This data release includes tables and plots of results for pesticide compounds (pesticides and degradates) analyzed in groundwater samples collected by the USGS National Water-Quality Assessment Project during water years 2013-18 and in associated quality-control samples that are used to assess the quality of the reported pesticide results. All samples were analyzed by the USGS National Water Quality Laboratory (NWQL) using laboratory schedule 2437. The table of groundwater data includes pesticide results as reported by the laboratory, along with results that represent the application of censoring levels at the 90-percent upper confidence limit of the 95th percentile of laboratory blank concentrations determined by water year. The other seven tables included in this data release contain pesticide results for the following types of quality-control samples: field blanks, matrix spikes, and replicates collected at field sites; laboratory blanks and reagent spikes prepared by the NWQL; and third-party blind blanks and blind spikes prepared by the USGS Quality Systems Branch. The table of pesticide results for field matrix spikes includes the paired groundwater results and other fields needed to calculate spike recovery as described in the data processing steps of the metadata file. The table of pesticide results for field replicates includes the paired groundwater results and other fields needed to calculate variability in detection and (or) concentration as described in the data processing steps of the metadata file. Results included in this data release for laboratory reagent spikes are for water year 2018 only; results for laboratory reagent spikes analyzed in water years 2013-15 are available in Shoda and others (2017) and in water years 2016-17 are available in Wieben (2019). Useful graphical representations of data in the tables are provided in various plots that compare detections and concentrations for groundwater and blank samples, compare recovery results for the different spike types, and illustrate variability in replicate-sample results across concentration ranges. Shoda, M.E., Nowell, L.H., Bexfield, L.M., Sandstrom, M.W., Stone, W.W., 2017, Recovery data for surface water, groundwater and lab reagent samples analyzed by the USGS National Water Quality Laboratory schedule 2437, water years 2013-15: U.S. Geological Survey data release, https://doi.org/10.5066/F7QZ28G4. Wieben, C.M., 2019, Pesticide recovery data for surface-water and lab reagent samples analyzed by the USGS National Water Quality Laboratory schedule 2437, water years 2016-17: U.S. Geological Survey data release, https://doi.org/10.5066/P93MWMVF. There are 8 tables included in this data release: Table1_GroundwaterData2013_2018.xlsx -- Pesticide results for groundwater samples collected by the National Water-Quality Assessment Project, 2013-18. This table includes pesticide results as reported by the laboratory, along with results that represent the application of censoring levels at the 90-percent upper confidence limit of the 95th percentile of laboratory blank concentrations determined by water year. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. Table2_FieldBlankData2013_2018.xlsx -- Pesticide results for field blanks collected at groundwater sites by the National Water-Quality Assessment Project, 2013-18. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. Table3_FieldSpikeData2013_2018.xlsx -- Pesticide results for field matrix spikes collected at groundwater sites by the National Water-Quality Assessment Project, 2013-18. Results of paired groundwater samples are included. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. Fields needed to calculate spike recovery as described in the data processing steps of the metadata file are included. Table4_FieldRepData2013_2018.xlsx -- Pesticide results for field replicates collected at groundwater sites by the National Water-Quality Assessment Project, 2013-18. Results of paired groundwater samples are included. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. Fields needed to calculate variability in detection and (or) concentration as described in the data processing steps of the metadata file are included. Table5_LabBlankData2013_2018.xlsx -- Pesticide results for laboratory blanks prepared by the National Water Quality Laboratory, 2013-18. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. Table6_LabReagentSpikeData2018.xlsx -- Pesticide results for laboratory reagent spikes prepared by the National Water Quality Laboratory, 2018. Table7_QSBBlindBlankData_2018.xlsx -- Pesticide results for third-party blind blanks prepared by the Quality Systems Branch, 2018. Table8_QSBBlindSpikeData2013_2018.xlsx -- Pesticide results for third-party blind spikes prepared by the Quality Systems Branch, 2013-18. Results that were rejected for data analysis for reasons described in the metadata document and in the associated Scientific Investigations Report are flagged. There are 5 sets of graphical representations of the data. Detailed descriptions of the plots included in this data release are provided in the associated Scientific Investigations Report: PlotGroup1_TimeSeries.pdf – Plots of reported detections and concentrations in groundwater samples (Table 1), field blanks (Table 2), and laboratory blanks (Table 5) for individual compounds by analysis date, showing the frequency, timing, and magnitude of detections among these sample types. Nondetections are plotted as open circles at the standard laboratory reporting level in effect at the time of analysis (identified on each graph) or, if applicable, at the raised reporting level specified for an individual sample. PlotGroup2_EDFsByWY.pdf – Empirical distribution functions illustrating upper percentiles of concentrations for groundwater samples (Table 1) relative to field blanks (Table 2) and laboratory blanks (Table 5) for selected pesticides and water years. Plots are provided for compounds and water years with at least one groundwater detection and a quantifiable (detected) 99th percentile of concentration for laboratory blanks. PlotGroup3_SpikeTimeSeries.pdf – Plots of recoveries for laboratory reagent spikes (Table 6), field matrix spikes (Table 3), and third-party blind spikes (Table 8) for individual pesticides by analysis date, illustrating the range of typical recoveries. Lowess (locally weighted scatterplot smoothing) curves are included to illustrate general changes in recovery through time. Results for laboratory reagent spikes analyzed in water years 2013-15 are available in Shoda and others (2017) and in water years 2016-17 are available in Wieben (2019). PlotGroup4_LabFieldSpikes.pdf – Box plots comparing recoveries for laboratory reagent spikes (Table 6) and field matrix spikes (Table 3). Results for laboratory reagent spikes analyzed in water years 2013-15 are available in Shoda and others (2017) and in water years 2016-17 are available in Wieben (2019). PlotGroup5_FieldRepVar.pdf – Plots of standard deviation and relative standard deviation against mean concentration of field replicate samples (Table 4) for selected pesticides, including assigned boundaries between the lower concentration range where standard deviation generally is more uniform and the upper concentration range where relative standard deviation generally is more uniform. Plots are provided for pesticides that had 10 or more replicate pairs with detections in both samples of the pair.