According to the Federal Aviation Administration guidelines, airports and airlines need to carry out deicing and anti-icing of airfield pavement and aircraft during extreme weather such as icy conditions. This is to ensure the safety of passengers, as well as cargo operations. Nonetheless, these deicing procedures have to be performed under discharge controls and guidelines put in place to avoid environmental damages. According to U.S. Environmental Protection Agency (1983), airports are required to obtain permits and ensure that deicing operation wastes are collected and treated in an orderly manner. All these rules and requirements apply to wastewater from the deicing of airfield pavements at the airports. They also govern wastewater discharges connected with aircraft deicing for new airports.
All airports have multifaceted storm water management systems that cater for the extensiveness of the open space, expansion projects history, numerous operations, as well as the mixture of extended grass surfaces and paved areas. Depending on the weather and operational factors, airport tenants and operators can use different deicing and anti-icing chemicals to clear the snow and ice from the pavements and aircrafts. These chemicals are then mixed with storm water runoff that pours out to the storm water drainage system at the airport. This water can be treated off-site or on-site, or to municipal storm sewers and surface waters. Therefore, water monitoring is essential to facilitate the control and characterization of the deicing discharges.
Storm water monitoring involves the obtainment of the measurements of the storm water qualities. Environmental permits guide airport operators to monitor their storm water. Otherwise, individual airport operators may also perform extra monitoring to help their storm water management. According to Shi (2008), airport personnel have to use the correct monitoring methods to collect parameter data.
A number of traditional off-site methods can be used to monitor storm water parameters. Samples have to be collected at various locations automatically or manually before passing through analytical testing at an off-site laboratory. Most of these methods have been approved by EPA and other regulatory agencies. Data from off-site monitoring usually have lesser samples of higher quality data; however, there can be delays between the process of sampling and analytical results acquisition.
According to the Transportation Research Board (2009), on-site monitoring methods can also be used to monitor storm water parameters. These methods combine both sampling and analysis that happen on the airport. There are some on-site monitoring methods that have been approved by regulatory agencies but the majority is not. Data from on-site monitoring may include many samples but with a shorter delay between the process of sampling and analytical result acquisition.
There are several factors that may drive the need to monitor airport and aircraft deicing procedures. Such drivers present the necessary information that go towards determining the sampling types and parameters monitoring, as well as, the frequency and locations of monitoring.
Off-site Monitoring Types
The traditional methods for gathering storm water monitoring data include sample collection and off-site laboratory analysis. Samples are automatically or manually collected at the sites before being sent off-site to a laboratory for analysis. Many laboratory analytical methods can be rigorous because of the performance of quality control procedures involved. However, off-site monitoring has several probable disadvantages:
- Manual sampling can be expensive because of the implicated labor costs.
- The timing and logistics involved in dispatching the staff can be hard especially when it is difficult to access the sampling sites.
- The handling, transportation, as well as, storage of samples follows several regulatory procedures and requirements.
- Measurements of storm water characteristics can only be taken during the time the sample is being collected.
- It takes a lot of efforts to capture desired conditions like peak deicer discharge time or the inconsistency of storm water characteristics.
- It is difficult to make real-time decisions using the sample results.
- There is a considerable amount of delay before results can be available which could take up to three weeks.
Parameters such as flow and temperature cannot be measured using off-site methods. Others like DO and pH have extremely short hold times. There are several methods associated with off-site monitoring.
On-site Monitoring Types
They include on-site collection and analysis of the samples. The analyses can be carried at the sampling location or anywhere else at the airport. It is advantageous over off-site monitoring because analytical results are available more quickly, which leads to a better ability to make crucial decisions. These methods are limited to those that can be performed using few simple steps or automatically.
Types of On-site Monitors
After identifying parameters that need on-site monitoring, the next step involves the selection of monitoring types, which include online, test kit, and handheld monitors. Selecting a proper monitoring type will ensure that the expected monitoring approach meets the data requirement while keeping the maintenance needs of the whole system at lower levels. Nonetheless, some monitoring types are unavailable for some parameters.
Online monitors refer to devices that are permanently mounted and designed to sample flow streams, as well as, analyze the samples regularly without the facility staff having to be present. They are the only monitors that involve a direct analysis of the sample without the involvement of airport personnel. The fact that data is collected automatically means that enough data quantities can be collected under different conditions, thereby dealing away with the need for the involvement of staff for sampling. Additionally, online monitors increase the options of characterizing swings that are unpredictable in storm water characteristics, which are common with deicer discharges.
Many online monitors can store and transmit the data over phone lines or computers. Since online monitors automatically collect and analyze samples, the data they collect can be used to make crucial decisions such as the diversion of storm water flow. Nonetheless, the staff needs to facilitate calibration, troubleshoot, verify results, carry out preventive maintenance, and also maintain a proper operation of all the instruments. Without intermittent personnel visits and proper care these data could be incorrect, hence affect the management of storm water and deicer control decisions. Online monitors can use one of the following in taking measurements:
- A sensor mounted on the sample stream
- A sample automatically collected and analyzed from within the unit.
Monitor types that have sensing units placed in the sample stream require intermittent maintenance of the sensors to verify that they are clean and properly submersed. Samples streams in water with deicer have considerable biogrowth, which might cover the electrode. Therefore, electrodes should be constantly cleaned to avoid any build-up of biogrowth. However, some submersible units can automatically clean themselves thereby reducing the frequency of manual cleaning. Monitors that deal with samples within a unit that is non-submerged require a sample collection system that will transmit the sample direct to the monitor. The system includes pumps that endlessly transfer stream samples to the whole unit, diverse sample-conditioning instruments, and piping that convey the sample to the monitor. Notably, the high presence of organic content in sample system will lead to biogrowth, which will require occasional cleaning. Small tubing inside the equipment can also be clogged, requiring periodic unit maintenance.
Depending on the method used, online monitors may not be fully continuous, since a few units will need huge amounts of time to carry out the individual analyses. Other methods may need several extra methods. Nonetheless, online monitors are more difficult to troubleshoot or operate than other types. Despite this, online monitors are not plug-and-play. Therefore, airport operators should understand the units require the set up, calibration, and maintenance to acquire accurate or reliable results. They should consider the surrounding environment, the sample characteristics and the data needed. According to a report by Levelton Consultants, Limited, (2007), it is essential to note that online monitors need periodic calibration and maintenance, as well as checks by airport employees. Many units perform well in temperature-controlled environments for the purposes of protecting the reagents or sample being taken. Furthermore, data should also be downloaded for the field for historical record unless the monitoring system has a communication system.
A test kit is a type of monitor system that allows the collection and analyses of samples by airport personnel away from the sample location but within the airport. The kits need reagents and a number of steps for analysis. The most common kit systems include a spectrophotometer and chemical test vials. Test kits are somehow more expensive to buy than monitors that are handheld; nonetheless, they have a longer service life if they are properly maintained. The methods used here depend on the procedures needed. While some tests kits can be carried to the field, typical analyses can be performed in a laboratory.
The analytical instruments used in test kits also need intermittent calibration and maintenance. It is recommended that comparison is done on test kit results to ascertain that results are similar enough. Many airport personnel have preferred test kit monitors because they are easy to use and can deliver a fast turnaround time for result analysis. According to Smith-Cunningham (2008), these analyses can also be carried out near the sampling site, which minimized the sample holding time, which then reduces any delay in acquiring analytical results. A sizeable number of test kit methods have been approved by the relevant authorities for compliance reasons.
Handheld monitors are on-site monitors that are carried out to the sample site for measurements. The portable monitor samples and analyses the water stream. These monitors have an electrode immersed into the stream for sampling purposes. The most common is known as the pH meter. They are less expensive to buy when compared to other monitors. They also need less capital to maintain as they have low operation and maintenance costs. The main function needed includes calibration. Handheld monitors are also easy to operate with proper understanding and study of the instruction manual provided. Their portability ensures that they can monitor multiple locations. Nonetheless, the units have shorter lives than the rest of the monitors since they are exposed to various field conditions. Monitoring can only take place when there are personnel to carry out the monitoring activities. The monitors need periodic calibration and some maintenance like battery, probe and solutions replacements. They are the most common types used to measure temperature, pH, and DO.
Screening of Monitoring Methods
After determining the monitor type suitable for each parameter, the next step in the selection process is the selection of monitoring methods. The Transportation Research Board (2009) defines the monitoring method as the specific process used in analyzing the parameter. Each parameter has a variety of methods for its analysis, for example, temperature can be analyzed using glass-bulb, thermocouple, infrared, or other various handheld methods.
Descriptions of Monitoring Methods
Many deicer management systems require the measurement of the primary deicer constituent concentration. It is essential to note that there is no on-site monitoring method that can directly measure constituents such as acetate, formate, or glycol in storm water. Each on-site method used in measuring concentrations of the above constituents can be taken as a surrogate measurement. If multiple organic constituents such as formates and glycols plus acetates are present, the accuracy of on-site monitor results may be affected, especially if the personnel did not calibrate the instrument to many compounds or if the correlations for deicer constituents and TOC, BOD, and COD, were derived wrongly. Care must, therefore, be taken while interpreting the results from the instruments used in measuring these parameters.
Good relations can be deduced between measurements of TOC, BOD, and COD and the individual constituent if there is only one constituent in the storm water. A low deicer concentration will mean that effects from various other parameters would be a significant part of the surrogate parameters measured. Therefore, it is essential to determine the presence and concentration of other compounds that would hamper the measurement in the storm water.
A number of on-site monitoring methods can measure glycols in a direct manner. Refractometers are commonly exploit because they can be used in deicer management systems to assess samples from areas with high concentration of ADF application including deicing pads (John D'Avirro, 2011). However, they do not directly measure glycol. They measure density by measuring refractance. A refractometer will have problems measuring glycol if there are numerous constituents in the sample with different densities. Only laboratory methods can identify glycols accurately, as well as isolate its fraction from the rest of the organics. According to Johnson (2001), refractometers can correlate well with glycol concentrations, which is good because refractometers function well in high glycol concentrations where other constituents have minimal effects.
Biochemical Oxygen Demand (BOD)
All BOD monitoring methods measure oxygen used by living bacteria in the monitoring device. The amount of oxygen a bacterium uses to degrade the compounds is useful in the calculation of oxygen demand (BOD). The monitor or method used has to use living bacteria otherwise they will be classified under different monitoring method. The closest online measurement to BOD5 is online BOD monitor because it employs the use of bacteria in analyzing a sample. It is more accurate in estimating the oxygen demand than TOC or COD in the receiving stream.
The difference between the online BOD monitor and laboratory BOD5 is the time the compounds get exposed to the bacteria. In a standard test, the chemical are exposed to bacteria for a maximum five days. The oxygen used in those five days will be measured and used to determine the BOD5. Since glycols degrade fast, the possibility of a correlation between BOD5, BOD and glycol concentration will be within a short time. Nonetheless, compounds that take a lot of time to degrade may not be compatible with online BOD monitors as a result of the minimal detention time. Storm water with many biodegradable compounds will also reduce the ability to attain a sufficient correlation with BOD5.
Furthermore, BOD5 laboratory method is performed at 200C while the online BOD monitor uses 30. These differences in temperature and contact time may end in different measurement responses, as well as, biological conditions. Online BOD should, therefore, be taken as a correlation to lab BOD5 similarly to TOC or COD. An online BOD monitor has a considerable start-up period that helps to develop a constant bacteria culture in the BOD monitor.
Chemical Oxygen Demand (COD)
These monitoring methods use a chemical or an energy source or both to degrade the deicers as well as other degradable compounds to CO2 and water. Furthermore, they measure the amount of oxygen utilized in the oxidation process to assess the primary deicer constituents and other concentrations. COD online measurement methods include electrochemical and photochemical oxidation methods. However, the photochemical oxidation method has no established applications at airports. It requires filtration of the sample since solids can block the tubing used in the monitor. The electrochemical oxidation method, on the other hand, has been used severally. It correlates well with lab COD analyses though the calibration would be unsuccessful at times. While this method might be useful in monitoring conditions with ADF presence only, it should be left out when there is a likelihood of pavement deicers presence.
Total Organic Carbon (TOC)
These monitoring methods are generally mounted as online methods. They convert organic portion of formates, acetates, and glycols, as well as other organic chemicals with carbon into carbon dioxide. They also use UV/ozone, UV/persulfate, or thermal methods to convert the organic chemical to CO2. Measurement of minimal TOC values will not be accurate if there is a high presence of inorganic carbon content in the sample. A number of methods can be used to measure TOC, for example, the use of thermal oxidation (furnace). It has minimal delays during start-up while the furnace warms. Manufacturers, however, warn that high levels of salts can lead to deposits in the furnace which will require an early furnace replacement.
These monitor methods apply one of the following to determine ammonia concentration: the optical method, the colorimetric method and the (ISE) ion-selective electrode method. Online methods for ammonia-nitrogen also use the above three methods. The handheld ammonia-nitrogen meters also use the ISE method. Its electrodes are very similar to pH electrodes, which have to be stored in damp places before measurement. They also have to be calibrated. Test kits for ammonia-nitrogen use the colorimetric method for measurements. It involves a number of simple sample preparations in the laboratory. The samples are then filtered if there is a high concentration of solids.
Schaepman (2005) states that, pH monitoring methods use colorimetric or ISE method to determine its concentration. Online monitors use ISE methods while handheld monitors use electrodes, which can be glass or non-glass. Test kit methods under this category use colorimetric method or test trips.
Dissolved Oxygen (DO)
Online and handheld DO monitors use the optical or amperometric method. Test kits for DO, on the other hand, use the colorimetric or Winkler method.
Online methods under this use the RTD (resistance temperature detector) electrode method or the thermocouple method. Handheld monitors employ various methods including the use of infrared, glass thermometer, RTD, thermocouple and bimetal thermometer methods.
Total Suspended Solids (TSS)
Online, handheld, and Test kits for TSS methods use the laser, scatter, or optical method, that are turbidity measurements that correlate to TSS concentration. All TSS methods need maintenance to keep the monitors always clean.
Discharge monitoring permits also demand measurement of flow. According to Grant (1995), monitoring methods for flow are divided by two different field conditions: full flow and partial pipe or open channel flow.
Undoubtedly, airplane deicing requirements have made travel using airplanes safe especially during winter. However, airport management and personnel are required to follow the new regulations that govern the environmental impact of these practices. Liptak (2003) agrees to the fact that, the process and methods used by airport personnel in managing these chemical will depend on the variety of sites. How much deicing takes place in the pavement? Which options are available for disposal? What type of infrastructure does the airport use? Airport facilities have to answer these questions before they can consider any possible solution for their waste management. According to the U.S. Environmental Protection Agency (1983), it is essential that airport engineers and personnel examine all the factors that affect deicing operation as well as the available options before picking on one treatment path.