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.

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 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.

In June and July of 2020, 45 groundwater wells in McHenry County, Illinois, were sampled for water quality (field properties, major ions, nutrients, and trace metals) and 12 wells were sampled for contaminants of emerging concern (pharmaceuticals, pesticides, and wastewater indicator compounds). Quality-assurance and quality-control samples were collected during the June and July 2020 sampling that included equipment blanks, field blanks, and replicates. The results of these samples were used to understand the sources of bias and variability associated with sample collection, processing, storage, and shipping. This data release contains one comma separated values files containing the results of the quality-control sample collection for general water quality (metals, nutrients, and major ions) and contaminants of emerging concern (wastewater indicator compounds and pharmaceuticals). Water-quality data from the associated groundwater monitoring well data are available at the National Water Information System (NWIS) web database (https://doi.org/10.5066/F7P55KJN). Results and discussion of the water quality and contaminants of emerging concern can also be found in the associated scientific investigation report referenced.

In June and July of 2020, 45 groundwater wells in McHenry County, Illinois, were sampled for water quality (field properties, major ions, nutrients, and trace metals) and 12 wells were sampled for contaminants of emerging concern (pharmaceuticals, pesticides, and wastewater indicator compounds). Quality-assurance and quality-control samples were collected during the June and July 2020 sampling that included equipment blanks, field blanks, and replicates. The results of these samples were used to understand the sources of bias and variability associated with sample collection, processing, storage, and shipping. This data release contains one comma separated values files containing the results of the quality-control sample collection for general water quality (metals, nutrients, and major ions) and contaminants of emerging concern (wastewater indicator compounds and pharmaceuticals). Water-quality data from the associated groundwater monitoring well data are available at the National Water Information System (NWIS) web database (https://doi.org/10.5066/F7P55KJN). Results and discussion of the water quality and contaminants of emerging concern can also be found in the associated scientific investigation report referenced.

The USGS conducted a combined wastewater facility pre/post-closure groundwater assessment adjacent to an effluent-impacted reach of Fourmile Creek, Ankeny, Iowa, USA. This data release includes pharmaceutical concentration data for Fourmile Creek determined by enzyme-linked immunosorbent assay (ELISA) and HPLC-MS/MS during the period October 2012 to October 2014, along with associated HPLC-MS/MS analyte and method performance information.

The USGS conducted a combined wastewater facility pre/post-closure groundwater assessment adjacent to an effluent-impacted reach of Fourmile Creek, Ankeny, Iowa, USA. This data release includes pharmaceutical concentration data for Fourmile Creek determined by enzyme-linked immunosorbent assay (ELISA) and HPLC-MS/MS during the period October 2012 to October 2014, along with associated HPLC-MS/MS analyte and method performance information.

This data release provides water chemistry results and quality assurance data for samples collected from Great Lakes tributaries in the states of Minnesota, Wisconsin, Michigan, Indiana, Ohio, and New York. In total, 158 chemicals were analyzed which are primarily pharmaceuticals. Between one and four water samples were collected at 37 sampling locations between November 2017 and July 2018 resulting in a total of 87 environmental, 95 field replicate, and 15 field blank samples. Of the 158 chemicals analyzed, 23 chemicals were detected in at least one regular sample. Detections per site ranged from 0 to 12 chemicals at concentrations of 1.56 to 30900 nanograms per liter. Sample collection and analysis was performed by the U.S. Geological Survey and summarized in the associated journal article (https://doi.org/10.1002/etc.5403). More detailed method descriptions will be published in the future.

This data release provides water chemistry results and quality assurance data for samples collected from Great Lakes tributaries in the states of Minnesota, Wisconsin, Michigan, Indiana, Ohio, and New York. In total, 158 chemicals were analyzed which are primarily pharmaceuticals. Between one and four water samples were collected at 37 sampling locations between November 2017 and July 2018 resulting in a total of 87 environmental, 95 field replicate, and 15 field blank samples. Of the 158 chemicals analyzed, 23 chemicals were detected in at least one regular sample. Detections per site ranged from 0 to 12 chemicals at concentrations of 1.56 to 30900 nanograms per liter. Sample collection and analysis was performed by the U.S. Geological Survey and summarized in the associated journal article (https://doi.org/10.1002/etc.5403). More detailed method descriptions will be published in the future.