Groundwater samples were collected and analyzed from 417 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and the water-quality data and quality-control data are included in this data release. The samples were collected from three types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality, and major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds (VOCs), pesticides, radionuclides, and microbial indicators. Data from samples collected between 2012 and 2019 are associated with networks described in a collection of data series reports and associated data releases (Arnold and others, 2016a,b, 2017a,b, 2018a,b; Kingsbury and others, 2020 and 2021). This data release includes data from networks sampled in 2019 that were not previously published and available data for networks sampled in 2020. For some networks, certain constituent group data were not completely reviewed and released by the analyzing laboratory in time for publication of this data release. For networks with incomplete data, no data were published for the incomplete constituent group(s). Datasets excluded from this data release because of incomplete results will be included in the earliest data release published after the dataset is complete. The compressed file (NWQP_GW_QW_DataRelease.zip) contains 23 files of groundwater-quality, quality-control data, and general information in ASCII text tab-delimited format, and one corresponding metadata file in xml format that includes descriptions of all the tables and attributes. A shapefile containing study areas for each of the sampled groundwater networks also is provided as part of this data release and is described in the metadata (Network_Boundaries.zip). The files are as follows: Description_of_Data_Field.txt: Information for all constituents and ancillary information found in Tables 3 through 21. Network_Reference_List.txt: References used for the description of the networks sampled by the USGS NAWQA Project. Table_1_site_list.txt: Information about wells that have environmental data. Table_2_parameters.txt: Constituent primary uses and sources; laboratory analytical schedules and sampling period; USGS parameter codes (pcodes); comparison thresholds; and reporting levels. Table_3_qw_indicators.txt: Water-quality indicators in groundwater samples collected by the USGS NAWQA Project. Table_4_nutrients.txt: Nutrients and dissolved organic carbon in groundwater samples collected by the USGS NAWQA Project. Table_5_major_ions.txt: Major and minor ions in groundwater samples collected by the USGS NAWQA Project. Table_6_trace_elements.txt: Trace elements in groundwater samples collected by the USGS NAWQA Project. Table_7_vocs.txt: Volatile organic compounds (VOCs) in groundwater samples collected by the USGS NAWQA Project. Table_8_pesticides.txt: Pesticides in groundwater samples collected by the USGS NAWQA Project. Table_9_radchem.txt: Radionuclides in groundwater samples collected by the USGS NAWQA Project. Table_10_micro.txt: Microbiological indicators in groundwater samples collected by the USGS NAWQA Project. Table_11_qw_ind_QC.txt: Water-quality indicators in groundwater replicate samples collected by the USGS NAWQA Project. Table_12_nuts_QC.txt: Nutrients and dissolved organic carbon in groundwater blank and replicate samples collected by the USGS NAWQA Project. Table_13_majors_QC.txt: Major and minor ions in groundwater blank and replicate samples collected by the USGS NAWQA Project. Table_14_trace_element_QC.txt: Trace elements in groundwater blank and replicate samples collected by the USGS NAWQA Project. Table_15_vocs_QC.txt: Volatile organic compounds (VOCs) in groundwater blank, replicate, and spike samples collected by the USGS NAWQA Project. Table_16_pesticides_QC.txt: Pesticide compounds in groundwater blank, replicate, and spike samples collected by the USGS NAWQA Project. Table_17_radchem_QC.txt: Radionuclides in groundwater replicate samples collected by the USGS NAWQA Project. Table_18_micro_QC.txt: Microbiological indicators in groundwater blank, replicate, and spike samples collected by the USGS NAWQA Project. Table_19_TE_SpikeStats.txt: Statistics for trace elements in groundwater spike samples collected by the USGS NAWQA Project. Table_20_VOCLabSpikeStats.txt: Statistics for volatile organic compounds (VOCs) in groundwater spike samples collected by the USGS NAWQA Project. Table_21_PestFieldSpikeStats.txt: Statistics for pesticide compounds in groundwater spike samples collected by the USGS NAWQA Project.
Select Groundwater-Quality and Quality-Control Data from the National Water-Quality Assessment Project 2019 to Present