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Interpreting the Results of Airport Water Monitoring (2017)

Chapter: Appendix B - Field Conditions Fact Sheets

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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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Suggested Citation:"Appendix B - Field Conditions Fact Sheets." National Academies of Sciences, Engineering, and Medicine. 2017. Interpreting the Results of Airport Water Monitoring. Washington, DC: The National Academies Press. doi: 10.17226/24752.
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B-1 A p p e n d i x B 1. Odor, B-2 2. Clarity/Turbidity/Solids, B-4 3. Foam, B-6 4. Color, B-8 5. Sheen, B-11 6. Nuisance Microbial Biofilms, B-13 7. Toxicity, B-17 Field Conditions Fact Sheets

B-2 interpreting the Results of Airport Water Monitoring Fact Sheet 1 Odor General Description Odors in stormwater or streams can be objectionable to the public as well as personnel working at an airport. The perception of odor can vary significantly by individual. In some cases, individuals may report feeling ill in the presence of odors. Odor is often the first indica- tor of a potential water quality issue, although it may also be an indicator of naturally occur- ring processes. The odor may be consistent with the odor of a released pollutant that is present within the water, or it may be associated with the degradation of the pollutants or naturally occurring organic matter. The identification of a distinct odor can be a clue to assessing the nature and source of a potential pollutant, especially when evaluated in conjunction with visual observations and analytical tests. Field Observation Approach Often odor is the first observation made by field personnel when arriving at a designated sampling location. If an odor source is present, the odor is often most noticeable at locations of higher flow rates and velocities, where turbulent conditions cause odor-causing substances to volatilize. Odor may also be observable in dry, stagnant water conditions when the water recedes. There is no universally accepted odor classification system. Generally odors can be considered to have a quality and intensity. Quality is associated with the type of odor and intensity can be best understood as its strength or concentration. The types of odors most typically observed at airports could be considered to fit in the following broad categories: chemical, pungent, and decayed. It is commonly understood that perceptions of odor vary by person and even by cir- cumstance for the same individual. Field personnel should attempt as best they can to describe if the odor is reminiscent of something that is commonly referenced (e.g., rotten eggs, sewage). Numerous conditions can affect the perception and intensity of the odor, including proxim- ity to the source, wind, and the presence of multiple odors. Relative comparisons of odors from location to location or from time to time may be most useful. Odor should be documented in conjunction with visual observations that may support identifying the source of the odor. Further analysis of the chemical composition of air that may have odors can be performed through collection and analysis. The gas collection method typically involves use of special- ized evacuated canisters or bags fed by pumps. The canisters and bags are sent to laboratories for analysis of volatile compounds. Compounds identified in the analysis can be compared to chemicals potentially present in airport stormwater or chemicals that may be breakdown prod- ucts of other chemicals. Variations and Sources Odor may be attributable to a variety of potential sources in an airport environment, to natural sources or man-made sources. Specific odors with some potential to be observed at airport outfalls are noted in the following list, as well as potential sources of these odors. It is

Field Conditions Fact Sheets B-3 recommended that field personnel assess the potential sources of these observations through sampling and analysis before drawing firm conclusions. • Rotten eggs or sulfur – A smell of rotten eggs indicates the presence of hydrogen sulfide, which is produced during the decay of organic matter in the presence of sulfate, due to sulfur-reducing bacteria. Sulfate may be present in receiving streams that receive ground- water exposed to naturally occurring sulfur and sulfate-reducing bacteria, and therefore is not always associated with a pollutant source. For example, while deicing materials are not typically a direct source of sulfur, deicers in stormwater can degrade anaerobically in storm sewers or storage tanks, with naturally occurring sulfur drawn from the stormwater by anaerobic bacteria. The likelihood of the odor being associated with deicing activities may increase if the odor is observed in conjunction with a deicing-related biofilm or at outfalls receiving drainage from deicing areas. The odor does not necessarily increase with greater volumes of discharged deicing runoff. Less commonly at airports, hydrogen sulfide can be an indication of sewage pollution, potentially associated with illicit connections between sanitary sewers and the stormwater drainage system, nearby septic fields, or fecal matter from wildlife. • Rotting onions – The odor resulting from the presence methyl mercaptan chemicals is com- monly described as smelling like rotting onions or garlic. Methyl mercaptan is produced as part of the degradation process for glycol-based aircraft deicing agents in the presence of sulfur compounds and is perhaps the most commonly observed odor associated with deicers. Odors of methyl mercaptan may be observed near airport stormwater outfalls or detention facilities during the deicing season. As with hydrogen sulfide, methyl mercaptan is a common source of odor complaints related to airports. • Fruity – Propionaldehyde, which is another degradation product of propylene glycol-based deicers, is noted as having an irritating fruity smell. As with methyl mercaptan (“rotting onions”) and hydrogen sulfide (“rotten eggs”), propionaldehyde is a common source of deicing-related odor complaints near airport outfalls. • Maple syrup/vinegar – The odor of deicing fluids as applied to aircraft has been described as a chemical smell reminiscent of maple syrup or vinegar. If this odor is noted in storm sewers or outfalls, it would suggest high concentrations of aircraft deicing fluid that has not yet degraded. • Petroleum – The odors of petroleum hydrocarbons such as gasoline, jet fuel, and organic solvents are distinctive and likely indicate that those substances are nearby. When observed in conjunction with a visible oily film or sheen on the water surface, this condition may be indicative of an accidental release of a petroleum-related pollutant. The odor could also be indicative of petroleum products escaping oil–water separators because of overloading or excessive flow. These observations should trigger the initiation of spill response activities, in accordance with the airport’s spill prevention control and countermeasure (SPCC) plan and stormwater pollution prevention plan (SWPPP) procedures and spill control, as well as a check of oil–water separators. • Musty – A musty odor is often associated with decaying vegetation. This type of odor is some- times also described as earthy or moldy. It is frequently associated with naturally occurring conditions and may be present in frequently wet areas. • Ammonia – The pungent odor of ammonia is associated with the degradation of nitrogen- containing organic compounds. This odor is associated with the application of urea as a deic- ing agent at airports where this practice is performed. Less commonly, it may be an indication of sewage pollution, potentially associated with illicit connections between sanitary sewers and the stormwater drainage system or nearby septic fields. Ammonia products are also often used as a nutrient source for deicer treatment systems.

B-4 interpreting the Results of Airport Water Monitoring Fact Sheet 2 Clarity/Turbidity/Solids General Description Clarity is often synonymous with transparency and represents the ability of light to be trans- mitted through the water. Low clarity in water, which is referred to as “turbidity,” is an optical indication of the presence of colloidal or suspended solids in water that reduces the ability of light to pass through the water. Turbidity is often attributed to sediment but may also be associ- ated with naturally occurring organic matter, the discharge of pollutants, or chemical reactions that precipitate or release solids. High levels of turbidity and solids content can result in human health and aquatic life risks depending upon the nature of the solids. Turbidity contributes to receiving-stream temperature increases, which may trigger lower dissolved oxygen concentrations because the maximum oxy- gen content that can be dissolved in water decreases as temperature increases. Turbid waters block the infiltration of sunlight, which can limit photosynthesis of aquatic plants, also leading to less dissolved oxygen added to the water. Turbidity is also a leading indicator of the potential presence of pollutants that adsorb to the solids. As a result, significant changes in turbidity should trigger consideration for monitoring additional pollutants such as dissolved metals, dissolved organics, pathogens, and nutrients. Turbid waters may create operations and maintenance challenges for those processing waters from streams. Field Observation Approach Turbidity may be noted in a receiving water or conveyance when there is a cloudy appearance or when it is difficult to see through the water to the bottom of the flow channel. It is more easily observed by collecting a sample in a clear jar, as this allows for field personnel to directly observe the ability of light to pass through the sample. Solids may be observable within sampling jars when allowed time to settle. Colloidal solids will not settle and may therefore cause turbidity after settled solids are deposited. Field observation of turbidity should be used primarily as an indicator of potential unusual conditions. Field personnel should document observations of turbidity or level of clarity, as well as the locations of these observations. Quantification of turbidity through monitoring is preferred to observation when monitoring equipment is available, especially in situations where turbidity regularly occurs. Turbidity may be quantified using a handheld analyzer, in nephelo- metric turbidity units (NTU). Variations and Sources Turbidity caused by solids in airport waters may be a result of natural conditions, derived from background (off-airport) sources, or may be associated with activities at the airport, especially those that lead to soil erosion. Turbidity in waters may occur in conjunction with other distin- guishing characteristics such as color and odor. It may also be associated with the presence of spe- cific chemical compounds or materials. To assess potential causes of turbidity, it is recommended that field personnel use quantifiable measurement of turbidity itself, as well as measurements of

Field Conditions Fact Sheets B-5 other related parameters such as total suspended solids (TSS) and specific chemical compounds. Numerous studies have explored the relationship between NTU and TSS, primarily because of the ability to collect real-time measurements for turbidity versus the laboratory analysis needed to measure TSS. The validity of a turbidity–TSS correlation, however, is site and situation spe- cific as not all substances leading to turbidity are measured as TSS and not all solids measured as TSS contribute to turbidity. The strength of the TSS–turbidity correlation depends upon which particular substances are present. Typical sources of turbidity are described in the following list: • Sediment – The presence of sediment in the form of colloidal or suspended solids is the most common cause of turbidity. Suspended solids can settle. Colloidal solids (which are a smaller particle size than suspended solids) will not settle or settle at an extremely slow rate. The pres- ence of solids may give the water a cloudy appearance with a color similar to local soils. Turbid- ity in streams may be a result of sediment re-suspended from the stream bottom or bank due to the actions of higher stream flows, aquatic organisms, or terrestrial organisms. Turbidity in runoff from airports is often associated with the occurrence of erosion and sedimentation along the flow path or in upstream tributary areas. When observed emanating from airport outfalls, it is often attributed to construction activities or other unstabilized soils without proper sediment and erosion controls. Intense rainfall conditions or extended wet periods can also wash out grass and soil covers, which leads to exposure of the soils. Extensive winds can also erode soils and result in sediment accumulation in streams or airport surfaces. It is recommended that field personnel document observations of turbid conditions or erosion in the receiving stream upstream of airport discharges to evaluate the potential contribution of sediment from non-airport sources. It may be possible to determine the source of discharged sediment by visually tracking it upstream although quantitative measurements are preferable. Those assessing sources of turbidity should be aware that turbidity from sediment can be highly variable as ambient conditions change. • Natural organic matter – Turbidity in a receiving stream may also be caused by the presence of naturally occurring solids such as plant material, dead wood, or microscopic life such as algae or plankton. Deposition of atmospheric materials (e.g., ash from burning forested areas or volcanic activity) can also create turbid conditions. Especially in streams, natural and non- point sources of turbidity often contribute to turbidity to a significantly higher degree than airport sources. Field personnel are encouraged to compare visual sample observations to the appearance of the receiving water upstream of airport discharges to determine whether there may be natural background sources contributing to the turbidity. • Pollutant release and reaction – The release of pollutants other than sediment may also contribute to turbidity, particularly for pollutants that are also turbid due to high solids content. The presence of pollutants contributing to turbidity may be inferred from related revealing characteristics such as color, odor, or sheen. The occurrence of these character- istics can help distinguish a pollutant cause of turbidity from naturally occurring sources or sediment. Pollutants that commonly contribute to turbidity include sewage and waste- water effluent including pathogens; animal wastes; particulates from runways, taxiways, and roadways; and airborne particulates from vehicle emissions. A less common source of turbidity is the precipitation of dissolved metals such as iron or manganese, which can occur in conditions of very low dissolved oxygen and pH (e.g., caused by the presence of deicers in stagnant waters).

B-6 interpreting the Results of Airport Water Monitoring Fact Sheet 3 Foam General Description Foam in stormwater can be easily observed. Foam typically requires two components to form: surfactants and air. Surfactants reduce the surface tension of a water surface, allowing bubbles to form in areas where water has the opportunity to mix with air. Foam can be an aesthetic issue, can coat material surfaces with undesirable material, can be a safety hazard if blown across the airfield, and can be difficult to clean up. Typically, however, the primary issue presented by foam is that it can be an indicator of pollutants. These pollutants may include foaming agents or surfactants, such as detergents from washing activities. Foam may also be caused by natural surfactants, including fatty acids or oils released during the decomposition of natural organic matter, including algae, plants, and animals. Field Observation Approach Foam may be observed by field personnel within the receiving water or conveyance where the sample is to be collected, particularly in areas of high flow or turbulent conditions where the water has the potential to mix with air. A sampling jar used for visual observations can also be used to check for foam by placing the lid on the jar and gently shaking it. If foam is observed, field person- nel should document its characteristics such as the extent of the bubbles (i.e., few or many), size of the bubbles, color of the foam, how much of the surface is covered by foam, foam thickness, and how long the bubbles last before bursting. Samples with little to no surfactants or foaming agents may have a few large bubbles that form, but these are likely to burst within 10 seconds. In contrast, samples with high amounts of foaming agents are likely to have more small bubbles, and these may last for several minutes. Changes in the extent of foaming (e.g., depth, width, length) in open channels, pipes, and streams should be documented to facilitate correlation with activities that may cause the foaming. Odors can sometimes be present with the foam and can indicate the foam source. Observations should also be made of changes in the possible sources of air entrain- ment (e.g., turbulent flow, mechanical aeration) as this can have a significant impact on the extent of foam. Documentation of associated ambient conditions such as water flow, temperature, and water hardness is also recommended. Variations and Sources In an airport environment, foam has the potential to be associated with on-site industrial activities involving surfactants, including the washing of vehicles, aircraft, or equipment or the discharge of fire-fighting foam. Aircraft deicing chemicals can also be a significant contributor to foaming in drainage structures, pipes, pump stations, open channels, and streams. The foaming from deicing chemicals is caused by the presence of surfactants intended to aid the distribution of the deicer on the aircraft wing. Often one of the first public complaints that leads to the iden- tification of issues associated with deicers is the presence of foam in streams. The discharge of surfactants from these various sources may be caused by allowing pollut- ants in runoff to drain directly into a storm drain or by a floor drain (e.g., in a car wash bay) or sanitary sewer having an illicit connection to the storm sewer system. It may also be associated

Field Conditions Fact Sheets B-7 with a spill of a detergent or other stored material containing surfactants. Alternatively, foam observed at outfalls may be associated with naturally occurring surfactant sources in the receiv- ing stream. Industrial sources of foaming may be distinguished from natural sources based on observations of bubble size, color, odor, and extent of foaming. Distinguishing characteristics are described in the following list: • Industrial or man-made surfactants – Foams caused by industrial or man-made surfactants are likely to have the following distinguishing characteristics compared to foam from natural sources: – Extent of foam: Detergents are designed to disperse easily in water, so these foams are likely to spread out further into the receiving water or conveyance in the direction of flow. – Persistence: Foams associated with man-made sources are also likely to be shorter-lasting than natural foams, due to their ability to disperse in the water and become diluted. – Odor: Such foams may also have an odor that suggests the presence of a perfume, chemical detergents, or deicers. – Bubble size: The bubbles in a detergent-based foam may have more variability in size than a naturally occurring foam and may have both large and small bubbles. – Color: Foams are likely to appear bright white or soapy if due to brightening agents found in detergents, while an orange color may indicate the presence of aircraft deicers. – Texture: Foams may have a slippery or slimy texture, similar to soapy water. • Natural surfactants – Naturally occurring surfactants have the following characteristics that distinguish them from foams caused by industrial activities or man-made surfactants: – Extent of foam: Foam has a more compact appearance than man-made surfactants and is likely to remain close to the source. At an airport outfall, this may be visible as a patch of foam that remains near the discharge end of a pipe and does not spread far out into the receiving water. It may be blown by wind or wave action to accumulate along the shoreline but is likely to retain a compact shape. – Persistence: Naturally occurring foams tend to be longer-lasting and may persist in the environment longer than man-made foams. – Odor: Foams tend to smell earthy or fishy, rather than like perfume or chemicals. – Bubble size: Bubbles are consistently small, with few to no large bubbles, because natural sources are less efficient surfactants. – Color: Naturally occurring foams are more likely to appear off-white or brown, due to the decomposition of organic materials and the presence of tannins in the water, in absence of the brightening agents found in man-made surfactants. – Texture: Naturally occurring foams typically feel light and non-slimy compared to foams caused by man-made surfactants.

B-8 interpreting the Results of Airport Water Monitoring Fact Sheet 4 Color General Description As water is naturally colorless, the observation of color in water to be sampled is an indicator that pollutants may be present. Color in water is typically categorized by “apparent color” (immediate color observed) and “true color” (color after settleable particulates have been removed). True color is most frequently used when tracking color in water samples as it represents the color imparted by the dissolved materials, free from the influence of particulates. The color may be derived from a variety of sources, including a characteristic of the pollutant itself (e.g., the color of a concentrated chemical spill), a result of chemical reactions, or a color associated with bacterial growth driven by degradation of a commonly occurring pollutant. Alternatively, it may be associated with the pres- ence of micro-organisms such as algae, which may flourish because of the availability of nutrients that are either naturally occurring or associated with runoff from point and non-point sources. The presence of color is often aligned with turbid conditions in the water. Besides the aesthetic issues of water color, color can affect light penetration in streams, influence dissolved oxygen levels, and indicate the presence of pollutants that create other human health and aquatic life impacts. Field Observation Approach Color is most easily observed within the receiving water or conveyance where the sample is to be collected. It may not be as easily observed within a collected sample, because of the small quantity and the potential for the colorful material to not be collected. Color is most commonly observed at airport outfalls where flows are concentrated into a channel, box culvert, or other observable conveyance system upstream of a receiving water. Color is less likely to be observed within a receiving water in well-mixed or high flow conditions where significant dilution is occurring. Field personnel should document a description of any unnatural colors observed within a sample jar, conveyance, or receiving water, as well as the location of the observations. To provide a more quantitative measurement of color, the platinum-cobalt color scale system, comprising 1,000 color units or platinum-cobalt units, can be used. Variations and Sources In an airport environment, a variety of colors may be observed at stormwater outfalls. Although each color may be associated with a variety of causes, the most commonly occurring color varia- tions and causes are summarized in the following list. It is recommended that field personnel confirm the potential causes of these observations through sampling and analysis before drawing firm conclusions. • Rainbow or multi-colored – The observation of a multi-color or rainbow reflection on the surface of the water is considered to be a sheen. Sheens may be caused by either microbial activ- ity (potentially naturally occurring) or the presence of oil, grease, or petroleum hydrocarbons. Please refer to Fact Sheet 5: Sheen for further information. • Silver – The observation of a silver or mirror-like reflection on the surface of the water is con- sidered to be a sheen. Sheens may be caused by either microbial activity (potentially naturally

Field Conditions Fact Sheets B-9 occurring) or the presence of oil, grease, or petroleum hydrocarbons. Please refer to Fact Sheet 5: Sheen for further information. • Yellow/orange/red/brown – Yellow, orange, red, or brown colors in stormwater are relatively common and can be caused by a variety of sources, including the following: – Dissolved organic matter from natural sources – In some locations, the receiving waters may have a yellow, orange, brown, or tea-like appearance due to natural tannins and lignins (complex organic polymers within plants) associated with the decay of leaves, roots, bark, and other organic material, which may be visible in the water. Water may also be discol- ored by the presence of naturally occurring minerals such as iron (red, orange, or brown) or sulfur (yellow). Visual observations should be compared to receiving water colors at locations upstream of airport discharges to determine whether there may be background sources contributing to the color. – Metal precipitates – Iron is frequently present in water because of the extensive quantities found in the soils and rock materials of many areas. Under the right conditions, iron oxides can form, with the precipitated material providing a red, orange, or brown color. – Microbial activity (non-algae) – Iron-reducing bacteria, which are commonly found at airport outfalls and often associated with the degradation of deicing compounds, fre- quently form a biofilm or slime that appears orange or brown. Bacteria colonies are gen- erally attached as a film or coating on the bottom or sides of conveyance channels, pipes, and rocks but can become detached and add color to the water. They may appear to have a texture or thickness, as opposed to simply staining the surfaces, and may also form as filaments that extend in the direction of flow. Microbial activity is also typically associated with an odor – refer to Fact Sheet 1: Odor for further information. – Algae growth – Particular varieties of algae may appear as red or brown. Algae may float on the surface of the water or may attach to surfaces along the sides or the conveyance. Algae growth downstream of airport outfalls may indicate elevated levels of nutrients, which may be naturally occurring or associated with the application of fertilizers as part of landscaping activities. – Pollutant release – Pollutant releases into the drainage system may also result in an orange or brown hue, particularly if released in large quantities where dilution has less of an effect. A large pollutant release is likely to be associated with odors or other characteristics that may allow the pollutant to be identified. Type I deicing chemicals are dyed orange and concentrated releases that occur as a result of a spill or limited precipitation in the runoff can result in orange coloration in the storm sewers and streams. If a sheen is also observed, the color may be attributable to petroleum products. – Sediment – The presence of sediment or solids within the water are likely to be associated with a turbid or cloudy appearance within the receiving water. The color may appear to be more consistent and distributed throughout the water compared to algae or microbial sources. The color is likely to be consistent with the color of local soils. Observations of ero- sion or sedimentation within open channels, or ongoing construction activities upstream of the sampling location, may be further indicators of sediment being present. Solids may also be observed within sampling jars when allowed time to settle. – Dyes – The presences of an intense red color could be associated with a dye test being conducted. • Black – A waterway that appears black may be an indication of anoxic (oxygen-free) conditions due to the microbial degradation of organic matter, such as deicing fluids or other pollutants. Often the color is derived from sulfur-reducing bacteria. The black coloration could be from a direct release of sewage into stormwater or from sewage-free runoff turning black as oxygen is depleted and anaerobic organisms proliferate. Black coloration may be observed underlying a biofilm (described above) because of the anoxic conditions created by the biofilm. Black may

B-10 interpreting the Results of Airport Water Monitoring also be associated with the release of a pollutant of that color, such as oil runoff from parking lots, and may be characterized in conjunction with observations of odor and sheen. Black may also be attributable to the presence of natural minerals such as manganese oxide. • Blue/Green – Water that appears blue or green may be caused by algae growth or naturally occurring processes associated with the presence of metals from groundwater. Visual obser- vations should be compared to receiving waters at locations upstream of airport discharges to determine whether there are background sources contributing to the color. Algae growth downstream of airport outfalls may be an indicator of elevated levels of nutrients, which may be naturally occurring or associated with the application of fertilizers as part of landscaping activities. Blue or blue-green can also indicate the presence of copper. Type IV aircraft deicing chemicals are green from dye, which can be seen in storm sewers and streams if insufficient dilution is present. • Pale White/Milky Blue – In the right combination of conditions, including higher pH, aluminum oxides can form, giving the water a white or milky color.

Field Conditions Fact Sheets B-11 Fact Sheet 5 Sheen General Description Sheen is a visually observed field condition that may be noted on the surface of water within a receiving stream or conveyance system, or within a collected sample. A sheen is observed in the reflection of light off of a floating film on the water surface. It may appear as a rainbow, with unnatural coloration such as pink, blue, green, brown, or yellow, or it may appear oily, lustrous, silvery, or iridescent, without being discolored. Although a sheen is typically associated with the presence of pollutants such as oil and grease or petroleum hydrocarbons, biofilms associated with microbial activity or algal blooms can produce sheens that are similar in appearance, result- ing in “false positives” for the presence of petroleum products. Field Observation Approach Sheen may be observed by field personnel within the receiving water or conveyance where the sample is to be collected, particularly in areas of high sunlight, low flow, or non-turbulent conditions where the surface of the water is flat and easily observable. A sampling jar used for visual observations can also be used to check for sheen by partially submerging the jar in the dis- charge and collecting a sample from the surface of the discharge. Field personnel should observe the sample jar at an angle that allows light to reflect off of the surface of the sample; inspect the sample for the presence of tiny transparent balls less than a tenth of an inch in diameter, which indicate the presence of Noctiluca algae cells; and, after shaking the jar, view the sample in a dark place to observe any bioluminescence that may indicate the presence of Noctiluca algal bloom. It is recommended that field personnel view the sample surface at different angles or directions to avoid mistaking reflected objects (e.g., clouds) for a sheen. If sheen is observed, field personnel should document the characteristics of any sheen on the surface, including color, light reflection, apparent texture, and any noted oily appearance such as a film or globules. Field personnel should document how much of the surface is covered by sheen, including locations upstream and downstream of the sample location. Odors can sometimes be present with the sheen and can give an indication as to the sheen source. The result of an attempt to disturb or break up the sheen by inserting a stick or other object into the water surface at the location of the sheen and moving it around can be an indicator of the sheen source. A sheen caused by oil and grease may temporarily disperse during this activity, but is likely to reform and consolidate afterwards, and may look similar in appearance as it did originally. A sheen caused by natural processes such as microbial activity or algae may break up into individual pieces that remain separate, floating on the surface. Variations and Sources In an airport environment, sheen has the potential to be associated with on-site industrial activities involving petroleum products, including maintenance, fueling, storage of petroleum products, and the washing of vehicles, aircraft, or equipment. The discharge of petroleum prod- ucts from these various sources may be caused by allowing pollutants in runoff to drain directly into a storm drain, by a floor drain in a maintenance bay or car wash having an illicit connection

B-12 interpreting the Results of Airport Water Monitoring to the storm sewer system, or by an oil–water separator not being properly maintained. It may also be associated with a spill or leak of a petroleum product from tanks, drums, equipment, vehicles, or aircraft. Alternatively, sheens observed at outfalls may be associated with microbial activity or algae in the receiving stream. Algal bloom sheens occur naturally when algae multiply quickly and form visible patches on the water surface. Petroleum product sources of sheen may be distinguished from microbial activity or algae based on observations of odor and the ability of the sheen to reform after being disturbed. Distinguishing characteristics are as follows: • Petroleum hydrocarbon sheens – In an airport environment, pollutants with the potential to cause a sheen include gasoline (for vehicles and equipment), aviation gasoline, jet fuel, diesel fuel, new and used oil, and hydraulic fluid. Sheens caused by petroleum hydrocarbons may appear oily, iridescent, rainbow, or lustrous. Sheens caused by oil and grease or petroleum hydrocarbons will also swirl, elongate, and reform after being disturbed; may be accompanied by a petroleum or oil odor; and may appear streaky or as rows of streamers (National Oceanic and Atmospheric Administration, 2010). If a sheen is not observed, it does not guarantee that oil and grease are not present in the water being sampled. The appearance of a visible sheen can be affected by a variety of fac- tors, including flow conditions, the concentration of the pollutant(s), and the density and nature of the pollutants. Although oil and grease may produce a sheen at concentrations as low as 1 mg/L (Office of Environmental Health Hazard Assessment, 2006), this sheen may not be visible if flow is turbulent and oils are emulsified within the water. When present at very high concentrations, oil may appear brown or dull colored, with less of a sheen (Office of Environmental Health Hazard Assessment, 2006). Additionally, oils and greases that are denser than water (e.g., halogenated solvents) will not float at the surface, and thus will not produce a sheen. • Noctiluca algal bloom sheens – Sheens caused by naturally occurring Noctiluca algal blooms appear red, similar to tomato soup, and may look similar to reddish emulsified oil. Algal blooms will appear as an amorphous mass and will not appear streaky. Noctiluca sheen is bioluminescent, which can be observed by gently shaking a sample jar of the sheen and view- ing it in a dark room. Tiny transparent balls resembling fish eggs also indicate the presence of Noctiluca algae cells (National Oceanic and Atmospheric Administration, 2010). • Leptothrix discophora bacteria sheens – Sheens caused by Leptothrix discophora bacteria appear either orange, red, or rust colored if the bacteria are feeding on iron, or black if they are feeding on manganese. Sheens caused by Leptothrix discophora bacteria will break apart into irregular mirror-like platelets when disturbed and will not reform (Washington State Department of Ecology, 2010). References National Oceanic and Atmospheric Administration (2010). Guide to Distinguishing Oil from Algal Blooms. NOAA’s Oil Spill Response. U.S. Department of Commerce. Office of Environmental Health Hazard Assessment (2006). Characterization of Used Oil in Stormwater Runoff in California. California Environmental Protection Agency. Washington State Department of Ecology (2010). How to Do Stormwater Sampling: A Guide for Industrial Facilities. Publication 02-10-071.

Field Conditions Fact Sheets B-13 Fact Sheet 6 Nuisance Microbial Biofilms General Description Microbial biofilms are complex ecosystems of micro-organisms bound together by a matrix of extracellular polymeric substances that are produced by algae and other micro-organisms (Mericas et al., 2014; Callow, 2000). The biofilms are composed mostly of water held in a matrix of microbial cells and polysaccharides. Microbial biofilms are ubiquitous in water bodies receiving airport stormwater discharges. Some level of biofilms is naturally occurring and at the appropriate extent biofilms play an important role in the aquatic ecosystem. In particular they facilitate ecosystem energy flow, nutrient cycling, and food supply. As the bio- film proliferates, however, it can achieve a dominant presence and negatively affect aspects of the aquatic ecosystem. Negative effects on the aquatic ecosystem of excessive biofilm growth include the production of toxins, reducing the ability of the water body to be used for recre- ational purposes; excessive accumulation of biofilms on structures residing in the water and structures used to convey the water; local decreases in dissolved oxygen; reductions in the ability of sunlight to penetrate the water; and coating of the benthic surfaces in a way that negatively affects other aquatic life. When the extent of the biofilm growth becomes significant enough, regulatory authori- ties may require airports to manage discharges in a way that reduces the extent of biofilm growth. According to The Water Quality Standards Handbook, U.S. EPA, along with states with designated authority to issue NPDES permits, has adopted narrative criteria in water quality standards that indicate all waters, including those within mixing zones, shall be free from substances attributable to other pollutant sources that (among other criteria) “pro- duce undesirable or nuisance aquatic life” (54 Federal Register 28627, July 6, 1989). U.S. EPA considers that the narrative criteria apply to all designated uses at all flows and are necessary to meet the statutory requirements of Section 303(c)(2)(A) of the Clean Water Act (U.S. EPA, 1994). Biofilms can flourish under combinations of ambient and discharge conditions that may be present at an airport. ACRP Report 115 explores microbial biofilm growth associated with deicing activities at airports. Through a combination of review of field data and labora- tory tests, the researchers of that work concluded that “in-stream concentrations of read- ily biodegradable organic material, as reflected in COD [chemical oxygen demand] or BOD [biochemical oxygen demand], appear to be the dominant factor for biofilm proliferation and accumulation” (Mericas et al., 2014). There may also be a relationship to nutrient levels, includ- ing nitrogen and phosphorus. It is clear that biofilm growth is a complex process that may be subject to the interactive effects of multiple variables. Field Observation Approach Field personnel looking to document nuisance biofilm growth are encouraged to document observations on the following: • Location • Extent

B-14 interpreting the Results of Airport Water Monitoring • Color • Texture • Ambient conditions A more detailed documentation of measured conditions associated with biofilm growth could include the following: • Analysis of water constituents • Classification of biofilm Location The most basic field observation to document is the location of microbial biofilm growth. The growth can be present on a number of surfaces at and near airports, including the following: • Storm sewers • Outfall pipes • Base of open channels • Structures supporting open channel or stream bed slopes (e.g., riprap, articulating block) • Aeration structures (e.g., cascade aerators) • Energy dissipation structures for stormwater • Stream bed • Mechanical equipment (pumps, pipes, tubing, valves, screens, monitoring devices) Extent At each location where extensive biofilm growth is observed, field personnel should estimate the extent that the local surface area is covered with biofilm. For example, does the biofilm extend the full width of the stream? Is the biofilm clustered in patches or does it extend for a significant distance downstream. Exact measurements are typically not necessary, but estimation of the areal extent can help assess changes over time. Visual estimates of the biofilm depth can be attempted, but it is often difficult to be accurate without measurement. Basic methods such as tape measures, rulers, or depth sticks could be used. Tracking changes in depth over time can be a useful means of assessing the effect of vari- ous conditions. Photo-documentation of the extent is recommended, preferably from the same location and vantage point each time. Color Biofilms can be composed of a variety of micro-organisms with individual color patterns. It is not uncommon for colors of the same patch of biofilm to change quickly as conditions change and different micro-organism groups proliferate. Ambient lighting conditions can also affect the perception of biofilm color. As a result, observed colors should not be relied upon as the sole means of identifying micro-organisms composing the biofilm. However, observation of color with each field inspection is recommended to assist in general classification and assess- ment of patterns. Typical colors seen in airport discharges or receiving streams include green, blue-green, orange, white, gray, brown, and black. Green and blue-green biofilms at airports are often, but not always, associated with algae. Orange and brown are often associated with Sphaerotilus bacteria that may proliferate in the presence of deicing chemicals. The orange coloration comes from the accumulation of iron oxide in the bacte- ria. Dark brown or black are indicative of bacteria in an anaerobic or anoxic (oxygen limited) state.

Field Conditions Fact Sheets B-15 Biofilm Structure/Texture Micro-organisms in biofilms are distinguished from planktonic micro-organisms by the presence of the extra polymeric substances (EPS) that bind the micro-organisms together in biofilms. The EPS–microbe combination results in structures and textures that are unique to biofilms. Visual observations of the biofilm plume structure and texture can provide infor- mation to help classify the biofilm type and to assess patterns. Common terms used to clas- sify the biofilm structure include filamentous (string-like arms that may exhibit oscillating behavior or have a netted appearance), matted (jelly-like film), balled, foamy/frothy, and shiny/oily. Ambient Conditions Observations should be made on the following ambient conditions associated with the area of biofilm growth: • Water channel shape – Classify as straight, sinuous, or meandering. • Water depth – Classify as shallow (<1 cm), moderate, or deep (>10 cm). • Water turbulence – Classify as stagnant, laminar, or turbulent. • Water velocity – Obtain measurements if possible but, at a minimum, indicate if flow velocity is fast or slow moving. • Shading/sunlight – Document if the area of biofilm growth is exposed to sunlight, always shaded, or shaded at the time. • Water temperature. • Negative effects – In some cases, negative effects such as fish kills, odors, equipment clog- ging, and impaired access may be observed that could have a relationship to the presence of biofilm. Analysis of Water Constituents If the airport undertakes a significant assessment of biofilm growth, quantification of cer- tain physical and chemical characteristics of the water can provide information to support the assessment. Commonly measured parameters in biofilm studies include: BOD, COD, total organic carbon, propylene glycol, acetate, formate, total dissolved solids, total Kjeldahl nitrogen (TKN), ammonia–nitrogen, orthophosphate, total phosphorus, iron, sulfate, nitrate+nitrite, temperature, and pH. Classification of Biofilm Samples of biofilms can be analyzed microscopically by specialized laboratories for the type of micro-organisms in the biofilm. The analyses are typically conducted either to characterize the situation or to support processes for reducing growth. Samples are typically either drawn directly from growth at the airport or cultivated on specially designed growth plates. The growth plates have the advantage of keeping the entire depth of biofilm intact. Variations and Sources Biofilms can be present at airports in a wide variety of forms. Both the areal extent and depth can vary significantly throughout a year and from year to year. Since micro-organisms are highly sensitive to ambient conditions, changes in any number of factors can result in a rapid change in the type of micro-organism that predominates the biofilm.

B-16 interpreting the Results of Airport Water Monitoring Biofilm management at airports is a significant challenge because of the high variability in both biofilm and ambient conditions. It is also a challenge because biofilms can appear in many locations. While the general consensus is that the organic compounds associated with deicers play a significant role in promoting excessive biofilm growth, much is yet to be understood about the other factors and their interactions. Reduction in BOD and COD concentrations in discharges is likely an essential component in any mechanism designed to reduce biofilm growth at an airport. References Callow, M. E. (2000). Algal Biofilms. Biofilms: Recent Advances in Their Study and Control, L. V. Evans (ed.), pp. 196–218. Amsterdam: Harwood Academic. Mericas, D., P. Sturman, M. Lutz, S. Corsi, C. Cieciek, J. Boltz, and E. Morgenroth (2014). ACRP Report 115: Understanding Microbial Biofilms in Receiving Waters Impacted by Airport Deicing Activities. Washington D.C.: Transportation Research Board. U.S. EPA (1994). The Water Quality Standards Handbook, Second Edition.

Field Conditions Fact Sheets B-17 Fact Sheet 7 Toxicity General Description This fact sheet covers monitoring considerations for aquatic toxicity. Through requirements in the Clean Water Act, NPDES permits include narrative criteria that indicate that discharges to surface waters shall be free from substances in amounts toxic to humans or aquatic life. The narrative criteria apply to all surface waters with designated uses at all flows. Field Observation and Monitoring Approach Background While toxicity is listed as a narrative criteria, toxicity in discharges or receiving streams is not easily observable like conditions associated with other narrative criteria such as odor, color, and solids. With the Clean Water Act revisions of 1987, the difficulty of quantifying and enforcing the general narrative prohibition on toxicity was addressed through requirements that U.S. EPA and states with authority to implement NPDES programs use specific, scientifi- cally defensible methods to implement the narrative toxics standard for all toxicants. These requirements apply to methods for chemical-specific criteria in permits to address toxicity of individual constituents, methods for developing and implementing whole effluent toxicity criteria, and methods for developing and implementing biological criteria. The whole efflu- ent criteria are typically addressed through whole effluent toxicity (WET) criteria and testing. Not all airport NPDES permits include WET requirements. Inclusion of WET monitoring requirements and criteria is at the discretion of the NPDES permit writer. Title 40 Code of Federal Regulations § 122.44(d)(1)(v) requires NPDES permits to contain WET limits where a permittee has been shown to cause, has the reasonable potential to cause, or contributes to an in-stream excursion of a narrative criterion. From a monitoring standpoint, WET requirements present unique challenges. The following paragraphs discuss the considerations for the sampling and analysis associated with WET moni- toring. For more guidance on WET monitoring at airports, readers are encouraged to consult ACRP Report 134: Applying Whole Effluent Toxicity Testing to Aircraft Deicing Runoff (Newfields Environmental & Engineering LLC et al., 2015). The basis for the WET approach is that reliance only on monitoring of individual param- eters may not allow for sufficient characterization of toxic impacts of stormwater dis- charges because (1) not all harmful contaminants are always identified and/or monitored; (2) interactive effects of multiple contaminants may not be known; and (3) the separate and combined impact of environmental variables such as temperature, salinity, pH, hardness, alkalinity, etc. on organism toxicity and ecosystem functioning is often not known with great assurance. The WET test provides a means for assessing potential toxic impacts in a single assessment but is not a single standardized monitoring procedure. It requires selection of WET test parameters appropriate to the regulatory requirements, ambient conditions, and aquatic organisms in the

B-18 interpreting the Results of Airport Water Monitoring receiving water body. Aquatic toxicity tests are either freshwater or marine and generally fall into one of two categories: 1. Acute toxicity tests involve short-term exposures (24 to 96 hours) where organism lethality is the test endpoint. 2. Chronic toxicity tests involve long-term exposures (hours to weeks) in which sub-lethal and lethal responses are used as the test endpoints. Typical chronic test endpoints include (a) larval development, (b) growth of juvenile organisms, or (c) a measure of reproductive success. Table B-1 identifies typical toxicity test endpoints in use. The aquatic organisms used for the testing must also be selected. Permits often require tests to use two or three different taxonomic types (e.g., molluscan, echinoderm, fish, and crusta- cean species) because not all aquatic organisms respond similarly to toxicants. The selected test organisms serve as surrogates for the whole spectrum of potentially impacted organisms in the water body. In general, early life stage tests are specified as they represent peak sensitivity to potential pollutants. Selection of WET Monitoring Stormwater Sampling Sites The sampling location for WET monitoring should be representative of the discharges and the potential impacts to the receiving streams. Factors that should be considered in selecting sampling locations include the following: 1. Drainage basin characteristics upstream of sampling point • The industrial activities in the drainage area upstream of the sample point must be verified. • The possibility of non-airport drainage being included in the overall drainage area to be sampled must be assessed. 2. Mixing and dilution downstream of the sampling point • If flows entering the discharge stream downstream of the sampling point have significant flow rates and minimal potential for pollutants, then the WET from the sampling point may overestimate the impact of discharges on the receiving waters. • If downstream flows containing potentially toxic pollutants are not WET monitored, it may be difficult to interpret the value of WET test results at the sampling point. 3. Proximity of separate discharges upstream of the sampling point • If multiple storm sewers or open channels are entering the flow upstream of the sampling point, there must be sufficient distance between the last confluence point and the sampling point to get adequate mixing at the sample point. 4. Representativeness of the sample • Sampling from stagnant areas could result in low dissolved oxygen, which could affect WET results. • Sampling should be of the full cross section of flow to avoid biasing the sampling with excessive amounts of surface contaminants (e.g., sheens) or material from the pipe or channel bottom. Endpoint How Measured Mortality/Survival Number alive; number alive and dead Growth Dry weight, ash-free dry weight, length Reproduction Number of young per female Development Appearance (normal/abnormal, fertilized/not fertilized) Table B-1. Typical biological endpoints.

Field Conditions Fact Sheets B-19 WET Monitoring Sample Timing and Type The sample type (grab, composite), timing, and frequency require an understanding of the variation in flow rate and contaminant concentrations. For non-deicing runoff, peak contami- nant concentrations are most likely to occur early in a storm event as part of the first flush. For intense storm events, contaminant levels may subsequently rapidly decline. In deicing situations, first flush is less important because the flow rate and pollutant concentrations vary independently with many possible combinations. The objectives for the WET monitoring need to be defined prior to determining the sample type and timing. If the objective is to understand the impact of peak contaminant concentrations (e.g., if acute WET criteria are applied), then individual grab samples are needed. Grab samples can be collected either manually or with an auto-sampler in discrete sample mode. The likelihood of capturing peak concentrations (and potentially peak WET effects) is increased with an auto-sampler. If the objective is to understand longer-term impacts (e.g., if chronic WET criteria are applied), then a composite sampling system is needed. Flow-weighted composite sampling is most representative. If time-weighted composites are used, the results will likely be biased toward concentrations at low flow conditions. WET Analysis Lead-Time Requirements A monitoring plan for WET monitoring requires consideration of the lead time the testing laboratory needs to obtain and acclimate test organisms of the appropriate age or life stage prior to beginning the analysis. The lead time will depend on what tests are required. For example, with chronic growth tests using fathead minnows, silversides, and mysids, laboratories will need lead time to order larvae of a specific age from commercial test organism suppliers. In preparing for a chronic test of the daphnid, Ceriodaphnia, as much as a week of lead time may be needed because young stock less than 24 hours old are required to be obtained from brood boards on the day of testing. Other test types have differing lead-time requirements. Since samples must be used within 36 hours of the collection, time factors such as the shipping time for samples are important. Sample Replacement and Holding-Time Requirements Several of the chronic test protocols used in WET testing require 7-day exposure periods to allow for measurable growth or for reproduction of the test organisms to occur. Therefore multiple collections of samples are needed because holding-time requirements remain less than 36 hours from sample collection. Typically three separate sampling/shipping events are required for the 7-day chronic tests. This is usually possible where industrial or municipal effluent pro- cesses and flows are relatively constant, but it creates a significant problem for sampling of storm- water events including instances where deicing activities may be occurring. In these instances, it is critical for airport environmental personnel and the laboratories to interact closely. Test schedul- ing needs to rely heavily on accurate forecasting of major storm events and constant coordination between the airport and laboratory personnel. Another issue is that samples taken at 2- to 3-day intervals during severe weather events are highly unlikely to be similar with regard to toxicity characteristics. In such instances, it may be highly desirable to use only one sample for the entire testing process, a circumstance that would require timely approval by the regulatory entity requir- ing the monitoring event. WET monitoring requires close coordination between field personnel and the laboratory’s project manager for samples to arrive not only at the expected date and time, but also with the correct amount of sample at the required shipping temperature (0–6°C), and accompanied by an accurately filled out and signed chain-of-custody form. If any of these U.S. EPA requirements are not met, the likely result will be postponement of the monitoring and the incurring of addi- tional costs associated with repeating test initiation activities.

B-20 interpreting the Results of Airport Water Monitoring Key Steps in WET Analytical Testing Process An overall understanding of the WET analytical testing process at the laboratory can help the airport reduce the risk of non-representative test results and track potential sources of error after results have been received. At the laboratory, steps for performing toxicity tests involve (1) acquiring test organisms of an appropriate age from suppliers or from the laboratory’s own cultures, (2) carrying out any method-required acclimation of the organisms prior to initiating testing, (3) receiving sample on time and at the correct temperature, (4) initiating the test on day 0, (5) performing daily monitor- ing of test environmental conditions (e.g., temperature, dissolved oxygen, pH, salinity or specific conductance) in the exposure chambers and of required biological observations (e.g., mortalities), and (6) terminating the test after the required number of days of test exposure (commonly on day 7 of many of the chronic exposure tests). Following completion of the test exposure period, additional days are usually required for such final steps as (1) completing data collection measure- ments (e.g., dry weights of fish or mysids), (2) tabulating young produced in Ceriodaphnia tests, (3) enumerating fertilized eggs in echinoderm fertilization tests, and (4) enumerating normal/ abnormal larvae in the mollusk larval tests. Final steps involve performing required data analysis, report writing, and quality assurance (QA) review. WET Analysis Structure Test initiation typically involves the preparation of five or more dilutions of the effluent to be tested beginning with a 100% concentration and with lower concentrations typically forming a 50% geometric dilution series. The resultant test concentrations are 100%, 50%, 25%, 12.5%, 6.25%, and a 0% laboratory control. The laboratory control uses the same water employed to make the test dilutions. A lower range of test concentrations may be employed if toxicity is expected to be high. Some permits require the use of the ACEC (acute critical effluent concen- tration) or CCEC (chronic critical effluent concentration) as one of the test concentrations. Two test replicates may be used in acute tests where only an LC50 is to be determined. Typically four replicates of each test concentration and the control are used in chronic tests in order to permit later statistical calculation of no-observed-effect concentrations (NOEC). On day 0, after equilibration of test media to the test temperature and achieving dissolved oxygen saturation, organisms are added to each test vessel to initiate the test exposures. The number of organisms added to each vessel is typically 10, but may vary for different species tests. U.S. EPA-Approved WET Tests U.S. EPA-approved toxicity test protocols are found in a suite of four guidance manuals (Table B-2) consisting of an acute test manual (U.S. EPA, 2002a), a freshwater chronic manual (U.S. EPA, 2002b), a marine chronic manual (U.S. EPA, 2002c), and a West Coast chronic manual (U.S. EPA, 1995). The current suite of U.S. EPA-approved test methods can be found Manual Number Title of EPA Manual EPA 821-R-02-012 Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms (Fifth Edition,October 2002) EPA 821-R-02-013 Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms (Fourth Edition,October 2002) EPA 821-R-02-014 Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms (Third Edition, October 2002) EPA/600/R-95/136 Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to West Coast Marine and Estuarine Organisms (August 1995) Table B-2. List of current published U.S. EPA WET test manuals.

Field Conditions Fact Sheets B-21 in Table B-3. Some of these WET test methods are used extensively, while others are used only infrequently due, in part, to limited organism availability or to limited regional applicability. Of the approved tests, the most commonly employed for freshwater environments are acute and chronic versions of the water flea, Ceriodaphnia dubia, and the fathead minnow, Pimephales promelas. In marine environments, acute and chronic tests with inland silversides, Menidia beryllina, and the mysid shrimp, Mysidopsis (Americamysis) bahia, are most common. Larval tests using the marine mussel, Mytilus, and fertilization tests of sea urchins or sand dollars are also very commonly employed as chronic test methods. In addition to the common U.S. EPA test methods, certain regional tests are sometimes required by permitting agencies. An example of this is Washington State’s use of an in-situ trout embryo test in the Seattle-Tacoma International Airport permit requirement (Washington State Department of Ecology, 2014). Types of Effects Data Collected and Results Computations In acute toxicity tests, the computed endpoint is typically the concentration resulting in 50% mortality of the organisms (LC50 or median lethal concentration) at the time of test termina- tion. In the case of tests, such as the echinoderm fertilization test or molluscan larval test, where Freshwater Test Type Species Type Species Options EPA Manual Acute Invertebrate Ceriodaphnia dubia* (daphnid) Daphnia pulex & Daphnia magna (daphnids) EPA 821-R-02-012 Fish Pimephales promelas* (fathead minnow) Oncorhynchus mykiss (rainbow trout) Chronic Invertebrate Ceriodaphnia dubia* (daphnid) EPA 821-R-02-013 Fish Pimephales promelas* (fathead minnow) Plant Raphidocelis subcapitata (green alga) Marine Test Type Species Type Species Options EPA Manual Acute Invertebrate Americamysis bahia* (mysid shrimp, AKA Mysidopsis bahia) Holmesimysis costata* (mysid shrimp), specific to Pacific Coast waters EPA 821-R-02-012 Fish Cyprinodon variegtus* (sheepshead minnow) Menidia beryllina* (inland silverside) Menidia menidia (Atlantic silverside) Menidia peninsulae (tidewater silverside) Atherinops affinis* (Topsmelt) Chronic Invertebrate Americamysis bahia* (mysid shrimp, AKA Mysidopsis bahia) Arbacia punctulata (sea urchin) EPA 821-R-02-014 Holmesimysis costata* (mysid shrimp) Strongylocentrotus purpuratus (sea urchin) Dendraster excentricus (sand dollar), specific to Pacific Coast waters Mytilus spp. (mussel) Crassostrea gigas (Pacific oyster) Haliotis rufescens (red abalone) EPA/600/R-95/136 Fish Cyprinodon variegtus (sheepshead minnow) EPA 821-R-02-014 Atherinops affinis (Topsmelt) EPA/600/R-95/136 Plant Champia parvula (red macroalga) EPA 821-R-02-014 Macrocystis pyrifera (giant kelp) EPA/600/R-95/136 *These species can be used for both acute and chronic toxicity testing in a “dual endpoint” test where the chronic test protocols are used with additional information on survival at 48 or 96 hours to evaluate acute toxicity. Table B-3. WET test types, species, and methods.

B-22 interpreting the Results of Airport Water Monitoring the endpoint is failure to fertilize or for embryos to develop, respectively, the endpoint is referred to as a 50% effect level (EC50 or median effective concentration). The LC50 and EC50 are point estimates computed using a statistical method (e.g., probit, Trimmed Spearman–Karber). Although EC50s and LC50s can also be computed for chronic tests, the desired endpoint is typi- cally a NOEC and a lowest-observed-effect concentration (LOEC). The NOEC is the test con- centration in which the endpoint response is statistically the same as the control response and is computed using hypothesis test methods. The statistical comparisons used are those specified by U.S. EPA (2002a; 2002b; 2002c). An additional chronic endpoint in common usage is the 25% inhibitory concentration (IC25). Permitting agencies sometimes request that toxicity test results be submitted as toxic units (TUs), which vary directly rather than inversely with toxicity. Acute and chronic TUs are the reciprocal of the LC50 or NOEC, respectively, expressed as a percentage (e.g., TUa = 1/LC50 × 100; TUc = 1/NOEC × 100). Quality Assurance Review of Toxicity Studies A thorough laboratory QA review of every WET test is an essential component of an accept- able test. This review requires that the laboratory have a QA person who performs a QA review of its data before reporting. Prior to beginning the laboratory component of the study, the airport staff should provide the laboratory with a copy of their discharge permit so that the laboratory QA person can check that the required species/method, endpoints, statistical analysis, and defi- nitions of toxicity or failure to meet limits will be used. In the QA process, the laboratory QA person verifies all data entry including the age of test organisms; the number of replicates; the test concentrations used; whether water quality parameters were within recommended ranges; that the reference toxicant test results are within control chart limits or, if not, whether it is due to lab error or statistical chance; and that the results are reported accurately. Recommendations for Airport Review of Laboratory WET Analysis Reports The reporting of aquatic toxicity test results may take the form of a simple printout of the analytical software or a narrative report with appended test details. The narrative report with appendices is the preferred option, because it permits a complete QA review by an independent third party, and should include the following standard information: • Name and identification of the test including a reference to the test protocol or test method • The name(s) of the investigator(s) and laboratory • Information on the sample(s) including date(s) of receipt, the type of sample, and storage information with all chain-of-custody records appended • Information on the test or dilution water • Information about the test organisms including source and acclimation or culture conditions • Description of the experimental design, test chambers, and other test conditions • Information about any aeration that may have been required • Definition of the effect criteria and other observations • Responses, if any, in the control treatment • Tabulation and statistical analysis of measured responses • A description of the statistical methods employed and the software used for computation • Any unusual information about the test and a full description of any deviations from procedures • The results of associated reference toxicant tests including a control chart assessment of the reference test result (usually in an appendix) The report should contain a test method summary and a copy of the laboratory’s raw data, including the reference toxicant test results. It is recommended that airport staff review the test reports and verify that all of the above items are present. Airport staff should request verification

Field Conditions Fact Sheets B-23 from the laboratory that the following conditions have been met and any deviations have been noted along with their effect on the acceptability of the test: 1. Samples have been held from 0°C to 6°C from the time of collection until used in the toxicity test, and holding times should not exceed 36 hours. 2. Daily measured temperatures were within the method-specified range (usually ± 1°C) of the method temperature and did not deviate more than 3°C throughout the test. 3. Daily measured dissolved oxygen concentrations were greater than 4.0 mg/L or less than 6.0 mg/L for warm or cold water species, respectively. 4. Water quality measurements were taken throughout the test as required by the method. 5. The age and number of test organisms and number of test replicates at test initiation were as required by the method, and organisms were properly acclimated. 6. Test solutions were renewed at least every 48 hours to avoid excessive waste product concen- trations in the test solutions. 7. End of test control survivals were at least 90% in acute tests, including reference toxicant tests, and as specified for chronic tests by the U.S. EPA method. For chronic tests, in addition to required control survival responses, control performance requirements relating to the non- lethal endpoints of interest, such as minimum larval size achieved in fish tests or minimum reproductive success in Ceriodaphnia tests at the conclusion of the tests, were met. 8. If toxic effects are observed at the conclusion of a test, a normal dose response should be observed where highest effects are observed at the highest test concentrations. 9. The latest reference toxicant test results, whether run concurrently or on a monthly schedule, should show a result for the appropriate endpoint that is within ± 2 standard deviations of the mean of the last 20 tests performed (on average one out of every 20 tests will fall out of this range). Control charts should be included with the reference toxicant test data to document that control chart limits were achieved. As further assurance that the test achieved acceptable results and was performed in complete compliance with the U.S. EPA protocols, airport staff should verify that the report contains a QA statement to that effect and that the report is signed by the study director/project manager, a representative of the laboratory’s QA unit, and laboratory management. Variations and Sources Airport stormwater runoff can be a source of toxicant exposure to aquatic organisms inhabit- ing receiving water bodies. Potential sources of toxicity in airport stormwater discharges include deicers, pollutants from vehicle cleaning, fuel, pollutants from air and ground vehicle operations and maintenance, herbicides, and pesticides. The composition of airport stormwater is typically erratic in constituent type and concentration because of variability in the industrial activities, as well as the timing and intensity of storm events. The likelihood that constituents from these sources cause toxicity to aquatic life is dependent upon constituent concentration and ambient conditions. If WET testing reveals that toxicity thresholds have been exceeded, further testing and evalu- ation of sources of the toxicity is typically required. This may include toxicity identification evaluation (TIE) and toxicity reduction evaluation (TRE) processes. Toxicity Reduction Evaluation Airport NPDES permits that contain a WET testing requirement typically include a require- ment to prepare a TRE work plan to be ready to respond to toxicity events. If a toxicity trigger is subsequently exceeded, the airport may be required to initiate the TRE program until it can

B-24 interpreting the Results of Airport Water Monitoring be demonstrated that the toxicity no longer occurs. The objective of the TRE is to determine those actions necessary to reduce the effluent’s toxicity to acceptable levels. U.S. EPA’s guidance manual (1989) for conducting a TRE identifies six sequential steps or tiers: 1. Initial data and information acquisition (Tier I) 2. Evaluation of remedial actions to reduce final effluent toxicity (Tier II) 3. Toxicity identification evaluation (TIE) (Tier III) 4. Identification of the source(s) of the toxicity in the facility (Tier IV) 5. Toxicity reduction approaches (Tier V) 6. Follow-up and confirmation that toxicity was reduced to acceptable levels (Tier VI) The first step in the TRE process is to acquire essential data and facility-specific information such as the following: • The regulatory events leading to the requirement for conducting a TRE • The monitoring data for other parameters, which may provide specific information on the possible causes of toxicity of the regulated discharge • Site-specific conditions such as various airport activities that may provide clues as to the causes and sources of toxicity. In the second step of the TRE process, possible remedial actions that may optimize the opera- tion of the facility to reduce toxicity are explored, and, where appropriate, remedial actions are taken. Possible remedial actions may include the following: • General housekeeping • Changes to airport operations • Modification to selection and use of process and treatment chemicals Toxicity Identification Evaluation If toxicity is reduced to acceptable levels, only further monitoring is needed to confirm that the toxicity problem has been resolved. If it is not, the study will proceed into a TIE. The TIE involves identification of specific causal agents of toxicity. Although possible toxicants may have been identified in the TRE, the actual conduct of the TIE is required in order to more definitively identify the actual toxicant or toxicants. Conducting a TIE is complicated for airports because of the high variability of discharge volumes and pollutant sources over time. The purpose of a TIE is to identify the toxic agent(s) in an effluent or discharge source to support corrective actions. TIEs of aqueous discharges typically involve a three-phase approach: • A Phase I TIE study involves characterization and asks the question, “what classes of toxi- cants are causing the observed effluent toxicity?” The Phase I approach involves subjecting the toxic effluent or aqueous phase to a number of discreet physical and chemical treat- ments such as aeration, filtration, exposure to chelating or reducing agents, pH adjustment, and solid phase extraction followed by comparing the residual toxicity after each treatment to a baseline value (U.S. EPA, 1991). In this way initial judgments can be made about whether the toxicants are volatile, filterable, subject to chelation, reducible, pH sensitive, or non-polar. • A Phase II TIE study is intended to identify the specific toxicants. Depending on which chemical class of toxicant is identified in the Phase I study, the Phase II approach relies on more complex chemical separations and analyses leading to a tentative specific identification of the toxicant or toxicants. While even smaller toxicity testing laboratories are usually capable of performing Phase I TIE studies, Phase II studies may require a team approach consisting of a sophisti- cated environmental chemistry laboratory in addition to a toxicity testing laboratory. Suggested

Field Conditions Fact Sheets B-25 approaches for the identification of various chemical classes are discussed in detail in U.S. EPA’s Phase II TIE manual (U.S. EPA, 1993a). • A Phase III TIE study includes application of methods for confirming the identity of the toxicants (U.S. EPA, 1993b). Airport staff need to be aware that the TIE process may require substantial preparation, and, as a result, close coordination with the laboratory’s project manager is required. Because toxic events may be highly ephemeral, the laboratory must be prepared to carry out all steps of a Phase I TIE using a single sample. Because of toxicant aging issues, the process must be carried out in as short a time frame as possible. It may also be desirable to store enough sample to permit at least some Phase II and Phase III studies. To add even more difficulty, it is understood that airport sampling will also likely need to be closely tied to extreme weather events as well. References Newfields Environmental & Engineering LLC; The Smart Associates; Environmental Consultants, Inc.; and Maryland Environmental Service (2015). ACRP Report 134: Applying Whole Effluent Toxicity Testing to Air- craft Deicing Runoff. Washington D.C.: Transportation Research Board. U.S. EPA (1989). Generalized Methodology for Conducting Industrial Toxicity Reduction Evaluations (TREs). EPA-600-2-88-070. Cincinnati, Ohio. U.S. EPA (1991). Methods for Aquatic Toxicity Identification Evaluations: Phase I Toxicity Characterization Procedures. EPA-600-R-91-003, 2. U.S. EPA (1993a). Methods for Aquatic Toxicity Identification Evaluations: Phase II Toxicity Identification Pro- cedures for Samples Exhibiting Acute and Chronic Toxicity. EPA-600-R-92-080. U.S. EPA (1993b). Methods for Aquatic Toxicity Identification Evaluations: Phase III Toxicity Confirmation Procedures for Samples Exhibiting Acute and Chronic Toxicity. EPA-600-R-92-081. U.S. EPA (1995). Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to West Coast Marine and Estuarine Organisms. EPA/600/R-95/136. Washington D.C.: U.S. EPA, Office of Water. U.S. EPA (2002a). Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms, Fifth Edition. EPA 821-R-02-012. Washington D.C.: U.S. EPA, Office of Water (4303T). U.S. EPA (2002b). Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Fresh- water Organisms, Fourth Edition. EPA 821-R-02-013. Washington D.C.: U.S. EPA, Office of Water (4303T). U.S. EPA (2002c). Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms, Third Edition. EPA 821-R-02-014. Washington D.C.: U.S. EPA, Office of Water (4303T). Washington State Department of Ecology. (2014). NPDES Permit No. WA0024651, Seattle-Tacoma International Airport Draft Permit 2014-09-30. 93. Acronyms Used in WET Testing DO Dissolved oxygen EC Effects concentration (e.g., EC50) IC Inhibitory concentration (e.g., IC25) LC Lethal concentration (e.g., LC50) LOEC Lowest-observed-effect concentration NOEC No-observed-effects concentration NPDES National Pollution Discharge Elimination System RPD Relative Percent Difference RSD Relative Standard Deviation QA Quality Assurance QC Quality Control TIE Toxicity Identification Evaluation TRE Toxicity Reduction Evaluation TU Toxic unit

B-26 interpreting the Results of Airport Water Monitoring Glossary of WET Terms Action limit: The limit on a control chart, which, if exceeded, requires corrective action to be taken. Action limits are usually placed at ± 3 standard deviations from the mean value. Acute: Having a sudden onset, lasting a short time. The duration of an acute toxicity test is generally 4 days or less and mortality is the response measured. Chronic: Involving a stimulus that is lingering or continues for a long time; for clarity, the length of the exposure and the nature of the effect endpoint should be specified. Composite sample: A composite sample is one where multiple temporally or spatially discrete, effluent or stormwater samples are combined, thoroughly mixed, and treated as a single sample. Control (or negative control): A treatment in a toxicity test that duplicates all the conditions of the exposure treatments but contains no test material. The control is used to determine the absence of toxicity of basic test conditions (e.g., health of test organisms, quality of dilution water). Control chart: A graphical presentation of quality control (QC) results indicating whether the measurement system (toxicity test) remains in statistical control. Control limits: Statistical warning and action limits calculated for control charts, used to make decisions on acceptability of QC results. Warning limits are usually established at 2 standard deviations above and below the mean of repeated analyses. Action limits are established at 3 standard deviations. Dilution water: Water used to dilute the test material in an aquatic toxicity test in order to prepare either different concentrations of a test chemical or a different percentage of an effluent for the various test treatments. The water (negative) control in a test is prepared with dilution water only. Effluent: A complex water material (e.g., liquid industrial discharge or sewage) that may be discharged into the environment. Endpoint: In toxicity testing and evaluation, it is the adverse biological response in question that is measured (e.g., mortality or survival, growth, reproduction). Grab sample: A discrete sample from a single point in the water column or sediment surface. Holding time: The allowed time from when a sample was taken or collected until the toxic- ity test must be started. For composited effluent samples, the holding time starts when the last composite aliquot is collected. Inhibition concentration (IC): A point estimate of the effluent or test material that would cause a given percent reduction (e.g., IC25) in a non-lethal biological measurement of the test organism, such as growth or reproduction. Lowest-observed-effect concentration (LOEC): The lowest concentration of a substance in a toxicity test having a statistically significant difference from a non-toxic control. The LOEC is an approximation of the toxic threshold for that substance. Because only the concentra- tions used in the toxicity test are available to be the LOEC, the closeness of the LOEC to the true toxic threshold depends on the number and distribution of the concentrations used in the toxicity test. Median effective concentration (EC50): The concentration of material in water to which test organisms are exposed that is estimated to be effective in producing some (defined) sub-lethal response in 50% of the test organisms. The EC50 is usually expressed as a time-dependent value (e.g., 24-hour or 96-hour EC50).

Field Conditions Fact Sheets B-27 Median lethal concentration (LC50): The concentration of a material in water that is esti- mated to kill 50% of the test organisms. The LC50 is usually expressed as a time-dependent value (e.g., 96-hour LC50; the concentration estimated to be lethal to 50% of the test organ- isms after 96 hours of exposure). Method: A formalized group of procedures and techniques for performing an activity (e.g., toxicity test), systematically presented in the order in which they are to be executed. No-observed-effects concentration (NOEC): The highest concentration of a substance in a toxicity test not having a statistically significant difference from a non-toxic control. The NOEC is an approximation of the safe concentration for that substance. Because only the concentra- tions used in the toxicity test are available to be the NOEC, the extent to which the NOEC is lower than the true safe concentration depends on the number and distribution of the concen- trations used in the toxicity test. Parameter: Water quality constituent being measured (e.g., temperature or pH). A parameter is a physical, chemical, or biological property whose values determine environ- mental characteristics or behavior. Point estimate: Point estimates, such as the LC50, IC25 or EC15, are derived from toxic- ity test results to represent the concentration of the toxic substance that would cause a percent reduction equal to the specified effect level. For example, the LC50 is usually described as the concentration predicted to cause 50% mortality in a population of the test organisms. The IC25 estimates the concentration that would cause a 25% reduction in growth or reproduction. A point estimate is not really a single number but a range within which there is 95% confidence that the true value occurs. Precision: A measure of the variability in the results of replicate measurements caused by random error. Precision is usually measured as standard deviation, relative standard deviation (RSD), or relative percent difference (RPD). Quality assurance (QA): A set of activities designed to establish and document the reliability and usability of measurement data. A program organized and designed to provide accurate and precise results. Included are selection of proper technical methods, tests, or laboratory proce- dures; sample collection and preservation; selection of limits; evaluation of data; quality control; and qualifications and training of personnel. Quality control (QC): Specific actions and tools required to provide information for the qual- ity assurance program. These include standardization, calibration, replicates, and control (nega- tive and positive) and check samples (e.g., reference sediments) suitable for statistical estimate of confidence of the data. Random error: Variability in the results of replicate measurements. This variability is because the size and magnitude of the difference between replicate results vary at random and not in any systematic way. Relative percent difference (RPD): The difference between results of duplicate analyses divided by the mean and expressed as a percentage. Relative standard deviation (RSD): The standard deviation of repeated measurement results divided by the mean and expressed as a percentage. Reference toxicant (or positive control): A chemical used in an aquatic toxicity test as a positive control (i.e., deliberately causes known adverse effects) in contrast to the negative control provided by exposure water without the test chemical. Information collected is used to determine the general health and viability of the test organisms and assess consistency in testing protocol implementation.

B-28 interpreting the Results of Airport Water Monitoring Standard: A solution of known and documented concentration, either a check or control standard, or a calibration standard that is used to prepare a calibration curve. Standard deviation: A statistic that describes the random variability in results of repeated measurements. Statistical significant effects: Effects (responses) in the exposed population that are different from those in the controls at a given statistical probability level, typically p ≤ 0.05. Biological endpoints that are important for the survival, growth, behavior, and perpetuation of a species are selected as criteria for effects. The endpoints differ depending on the type of toxicity test conducted and the species used. The statistical approach also changes with the type of toxicity test conducted. Stormwater: The portion of precipitation that does not naturally percolate into the ground or evaporate but instead runs off roads, pavement, and roofs during rainfall or snow melt. Storm- water can also come from hard or saturated grass surfaces such as lawns, pastures, and playfields and from gravel roads and parking lots. Systematic errors: Errors that cause measurement results to be consistently greater or smaller than the true value. Usually bias can be considered to be equivalent to systematic error. Toxicity identification evaluation (TIE): A set of procedures to identify the specific chemicals responsible for the toxicity of effluents (or sediments). Toxicity reduction evaluation (TRE): A site-specific study conducted in a step-wise process designed to identify the causative agents in a toxic effluent (or sediment), isolate the sources of toxicity, evaluate the effectiveness of toxicity control options, and then confirm the reduction in effluent toxicity. Toxicity test: The means by which the toxicity of a chemical or other test material is deter- mined; measures the degree of response produced by exposure. Toxic unit (TU): A toxic unit is a unit of measure for effluent toxicity. It is not a percentage. The major advantage of using toxic units to express toxicity test results is that they increase as the toxicity increases. A TU of 4.00 is twice as toxic as a TU of 2.00. (The LC50 and IC25 are just the opposite; a higher LC50 is less toxic than a lower LC50.) TUa is used for acute tox- icity and TUc is used for chronic toxicity. TUa is derived by dividing 100 by the concentration of effluent which is lethal to 50% of the animals, the LC50 (TUa = 100/LC50). TUc is frequently derived by dividing 100 by the no-observed-effect concentration (TUc = 100/NOEC). Whole effluent toxicity (WET): The total toxic effect of an effluent measured directly with aquatic organisms in a toxicity test.

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TRB's Airport Cooperative Research Program (ACRP) Research Report 166: Interpreting the Results of Airport Water Monitoring provides comprehensive guidance and a set of tools that operators of airports of varying sizes can use to understand, diagnose, and interpret airport water quality. This guidebook addresses water leaving the airport that does not go to an off-site treatment facility. Accompanying the report are the following tools to assist practitioners in diagnosing root causes and possible sources of specific problems that may require attention or mitigation:

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