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.

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.

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.

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.

This data release includes all pesticide results from selected batches of water samples analyzed by the U.S Geological Survey National Water Quality Laboratory (NWQL). Samples were analyzed using gas chromatography/mass spectrometry (GCMS) or liquid chromatography/mass spectrometry (LCMS) methods. Eight datasets are included in this data release; 1) all environmental and field quality control (QC) results for 11 pesticide compounds from 70 selected batches of GCMS data from schedules 2001, 2003, 2032, and 2033 (Sandstrom and others, 2001; Zaugg and others, 1995) from May 2001-June 2015, 2) all environmental and field QC results for 10 pesticide compounds from 43 selected batches of LCMS data from schedule 2060 (Furlong and others, 2001) from October 2001-July 2015, 3) All available GCMS set blank results from January 2001-May 2016, 4) All available LCMS set blank results from May 2001-August 2015, 5 and 6) All available blind-blank GCMS and LCMS results from the NWQL from 2004 and from the USGS Branch of Quality systems from 2007 through 2012, and 7 and 8) Blind-spike results from the USGS Organic Blind Sample Project from 2001 through 2016 for the 11 GCMS and 10 LCMS compounds that were investigated in the larger work cited in this metadata record. In addition to the pesticide data originally analyzed and published by the NWQL, a reevaluation of the data in the first two datasets listed in this abstract was performed using current 2017 identification practices. NWQL standard operating procedures have evolved over the 15 years encompassed by this study to provide more specific guidance on the application of identification rules for determining detections. In addition, technology advances were implemented at the NWQL that resulted in improvements in method performance and sample analysis over time. In the data reevaluation process, NWQL reevaluated every result from the 70 GCMS batches and 43 LCMS batches of samples using current 2017 operating procedures and consistently applied criteria for the qualitative identification of pesticides as described in the methods documents (Sandstrom and others, 2001; Zaugg and others, 1995; Furlong and others, 2001). This data release supports the following publication: Medalie, L., Sandstrom, M.W., Toccalino, P.L., Foreman, W.T., ReVello, R.C., Bexfield, L.M., and Riskin, M.L., 2019, Use of set blanks in reporting pesticide results at the U.S. Geological Survey National Water Quality Laboratory, 2001–15: U.S. Geological Survey Scientific Investigations Report 2019–5055, 147 p., https://doi.org/10.3133/sir20195055. References: Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., Coffey, L.J., and Burkhardt, M.R., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of pesticides in water by graphitized carbon-based solid-phase extraction and high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations Report 01–4134, 73 p. [Also available at https://doi.org/10.3133/wri014134.] Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and Schroeder, M.P., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of moderate-use pesticides and selected degradates in water by C-18 solid-phase extraction and gas chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations Report 01–4098, 70 p. [Also available at https://nwql.usgs.gov/Public/pubs/WRIR/WRIR-01-4098.pdf.] Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, K.M., 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of pesticides in water by C–18 solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey Open-File Report 95–181, 49 p. [Also available at https://doi.org/10.3133/ofr95181.]

This data release includes all pesticide results from selected batches of water samples analyzed by the U.S Geological Survey National Water Quality Laboratory (NWQL). Samples were analyzed using gas chromatography/mass spectrometry (GCMS) or liquid chromatography/mass spectrometry (LCMS) methods. Eight datasets are included in this data release; 1) all environmental and field quality control (QC) results for 11 pesticide compounds from 70 selected batches of GCMS data from schedules 2001, 2003, 2032, and 2033 (Sandstrom and others, 2001; Zaugg and others, 1995) from May 2001-June 2015, 2) all environmental and field QC results for 10 pesticide compounds from 43 selected batches of LCMS data from schedule 2060 (Furlong and others, 2001) from October 2001-July 2015, 3) All available GCMS set blank results from January 2001-May 2016, 4) All available LCMS set blank results from May 2001-August 2015, 5 and 6) All available blind-blank GCMS and LCMS results from the NWQL from 2004 and from the USGS Branch of Quality systems from 2007 through 2012, and 7 and 8) Blind-spike results from the USGS Organic Blind Sample Project from 2001 through 2016 for the 11 GCMS and 10 LCMS compounds that were investigated in the larger work cited in this metadata record. In addition to the pesticide data originally analyzed and published by the NWQL, a reevaluation of the data in the first two datasets listed in this abstract was performed using current 2017 identification practices. NWQL standard operating procedures have evolved over the 15 years encompassed by this study to provide more specific guidance on the application of identification rules for determining detections. In addition, technology advances were implemented at the NWQL that resulted in improvements in method performance and sample analysis over time. In the data reevaluation process, NWQL reevaluated every result from the 70 GCMS batches and 43 LCMS batches of samples using current 2017 operating procedures and consistently applied criteria for the qualitative identification of pesticides as described in the methods documents (Sandstrom and others, 2001; Zaugg and others, 1995; Furlong and others, 2001). This data release supports the following publication: Medalie, L., Sandstrom, M.W., Toccalino, P.L., Foreman, W.T., ReVello, R.C., Bexfield, L.M., and Riskin, M.L., 2019, Use of set blanks in reporting pesticide results at the U.S. Geological Survey National Water Quality Laboratory, 2001–15: U.S. Geological Survey Scientific Investigations Report 2019–5055, 147 p., https://doi.org/10.3133/sir20195055. References: Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., Coffey, L.J., and Burkhardt, M.R., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of pesticides in water by graphitized carbon-based solid-phase extraction and high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations Report 01–4134, 73 p. [Also available at https://doi.org/10.3133/wri014134.] Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and Schroeder, M.P., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of moderate-use pesticides and selected degradates in water by C-18 solid-phase extraction and gas chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations Report 01–4098, 70 p. [Also available at https://nwql.usgs.gov/Public/pubs/WRIR/WRIR-01-4098.pdf.] Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, K.M., 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of pesticides in water by C–18 solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey Open-File Report 95–181, 49 p. [Also available at https://doi.org/10.3133/ofr95181.]

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

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).