Stephanie R. James Burke J. Minsley 20240725 Raster Digital Data Denver, CO U.S. Geological Survey Additional information about Originator: James, S.R., https://orcid.org/0000-0001-5715-253X; Minsley, B.J., https://orcid.org/0000-0003-1689-1306; Suggested Citation: James, S.R. and Minsley, B.J., 2021, Combined results and derivative products of hydrogeologic structure and properties from airborne electromagnetic surveys in the Mississippi Alluvial Plain (ver. 2.0, July 2024): U.S. Geological Survey data release, https://doi.org/10.5066/P9382RCI. https://doi.org/10.5066/P9382RCI Burke J. Minsley J.R. Rigby Stephanie R. James Bethany L. Burton Katherine J. Knierim Michael D.M. Pace Paul A. Bedrosian Wade H. Kress 2021 journal article Volume 2 1 Nature Communications Earth & Environment https://doi.org/10.1038/s43247-021-00200-z Electrical resistivity results from four regional airborne electromagnetic (AEM) surveys (Burton et al. 2024, Hoogenboom et al. 2023, Minsley et al. 2021, Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey (USGS) to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. The 3D elevation grid was used to quantify across the MAP region 1) the occurrence and thickness of surficial (< 15 meter (m) depth) confining material, 2) the top and bottom elevation corresponding to the surficial confining material, and 3) a metric representing the degree of surface confinement or connectivity that ranges from fully confining conditions to high potential hydrologic connectivity. These products were generated using the updated 12-class facies classifications of the 3D electrical resistivity model. See child item “Mississippi Alluvial Plain (MAP): Electrical Resistivity & Facies Classification Grids” for more details on the facies classes: https://www.sciencebase.gov/catalog/item/5f03a7bc82ce0afb2446e11f. The final surfaces and hydrogeologic metrics were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF) format. Burton, B.L., Adams, R.F. Adams, Minsley, B.J., Pace, M.D.M., Kress, W.H., Rigby, J.R., and Bussell, A.M., 2024, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, March 2018 and May - August 2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KPK3UJ. Hoogenboom, B.E., Minsley, B.J., James, S.R., and Pace, M.D., 2023, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, Mississippi Embayment, and Gulf Coastal Plain, September 2021 - January 2022: U.S. Geological Survey data release, https://doi.org/10.5066/P93DO0EO. Burton, B.L., Minsley, B.J., Bloss, B.R., and Kress, W.H., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2018 - February 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9XBBBUU. Minsley, B.J., James, S.R., Bedrosian, P.A., Pace, M.D., Hoogenboom, B.E., and Burton, B.L., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2019 - March 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9E44CTQ. These data were combined and created to provide high-resolution information about hydrogeologic structure and properties to aid interpretations, hydrologic models, water resource studies, and local decision-making concerning the Mississippi River Valley Alluvial aquifer. See Source Information section for details on all external sources used in this work. 20191101 20240223 product creation date Complete As needed -95.8879 -86.4055 37.9327 28.5179 USGS Thesaurus electromagnetic surveying geophysics hydrogeology resistivity geospatial datasets engineering sciences water resources groundwater ISO 19115 Topic Category geoscientificInformation environment None electromagnetics hydrogeology Geology, Geophysics, and Geochemistry Science Center GGGSC U.S. Geological Survey USGS Water Availability and Use Science Program WAUSP USGS Metadata Identifier USGS:5f08f37d82ce21d4c3fe629b Common Geographic Areas Arkansas Illinois Louisiana Mississippi Missouri Tennessee Arkansas River Mississippi River None Mississippi Alluvial Plain Mississippi River Valley Alluvial aquifer MRVA None. Please see 'Distribution Info' for details. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Stephanie R James U.S. Geological Survey Geophysicist mailing and physical address

Denver Federal Center, Bldg 20, Box 25046, MS973

Denver CO 80225 United States 303-236-1405 sjames@usgs.gov This data release was funded by the U.S. Geological Survey Water Availability and Use Science Program. These data products were generated with Python 3.7. GeoTIFF rasters were created using GDAL version 3.0.2. No formal attribute accuracy tests were conducted. These data have been peer reviewed and compared with related ancillary data. No formal logical accuracy tests were conducted. Data were plotted and visually inspected. Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. No formal positional accuracy tests were conducted in this data release. Please refer to the source AEM data releases (Burton et al. 2024, Hoogenboom et al. 2023, Minsley et al. 2021, and Burton et al. 2021) for information on positional accuracy reported by the contractor. No formal positional accuracy tests were conducted in this data release. Please see The National Map digital elevation model specifications for more information on vertical accuracy. U.S. Geological Survey 2017 raster digital data accessed October 28, 2019 https://www.usgs.gov/core-science-systems/ngp/3dep/data-tools Digital and/or Hardcopy 2017 publication date The National Map Digital Elevation Model All depths and ground surface elevations were referenced from the National Map Using the 12-class facies classifications of the 3D elevation grid made from all four AEM surveys, since the elevation layers were previously clipped to the National Map Digital Elevation Model (DEM) values for the shallowest 15 m depth at each x-y location (1 km x 1 km cell) were found by removing any upper no-data mask values and then selecting the top three 5 m-thick layers. The occurrence of low resistivity material (classes 1-6, ≤ 27.38 ohm-m) within those top three layers was counted in order to estimate the thickness of confining material. For example, if 1 out of 3 layers was class 1-6 then the confining layer thickness would be 1 x 5 m = 5 m, or if all 3 layers were class 1-6 then the confining layer thickness would be 3 x 5 m = 15 m, or if there were no class 1-6 material in the top 3 layers then the confining layer thickness would be 0 x 5 m = 0 m. The resulting two-dimensional (2D) grid of confining layer thickness values was exported to a raster image in Georeferenced Tagged Image File Format (GeoTIFF) format, entitled “MAP_RegionalAEM_2022_ConfiningLayer_Thickness.tif”. See child item “Mississippi Alluvial Plain (MAP): Electrical Resistivity & Facies Classification Grids” for more details on the facies classes: https://www.sciencebase.gov/catalog/item/5f03a7bc82ce0afb2446e11f. The National Map Digital Elevation Model 2024 The top and bottom elevation of surface confining material was also estimated during the calculation of the confining layer thickness. For locations where low resistivity material (classes 1-6) was present in the shallowest 15 m, the top elevation was taken as the upper boundary of the uppermost elevation layer containing class 1-6 material and then corrected from the DEM. Similarly, the bottom elevation was taken as the bottom boundary of the lowermost elevation layer containing class 1-6 material, corrected with the DEM. For example, if the second and third layers (depths 5-10 m and 10-15 m below the ground surface) contained class 1-6 material while the uppermost layer did not, then the top elevation was the DEM elevation minus 5 m and the bottom elevation was the DEM elevation minus 15 m. Areas where no shallow confining material was detected (i.e. no class 1-6 material in the upper 15 m) the top and bottom elevations were both set to the DEM ground surface elevation. The resulting 2D grids of top and bottom elevations of surface confining material were exported to raster images in GeoTIFF format, entitled “MAP_RegionalAEM_2022_ConfiningLayer_TopElevation.tif” and “MAP_RegionalAEM_2022_ConfiningLayer_BottomElevation.tif,” respectively. The National Map Digital Elevation Model 2024 Lastly, to produce a metric for both surface confining conditions and surface connectivity potential (e.g. areas with increasing potential for aquifer recharge), the occurrence of low electrical resistivity material (facies classes 1-6) in the previous step was added to a separate grid using the relative scale of -3, -2, and -1 to represent the cells where confining material was present in the upper 15 m, either in all three layers (-3), 2 out of 3 layers (-2), or 1 out of 3 (-1). Thus, the negative end of the scale represents the confining (low recharge potential) end of the spectrum. To complete the high connectivity end of the spectrum, cells where low-resistivity material was absent were assigned values on the relative scale of +1, +2, and +3, representing increasing connectivity (or recharge) potential, based on the facies class of the average electrical resistivity across all three layers: class 7 = +1, class 8 = +2, class 9 or greater = +3. The resulting 2D grid of surface connectivity values (ranging from -3 to +3 with no zero) was exported to a raster image in GeoTIFF format, entitled “MAP_RegionalAEM_2022_ConfiningLayer_SurfaceConnectivity.tif”. 2024 None Raster Grid Cell 1012 827 Albers Conical Equal Area 29.5 45.5 -96.0 23.0 0.0 0.0 coordinate pair 0.6096 0.6096 meters World Geodetic System 1984 (WGS 84) WGS_84 6378137.0 298.257223563 North American Vertical Datum of 1988 0.1 meters Explicit elevation coordinate included with horizontal coordinates MAP_RegionalAEM_2022_ConfiningLayer_Thickness.tif,MAP_RegionalAEM_2022_ConfiningLayer_Thickness.tfw 32-bit floating point GeoTiff (.tif) and associated world file (.tfw) of the 1-band raster image containing measurements of confining material thickness for the MAP region within 0-15 m depth, calculated from the 2022 version of the 3D resistivity and facies classification elevation grid. Values are discrete: 0 m, 5 m, 10 m, 15 m. A no data value of 9999 is encoded. Data are available for download at: https://www.sciencebase.gov/catalog/item/5f08f37d82ce21d4c3fe629b. MAP_RegionalAEM_2022_ConfiningLayer_TopElevation.tif, MAP_RegionalAEM_2022_ConfiningLayer_TopElevation.tfw 32-bit floating point GeoTiff (.tif) and associated world file (.tfw) of the 1-band raster image containing estimates of the top elevation of surface confining material in the MAP region within the upper 15 m depth, calculated from the 2022 version of the 3D resistivity and facies classification elevation grid. Note, areas with no confining material present were given a top elevation equal to the ground surface elevation. These areas can be masked with the 0 m thickness values from the “MAP_RegionalAEM_2022_ConfiningLayer_Thickness.tif” layer to show top elevations only where confining material was detected. A no data value of 9999 is encoded. Data are available for download at: https://www.sciencebase.gov/catalog/item/5f08f37d82ce21d4c3fe629b. MAP_RegionalAEM_2022_ConfiningLayer_BottomElevation.tif, MAP_RegionalAEM_2022_ConfiningLayer_BottomElevation.tfw 32-bit floating point GeoTiff (.tif) and associated world file (.tfw) of the 1-band raster image containing estimates of the bottom elevation of surface confining material in the MAP region within the upper 15 m depth, calculated from the 2022 version of the 3D resistivity and facies classification elevation grid. Note, areas with no confining material present were given a bottom elevation equal to the ground surface elevation. These areas can be masked with the 0 m thickness values from the “MAP_RegionalAEM_2022_ConfiningLayer_Thickness.tif” layer to show bottom elevations only where confining material was detected. A no data value of 9999 is encoded. Data are available for download at: https://www.sciencebase.gov/catalog/item/5f08f37d82ce21d4c3fe629b. MAP_RegionalAEM_2022_ConfiningLayer_SurfaceConnectivity.tif, MAP_RegionalAEM_2022_ConfiningLayer_SurfaceConnectivity.tfw 32-bit floating point GeoTiff (.tif) and associated world file (.tfw) of the 1-band raster image containing a metric representing the degree of confinement or connectivity in the MAP region within material in the upper 15 m depth, calculated from the 2022 version of the 3D resistivity and facies classification elevation grid. The values are discrete: -3, -2, -1, 1, 2, 3, where negative values indicate low or inhibited hydraulic connection, i.e. areas of confining, low permeability material. Positive values indicate high connectivity, i.e. areas of high recharge potential, clean sands and gravels. The full range of values represent a spectrum between no connection (-3) and high connection (+3) and the gradient in between. A no data value of 9999 is encoded. Data are available for download at: https://www.sciencebase.gov/catalog/item/5f08f37d82ce21d4c3fe629b. ScienceBase U.S. Geological Survey mailing and physical address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase_datarelease@usgs.gov https://www.sciencebase.gov/catalog/item/5f08f37d82ce21d4c3fe629b Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. None. 20240725 Stephanie R James U.S. Geological Survey Geophysicist mailing and physical address

Denver Federal Center, Bldg 20, Box 25046, MS964

Denver CO 80225 United States 303-236-1405 gs_gggsc_dm_team@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998