This Data release presents results for pesticide constituents in 460 samples collected from domestic and public-supply wells in August 2013-May 2018 for the California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP). The samples were analyzed for 225 pesticide constituents on USGS National Water Quality Laboratory analytical schedule 2437. Results from quality-control samples collected with the environmental samples and results from laboratory quality-control samples were used to re-process the data to meet project data-quality objectives. The data release includes the final approved results tabulated by result and by sample, the original and final values for results affected by the quality-control re-processing, ancillary and summary information about the pesticide constituents, and results from field replicate and field blank samples.

The California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP) submitted 2,994 samples in 2004-2018 to the USGS National Water Quality Laboratory (NWQL) for analysis of pesticide constituents on NWQL schedules 2003, 2032, or 2033, and 840 samples in 2004-2011 for analysis of pesticide constituents on NWQL schedule 2060. Fram and Stork (2019) describe the GAMA-PBP data quality objectives for pesticide constituents and present a 5-step protocol for review and quality-control censoring of data from these NWQL schedules. This data release presents the original and final values for the 1,056 results censored by Fram and Stork (2019) and the entire final dataset for pesticide constituents on NWQL schedules 2003, 2032, 2033, or 2060 in GAMA-PBP samples collected in 2004-2018.

The California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP) submitted 2,994 samples in 2004-2018 to the USGS National Water Quality Laboratory (NWQL) for analysis of pesticide constituents on NWQL schedules 2003, 2032, or 2033, and 840 samples in 2004-2011 for analysis of pesticide constituents on NWQL schedule 2060. Fram and Stork (2019) describe the GAMA-PBP data quality objectives for pesticide constituents and present a 5-step protocol for review and quality-control censoring of data from these NWQL schedules. This data release presents the original and final values for the 1,056 results censored by Fram and Stork (2019) and the entire final dataset for pesticide constituents on NWQL schedules 2003, 2032, 2033, or 2060 in GAMA-PBP samples collected in 2004-2018.

Surface water samples were collected from four stream/agricultural drain sites in the Sacramento Valley of California to measure pesticides commonly applied to rice. Samples were collected weekly from May through August 2010 to capture the rice pesticide application season. Water samples were filtered (0.7 µm) and extracted via solid-phase extraction. Additionally, the filter paper was solvent extracted to measure suspended sediment-associated pesticides. Both fractions were analyzed via gas chromatography-mass spectrometry. A total of 89 pesticides and pesticide degradates were measured in the dissolved water phase, while 14 pyrethroid insecticides were measured in the suspended sediment-associated fraction (pyrethroids are hydrophobic and known to associate with particulates). For the dissolved phase, 18 compounds were detected. The most frequently detected compounds included those pesticides applied to rice: azoxystrobin (detection frequency 100%, maximum concentration 128,000 ng/L), clomazone (96%, 19,400 ng/L), 3,4-dichloroaniline (propanil degradate; 92%, 13,600 ng/L), thiobencarb (83%, 12,400 ng/L), and propanil (57%; 6,500 ng/L). Other frequently detected dissolved pesticides not applied to rice included boscalid (45%, 75.7 ng/L) and metolachlor (43%, 600 ng/L). Only two pyrethroids were detected in the suspended sediment fraction; this included lambda-cyhalothrin (17%, 14.8 ng/L), which was applied to rice, and bifenthrin, which is not specific to rice (6%, 26.3 ng/L).

Surface water samples were collected from four stream/agricultural drain sites in the Sacramento Valley of California to measure pesticides commonly applied to rice. Samples were collected weekly from May through August 2010 to capture the rice pesticide application season. Water samples were filtered (0.7 µm) and extracted via solid-phase extraction. Additionally, the filter paper was solvent extracted to measure suspended sediment-associated pesticides. Both fractions were analyzed via gas chromatography-mass spectrometry. A total of 89 pesticides and pesticide degradates were measured in the dissolved water phase, while 14 pyrethroid insecticides were measured in the suspended sediment-associated fraction (pyrethroids are hydrophobic and known to associate with particulates). For the dissolved phase, 18 compounds were detected. The most frequently detected compounds included those pesticides applied to rice: azoxystrobin (detection frequency 100%, maximum concentration 128,000 ng/L), clomazone (96%, 19,400 ng/L), 3,4-dichloroaniline (propanil degradate; 92%, 13,600 ng/L), thiobencarb (83%, 12,400 ng/L), and propanil (57%; 6,500 ng/L). Other frequently detected dissolved pesticides not applied to rice included boscalid (45%, 75.7 ng/L) and metolachlor (43%, 600 ng/L). Only two pyrethroids were detected in the suspended sediment fraction; this included lambda-cyhalothrin (17%, 14.8 ng/L), which was applied to rice, and bifenthrin, which is not specific to rice (6%, 26.3 ng/L).

Dissolved pesticides were measured in weekly water samples from 85 wadeable streams in Central Coastal California over a variable six-week period during March–May, 2017, as part of the California Stream Quality Assessment (CSQA) study conducted by the U.S. Geological Survey's (USGS) Regional Stream-Quality Assessment (RSQA) Project. The 85 streams consisted of 40 urban sites (5–100% urban land in the lower basin), 9 agricultural sites, 24 mixed land-use sites, and 12 undeveloped sites. Water samples were filtered (0.7 micrometers) and analyzed for 253 pesticide compounds by direct-injection liquid chromatography with tandem mass-spectrometry (LC-MS/MS). Two similar LC-MS/MS methods were used: a broad-spectrum (223 compounds) method in use since 2012 and a newly developed method for 30 new-generation fungicides and diamide and neonicotinoid insecticides. This Data Release provides sampling-site locations, analyte information, concentration data for pesticide compounds in environmental weekly water samples, quality-control data for the new method (to supplement previously published quality control data for the standard method), aquatic-life benchmark and Pesticide Toxicity Index toxicity concentration values that were used to assess potential toxicity, estimates of agricultural and nonagricultural pesticide-use data, and streamflow data for gaged sites, in support of the journal article, “New-generation pesticides are prevalent in California’s Central Coast streams,” by Sandstrom, M.W., Nowell, L.H., Mahler, B.J., and Van Metre, P.C.

Dissolved pesticides were measured in weekly water samples from 85 wadeable streams in Central Coastal California over a variable six-week period during March–May, 2017, as part of the California Stream Quality Assessment (CSQA) study conducted by the U.S. Geological Survey's (USGS) Regional Stream-Quality Assessment (RSQA) Project. The 85 streams consisted of 40 urban sites (5–100% urban land in the lower basin), 9 agricultural sites, 24 mixed land-use sites, and 12 undeveloped sites. Water samples were filtered (0.7 micrometers) and analyzed for 253 pesticide compounds by direct-injection liquid chromatography with tandem mass-spectrometry (LC-MS/MS). Two similar LC-MS/MS methods were used: a broad-spectrum (223 compounds) method in use since 2012 and a newly developed method for 30 new-generation fungicides and diamide and neonicotinoid insecticides. This Data Release provides sampling-site locations, analyte information, concentration data for pesticide compounds in environmental weekly water samples, quality-control data for the new method (to supplement previously published quality control data for the standard method), aquatic-life benchmark and Pesticide Toxicity Index toxicity concentration values that were used to assess potential toxicity, estimates of agricultural and nonagricultural pesticide-use data, and streamflow data for gaged sites, in support of the journal article, “New-generation pesticides are prevalent in California’s Central Coast streams,” by Sandstrom, M.W., Nowell, L.H., Mahler, B.J., and Van Metre, P.C.

The National Water-Quality Assessment (NAWQA) Program and National Stream Quality Accounting Network (NASQAN) are U.S. Geological Survey (USGS) monitoring programs that measure pesticide concentrations in the Nation’s streams and rivers, herein collectively referred to as streams. The NAWQA Program began monitoring pesticides in 1992 and the NASQAN Program began monitoring pesticides in 1995. The programs were recently merged to form the USGS National Water Quality Network for Rivers and Streams. Water samples are analyzed for pesticides by the USGS National Water Quality Laboratory (NWQL) using methods developed by the NWQL’s Methods Research and Development team. The NWQL extensively used two analytical methods, gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry, to measure pesticides in filtered water samples during 1992–2012 (old method). In October 2012, the monitoring programs began using direct aqueous-injection liquid chromatography tandem mass spectrometry as a new analytical method for pesticides (new method). The change in analytical methods, however, has the potential to inadvertently introduce bias in analysis of datasets that span the change. The data sets provided in this report were used to document performance of the new method in a variety of stream-water matrices and help quantify potential changes in measurement bias or variability that could be attributed to changes in analytical methods (Martin and others, 2016). Users should consult the report by Martin and others (2016) to understand how these data were collected and used. Measured concentrations and calculated recoveries of 281 pesticides and degradates in paired environmental background water samples and matrix spiked water samples collected at 48 stream-water sites from June 11, 2012 to September 6, 2012 are provided in seven tab-delimited ASCII files with relational database (RDB) format header. A tab-delimited ASCII file (DataDictionaryList.txt) listing DataSet attributes and RDB column formats is also included in this data release. Martin, J.D., Norman, J.E., Sandstrom, M.W., and Rose, C.E., 2016, A field study of selected U.S. Geological Survey analytical methods for measuring pesticides in filtered stream water, June-September 2012: U.S. Geological Survey Scientific Investigations Report, 2017-5049

The National Water-Quality Assessment (NAWQA) Program and National Stream Quality Accounting Network (NASQAN) are U.S. Geological Survey (USGS) monitoring programs that measure pesticide concentrations in the Nation’s streams and rivers, herein collectively referred to as streams. The NAWQA Program began monitoring pesticides in 1992 and the NASQAN Program began monitoring pesticides in 1995. The programs were recently merged to form the USGS National Water Quality Network for Rivers and Streams. Water samples are analyzed for pesticides by the USGS National Water Quality Laboratory (NWQL) using methods developed by the NWQL’s Methods Research and Development team. The NWQL extensively used two analytical methods, gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry, to measure pesticides in filtered water samples during 1992–2012 (old method). In October 2012, the monitoring programs began using direct aqueous-injection liquid chromatography tandem mass spectrometry as a new analytical method for pesticides (new method). The change in analytical methods, however, has the potential to inadvertently introduce bias in analysis of datasets that span the change. The data sets provided in this report were used to document performance of the new method in a variety of stream-water matrices and help quantify potential changes in measurement bias or variability that could be attributed to changes in analytical methods (Martin and others, 2016). Users should consult the report by Martin and others (2016) to understand how these data were collected and used. Measured concentrations and calculated recoveries of 281 pesticides and degradates in paired environmental background water samples and matrix spiked water samples collected at 48 stream-water sites from June 11, 2012 to September 6, 2012 are provided in seven tab-delimited ASCII files with relational database (RDB) format header. A tab-delimited ASCII file (DataDictionaryList.txt) listing DataSet attributes and RDB column formats is also included in this data release. Martin, J.D., Norman, J.E., Sandstrom, M.W., and Rose, C.E., 2016, A field study of selected U.S. Geological Survey analytical methods for measuring pesticides in filtered stream water, June-September 2012: U.S. Geological Survey Scientific Investigations Report, 2017-5049

A novel U.S. Geological Survey-developed active water sampler was deployed at Ulatis Creek in Solano County, California for 24 hours from November 15, 2023 to November 16, 2023. Discrete surface water samples were collected at the start and end points of the active water sampler deployment interval for comparison to the active water sampler. Samples from the active water sampler and the discrete surface water samples were analyzed for 183 pesticides dissolved in water and 178 pesticides in suspended sediment at the U.S. Geological Survey Organic Chemistry Research Laboratory in Sacramento, California. Twenty-seven out of 183 pesticide compounds measured in sample extracts were detected in at least one of the grab sample or active sampler dissolved water extracts with concentrations ranging from 0.9 nanograms per liter to 32.2 nanograms per liter. No pesticides were detected in the suspended sediment filtered from the water.