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Interpreting the Results of Airport Water Monitoring (2017)

Chapter: Chapter 1 - Acquiring Monitoring Data

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Suggested Citation:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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:"Chapter 1 - Acquiring Monitoring Data." 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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16 C h a p t e r 1 1.1 Introduction A multitude of consequential decisions are made at airports based on interpretation and application of water monitoring data. The soundness of the decisions is directly related to the data accuracy and data representativeness. While questionable data can be analyzed to tease out understanding of errors or anomalies, it is far more productive to establish a strong foundation for the initial data acquisition. As such, the guidance in this document regarding the interpretation and application of monitoring data (Chapters 2 and 3, respectively) is built upon the premise that steps have been taken to initially acquire an accurate and representative data set. This chapter provides guidance on establishing a sound process for initially acquiring monitoring data. Acquiring Monitoring Data Topical Tips Guidelines for Initial Water Monitoring Data Acquisition • Establish a clear understanding of the drivers and objectives for acquiring the monitoring data. • Select parameters that appropriately represent the pollutants and water char- acteristics for the specific application situation. • Collect data from monitoring locations that are representative of the water to be characterized. • Monitor at an appropriate frequency and extent to meet the monitoring goals while considering budgetary restrictions and practical implementation issues. • Develop consistent and appropriately detailed sampling procedures that mini- mize error. • Provide observations on ambient conditions at the time of sampling. • Prepare thorough and consistent documentation of the sampling, analytical, and evaluation process. • Emphasize targeted communication to appropriate stakeholders. Personnel involved in monitoring programs can review this chapter and ask themselves questions regarding the strength and completeness of their own water monitoring data acquisi- tion plans. By strengthening the fundamental data acquisition programs, all users will have an increased degree of confidence when interpreting and applying the monitoring data.

acquiring Monitoring Data 17 The information in this chapter can also be referenced when issues with the data accuracy and representativeness arise in day-to-day activities. For example, personnel often become aware of monitoring data issues when in the midst of activities such as development planning, infrastruc- ture design, stormwater management system operations, or non-compliance response. In these situations, the information in this chapter should be consulted, and the data acquisition process re-examined, for the purpose of avoiding such mistakes in the future. Figure 8 lists the key concepts in this chapter. In the electronic version of this document, hyperlinks to the referenced sections are provided. Key terms used in this chapter are provided in the next section. 1.2 Terminology Critical to Acquiring Monitoring Data A variety of terms are used in reference to stormwater monitoring data acquisition at air- ports, including terms related to monitoring approaches, objectives, field activities, samples, and equipment. Although many of these terms are used interchangeably by airport staff and 1.4 Dening Monitoring Parameters • 1.4.1 Using Potential Pollutant Sources to Identify Parameters • 1.4.2 Typical Monitoring Parameters • 1.4.3 Sample Collection Method • 1.4.4 Monitoring Types • 1.4.5 Factors Influencing Monitoring Parameter, Sample Collection Method, Monitoring Type, and Monitoring Method Selection 1.8 Collecting, Reporting, and Maintaining Data • 1.8.1 Effective Collection of Data to Facilitate Review of Results • 1.8.2 Compilation and Management of Results to Support Interpretation of Data • 1.8.3 Understanding Requirements for Reporting Results 1.7 Executing Monitoring • 1.7.1 Field Activity Execution • 1.7.2 Documentation of Field Conditions • 1.7.3 Event-Based Monitoring Execution • 1.7.4 Continuous Monitoring Execution • 1.7.5 Monitoring Efficiently to Reduce Costs and Save Time 1.5 Identifying Monitoring Locations • 1.5.1 Objectives for Selecting Monitoring Locations • 1.5.2 Selection of a Representative Location • 1.5.3 Potential Limitations of Monitoring Locations 1.6 Selecting Monitoring Frequency and Extent • 1.6.1 Monitoring Frequency • 1.6.2 Monitoring Extent 1.3 Identifying Drivers and Objectives for Monitoring • 1.3.1 Regulatory-Required Routine Monitoring • 1.3.2 Monitoring Not Directly Prescribed in Discharge Permits Figure 8. Key concepts for the acquisition of water monitoring data.

18 Interpreting the results of airport Water Monitoring consultants, they are uniquely defined in this section to facilitate a consistent understanding of the detailed concepts presented herein. Additionally, the glossary at the end of this guide- book provides definitions for a variety of other terms that are relevant to overall guidebook content. 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. Environmental Protection Agency (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 indicator of pollutant control measure perfor- mance. 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 (col- lected when a volume of water passes the sample location). 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. 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 moni- toring parameters are obtained. For purposes of this 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 ana- lyzed. Includes off-site types (i.e., manual or automatic sample collection for off-site analysis by a laboratory) and on-site types (i.e., sampling and analysis with test kits at the airport, analysis on continuous flowing sample streams with online monitors, and insertion of handheld moni- tors into the sample or stream).

acquiring Monitoring Data 19 MS4 – Municipal separate storm sewer system. MSGP – Multi-sector General Permit for Stormwater Discharges Associated with Industrial Activity. National Pollutant Discharge Elimination System (NPDES) – U.S. EPA’s program for per- mitting point-source discharges to waters of the United States. National Pretreatment Program – A component of the NPDES program that requires indus- trial and commercial dischargers, called industrial users, to obtain permits or other control mechanisms to discharge to the 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 sam- ple 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 mea- suring 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 labora- tory (e.g., BOD, zinc). Precision – A measure of mutual agreement among individual measurements of the same property, usually under prescribed similar conditions expressed generally in terms of the stan- dard deviation (U.S. EPA, 1998). 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 autosamplers, and use of online samplers. 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 empiri- cal or theoretical relationship must exist between the two parameters such that the surro- gate parameter’s measured monitoring value can be used to estimate the desired parameter concentration. Technology-based effluent limit – Discharge limits established as part of the NPDES pro- gram based on the ability of dischargers in the same industrial category to treat discharges using the “best available technology economically achievable.” Water quality-based limit – Discharge limits established as part of the NPDES program to protect the quality of the local receiving water.

20 Interpreting the results of airport Water Monitoring 1.3 Identifying Drivers and Objectives for Monitoring Water quality monitoring supports a variety of regulatory compliance, environmental, or facility management objectives. The purpose for monitoring can be understood by considering the water monitoring “drivers.” A driver represents an impetus for action. Filling in the blank to the statement “I need to collect water monitoring data because ____” with phrases like “my permit requires it” or “I’m concerned with how the treated effluent concentrations have been trending the last month” is a simple, yet effective means for focusing water monitoring activities. Topical Tips Common Steps in the Process of Defining Water Monitoring Drivers • Examine applicable regulations and permits. • Seek to understand the pollutants causing issues. • Research parameters used to describe the identified pollutants. • Review potential sources of pollutants to help identify monitoring locations. • Assess the likely variability in pollutant concentrations as conditions change. Airport personnel can better understand the drivers and more effectively determine the nature and extent of the selected monitoring activities by going through the process of defining water monitoring drivers further described in the following sections. Guidebook users are encouraged to apply these general considerations for monitoring drivers to their site-specific situations and document the water monitoring drivers as part of water monitoring plans. 1.3.1 Regulatory-Required Routine Monitoring Regulatory-required routine monitoring activities are those performed in accordance with requirements that are explicitly prescribed within a permit or other regulatory documents such as a notice of violation or consent order. Environmental regulations and associated site-specific water discharge permits are the most common drivers for water monitoring. Understanding the broadly applicable regulations, permits, orders, and agreements is the first step toward identify- ing regulatory-required drivers. Guidebook users will need to further research their situation-specific regulations and permits to appropriately understand each unique monitoring situation. Overview of Applicable U.S. Regulations The federal Water Pollution Control Act amendments of 1972 and subsequent amend- ments, known as the Clean Water Act (CWA), establish the structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. Through Section 402 of the CWA, the National Pollutant Discharge Elimination System (NPDES) was created as a system for permitting point-source discharges to waters of the United States. Point sources are discrete conveyances, such as pipes or man-made ditches, and include stormwater contaminated with pollutants from industrial activities and treated wastewater. The NPDES permit program requires that point-source dischargers of pollutants to waters of the United States (i.e., direct dischargers) obtain NPDES permit coverage. The U.S. EPA has autho- rized regulatory agencies in most states to administer their NPDES programs, but there are four states, several U.S. territories, and the District of Columbia for which the U.S. EPA retains this authority and issues NPDES permits to all direct dischargers. For more information about U.S. regulations and deicing parameters, see: ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials ACRP Report 99: Guidance for Treatment of Airport Stormwater Containing Deicers

acquiring Monitoring Data 21 Direct Discharges. Airports that directly discharge stormwater runoff into surface waters from areas with industrial activities or from areas with certain construction sites that are exposed to stormwater are required to obtain coverage under one of two types of NPDES permits: • An applicable general NPDES permit. • An individual NPDES permit issued specifically for their facility. General NPDES permits cover many facilities that have similar operations or similar types of discharges, whereas individual NPDES permits are issued based on site-specific activi- ties or discharges and receiving water considerations. General NPDES permits typically have requirements to implement control measures to minimize pollution and may or may not have specific numeric effluent limitations. U.S. EPA developed a Multi-sector General Permit for Stormwater Discharges Associated with Industrial Activity (MSGP) and a Con- struction General Permit for stormwater discharges from construction activities and many states have adapted general permits modeled after these U.S. EPA permits. These permits are applicable to states and territories that are not authorized to implement the NPDES program. States which have been delegated NPDES regulatory authority can issue their own general permits, although most closely resemble U.S. EPA’s MSGP and Construction General Permit. The most recent U.S. EPA MSGP (2015) includes sector-specific require- ments that apply to air transportation facilities and, specifically, to discharges from airfield and aircraft deicing activities. States may also apply non-sector-driven statewide conditions in general permits. Individual NPDES permits are typically required when the state agency believes there is a reasonable potential for violation of water quality standards in the receiving water body as a result of the airport’s stormwater discharges. Individual NPDES permits typically have specific numeric effluent limitations for one or more pollutants. Exceedance of efflu- ent limits constitutes a permit violation. Effluent limits in NPDES permits are established in one of two ways: water quality-based limits (based on the water quality criteria and conditions of water bodies receiving the stormwater discharges) or technology-based lim- its (based on a treatment technology that is considered appropriate for dischargers in the same industrial category). If both technology-based limits and water quality-based limits are applicable for a given parameter, the most restrictive of the limits is incorporated into the permit. U.S. EPA or the authorized state agency will determine whether an airport is required to obtain a general or individual NPDES permit. As do general permits, a typical individual NPDES permit for an airport will include requirements that appropriate control measures be implemented and that a stormwater pollution prevention plan (SWPPP) be prepared and implemented. Water Quality-Based Limits. Water quality-based effluent limits are developed to ensure that the permitted discharge will not result in an exceedance of in-stream water quality criteria applicable to the receiving water body. In-stream water quality criteria are developed by the regulatory agency based on the quality of water needed to sustain the designated uses of the waterbody and prevent degradation of the waterbody. Effluent limits are often derived from wasteload allocation calculations that factor in existing upstream pollutant concentrations and the corresponding water quality criteria applicable downstream of the discharge. Permit effluent limits can also be derived by regulatory authorities from the total maximum daily load (TMDL) assessment process. A TMDL is developed when a stream is determined to be impaired, meaning it cannot meet its beneficial use designation because of effects of pollut- ants. The agency provides allocations to individual dischargers in the affected stream water- shed for the maximum load or concentration of specific pollutants that can be discharged. TMDL-derived effluent limits can be applied for parameters that do not have a corresponding Understanding the regula- tory source for effluent limits, benchmarks, and monitoring requirements in permits helps interpretation of the monitoring results. For more information about how to determine if your airport is subject to impaired waters monitoring requirements, see: U.S. EPA Industrial Storm­ water Monitoring and Sampling Guide

22 Interpreting the results of airport Water Monitoring water quality standard. They can also be more restrictive than the limits would be if only water quality standards are applied. Technology-Based Limits. Regulations under the CWA direct the U.S. EPA to develop treatment technology-based effluent limits for certain groups of industrial facilities (“catego- ries”) that are similar in their activities or the nature of wastewater generated. The limits apply to all industries within the same category regardless of their location in the United States. Tech- nology-based limits are integrated into the facility’s NPDES permit by the governing agency’s permit writer and are based upon performance of the technology representing the best available technology economically achievable for control of a specific pollutant, although a permit holder may use any alternative technology. The technology-based effluent limits do not specifically consider water quality impacts in the local receiving stream. In 2012, the U.S. EPA published final technology-based effluent limitations guidelines and new source performance standards to control discharges of pollutants from airport deicing opera- tions. The rule establishes new source performance standards for discharges associated with air- craft deicing for a subset of new airports but does not establish uniform, national requirements for aircraft deicing discharges at existing airports. Requirements will continue to be established in general permits, or for individual permits on a site-specific, best professional judgment basis by U.S. EPA or state permit writers, as appropriate. Additionally, existing and new primary air- ports with 1,000 or more annual jet departures (non-propeller aircraft) with stormwater discharges that generate wastewater associated with airfield pavement deicing are to use non-urea-containing deicers or, alternatively, meet a numeric effluent limitation for ammonia (14.7 mg/L) prior to any dilution or commingling with any non-deicing discharge [Airport Deicing Point Source Category, 40 Code of Federal Regulations §449 (2014)]. U.S. airports may also be subject to the requirements of the Construction and Development Effluent Limit Guidelines [40 CFR §450 (2009, revised 2014)]. The rule is generally applicable to facilities with construction projects that disturb more than one acre and discharge storm- water through a point source. The revised rule does not place a specific effluent limitation on stormwater discharges from construction areas. It includes requirements to implement ero- sion and sediment controls, stabilize soils, manage dewatering activities, implement pollution prevention measures, prohibit certain discharges, and use surface outlets for discharges from basins and impoundments. For large construction projects, airports should review the rule to determine its applicability and whether applicable requirements are different than those contained in many state-required construction stormwater permits or erosion and sediment control plans. Benchmarks. Benchmarks are numeric thresholds for specific water quality parameters defined in stormwater and wastewater discharge permits typically associated with the NPDES program. The definition and interpretation of benchmarks is often variable among permit types and issuing agencies. The most common rationale for benchmarks is that they serve as an indica- tion of the effectiveness of pollutant control measures. As opposed to numeric effluent limits, the act of exceeding a benchmark value is not typically considered a permit violation. Exceedance of a benchmark, however, can trigger regulatory actions. Failure to implement corrective actions asso- ciated with benchmark exceedances can be considered a permit violation. Repeated benchmark exceedances can lead to required implementation of active treatment controls and associated water storage and conveyance infrastructure. These large capital expenditures can often be avoided by proactive response to exceedances. The concept behind benchmarks is rooted in an adaptive management philosophy. The adaptive management process may include the following:

acquiring Monitoring Data 23 • Setting of benchmarks for specific parameters by regulators • Monitoring for specified parameters by the airports, typically at quarterly intervals, to evalu- ate the performance of control measures such as source controls, volume reduction, or treat- ment controls • Devise, implement, and document remedial actions to reduce the pollutant content. Potential actions include the following: – Additional monitoring – Investigation of pollutant sources – Evaluation of causes for benchmark exceedances – Revisions to SWPPPs and stormwater pollution control plans (SWPCPs) – Implementation of additional source controls – Implementation of treatment-based control measures • Revise and potentially resubmit SWPPP and SWPCPs to regulatory agencies • Report monitoring values, assessment results, remedial actions, and results to the regulatory agency. Exceedance of benchmarks is typically determined by whether the average of four (or more) samples in a year has a value greater than the benchmark. Initial exceedance triggers remedial actions. In many cases, continued exceedance of benchmarks results in an escalating level of remedial actions, including control measures, because the repeated exceedance is considered an indicator of increasing risk of causing water quality issues in receiving waters and an indicator of underperformance of control measures. The escalation can be potentially structured as a tiered program, with initial tiers requiring remedial or corrective actions that are adaptive management based. Frequent exceedances over long periods of time (e.g., 2 to 4 years) have more stringent corrective actions that often include requirements for imple- menting structural treatment control measures. In some situations, exceedance of bench- marks can lead to implementation of enforceable numeric effluent limits that typically result in fines if exceeded. The general permits may allow waivers for the presence of natural background concentrations of pollutants. If it is determined that exceedance of a benchmark is attributable solely to the pres- ence of that pollutant in the natural background, corrective actions or additional benchmark monitoring may not be required provided certain conditions are met. Natural background pol- lutants are those substances that are naturally occurring in soils or ground water. Natural back- ground pollutants do not include legacy pollutants from earlier activity at the site or pollutants in run-on from neighboring sources that are not naturally occurring, such as other industrial sites or roadways (U.S. EPA, 2015). Regulatory agencies typically document the procedures used to establish the benchmark val- ues. The benchmarks can be derived from statewide values for protecting water quality or from sector-specific values. Often times the procedures for setting statewide benchmarks are based on models used to help assess the risk of violating water quality standards or the risk of further damaging impaired waters. When setting benchmark values, regulators may also consider the expectations for treatment performance of commonly used control measures. The evaluation of performance of the control measures [also known as best management practices (BMPs)] can include a statistical analysis of the performance of similar existing systems. The regulatory agencies frequently re-assess benchmark values, often with each 5-year cycle for re-issuance of the general permits. Airports should consider these renewal cycles, particularly general permit renewals, as potential opportunities to weigh in on the setting of reasonable and achievable benchmarks. Parameters commonly receiving benchmark values include BOD, chemical oxygen demand (COD), total suspended solids (TSS), ammonia-nitrogen, phosphorus, metals, patho- gens, and pH. In recent years, benchmark values for certain metals, ammonia-nitrogen, and TSS

24 Interpreting the results of airport Water Monitoring have had a tendency to decrease from benchmark values in previous permits. Some benchmarks for metals are tied to hardness levels and differ for fresh and saltwater. Some permits contain both benchmarks and effluent limitations for the same pollutant. Benchmarks apply to the entire stormwater discharge associated with industrial activity from the facility while the effluent limitation guidelines only apply to the specific activity identified by the applicable national effluent limitation guideline. Benchmark values and requirements are usually, but not always, associated with general NPDES permits rather than individual NPDES permits. Most often, if an individual NPDES permit is required, numeric effluent limits are included in the permit instead of benchmarks. U.S. EPA has developed sector-specific benchmarks for 29 industrial sectors or subsectors in its multi-sector general permit. The benchmark parameters and values are based on infor- mation provided by industries with common industrial practices, materials and processes exposed to precipitation. In states not delegated to issue their own general permits, airports whose stormwater dis- charges are authorized under a general NPDES permit are subject to benchmarks covered under Sector S: Air Transportation Facilities of the U.S. EPA Multi-Sector General Permit. In states with the authority to implement their own NPDES permits, airports authorized to discharge stormwater under general NPDES permits are subject to the general permits in those states. Most states with authority to implement the NPDES program use the MSGP directly or as a template for their own industrial general NPDES permits. Therefore, many airports are subject to the benchmarks identified in the MSGP. Airports should directly consult the general permit applicable to them, whether it is the U.S. EPA MSGP or the state-issued general permit for specific requirements. Topical Tips Benchmarks Applicable to Sector S: Air Transportation Facilities— Multi-sector General Permit* BOD5: 30 mg/L COD: 120 mg/L Ammonia: 2.14 mg/L pH: 6 to 9 mg/L *Only applicable to airports where a single permittee, or a combination of permitted facilities, uses more than 100,000 gallons of pure glycol in glycol-based deicing fluids and/or 100 tons or more of urea on an average annual basis and monitors these four parameters in only those outfalls that collect runoff from areas where deicing activities occur. Indirect Discharges. Airports may also discharge stormwater into a municipal separate storm sewer system (MS4) or sanitary sewers. An MS4 is a system of conveyances used to collect or convey stormwater that is owned by a public body that itself discharges to waters of the United States. An entity designated as an MS4, such as a local municipality, may impose conditions on airport stormwater discharges within the municipality’s MS4 drainage area, typically through conditions in the municipality’s stormwater management plan. This may result in the need for additional monitoring and control of pollutants within the airport’s drainage area. Some airports may also be classified as MS4s themselves, which can result in the need to develop targets for reducing the quantities of particular pollutants in their

acquiring Monitoring Data 25 discharges, and methods for measuring achievement of those targets. This may result in the need for additional monitoring and control of pollutants. MS4 storm sewers often discharge to surface waters without treatment while flows to sani- tary sewers are treated in a local sewage treatment plant before discharge to surface waters. Discharges to MS4 storm sewers and sanitary sewers are considered “indirect discharges” for airports because, while the airport’s stormwater discharges do ultimately discharge to a surface water, the airport does not hold the NPDES permit for that surface water discharge. Much of the guidance in this document can apply to monitoring performed by the airport for direct or indirect discharges. This guidebook does not address specific MS4 or sanitary sewer monitoring requirements. Airports should refer to their local MS4 and industrial user permits for specific monitoring requirements. Overview of Applicable Canadian Regulations Stormwater discharges in Canada are required to comply with the Canadian Environmental Quality Guidelines (EQGs), a broad set of national environmental criteria pertaining to water, soil, air, and other environmental media, which was established by the Canadian Council of Ministers of the Environment in 1996. The Canadian Water Quality Guidelines, a component of the EQGs, provide specific water quality criteria pertaining to the protection of freshwater and marine aquatic life as well as agricultural, drinking water, recreational, aesthetic, and industrial water uses. The present water quality guidelines for various chemicals can be found on their website at http://st-ts.ccme.ca/en/index.html. In addition to the EQGs, the Canadian Environmental Protection Act established a total glycol discharge limit of 100 mg/L for airport stormwater impacted by deicing activities. These guide- lines are applicable to airports that are owned or operated by the federal government or located on land that is owned by the federal government. Yearly reports containing the results from monitoring glycol must be prepared after each deicing season and made available upon request. Other regulations include the following: • Guidelines for Effluent Quality and Wastewater Treatment at Fed- eral Establishments establish an acceptable level of 5-day biochemi- cal oxygen demand (BOD5) in stormwater samples of 20 mg/L for land-based establishments under the direct authority of the federal government. • Transport Canada requires that airports prepare detailed glycol man- agement plans and procedures to ensure responsible environmental management of glycol-based deicing chemicals. • The Fisheries Act prohibits activities that could affect fish, fish hab- itat, or the use of fish, which includes airport activities that could destroy fish passageways, alter fish habitat, or deposit substances del- eterious to fish. In addition to federal regulations, provincial and municipal laws may also specify water quality standards and guidelines depending on the location of the airport and the receiving waters. Discharge Permit­Driven Monitoring Requirements While a broad understanding of the regulations adds context to the monitoring process, site-specific regulatory monitoring requirements are defined by NPDES discharge permits in the United States. These Topical Tips Typical Monitoring Requirements Prescribed in Discharge Permits • Parameters • Field observations (visual, olfactory) • Frequency (weekly, monthly) • Sample collection method (grab, continuous) • Monitoring type (handheld test kit, online, off-site) • Monitoring method (analytical method) • Monitoring locations • Discharge conditions (first flush, deicing) • Reporting requirements

26 Interpreting the results of airport Water Monitoring prescribed permit monitoring requirements typically represent the minimum monitoring that is necessary. The permit monitoring requirements can often be applied directly, although some airports have challenges in matching the permit monitoring requirements with logistical realities of sample collection. Permit Monitoring Parameters. Discharge permits usually prescribe monitoring require- ments for specific parameters. The listed parameters may also include numeric effluent limita- tions that apply to outfall discharges. Monitor-only parameters are specified when pollutants are likely to be present but not in quantities that are reasonably likely to exceed water quality criteria, or to assess whether it is a pollutant of concern or there is a need to establish a baseline condition. Figure 9 illustrates an example of requirements listed in a permit. Permit Monitoring Frequency and Sample Type. Monitoring frequency and sample type are also often prescribed in permits. Frequency may be expressed in terms of the num- ber of samples collected within a week, month, season, or permit cycle. Sample type may be described as grab (a single aliquot collected at a point in time) or composite (a sample made up of multiple aliquots collected over a period of time and mixed together before analysis). Composite samples may further be specified as either time-weighted (aliquot collected at set intervals) or flow-weighted (aliquot collected when a volume of water passes the sample location). Permit-Specified Monitoring Types and Methods. Stormwater discharge permits may specify the monitoring type and monitoring method. • Monitoring type refers to the means by which samples are collected and analyzed and includes – Off-site monitoring where the sample is collected and shipped to an off-site laboratory for analysis. – On-site monitoring types where the sample is collected and analyzed on-site at the airport. For more information about monitoring types and moni- toring methods for deicing parameters, see: ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials Discharge Limitations Monitoring Requirements Average Monthly Maximum Daily Measurement Frequency Sample Type Page 2 Flow Rate, MGD 6.0 to 8.5 1/Month Estimate pH, Range, standard units --- 15 1/Month Grab Oil & Grease, mg/l Report 100 1/Month Grab TSS mg/l Report Report 1/Month Grab Benzene ug/l 1/Month Grab Effluent Characteristic Part I, A. - FINAL EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS 1. During the period beginning on the effective date of this NPDES permit modification and lasting until the expiration date, the permittee is authorized to discharge in accordance with the following limitations and monitoring requirements from outfall 001. See Part II, OTHER REQUIREMENTS, for locations of effluent sampling. Table - Final Outfall - Final Figure 9. Example permit requirements.

acquiring Monitoring Data 27 • Monitoring method refers to the specific process by which the parameter is analyzed. – For off-site monitoring types, the monitoring method is synonymous with the analytical method used by the laboratory. Some permits may explicitly allow only analytical methods based on published regulatory standards (e.g., U.S. EPA Methods) or published industry standards (e.g., “Standard Methods”). – For on-site monitoring types, there are three possible monitoring methods: b Integrated sampling and analytical methods (e.g., a pH probe). b Sampling plus analysis with test kits (e.g., COD colorimetric analyses). b Online instruments that continuously or near-continuously draw sample into an analysis device [e.g., total organic carbon (TOC) monitor]. Permit Monitoring Locations. Permits specify locations where permit conditions apply. Locations may be described with precise latitude and longitude coordinates, or simply specify the location that stormwater leaves airport property or discharges into a receiving water. Note that accessibility, safety, or accuracy concerns may cause an airport to conduct monitoring activities at a location other than the location specified in the permit. Additional Monitoring Beyond Permit Requirements. Airports may choose to do more extensive monitoring than required by their permit to support permit compliance. A typical driver for this additional monitoring is an attempt to get a better representation of effluent val- ues of a time period specified in the permit. For example, for an airport with a monthly average COD limit that specifies two samples per month, the airport may believe that collecting four samples in the month is a better representation of the average monthly concentration. These additional monitoring results have to be reported in monthly discharge monitoring reports. Monitoring performed at locations not specified in a permit or conducted for parameters not specified in the permit often does not need to be reported on discharge monitoring reports, although it is best to verify this with individual regulators. Special Permit Conditions. Special conditions for the monitoring process are also com- monly prescribed in permits and may include language indicating that monitoring should occur in conjunction with situations such as deicing activities and wet weather or dry weather condi- tions. An example of special conditions from the MSGP is presented in the box. For more information about defining the elements of your monitoring program not prescribed in a permit, see: 1.4 Defining Monitoring Parameters 1.5 Identifying Monitoring Locations 1.6 Selecting Monitoring Frequency and Extent Topical Tips Example of Special Conditions from Multi-sector General Permit for Stormwater Discharges ’All required monitoring must be performed on a storm event that results in an actual discharge from your site (“measurable storm event”) that follows the preced- ing measurable storm event by at least 72 hours (3 days). The 72-hour (3-day) storm interval does not apply if you are able to document that less than a 72-hour (3-day) interval is representative for local storm events during the sampling period. In the case of snowmelt, the monitoring must be performed at a time when a measur- able discharge occurs at your site. . . . You must take a minimum of one grab sample from a discharge resulting from a measurable storm event. . . . Samples must be col- lected within the first 30 minutes of a discharge associated with a measurable storm event. If it is not possible to collect the sample within the first 30 minutes of a mea- surable storm event, the sample must be collected as soon as practicable after the first 30 minutes and documentation must be kept with the SWPPP explaining why it was not possible to take samples within the first 30 minutes‘ (U.S. EPA, 2015).

28 Interpreting the results of airport Water Monitoring Permit-Required Record Keeping. Permits require the airport to keep records of monitor- ing data and either make them available upon request or submit them to the regulator at specific intervals. Understanding reporting requirements before conducting monitoring enables moni- toring to be conducted in a way that will facilitate reporting. While regulators often have specific formats (paper or electronic) for the reporting of monitoring data, these forms can sometimes be limiting and not allow for sufficient documentation of all data and critical observations. As such, airports are encouraged to develop databases or other documentation methods that are suited to their internal data management needs. Upon review of the monitoring requirements specified in the permit, airports should compare the permit requirements with the practical real- ities of monitoring and identify the monitoring program elements that need further definition. Compliance with Narrative Criteria. In addition to numeric requirements in permits, storm- water discharge regulations include narrative requirements that may be demonstrated through monitoring. In the United States, these are commonly referred to as the “free froms.” The narrative criteria typically state that stormwater discharges must be free from any “color, odor, diminished clarity, floating solids, settled solids, suspended solids, foam, oil sheen and other obvious indica- tors of stormwater pollution” (U.S. EPA, 2015). This includes substances that “produce undesir- able or nuisance aquatic life” (54 Federal Register 28627, July 6, 1989). The narrative criteria are broadly written and could result in permit violations even if no specific numeric effluent limits are exceeded. 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 CWA (U.S. EPA, 1994). The Canadian guidelines identify this objective as having “no observable adverse effects on atmospheric, aquatic, and terrestrial ecosystems over the long term” (Canadian Council of Minis- ters of the Environment, 2007). 1.3.2 Monitoring Not Directly Prescribed in Discharge Permits Regulatory and compliance situations are frequently encountered that require water monitor- ing beyond what is prescribed in discharge permits. Typical categories of monitoring not directly driven by discharge permits are listed and described in the following section. Monitoring to Inform Assessment and Response to a Permit Compliance Issue A stormwater discharge compliance issue is considered a circumstance where the character- istics of the stormwater discharge violate, or have the potential to violate, permit conditions. Compliance issues can arise from exceedances of numeric effluent criteria, exceedance of bench- marks, violation of narrative criteria, observation of unusual conditions, failure to implement necessary control measures, or failure to implement corrective actions within a specified time period, or through public complaint. Monitoring associated with compliance issues may be required through the following sources: • Permits where monitoring may be explicitly specified in response to limit or benchmark exceedances • Enforcement documents such as – Notice of violation – Enforcement letters from regulatory agencies – Administrative Orders – Consent Orders and Decrees • Permit-required planning documents in which the airport committed to monitoring, such as – SWPPPs – Stormwater Pollution Control Plans (SWPCP) – Spill Prevention Control and Countermeasures plans

acquiring Monitoring Data 29 • Contractual documents with other entities • The discretion of the airport to inform an issue and solutions, such as monitoring to – Further characterize the discharges – Support root cause analysis – Assess potential solutions. Monitoring requirements in these types of documents may or may not be specific regarding the location, pollutants, and time frame for monitoring. Airports often have the opportunity to provide input on these requirements and are encouraged to do so, especially if the extent, loca- tion, or timing of the monitoring requirements has practical limitations. Monitoring to Support Discharge Permit Development Discharge permits can be modified through several mechanisms, which can affect monitoring needs and requirements: • Standard 5-year renewals for NPDES permits • Mid-cycle permit modifications • Changes driven by special conditions in permits, such as allowances for stream water quality studies. NPDES permit renewal applications must be submitted to the regulatory agency 6 or more months in advance of the next permit cycle. Monitoring may be needed to support these permit renewal applications. Permit modifications are typically classified by the extent of the changes (e.g., major or minor modifications). Permit modifications can be driven by a variety of circumstances that change stormwater pollutant composition and the likelihood of pollutants being present in stormwater at a specific outfall. Typical drivers for stormwater discharge permit modifications at airports are provided in the Topical Tips box. For more information on techniques for managing compliance situations, see: 3.3 Application 1: Responding to Regulatory Compliance Issues For more information about monitoring for the purpose of proposing or establishing permit conditions, see: 3.4 Application 2: Using Data in Establishing Permit Conditions Topical Tips Identifying Drivers for Discharge Permit Modifications • Adding new outfalls • Moving outfalls • Changing the areas draining to an outfall • Adding new industrial activities (e.g., deicing pad in a new drainage area) • Removing industrial activities (e.g., demolition of a maintenance facility) • Changing operations that affect the magnitude of pollutant discharges • Changing or adding treatment processes • Collecting additional data to define effluent pollutant loads or stream assimi- lative capacity It is often not clear how to determine whether a change in the magnitude of pollutant loads to an outfall is significant enough to warrant a permit modification compared to waiting for the next permit cycle. When considering such decisions, airports should keep in mind that monitoring requirements and effluent limitations are dependent on the risk of stormwater discharges exceed- ing a water quality benchmark or limit. Monitoring data collected in the area of the change can be used to assess the extent of the change. If the change in pollutants is discernible, the airport may want to consult with the regulator to determine if a mid-cycle modification is necessary.

30 Interpreting the results of airport Water Monitoring Monitoring data in permit renewal or modification applications is used by regulators to assess the risk of future stormwater discharges exceeding water quality standards. This analysis is used to determine the following: • Whether an airport can obtain coverage under a general permit, or if they need to apply for an individual permit • If effluent limits or benchmarks are applicable • Monitoring requirements. Monitoring to Support Biological Stream Assessment NPDES regulations often contain biological water quality standards intended to protect aquatic life in the stream and their habitat. Many permits do not contain specific biological monitoring requirements, but some do, especially in areas where stormwater is discharged to sensitive water bodies. The monitoring requirements typically take the form of biological stream assessments and follow-up monitoring. Receiving waters have use designations that define the water body’s standard for supporting aquatic life. Periodically, or in cases of sus- pected impacts, the receiving water is monitored for its aquatic life status. This typically takes the form of collecting in-stream data on fish and macroinvertebrate assemblages (i.e., the type, number, and location of individual species). Most often, biological stream monitoring and the associated assessment is conducted by the regulatory agencies or by environmental interest groups. Airports or other dischargers may be required to perform biological moni- toring in some cases and may also have cause to independently perform biological stream monitoring. For example, an airport may initiate a biological monitoring program to pro- vide better information on the impacts of its stormwater discharges to assist in resolution of a compliance issue or to help set permit conditions. Because of the specialized nature of biological data collection and assessment, airports should seek assistance from entities with appropriately trained staff. Monitoring to Support Operation of Stormwater Management Controls Airports frequently operate stormwater management systems to meet operational objec- tives or general regulatory stormwater management requirements. Operation and main- tenance of these systems often require monitoring of individual stormwater management processes at the discretion of the airport. Process-driven monitoring activities are performed to support decision making for the operation of control measures for managing stormwater quality and quantity. This type of monitoring is often performed at locations internal to an airport’s drainage system and upstream of compliance outfalls, and is highly site and process specific. Monitoring to Support Stormwater Management Infrastructure and Controls Implementation Often times, the selection, design, and sizing of stormwater management infrastructure con- trols require significant water monitoring data. Stormwater monitoring may be needed to define the design criteria for new control measures. This may require a data set that covers more loca- tions, a greater variety of conditions, and a longer period of time than is available from permit monitoring data sets. Because of the often extensive need for data for design of control systems, airports and their design consultants need to assess how to obtain the data. The Seattle-Tacoma International Airport case study, included in Appendix C, describes how the airport used monitoring data to identify the location where controls were needed, to deter- mine the size and type of controls to implement, to measure performance of the controls, and to use adaptive management to improve performance through modifications to existing controls and construction of additional controls. For more information about process-driven monitoring, see: 3.5 Application 3: Applying Monitoring Data to Support Operations and Improve Airport Stormwater Quality ACRP Report 99: Guidance for Treatment of Airport Storm­ water Containing Deicers For more information about monitoring to evaluate the performance of control mea- sures, see: Urban Stormwater BMP Performance Monitoring: A Guidance Manual for Meet­ ing the National Stormwater BMP Database Requirements For more information about using monitoring data to design and size control measures, see: 3.5.1 Planning and Design C.1 Seattle-Tacoma Inter- national Airport

acquiring Monitoring Data 31 Monitoring to Provide General Stormwater Characterization An airport may monitor to generally characterize their stormwater discharges or to support improving water quality beyond what is specified in the permits. Potential objectives for this monitoring include the following: • Assess progress toward airport sustainability goals for water quality or flow • Provide information to support public relations ventures on airport environmental performance • Provide data to support future airport development projects • Establish a baseline prior to selling or leasing airport property • Understand background or off-site conditions that may be affecting airport stormwater For more information about using monitoring data to generally characterize stormwater, see: 3.5.3 Tracking and Improving Environmental Performance Key Takeaways Identifying Drivers and Objectives for Monitoring • Clearly identifying monitoring drivers is key to appropriately defining monitoring parameters, frequency, extent, and locations. • Most monitoring is driven by regulatory requirements in permits or other enforceable documents. • Airports should coordinate with regulators during the permit development process to align the monitoring conditions for location, timing, and number of samples with practical site limitations. • Before performing monitoring beyond what is required in permits, review reg- ulatory reporting requirements. Typically data must be submitted to regulators when monitoring for parameters listed in permits at permit monitoring locations. • Seek to align monitoring driven by different sources such as permit-driven outfall monitoring and monitoring used to manage control measures and treatment systems. 1.4 Defining Monitoring Parameters Once an airport has an understanding of its water monitoring drivers and implications, it can identify the parameters to be included in the water monitoring plan. A monitoring parameter is defined as a stormwater characteristic that is targeted for monitoring. Monitoring parameters include physical properties (e.g., flow rate, temperature), observed characteristics (e.g., sheen, odor), individual chemicals (e.g., zinc, benzene) and aggregate chemical analyses [e.g., BOD, total petroleum hydrocarbons (TPH)]. Parameters requiring monitoring may be specified in the permit. In some situations, airport staff need to define monitoring parameters not listed in permits. The following sections describe a process for identifying the monitoring parameters as well as the appropriate sample collection method, monitoring type, and monitoring method for each parameter. Figure 10 illustrates examples of the monitoring parameter attributes that must be defined. 1.4.1 Using Potential Pollutant Sources to Identify Parameters Depending upon situational needs, potential pollutant sources can inform the parameter list. At airports, common pollutant sources can be associated with aviation activities and non- aviation activities.

32 Interpreting the results of airport Water Monitoring Pollutant Sources Associated with Typical Airport Activities Airport staff can draw upon existing documentation to define potential pollutants from air- side and landside activities at the airport. Potential existing references are shown in the Topical Tips box. Table 2 lists typical airport airside and landside industrial activities, stormwater pollutants that may be generated from these activities, parameters to monitor to identify the presence of Topical Tips References at Airports for Identifying Potential Pollutant Sources • Existing monitoring data • NPDES permit applications • SWPPPs and SWPCPs • Spill prevention control and countermeasures plans • BMP plans • MS4 documents • Records of evaluation of non-stormwater discharges • Purchase records, Material Safety Data Sheets, and cut sheets for chemicals applied by the airport (e.g., deicers, fuel, cleaners, solvents, paint, fertilizers, pesticides, herbicides, nutrients) • Waste disposal characterization documents • Maintenance material logs • Specifications for materials exposed to stormwater (e.g., roofing materials, pavement coatings) • Treatment control measure design studies • Control device or treatment system performance data • Documents on construction activities, including SWPPPs and materials handled by contractors. • Documents on historical activities including past contamination – Aerial photos – Phase I Environmental Due Diligence Audits – Data from remediation projects – Interview notes from staff who may have institutional knowledge about historical activities, spills, or waste disposal practices or locations • Information on airport tenant operations (Regular visits and annual site com- pliance evaluations are good ways to keep track of tenant activities that may contribute pollutants.) Monitoring Parameter • Propylene Glycol • BOD • COD • etc. Sample Collection Type • Grab • Composite • Continuous Monitoring Type • Handheld • Online • Test kit • Off-site Monitoring Method • Colorimetric • Gas Chromatograph Figure 10. Monitoring parameter attributes.

acquiring Monitoring Data 33 Airport Industrial Activity Potential Pollutants Exposed to Stormwater Parameters Field Condition Fact Sheets to Reference Aircraft lavatory service Lavatory waste Fecal coliform, Escherichia coli, fecal streptococcus, enterococcus, toxicity Odor, sheen, foam, color, clarity/turbidity/solids Lavatory chemicals Chlorine, pH, toxicity Odor Lavatory truck wash water Propylene glycol, ethylene glycol, DO, BOD, TOC, COD, ORP, toxicity Odor, foam, color, nuisance microbial biofilms Building and grounds maintenance Pesticides, herbicides, rodenticides DDT, dioxin, toxicity Nuisance biofilm Fertilizers Phosphorus, nitrogen, toxicity Toxicity, nuisance microbial biofilms Landscape wastes DO Odor Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Salts Magnesium, chloride, acetate, formate, sodium, potassium, conductivity, TDS, toxicity Clarity/turbidity/solids Sediment Copper, zinc, cadmium, chromium, arsenic, iron, toxicity, TSS Clarity/turbidity/solids Cargo handling Battery acid pH, toxicity Toxicity Cleaning products (solvents, surfactants, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Toxicity Pesticides, herbicides, rodenticides DDT, dioxin, chlordane, toxicity Nuisance microbial biofilms Fertilizers Phosphorus, nitrogen, toxicity Nuisance microbial biofilms, toxicity Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Deicing/anti-icing Aircraft deicer/anti-icer Propylene glycol, ethylene glycol, DO, BOD, TOC, COD, ORP, toxicity Odor, foam, color, nuisance microbial biofilms Airfield pavement deicer BOD, TOC, COD, DO, acetate, formate, propylene glycol, sodium, potassium, conductivity, TDS, toxicity, ammonia Clarity/turbidity/solids Sand TSS, metals, phosphorus, nitrogen Clarity/turbidity/solids Landside pavement deicer Magnesium, chloride, acetate, formate, sodium, potassium, conductivity, TDS, toxicity, ammonia Clarity/turbidity/solids Firefighting equipment testing/flushing Aircraft firefighting foam PFOS Foam Fueling—aircraft, vehicle, equipment Petroleum hydrocarbons (fuel) BTEX, PAHs, TPH, DRO, GRO, toxicity Odor, sheen, color Maintenance—aircraft, vehicle, equipment Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Cleaning products (solvents, surfactants, degreasers, paint stripper, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Toxicity Antifreeze Ethylene glycol, DO, BOD, TOC, COD, ORP, toxicity Odor, foam, color, nuisance microbial biofilms Painting/stripping— aircraft, vehicle, equipment Paint Lead, PCBs Color Cleaning products (solvents, paint strippers) Toxicity, cadmium, chromium Clarity/turbidity/solids Runway rubber removal Rubber particles TSS Clarity/turbidity/solids Sand TSS Clarity/turbidity/solids Sediment Copper, zinc, cadmium, chromium, iron, toxicity, TSS Clarity/turbidity/solids Storage—chemical Cleaning products (solvents, surfactants, degreasers, paint strippers, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Toxicity Deicing fluid/materials Magnesium, chloride, acetate, formate, sodium, potassium, conductivity, TDS, toxicity, ammonia, propylene glycol, ethylene glycol, DO, BOD, TOC, COD, ORP, toxicity Odor, foam, color, nuisance microbial biofilms, clarity/turbidity/solids Table 2. Typical airport industrial activities and potentially associated pollutants. (continued on next page)

34 Interpreting the results of airport Water Monitoring these pollutants in stormwater, and field conditions that might indicate the presence of these pollutants. It may be useful to create a similar table that lists the activities occurring in each drainage area and identifies the pollutants, parameters, and field conditions that might be present in stormwater discharges. Other Potential Sources of Pollutants from Outside the Airport Airport discharges also have the potential to be contaminated by pollutants not directly asso- ciated with airside and landside activities at the airport. Understanding sources of non-airport For more information about pollutant parameters and potential sources, see: Customizable Parameter Fact Sheet Tool Storage—fuel/oil Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Storage— equipment/vehicles Antifreeze Ethylene glycol, DO, BOD, TOC, COD, ORP, toxicity Odor, foam, color, nuisance microbial biofilms Airport Industrial Activity Potential Pollutants Exposed to Stormwater Parameters Field Condition Fact Sheets to Reference Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Sediment/solids Copper, zinc, cadmium, chromium, iron, toxicity, TSS Clarity/turbidity/solids Washdown— apron/floor Cleaning products (solvents, surfactants, degreasers, paint strippers, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Sediment/solids Copper, zinc, cadmium, chromium, iron, toxicity, TSS Clarity/turbidity/solids Washing/degreasing— aircraft, vehicle, equipment Cleaning products (solvents, surfactants, degreasers, paint strippers, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color Sediment/solids Copper, zinc, cadmium, chromium, iron, toxicity, TSS Clarity/turbidity/solids Waste storage and disposal Cleaning products (solvents, surfactants, degreasers, paint strippers, detergents) MEK, chlorine, pH, toxicity, TCE, ammonia, alkalinity, conductivity Petroleum hydrocarbons (fuel, oil and grease) Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO, toxicity Odor, sheen, color BOD – biochemical oxygen demand; BTEX – benzene, toluene, ethylbenzene, and xylenes; COD – chemical oxygen demand; DDT – dichlorodiphenyl- trichloroethane; DO – dissolved oxygen; DRO – diesel-range organics; GRO – gasoline-range organics; MEK – methyl-ethyl ketone; ORO – oil-range organics; ORP – oxidation reduction potential; PAH – polycyclic aromatic hydrocarbon; PCB – polychlorinated biphenyl; PFOS – perfluorooctane sulfonate; TCE – trichloroethylene; TDS – total dissolved solids; TOC – total organic carbon; TPH – total petroleum hydrocarbons, TSS – total suspended solids Table 2. (Continued). Topical Tips Identifying Non-airport Pollutant Sources • Stormwater from off-site residential, commercial, or industrial areas or facilities • Road deicing • Storm sewers owned by other entities carrying unknown pollutants • Atmospheric deposition • Historical groundwater contamination in local area • Naturally occurring chemicals in groundwater • Chemicals resulting from reactions in soils or groundwater

acquiring Monitoring Data 35 pollutants may help the airport identify monitoring locations that will minimize the influence from these outside sources on airport stormwater monitoring. Potential sources are provided in the Topical Tips box. 1.4.2 Typical Monitoring Parameters This section introduces typical parameters associated with various pollutants. Along with the customizable parameter fact sheets, the information presented here supports determina- tion of situation-specific parameters. For many of the pollutants identified in Table 2, there are several parameters listed that could be used to characterize that pollutant. Several fac- tors may influence an airport’s decision to choose one monitoring parameter over another, including the sample method, monitoring type, and monitoring method available for each parameter; the timeliness, accuracy, and precision needed to support monitoring objectives; and the cost of monitoring a specific parameter. This section describes groups of various parameters that may be used to monitor a given pollutant and nuances associated with par- ticular parameters. Table 3 summarizes the parameters included in each constituent category described in this section. Petroleum Organics Composed of various organic compounds, petroleum products are used for many functions at airports on aircraft, ground vehicles, and fixed equipment. Petroleum products can contami- nate stormwater through leaks, spills, and fueling operations. Monitoring parameters for petro- leum can be categorized as chemical-specific (e.g., naphthalene) or aggregate measures [e.g., oil and grease, polycyclic aromatic hydrocarbons (PAHs), and TPH]. Some of the parameters used to characterize petroleum organics, like oil-range organics (ORO), diesel-range organics (DRO), and gasoline-range organics (GRO), identify petroleum organics associated with a spe- cific source. Petroleum organics analyses are generally conducted at an analytical laboratory, although some on-location measures are available. Because the laboratory analyses typically For more information about specific parameters, see: Customizable Parameter Fact Sheet Tool Constituent Category Parameters Field Condition Fact Sheets to Reference Petroleum organics Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO Odor, sheen, color Freezing-point depressant organics Propylene glycol, ethylene glycol, DO, BOD, TOC, COD, ORP Odor, foam, color, nuisance microbial biofilms Other organics Dioxin, TCE, MEK, PFOS Odor, color, nuisance microbial biofilms Solids TSS, TDS, turbidity Clarity/turbidity/solids Pathogens Fecal coliform, Escherichia coli, fecal streptococcus, enterococcus Odor, sheen, foam, color Nutrients Phosphorus, nitrogen, sulfur, potassium Metals Copper, zinc, cadmium, chromium, arsenic, iron, TSS Clarity/turbidity/solids Bases Ammonia, alkalinity, pH, conductivity Odor Acids Chlorine, pH Odor Salts Magnesium, chloride, acetate, formate, sodium, potassium, conductivity, TDS Clarity/turbidity/solids BOD – biochemical oxygen demand; BTEX – benzene, toluene, ethylbenzene, and xylenes; DO – dissolved oxygen; DRO – diesel-range organics; GRO – gasoline-range organics; MEK – methyl-ethyl ketone; ORO – oil-range organics; ORP – oxidation reduction potential; PAH – polycyclic aromatic hydrocarbon; PFOS – perfluorooctane sulfonate; TCE – trichloroethylene; TDS – total dissolved solids; TOC – total organic carbon; TPH – total petroleum hydrocarbons; TSS – total suspended solids Table 3. Typical airport pollutants and associated monitoring parameters.

36 Interpreting the results of airport Water Monitoring have a turn-around time of several days, field observations of the potential presence of petro- leum products in stormwater (e.g., odors, color, sheen) are critical to timely identification and containment of spills and illicit discharges. Freezing­Point Depressant Organics Freezing-point depressant organics are chemicals used to reduce the freezing point of water to facilitate melting or prevent freezing from happening. Freezing-point depressants are found in aircraft deicers, pavement deicers, vehicle antifreeze, and lavatory fluid (if added to prevent freezing). If necessary, the individual constituents of chemical mixes containing freezing-point depres- sants (e.g., propylene glycol, ethylene glycol, formate, acetate) can be measured directly with appropriate laboratory analyses. The aggregate presence of the organics can also be character- ized through measures of oxygen demand or TOC. Some of these indicators, like TOC, dis- solved oxygen (DO), and COD, may be measured in the field allowing for timely response to monitoring data. Note that there is a wide range of accuracy and precision associated with these parameters, and some parameters are more susceptible to interferences from other constituents in airport stormwater. Other Organics This category of parameters covers organics not associated with petroleum or freezing-point depressants. Some of these organics, like methyl-ethyl ketone (MEK) and trichloroethylene (TCE), are associated with cleaning solutions and may be present in some solvents, degreasers, and strippers. Perfluorooctane sulfonate (PFOS), which is present in some firefighting foam, is also an organic. Dioxin may be present in some herbicides and pesticides. Solids This category of parameters covers solids in the water column. Solids can include settable solids (e.g., sand), colloidal solids (solids that do not settle or take a very long time to settle), and dissolved solids (e.g., sodium). Solids can be inorganic (e.g., silt) or organic (e.g., biofilm). Common analytical methods include TSS, total dissolved solids (TDS), and turbidity. Solids are important to manage because several other pollutant types such as metals, nutrients, and certain organics can adhere to solids. Solids can be derived from multiple sources, with the most com- mon being erosion from construction activities. See the field observation fact sheet on solids for more information. Pathogens Pathogens are infectious agents such as a virus, bacterium, fungus, or parasite that causes disease in its host and presents a human health threat. Parameters used to characterize patho- gens in airport stormwater are specific to the type of pathogens and are typically related to constituents found in human or animal waste. The most common source of these pollutants is used lavatory fluid, but these parameters might also be present in stormwater if the airport experiences a sanitary sewer backup, overflow that enters the storm system, or waste from animals. Nutrients Nutrients are elements or compounds essential for animal and plant growth. Nutrients in stormwater are often subcategorized as major or macronutrients (e.g., nitrogen, phospho- rus) rather than minor or micronutrients (e.g., zinc, copper). Nutrients can be problematic in receiving waters because of their effects on dissolved oxygen, algae growth, and nuisance biofilm growth. As such, permits often place limits on nutrient concentrations. At airports, nutrients in For more information about deicing-related parameters, see: ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials

acquiring Monitoring Data 37 stormwater can be derived from off-site flows, groundwater, fertilizer application, eroding soils, leaf litter, and from additions to deicer treatment systems. While fertilizer application is not typi- cal in airport operation areas, many airports lease property for farming, and parameters that may contribute to the growth of nuisance microbial biofilm may be present in stormwater discharges commingled with runoff from farming operations. Monitoring parameters associated with nutri- ents are typically specific to the chemical species (e.g., ammonia-nitrogen, orthophosphate). Metals Metals may be present in airport runoff in both dissolved and suspended forms and come from maintenance and operations activities, including plating and paint stripping, automotive fluids, aircraft brake and tire wear, and leaching from exposed metals (e.g., heating, ventilation and air con- ditioning systems; metal roofs and downspouts; fencing; and guardrails). Metals are typically char- acterized as an individual parameter in laboratory analyses. Metals may also be detected through an increase in TSS, although elevated TSS may be the result of other suspended solids and may not necessarily be indicative of the presence of metals. The Seattle-Tacoma International Airport case study in Appendix C contains an example of how an airport used stormwater monitoring to design and measure performance of controls to manage metals in stormwater discharges. Acids and Bases The most common source of acids at an airport are acid-based cleaners. Acids may also be formed through anaerobic degradation of organics in stormwater and soils, resulting in a drop in pH. The most common basic parameter associated with airport stormwater discharges is ammonia. Ammonia may be present if urea is used as a pavement deicer. Salts The most common source of salts at an airport are pavement deicing chemicals. Potassium acetate, sodium acetate, sodium formate, magnesium chloride, and sodium chloride are all included in the salt category. Salts may also be naturally occurring in stormwater discharge at airports in proximity to the ocean or where there are naturally occurring salts in the local geology. Roadway salts applied in areas where runoff commingles with airport runoff may also be a source of salts in airport stormwater discharges. It may be difficult to differentiate contributions of salt from naturally occurring sources, commingled discharges, and airport deicing activities. Toxicity Some permits contain requirements for toxicity testing of stormwater discharges to surface waters. Monitoring for toxicity is unique among water monitoring parameters. An overview of toxicity monitoring considerations is provided in Appendix B: Field Conditions Fact Sheets. 1.4.3 Sample Collection Method Once potential pollutants and possible monitoring parameters have been identified, it is important to consider how the stormwater will be collected and transported to the device that conducts the analysis. There are several methods for sample collection and several factors that may influence an airport’s decision to use each method. Table 4 summarizes sample collection methods available for typical airport parameters. Grab Samples Grab samples are used to characterize the constituents in the stormwater at a single point in time. Many permits directly authorize use of grab samples for certain parameters. Grab samples are used to get a snapshot of discharge characteristics for a varying discharge or when moni- toring a parameter whose concentrations are unlikely to vary. Grab sampling is the method of For more information about metals parameters, see: C.1 Seattle-Tacoma Inter- national Airport

38 Interpreting the results of airport Water Monitoring choice for many airports when it is logistically difficult or costly to collect composite samples or take real-time measurements. Grab samples are also the only sample collection method for certain parameters, like some organics that may quickly decompose or volatilize if the collected stormwater is left open to the air over time. U.S. EPA (2010) indicates that grab samples are most appropriate when one or more of the following conditions exist: • The flow and characteristics of the water being sampled are relatively constant. • The effluent does not discharge on a continuous basis. • Information about instantaneous concentrations is needed. • Collection of a variable sample volume is needed to corroborate composite samples. • Parameters not amenable to compositing are being monitored. When grab sampling is used in discharges that likely have varying pollutant concentrations, the following limitations of the method should be understood: • It is unlikely that a grab sample will be timed to capture peak discharge concentrations or peak pollutant loads. • It should not be assumed that the grab sample results represent a mean or median of the pollutant discharges. • Calculating pollutant loads from grab sample concentrations from a single point in time and flow rates over a long period is not likely to produce an accurate result. For more information about choosing grab or composite sample collection, see: U.S. EPA Industrial Storm­ water Monitoring and Sampling Guide Urban Stormwater BMP Performance Monitoring: A Guidance Manual for Meet­ ing the National Stormwater BMP Database Requirements Constituent Category Parameters Sample Collection Method Monitoring Type Petroleum organics Oil and grease, BTEX, PAHs, TPH, ORO, DRO, GRO Grab samples Laboratory analysis Freezing-point depressant organics Propylene glycol, ethylene glycol, DO, BOD, TOC, COD, ORP Grab samples, composite samples, direct measurement, continuous (BOD, TOC, COD) Handheld instruments (not BOD), online monitoring (not glycols), test kit (not BOD, TOC) Pathogens Fecal coliform, Escherichia coli, fecal streptococcus, enterococcus Grab samples Laboratory analysis Other organics Dioxin, TCE, MEK, PFOS Grab samples, composite samples Laboratory analysis Nutrients Phosphorus, nitrogen Grab samples, composite samples Laboratory analysis Metals Copper, zinc, cadmium, chromium, arsenic, iron, TSS Grab samples, composite samples Laboratory analysis, test kit (ferrous iron) Bases Ammonia, alkalinity, pH, conductivity Grab samples, composite samples (not pH), direct measurement Handheld instruments, online monitoring, laboratory analysis (not recommended for pH) Acids Chlorine, pH Grab samples, composite samples (not pH), direct measurement Handheld instruments (not chlorine), online monitoring (not chlorine), laboratory analysis (not recommended for pH) Salts Magnesium, chloride, acetate, formate, sodium, potassium, conductivity, TDS Grab samples, composite samples, direct measurement Handheld (conductivity and TDS), online (conductivity) BOD – biochemical oxygen demand; BTEX – benzene, toluene, ethylbenzene, and xylenes; DO – dissolved oxygen; DRO – diesel-range organics; GRO – gasoline-range organics; MEK – methyl-ethyl ketone; ORO – oil-range organics; ORP – oxidation reduction potential; PAH – polycyclic aromatic hydrocarbon; PFOS – perfluorooctane sulfonate; TCE – trichloroethylene; TDS – total dissolved solids; TOC – total organic carbon; TPH – total petroleum hydrocarbons; TSS – total suspended solids Table 4. Sample collection method and monitoring types for typical airport parameters.

acquiring Monitoring Data 39 Composite Samples Composite samples are used to characterize stormwater over a longer period of time. In most cases, composite samples will produce a more accurate and representative quantification of pollutant loads and concentrations than grab samples. However, composite sampling is more difficult, and costly, to implement than grab sampling. Composite samples are often used to calculate average pollutant concentrations or total pol- lutant loads over an extended period. They are ideal for constituents where long-term loads or long-term concentrations are a concern and may be an option for locations where it may be difficult to catch the first flush with a grab sample. Composite samples are not a good choice for organics that may volatilize or decompose or parameters like pH that may change in the sample collection vessel during the sample collection time frame. Composite samples may be either flow-weighted or time-weighted averages. • Time-weighted composite. A time-weighted composite sample is derived from equal volume aliquots collected at regular time intervals. Time-weighted composites are easier to imple- ment than flow-weighted composites. However, if flow rates and pollutant concentrations vary significantly over the compositing time, the samples can be biased. • Flow-weighted composite. A flow-weighted composite sample is derived from equal volume aliquots collected after a specified flow volume passes by the sampling unit. Flow-weighted composites are more accurate than time-weighted composites but can be difficult to execute because of the large variability in stormwater flow rates. When the flow rate is low, aliquots are collected less frequently, and when the flow rate is high, aliquots are collected more fre- quently resulting in a sample with a concentration that represents the average concentration of all water discharged during the sample collection period. This can lead to challenges in selecting the correct volume for the aliquots and can result in composite sample containers that are not large enough to hold the frequent aliquot collection that occurs when flow rates are high. Some airports have developed custom-made storage devices for composite samplers to compensate for the lack of volume in off-the-shelf models. Continuous Sample Collection for Online Monitoring Continuous sampling is associated directly with use of an online analytical device such as a COD measurement instrument that is fed samples from a continuously flowing sample stream. While the term “continuous” is frequently used colloquially, many sampling/analysis systems designed for online data monitoring in fact measure at discrete intervals ranging from every few seconds to every few minutes. Continuous sampling is only an option for a small subset of parameters that can be monitored online in real time. Continuous sampling is ideal for monitor- ing conducted to facilitate control of diversion of stormwater for treatment, storage, or alternate disposal. When considering an online, continuous system, airport staff must have a clear under- standing of the range of intervals between measurements. Direct Measurement of Parameter (No Sample Collection) Some parameters may be measured with instruments that are placed directly in the storm- water discharge, called “handheld monitoring,” and sample collection is not required. This is ideal for parameters measured to characterize pollutants that may change over time due to volatilization or decomposition, like pH and dissolved oxygen. 1.4.4 Monitoring Types Closely related to sample collection method is the monitoring type. ACRP Report 72 categorizes monitoring types as either off-site or on-site and provides a detailed description of monitoring For more information about composite sample collection procedures, see: U.S. EPA Industrial Storm­ water Monitoring and Sampling Guide For more information about sampling types, see: ACRP Report 72 Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials

40 Interpreting the results of airport Water Monitoring types for many deicing parameters. Applicable monitoring types for typical airport parameters are summarized in Table 4. The following subsections describe some of the benefits and drawbacks of each monitoring type. Off­Site Analysis Off-site analysis of samples is ideal for parameters that cannot be measured on-site, or for parameters where on-site methods do not provide the level of accuracy or precision required to support the purpose of the monitoring. In some instances, off-site analysis may be used to verify field-measured data. Off-site analysis is not ideal for parameters with short hold times like DO or pH, or when real-time decisions need to be made based on monitoring data. Handheld Instruments Handheld instruments do not technically collect a sample but measure the parameter directly in the stormwater discharge flow. Handheld instruments are ideal for providing data to make real-time decisions but are only available for a limited number of constituents. If well calibrated, maintained, and used by experienced and trained staff, some handheld instruments provide more accurate measurement of parameters than off-site laboratory analysis. Other handheld instruments have limited precision. It is important to consider the level of precision and accu- racy necessary to meet monitoring objectives when considering handheld instruments. Consis- tent placement of the instrument in the sample stream from one sampling event to the next is also important to getting consistent results. Test Kit Test kits allow airport or hired field personnel to perform analytical tests of collected samples on-site. Because test kit results can typically be obtained in less than 2 to 3 hours, rather than the multiple days required to obtain results from a laboratory, they can assist in making immediate decisions. They also do not require the expense of online monitors. Test kits are available for a limited number of constituents (e.g., ferrous iron, nitrate, orthophosphate). If well calibrated and used by experienced and trained staff, test kits can provide relatively accurate measurement of parameters. It is important to consider the level of precision and accuracy necessary to meet monitoring objectives when considering the use of test kits. Online Monitoring Online monitors are permanent mounted devices that facilitate near-continuous measure- ment of water stream characteristics. Online monitors are typically equipped with a sample pump and tube to continuously supply the monitor with sample from the stormwater. Online monitors are ideal for facilitating real-time decisions and may be integrated into stormwater controls to allow data from the online monitor to facilitate automatic initiation of stormwater diversion. The most common type of online monitoring is measurement of water level and flow. Online monitoring is also available for a limited number of constituents, such as turbidity, conductivity, DO, pH, and oxidation reduction potential (ORP). 1.4.5 Factors Influencing Monitoring Parameter, Sample Collection Method, Monitoring Type, and Monitoring Method Selection Many factors may lead an airport to select one monitoring parameter, sample collection method, or monitoring type over another. Additionally, some parameters can be measured using more than one method and more than one type. The following sections describe some of the factors that may influence an airport’s monitoring decisions. For more information about applicable monitoring methods for specific parameters, see: Customizable Parameter Fact Sheet Tool

acquiring Monitoring Data 41 Specific Chemical Versus Aggregate Measures Many analytical tests measure individual chemical constituents (e.g., chloride, propylene glycol). Other analytical tests measure parameters whose values are an aggregate measure of the effects of one or more chemical constituents. For example, the aggregate parameter TOC analy- sis measures the combined carbon contributions from whatever organic constituents happened to be in a given sample (e.g., propylene glycol, ethylene glycols, and acetates). The aggregate parameter TDS measures the combined dissolved solids contributions from whatever individual ionic constituents happened to be in a sample (e.g., chloride, potassium). Aggregate parameters provide an advantage over parameters that measure individual constituents in certain situations such as the following: • When the identity of the individual constituents is not known • When it is not necessary for compliance or stormwater management purposes to know indi- vidual constituents • When the cost of analyzing individual constituents outweighs the value of understanding the individual constituents In some cases, the most economical path may be an initial characterization with aggregate parameters to determine the total magnitude of like constituents, followed by targeted analysis of individual constituents. Timeliness For certain analyses conducted by a laboratory, samples may be held for several days to several weeks before analysis is performed. Additionally, some analyses, like a BOD5 analy- sis, may take several days to conduct. Other parameters may be measured directly, using online monitors, or with a test kit and may provide real-time or near-real-time data. Con- sider when the data will need to be used when selecting the monitoring parameter, sample collection method, monitoring type, and monitoring method. If the data is being used to support ongoing stormwater management operations, often time is of the essence, and the airport should determine if there is a parameter that can be measured in real time or near real time that will provide a good indicator of the presence of the identified pollutant. If data is being collected to support permit compliance, or the development of new permit conditions, often time is not as critical and other factors may have greater influence on the selection of the monitoring parameter, sample collection method, monitoring type, and monitoring method. Accuracy Another important factor when selecting monitoring parameter, sample collection method, monitoring type, and monitoring method is the level of accuracy needed in the results. When developing data acquisition plans, it is important to characterize both the accuracy needed to support the applications for the data and the accuracy that can be achieved. Considerations associated with accuracy are presented in the following paragraphs, with detailed discussion of terms and potential sources of error deferred to Chapter 2: Interpreting Monitoring Data. Required Accuracy. The required accuracy depends upon the application for the moni- toring data. There are no absolute guides to the level of accuracy required for various water monitoring applications. Often, it is best to think about required accuracy in terms of the consequences of inaccurate data. Potential consequences to consider are shown in the Topical Tips box. Achievable Accuracy. It should be understood that no monitoring data is perfect. Errors can be introduced at a number of points in the process of acquiring data. It can be difficult

42 Interpreting the results of airport Water Monitoring to quantify the potential error. However, understanding the general sources of error is an important exercise in developing a monitoring plan. See Chapter 2: Interpreting Monitoring Data for details on potential sources of error. As described in that chapter, most analytical devices have an inherent level of error, which can be compounded significantly by the many variables involved in collection of data in the field. Instrument error or accuracy provided by the manufacturers is a good starting point, but it should be recognized that both the sampling process and field analytical process can introduce additional error. One source of additional error to consider is the bias potentially created based on interactions of stormwater constitu- ents in certain analyses. The parameter fact sheets derived from the Customizable Parameter Fact Sheet Tool accompanying this guidebook contain information about interactions for various methods. The relative values of the detection limits and permit conditions should also be considered. If the monitoring method detection limit (MDL) is higher than the benchmark or effluent limit, it may not have the accuracy needed, and an alternative method or alternative param- eter may need to be identified. Some water quality criteria are less than the MDL for the U.S. EPA-approved analytical method. If this is the case for monitoring specified in a permit or regulation, alternative methods or parameters should be discussed with the regulator or permit writer. Often, there is a direct relationship between the extent of resources applied to monitoring and the achievable accuracy and data representativeness. More resources can equate to collection of more data as well as more time and effort applied to the following processes: • Quality assurance procedures for minimizing error • Quality control processes for reviewing data for potential errors Topical Tips Consider Consequences of Inaccurate Monitoring Data When Developing Data Acquisition Plan 1. Permit non-compliance • If the monitoring data is used in decision making that affects the ability to comply with permit requirements, then more resources should be applied to get more accurate data. 2. Operational impacts and cost • Often getting more accurate data requires more time from monitoring staff and more analytical costs. • If inaccurate monitoring data is used to control a stormwater management process, it can affect treatment performance, material usage, and downtime. 3. Schedule • If insufficient resources are applied to the initial data acquisition and the data is found after the fact to be in error, more monitoring may be required, extending schedules. 4. Capital cost • Some monitoring data is used for selecting and sizing stormwater infra- structure and controls. Significant errors in monitoring data can lead to oversizing infrastructure. For more information about interactions from other components in stormwater biasing data, see: Customizable Parameter Fact Sheet Tool

acquiring Monitoring Data 43 • Experimental testing to quantify variance and error, often through isolation of variables – Creating replicate samples to test the consistency of a single analytical instrument – Comparing analytical results from multiple analytical methods – Comparing analytical results from multiple devices using the same method If the consequences of inaccurate data are significant, then greater resources should be allocated to the monitoring effort. Cost The costs for acquiring monitoring data include the following potential line items: • Purchase or rental of sampling equipment • Purchase or rental of field analytical devices • Installation, operation, and maintenance of field devices • Labor for sample collection crews • Sample shipping • Laboratory analytical tests • Labor for data review • Consultant support The costs for various analytical tests vary greatly, and it may be helpful when budgeting for monitoring to get quotes from a few local laboratories for comparison and to allow the airport to consider cost in choosing the appropriate monitoring method and laboratory. It is recommended that airports create an analysis cost calculation template in a spreadsheet that is prepopulated with their monitoring locations, analytical parameters, and unit costs for the analyses. Calculating costs for the sample collection portion of the work is more difficult because it can be a challenge to adequately determine the time needed for the field work, but sampling costs potentially could be linked with analytical costs in the same spreadsheet. Note that higher cost does not neces- sarily mean better results. Always consider the purpose of the monitoring and the minimum cost to achieve the timeliness and level of accuracy necessary to meet monitoring objectives. For example, the cost for analysis of some specific parameters, like benzene, toluene, ethylbenzene, and xylenes (BTEX), are particularly expensive, and a more general parameter, like oil and grease, may be sufficient to conduct sampling to identify the location of a suspected fuel spill at a third of the cost. A common decision point regarding costs is whether to use a sam- pling crew to collect grab samples or to use an automatic sampler. This decision is situation specific. Considerations in the decision-making process include the following: • Often the cost for an extended rental of autosampling equipment is the same order of magnitude as purchasing the equipment. • If the sampling occurs regularly, it is generally most cost effective over the long term to purchase autosamplers. • In some cases, logistical limitation may prevent either use of autos- amplers or easy access to sampling locations by sampling crews. 1.5 Identifying Monitoring Locations Establishing monitoring locations is an important part of a moni- toring plan. It is especially critical to carefully consider the location where monitoring will occur so that a safe, efficient, and effective For more information about cutting cost, see: 1.7.5 Monitoring Efficiently to Reduce Costs and Save Time Topical Tips Monitoring Location Considerations The location maximizes: • Consistency with permit requirements • Safety • Access to required utilities • Capture of desired runoff flow • Ability to conduct field observations The location minimizes: • Stagnation • Commingled flows • Backflow • Interference with airport operations • Potential for fouling of or damage to monitoring equipment • Safety or wildlife hazards • Potential for inundation

44 Interpreting the results of airport Water Monitoring location is established that provides for the best possible characterization of your stormwater discharges. Considerations for identifying appropriate monitoring locations are presented in the following sections. 1.5.1 Objectives for Selecting Monitoring Locations Selection of a monitoring location requires careful consideration in order for monitoring to appropriately characterize stormwater discharges without compromising the safety of mon- itoring personnel or requiring excessive cost. A good monitoring location has the following characteristics: • It is consistent with the permit requirements for the areas subject to monitoring. • It receives runoff from airport property where industrial activities subject to stormwater occur and from the drainage area identified on the SWPPP map associated with that outfall. • It is isolated from influences of non-airport drainage. • It is isolated from groundwater influences. • It is sufficiently close to the compliance point for it not to misrepresent stormwater composi- tion at the outfall location. • It allows for safe and timely access by monitoring staff during all anticipated weather conditions: – It avoids areas with potentially slippery or icy steep sidewalls, confined spaces, risk of sub- mergence, wildlife hazards, or vehicle or aircraft movement areas where possible. • It allows for installation of necessary equipment including access to utilities like power, com- munications, and potable water, if required, and minimizes the risk for equipment to be fouled or damaged during storm events. • It has a good movement and depth of flow and avoids areas where: – Flow is stagnant – Flow depth is too shallow to collect samples – There is risk of high velocities that may damage monitoring equipment – There is high risk of backflow from the receiving water. • It facilitates the ability to conduct field observations by avoiding monitoring in enclosed pipes that cannot be easily observed. 1.5.2 Selection of a Representative Location Stormwater monitoring at airports is generally conducted in one of three locations: at the outfall where the stormwater leaves the airport property, at an internal monitoring location targeting runoff from a specific activity, or in the receiving stream. When a representative loca- tion is being selected, it is important that the purpose and drivers for conducting monitoring are considered to ensure the monitoring location is going to provide appropriate and applicable information to support drivers for monitoring. Outfall Monitoring Outfall monitoring is typically conducted at, or as close as possible to, the point where stormwater leaves airport property. This usually provides the best representation of the over- all impact on airport stormwater discharges from airport activities, including effects from industrial and construction activities, and benefits from airport control measures. Note that outfall monitoring characterizes the impact that airport activities have on airport stormwater discharges but does not account for how those stormwater discharges may affect receiving stream quality. If the interaction between airport stormwater discharges and the receiving For more information about defining the purpose and drivers for monitoring, see: 1.3 Identifying Drivers and Objectives for Monitoring

acquiring Monitoring Data 45 stream is not well understood, receiving stream monitoring (discussed in the following section) may be used to characterize the impact that airport stormwater discharges may have on the receiving water. Most airports have several locations where stormwater runoff leaves airport property, and it is important from a monitoring perspective to understand the lands draining to the outfall and the activities within those drainage areas. This allows the effects of areas with and without regulated industrial activities to be considered when selecting monitoring locations, interpreting monitoring results, and perhaps modifying drainage networks or outfall locations. Documenting the drainage area and associated activities may also allow identification of outfall drainage areas containing similar industrial or construction activities with similar pollutant composi- tion. Comparison of drainage area characteristics or monitoring data between outfalls can support regulatory cases for making one outfall representative of one or more other outfalls. In identifying a represen- tative outfall, it is important to consider similarities in all aspects of the drainage area that might affect the runoff, including the size of the drainage areas, the percentage of the area that is landscaped or pervi- ous, the percentage of the area covered with impervious surfaces (e.g., runways, taxiways, ramps, buildings), the types and scale of industrial and construction activities, the type and volume of materials stored in areas subject to stormwater, and the receiving water. Once similar outfalls have been identified, the airport and regulator must identify one that will serve as a representative outfall where monitoring activi- ties will occur. This may be based on the outfall with a slightly higher risk of contaminants from industrial activities, or the one with the best monitoring location as described in Section 1.5.1: Objectives for Select- ing Monitoring Locations. Once the airport has identified the outfalls that will be monitored, the next step is determining where to conduct monitoring at each outfall, considering the factors described in Section 1.5.1: Objectives for Selecting Monitoring Locations. Internal System Monitoring Locations Internal system monitoring is conducted to understand stormwater discharges from a spe- cific activity or land cover. Monitoring is typically conducted at a location that captures only runoff affected by that activity. Internal system monitoring is often conducted for the following purposes: • To quantify performance of a specific control measure • To understand the effect from a specific industrial activity • As part of a root cause analysis to identify pollutant sources • To support operational decisions in stormwater management Internal system monitoring should be conducted upstream of any diversion locations, and at a point that is close to the potential source of pollutants and best isolates runoff affected by the industrial activity or control measure from the rest of the drainage area. Receiving Stream Monitoring Receiving stream monitoring is typically conducted for the purpose of understanding how airport stormwater discharges affect the water quality in the receiving stream. Many permits For more information about selecting an outfall monitor- ing location, see: U.S. EPA NPDES Permit Writers’ Manual Urban Stormwater BMP Performance Monitoring: A Guidance Manual for Meet­ ing the National Stormwater BMP Database Requirements Topical Tips Representative Outfall Drainage Area Characteristics Discharges with similar: • Size of the contributing drainage area • Percentage of impervious/pervious areas • Type and amount of industrial and construction activities • Type and volume of materials stored in areas subject to stormwater • Stormwater conveyance methods • Receiving water

46 Interpreting the results of airport Water Monitoring contain requirements for regular monitoring of streams upstream and downstream of airport stormwater discharges. Other drivers for stream monitoring include gathering data to support reasonable potential analyses or wasteload allocation studies as well as assessments of the effects of compliance issues. Since the receiving stream may be subject to pollutants from other dischargers, it is impor- tant to understand not only the impact that airport stormwater discharges have on the receiv- ing stream, but also the impact that other dischargers have on the receiving stream and how those cumulative (airport and other dischargers) impacts may affect the overall water quality in the receiving stream. In instances where a receiving stream has a TMDL established for a given pollutant, airport stormwater discharges may be limited to an allocated portion of the TMDL as there may be other entities also permitted to discharge pollutants contributing to the TMDL. Receiving stream monitoring may be conducted upstream or downstream of the point where airport stormwater discharges flow into the receiving stream. Monitoring upstream of the airport stormwater discharges will facilitate understanding of pollutant levels and water quality in the receiving stream prior to airport stormwater discharges. This could include effects from other discharges or background concentrations from naturally occur- ring sources. Upstream concentration information may be used by a regulator in a reason- able potential analysis to understand cumulative impacts on water quality. This analysis would inform development of appropriate permit conditions for the airport. The area of the receiving stream immediately downstream of airport stormwater discharges may be monitored to characterize immediate or acute effects of airport stormwater discharges on water quality. Further downstream may be monitored to characterize chronic or far-field effects of airport stormwater discharges on water quality. Downstream monitoring may be conducted at specific critical locations like the intake for a public water supply, within a sensitive aquatic habitat, or in a public recreation area to characterize airport effects on water quality in these areas. 1.5.3 Potential Limitations of Monitoring Locations Even with thoughtful planning and consideration, the characteristics of the airport storm- water conveyance system often necessitate monitoring in less than ideal locations. In these instances, it is important to recognize the limitations of the monitoring location and the effect that may have on the data gathered from that location. If limitations are identified, potential remedies that might improve safety for monitoring personnel or improve the quality of the data should be considered. The following subsections describe a few of the more common monitoring location limitations, potential impacts on the quality of the data, and some steps to overcome limitations. Access to Utilities Because airports often own large tracts of land to accommodate required airfield safety restric- tions, airport outfalls are often located in areas where there is limited access to utilities. Automatic composite samplers require power to run the pump that collects the sampler; many online monitors require potable water and electricity; and some units require communications so that they can be initiated and communicate data remotely. If electricity, potable water, or communications/controls are not available at a location, the types of sample collection and monitoring methods that are feasible may be limited. There are some ways to overcome the lack of utilities. Use of batteries or solar power may be an option in certain circumstances, although batteries may freeze in cold For a brief introduction to reasonable potential analysis see: 1.3 Identifying Drivers and Objectives for Monitoring For more information about telemetry, see: C.1 Seattle-Tacoma Inter- national Airport 1.7 Executing Monitoring

acquiring Monitoring Data 47 climates, and solar panel use may be restricted in certain areas at an airport. The need for potable water may be resolved by installation of a potable water tank that is accessible for refilling and designed to prevent freezing. The need for communications to control sample collection or online monitoring may be resolved by using telemetry systems where data can be transmitted via wireless technologies. If desired utilities are simply unavailable, then samples may need to be collected manually. Manual collection may limit the monitoring methods available for a given parameter. It may also delay decision making and increase the cost of labor required for manual monitoring. Presence of Safety Risks or Access Issues Safety risks and access issues come from a variety of sources. Since monitoring often must be conducted during storm events, weather-related safety and access issues are a common concern. Weather-related safety issues include the potential for slips and falls during wet or icy conditions; the potential for submergence during high stream flow, high stormwater discharge, or high tide conditions; lightning strikes and flying debris during storms; and health affects due to exposure including heat stroke or frost bite. Weather-related access issues include frozen gates or locks, piled or drifted snow, frozen discharge, and flooding. Weather-related access issues can be mitigated by using an alternative location when weather risks are limited, or by considering weather-related risks when scheduling monitoring activi- ties. Finally, monitoring personnel should be trained and equipped appropriately for the weather conditions. Another common issue at airports are hazards associated with airport operations; this could include monitoring locations in aircraft movement areas and vehicle movement areas, and height restrictions on monitoring equipment. Airport operations hazards can be mitigated by informing appropriate airport operators about monitoring activities and coordinating to allow for safe access. Other common issues may be associated with the physical features at the site, including brush or debris, riprap, steep side slopes, deep structures requiring confined-space entry, bolted man- holes, and lack of roads limiting access by vehicle and equipment that may be needed at the site. Any monitoring personnel entering a confined space should have appropriate confined-space training. Finally, wildlife hazards like snapping turtles, snakes, ticks, mosquitoes, bees, wasps, hornets, deer, bears, alligators, poison ivy, poison oak, or poison sumac may also be present. Appropriate personal protective equipment for monitoring personnel might include long pants and sleeves, waders, and bug spray. If the monitoring location is not in a protected area like a wetland, removal of brush and debris at the site may reduce physical feature hazards, improve flow, and discourage hazardous wildlife. Ultimately, the safety of monitoring personnel is more important than the conduct of moni- toring activities, and there may be instances when monitoring must be delayed or skipped due to safety risks resulting in an incomplete characterization of airport stormwater discharges. It is important to discuss these concerns in advance with the regulator so that appropriate language allowing for suspension of monitoring activities during unsafe conditions can be considered in the airport’s permit. It is also important to document the reason for not monitoring in the event a required monitoring event is skipped. Configuration of Stormwater Conveyance Sometimes the configuration of the stormwater conveyance can put limitations on monitor- ing that can affect the accuracy and representativeness of monitoring data. In addition to the potential for confined-space entry discussed in the previous subsection, piped conveyance may For a more information about exceptions to moni- toring during hazardous weather conditions, see: U.S. EPA MSGP

48 Interpreting the results of airport Water Monitoring make it difficult to observe stormwater for the purpose of collecting field observations. In some cases, it is important to take a sample in a specific location to limit collection of commingled flows, but field observations may be collected in a more observable location. Note that field observations made in a location other than the sample location may not directly correspond to measured data. If the field location includes additional flows, the field observations may repre- sent conditions introduced by the commingled discharge. The configuration of piped conveyance may also lead to difficulty measuring flow. Shallow conduit can allow for sedimentation or stagnant flow. Corrugated pipes may impact the accuracy of measurements at lower flows. Open channel conveyance also presents difficulty with measur- ing flow, as the velocity may vary widely across the cross section of stormwater discharge, the stream bank may be highly irregular, and the slope may be difficult to calculate. Weirs and flumes may be used to facilitate collection of flow data; however, they should be carefully (1) evaluated to reduce the risk of restricting flow in critical pipes that may be at capacity and (2) maintained after installation to prevent the buildup of debris or sediment around the flow control device. Weirs tend to enhance the settling of solids immediately upstream and accumulation of floating oil or grease immediately downstream. Therefore, sampling near weirs should be avoided where possible (U.S. EPA, 2010). Depth-discharge curves can also be developed through the measure- ment of flow velocity and cross-sectional area. In larger flows, however, safety and accessibility concerns limit the ability to collect data, resulting in the need to extrapolate curves, which can introduce errors. Consider the importance of collecting precise flow rates. For load-based limits, an accurate flow rate may be vital to accurately converting the concentration measurement to load. In other cases, precise flow rates may not be needed, and an estimate based on visual observation, or a single depth and velocity measurement, may be sufficient to characterize the stormwater discharge. In some locations, backflow or inundation from the receiving water due to flooding or tides is a common problem. Backflow preventer, tideflex, or duckbill valves are an option for some types of pipe flow to prevent water from entering the discharge pipe from the receiv- ing stream, but this is infeasible for open channel flow and may also affect accuracy of flow measurements. If the flow being monitored represents the characteristics of the receiving water and not the characteristics of the actual stormwater discharge, it is important to note this when documenting field conditions. If it is suspected that a permit-required monitoring location may frequently experience backflow or inundation conditions, it may be useful to discuss this with the regulator and understand if monitoring should be suspended during these conditions. Some locations may experience stagnation of water, particularly during prolonged dry weather conditions. If there is no actual flow, the water being monitored may not in fact be discharging. Additionally, if there is a stormwater discharge, but samples are taken from a stagnant pool, or sump, and not part of the flowing stormwater, monitoring data is likely more representative of the stagnant area than continuously discharging water. Monitoring personnel should attempt to conduct monitoring of the turbulent flow portion of the stormwater discharge and should clearly note if a stagnant pool was monitored. Outfall monitoring should be conducted only when there is an actual discharge. Sometimes monitoring of discharges that represent only airport stormwater runoff is infea- sible because off-site stormwater enters the upstream end of the airport stormwater drainage system, or because the stormwater conveyance system is inaccessible in the desired location and monitoring can only be conducted downstream of a location where airport stormwater discharges have been commingled with off-site discharges. In these instances, it is important For a more information about solutions to problems like run-on from off-site or managing numerous outfalls in one area, see: U.S. EPA Industrial Storm­ water Monitoring and Sampling Guide

acquiring Monitoring Data 49 to characterize the co-mingled flow to the greatest extent possible to understand its poten- tial effect on the monitored discharges. Understanding the drainage area contributing to the co-mingled flow will help characterize the portion of the flow that is associated with airport drainage areas and the portion that is not (i.e., is 90 percent of the flow from the airport or is 10 percent of the flow from the airport). Understanding the activities that might contribute pollutants from those co-mingled areas is also important. Are the pollutants similar to those that might be found in airport stormwater discharges at that location? If so, one way to determine if any pollutants detected in outfall monitoring data are from the airport is to conduct internal system monitoring of stormwater upstream of the outfall that represents stormwater discharges from the airport industrial area. If the potential constituents from the co-mingled flow are different from those that might be present in airport stormwater discharges, it is still important to document them as some constituents may interfere with the measurement of certain airport parameters (e.g., arsenates can interfere with phosphate determination). Many airports were first constructed during or shortly after World War II, and storm- water infrastructure may date back to the 1940s and 1950s. This stormwater infrastructure may be in poor or failing condition, resulting in opportunities for groundwater inflow into the conveyance system depending on the geology at the airport. This groundwater inflow could contain naturally occurring constituents like arsenic, iron, phosphorus, and dissolved solids, or it could contain contamination from historical activities or spills. If an airport sus- pects that constituents identified in monitoring data may be attributable to groundwater, it may be worth conducting a root cause investigation to determine if the primary constituent source is groundwater. Should a specific source be identified, the airport could consider repair or replacement of stormwater conveyance in that area to prevent further inflow of groundwater. For more information about interferences, see: Customizable Parameter Fact Sheet Tool 3.4 Application 2: Using Data in Establishing Permit Conditions For more information about conducting a root cause investigation, see: 3.3.4 Conduct Source and Root Cause Investigations For more information about contaminated groundwater inflow, see: C.3 Victoria International Airport Topical Tips Overcome Outfall Location Limitations When utilities are limited, consider: • Battery or solar power • Potable water tank • Telemetry Where there are safety risks or access issues, consider: • Identifying an alternative location • Weather-related safety concerns when scheduling monitoring activities • Coordinating with operations to allow safe access When there are stormwater conveyance structure issues, consider: • Conducting visual field conditions assessments at another location • Installing a weir or flume • Installing a backflow preventer • Avoiding monitoring of stagnant pools • Conducting monitoring only when there is a discharge • Conducting a root cause investigation to identify whether dominant pollutant sources are from groundwater inflow • Repairing or replacing aging stormwater infrastructure

50 Interpreting the results of airport Water Monitoring 1.6 Selecting Monitoring Frequency and Extent In addition to selecting a monitoring location, an airport must determine how frequently to monitor and how much data to collect. For permit-required monitoring, frequency and extent are often specifically prescribed in the permit, but, when monitoring is for other purposes, how frequently to monitor or how much data is needed to achieve the purpose of the monitoring may not be clear initially. The key is to consider the driver or purpose for the monitoring and use that along with the considerations in the next two sections to establish monitoring frequency and extent. In many cases, the ultimate extent and frequency of monitoring may change based on review of initial data collected, so it is important to be flexible and use the data to help inform decisions about future monitoring frequency and extent. 1.6.1 Monitoring Frequency Monitoring frequency describes the time interval between samples or monitor readings. The purpose for conducting monitoring, and the characteristics and variability of the monitored stormwater are two factors that might affect monitoring frequency. U.S. EPA’s permit writers’ manual states that monitoring frequency should be sufficient to characterize the effluent qual- ity and detect events of non-compliance, considering the need for data and, as appropriate, the cost to the permittee (U.S. EPA, 2010). Consider the questions in the following Topical Tips box when determining how frequently to monitor: For more information about defining the purpose and drivers for monitoring, see: 1.3 Identifying Drivers and Objectives for Monitoring For more information about proposing reductions to monitoring frequency, see: U.S. EPA Interim Guidance for Performance­Based Reductions of NPDES Permit Monitoring Frequencies Topical Tips Monitoring Frequency Considerations Seasonal Variation • Is there potential for seasonal variation in the parameter the airport is monitoring? • Is it important that these seasonal variations be understood? • Is there a specific season the airport is particularly interested in understanding? Flow Conditions • How might the flow rate of the airport’s discharge affect the concentration of the parameter the airport is monitoring? • How might the flow rate of the airport’s discharge affect the load of the parameter the airport is monitoring? • Is it suspected that the load contribution of the parameter is constant and higher flows would result in a lower concentration of that parameter and lower flows would potentially result in a higher concentration of that parameter? • Is it suspected that the load contribution of the parameter varies with flow? • Is the parameter the airport is monitoring expected to exhibit first flush characteristics where the concentrations are higher at the beginning of the event than at the end? • Is it important for the characteristics of this parameter in the airport’s discharge to be understood under high flow, low flow, or a variety of flow conditions?

acquiring Monitoring Data 51 Airport Activities • Is this parameter only likely to be found in the airport’s stormwater discharges during or shortly after certain airport activities are performed (e.g., deicing, runway rubber removal)? • Do the characteristics of this parameter in the airport’s discharge need to be understood at all times or only when those activities occur that make it likely to be present? Variation in Discharge Concentrations • Is there significant variation in the discharge concentrations or is the concen- tration relatively constant? • Is it important to characterize this variation? • Is the variation predictable (e.g., always higher after storm events following long dry periods)? • Can monitoring activities be strategically timed to capture predictable variation? Root Cause Investigation • Is the airport trying to conduct a root cause investigation? • What is the suspected cause of the issue and how frequently does monitoring need to occur in order to confirm or deny the suspicion? Background Characterization • Is the airport trying to understand constituents present in its base flows? • Is the airport trying to understand the background concentrations in the receiving stream? • Should storm events or dry periods be targeted to best understand these back- ground conditions? Characterization of Average Concentrations • Is the airport subject to an average effluent limit? • What frequency of monitoring was used to establish the average limit? • Is the airport monitoring frequently enough to adequately characterize the average concentration to meet that limit? Cost • How much does it cost to conduct monitoring? • What is the airport’s budget? • Are there cheaper methods the airport could use or alternative parameters it could monitor that might allow it to monitor more frequently at a lower cost? • Is there an opportunity to conduct high-frequency short-term monitoring to establish a trend with the potential to reduce monitoring frequency if no or limited issues are identified? 1.6.2 Monitoring Extent Monitoring extent is defined as the number of monitoring data points over the range of con- ditions associated with the monitoring plan in a specific period of time. Where monitoring fre- quency is specified, multiplying the desired monitoring time frame by the monitoring frequency provides the monitoring extent. Determining whether sufficient data has been collected is often

52 Interpreting the results of airport Water Monitoring one of the most difficult and most important decisions in developing a monitoring plan. From an airport’s perspective, the monitoring extent is a balance among factors such as cost, staff resources, operational impacts, and ability to practically obtain monitoring data that represents the monitored flows in space and time. Regulators are able to focus more on the question of representative monitoring. The more data that is available, the more confidence a regulator has that the data set adequately characterizes the range of conditions, including the extremes, in an airport’s stormwater discharges. A lack of representative field-monitored data when setting permit conditions results in the need to supplement the data with data from similar sites and model estimates and/or to set more conservative permit conditions if the regulator does not feel extreme conditions are adequately represented by available field- monitored data. When the extent of monitoring activities is not defined by regulation or permit, several factors weigh into the decision regarding how much monitoring to perform, including the following: • Minimum number of samples required by the statistical analysis technique (see Chapter 2: Interpreting Monitoring Data) • The expected degree of variation in analytical results (more expected variation requires more monitoring data points) • Anticipated degree of difficulty in collecting representative and accurate data (more monitoring data points may be needed to account for error-generated outliers) • Whether another source of stormwater characterization data is available (such as modeled flows and pollutant concentrations) • The impacts of insufficient monitoring on compliance and stormwater controls • Available budget • Staff resources available for sample collection • Time frame in which the data is needed Some of the same questions considered in determining monitoring frequency relate to moni- toring extent. Consider that the amount of monitoring data required to adequately characterize a discharge depends on the variability in that discharge. Historical data may be able to be used as a guide to variability. An understanding of the factors affecting the variability helps to assess whether variability is likely to be significant. For example, if it is known that the monitoring will occur during times of significant variation in flow rates or that the industrial activities contributing pollutants are not consistent, more samples will be needed to characterize the range of conditions. Some activities like deicing are known to produce extreme variations in parameters like COD and TDS, and it may take multiple deicing events or even multiple seasons of deicing to reasonably understand the expected range of stormwater characteristics. If possible, collect enough data to be confident that the extremes and the typical stormwater discharges are characterized with multiple data points. If monitoring data is obtained from locations that have challenging conditions, the data may be more subject to error, which might cause the need to plan for more monitoring. For example, if flow-weighted composite sampling is used for stormwater sampling, it can be difficult to cor- rectly determine the sample aliquots such that the sample container does not overflow during high flow conditions. An overflow condition affects the representativeness of the sample. In that situation, multiple monitoring events may be needed to more fully understand the pollutant variation. In some cases, other means of characterizing stormwater discharges may be available that can reduce the needs for in-field monitoring. For example, pollutant loads models that inte- grate modeled stormwater flow and an understanding of pollutant content associated with For more information about developing a monitoring plan, see: I.2 Developing a Monitoring Plan to Effectively Coordinate and Implement Monitoring Activities For more information about cutting costs, see: 1.7.5 Monitoring Efficiently to Reduce Costs and Save Time

acquiring Monitoring Data 53 different land use activities can be used to estimate flow rates and pollutant loads at outfalls. The degree of field monitoring data needed to support such modeling depends upon how the model is calibrated, techniques used to verify model output, and the degree of confidence in the model output. It is also important to consider the impacts that decisions on the extent of monitoring can have on affected issues. For example, if monitoring data is used to size stormwater controls, having insufficient monitoring data can cost hundreds of thousands of dollars because larger safety factors will be needed in design. Despite the desire to collect more data, ultimately, the amount of data collected may be determined by the cost of monitoring and the available budget, or limitations on the time available to collect data. While it is often difficult to justify funds for monitoring activities in airport budgets, airport staff should consider that impacts from insufficient monitoring on future capital projects could be an order of magnitude greater than the difference in the cost of additional monitoring. Justification for the costs, risks, and benefits of more extensive monitoring should always be provided to airport decision makers. While often the decision on the extent of monitoring is not as black and white as everyone would like, having an informed discussion of the risks of collect- ing more or less monitoring data is critical. In some cases, it might be possible to use an adaptive management approach to determine the extent of monitoring data that is needed to meet objectives. Using this approach, an ini- tial set of monitoring data is collected and assessed, then a judgment made as to whether additional data is needed to reduce the regulatory, functional, cost, and schedule risks. This approach could lead to a multi-step data collection process if time allows. Obviously this method is not helpful from a total budget perspective, but it is something to consider when planning monitoring activities. An adaptive management approach can also be used when selecting monitoring locations; monitoring would first occur at several locations and be followed by a targeted monitoring after review of the initial data set and assessment of differences and similarities in monitor- ing results. 1.7 Executing Monitoring Once the sample collection methods, monitoring parameters, methods, location and extent are determined the next step is execution. This section describes some of the impor- tant considerations when defining how to execute monitoring. 1.7.1 Field Activity Execution The execution of the field activities associated with monitoring can significantly influence the quality of monitoring data. Sloppy field practices, inexperienced monitoring staff, or poor train- ing can lead to data that does not accurately represent airport stormwater discharges or that is erroneous or invalid. Experienced monitoring staff with appropriate training not only acquire more reliable data, but they also collect additional information in the field that may help explain unusual or unexpected results. Understanding the quality of field activity execution is especially important when interpreting monitoring data results. If field execution practices are sloppy it is hard to know if an unexpected result is due to a change in the airport stormwater discharges or an error in field execution.

54 Interpreting the results of airport Water Monitoring Field personnel should have experience conducting stormwater monitoring and should receive training appropriate to the type of stormwater monitoring activities conducted. The level of expertise and training required depends on the complexity of monitoring activities conducted. At a minimum, field personnel should be trained on how to appropriately collect samples for laboratory analysis, including labeling procedures, chain of custodies, sample hold time requirements, sample storage requirements, how and where to collect a sample from the flow, and how to decontaminate sample collection equipment and avoid cross-contamination of samples and trip blanks. The Topical Tips box provides an example of the type of equipment that monitoring personnel may need to use in the field. Field personnel should always receive appropriate safety training based on potential hazards at each sampling location and use appropriate personal protective equip- ment. This could include confined-space training or training to drive on the airfield if necessary. Field personnel should be trained on how to conduct field observations, and what types of unusual condi- tions should be documented that might explain unusual monitor- ing results (e.g., backflow from receiving water, stagnant or partially frozen discharge). If specialized equipment is used, field personnel should be trained on the appropriate use of the specialized equip- ment, including any required maintenance, decontamination, or calibration procedures. Some airports use airport staff to conduct field monitoring activities and others choose to hire a consultant or laboratory to conduct field activities. There are a few factors that might influence an airport’s deci- sion to use airport staff or to hire outside staff to conduct field activities. Some permit-required monitoring must be conducted within a speci- fied short time frame following the beginning of a storm event. Moni- toring staff need to be available and able to access monitoring locations within this time frame. Sometimes the decision to hire outside staff or use airport staff depends on the amount of time it takes to conduct monitoring, other workload demands on airport staff, and their availability to take on additional responsibilities. At some airports, field activities associated with monitoring could require a significant amount of time. If the airport does not have staff with adequate experience or the ability to train staff to conduct the field activities, then outside staff may be used. Finally, the cost and availability of appropriately experienced and trained staff provided by a consultant or at a laboratory should be considered before deciding to hire out for field activities. 1.7.2 Documentation of Field Conditions While in the field, one of the key responsibilities of the field personnel is to document the field conditions. Documenting the conditions when monitoring is conducted can be critical to interpreting the data. If in review of a data set, an airport identifies occasional spikes in concentration, review of field conditions data may facilitate understanding of any unique conditions contributing to the spikes, which is the first step in investigating the root cause of an issue. Field observations may also help identify malfunctioning equipment (e.g., slime buildup noted on DO probe), calibration issues (e.g., pH measured is 6.0 s.u. at all outfalls during a torrential rain storm), and the need for maintenance (e.g., evidence of beaver dam activity noted in outfall). For more information about conducting a root cause investigation, see: 3.3.4 Conduct Source and Root Cause Investigations For more information about interpreting monitoring data, see: 2.4 Analyzing the Data Topical Tips Equipment Checklist for Field Activities • Cooler • Ice • Sealable plastic bags for samples • Required containers for sample collection prefilled with preservative, if necessary • Chain of custody form • Trip blanks as necessary • Field blanks as necessary • Field conditions form • Pen for labeling sample containers and taking notes • Labels for sample containers • Appropriate personal protective equipment (e.g., gloves, waders) • Camera to document unusual field conditions • Decontamination equipment • Sample collection equipment (bailer, cup on a stick, tube with peristaltic pump) • Watch or phone to document time • Stopwatch for flow monitoring if needed

acquiring Monitoring Data 55 U.S. EPA’s MSGP requires that samples be collected for visual inspection of the following water quality characteristics: • Color • Odor • Clarity • Floating solids • Settled solids • Suspended solids • Foam • Oil sheen • Other obvious indicators of stormwater pollution While a field notebook and laboratory chain-of-custody forms are good practices for documenting monitoring activities, a good field data collection form facilitates consistent documentation and management of field data and is key to ensuring that field personnel collect all necessary data. Included in Appendix A is an example field data collection form that can be printed out and completed by hand, or completed electronically on a tablet. The following subsections provide examples of information to include on the field data collec- tion form. Monitoring Activities Performed and Resources Used A record of the monitoring activities performed and resources used not only provides useful data for scheduling routine maintenance of equipment and budgeting for future monitoring activities, but also may identify issues. For example, if high pH readings are only measured when using one specific meter, there may be a calibration issue with that meter. In addition to identifying the date, time, and location of the monitoring activities, identifi- cation of the staff member executing monitoring activities will allow for follow-up to col- lect additional information if needed. A detailed list of the monitoring activities performed helps connect the appropriate laboratory analytical data with the field report. Developing a detailed list of monitoring activities planned at each monitoring location is a good way to make sure something does not get missed in the field. Also documenting any equipment maintenance, battery or other parts replacement, cleaning, or calibration conducted while in the field will help to facilitate tracking of maintenance, calibration, and planning for future maintenance activities. Characteristics of Flow Being Sampled Qualitative characteristics, such as the nature of the discharge (i.e., stormwater runoff or snowmelt), presence of sheen, color, clarity (turbidity), foam, floatables/debris, odor, and nuisance microbial biofilms should be noted, and photographs should be logged of any unusual visual observations. Field conditions fact sheets, in Appendix B, include a general description of each characteristic, an approach to observing the characteristic, variations that may be noted, and potential sources. Quantitative data measured in the field should also be noted. Commonly, this may include temperature, pH, turbidity, flow rate, water level, conductivity, oxidation reduction potential, or dissolved oxygen. A description of the flow conditions at the monitoring location should be noted. Examples of flow conditions that may be noted include stagnant pools with little flow, no observable flow, stormwater that has flooded banks, back flow from the receiving water affect- ing monitoring, buildup of water upstream of large debris in outfall, outfall partially frozen. If observable, flow conditions upstream and downstream of the sampling location in the receiving water should also be noted. For more information about documenting field condi- tions, see: Appendix A: Field Data Collection Form U.S. EPA Industrial Storm­ water Monitoring and Sampling Guide U.S. EPA MSGP For more information about observing and determining the source of unusual field conditions, see: Appendix B: Field Conditions Fact Sheets

56 Interpreting the results of airport Water Monitoring Observations of Other Field Conditions and Activities that Might Affect Sample Quality Other observations that might affect the water quality or the quality of the data gathered should be noted. This would include a description of the weather, including the outside air temperature, the type of precipitation (if any), and how long it has been precipitating prior to conducting monitoring activities. If the visual observations were not conducted at the appro- priate time prescribed in the permit (e.g., within 30 minutes of a discharge), the reason for the deviation should be noted. This information could be used to identify if the monitoring data represents the characteristics of the first flush. Observations of airport operations or observed activities that could be potential pollutant sources should be noted. This may include deicing activities, construction activities, vehicle maintenance activities, pavement painting, sealing, or resurfacing, runway rubber removal, or recent spill reports logged. The condition of the sampling equipment should also be noted. This will help facilitate timely maintenance, and identify issues that may affect the quality of the data. Examples of sampling equipment notes could include fouling of or slime on sensors; meters buried under snowpack, sediment, or debris; dislodgement of an installed flow meter; lightning damage; calibration dif- ficulties; frozen battery; and DO meter malfunctioning. Finally, other observations about the monitoring location that might be useful in character- izing the data and identifying maintenance needs would include wildlife observations (e.g., dead deer in ditch, aquatic life, turtle caught in pump station) and conditions that may have limited access to monitoring locations or equipment (e.g., frozen or locked gates, debris, or brush). 1.7.3 Event-Based Monitoring Execution Water quality monitoring is typically either event based, where monitoring is conducted to understand the characteristics of stormwater discharges during discrete events, or continuous, where monitoring is conducted to understand the characteristics of stormwater discharges at all times. Aspects of event-based and continuous monitoring affecting monitoring execution are somewhat different, so execution of these two types of monitoring is discussed in separate sections. Event-based monitoring activities may include collection of grab or composite samples, direct measurement of parameters using a handheld device, conduct of analysis using a test kit, and collection of field conditions data. Inherent in event-based monitoring is the requirement to execute monitoring activities within a specified time frame. Depending on the purpose of the monitoring, this may require monitoring staff to be available around the clock, or to conduct monitoring in inclement conditions. Depending on the frequency of the monitoring, and the number of monitoring locations, this may require a significant time commitment from the monitoring personnel. The airport should identify the criteria for a qualifying event, including the following: • Minimum precipitation or flow and the time between events (also referred to as the ante- cedent dry period) • Event-based triggers to commence monitoring, including time from the start of precipitation or flow • Non-event-based triggers that may affect the timing of monitoring including tides, receiving water elevations, airport operations, groundwater elevations, and ice or snow conditions at the outfall

acquiring Monitoring Data 57 • Staff availability • Visibility • Safety • Interference with airport operations and site access The airport should also identify and document in the monitoring plan the equipment that will be used, including pre-labeled sample bottles (see list in Section 1.7.1: Field Activity Execu- tion for checklist of typical equipment); the number of staff, level of expertise, and anticipated time commitment required; procedures for initiating monitoring activities; procedures for stor- age and handling of samples and data; and procedures for conducting analysis or shipment of samples to a laboratory. 1.7.4 Continuous Monitoring Execution Continuous monitoring activities may include mounting of monitoring devices in the dis- charge stream, like pH, DO, or conductivity data sondes; installation of online monitors like TOC or COD monitors, which require samples from the monitored stream; maintenance and calibration of continuous monitoring equipment; and download of data from monitoring equipment. Online monitoring requires special attention as there are additional considerations associ- ated with continuous operation of monitoring equipment. In addition to the equipment and staffing considerations discussed in Section 1.7.3: Event-Based Monitoring Execution, con- tinuous monitoring typically requires more specialized equipment and generates more data. Equipment for conducting continuous monitoring may be more expensive and more utility intensive, requiring power to operate pumps or potable water to flush lines, and may require structures to contain online monitors and pumps. In addition, the analytical mechanisms used in some online instruments may differ somewhat from their laboratory counterparts. As a result, it is recommended that monitored values from online instruments be compared to measurements on the same sample made on laboratory instruments. If a consistent correla- tion between online and laboratory results reveals a bias (e.g., if online CODs are consistently 10 percent higher than the laboratory CODs), airport staff should consider whether a correla- tion factor should be applied to the online data results. Plans for data download, should that be necessary, and data management should be carefully considered. A supervisory control and data acquisition (SCADA) system may be useful for remote control of online monitoring equipment and collection of data. Because monitoring is conducted continuously and automatically, and field conditions are not collected with monitoring data, field condition information is often not available to assist with understanding of unusual monitoring data. In addition to identification of maintenance and calibration needs, documentation of field conditions is an important reason to regularly visit continuous monitoring locations. 1.7.5 Monitoring Efficiently to Reduce Costs and Save Time Monitoring can be a labor-intensive and costly activity, and since it is a non-revenue- generating activity for the airport, the less time and money an airport needs to dedicate to moni- toring, the better. Reducing costs and time spent monitoring may free up limited budget or personnel hours for conducting additional monitoring, or for other environmental programs. Monitoring efficiently may not only reduce costs, but also save valuable time for monitoring personnel (which also saves money). This section describes some tips for increasing efficiency in monitoring.

58 Interpreting the results of airport Water Monitoring Coordinating Simultaneous Monitoring to Satisfy Multiple Monitoring Needs with One Trip Whether airport personnel or an outside laboratory or consultant is used, labor time or expense is often one of the greatest costs associated with monitoring. There are several ways to minimize the amount of time spent dedicated to monitoring. Start by identifying the monitoring requirements in the permit, or monitoring needed to support the purpose of the monitoring. Determine if any of the monitoring can be conducted simultaneously. Consider if monitor- ing for multiple purposes, at multiple locations, for multiple parameters, or for multiple per- mit conditions can be conducted simultaneously. For example, can deicing event monitoring be conducted at the same time as regular event monitoring? This may require a review of the requirements for conducting the monitoring (e.g., amount of precipitation, timing during event) to determine if two monitoring needs can be met with one event. Conducting monitor- ing activities simultaneously reduces the number of trips monitoring personnel must make to a monitoring location, and the frequency with which personnel must devote time to monitoring, which saves time and money. Using Automatic Samplers, Installed Handheld Monitors, and Online Monitors to Reduce Labor The next way to reduce labor costs is to determine if any sampling could be conducted with an automatic sampler. Once initiated, an automatic sampler collects aliquots of storm- water runoff at specific time or flow frequency without additional action by monitoring personnel. An automatic sampler may be particularly useful for composite sample collec- tion, which often requires multiple aliquots to be collected in a 24-hour period. Consider physical limitations present at monitoring locations that may make use of an automatic sam- pler infeasible, including the need for power, and the need to mount or install the sampler. Determine whether samples for the parameters that need to be measured can be collected with an automatic sampler. For example, oil and grease samples must be collected manually in a container with no headspace and may not be collected via automatic sampler because automatic samplers may allow the oil and grease to volatilize before analysis is completed, and oil and grease may stick to sample tubing and other equipment. Compare the cost of the equipment (e.g., sampler, battery, housing, pump), installation, operation (e.g., power, potable water), and maintenance to the cost associated with hours saved using the automatic sampler to determine if the payback period is reasonable. Online monitors and permanently installed handheld devices also provide an opportunity to reduce labor associated with monitoring. For example, if regular dissolved oxygen measure- ments can be collected using a data sonde installed in the discharge stream, then monitoring personnel only need to visit the monitoring location to download data and collect field condi- tion information. The cost of the equipment (e.g., monitoring unit, housing, battery, pump, software), installation (e.g., feasibility of installation), operation (e.g., power, potable water), maintenance (cleaning, recalibration, parts replacement), accuracy, and potential issues (e.g., fouling, destruction of equipment during heavy flows or from debris) should be taken into account when the use of online monitors or permanently installed handheld devices is being considered. Using Telemetry to Automate Monitoring to Reduce Staff Time Another way to reduce labor costs is to consider using telemetry, or remote initiation of sample collection with automatic samplers. Telemetry is an automated communication pro- cess by which sampling is initiated remotely or data from online monitors is collected from monitoring locations remotely. The monitoring execution subsection of the Seattle-Tacoma For more information about deciding whether to hire outside help to conduct monitoring activities, see: 1.7.1 Field Activity Execution For more information about selecting monitoring locations, see: 1.7.1 Field Activity Execution For more information about telemetry, see: C.1 Seattle-Tacoma International Airport

acquiring Monitoring Data 59 International Airport case study describes how telemetry is used at the Seattle-Tacoma airport. If composite monitoring can be initiated remotely, the monitoring personnel only need to visit the monitoring location once to collect the sample, not twice to initiate then to col- lect the sample. In addition to added efficiency, telemetry has other benefits. Often mon- itoring must be initiated during a storm event, which without telemetry would require personnel to be in the field during potentially hazardous weather conditions. Additionally, using telemetry to initiate monitoring allows sample collection at all monitoring locations to start simultaneously resulting in monitoring results across the airport representing the same time period and conditions, eliminating staggered start times with different samplers collecting flow from different stages of the storm event. Field conditions would be noted only when the samples are collected, and not both when sampling is initiated and when it is collected. Coordinating Monitoring Activities with Landscaping or Maintenance Tasks to Save Time For non-event-based monitoring, consider training maintenance or landscaping staff to conduct monitoring activities. If regular mowing, brush removal, or foreign object debris removal is required at remote monitoring locations, landscaping staff may be able to incor- porate monitoring activities into these regular activities, saving a separate trip specifically for monitoring. If monitoring equipment installed at monitoring locations require regular maintenance, consider conducting maintenance activities at the same time as monitoring is required to reduce visits to monitoring locations. When using other staff for monitoring activities, carefully consider the skills required to conduct monitoring and adequately train and equip staff. Strategic Selection of Parameters to Reduce Costs Expenses for laboratory analysis are also one of the highest costs associated with moni- toring. Consider first if there are any analyses that can be conducted on-site instead of in a laboratory with the level of accuracy needed to meet monitoring objectives. Test kits, handheld devices, and online monitors may be less expensive over time and provide the level of accuracy needed to meet monitoring objectives. An additional benefit of test kits, handheld devices, and online monitors is that data may be available much faster to support real-time or near-real-time data needs. If non-laboratory analysis methods are used, be sure to obtain a correlation between the laboratory data and the output from the alternative analytical device. Obtaining accurate low concentration measurements, in particular, can be a challenge with some field instruments because they have less sensitivity than laboratory instruments. Review the parameters that were initially selected for monitoring and determine if other sur- rogate parameters with lower cost analyses might be sufficient to meet monitoring objectives. For example, is it necessary to measure propylene glycol or is a TOC measurement sufficient to characterize aircraft deicing activities affecting stormwater quality? Consider conducting limited monitoring of both the expensive desired parameter and the inexpensive surrogate to establish a relationship between the parameters. An established desired parameter:surrogate relationship will enhance the usefulness of future inexpensive surrogate parameter measurements in estimat- ing concentrations of the desired expensive parameter. Another way of using surrogates may be to substitute the surrogate parameter for a limited number of the required analyses. For example, maybe the oil and grease parameter is measured For more information about skills, training, and equip- ment needed for monitoring personnel, see: C.1 Seattle-Tacoma Inter- national Airport When using non- environmental staff for monitoring activities, carefully consider the skills required to conduct moni- toring and adequately train and equip staff. For more information about the use of surrogates, see: 3.4.3 Proposing Alternative Monitoring Parameters and Methods ACRP Report 72: Guidebook for Selecting Methods to Monitor Airport and Aircraft Deicing Materials

60 Interpreting the results of airport Water Monitoring weekly or monthly and BTEX is measured quarterly. Section 3.5.2: Management of Ongoing Operations and Maintenance Activities provides more information about surrogates, including a table listing typical surrogates used for specific parameters. Strategic use of surrogates can be very cost effective. Regular Review of Monitoring Data to Prevent Excessive Monitoring The final tip for monitoring efficiently is to regularly review data to ensure the data collected continues to meet monitoring objectives. This will reduce the likelihood of collecting data that does not directly support the monitoring objectives. Regular review of monitoring objectives is also particularly important with a root cause analysis. This review may lead to changes in the monitoring plan indicating more or less frequent monitoring; selection of different param- eters or locations; or the determination that the root cause has been identified and sufficiently characterized, and monitoring can cease. For more information about determining the appropriate extent of monitoring, see: 1.6.2 Monitoring Extent For more information about U.S. EPA-approved analytical methods, see: Clean Water Act Analytical Methods Update Rule Topical Tips Questions to Ask When Determining If Additional Data Is Needed for a Root Cause Analysis • Will more data provide better information, or is more data being collected for the sake of more data? • Is more or better information actually required to characterize the root cause? • How much more data, and what data is needed? • Would different data (alternative parameters, locations, frequency) be more appropriate? • What is the value added from collecting more data, and what is the cost? Topical Tips Efficient Monitoring Tips to Save Time and Money • Can monitoring for multiple purposes, parameters, or locations be conducted simultaneously? • Would use of an automatic sampler be feasible and cost effective? • Would use of a permanently installed handheld device or online monitor be feasible and cost effective? • Can telemetry be used? • Can maintenance or landscaping staff conduct monitoring as part of other responsibilities at monitoring locations? • Can analysis be conducted on-site less expensively than at the laboratory and still maintain the level of accuracy required? • Are less expensive surrogate parameters available that could be monitored that would still meet monitoring objectives? • Is more data needed, or has enough already been collected to meet monitoring objectives? • Is the data being collected the most appropriate to meet monitoring objectives?

acquiring Monitoring Data 61 1.8 Collecting, Reporting, and Maintaining Data Careful advanced planning for the collection, reporting, and maintenance of data is key to an effective and efficient monitoring program. Collecting, maintaining, and reporting data now in a way that supports potential future data needs can save significant time and efforts later. Hours spent searching through old boxes of laboratory reports, or money spent repeating monitoring activities because data has been lost or cannot be correlated to field conditions can be avoided. The next three sections discuss tips for collecting and compiling results, reporting results, and managing data. 1.8.1 Effective Collection of Data to Facilitate Review of Results The first step in managing monitoring data is understanding its sources. Airport monitoring data can come from a variety of sources, including the following: • Chain-of-custody forms • Field observations • Laboratory analytical reports (see more information in the following paragraphs) • Field data collection forms with analysis results from direct-measurement handheld devices and test kits (e.g., pH, DO, temperature, TOC) • Calibration records for field equipment • Maintenance records for field equipment • Weather data from local weather stations • Manual data downloads from online monitors or data sondes • Online monitoring logged with a SCADA system or programmable logic controller. The next step in managing data is ensuring the airport receives the data it needs from each of its data sources. For online monitors and handheld devices where data is downloaded, that means making sure the appropriate data is collected and logged with the appropriate frequency. Data sondes can often measure multiple parameters; therefore, they must be programmed to capture the parameters needed. Also, consider how frequently data should be measured and logged. For example, do measurements need to be logged at 5-minute intervals or 6-hour inter- vals? Remember that more data collected means more data managed, so choose the time interval carefully, and consider the purpose of the monitoring and the type of data analysis or interpreta- tion to be conducted with the data. For data collected manually in the field, ensuring the airport receives the data it needs means making sure monitoring personnel measure, observe, and document the appropriate data. Pro- viding a form that specifies the required data will facilitate consistent collection and tracking of field data. For laboratory analyses, ensuring the airport receives the data it needs means communicating effectively with the laboratory to make sure the laboratory has all relevant information about the samples collected and analysis requested, that the laboratory knows what information an airport expects in the laboratory report, and that the airport knows how to read and interpret the labora- tory report. The Topical Tips box in this section describes some of the information that would be helpful to exchange with a laboratory when delivering samples and when reviewing analyses. 1.8.2 Compilation and Management of Results to Support Interpretation of Data Once the sources of data have been identified, and the data needs effectively defined and communicated, the next step in managing data is deciding how and where to compile the data. For more information about field data collection, see: 1.7.2 Documentation of Field Conditions Appendix A: Field Data Collection Form

62 Interpreting the results of airport Water Monitoring Topical Tips Information to Obtain from Laboratory When Delivering Samples • Verification that samples were received in good condition and at the appropriate temperature • Verification that there are no issues or questions with the chain of custody • Confirmation of method for delivering results (e.g., paper report via mail, PDF file, Excel table, online database download) Information to Provide to Laboratory When Delivering Samples • Time frame for when laboratory analysis report is needed (e.g., is a rush designation required, or is the standard time frame acceptable?) • Laboratory analyses to be performed • Expected range of concentration (this helps the laboratory plan the appropriate dilutions) • Potential constituents that the laboratory might not be expecting that might cause interferences with the analysis • Which constituents are particularly important to the airport that may be worthy of extra scrutiny • Field conditions that could affect analysis (e.g., sheen on top of water, unusually high amount of suspended solids) • Issues (e.g., trip blank sample bottle broke in field, ice not taken in cooler thus temperature requirements not met) • Detection limit needed to meet permit requirements to quantify concentrations at the effluent limit or benchmark Information to Obtain from Laboratory When Reviewing Analyses • Date analysis was performed • Analysis results (e.g., concentrations, detects, nondetects) • QA/QC sample results (e.g., trip blanks, duplicates) • Indicate if dilutions of samples were performed, why they were performed, and possible effects on interpretation of the results • Method detection limit for any nondetects, and any significant variation in method detection limits • Information on possible interferences for individual parameter analysis • Meaning of results reported as “<” or “>” • Explanation for any missed hold times • Explanation of possible reasons for any unusual results (e.g., ethylene glycol detected in runoff at an airport that does not use ethylene glycol–based deicers) • Guidance on interpretation of any flags or QA/QC results There are several factors to consider when deciding how and where to compile data. Consider the following questions: • Who needs to be able to access the data? Is it only airport personnel, or will consultants or regulators need regular access to the data? Does regulatory reported data need to be main- tained separately from other data? • Where will data need to be accessed? Will data be accessed only from one person’s office, or do personnel need to be able to access data remotely? What risks are associated with allowing For more information about managing public perception, see: 3.6 Application 4: Stake- holder Communication and Public Outreach

acquiring Monitoring Data 63 remote access to the airport server? How many people need access to the data? Are there con- cerns about accidental or deliberate modification or corruption of data? • What format will best support review, analysis, and interpretation of the data? Is a box of paper records going to be the best format for saving data, or is a spreadsheet a better platform to support data analysis? Are paper copies of laboratory reports necessary, or can laboratory data be received in PDF or spreadsheet format? Can chain-of-custody forms be scanned and maintained electronically? Can field data be collected electronically on a mobile device? • How can data from different sources describing the same monitoring event be associated? How can information on field conditions best be correlated with laboratory analytical results; can this information be stored in the same spreadsheet organized by date and location? Should data file names be consistent and coded with the date and location so they are easily sortable and searchable? • For how long will data need to be maintained? Will data be kept in perpetuity, or will old data be deleted? How far back is data relevant given the purpose of the monitoring? Have major changes to airport infrastructure and operations occurred that would make historical data collected prior to the changes irrelevant and unrepresentative of current conditions? • How much data will be compiled? What size data files will be generated? How much space is needed/available to store data files (electronic and paper copies)? • How will data be used? Can data be formatted so that it automatically calculates basic statisti- cal analyses like averages, minimums, maximums, and standard deviation as data is added? Can graphs or charts be set up in advance to facilitate visual review of trends, detections, and outliers as data is added? Does data need to be reported to a regulator? Should data be main- tained in the format required for the regulatory report? 1.8.3 Understanding Requirements for Reporting Results It is of vital importance when planning monitoring activities to understand what the require- ments will be for reporting results to a regulator or providing results to the public. U.S. EPA’s NPDES Permit Writers’ Manual states that data reported should include both data required by the permit and any additional data the permittee has collected consistent with permit require- ments. Monitoring records must be kept for 3 years and must include the date, place, time of sampling, name of the sampler, date of analysis, name of analyst, analytical methods used, and analytical results (U.S. EPA, 2010). In addition to requirements to report monitoring results prescribed in the permit, some permits or regulations require an airport to report other data collected from permitted outfalls, or from other locations for parameters identified in the permit. In lieu of reporting voluntary monitoring activities, some permits or regulations may require that the airport maintain non-reportable data and provide it to a regulator upon request. Requirements differ by permit and by state, and it may be worth a call to the regulator to understand their requirements and expectations for reporting of non-permit-prescribed monitoring data. Monitoring data may also need to be made available to the public. For public agencies, most information is discoverable with a Freedom of Information Act request. Even data that is within permit limits could be misconstrued by an uneducated interest group as causing environmental harm and could result in a public relations nightmare. Careful public out- reach includes providing appropriate background to facilitate public understanding of data provided. For more information about reporting requirements, see: U.S. EPA NPDES Permit Writers’ Manual

64 Interpreting the results of airport Water Monitoring Appropriate Reporting of Nondetects and Qualified Data In addition to understanding what data should be reported, and what data needs to be main- tained and made available upon request to the regulator or the public, it is important to under- stand how to handle reporting of parameters that were not detected during analysis, or data that is qualified in some way. Requirements for reporting these values vary by state and by permit and may include reporting of a code for qualified or nondetect value. Some regulatory agencies require reporting of 0, the detection limit, or half the detection limit. Other requirements may be more complex. Be sure to understand the expectations for reporting of nondetect or qualified values. For more information about using nondetects or qualified data in data analysis, see: 2.3.3 Analytical Considerations 2.4.7 Censored Data (Nondetects)

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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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