The U.S. Geological Survey collected groundwater samples from 17 wells in the Indio subbasin (CA basin designation 7-21.01) of the Coachella Valley and surface water samples from two sites representing sources of recharge to the Indio subbasin in 2021. These samples are intended to provide inorganic water quality data, particularly total dissolved solids (TDS), within areas of the Indio subbasin not sampled for the Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater used for domestic and small system drinking water supplies in Coachella Valley (CODA). Other areas of special interest for the Indio salinity study were nearby managed aquifer replenishment facilities. Various well types were sampled including domestic, public supply, irrigation, and monitoring wells. The two surface water samples were collected in order to better understand primary sources of recharge to the Indio subbasin: the Whitewater River and the Colorado River via the Coachella Canal. Groundwater samples from all 17 wells were analyzed for field water-quality parameters, major ions and trace elements, chromium (VI), perchlorate, nutrients, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, isotopes of sulfur in sulfate, sulfur hexafluoride, and noble gases. Groundwater levels were measured in 9 of the 17 wells. Surface water samples from both sites were analyzed for field water-quality parameters, major ions and trace elements, chromium (VI), perchlorate, nutrients, and stable isotopic ratios of water. All results are presented in this data release except for the isotopic ratios of strontium and boron in water. Data collected from 23 wells sampled in the Indio subbasin for the CODA assessment are not included in this data release but can be found here: https://doi.org/10.5066/P9UYXI95

Groundwater salinity presents a challenge to the management of water quality in the Indio subbasin of the Coachella Valley where a growing population is dependent primarily on groundwater for drinking water. The U.S. Geological survey, along with the Colorado River Basin regional water quality control board, are working to provide an assessment of salinity trends and sources in the Indio subbasin (California (CA) basin designation 7-21.01; California Department of Water Resources (2020). As part of this work, salinity data and other selected inorganic water quality data, along with well construction information, for wells with available total dissolved solids (TDS) or conductance data were compiled from published reports, public databases, and unpublished archives into a tabulated file, Indio_data_v2.txt. The database in this data release represents a synthesis of available data on groundwater salinity in the Coachella Valley, however it does not include all data ever published in the region. This database was updated in March, 2025 to include salinity data collected from groundwater samples through the year 2024. Version History Summary: First Published: July 2022 Version 2.0: July 2025

Groundwater salinity presents a challenge to the management of water quality in the Indio subbasin of the Coachella Valley where a growing population is dependent primarily on groundwater for drinking water. The U.S. Geological survey, along with the Colorado River Basin regional water quality control board, are working to provide an assessment of salinity trends and sources in the Indio subbasin (California (CA) basin designation 7-21.01; California Department of Water Resources (2020)). As part of this work, salinity data and other selected inorganic water quality data, along with well construction information, for wells with available total dissolved solids (TDS) or conductance data were compiled from published reports, public databases, and unpublished archives into a tabulated spreadsheet. This spreadsheet represents a synthesis of available data on groundwater salinity in the Coachella Valley, however it does not include all data ever published in the region.

Data provided here describe the contribution of up to 7 different water sources to the major ion geochemistry of U.S. Geological Survey (USGS) and California State Water Resources Control Board Division of Drinking Water (CA-DDW) groundwater samples within the Indio Subbasin of the Coachella Valley, California. The Inverse Geochemical Modeling was performed in the USGS's PHREEQC ver. 3 program and the results are discussed in the associated publication of Harkness and others (2023). Datasets include the major ion chemistry and model input parameters of 1593 samples included in the analysis, the median model results for each sample, and a data dictionary describing the tables. Analyses completed as part of this assessment relied on the previously published data of Harkness (2022) and no new data were collected.

Data provided here describe the contribution of up to 7 different water sources to the major ion geochemistry of U.S. Geological Survey (USGS) and California State Water Resources Control Board Division of Drinking Water (CA-DDW) groundwater samples within the Indio Subbasin of the Coachella Valley, California. The Inverse Geochemical Modeling was performed in the USGS's PHREEQC ver. 3 program and the results are discussed in the associated publication of Harkness and others (2023). Datasets include the major ion chemistry and model input parameters of 1593 samples included in the analysis, the median model results for each sample, and a data dictionary describing the tables. Analyses completed as part of this assessment relied on the previously published data of Harkness (2022) and no new data were collected.

The U.S. Geological Survey collected groundwater samples from 38 wells used for domestic and small system drinking water supply in the Coachella Valley of California in 2020. The wells were sampled for the Coachella Valley Basin (CODA) Domestic Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Coachella Valley is located in the Desert hydrogeologic province (Johnson and Belitz, 2003) and is structurally divided into four subbasins by the San Andreas fault: the Indio subbasin, the Mission Creek subbasin, the Desert Hot Springs subbasin, and the San Gorgonio Pass subbasin (California Department of Water Resources, 2016). These basins have CA basin designations 7-21.01, 7-21.02, 7-21.03, and 7-21.04 respectively. The study area was divided into 30 equal-area grid cells with at least one well sampled in 26 of the 30 cells. The 10 understanding wells were selected to provide more data in areas where wells were more abundant and to provide more water quality data for wells in the State Small Water System program. In three cases, Sampled wells within 1 mile of an unsampled cell were used to represent unsampled grid cells. Groundwater samples from all 38 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, per- and polyfluoroalkyl substances (PFAS), sulfur hexafluoride, and noble gases. Groundwater levels were measured in 31 of the 38 wells. All results are presented in this data release, except results sulfur hexafluoride and noble gases. NOTE: The only difference between the original version of this data release and this version is that this data release includes results for tritium. Tritium results were not included in the original version because they were not available at the time of publication.

The U.S. Geological Survey collected groundwater samples from 38 wells used for domestic and small system drinking water supply in the Coachella Valley of California in 2020. The wells were sampled for the Coachella Valley Basin (CODA) Domestic Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Coachella Valley is located in the Desert hydrogeologic province (Johnson and Belitz, 2003) and is structurally divided into four subbasins by the San Andreas fault: the Indio subbasin, the Mission Creek subbasin, the Desert Hot Springs subbasin, and the San Gorgonio Pass subbasin (California Department of Water Resources, 2016). These basins have CA basin designations 7-21.01, 7-21.02, 7-21.03, and 7-21.04 respectively. The study area was divided into 30 equal-area grid cells with at least one well sampled in 26 of the 30 cells. The 10 understanding wells were selected to provide more data in areas where wells were more abundant and to provide more water quality data for wells in the State Small Water System program. In three cases, Sampled wells within 1 mile of an unsampled cell were used to represent unsampled grid cells. Groundwater samples from all 38 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, per- and polyfluoroalkyl substances (PFAS), sulfur hexafluoride, and noble gases. Groundwater levels were measured in 31 of the 38 wells. All results are presented in this data release, except results sulfur hexafluoride and noble gases. NOTE: The only difference between the original version of this data release and this version is that this data release includes results for tritium. Tritium results were not included in the original version because they were not available at the time of publication.

The U.S. Geological Survey collected groundwater samples from 38 wells used for domestic and small system drinking water supply in the Coachella Valley of California in 2020. The wells were sampled for the Coachella Valley Basin (CODA) Domestic Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Coachella Valley is located in the Desert hydrogeologic province (Johnson and Belitz, 2003) and is structurally divided into four subbasins by the San Andreas fault: the Indio subbasin, the Mission Creek subbasin, the Desert Hot Springs subbasin, and the San Gorgonio Pass subbasin (California Department of Water Resources, 2016). These basins have CA basin designations 7-21.01, 7-21.02, 7-21.03, and 7-21.04 respectively. The study area was divided into 30 equal-area grid cells with at least one well sampled in 26 of the 30 cells. The 10 understanding wells were selected to provide more data in areas where wells were more abundant and to provide more water quality data for wells in the State Small Water System program. In three cases, Sampled wells within 1 mile of an unsampled cell were used to represent unsampled grid cells. Groundwater samples from all 38 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, per- and polyfluoroalkyl substances (PFAS), sulfur hexafluoride, and noble gases. Groundwater levels were measured in 31 of the 38 wells. All results are presented in this data release, except results sulfur hexafluoride and noble gases. NOTE: The only difference between the original version of this data release and this version is that this data release includes results for tritium. Tritium results were not included in the original version because they were not available at the time of publication.

The U.S. Geological Survey collected groundwater samples from 38 wells used for domestic and small system drinking water supply in the Coachella Valley of California in 2020. The wells were sampled for the Coachella Valley Basin (CODA) Domestic Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Coachella Valley is located in the Desert hydrogeologic province (Johnson and Belitz, 2003) and is structurally divided into four subbasins by the San Andreas fault: the Indio subbasin, the Mission Creek subbasin, the Desert Hot Springs subbasin, and the San Gorgonio Pass subbasin (California Department of Water Resources, 2016). These basins have CA basin designations 7-21.01, 7-21.02, 7-21.03, and 7-21.04 respectively. The study area was divided into 30 equal-area grid cells with at least one well sampled in 26 of the 30 cells. The 10 understanding wells were selected to provide more data in areas where wells were more abundant and to provide more water quality data for wells in the State Small Water System program. In three cases, Sampled wells within 1 mile of an unsampled cell were used to represent unsampled grid cells. Groundwater samples from all 38 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, per- and polyfluoroalkyl substances (PFAS), sulfur hexafluoride, and noble gases. Groundwater levels were measured in 31 of the 38 wells. All results are presented in this data release, except results sulfur hexafluoride and noble gases. NOTE: The only difference between the original version of this data release and this version is that this data release includes results for tritium. Tritium results were not included in the original version because they were not available at the time of publication.

The U.S. Geological Survey collected groundwater samples from 38 wells used for domestic and small system drinking water supply in the Coachella Valley of California in 2020. The wells were sampled for the Coachella Valley Basin (CODA) Domestic Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Coachella Valley is located in the Desert hydrogeologic province (Johnson and Belitz, 2003) and is structurally divided into four subbasins by the San Andreas fault: the Indio subbasin, the Mission Creek subbasin, the Desert Hot Springs subbasin, and the San Gorgonio Pass subbasin (California Department of Water Resources, 2016). These basins have CA basin designations 7-21.01, 7-21.02, 7-21.03, and 7-21.04 respectively. The study area was divided into 30 equal-area grid cells with at least one well sampled in 26 of the 30 cells. This dataset identifies the well locations, study unit boundary, and grid cells for the Coachella Valley Domestic-Supply Aquifer study unit. Note: The only difference between the original version of this data release and this version is that this data release includes results for tritium. Tritium results were not included in the original version because they were not available at the time of publication.