This data release presents chemical results from investigations of surface-water quality in the Potomac River watershed (encompassing Washington, D.C. and parts of West Virginia, Virginia, Pennsylvania, and Maryland) conducted during low-flow conditions in July through September of 2022 and modeling results that support interpretative products. Water-quality sampling: A sampling campaign was conducted at 32 stream sites throughout the watershed (Table 1). A suite of field parameters and inorganic and organic chemical characteristics at each site were characterized using seven separate analytical methods at five laboratories (Table 2). The water-quality results are presented in Tables 3 and 4. Analytical methods and laboratories used were (1) major anions by ion chromatography at the U.S. Geological Survey Integrated Water Chemistry Assessment Laboratory in Boulder, Colorado (USGSIWCAL); (2) full fluorescence spectra in vectorized format, excitation-emission-matrix (EEM) fluorescence spectroscopy dissolved organic carbon (DOC), and total dissolved nitrogen (TDN) at the U.S. Geological Survey California Water Science Center Organic Matter Research Laboratory in Sacramento, California (CAWSCOMRL); (3) per-and polyfluoroalkyl substances (PFAS) using liquid chromatography with tandem mass spectrometry (LC-MS/MS), at the U.S. Geological Survey National Water Quality Laboratory in Denver, Colorado (USGSNWQL); (4) pesticides (PEST) by LC-MS/MS or gas chromatography with tandem mass spectrometry (GS-MS/MS) at the U.S. Geological Survey Organic Research Laboratory (USGSOGCA); (5) pharmaceuticals (PHARM) using LC-MS/MS at the USGSNWQL; and (6) Major elements and trace elements (TEs) using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) at the USGSIWCAL. Enzyme-Linked Immunosorbent Assay (ELISA) analyses were additionally performed at the U.S. Geological Survey Strategic Laboratory Science Branch in Boulder, Colorado (USGSSLSB) for the herbicides atrazine and glyphosate, the insecticide imidacloprid, and the consumer product chemical linear alkylbenzene sulfonate. Three analytes (atrazine, piperonyl butoxide, thiabendazole, and the thiabendazole surrogate standard thiabendazole-d4) were analyzed by the U.S. Geological Survey National Water Quality Laboratory (USGSNWQL) included with the pharmaceutical data in addition to being analyzed by the USGSOGCA with the pesticide data. The USGSNWQL results for these analytes were coded as replicate samples and additional time offsets were applied to create distinct times for these sample results. Samples were collected according to U.S. Geological Survey (USGS) protocols and procedures. A field blank and field replicate was collected for every analytical method, a matrix spike for PFAS, PHARM, and PEST was performed at three sites for quality assurance. Most sites were only sampled once for each parameter with the exception of four sites that had to be resampled due to samples arriving too warm to be processed for PFAS and PHARM parameters. Therefore samples for the remaining parameters were collected twice at these four sites. Water-quality modeling: This data release also contains inputs for and results from a wastewater reuse model that used data compiled from multiple sources to calculate the following estimates for each non-tidal National Hydrography Dataset Version 2.1 (NHDPlus V2) stream segment in the Potomac River watershed: (1) accumulated wastewater as a percent of total streamflow (ACCWW%) from municipal as well as municipal plus industrial PFAS wastewater treatment plants; and (2) predicted environmental concentrations (PECs, in nanograms per liter) of 14 pesticides and eight PFAS as well as the sum of the eight PFAS. ACCWW% values were calculated for mean-monthly and mean-annual streamflow conditions for municipal wastewater treatment plants (model results table: Table5_PotomacACCWW_municipal.csv) as well as

This data release presents chemical results from investigations of surface-water quality in the Potomac River watershed (encompassing Washington, D.C. and parts of West Virginia, Virginia, Pennsylvania, and Maryland) conducted during low-flow conditions in July through September of 2022. This sampling campaign was conducted at 32 stream sites throughout the watershed (Table 1). A suite of field parameters and inorganic and organic chemical characteristics at each site were characterized using seven separate analytical methods at five laboratories (Table 2). The water-quality results are presented in Table 3. Analytical methods and laboratories used were (1) major anions by ion chromatography at the U.S. Geological Survey Integrated Water Chemistry Assessment Laboratory in Boulder, Colorado (USGSIWCAL); (2) excitation-emission-matrix (EEM) fluorescence spectroscopy dissolved organic carbon (DOC), and total dissolved nitrogen (TDN) at the U.S. Geological Survey California Water Science Center Organic Matter Research Laboratory in Sacramento, California (CAWSCOMRL); (3) per-and polyfluoroalkyl substances (PFAS) using liquid chromatography with tandem mass spectrometry (LC-MS/MS), at the U.S. Geological Survey National Water Quality Laboratory in Denver, Colorado (USGSNWQL); (4) pesticides (PEST) by LC-MS/MS or gas chromatography with tandem mass spectrometry (GS-MS/MS) at the U.S. Geological Survey Organic Research Laboratory (USGSOGCA); (5) pharmaceuticals (PHARM) using LC-MS/MS at the USGSNWQL; and (6) Major elements and trace elements (TEs) using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) at the USGSIWCAL. Enzyme-Linked Immunosorbent Assay (ELISA) analyses were additionally performed at the U.S. Geological Survey Strategic Laboratory Science Branch in Boulder, Colorado (USGSSLSB) for the herbicides atrazine and glyphosate, the insecticide imidacloprid, and the consumer product chemical linear alkylbenzene sulfonate. Three analytes (atrazine, piperonyl butoxide, thiabendazole, and the thiabendazole surrogate standard thiabendazole-d4) were analyzed by the U.S. Geological Survey National Water Quality Laboratory (USGSNWQL) included with the pharmaceutical data in addition to being analyzed by the USGSOGCA with the pesticide data. The USGSNWQL results for these analytes were coded as replicate samples and additional time offsets were applied to create distinct times for these sample results. Samples were collected according to U.S. Geological Survey (USGS) protocols and procedures. A field blank and field replicate was collected for every analytical method, a matrix spike for PFAS, PHARM, and PEST was performed at three sites for quality assurance. Most sites were only sampled once for each parameter but four sites had to be resampled due to samples arriving too warm to be processed for PFAS and PHARM parameters. Therefore samples for the remaining parameters were collected twice at these four sites.

Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the Water Quality Portal (WQP), which is a data repository developed by the National Water Quality Monitoring Council and supported by the U.S. Environmental Protection Agency and U.S. Geological Survey, and the U.S. Geological Survey National Water Information System (NWIS). Both discrete measures of SC, which are single measures taken on a particular time and day, and continuous measures of SC, which are repeated measures of SC taken at regular, short intervals, such as 15-minute or hourly intervals, were compiled for this data release. The discrete data were also processed to screen out non-relevant observations and harmonize units. The WQP uses "MonitoringLocationIdentifier" to identify each unique site and monitoring activities, and this term is used throughout the data release to differentiate among unique sites and monitoring activities as well. The data release includes four items: 1. ["Site_inventory_for_specific_conductance_measures.csv"]: This is a site inventory of all locations where SC data had been collected and compiled for the data release. This file includes information on the monitoring location (coordinates, state, and county), the organization responsible for the data collection, the type of data available (discrete, continuous, or both) and its unique monitoring location and activity. 2. ["Discrete_specific_conductance_results.txt"]: This file contains all discrete SC observations. Identifying information (coordinates, monitoring location name and identifier), along with the observation value, units, and multiple flagging columns which denoted whether any changes were made to the observation or units during the processing steps. Full details are included in the "readme_file_for_Ches_Bay_specific_conductance_inventory.pdf" file. 3. ["Continuous_specific_conductance_results.zip"]: This zipped folder contains 89 .csv files for all the continuous USGS SC data available in the Chesapeake Bay watershed. Each file name includes each unique MonitoringLocationIdentifier. 4. ["readme_file_for_Ches_Bay_specific_conductance_inventory.pdf"]: This document describes all the processing and harmonization steps to generate the site inventory and discrete SC dataset, and for downloading the high frequency SC datasets.

Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the Water Quality Portal (WQP), which is a data repository developed by the National Water Quality Monitoring Council and supported by the U.S. Environmental Protection Agency and U.S. Geological Survey, and the U.S. Geological Survey National Water Information System (NWIS). Both discrete measures of SC, which are single measures taken on a particular time and day, and continuous measures of SC, which are repeated measures of SC taken at regular, short intervals, such as 15-minute or hourly intervals, were compiled for this data release. The discrete data were also processed to screen out non-relevant observations and harmonize units. The WQP uses "MonitoringLocationIdentifier" to identify each unique site and monitoring activities, and this term is used throughout the data release to differentiate among unique sites and monitoring activities as well. The data release includes four items: 1. ["Site_inventory_for_specific_conductance_measures.csv"]: This is a site inventory of all locations where SC data had been collected and compiled for the data release. This file includes information on the monitoring location (coordinates, state, and county), the organization responsible for the data collection, the type of data available (discrete, continuous, or both) and its unique monitoring location and activity. 2. ["Discrete_specific_conductance_results.txt"]: This file contains all discrete SC observations. Identifying information (coordinates, monitoring location name and identifier), along with the observation value, units, and multiple flagging columns which denoted whether any changes were made to the observation or units during the processing steps. Full details are included in the "readme_file_for_Ches_Bay_specific_conductance_inventory.pdf" file. 3. ["Continuous_specific_conductance_results.zip"]: This zipped folder contains 89 .csv files for all the continuous USGS SC data available in the Chesapeake Bay watershed. Each file name includes each unique MonitoringLocationIdentifier. 4. ["readme_file_for_Ches_Bay_specific_conductance_inventory.pdf"]: This document describes all the processing and harmonization steps to generate the site inventory and discrete SC dataset, and for downloading the high frequency SC datasets.

Surface-water samples were collected, processed, and analyzed for organics, estrogen equivalents, and fecal indicator bacteria. Filtered organic samples were sent to the National Water Quality Laboratory in Denver, Colorado. Unfiltered estrogen equivalent samples were sent to the Organic Geochemistry Research Lab in Lawrence, Kansas, for extraction, after which they were sent to the National Fish Health Research Laboratory in Leetown, West Virginia. Bacteria samples were processed at the Central-Midwest Water Science Center Iowa City, Iowa, office. Staff collected field parameters in-situ.

Surface-water samples were collected, processed, and analyzed for organics, estrogen equivalents, and fecal indicator bacteria. Filtered organic samples were sent to the National Water Quality Laboratory in Denver, Colorado. Unfiltered estrogen equivalent samples were sent to the Organic Geochemistry Research Lab in Lawrence, Kansas, for extraction, after which they were sent to the National Fish Health Research Laboratory in Leetown, West Virginia. Bacteria samples were processed at the Central-Midwest Water Science Center Iowa City, Iowa, office. Staff collected field parameters in-situ.

Filtered water samples were collected by the USGS National Water Quality Program (NWQP) Southeastern Stream Quality Assessment (SESQA) from 59 perennial, wadeable (less than 10 m width and 1 m depth at base-flow) headwater stream sites in watersheds with varying degrees of urban land use in four states. Dataset includes sample site locations and information, analytical method information, water sample pharmaceutical concentrations and summary statistics, and corresponding watershed land-use-land-cover data and data dictionary.

Filtered water samples were collected by the USGS National Water Quality Program (NWQP) Southeastern Stream Quality Assessment (SESQA) from 59 perennial, wadeable (less than 10 m width and 1 m depth at base-flow) headwater stream sites in watersheds with varying degrees of urban land use in four states. Dataset includes sample site locations and information, analytical method information, water sample pharmaceutical concentrations and summary statistics, and corresponding watershed land-use-land-cover data and data dictionary.

Here we report optical data collected as part of a collaborative study between USGS Pennsylvania Water Science Center, Pennsylvania Department of Environmental Protection and Water Mission Area Proxies Project. The optical measurements reported here were collected to aide in the characterization of water sources and mixtures and establish proxies (surrogates) for per- and poly-fluorinated alkyl substances within the Neshaminy Creek basin. Data are compiled into three tables: 1) full fluorescence spectra in vectorized format, 2) full absorbance spectra, and 3) summary file of commonly extracted optical indicators and field-based sensor arrays.

Here we report optical data collected as part of a collaborative study between USGS Pennsylvania Water Science Center, Pennsylvania Department of Environmental Protection and Water Mission Area Proxies Project. The optical measurements reported here were collected to aide in the characterization of water sources and mixtures and establish proxies (surrogates) for per- and poly-fluorinated alkyl substances within the Neshaminy Creek basin. Data are compiled into three tables: 1) full fluorescence spectra in vectorized format, 2) full absorbance spectra, and 3) summary file of commonly extracted optical indicators and field-based sensor arrays.