfall Monitoring Outfall monitoring is generally end-of-pipe monitoring or in-ditch monitoring where storm- water is determined to be discharging into waters of the state (i.e., a receiving stream) or dis- charging from a process (i.e., treatment). Both on- and off-site methods are appropriate for outfall monitoring. Criterion Description Notes Capital c osts Estimated range for cost of the equipment and installation for online equipment Costs are in ranges so that qualitative comparisons can be made . Costs should be confirmed with suppliers during detailed comparisons . Typical additional capital costs ( online only) Estimated range for capital cost for other recommended system equipment Cost s for utility connection and small shelter are not included . Annual operation and maintenance costs Estimated range for annual operating and maintenance costs Contract maintenance costs typical for airports are included , but O&M labor by airport personnel is not included . The typical range listed under “Staff Time Requirements” should be used with the airport’s labor rate to estimate the airport’s labor cost. Table 4.6. Fact sheet typical costs criteria. Criterion Description Reason It Is Important Typical installation locations Examples of airport processes for which method is applicable See following text for discussion of the airport processes. Regulatory-approved method Does the method have a federal or local regulatory approval? Significant consideration for NPDES discharge or compliance monitoring. Not important for internal monitoring. Measurement range Range in which method can accurately measure Compare to the expected range. Accuracy Measurement accuracy as a percentage of measurement Provided by manufacturers. Other factors may influence the actual accuracy. Response time Typical time from sample collection to result Consideration for systems that use results for diversion. Siting constraints/needs (online only) Utility or other needs for implementation Getting utilities to the sampling point may be a significant cost. Flow and stream constraints Requirements for the sample collection Sample stream may need continuous water supply, or filtering may be required. Interferences Parameters that can cause a measurement malfunction Determine if these are present in the stormwater at critical concentration. Staff time requirements Provides information on expected labor needs Significant consideration for airports with limited environmental staff or for installations in remote locations. Level of staff knowledge Provides information on complexity of method Consideration for potential staff training requirements. O&M issues Provides information on expected maintenance labor needs Significant consideration for airports with limited maintenance staff. Data retrieval Typical communication connection supplied by manufacturers Consideration for remote systems or automatic control of systems. Recommended features Recommended additional equipment of successful operation Considerations for all airport installations. Optional features Additional equipment that may be required for successful operation Considerations for special cases. Table 4.5. Fact sheets’ implementation consideration criteria.

Identify Applicable Monitoring Methods 27 Since outfall monitoring tends to be for discharges to a receiving stream, the regulated levels of allowable deicer concentration (i.e., effluent limits) tend to be in the lower range, and the monitoring method requires high accuracy. Also, the primary deicer constituents generally are not significantly degraded, and correlation between surrogate parameters and deicer concentra- tions is generally accurate. 4.2.3.2 Flow Diversion Within a Stormwater Drainage System Flow diversion is defined as a deicer management method where stormwater drainage from a single stream is routed to multiple locations on the basis of the stormwater characteristics. The most typical means for segregating portions of the drainage is on the basis of primary deicer constituent concentration. The most effective means of flow segregation and diversion uses online monitoring systems to measure concentrations on a near-continuous basis, with the monitoring data transmitted to control systems that execute the mechanical diversion process. This is usually performed by online or frequent monitoring that triggers an action to divert stormwater using equipment such as a valve closing or a pump activating. Online monitoring for the purpose of flow diversion typically requires monitoring accuracy in the middle range of deicer concentrations. In many cases, the online monitoring instrument and data transmittal settings are tuned to improve the accuracy at deicer concentrations near the diversion concentration. The accuracy of the monitors may decrease as the deicer concentrations move away from the diversion concentration. 4.2.3.3 Load Accounting Within a Deicer Management System Load accounting is defined as a process by which the mass load of deicer is calculated based on flow rate and concentration data. Typically, accurate accounting for load requires online flow monitors and online concentration monitors. The online monitors must be capable of accurate measurements over a wide range of concentrations and flows. Some methods have wide ranges of accuracy but only at the lower or higher deicer concentrations. Load accounting may be performed for determining the percentage of deicer capture or for billing for deicer discharge to a POTW. 4.2.3.4 Treatment System Effluent Monitoring Treatment system effluent is defined as a discharge that has undergone the treatment process. The treated effluent flow stream is assumed to be discharged to surface waters or a POTW. Both on- and off-site methods are appropriate for treatment system effluent monitoring. Since the deicer has been treated, the primary deicer constituents may not be present, but degradation compound may be present. Online monitors are used at some airports to measure concentrations of parameters such as BOD, COD, or TOC that are typically used to determine the treatment efficiency. The monitoring results could also be used for compliance purposes. The monitored effluent concentrations are typically in the lower range of measurable concentrations. 4.3 Descriptions of Monitoring Methods The monitoring methods most typically applicable to deicer-affected stormwater at airports are listed in Table 4.7 and are described in the following sections. The criteria tables for compar- ing handheld and test kit methods are presented in Appendix A. The criteria tables for comparing online methods are also presented in Appendix A. 4.3.1 Deicer Parameters Measurement of the concentration of the primary deicer constituents is required for most deicer management systems. When considering the methods for monitoring these deicer constituents,

28 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials Monitor Type Parameter BOD COD TOC BOD/COD/TOC by correlation Online oxidation (58) Photochemical oxidation (59) Thermal catalytic combustion (63) Refractometry (66) Electrochemical oxidation (60) UV/persulfate oxidation (64) Optical/absorbance (67) UV/ozone oxidation (65) Optical/absorbance, reflectance, and fluorescence (68) Handheld N/A N/A N/A Refractometry (69) Test kits N/A Photochemical oxidation (61) N/A Colorimetric (EG in water) (70) Colorimetric (dichromate) (62) Note: The fact sheet number is listed in parentheses under the analytical method. Biochemical Table 4.7. Analytical methods by parameter and type of monitoring. it is critical to understand that there is no on-site monitoring method that directly measures the primary deicer constituents (glycol, formate, or acetate) in stormwater. Every on-site method used to measure concentrations of these constituents acts as a surrogate measurement by reacting a chemical with the deicer constituent or measures a physical response of the deicer constituent. The presence of multiple organic constituents (e.g., glycols plus acetates and for- mates from pavement deicers) may affect the accuracy of the on-site monitor output, espe- cially if the instrument was not calibrated to multiple compounds or if the correlations for BOD, COD, TOC, and deicer constituents were not derived based on the presence of multiple deicer organic compounds. Therefore, care must be taken in interpreting the results from instruments used to measure these parameters. If the stormwater is dominated by a single constituent (e.g., propylene glycol), with only minor contributions from other organics, then good correlations can be established between the measurements of surrogate parameters (COD, BOD, TOC) and the individual constituent [propylene glycol (PG) in this case]. The higher the concentration of the primary deicer con- stituent relative to concentrations of other organic compounds, the better the correlation. When the deicer concentration is low, effects from other parameters in the stormwater can be a significant part of the measured value of surrogate parameters. Although a monitor may be able to achieve accurate measurements at low concentrations when only deicer is monitored, the presence of other compounds in the stormwater may determine the lower range at which the instrument accurately measures deicer concentrations. It is important, therefore, to determine if other compounds that could interfere with the measurement are present in the stormwater in significant concentrations. On-site monitoring methods for commonly identified parameters are discussed in the fol- lowing sections. The typical measurement ranges of online deicer monitoring are compared in Figure 4.1.

Identify Applicable Monitoring Methods 29 4.3.1.1 Glycols There are no on-site monitoring methods that measure glycols directly. Refractometers have acquired the reputation of measuring glycol because they most typically have been applied in deicer management systems to measure samples from areas of highly concentrated ADF application such as deicing pads. Refractometers, in fact, do not measure glycol directly. Refracto meters measure the density of a sample by measuring the light-bending property (refractance). If multiple constituents with varying densities are in the sample, the ability of a refractometer to accurately measure glycol may be compromised. Only laboratory methods, such as the gas chromatograph/mass spectrometry (GCMS) method, will accurately identify compounds as glycols and isolate the glycol fraction from other organics in the sample. Refractometers have the capability of achieving good correlations with glycol concentrations. The correlation is generally good because refractometers are used at high glycol concentrations (>1% or 10,000 mg/L), where the effects of other constituents are small. In cases where glycol Monitor Type Parameter NH3-N pH DO Temp TSS Online Colorimetric ( 71 ) Glass electrode ( 76 ) Amperometric/ polarographic s ensor ( 82 ) Thermocouple ( 88 ) Ultraviolet a bsorbance ( 72 ) Glass free ( 77 ) Optical/ fluorescence sensor ( 83 ) Resistance - temperature detectors (RTD)/ thermistors ( 89 ) Optical/a bsorbance ( 96 ) Ammonia selective e lectrode ( 73 ) Laser diffraction ( 97 ) Handheld Ammonia selective e lectrode ( 74 ) Glass electrode ( 78 ) Amperometric/ p olarographic s ensor ( 84 ) Infrared detector ( 90 ) Optical/ absorbance ( 98 ) Glass free ( 79 ) Optical/ fluorescence sensor ( 85 ) Bimetal ( 91 ) Glass l iquid thermometer ( 92 ) Thermocouple ( 93 ) thermistors ( 94 ) Test kits Colorimetric ( 75 ) Test strips ( 80 ) Winkler titration ( 86 ) N/A Optical/ absorbance ( 99 ) Colorimetric ( 81 ) Colorimetric ( 87 ) Laser diffraction ( 100 ) Note: The fact sheet number is listed in parentheses under the analytical method. Scattered light detection (95) Resistance- Temperature Detectors (RTD)/ Table 4.7. (Continued).

30 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials concentrations lower than 1% are to be measured or where the stormwater contains a variety of compounds in significant proportions, refractometers are not appropriate, and indirect analyses such as BOD, COD, TOC, or other surrogates to deicer are used to estimate the deicer concentra- tion in stormwater. Refractometers are discussed in more detail in Section 4.3.1.6.1, Online BOD/COD/TOC by Correlation with Other Measurements. Laboratory analysis for propylene and ethylene glycol is typically performed using a modified EPA 8015 method by gas chromatography (GC) and flame ionization detection (FID). Samples are collected in two to three unpreserved amber 40-ml volatile organic analysis (VOA) vials and must be delivered to the laboratory within 14 days. 4.3.1.2 Acetate/Formate There are no on-site monitoring methods that measure acetate or formate directly, and there is currently no EPA-approved method. Some laboratories have developed their own methods or use the Association of Official Agricultural Chemists Method 16 986.13 via a high-performance liquid chromatograph (HPLC). Water samples should be collected into two to three 40-ml VOA vials and held at ≤6°C until time of analysis. Water samples have a hold time of 21 days from the date of collection. 4.3.1.3 Biochemical Oxygen Demand For purposes of this report, all BOD monitoring methods, whether on-site or off-site, measure oxygen used in the degradation of biodegradable constituents by living bacteria housed in the 1 10 100 1,000 10,000 100,000 1,000,000 Propylene Glycol Concentration Typical Operations % mg/L 0.001 0.01 0.1 1 10 100 BOD1 COD2 TOC2 Method and Factsheet Number 9.8 980 9,800 17.0 1,700 17,000 4.7 470 4,700 1. 1 B io ch em ic al O xi da tio n F ac t S he et 5 8 2. 2 E le ct ro ch em ic al O xi da tio n F ac t S he et 6 0 2. 1 P ho to ch em ic al O xi da tio n F ac t S he et 5 9 3. 1 T he rm al C at al yt ic C om bu st io n F ac t S he et 6 3 3. 2 U V/ Pe rs ul fa te O xi da tio n F ac t S he et 6 4 3. 3 U V O xi da tio n F ac t S he et 6 5 4. 1 R ef ra ct om et ry F ac t S he et 6 6 4. 2 O pt ic al /A bs or ba nc e F ac t S he et 6 7 a nd F lu or es ce nc e Fa ct S he et 6 8 Normal Range Extended Range For Some Manufacturers Concentration mg/L Notes: (Johnson, Varney, and Switzenbaum 2001, p. 46) H O + 4O + 4 H O O U TF AL L D IV ER SI O N R EC YC LI N G 98 170 47 4. 3 O pt ic al /A bs or ba nc e, R efl ec ta nc e, Figure 4.1. Typical ranges for online deicer monitoring methods.

Identify Applicable Monitoring Methods 31 monitoring device. The amount of oxygen consumed by bacteria to degrade the compounds is used to calculate oxygen demand expressed as BOD. Some methods or monitors can be set up to correlate their output to BOD—and may even have “BOD” or a similar biological reference in their name—but unless the method or monitor uses living bacteria, it is classified as a different monitoring method. Laboratory analysis of BOD is typically performed using EPA Method 405.1. This is an empir- ical bioassay-type procedure that measures the dissolved oxygen consumed by microbes as they assimilate and oxidize the organic matter present. The standard test conditions include dark incubation at 20°C for a specified time period (often 5 days). The in situ environmental condi- tions of temperature, biological population, water movement, sunlight, and oxygen concentra- tion cannot be accurately reproduced in the laboratory. Water samples are typically collected in a 500-ml unpreserved polyethylene container and held at ≤4°C until time of analysis. Water samples must be received by the laboratory within 48 hours of the time of collection. Because the online BOD monitor uses bacteria in the analysis of a sample, it is the closest online measurement to a BOD5 analysis. In this regard it could more accurately estimate the oxygen demand in the receiving stream than COD or TOC. One major difference between the laboratory BOD5 methods and the online BOD monitor is the time that the compounds are exposed to the bacteria. For a standard BOD5 laboratory test, the chemicals are exposed to the bacteria for 5 days. The oxygen used by bacteria in that 5-day period is measured and used to calculate BOD5. In a typical online BOD monitor, the contact time for the flow-through cell is approximately 4 min. The fact that glycols degrade quickly facilitates the likelihood of a correlation between online BOD, BOD5, and glycol concentra- tion with a short contact time. However, compounds that are more difficult to degrade may not be degraded significantly by the online BOD monitors because of the short detention time. Therefore, the correlation to laboratory measurements (BOD5) will be more difficult if there are compounds that are difficult to degrade. The presence of multiple biodegradable compounds in the stormwater with different degradation rates also reduces the ability to achieve a satisfactory correlation with BOD5. Another difference between the laboratory methods and the online monitors for BOD is that the laboratory method for BOD5 is performed at 68°F (20°C) (American Public Health Association, American Water Works Association, and Water Environment Federation, 2005, p. 5-5) and the online BOD monitor operates at 86°F (30°C). The differences in contact time and temperature may lead to different biological conditions and measurement responses. Therefore, online BOD should be considered a correlation to laboratory BOD5 concentrations in a similar way to COD or TOC. As a result of the differences in test conditions, when using the online BOD instruments, it is important to field test the instrument output in response to samples with vari- ous combinations of expected constituents at known concentrations and compare the results to laboratory BOD5 test results. There is a substantial start-up period for an online BOD monitor. The lengthy start-up period is required to develop a stable bacteria culture in the monitor. Several airports with BOD monitors will freeze the bacteria culture for storage over the summer and then thaw the frozen seed to start the culture the next season. This technique can shorten the start-up period from 14 days to between 2 and 5 days. If a frozen seed culture is not available, splitting a culture from an operating BOD monitor will also reduce the start-up time. Otherwise, the bacteria culture must be grown using the bacteria in the stormwater and a whole milk mixture recommended by the manufacturer. During operation, if there is a sudden change in concentration, up to 45 min may be required for the online BOD monitor to stabilize on the concentration value. There is a delay in the result because the monitor increases or decreases the feed rate of the sample to the unit to achieve a

32 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials constant DO decrease across the reaction chamber. The larger the concentration change, the longer the duration for the mechanical and biological system to stabilize on the new reading. The online BOD monitor performs several functions to keep the bacterial culture alive. The monitor adds DO and nutrients to the water and heats the water to approximately 86°F. If a very high concentration spike or toxic material is fed to the monitor, the bacteria population will die and the bacteria in the monitor will have to be reestablished. Since the online BOD monitors use DO probes in the measurement, the items discussed in Section 4.3.4.1, Online DO, are also applicable. Laboratory-grade equipment to perform BOD measurements on-site according to the EPA- approved method can be purchased. Analyses of samples on-site using standard laboratory methods, other than the simplified methods mentioned in this guidebook, are considered the same as off-site laboratory analyses. Other features of the online BOD monitors can be found on Fact Sheet 58. 4.3.1.4 Chemical Oxygen Demand All COD monitoring methods use a chemical or an energy source (i.e., light or electricity) to degrade the deicers and other degradable compounds to carbon dioxide (CO2) and water. The methods then measure the amount of oxygen used in the oxidation process to determine the primary deicer constituents and other degradable organic compound concentrations. A com- mon laboratory method for COD analysis is EPA Method 410.4. The method involves using a strong oxidizing chemical, potassium dichromate (K2Cr2O7), to oxidize the organic matter in solution to carbon dioxide and water under acidic conditions. Often, the test also involves a silver compound to encourage oxidation of certain organic compounds and mercury to reduce the interference from oxidation of chloride ions. The sample is then digested for approximately 2 hours at 150°C. The amount of oxygen required is calculated from the quantity of chemical oxidant consumed. Water samples are collected in a 50-ml polyethylene container preserved with sulfuric acid. Samples must be held at ≤4°C and delivered to the laboratory within 28 days of sample collection. 4.3.1.4.1 Online COD. Online methods for COD measurement include the photochemical oxidation method and the electrochemical oxidation method. The photochemical oxidation method is a relatively new method that has no known applica- tions at airports. The photochemical oxidation method requires filtration of the sample because solids can block the small-diameter tubing used in the monitor. The method does not generate hazardous waste like the EPA-approved method for COD because the photochemical oxidation method uses titanium dioxide and ultraviolet (UV) light rather than chromium and mercury. Other features of the COD photochemical oxidation method can be found on Fact Sheet 59. The electrochemical oxidation method was used for several years at the Wilmington Air Park for monitoring the treatment system performance. The electrochemical oxidation method cor- related well to laboratory COD analyses for short time periods; however, the calibration would fail at various times. It is suspected that pavement deicers were changing the conductance of the stormwater and interfering with the instrument. The electrochemical method may be appropri- ate for monitoring conditions when only ADFs are present but should be avoided when there is potential for pavement deicers to be present. Other features of the COD electrochemical oxida- tion method can be found on Fact Sheet 60. 4.3.1.4.2 Test Kits for COD. Test kit methods include the photochemical oxidation method and the dichromate method.

Identify Applicable Monitoring Methods 33 The test kit photochemical oxidation method is essentially the same process as the online method but performed manually on individual samples. The photochemical oxidation method is inexpensive to operate per sample, and results are available in a few minutes. The method generally correlates well with the EPA-approved method for COD. Other features of the COD photochemical oxidation method can be found on Fact Sheet 61. The dichromate method is the EPA-approved method for COD analyses, is widely used, and is a very simple procedure. The dichromate method requires a 2-hour digestion period to chemi- cally oxidize the organics, followed by a cooling period for the samples. The COD in the sample test tube is measured by colorimetric means in a spectrophotometer. This method also generates a hazardous waste because mercury and chromium are used in the reagents. The spent reagents must be disposed of as hazardous waste, and this increases the costs and labor required for per- forming the analyses. An alternate method that is not approved by the EPA does not include the hazardous metals as reagents. The acids in the non-approved method are not as strong; however, glycol is readily degradable and the test results should not be significantly different from the EPA- approved method. Airport personnel may wish to request that the alternate method be used for monitoring if COD parameters are not required for compliance monitoring. Other features of the COD dichromate method can be found on Fact Sheet 62. 4.3.1.5 Total Organic Carbon On-site TOC monitoring methods are generally installed as online methods. TOC analy- sis performed by airport personnel according to the EPA-approved method is considered an off-site method for purposes of this guidebook. Laboratory analysis of TOC is typically performed via EPA Method 415.1. Organic carbon in a sample is converted to carbon diox- ide by catalytic combustion or wet chemical oxidations. The carbon dioxide formed can be measured directly by an infrared detector or converted to methane and measured by a flame ionization detector. The amount of carbon dioxide or methane is directly proportional to the concentration of carbonaceous material in the sample. Water samples are collected in two 40-ml amber VOA vials preserved with sulfuric acid. Samples must be held at ≤4°C and have a hold time of 28 days. All TOC monitor methods convert the organic portion of primary deicer constituents (gly- cols, acetates, formates) and other organic chemicals containing carbon to carbon dioxide. The TOC methods then measure the amount of carbon dioxide produced to determine the total concentration of carbon compounds (including those from deicers and other constituents). The methods use one of three oxidation methods to convert the organic chemicals to carbon dioxide: thermal (heat), UV/persulfate, or UV/ozone. If the inorganic carbon content in the sample stream is high, measurement of low TOC values may not be accurate. One issue common to TOC measurements is that most monitors measure total carbon (TC) and total inorganic carbon (TIC) and then subtract one value from the other to get the organic portion or TOC. When two measurements that are nearly the same value are subtracted, the result has a high degree of uncertainty. A graphical illustration of using TIC and TC to determine the TOC is shown in Figure 4.2. TIC is mainly from carbonates, so in areas where groundwater has been in contact with limestone bedrock, the accuracy for low TOC con- centrations may be an issue. There are several methods available for measuring TOC. Each TOC method requires sample filtering because the monitors will not handle solids. One method of oxidizing carbon for TOC is by using a furnace (thermal oxidation). The ther- mal oxidation method has a slight delay in start-up while the furnace comes up to tempera- ture (a few hours). Manufacturers warn that high concentrations of dissolved solids (salts) can cause deposits in furnaces, requiring early replacement. The thermal oxidation method also has a

34 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials slightly higher utility demand than the UV/persulfate method. Other features of the TOC thermal oxidation method can be found on Fact Sheet 63. A second method of oxidizing carbon is by using UV light and persulfate to oxidize the organic compounds (UV/persulfate oxidation). The UV/persulfate method requires use of the chemical reagents sodium persulfate and phos- phoric acid. Phosphoric acid is a strong acid and should be handled with care. Other features of the TOC UV/persulfate oxidation method can be found on Fact Sheet 64. A third method of oxidizing organic compounds is by using UV, ozone, and a caustic (UV/ ozone oxidation). The UV/ozone oxidation method requires the chemical reagent caustic soda, also known as sodium hydroxide. Caustic soda is a strong base and should be handled with care. Other features of the TOC ozone/caustic soda oxidation method can be found on Fact Sheet 65. 4.3.1.6 BOD/COD/TOC by Correlation Monitors that measure BOD, COD, and TOC directly can be purchased. It is also possible to indirectly obtain BOD, COD, TOC, and PG output from virtually any on-site monitor measur- ing organic compounds through means of correlation. In the correlation method, monitor mea- surements can be converted to output in terms of BOD, COD, TOC, or PG through the use of mathematical relationships between the measured parameter and the desired output parameter. The correlated methods measure some feature of the chemicals in the sample and then correlate the measurement to a known standard. It is important to note when setting up an instrument that correlation is not the same as calibration. Calibration is tuning the instrument output to a known standard for the instru- Inorganic Carbon (TIC) Total Carbon (TC) Organic Carbon (TOC) Ca rb on C on ce nt ra tio n (m g/L ) 100±5 mg/L 5% uncertainty in measurements 45% uncertainty in result 125±6.3mg/L 25±11.3mg/L 0 25 50 75 100 125 150 Figure 4.2. Example of organic carbon measurements and uncertainty. TOC monitor usage tip: High concentrations of inorganic carbon may affect low TOC concentration accuracy.

Identify Applicable Monitoring Methods 35 ment’s inherent measurement parameter. Correlation is converting the instrument output from the instrument’s inherent measurement parameter to another parameter through mathemati- cal relationships developed offline. For some applications, only the calibration step is needed. In other applications, both the calibration and correlation steps are required. To determine the calibration and correlation needs, it is critical to understand the instrument’s inherent measure- ment parameter and the desired output parameter. 4.3.1.6.1 Online BOD/COD/TOC by Correlation with Other Measurements. BOD, COD, and TOC values can be obtained by correlation with refractometry measurements under certain conditions. Refractometry is a relatively quick and easy method used as a means of determining glycol concentrations greater than 1% when glycol is the primary constituent in the sample. At concentrations below 1%, refractometry often loses accuracy due to other compounds in the sample influencing the measurement. Refractometry measures the light-bending property of a sample related to the sample den- sity. At high concentrations, the density will be significantly related to the concentrated com- pound. At low concentrations, other parameters in the water will also have a significant effect on the density. Therefore, the correlation between refractometer measurement (density) and primary deicer constituent concentration will fail when other chemicals also have an effect. Because the concentration of other chemicals in the water is dependent on the site-specific conditions, the concentration at which the correlation between refractometer measurement and primary deicer constituent concentration ceases to be accurate is also site-specific. Exam- ple correlations of actual glycol concentrations to refractometer-measured glycol concentra- tions are presented in Figures 4.3 and 4.4. Other features of the refractometer method can be found on Fact Sheet 66. Other online methods for getting output in terms of BOD/COD/TOC/PG through cor- relations generally use some kind of optical method. Optical methods include absorbance, reflectance, and fluorescence. Most chemicals will absorb light at several specific wavelengths. Chemicals may also reflect light at other wavelengths or fluoresce (give off light) under certain conditions. Optical monitors use absorbance at one or multiple wavelengths to determine the primary deicer constituent concentration. Glycols have poor absorbance response, so some manufacturers correlate to other constituents in the deicer. If the other constituents in the stormwater change, for example, through switching deicer manufacturers, the correlation would no longer be valid. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 30 60 90 120 150 R ef ra ct om et er R es po ns e (u nit les s) COD by Laboratory Method (mg/L) Thousands Figure 4.3. Online refractometer high-concentration correlation.

36 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials Solids in the water may interfere with the measurements. Also, bacterial growth may block the light used for measurement and cause maintenance issues. Other features of the optical methods can be found on Fact Sheets 67 and 68. 4.3.1.6.2 Handheld BOD/COD/TOC by Correlation. Correlations of BOD, COD, and TOC can also potentially be obtained using correlations to handheld refractometers. The hand- held refractometer method has the same limitation as the online method regarding low con- centration accuracy. Handheld units are generally not as accurate as online refractometer units because they are more influenced by field conditions. Laboratory refractometers tend to be the most accurate because of the clean environment; however, the limitation regarding other chemi- cals in the sample affecting the density measurement will lead to inaccurate correlations at low concentrations. Other features of the refractometer method can be found on Fact Sheet 69. 4.3.1.6.3 Test Kits for BOD/COD/TOC by Correlation. Test kits for EG in water were developed for use in boiler feed applications. These test kits measure PG in addition to EG. Since EG test kits were developed for specific concentration ranges and water that has few other interferences, the accuracy of this method for general stormwater analysis is unknown. Test kits that measure glycols may be useful as presence/absence indication in the field. Other features of the test for EG in water can be found on Fact Sheet 70. 4.3.2 Ammonia–Nitrogen Ammonia–nitrogen monitor methods use one of three ways to determine the concentration of ammonia: (1) the colorimetric method, (2) the optical method, or (3) the ion-selective elec- trode (ISE) method. Ammonia–nitrogen is typically measured in the laboratory by semi-automated colorimetry via EPA Method 350.1. The sample is buffered at a pH of 9.5 with a borate buffer in order to decrease hydrolysis of cyanates and organic nitrogen compounds; it is then distilled into a solu- tion of boric acid. Alkaline phenol and hypochlorite react with ammonia to form indophenol blue that is proportional to the ammonia concentration. The blue color formed is intensified with sodium nitroprusside and measured colorimetrically. Water samples are collected in 250-ml amber polyethylene containers preserved with sulfuric acid. Samples must be held at ≤4°C and have a hold time of 28 days. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0 1,000 2,000 3,000 4,000 5,000 COD by Laboratory Method (mg/L) R ef ra ct om et er R es po ns e (u nit les s) Figure 4.4. Online refractometer low-concentration correlation.

Identify Applicable Monitoring Methods 37 4.3.2.1 Online Ammonia–Nitrogen Online monitors for ammonia–nitrogen also use the methods mentioned previously: colori- metric, optical, or ISE. The colorimetric method collects a sample, reacts the sample with an indicator chemical, and measures the color response. Colorimetric method monitors require filtering of the samples because they do not tolerate solids. The monitors may also experience bacteria growth and plugging of the internal tubing. Other features of the colorimetric test method can be found on Fact Sheet 71. Optical methods for ammonia–nitrogen are similar to the optical methods used in the BOD/ COD/TOC by correlation method. The amount of ammonia–nitrogen in the sample is estimated by the absorbance of light at a specific wavelength. Unlike glycol, ammonia–nitrogen has a strong absorbance. Similar to the other optical methods, solids in the water may interfere with the mea- surements, and bacterial growth in the monitors may block the light used for measurement. Filter- ing of the sample and regular cleaning of the optics are required for accurate measurements. Other features of the absorbance method can be found on Fact Sheet 72. ISE methods use an electrode similar to a pH electrode. The electrode is inserted into the flow stream and connected to the monitor unit. If deicers are also present to provide a food source, bacteria may grow and cover the electrode in slime. The slime will degrade the primary deicer compounds to form acids, which will cause the electrode to measure a pH that is more acidic than the stream concentration. Automatic cleaning systems are recommended to extend the duration between manual cleanings. Other features of the ISE method can be found on Fact Sheet 73. 4.3.2.2 Handheld Ammonia–Nitrogen Handheld ammonia–nitrogen meters use the ISE method. The electrodes, like the online ver- sions, are similar to pH electrodes. Electrodes must be stored in damp conditions and calibrated prior to measurement. Calibration of an ISE probe is similar to calibration of a pH probe using two buffer solutions. Other features of the ISE method can be found on Fact Sheet 74. 4.3.2.3 Test Kits for Ammonia–Nitrogen Test kits for measuring ammonia–nitrogen use the colorimetric method. The colorimetric method may require some simple laboratory preparation of the samples. Samples may have to be filtered if the solids concentration is high. See Chapter 5 for a discussion of laboratory acces- sories that improve the efficiency of sample analyses. Other features of the colorimetric method can be found on Fact Sheet 75. 4.3.3 pH Monitoring methods for pH use either the ISE method or colorimetric method to determine the pH concentration. On-site methods are recommended for pH analysis as samples should be performed in situ or analyzed immediately following collection. 4.3.3.1 Online pH Online monitors use ISE methods to determine the pH. The pH electrodes come in two different forms: glass and non-glass electrodes. Glass electrodes are the most common type of pH electrode. The electrode is inserted into the flow stream and connected to the monitor unit. Because the tip of the electrode has a glass bulb, it must be protected from damage from solids in the stream or contact with the walls. If deicers are also present in the stream to provide a food source, bacteria may grow and cover the electrode in slime. Slimes may produce acidic products and will cause the electrode to read

38 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials more acidic. The actual pH value of the stream may not be significantly affected by the slime, and measurement of the electrode will be inaccurate for the stream. Automatic cleaning systems are recommended to extend the duration between manual cleanings, but automatic cleaning will not completely replace manual cleaning. Periodic calibration and electrode cleaning are the two most important elements of successful pH monitoring. Other features of the glass electrode method can be found on Fact Sheet 76. The non-glass electrodes are less susceptible to damage and hold a calibration slightly longer. Non-glass electrodes were developed for the food industry. These electrodes are more expensive than similar glass electrodes and may not be suitable for long-term deployment in a stream (Schaepman, 2005). Other features of the non-glass electrode method can be found on Fact Sheet 77. 4.3.3.2 Handheld pH Methods for handheld monitors use glass or non-glass electrodes similar to the online methods. Care and maintenance are similar for the two types of electrodes. The non-glass elec- trodes are slightly less susceptible to damage and are slightly more expensive. Other features of the glass electrode method can be found on Fact Sheet 78. Other features of the non-glass electrode method can be found on Fact Sheet 79. 4.3.3.3 Test Kits for pH Test kit methods for pH use either test trips or a colorimetric method. Test strips are easy-to-use, disposable paper strips. They are generally made for a specific pH range. The test strips are inserted into the sample and then compared to a color chart. If the test strips get wet prior to use, they should not be used for measurement. Test strips give qualitative results (i.e., test strips give a range of concentration that the pH is within and not a specific value). Because test strips are qualitative, they may not be accepted by regulatory agencies for discharge monitoring. Other features of the test strip method can be found on Fact Sheet 80. Colorimetric methods use an indicator chemical that changes color depending on the pH concentration. The indicator is accurate only within a range of pH values, and a sample with high turbidity or existing color may make reading of the color difficult. To obtain a pH value, the sample color is compared to a color chart, or a colorimeter or spectrophotometer can be used to read the intensity of the color to obtain a precise pH value. Other features of the colorimetric method can be found on Fact Sheet 81. 4.3.4 Dissolved Oxygen 4.3.4.1 Online DO Online DO monitors use one of two types of DO method: the amperometric method or the optical method. On-site methods are recommended for the measurement of DO and should be performed in situ or in a manner that minimizes air exposure to the water sample. The amperometric method has been the industry-standard method for measuring DO for many years. Obtaining accurate and consistent results using this method requires periodic mem- brane replacement. The installation of the membrane is not a simple procedure. During use, the membrane can foul or tear, leading to inaccurate measurements. The electrode tip near the membrane needs to be kept clean because bacterial growth near the tip will consume DO local to the electrode and will cause a lower DO measurement than what is in the sample stream. The fre-

Identify Applicable Monitoring Methods 39 quency of cleaning can be high in streams containing deicer. Other features of the amperometric method can be found on Fact Sheet 82. The optical method uses light to detect the DO of the sample stream. The optical method consumes DO near the electrode, so if the stream is stagnant and the DO is low, the electrode will consume all of the DO local to the electrode and read a concentration lower than the actual DO of the sample stream. Consumption of DO by the electrode is not an issue when the stream is moving. Optical electrodes generally hold their calibrations longer than amperometric electrodes because they are less influenced by biofouling. The electrode for the optical method requires much less maintenance but still requires cleaning to prevent bacterial growth on the electrode. Other features of the optical method can be found on Fact Sheet 83. 4.3.4.2 Handheld DO As with online units, handheld DO monitors use amperometric or optical electrodes. The issues with the electrodes are similar to those of the online methods. Care and maintenance of the electrodes during storage are critical to long-term, accurate measurements. Handheld DO monitoring may be subject to inconsistency because of variation in the sample point from one monitoring event to the next. Other features of the amperometric method can be found on Fact Sheet 84. Other features of the optical method can be found on Fact Sheet 85. 4.3.4.3 Test Kits for DO Test kits use either the Winkler method or the colorimetric method. The Winkler method was the initial laboratory method to determine DO concentration. The method is complex, labor intensive, and requires multiple titration steps. The method has been extensively tested in a wide variety of water samples because it was the primary method for deter- mining DO for over 100 years (American Public Health Association, American Water Works Association, and Water Environment Federation, 2005, pp. 4–136). Other features of the Winkler method can be found on Fact Sheet 86. The colorimetric method uses an indicator chemical to determine the DO concentration. The indicator compound reacts with DO in the sample and changes color, similar to a pH indicator. A sample with high turbidity or existing color may make reading of the color difficult. To obtain a DO concentration, the sample color is compared to a color chart, or a colorimeter or spectro- photometer can be used to read the intensity of the color to obtain a precise DO concentration. Other features of the colorimetric method can be found on Fact Sheet 87. 4.3.5 Water Temperature 4.3.5.1 Online Temperature On-site methods are recommended for the measurement of temperature and should be per- formed in situ or immediately following sample collection. Online water temperature moni- tors use either the thermocouple method or resistance-temperature detector (RTD) electrode method. In practical use, the thermocouple and RTD methods are similar. The electrode is placed in the sample stream and connected to the monitor. Some other monitor units for other parameters may also measure the water temperature internal to the units. However, if the monitor is one that requires a sampling system, the sample passing through a pump and into a heated shelter may be several degrees warmer than the ambi- ent water temperature, so temperatures measured by online monitors may not be appropriate

40 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials for airport stormwater monitoring. Other features of the thermocouple method can be found on Fact Sheet 88. Other features of the RTD method can be found on Fact Sheet 89. 4.3.5.2 Handheld Temperature Handheld monitors use several different methods to measure water temperature. The meth- ods include the infrared method, the bimetal thermometer method, the glass thermometer method, the thermocouple method, and the RTD method. Infrared monitors measure the infrared radiation from an object. Infrared monitors only measure the surface temperature, so if there are solids or ice on the surface, the infrared monitor will not measure the true water temperature. The infrared method may be applicable where access to the stream is limited. Other features of the infrared method can be found on Fact Sheet 90. Bimetal thermometers have a dial readout and are the type used as oven or grill thermo- meters. Bimetal thermometers are sturdy for field use but slower to react to temperature changes. Accuracy of the reading is dependent on the scale of the dial used. Other features of the bimetal thermometer method can be found on Fact Sheet 91. Glass thermometers are the typical fluid-filled, glass-tube thermometers that are familiar to most people. Thermometers were historically typically filled with mercury, but other flu- ids are now more common because of the toxicity of mercury. Because glass thermometers are fragile, they are not recommended for field use, and mercury-containing thermometers should never be used in the field. Other features of the glass thermometer method can be found on Fact Sheet 92. Thermocouple and RTD monitors are similar to online monitors. Other features of the thermo couple method can be found on Fact Sheet 93. Other features of the RTD method can be found on Fact Sheet 94. 4.3.6 Total Suspended Solids TSS analysis is typically performed in the laboratory using EPA Method 160.2. A well-mixed sample is filtered through a glass fiber filter, and the residue retained on the filter is dried to constant weight at 103°C to 105°C. Samples are collected in a 1,000-ml polyethylene container, maintained at ≤4°C, and delivered to the laboratory within 7 days. 4.3.6.1 Online TSS Online monitors for TSS use one of three methods: (1) the scatter method, (2) the optical method, and (3) the laser method. The TSS methods are actually turbidity measurements that are correlated to TSS concentration. Turbidity is the cloudiness in water caused by suspended particles. All of the methods for TSS require maintenance to keep the monitors clean. Sample streams that contain deicers tend to have bacterial growth that will need to be cleaned from the measure- ment section of the sensors. The scatter method is the standard turbidity measurement that measures the amount of light that is scattered at an angle from a beam of light. The standard turbidity measurement using the scatter method is referred to as nephelometric turbidity (measured in nephelometric turbidity units, or NTUs) and measures the light intensity at a 90-degree angle from the light beam. Other features of the scatter method can be found on Fact Sheet 95. The optical method uses absorbance of light beams by the sample to correlate to the TSS concentration.

Identify Applicable Monitoring Methods 41 Other features of the optical method can be found on Fact Sheet 96. The laser method is similar to the scatter method except that a laser is used to provide the light source. Other features of the laser method can be found on Fact Sheet 97. 4.3.6.2 Handheld TSS Handheld monitors use an optical method similar to the online monitor. Other features of the optical method can be found on Fact Sheet 98. 4.3.6.3 Test Kits for TSS Test kits use optical or laser methods similar to the online monitors. Other features of the optical method can be found on Fact Sheet 99. Other features of the laser method can be found on Fact Sheet 100. 4.3.7 Flow Flow is generally defined as a unit of volume passing a point over a period of time. Typical reporting units for stormwater flow include cubic feet per second (cfs), million gallons per day (mgd), and gallons per minute (gpm). Measurement of flow is typically required by dis- charge monitoring permits and sewer discharge permits. Monitoring methods are generally divided by two field conditions: full flow in pipes and partial pipe flow or open channel flow. 4.3.7.1 Monitoring in Pipes Flowing Full Determining the flow rate of a pipe that is flowing full requires only measurement of the velocity and knowledge of the cross-sectional area based on pipe size [flow (Q) equals veloc- ity (V) times cross-sectional area (A)]. Several types of meters are available for full-pipe flow applications. Only flow meters that are intended for use with flow that has solids should be used for stormwater applications. Magnetic flow meters (magmeters—see Figure 4.5) are the most common flow meters for full-pipe flow applications for stormwater applications. Magmeters are installed directly in a pipe to measure velocity and calculate flow based on the known cross- sectional area. Their readings are highly accurate when a pipe is under full flow conditions, and as such they are most frequently used in force mains under pressure. Use of magmeters in gravity piping presents risks since often the gravity storm drain pipes are not flowing full. If a pipe is not flowing full, the velocity readings from the magmeter and the calculated flow rate (which assumes full diameter of the pipe being used) will be in error. 4.3.7.2 Monitoring in Pipes Not Flowing Full or in Open Channels Determining the flow rate of a pipe that is not flowing full or in an open channel is more dif- ficult than determining the flow rate of pipes flowing full. The accuracy of results from non-full pipes or open channels is typically less than for full pipes. As a result, care must be taken when comparing flow rates based on different measurement methods. Flow monitoring methods in non-full pipes and open channels include flumes, weirs, and area-velocity meters. 4.3.7.2.1 Flumes. The most accurate method of flow measurement for open channel flow over a wide range of flow rates is a flume (Grant and Dawson, 1995, p. 60). A flume is a designed flow constriction in which the flow rate is related to the water level in the flume. An automatic or manual level-sensing instrument is part of the flume device. The accuracy of the flow measure- ment is related to the device used to make the level measurement and is within approximately 2% for most applications. Several types of flumes have been developed, but the most common is the Parshall flume (see Figure 4.6). Figure 4.5. Example of a magmeter. Figure 4.6. Example of a Parshall flume.

42 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials There are three critical considerations associated with use of flumes for monitoring storm- water flow: 1. Capital expense for installation, 2. Size needed to capture the defined flow range, and 3. Handling and management of solids. In a new stormwater system being designed with flow monitoring needs, flumes should be considered in the design first. Retrofitting existing stormwater systems to incorporate flumes can be costly. Flumes can be placed in large manholes or at the discharge end of the system. Placement of a flume requires consideration of the downstream hydraulics. A Parshall flume can tolerate slight submergence of the discharge end, but the discharge flow must generally be free flowing or unobstructed. Obstruction of downstream flow will interfere with the flow measurement. If flow is obstructed (i.e., there is a downstream constriction that causes water to back up), and the obstruction cannot be removed, then a flume cannot be used. Flumes are sized for the expected flow range. Therefore, the hydraulics of the upstream system must be known to determine the flume size. The maximum flows and associated pipe diameters at a typical slope (1%) for Parshall flumes are listed in Table 4.8. Care must be taken in using flumes to measure the full range of flows in stormwater drainage structures. Peak flows can often exceed the capacity of the flume, and flow measurements will give inaccurate results if the water levels exceed the flume height. Smaller Parshall flumes may trap solid objects because of the narrowing of the flow in the throat. Tree branches or ice have been known to get caught in flumes and disrupt the flow measurement. Access to the flume should be included for cleaning of the flume as well as level instrument maintenance (See Chapter 5). 4.3.7.2.2 Weirs. A weir is a raised obstruction in the flow—generally a metal plate or flat concrete surface—that causes water to flow over it (see Figure 4.7). The water level upstream of the weir is related to the flow rate. An automatic or manual measuring device is part of the weir device. Two common types of weirs are the v-notch weir and the rectangular weir. A v-notch weir is a plate with a “v” shape cut into it with a defined angle. A rectangular weir is a horizontal plate. For stormwater systems, v-notch weirs are typically used for low flow measurements, and rectangular weirs are used for high flow measurements. The accuracy of the flow measurement Figure 4.7. Example of a weir. Table 4.8. The maximum flows for Parshall flumes and example storm sewer system sizes. Flume Size (ft) Maximum Flow (gpm) Size of Concrete Pipe Flowing Full (in.) 0.75 3,980 15 1 7,240 18 2 14,900 24 3 22,600 30 4 30,500 30 5 38,400 36 6 46,400 42 Notes: (1) Flume size for Parshall flumes is the width of the throat . (2) Maximum flow is for 2 ft of head for a 0.75 - f t flume and 2.5 ft of head for larger flumes. (3) Concrete pipe is for a 1% slope with a Manning friction factor of 0.013. Source: Grant and Dawson, 1995, p.74.

Identify Applicable Monitoring Methods 43 is related to the device used to make the level measurement and is within approximately 2% to 5% for most applications. Water must freely discharge over the weir. Obstruction of downstream flow will interfere with the flow measurement. If flow is obstructed (i.e., there is a downstream constriction that causes water to back up), and the obstruction cannot be removed, then a weir cannot be used. Because water must flow over a weir freely, floating solids that tend to get caught on the weir disrupt the flow measurement. Also, because water ponds upstream of a weir, solids will settle behind the weir. Frequent removal of the floating solids and periodic removal of the settled solids at the weir are required to maintain accurate flow measurement. Weirs placed in the flow path of a pipe, culvert, or open channel may also reduce the peak flow capacity of the conveyance structures when the structures are flowing full. The loss of flow capacity can be calculated with basic hydraulic calculations and should be checked before a weir is installed. 4.3.7.2.3 Area-Velocity Meters. Area-velocity meters measure both the depth of flow and the velocity to determine the flow rate. Area-velocity meters do not require a flow-altering device such as a weir or flume. Instead they rely on velocity measurement, flow depth measurements, and a calculation of flow rate based on the shape and size of the conveyance structure. Area-velocity flow meters have technology-based limits on capabilities at the lower end of both depth and velocity measurements. Most units place a sensor in the bottom of the pipe that measures the flow velocity rate using ultrasonic or Doppler methods. The flow depth must be a minimum of approximately 1.5 in. above the sensor for the sensor to measure the velocity. The meter can typically measure to a minimum velocity of approximately 1 ft/s. The accuracy of the flow measurement is within approximately 5% for most applications. The minimum measur- able flow rates by an area-velocity meter for various pipe sizes are listed in Table 4.9. Area-velocity meters cannot be used in corrugated pipes because of the turbulence caused by the corrugations. A smooth insert can be placed in the lower half of the pipe section to eliminate the turbulence. The area-velocity sensors also tend to be susceptible to siltation and damage from debris in stormwater pipes. If the sensor and electric/communication cords are not properly secured, they may dislodge due to the force of the water at higher flow rates. Accumulation of solids over the sensor will obstruct the ability of the sensor to make accurate flow measurements. 4.3.7.2.4 Selection of a Flow Meter. The type of flow meter selected should be based on the need for and desired use of the data and the environment in which the flow monitoring will occur. Several factors should be considered in the selection: • How accurate does the data need to be? • What are the ranges of flow that need to be measured? Table 4.9. Estimated minimum measurable flow rates for area-velocity meters in various sized pipes. Pipe Diameter (in . ) Minimum Detected Flow (gpm) 12 25 18 32 24 38 36 45 48 52

44 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials • Is flow information critical in real time? • What is the infrastructure in which the flow monitoring equipment will be mounted? • What are the potential power sources for the flow monitoring equipment? Accuracy is an important consideration in the selection of a flow monitor. Do the flow values need to be accurate or are qualitative trends in the flow important? Also, is accuracy critical over the entire flow range or are there times when accuracy is more critical, such as peak-flow or low-flow periods? In cases where accurate low-flow measurements and measurement of a wide range of flow rates are required, compound flow measurement may be used. An example of a compound flow measurement device is a v-notch weir cut into a rectangular weir. When the flow rate exceeds the v-notch weir, the flow rate is calculated by the combination of the v-notch weir and the rectan- gular weir. Another example is a v-notch weir that is upstream of an area-velocity meter. Flow measurements are made at both devices, but the reading for the v-notch is used at low flows and the reading from the area-velocity meter is used at higher flows. If the flow data are not critical for real-time decisions, a monitor with local data storage can be used and the data downloaded as needed. If the data are critical for real-time decisions, a flow meter must be able to communicate with the other equipment. The flow meter must also have a high degree of reliability because when the device is not functioning, the ability to make real- time decisions is lost. All automatic flow monitoring devices require electrical power to operate. If electrical power is not already available, it will need to be supplied to the monitoring site. Some flow meters have an option for solar-power–compatible collectors to supply power.

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TRB’s Airport Cooperative Research Program (ACRP) has released the second edition of Research Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials. The report provides a step-by-step process for identifying, evaluating, and selecting methods to monitor stormwater that is subject to runoff containing deicing materials.

The report addresses identifying the parameters to be monitored and discusses the appropriateness of various monitoring methods and instrument types to meet an airport’s specific needs. The report also provides guidance for setup, operation, and maintenance of each monitoring method.

Technical information on various on-site monitoring methods is provided in a series of fact sheets. These fact sheets, which are organized by the parameter being monitored, describe key factors such as how the method works, its current level of adoption within the industry, implementation considerations, cost, and advantages/disadvantages.

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