The purpose of this report is to describe the sampling and analysis plan (SAP) of the USGS Koocanusa/Kootenai long-term water-quality monitoring program. This SAP follows the policies and procedures of the USGS; specifically, the USGS “National Field Manual for the Collection of Water-Quality Data” (NFM) (U.S. Geological Survey, variously dated) and “Guidelines and Standard Procedures for Continuous Water-Quality Monitors—Station Operation, Record Computation, and Data Reporting” (Wagner and others, 2006). Deviations from standard USGS procedures or procedures used where no standard procedures were available are detailed in this SAP. This report includes the logistics, sampling data-collection scheme and design, pre- and post-collection processes, and quality-assurance and quality-control procedures. The requirements for data management and review, as well as procedures to ensure health and safety, are also provided.

Lake Koocanusa was created by the construction of Libby Dam in 1972, 26 km upstream from the town of Libby, Mont., and impounds water from about 23,271 square kilometers (km²), or 47 percent, of the Kootenai River drainage basin (Woods, 1982). Three Canadian rivers (Kootenay [Canadian spelling of Kootenai], Elk, and Bull Rivers (not shown)) supply 87 percent of the inflow to Lake Koocanusa (Bonde and Bush, 1982). The lake has a volume of 7.16 cubic kilometers (km³), and it reaches 77 km from Libby Dam in Montana to the Canada–U.S. border and 68 km farther into British Columbia (U.S. Army Corps of Engineers, 2020). Lake Koocanusa has a mean depth of 38 meters (m), a maximum depth of 106 m at the Libby Dam forebay, and a mean water residence time of about 9 months (Easthouse, 2013). Normal full pool and minimum regulated lake elevations are 750 and 697 m, respectively (Easthouse, 2013). Downstream from the lake, below Libby Dam, the flow of Kootenai River is reduced for most of the year, with peak outflows of as much as 750 cubic meters per second from late May through June and in December (Easthouse, 2013).

Selenium in Lake Koocanusa has been detected at concentrations above State and Federal water-quality and aquatic life standards (Montana Department of Environmental Quality, 2020b). Selenium is a required micronutrient for most organisms, but elevated concentrations in water bioaccumulate in egg-laying fish and birds, causing various sublethal effects and death (Hamilton, 2004). Nitrate and sulfate loads to the reservoir also are of concern (Storb and others, 2023). Nitrate loading has potentially negative effects on phytoplankton and zooplankton community composition, and high nitrogen to phosphorus ratios can cause alteration of the lake’s trophic status (Elser and others, 2000). One source of selenium and nitrate in the Kootenai River Basin is the excavation of bedrock in the Elk Valley to access coal seams for metallurgical steelmaking and coal production (Mahmood and others, 2017; Wellen and others, 2018). There are currently (2026) five open-pit coal mines in this region of southeastern British Columbia, all operated by Elk Valley Resources (formerly Teck Coal, a subsidiary of Teck Resources Limited), with an annual production volume in 2020 of approximately 21 million tons of metallurgical coal (Teck Resources Limited, 2020).

Since 1984, total selenium concentrations in the Elk River have been measured at a British Columbia environmental monitoring station (site 0200016; not shown) (British Columbia Ministry of Forests, Lands, Natural Resource Operations, and Rural Development, 2022) 3.5 km above its discharge into Lake Koocanusa. Detected concentrations of total selenium ranged from 0.70 microgram per liter (µg/L; 1984) to 9.65 µg/L (2021). Since 1998, dissolved selenium concentrations have been reported in the Elk River at the same monitoring location and ranged from 1.10 µg/L (1999) to 9.46 µg/L (2021). In 2012, the Montana Department of Environmental Quality (MTDEQ) listed the lake as threatened by selenium (reporting as required by section 305(b) of the United States Federal Clean Water Act [33 U.S.C. 1251 et seq.]). In April 2013, the British Columbia Minister of Environment issued a Ministerial Order (No. M113) under the Environmental Management Act to reduce water-quality effects of mining activities to the Elk River and Koocanusa Reservoir (Province of British Columbia, 2013). Site-specific selenium standards of 0.8 µg/L for dissolved selenium in the water column and 15.1 mg/kg dry weight for fish egg (ovary) tissue (in addition to the muscle and whole-body standards) were established for the lake in 2020 following collaborative work by the MTDEQ, the British Columbia Ministry of Environment and Climate Change Strategy, the Lake Koocanusa Monitoring and Research Working Group, and a Selenium Technical Subcommittee (Administrative Rules of Montana 2020; Montana Department of Environmental Quality, 2020b). Simultaneously, this administrative rule maintained the existing selenium standard for the Kootenai River in Montana of 3.10 µg/L for dissolved selenium in the water column and 15.1 mg/kg dry weight for fish egg (ovary) tissue (in addition to the muscle and whole-body standards). The standards were adopted into Montana State law in 2020 and approved by the EPA in 2021 (EPA, 2021).

Monitoring water quality (and fish populations) in Lake Koocanusa and the Kootenai River has been ongoing since at least 1967, when the U.S. Army Corps of Engineers (USACE) and the USGS began collecting water samples (Easthouse, 2013) to better understand the relation between Libby Dam (completed in 1972) operations on the lake and downstream effects on the Kootenai River. Monitoring and research by these and other agencies have increased recently because of concerns that discharge from coal mining operations has led to increased selenium concentrations in the lake and the Kootenai River (Montana Department of Environmental Quality, 2020a).

In calendar year 2019, the USGS began a water-quality monitoring program in Lake Koocanusa and the Kootenai River just below Libby Dam (hereafter referred to as the “Koocanusa/Kootenai water-quality monitoring program”) to provide high-frequency water-quality data. In water years 2022–23 (October 1, 2021 to September 30, 2023), the specific objectives of this study were to (1) collect weekly composite water-quality samples for selenium from multiple depths in Lake Koocanusa at the International Boundary; (2) collect nitrate and sulfate samples from the lake and the river below the dam to understand their effect on hydrologic processes in the lake; (3) collect high-frequency continuous vertical profile data to understand limnological processes contributing to variations in selenium concentrations 4 to 12 profiles per day; and (4) establish a baseline water-quality dataset based on selenium concentrations measured in samples collected at lake and river sites.

Water-quality samples in the Koocanusa/Kootenai monitoring program were collected to measure concentrations of selenium, nutrients, anions, organic carbon, and other constituents. The overall approach for sample and data collection included the following components.

The USGS personnel collected water-quality samples, data, and related information for the Koocanusa/Kootenai water-quality monitoring program during water years 2022 and 2023. Specific responsibilities of key personnel are listed in table 3. The project lead and field lead are responsible for ensuring that personnel who perform sample collection have appropriate training and are cognizant of onsite safety considerations. Water-quality samples were shipped to two laboratories for chemical analyses: the USGS National Water Quality Laboratory (NWQL; Denver, Colorado) and the Brooks Applied Laboratory (Bothell, Washington). The Brooks Applied Laboratory was used primarily to analyze samples for selenium concentrations (total and dissolved) and selenium speciation (selenium speciation was discontinued in April 2022). All other samples were analyzed at the NWQL (tables 4 and 5).

The addresses and contacts for the laboratories are:

U.S. Geological Survey, National Water Quality Laboratory

P.O. Box 25585

Denver, Colorado 80225-0585

(303) 236-3500

Brooks Applied Laboratory

18804 North Creek Parkway, Suite 100

Bothell, Washington 98011

(206) 632-6206

Amanda Royal, Laboratory Project Manager

Samples and data were collected at six sites during water years 2022–23 in the Koocanusa/Kootenai water-quality monitoring program. The sites, frequencies, data types, and equipment used for data and sample collection are described in tables 1 and 2. The abbreviated identifiers for USGS stations were based on but different from the abbreviated site identifiers used by the USACE (Easthouse, 2013).

Site LIBB had a pontoon platform with an automated ServoSipper sampler, a novel automated water sampler that uses a peristaltic pump and a series of valves to collect water samples, and a continuous vertical profile monitor (fig. 1; table 1; the vertical profile monitor was discontinued in November 2022). During the winter (November–April), a submersible ServoSipper sampler was deployed at this site with two ice buoys tethered together to collect samples under ice. Site LIBB was also equipped with an ADCP (until November 2022) to measure water current velocities using the Doppler effect of sound waves scattered back from particles within the water column (Côté and others, 2000; tables 1 and 2). Vertical profile and ADCP data were transmitted remotely in near real-time during operation. In addition to automated sampling, discrete samples were collected at site LIBB every 4–6 weeks between April and November.

Site TOBR in the Tobacco River included a streamgage and was sampled every 4–6 weeks, year round, beginning in November 2022 (fig. 1; tables 1 and 2). Site LIBP was sampled from a boat during the summer and from a bridge during winter, every 4–6 weeks year round beginning in August 2022. Site LIBT was sampled every 4–6 weeks beginning in April 2022 and ending in June 2022 (3 sampling events), when sampling was discontinued at this site. Site LIBF was sampled every 4–6 weeks between April and November (tables 1 and 2). Site LIBW on the Kootenai River included a streamgage, a stationary water-quality monitor, and a ServoSipper housed in the gage house. This site was sampled every 4–6 weeks, year round.

This section describes the procedures for discrete and high-frequency water-quality sample collection, including sample trip and site visit preparation, documentation, sample tracking, and shipping to laboratories for analyses. Sampling equipment was cleaned at the WY–MT WSC water-quality laboratory in Helena, Mont., before taking the equipment into the field and after the first use. The Kemmerer sampler was also field-cleaned with deionized water and 5-percent hydrochloric acid (HCl) between sampling sites. All samples were collected following strict adherence to USGS guidelines for obtaining representative samples from the environment. This required field personnel to (1) understand the study objectives, including data-quality requirements, in the context of the water system being sampled; (2) minimize contamination and error during the sampling process; and (3) be aware of and document conditions that could compromise the quality of a sample (U.S. Geological Survey, variously dated). In addition, field personnel were expected to perform the following throughout the sampling process:

A pontoon platform (figs. 2 and 3) was deployed at site LIBB (fig. 1) to provide daily monitoring of total and dissolved selenium concentrations (table 4), vertical profile data, and ADCP velocity data. The vertical profile and ADCP velocity data collection were discontinued in November 2022 (tables 1 and 2). The platform at site LIBB was moored 1.21 km south of the Canadian border and accessed by boat. ServoSipper sampling systems developed by Thomas Chapin (USGS, Denver, Colo.) were mounted to the pontoon platform. These systems were set up differently for deployment during the winter to early spring so that samples could be stored longer; the field crew was unable to visit the site during icy conditions. Operation and use of the vertical profile and water-sampling equipment and discrete sample collection procedures at the lake sites are described in the following sections.

This section describes the sampling and data-collection procedures at site LIBW in the Kootenai River and site TOBR in the Tobacco River. Site LIBW was located at a USGS streamgage and was equipped with a stationary water-quality monitor (until February 2023) to collect data continuously at a fixed point and an automated ServoSipper to collect high-frequency water-quality samples (tables 1 and 2). Discrete water-quality samples also were collected at the thalweg from a cableway at this site. Site TOBR did not have a ServoSipper or unattended sensors, and only discrete samples were collected here from a pedestrian bridge or by wading.

Site files containing descriptive information on location, conditions, purpose, and ancillary information were kept for each data-collection site (Schroder and Shampine, 1992). Much of this information was stored electronically. A site description was prepared for each water-quality site where continuous data was recorded. The mandatory site information included the following: agency code, project number, USGS site identifier, latitude, longitude, latitude-longitude accuracy, horizontal datum, Water Science Center code, State code, county code, land net location, location map, map scale, altitude, method of altitude measurement, accuracy of altitude, vertical datum, hydrologic unit code, topographic setting, agency use of site, date inventoried, site type, data type, data reliability code, and use of site.

Field notes must contain sample information, including the USGS site identifier, agency code, sample date and time, sample conditions, sample purpose, quality-assurance activities, weather conditions, field parameters, and lot numbers of chemicals and equipment. These notes were maintained using a USGS-developed Microsoft Excel workbook called Superfly.

All samples were collected and stored in the required container type (tables 4 and 5) and clearly labeled. Labels were preprinted or hand-written in the field with a permanent waterproof marking pen using a waterproof label (for example, Avery Waterproof Laser Address Labels, product 5520) securely attached to the sample container. When preprinted labels were used, field personnel ensured the label and the information on it remained intact and legible throughout the processing and shipping process.

Further guidance on sample processing and container types is available in chapter 5 of the NFM (U.S. Geological Survey, variously dated). Each sample label and the analytical service request (ASR) forms that accompany the samples showed the USGS site identifier, project identification number (on ASR only), sample type, sample depth, date of collection (month/day/year), time of collection (24-hour format) and bottle type.

A sample tracking spreadsheet was created and maintained to record all samples collected and shipped to analyzing laboratories to ensure the complete and timely receipt of analytical results and accurate transfer of data to NWIS (U.S. Geological Survey, 2025n). Technical personnel were responsible for recording the required information. The project lead or designated technical personnel reviewed the sample tracking spreadsheet to determine if analyses were missing or if corrective action(s) were taken.

All samples collected in the Koocanusa/Kootenai water-quality monitoring program were documented according to the procedures outlined in book 9, chapter A4 of the NFM (U.S. Geological Survey, variously dated). To maintain a clear record of sample custody from collection through sample analysis and to inform the laboratory of the analysis being requested for each sample, samples shipped to Brooks Applied Laboratory included CoC and ASR forms. Samples shipped to NWQL included ASR forms, but they did not include CoC forms because they were not required. The NWQL is a research laboratory that does not provide methods for regulatory purposes and, therefore, does not require the CoC process. Samples received at the NWQL were promptly logged, checked for proper preservation (if required), and placed in storage areas for each sample type to await analysis. No further security procedures were involved. Samples were disposed of after normal holding times using routine disposal procedures. CoC (if required) and ASR forms were sealed in plastic bags inside the shipping containers.

Samples were packaged and sent for analysis as a batch shipment, when feasible. Three copies of the CoC form and two copies of the ASR form were completed for each sample. Two copies of the CoC and one copy of the ASR accompanied each shipment, and one copy of each was saved for project records. CoC forms, when required, were signed and dated by a member of the field team with the date and time of sample transfer. Upon receipt of the samples, the laboratory receiver completed the transfer by signing and dating the CoC form. One copy of the CoC was left at the laboratory, and another copy was returned to USGS project personnel.

All samples were collected in the containers specified in tables 4 and 5. Following collection, sample bottle caps were checked to ensure tight, secure seals. Glass containers were wrapped in foam sleeves or bubble packs designed for shipping glass containers to prevent breakage during shipping. Chilled samples were packed with sufficient ice to keep the temperature at or below 4 degrees Celsius. The volume of ice should be equal to or greater than the volume occupied by the samples. Twice the volume of ice was used during warm months. During winter months, samples were packed to prevent freezing during shipment. “Blue ice” or other types of commercially available re-freezable ices were not used because samples could become contaminated or may not maintain an adequate temperature. Chlorophyll-a and selenium speciation samples were shipped using dry ice to keep the contents of the shipping containers frozen. These samples were placed in separate shipping containers. Due to potential overpressure from carbon dioxide from the dry ice, these shipping containers were ventilated. When shipping dry ice, guidelines provided by the shipping service were strictly followed.

Sample containers were sealed in two plastic, sealable bags (double bagged). Prior to shipping, each sample was compared to entries on the CoC and ASR forms to ensure bottles and CoC/ASR entries matched. If ice was required for sample preservation, samples were packaged in thermally insulated, rigid coolers; samples shipped with dry ice were placed in small, rigid coolers that could be ventilated (for example, Styrofoam). Each package of samples was sealed with shipping tape and shipped by the most expedient means possible. The temperature of each cooler shipped to NWQL was measured during sample login and documented in the Laboratory Information Management System. Samples were also checked for proper preservation upon receipt. Samples or coolers that arrived at NWQL above the minimum temperature requirement were processed and flagged accordingly. The resulting laboratory analytical data were reviewed and either maintained (with the appropriate remark code in NWIS) or rejected and not reported.

Coolers were inspected before packing samples to ensure that they were in acceptable condition; coolers with missing handles, loose fitting lids, and cracks were not used. Shipping containers were lined with two (one bag inside of the other) heavyweight plastic bags. To isolate the samples from the ice melt, samples were placed in heavy, sealable bags. Bagged sample containers and ice were placed inside the plastic bags, and the bags were sealed with a knot, filament tape, or twist ties. Shipping containers were securely taped around the outside to minimize leaking and to maintain sample integrity. Coolers with spigots were sealed around the spigot opening with silicone or epoxy to prevent leakage. Excess packaging, such as bubble wrap, was not used.

To address QC issues related to water-quality activities, the USGS Water Mission Area has implemented policies and procedures designed to ensure that all scientific work by or for the Water Mission Area is consistent and of documented quality. One tool used to ensure compliance is the technical review of water activities in USGS Water Science Centers. Each USGS Water Science Center has developed Internal Technical Review Procedures describing the Center’s plan to ensure quality assure their programs. These Internal Technical Review Procedures are submitted to the USGS Office of Quality Assurance and are conducted by multidiscipline teams that visit and review each Center regularly. These reviews include, but are not limited to, the following activities:

In addition, the USGS Quality Systems Branch (U.S. Geological Survey, 2025g) produces water and sediment performance-assessment samples and data to provide the USGS laboratory users, USGS laboratories, and field personnel with quantitative performance information to assess data quality. Specific QA programs within the Quality Systems Branch include the Inorganic Blind Sample Project (U.S. Geological Survey, 2025h), the Organic Blind Sample Project (U.S. Geological Survey, 2025i), the Laboratory Evaluation Project (U.S. Geological Survey, 2025j), the National Field Quality Assurance (NFQA) project (U.S. Geological Survey, 2025k), and the Standard Reference Sample Project (U.S. Geological Survey, 2025l), among others.

The USGS NWQL is accredited by the National Environmental Laboratory Accreditation Conference (NELAC) Institute (National Environmental Laboratory Accreditation Conference Institute, 2025), actively participates in the NELAC Institute National Environmental Laboratory Accreditation Program and participates in the proficiency testing program specified by the NELAC Institute. The NWQL also operates under the Quality Management System (QMS) required of all USGS laboratories. The QMS defines the policies, procedures, and documentation that ensure the laboratory continually meets a defined standard of quality that is designed to provide customers with legally defensible data of known and documented quality and, where applicable, demonstrates regulatory compliance. The QMS establishes the standard under which all laboratory operations are performed, including the laboratory’s organization, objectives, and operating philosophy. The QMS has been prepared to ensure that the laboratory operates a quality system in compliance with the 2003 NELAC standard.

Additionally, all field personnel in the USGS Koocanusa/Kootenai water-quality monitoring program participate in the USGS NFQA program. For QA and consistency among instruments and users, the NFQA program was created in 1979. The program monitors the proficiency of alkalinity, pH, and specific conductance measurements determined by the USGS water-quality field analysts. Field personnel and water-quality analysts are sent proficiency samples of pH, specific conductance, and alkalinity (added in 1984) annually. Participants who receive an unsatisfactory performance rating are given a second round of samples (Stanley and others, 1992). Results of the NFQA program are reviewed by a Water Science Center Water-Quality Specialist. If unsatisfactory performance persists, additional training and testing are provided to achieve satisfactory performance or staff are reassigned.

Quality-control samples were collected to determine the acceptability of performance in the data-collection process and to provide a basis for evaluating the adequacy of procedures that were used to obtain the data. The QA plan for this project followed the QA Plan for Water-Quality Activities for the WY–MT WSC (unpublished, internal document that follows the recommended USGS practices described at U.S. Geological Survey, 2025m). The QC samples were collected along with all primary environmental samples following USGS protocols described in chapter A4 of the NFM (U.S. Geological Survey, variously dated). Between 10 and 20 percent (or more) of all samples analyzed consisted of QC samples (table 3.1), and these QC sample types are described in table 6. Field blank samples consisted of American Chemical Society reagent-grade inorganic blank water or pesticide-grade organic blank water (for organic carbon analysis) processed through clean sampling equipment prior to collection of environmental samples.

Equipment was calibrated and maintained as described in the USGS NFM (U.S. Geological Survey, variously dated), Wagner and others (2006), and in the manufacturer’s instructions (YSI, undated). Instruments that were not left in the field for unattended deployments were calibrated and checked the first day of the sampling trip. Instruments left in the field for unattended operation were calibrated just prior to deployment and checked against a recently calibrated field monitor following the criteria in table 7. Sensors on the field sonde, including pH, specific conductance, and dissolved oxygen were recalibrated in the field if they did not meet these criteria. Service visits (every 4–6 weeks) for unattended instruments were also routinely conducted. During these service visits, a calibrated “reference” sonde equipped with the same sensors as the site monitor was used to check the reasonableness of the deployed site sonde and to independently check for environmental changes that occurred during instrument servicing. Side-by-side comparison measurements were recorded, ensuring that the reference and site sonde readings were closely aligned in time. The site sonde was then removed, cleaned, and redeployed. After cleaning, readings from the site and reference sondes were recorded again. Environmental changes observed by the reference sonde during cleaning were considered when calculating fouling errors (Wagner and others, 2006).

Calibration checks were then performed on the site sonde, with careful documentation of calibrations and checks to ensure data accuracy. Calibration drift corrections were calculated following the procedures outlined in Wagner and others (2006). Sensors were cleaned every 4–6 weeks but were not recalibrated unless they were outside the criteria specified in table 7. In addition to calibration information, the date, personnel initials, and maintenance activities (for example, battery or sensor replacement, cleaning, or wiper repair/replacement) were documented. Maintenance records of field equipment, including the manufacturer, make, model, and serial number were maintained.

Documentation of sonde calibrations and calibration checks are critical for ensuring accuracy of the data. All sensor values were recorded before and after each cleaning and calibration so that the data could be adjusted proportionately to the amount of drift (Wagner and others, 2006).

All water-sampling equipment used in the USGS Koocanusa/Kootenai water-quality monitoring program was cleaned (decontaminated) to the extent required for low-level chemical analyses before sample collection (U.S. Geological Survey, variously dated). Equipment was decontaminated to ensure the equipment was not a source of contamination that could affect the ambient concentrations of target analytes. The proper removal of contaminants from equipment minimizes the likelihood of sample cross-contamination and reduces or eliminates the transfer of contaminants to the sites that were sampled. A description of samples collected as part of the quality control of cleaning procedures for this study is included in the “Field Quality Control” section of this report.

Equipment cleaning procedures vary depending on the types of water samples collected and the sensitivities of the analyses. Collection equipment and re-used sample bottles were thoroughly decontaminated with phosphate-free detergent, a dilute acid (5-percent HCl) solution, and deionized water before taking them into the field. Between site visits, equipment was field cleaned by first rinsing with deionized water, then a 5-percent HCl solution, and then rinsed again with deionized water. Prior to collecting the sample, the sampling equipment was rinsed three times with native water. The sequence for equipment cleaning prior to sample collection for inorganic and (or) organic analytes was as follows:

This section describes the different laboratories, types of analyses performed, and an overview of how data quality was determined in the Koocanusa/Kootenai water-quality monitoring program in water years 2022–23.

Laboratory analytical procedures followed approved and standard (when possible) methods, which provided reporting levels (table 1.1) that were below regulatory criteria or guidelines (where applicable) and enabled direct comparison of analytical results with these criteria. Sample and QC data for this study are reported in standard format, such as USGS open-file reports or scientific investigations reports, or as USGS data releases. The reports include a case narrative summarizing any problems encountered in the analyses.

The data-quality objectives for this study followed the guidelines outlined in U.S. Department of the Interior (2008) to ensure that data of known and acceptable quality were obtained. All measurements were performed, and samples were collected, to yield consistent results that were representative of the media and conditions measured. In the USGS Koocanusa/Kootenai water-quality monitoring project, water-quality data were documented to ensure they were meaningful, representative, complete, precise, accurate, comparable, and admissible as legal evidence to meet the scientific, engineering, and regulatory needs of our cooperators. Documentation of basic information, such as compatible monitoring objectives and program design features; metadata (when, where, and how the data were collected and who collected and analyzed the data); ancillary information (explanatory variables and study-site characteristics); and legal requirements were used to evaluate data. Documentation of sufficient QA and QC information to establish the quality and uncertainty in the data and interpretations were also maintained to determine the comparability and utility of datasets for intended users.

The QC samples were analyzed along with the corresponding constituents, and the results were compared with those of the co-collected primary samples. A thorough discussion of the data quality is included in all written products. These sample comparisons were based on the relative percent difference calculated for each type of analysis as the absolute value of the difference between the primary and QC sample results divided by the average of the primary and QC sample results (multiplied by 100 to convert to percentage). Other factors considered in each data review included compliance with sample hold times and receipt conditions (samples arrived at the laboratory at the appropriate temperatures), results of sample blank analyses, detection limits, and adherence to laboratory control standards. Estimated values were used for evaluation purposes, whereas rejected values were not used.

Sampling information, metadata, and ancillary information were recorded electronically as field notes that were considered original record. These data were combined with analytical data from the laboratory in computer data files.

Data validation is the process whereby water-quality and associated data are checked for completeness and accuracy. After validation, data records are finalized in NWIS (U.S. Geological Survey, 2023a).

All water-quality data were stored in NWIS (U.S. Geological Survey, 2023a). Supporting project information or metadata that could not be entered into NWIS were stored in electronic project files. The USGS WY–MT WSC site administrator maintains backups of all locally stored electronic information. Nonelectronic information, if any, is retained by the project lead or designated personnel. Water-quality data for this study were disseminated to the public through NWIS, USGS data releases, interpretive reports, or other published documents.