Interpreting the Results of Airport Water Monitoring (2017)

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123 Accuracy – A measure of the closeness of an individual measurement or the average of a number of measurements to the true value. Accuracy includes a combination of random error (precision) and systematic error (bias) components that are due to sampling and analytical operations; the U.S. EPA recommends using the terms “precision” and “bias,” rather than “accuracy,” to convey the information usually associated with accuracy (U.S. EPA, 1998). Aliquot – Individual volumes of sampled water that together constitute the full sample to be analyzed. Analysis – A quantitative measurement of the physical or chemical characteristics of the water being monitored. Includes laboratory analysis and field analytical methods [e.g., test kits, data sondes, handheld water quality meters, biochemical oxygen demand (BOD) monitors]. Does not include qualitative observations. Benchmark – Numeric threshold for pollutant quantity (typically concentration or mass load) in a water discharge permit often used as an indicator of pollutant control measure performance. Exceedance of a benchmark is not, in itself, typically a violation of the permit but often triggers corrective actions by the permittee. Bias – The systematic or persistent distortion of a measurement process, which causes errors in one direction (i.e., the expected sample measurement is higher or lower than the sample’s true value) (U.S. EPA, 1998). Composite sample – A sample composed of individual aliquots of water collected over a period of time. Samples may be time weighted (collected at set intervals) or flow weighted (collected when a volume of water passes the sample location). Data analysis – The process of summarizing data using statistical quantities and graphics to assist in the interpretation and application of monitoring results. Descriptive statistic – A quantity computed from the data to describe or summarize the data. Example descriptive statistics include the mean, median, and standard deviation. Detection limit – The minimum concentration of a pollutant that a laboratory can measure and report with a 99 percent confidence that its concentration is greater than zero as determined by a specific laboratory method. Effluent limitation – Any quantitative, “not-to-exceed” restriction on quantities, discharge rates, and concentrations of pollutants discharged from point sources into waters of the United States. Exceedance of the numeric effluent limitation in a discharge permit typically constitutes a permit violation. Grab sample – Single aliquot of sample that is collected at one point in time. Glossary

124 Interpreting the Results of Airport Water Monitoring Metadata – Information that describes the contents and context of the data. Monitoring – Process of quantifying physical and chemical characteristics of water. Includes observation of conditions as well as sampling and analysis processes. Monitoring driver – Requirement or objective that creates or fuels the need to monitor water characteristics. Drivers can be considered as the reasons that monitoring is needed. Monitoring method – The process by which the analytical measurements of selected monitoring parameters are obtained. For purposes of the guidebook, methods include laboratory analytical processes performed off-site, as well as on-site analytical processes performed by test kits, online monitors, and handheld devices. Monitoring types – Refers to the integrated process by which samples are collected and analyzed. Includes off-site types (i.e., manual or automatic sample collection for off-site analysis by a labora- tory), and on-site types (i.e., sampling and analysis with test kits at the airport, analysis on con- tinuous flowing sample streams with online monitors, and insertion of handheld monitors into the sample or stream). National Pollutant Discharge Elimination System (NPDES) – U.S. EPA’s program for permit- ting point source discharges to waters of the United States. National Pretreatment Program – A component of the NPDES program that requires industrial and commercial dischargers, called industrial users, to obtain permits or other control mecha- nisms to discharge to publicly owned treatment works. Observations – Qualitative judgment of stormwater characteristics and ambient conditions made in the field at the time of sampling. Includes characteristics observed by visual means (e.g., color, sheen, foam, biofilm, flow regime) as well as odor. This type of monitoring may be explicitly required by discharge permits, in addition to or in place of sampling and analysis, as an indicator of potential water quality issues. Off-site monitoring – Collecting samples and sending them to an analytical laboratory for analysis. Online monitor – Permanently mounted instruments and systems designed to regularly sample flow streams and analyze the samples local to the water source without direct involvement of facility staff. Online monitoring is a form of on-site monitoring. On-site monitoring – Collecting and analyzing samples at the airport or directly measuring parameters in the stream. Includes online monitoring, sampling with quantitative analysis using off-line instruments at the airport, and direct-measurement devices (e.g., pH probes). Parameter – Stormwater characteristic that is targeted for monitoring. In the context of this guidebook, monitoring parameters include physical properties that may be measured in the field (e.g., flow rate, temperature), qualitative characteristics that may be manually observed in the field (e.g., sheen, odor), and chemical components that may be analyzed in the field or laboratory (e.g., BOD, zinc). Precision – A measure of mutual agreement among individual measurements of the same prop- erty, usually under prescribed similar conditions expressed generally in terms of the standard deviation (U.S. EPA, 1998). Probability distribution – A theoretical or empirical description of the frequency or proba- bility of various parameter quantities. Common theoretical distributions for water resources data are the Gaussian (or normal) distribution, the lognormal distribution, exponential, and gamma.

Glossary 125 Quantitation limit – The level at which a laboratory can reliably report concentrations with a specified level of error. Random error – Unknown or unpredictable changes in the measuring instrument or the envi- ronmental conditions or variables that may affect measured quantities. Representativeness – A qualitative term that expresses the degree to which data accurately and precisely represents a characteristic of a population. Root cause analysis – A process to identify and evaluate the fundamental cause of an undesirable condition or issue. Sampling – Collection of a specific size stormwater aliquot at a specific location and specific time, for the purpose of analysis. Includes manual sample collection, use of auto-samplers, and use of online samplers. Supervisory control and data acquisition (SCADA) system – Used in online computer-based management of stormwater controls to process data inputs from monitoring instruments, pro- vide feedback to system equipment, and provide graphic data to system operators. Stormwater – Precipitation runoff, including rain and snowmelt. Stormwater can also include baseflow contributions from groundwater and off-site runoff. Surrogate – A parameter that is measured in place of another parameter. An empirical or theo- retical relationship must exist between the two parameters such that the surrogate parameter’s measured monitoring value can be used to estimate the desired parameter concentration. Stormwater pollution prevention plan (SWPPP) – Alternatively referenced as stormwater pollution control plan (SWPCP) in some areas. Required to be developed as part of NPDES permit compliance. Often details potential pollutant sources in specific airport drainage areas. Systematic error – Also referred to as bias, is caused by consistently high or low values reported by an instrument or analyst due to a variety of potential issues, such as device malfunction, cali- bration errors, inexperience, or incorrect application of monitoring protocols. Technology-based effluent limit – Discharge limits established as part of the NPDES program based on the ability of dischargers in the same industrial category to treat discharges using the best available technology economically achievable. Total Maximum Daily Load (TMDL) – A regulatory mechanism for allocating pollutant loadings to individual discharges in a watershed to address impairments to the receiving stream that prevent the water body from meeting its designated uses. Water quality-based limit – Discharge limits established as part of the NPDES program to protect the quality of the local receiving water.