This data release contains data used to develop models and maps that estimate the occurrence of lithium in groundwater used as drinking water throughout the conterminous United States. An extreme gradient boosting model was developed to estimate the most probable lithium concentration category (≤4, >4 to ≤10, >10 to ≤30 or >30 µg/L). The model uses lithium concentration data from wells located throughout the conterminous United States and predictor variables that are available as geospatial data. The model is included in this data release in the zipped folder named Model_Archive and was used to produce maps that are also included in this data release. The model input data (predictor variables) that were used to make the maps are within a zipped folder (Map_Input_Data.zip) that contains 20 tif-raster files, one for each model predictor variable. The map probability estimates that are outputs from the model are in a zipped folder (Map_Output_Data.zip) that contains 10 tif-raster files, two model estimate maps for each of the lithium concentration categories and the category with the highest probability for public supply well depths and domestic supply well depths.

The map graphic image at https://www.sciencebase.gov/catalog/file/get/63140561d34e36012efa2b7f?name=arsenic_map.png illustrates arsenic values, in micrograms per liter, for groundwater samples from about 31,000 wells and springs in 49 states compiled by the United States Geological Survey (USGS). The map graphic illustrates an updated version of figure 1 from Ryker (2001). Cited Reference: Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36 at http://www.agiweb.org/geotimes/nov01/feature_Asmap.html. An excel tabular data file, a txt file, along with a GIS shape file of arsenic concentrations (20,043 samples collected by the USGS) for a subset of the sites shown on the map. Samples were collected between 1973 and 2001 and are provided for download.

The Dynamic Surface Water Extent MODIS (DSWEmod) surface water maps for the conterminous United States were used for a study conducted by the U.S. Geological Survey (USGS) Patterns in the Landscape - Analyses of Cause and Effect (PLACE) team quantifying seasonal and annual surface water trends within Environmental Protection Agency (EPA) Level I and Level III Ecoregions (Omernik, 1987) across the U.S. from 2003 through 2019. The overarching objectives of this study were to, (i) generate the monthly DSWEmod maps for the conterminous United States, (ii) review the spatial and temporal dynamics of surface water extent across ecoregions, and (iii) compare surface water area trends to streamgage discharge trends to determine where and how well different approaches to measuring water dynamics align. The DSWEmod model classifies the landscape (i.e., each 250-meter Moderate Resolution Imaging Spectroradiometer, or MODIS, pixel) into different classes of surface water based on quantified levels of confidence, including, (i) high-confidence surface water (class 1), (ii) moderate-confidence surface water (class 2), (iii) potential wetland (class 3), and (iv) low-confidence water/wetland (class 4), as well as a not-water class (class 0) and a no-data class (class 9). The confidence level is based on thresholds within various water- and vegetation-based indices. The level of confidence is based on how many, and, which index thresholds are met. Only high-confidence surface water (class 1) was considered in this study. This data release includes a vector shapefile consisting of 85 polygons, delineating EPA Level III Ecoregions for the conterminous United States. For each Level III Ecoregion, we include attributes identifying, (i) their respective Level I Ecoregion name and identification number, (ii) quantified seasonal and overall mean water area, (iii) comparisons with U.S. Geological Survey (USGS) National Water Information System (NWIS) streamgage discharge trends, (iv) mean surface water extent statistics (mean, minimum, maximum, standard deviation, coefficient of variation, percent of ecoregion), and (v) seasonal and overall results from the Mann-Kendall statistical analysis. An associated manuscript describes the methodology, results, and conclusions from this study.

This is the 2022 version of the Aquifer Risk Map. The 2021 version of the Aquifer Risk Map is available here.This aquifer risk map is developed to fulfill requirements of SB-200 and is intended to help prioritize areas where domestic wells and state small water systems may be accessing raw source groundwater that does not meet primary drinking water standards (maximum contaminant level or MCL). In accordance with SB-200, the risk map is to be made available to the public and is to be updated annually starting January 1, 2021. The Fund Expenditure Plan states the risk map will be used by Water Boards staff to help prioritize areas for available SAFER funding. This is the final 2022 map based upon feedback received from the 2021 map. A summary of methodology updates to the 2022 map can be found here.This map displays raw source groundwater quality risk per square mile section. The water quality data is based on depth-filtered, declustered water quality results from public and domestic supply wells. The process used to create this map is described in the 2022 Aquifer Risk Map Methodology document. Data processing scripts are available on GitHub. Download/export links are provided in this app under the Data Download widget.This draft version was last updated December 1, 2021. Water quality risk: This layer contains summarized water quality risk per square mile section and well point. The section water quality risk is determined by analyzing the long-tern (20-year) section average and the maximum recent (within 5 years) result for all sampled contaminants. These values are compared to the MCL and sections with values above the MCL are “high risk”, sections with values within 80%-100% of the MCL are “medium risk” and sections with values below 80% of the MCL are “low risk”. The specific contaminants above or close to the MCL are listed as well. The water quality data is based on depth-filtered, de-clustered water quality results from public and domestic supply wells.Individual contaminants: This layer shows de-clustered water quality data for arsenic, nitrate, 1,2,3-trichloropropane, uranium, and hexavalent chromium per square mile section. Domestic Well Density: This layer shows the count of domestic well records per square mile. The domestic well density per square mile is based on well completion report data from the Department of Water Resources Online System for Well Completion Reports, with records drilled prior to 1970 removed and records of “destruction” removed.State Small Water Systems: This layer displays point locations for state small water systems based on location data from the Division of Drinking Water.Public Water System Boundaries: This layer displays the approximate service boundaries for public water systems based on location data from the Division of Drinking Water.Reference layers: This layer contains several reference boundaries, including boundaries of CV-SALTS basins with their priority status, Groundwater Sustainability Agency boundaries, census block group boundaries, county boundaries, and groundwater unit boundaries. ArcGIS Web Application

This map layer shows areal and linear water features of the United States, Puerto Rico, and the U.S. Virgin Islands. The original file was produced by joining the individual State hydrography layers from the 1:2,000,000- scale Digital Line Graph (DLG) data produced by the USGS. This map layer was formerly distributed as Hydrography Features of the United States. This is a revised version of the January 2003 map layer.

Here we present a geospatial dataset representing local- and regional-scale aquifer system boundaries, defined on the basis of an extensive literature review and published in GebreEgziabher et al. (2022). Nature Communications, 13, 2129, https://www.nature.com/articles/s41467-022-29678-7

The database contains 440 polygons, each representing one study area analyzed in GebreEgziabher et al. (2022). The attribute table associated with the shapefile has two fields (column headings): (1) aquifer system title (Ocala Uplift sub-area of the broader Floridan Aquifer System), and (2) broader aquifer system title (e.g., the Floridan Aquifer System).

• to explore the available data via an interactive app please visit the following URL: https://ucsb.maps.arcgis.com/apps/instant/nearby/index.html?appid=2a238e4ed2434d21b3b53c861a064d8f
• to explore the 3D nature of a dozen aquifer systems please see the following storymap: https://storymaps.arcgis.com/stories/a91f061759e64e44af38daf6cefa4259

Statistical analyses and maps representing mean, high, and low water-level conditions in the surface water and groundwater of Miami-Dade County were made by the U.S. Geological Survey, in cooperation with the Miami-Dade County Department of Regulatory and Economic Resources, to help inform decisions necessary for urban planning and development. Sixteen maps were created that show contours of (1) the mean of daily water levels at each site during October and May for the 2000-2009 water years; (2) the 25th, 50th, and 75th percentiles of the daily water levels at each site during October and May and for all months during 2000-2009; and (3) the differences between mean October and May water levels, as well as the differences in the percentiles of water levels for all months, between 1990-1999 and 2000-2009. The 80th, 90th, and 96th percentiles of the annual maximums of daily groundwater levels during 1974-2009 (a 35-year period) were computed to provide an indication of unusually high groundwater-level conditions. These maps and statistics provide a generalized understanding of the variations of water levels in the aquifer, rather than a survey of concurrent water levels. Water-level measurements from 473 sites in Miami-Dade County and surrounding counties were analyzed to generate statistical analyses. The monitored water levels included surface-water levels in canals and wetland areas and groundwater levels in the Biscayne aquifer. Maps were created by importing site coordinates, summary water-level statistics, and completeness of record statistics into a geographic information system, and by interpolating between water levels at monitoring sites in the canals and water levels along the coastline. Raster surfaces were created from these data by using the triangular irregular network interpolation method. The raster surfaces were contoured by using geographic information system software. These contours were imprecise in some areas because the software could not fully evaluate the hydrology given available information; therefore, contours were manually modified where necessary. The ability to evaluate differences in water levels between 1990-1999 and 2000-2009 is limited in some areas because most of the monitoring sites did not have 80 percent complete records for one or both of these periods. The quality of the analyses was limited by (1) deficiencies in spatial coverage; (2) the combination of pre- and post-construction water levels in areas where canals, levees, retention basins, detention basins, or water-control structures were installed or removed; (3) an inability to address the potential effects of the vertical hydraulic head gradient on water levels in wells of different depths; and (4) an inability to correct for the differences between daily water-level statistics. Contours are dashed in areas where the locations of contours have been approximated because of the uncertainty caused by these limitations. Although the ability of the maps to depict differences in water levels between 1990-1999 and 2000-2009 was limited by missing data, results indicate that near the coast water levels were generally higher in May during 2000-2009 than during 1990-1999; and that inland water levels were generally lower during 2000-2009 than during 1990-1999. Generally, the 25th, 50th, and 75th percentiles of water levels from all months were also higher near the coast and lower inland during 2000–2009 than during 1990-1999. Mean October water levels during 2000-2009 were generally higher than during 1990-1999 in much of western Miami-Dade County, but were lower in a large part of eastern Miami-Dade County.

Use Constraints:This mapping tool is for reference and guidance purposes only and is not a binding legal document to be used for legal determinations. The data provided may contain errors, inconsistencies, or may not in all cases appropriately represent the current boundaries of PWSs in California. The data in this map are subject to change at any time and should not be used as the sole source for decision making. By using this data, the user acknowledges all limitations of the data and agrees to accept all errors stemming from its use.Description:This mapping tool provides a representation of the general PWS boundaries for water service, wholesaler and jurisdictional areas. The boundaries were created originally by collection via crowd sourcing by CDPH through the Boundary Layer Tool, this tool was retired as of June 30, 2020. State Water Resources Control Board – Division of Drinking Water is currently in the process of verifying the accuracy of these boundaries and working on a tool for maintaining the current boundaries and collecting boundaries for PWS that were not in the original dataset. Currently, the boundaries are in most cases have not been verified. Map Layers· Drinking Water System Areas – representation of the general water system boundaries maintained by the State Water Board. This layer contains polygons with associated data on the water system and boundary the shape represents.· LPA office locations – represents the locations of the Local Primacy Agency overseeing the water system in that county. Address and contact information are attributes of this dataset.· LPA office locations – represents the locations of the Local Primacy Agency overseeing the water system in that county. Address and contact information are attributes of this dataset· California Senate Districts – represents the boundaries of the senate districts in California included as a reference layer in order to perform analysis with the Drinking Water System Boundaries layers.· California Senate Districts – represents the boundaries of the assembly districts in California included as a reference layer in order to perform analysis with the Drinking Water System Boundaries layers.· California County – represents the boundaries of the counties in California included as a reference layer in order to perform analysis with the Drinking Water System Boundaries layers.Informational Pop-up Box for Boundary layer· Water System No. – unique identifier for each water system· Water System Name – name of water system· Regulating Agency – agency overseeing the water system· System Type – classification of water system.· Population the approximate population served by the water system· Boundary Type – the type of water system boundary being displayed· Address Line 1 – the street or mailing address on file for the water system· Address Line 2 – additional line for street or mailing address on file for the water system, if applicable· City – city where water system located or receives mail· County – county where water system is located· Verification Status – the verification status of the water system boundary· Verified by – if the boundary is verified, the person responsible for the verification Date Created and Sources:This web app was most recently updated on July, 21, 2021. Each layer has a data created date and data source is indicated in the overview/metadata page and is valid up to the date provided.

USGS researchers with the Patterns in the Landscape – Analyses of Cause and Effect (PLACE) project are releasing a collection of high-frequency surface water map composites derived from daily Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Using Google Earth Engine, the team developed customized image processing steps and adapted the Dynamic Surface Water Extent (DSWE) to generate surface water map composites in California for 2003-2019 at a 250-m pixel resolution. Daily maps were merged to create 6, 3, 2, and 1 composite(s) per month corresponding to approximately 5-day, 10-day, 15-day, and monthly products, respectively. The resulting maps are available as downloadable files for each year. Each file includes 72, 36, 24, or 12 bands that coincide with the number of maps generated in the 5-day, 10-day, 15-day, and monthly products, respectively. The bands are ordered chronologically, with the first band representing the beginning of the calendar year and the last band representing the end of the year. Each set of maps is labeled according to year and product type. There are 17 GeoTIF (.tif) raster data files for each composite product.

Aquifers are underground layers of gravel, sand, or permeable rock that contain ground water. This water can be extracted using a well and provides an important source of water in many regions of the world.This layer, produced as part of the Ground Water Atlas of the United States, provides access to the areal extent of the principal aquifers of the United States. In areas where multiple aquifers exist at different depths below the surface only the shallowest aquifer is included.This layer does not display all areas where ground water exists. The U.S. Geologic Survey (USGS) mapped these aquifers by interpreting surface features and aquifers may extend beyond these features. Ground water areas along watercourses and ground water in unconsolidated glacial sand and gravel deposits are not included in this layer. Data on these areas are provided in the layer Aquifers of Alluvial and Glacial Origin from the USGS.Dataset SummaryPhenomenon Mapped: Aquifers of the United StatesCoordinate System: Web Mercator Auxiliary SphereExtent: 48 Contiguous United States, Hawaii, Puerto Rico, and the U.S. Virgin IslandsVisible Scale: All ScalesSource: Groundwater Atlas of the United StatesPublication Date: October 1, 2003Please note: "This dataset, published in 2003, contains the shallowest principal aquifers of the conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands, portrayed as polygons. The map layer was developed as part of the effort to produce the maps published at 1:2,500,000 in the printed series Ground Water Atlas of the United States. The published maps contain base and cultural features not included in these data. Please note that the maps do not show the entire extent of an aquifer, only its subcrop or outcrop area. Refer to the metadata for a complete description of the files and how they were generated." (Source USGS)What can you do with this layer?This layer can be used throughout the ArcGIS system. Feature layers can be used just like any other vector layer. You can use feature layers as an input to geoprocessing tools in ArcGIS Pro or in Analysis in ArcGIS Online. Combine the layer with others in a map and set custom symbology or create a pop-up tailored for your users. For the details of working with feature layers the help documentation for ArcGIS Pro or the help documentation for ArcGIS Online are great places to start. The ArcGIS Blog is a great source of ideas for things you can do with feature layers. This layer is part of ArcGIS Living Atlas of the World that provides an easy way to find and explore many other beautiful and authoritative layers, maps, and applications on hundreds of topics.

Members from the U.S. Geological Survey (USGS) Patterns in the Landscape - Analyses of Cause and Effect (PLACE) team are releasing monthly surface water maps for the conterminous United States (U.S.) from 2003 through 2019 as 250-meter resolution geoTIFF files. The maps were produced using the Dynamic Surface Water Extent (DSWE) algorithm applied to daily Moderate Resolution Imaging Spectroradiometer (MODIS) imagery (DSWEmod) (Soulard et al., 2021) - see associated items. The DSWEmod model classifies the landscape (i.e., each MODIS pixel) into different classes of surface water based on quantified levels of confidence, including, i) high-confidence surface water (class 1), ii) moderate-confidence surface water (class 2), iii) potential wetland (class 3), and iv) low-confidence water/wetland (class 4), as well as a not-water class (class 0) and a no-data class (class 9). This data release consists of a Parent Directory and 18 Child Items. The Parent Directory includes a zipped folder housing the complete monthly DSWEmod surface water maps for the conterminous United States from 2003 through 2019 represented in 17 multiband images, equating to one image for each year from 2003 through 2019. Each annual image – available as separate Child Items (n = 17) – consists of 12 bands, where each band value from 1-12 represents sequential months from January (Band 1) to December (Band 12). Such a structure allows for a user to download either the full time-series of DSWEmod products or a user-specified set of years. The DSWEmod surface water maps were used for a study conducted by the PLACE team quantifying seasonal and annual surface water trends within Environmental Protection Agency (EPA) Level I and Level III Ecoregions (Omernik, 1987) across the U.S. from 2003 through 2019. The results from this study are also being released as a Child Item - Surface Water Trends for the Conterminous United States using monthly DSWEmod Surface Water Maps, 2003–2019. This portion of the data release includes a vector shapefile consisting of 85 polygons, delineating EPA Level III Ecoregions for the conterminous United States. For each Level III Ecoregion, we include attributes identifying, (i) their respective Level I Ecoregion name and identification number, (ii) quantified seasonal and overall mean water area, (iii) comparisons with U.S. Geological Survey (USGS) National Water Information System (NWIS) streamgage discharge trends, (iv) mean surface water extent statistics (mean, minimum, maximum, standard deviation, coefficient of variation, percent of ecoregion), and (v) seasonal and overall results from the Mann-Kendall statistical analysis. An associated manuscript describes the methodology, results, and conclusions from this study.

The USGS compiles online access to water-resources data collected at approximately 1.5 million sites in all 50 States, the District of Columbia, Puerto Rico, the Virgin Islands, Guam, American Samoa and the Commonwealth of the Northern Mariana Islands.

This map shows current flood conditions in the United States using live data from the National Weather Service, including observed flooding locations, river and precipitation forecasts, and flood warning areas. For a map that focuses on more general weather reports and current radar, see our Severe Weather Map.About the dataStream Gauges: This is Esri's Live Stream Gauges layer, symbolized to show only those gauges that are currently at or above flood stage. Click on a gauge to see the current depth, flow rate, and alert level. Five day forecasts from Advanced Hydrologic Prediction Service are shown where available.Population Density: This is Esri's World Population Estimate, which models the likely population of each 250 meter square cell, globally. It provides import context to the map, showing where flooding is likely to have a human impact.Flood Warnings (short and long term): These weather alerts are NOAA Weather Warnings, Watches, and Advisory data provided through the Common Alerting Protocol (CAP) Alert system. The long term warnings (flood warnings) are done on a county basis, while the short term warnings (flash flood and marine warnings) are more spatially precise. 72-hour Precipitation Forecast: This is the Quantitative Precipitation Forecast (QPF) from NOAA's National Digital Forecast Database. By default it shows the predicted total over the next 72 hours, but this forecast can also be viewed in six hour intervals.

Statistical analyses and maps representing mean, high, and low water-level conditions in the surface water and groundwater of Miami-Dade County were made by the U.S. Geological Survey, in cooperation with the Miami-Dade County Department of Regulatory and Economic Resources, to help inform decisions necessary for urban planning and development. Sixteen maps were created that show contours of (1) the mean of daily water levels at each site during October and May for the 2000-2009 water years; (2) the 25th, 50th, and 75th percentiles of the daily water levels at each site during October and May and for all months during 2000-2009; and (3) the differences between mean October and May water levels, as well as the differences in the percentiles of water levels for all months, between 1990-1999 and 2000-2009. The 80th, 90th, and 96th percentiles of the annual maximums of daily groundwater levels during 1974-2009 (a 35-year period) were computed to provide an indication of unusually high groundwater-level conditions. These maps and statistics provide a generalized understanding of the variations of water levels in the aquifer, rather than a survey of concurrent water levels. Water-level measurements from 473 sites in Miami-Dade County and surrounding counties were analyzed to generate statistical analyses. The monitored water levels included surface-water levels in canals and wetland areas and groundwater levels in the Biscayne aquifer. Maps were created by importing site coordinates, summary water-level statistics, and completeness of record statistics into a geographic information system, and by interpolating between water levels at monitoring sites in the canals and water levels along the coastline. Raster surfaces were created from these data by using the triangular irregular network interpolation method. The raster surfaces were contoured by using geographic information system software. These contours were imprecise in some areas because the software could not fully evaluate the hydrology given available information; therefore, contours were manually modified where necessary. The ability to evaluate differences in water levels between 1990-1999 and 2000-2009 is limited in some areas because most of the monitoring sites did not have 80 percent complete records for one or both of these periods. The quality of the analyses was limited by (1) deficiencies in spatial coverage; (2) the combination of pre- and post-construction water levels in areas where canals, levees, retention basins, detention basins, or water-control structures were installed or removed; (3) an inability to address the potential effects of the vertical hydraulic head gradient on water levels in wells of different depths; and (4) an inability to correct for the differences between daily water-level statistics. Contours are dashed in areas where the locations of contours have been approximated because of the uncertainty caused by these limitations. Although the ability of the maps to depict differences in water levels between 1990-1999 and 2000-2009 was limited by missing data, results indicate that near the coast water levels were generally higher in May during 2000-2009 than during 1990-1999; and that inland water levels were generally lower during 2000-2009 than during 1990-1999. Generally, the 25th, 50th, and 75th percentiles of water levels from all months were also higher near the coast and lower inland during 2000–2009 than during 1990-1999. Mean October water levels during 2000-2009 were generally higher than during 1990-1999 in much of western Miami-Dade County, but were lower in a large part of eastern Miami-Dade County.

The US Map of Suspected Well Water Impacts includes incidents in which oil and gas related events are suspected in events that have an impact upon ground water in the United States. There are multiple layers to the map, each with its own source, and therefore credibility.Visitor Submitted Impacts: This layer consists of viewer submitted form data describing suspected incidents of groundwater contamination by oil and gas extraction and related industries. The locations have been determined using the centroids or geometric center-points of the zip code in which the suspected incident occurred. If you are aware of additional incidents, please submit them here.Pipeline Incidents Contaminating Groundwater: This data layer includes hazardous liquid pipeline incidents that were indicated as resulting in groundwater contamination between 1/1/2010 and 3/29/2013. The data were obtained by the US Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA). The data have been altered by the FracTracker Alliance in that it only includes incidents leading to groundwater contamination, and by the removal of several dozen columns of data about the incident.NRDC Suspected Contamination Events: Amy Mall of the Natural Resources Defense Council compiled a list of 37 incidents where hydraulic fracturing is suspected of contributing to groundwater contamination. The list was compiled in December 2011, and each entry is linked to news reports of the event. This layer was mapped by the FracTracker Alliance based on the centroids or geographic center-points of the municipality, county, or state of the incident, depending on the best information available.List of the Harmed Suspected Water Incidents: Jenny Lisak, co-director of the Pennsylvania Alliance for Clean Water and Air, maintains a list of people claiming to be harmed by hydraulic fracturing or related processes, called the List of the Harmed. This data layer is based on the February 23, 2013 update of the list, and contains only the events in which water is the suspected exposure pathway. This data was mapped by the FracTracker Alliance based on the centroids or geographic center-points of the municipality, county, or state of the incident, depending on the best information available. NM Pit Contamination Events: This layer consists of events where the New Mexico Oil Conservation Division determined that substances from oil and gas pits contaminated groundwater. Altogether, there are 369 incidents included in the data. The document on which this map was based was published in 2008.Complaints to PADEP: Laura Legere, a reporter with the Scranton Times-Tribune, submitted a Right-to-Know law request to PADEP for documents related to people complaining of their well water being impacted by oil and gas drilling, hydraulic fracturing, and related activities. Inclusion on this map layer just means that there was a complaint to PADEP, and should not be construed as proof of a causal relationship between the gas well activity and supposed ground water impact. However, 161 of the incidents have documentation where PADEP establishes a connection between drilling activity and well water impacts. Please note that locations are not exact. They were created by finding the centroid, or geographic center-point, of each municipality. Names of those claiming well water impacts are not included in the data for this map.

Information on water depth in river channels is important for a number of applications in water resource management but can be difficult to obtain via conventional field methods, particularly over large spatial extents and with the kind of frequency and regularity required to support monitoring programs. Remote sensing methods could provide a viable alternative means of mapping river bathymetry (i.e., water depth). The purpose of this study was to develop and test new, spectrally based techniques for estimating water depth from satellite image data. More specifically, a neural network-based temporal ensembling approach was evaluated in comparison to several other neural network depth retrieval (NNDR) algorithms. These methods are described in a manuscript titled "Neural Network-Based Temporal Ensembling of Water Depth Estimates Derived from SuperDove Images" and the purpose of this data release is to make available the depth maps produced using these techniques. The images used as ...

The High Plains aquifer extends from approximately 32 to 44 degrees north latitude and from 96 degrees 30 minutes to 106 degrees west longitude. The aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital data set contains water-level measurements from wells screened in the High Plains aquifer and measured in both predevelopment (about 1950) and for 2017. There were 2,928 wells measured in both predevelopment (about 1950) and 2017 as well as 63 wells located in New Mexico, which were measured in predevelopment and at least once between 2013 and 2016. These water-level measurements were used to map water-level changes, predevelopment (about 1950) to 2017. The map was reviewed for consistency with the relevant data at a scale of 1:1,000,000.

The aquifer risk map is being developed to fulfill requirements of SB-200 and is intended to help prioritize areas where domestic wells and state small water systems may be accessing groundwater that does not meet primary drinking water standards (maximum contaminant level or MCL). In accordance with SB-200, the risk map is to be made available to the public and is to be updated annually starting January 1, 2021. The Fund Expenditure Plan states the risk map will be used by Water Boards staff to help prioritize areas for available SAFER funding.Methodology for the draft aquifer risk map available for download.Water quality risk: This layer contains summarized water quality risk per census block group, square mile section, and well point. The overall census block group water quality risk is based on four risk factors (the count of chemicals with a long-term average (20 year) or recent result (within 2 years) above the MCL, the count of chemicals with a long-term average (20 year) or recent result (within 2 years) within 80% of the MCL, the average magnitude or results above the MCL, and the percent area with chemicals above the MCL or within 80% of the MCL). The specific chemicals that contribute to these risk factors are listed as well. Higher values for each individual risk factor contribute to a higher overall score. The scores are converted to percentiles to normalize the results. The water quality data is based on depth-filtered, declustered water quality results from public and domestic supply wells, collected following a similar methodology as the Domestic Well Needs Assessment White Paper. This layer also displays the total estimated count of domestic wells per census block group, based on the Department of Water Resources Online System for Well Completion Reports, and the total estimated count of domestic well user population, based on the United States Geological Survey Road-Enhanced Methodology (Johnson and Belitz, 2019). To provide comments or feedback on this map, please email SAFER@waterboards.ca.gov or Emily.Houlihan@Waterboards.ca.gov. Individual chemicals: This layer shows declustered water quality data for arsenic, nitrate, 1,2,3-trichloropropane, uranium, and hexavalent chromium per square mile section. The intent of the aquifer risk map is to help prioritize areas where domestic well users and state small water systems may be accessing groundwater that does not meet primary drinking water standards (maximum contaminant level or MCL) and will be updated annually starting January 1, 2021. The section water quality data is based on depth-filtered water quality results from public and domestic supply wells, collected following a similar methodology as the Domestic Well Needs Assessment White Paper. This layer contains the long-term average (20 years) as well as the count of recent results (within 2 years) above the MCL, between 80% - 100% of the MCL, and below 80% of the MCL for each square mile section. Drinking water users: This layer shows the locations of state small water systems and domestic well density. The state small water system locations were collected by the Rural Community Assistance Corporation. The locations are approximate and may not exactly represent well locations or service boundaries. The domestic well density per square mile is based on well completion report data from the Department of Water Resources Online System for Well Completion Reports. This layer also contains the public water system boundaries (available on the State Water Board REST endpoint) for reference.Reference layers: This layer contains several reference boundaries, including boundaries of CV-SALTS basins with their priority status, Groundwater Sustainability Agency boundaries, census block group boundaries, county boundaries, and groundwater unit boundaries.

The High Plains aquifer extends from south of about 32 degrees to almost 44 degrees north latitude and from about 96 degrees 30 minutes to 106 degrees west longitude. The aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital data set is the water-level measurements from 7,526 wells measured in both 2013 and 2015, which was used to map water-level changes, 2013 to 2015. The map was reviewed for consistency with the relevant data at a scale of 1:1,000,000.

This USGS data release consists of two geospatial raster datasets and three geospatial vector data sets of water-level data. The data sets include a raster (A1) representing water-level change from predevelopment (about 1950) to 2015; the primary vector dataset (A2) of water-level-change data of static or near-static water levels in wells measured in predevelopment and 2015 (for wells in Colorado, Kansas, Nebraska, Oklahoma, South Dakota, and Texas) and in wells measured in predevelopment and the latest available static or near-static water level from 2011 to 2015 (for wells in New Mexico and Wyoming), a supplemental vector dataset (A3) of water-level data used to manually substantiate the raster of water-level change from predevelopment (about 1950) to 2015, a raster (B1) representing water-level change from 2013 to 2015; and the vector dataset (B2) of water-level-change data for wells measured in 2013 and 2015. The supplemental vector data sets of water-level-change data used to ...