The data set pp1773_extents contains polygon datasets that represent the areal extents of each of the 16 hydrogeologic units of the of the Atlantic Coastal Plain of North and South Carolina. [The total areal extent includes a small area in southeastern Virginia, the Atlantic Coastal Plain within North Carolina and South Carolina, and a region in southeast Georgia within the Atlantic Coastal Plain.] Each hydrogeological unit is referred to as its model layer number as represented in the report PP1773. For clarity, they are listed below along with the aquifer unit or confining unit name in North Carolina and its correlated unit name in South Carolina. L1 Surficial aquifer L2 Yorktown confining unit / Upper Floridan confining unit L3 Yorktown aquifer / Upper Floridan aquifer L4 Castle Hayne - Pungo River confining unit / Middle Floridan confining unit (To be referred to as "Castle Hayne / Middle Floridan confining unit" in this document) L5 Castle Hayne - Pungo River aquifer / Middle Floridan aquifer (To be referred to as "Castle Hayne - Middle Floridan aquifer" in this document) L6 Beaufort confing unit / Gordon confining unit L7 Beaufort aquifer / Gordon aquifer L8 Peedee confining unit / Crouch Branch confining unit L9 Peedee aquifer / Crouch Branch aquifer L10 Black Creek confining unit / McQueen Branch confining unit L11 Black Creek aquifer / McQueen Branch aquifer L12 Upper Cape Fear confining unit / Charleston confining unit L13 Upper Cape Fear aquifer / Charleston aquifer L14 Lower Cape Fear confining unit / Gramling confining unit L15 Lower Cape Fear aquifer / Gramling aquifer L16 Lower Cretaceous confining unit and aquifer Spatial data set pp1773_layer1_extent represents the extent of the top of the surficial aquifer, which is Layer 1 in the groundwater model used to simulate the aquifer system described in PP 1773. The surficial aquifer is the uppermost aquifer. It is an unconfined aquifer that is uniformly present except where it is incised by streams. The top of the surficial aquifer is equivalent to the land surface. The extent was derived primarily by geologic and hydraulic properties, as the surficial aquifer is an unconfined layer primarily composed of sediments of Quaternary age, plus some older sediments in areas due to a different stratigraphic position of the first underlying confining layer. Spatial data set pp_1773_layer_2 is the Yorktown/Upper Floridan confining unit. It is not composed of a single unit because the unit's series of clay and silt beds vary greatly in stratigraphic position. Spatial dataset pp1773_layer3_extent represents the extent of the Yorktown/Upper Floridan aquifer. The Yorktown aquifer is present only in the northern half of the North Carolina Coastal Plain. Outliers exist in Robeson, Bladen and Dublin counties, but are not separated from the surficial aquifer by a confining unit, and not considered a distinct aquifer in these areas. The Upper Floridan aquifer extent covers a southern portion of South Carolina and southern portion of Georgia. Spatial dataset pp1773_layer4_extent represents the extent of the Castle Hayne/Middle Floridan confining unit. The Castle Hayne confining unit consists of beds of clay and silt that vary in stratigraphic position and are absent in a number of areas in the central and southern North Carolina Coastal Plain. The Middle Floridan confining unit extends from South Carolina to southern Georgia. It is not continuous with the Castle Hayne confining unit. Spatial dataset pp1773_layer5_extent represents the extent of the Castle Hayne/Middle Floridan aquifer. The Castle Hayne aquifer is located in the central and southern North Carolina Coastal Plain; the Middle Floridan aquifer is more south, in southern South Carolina and southern Georgia. Spatial dataset pp1773_layer6_extent represents the extent of the Beaufort/Gordon confining unit. The Beaufort confining unit is located in northeastern North Carolina and southeastern Virginia. It is best developed in

PP1773_unit_alt_grid is a polygon shapefile of surface altitudes for 16 hydrogeologic units as described in report Professional Paper 1773. Surface altitudes were interpolated and discretized to the 2-mile by 2-mile rotated grid used to simulate groundwater flow in the Atlantic Coastal Plain of North and South Carolina. Altitudes are available for 17 surfaces, hydrogeologic unit layer 1 (top - land surface) through Layer 16 (top and bottom). Each hydrogeologic unit is referred to as its model layer number as represented in the report PP1773. For clarity, they are listed below along with the aquifer unit or confining unit name in North Carolina and its correlated name in South Carolina L1 Surficial aquifer L2 Yorktown confining unit / Upper Floridan confining unit L3 Yorktown aquifer / Upper Floridan aquifer L4 Castle Hayne - Pungo River confining unit / Middle Floridan confining unit (To be referred to as "Castle Hayne confining unit / Middle Floridan confining unit" in this document) L5 Castle Hayne - Pungo River aquifer / Middle Floridan aquifer (To be referred to as "Castle Hayne aquifer / Middle Floridan aquifer" in this document) L6 Beaufort confining unit / Gordon confining unit L7 Beaufort aquifer / Gordon aquifer L8 Peedee confining unit / Crouch Branch confining unit L9 Peedee aquifer / Crouch Branch aquifer L10 Black Creek confining unit / McQueen Branch confining unit L11 Black Creek aquifer / McQueen Branch aquifer L12 Upper Cape Fear confining unit / Charleston confining unit L13 Upper Cape Fear aquifer / Charleston aquifer L14 Lower Cape Fear confining unit / Gramling confining unit L15 Lower Cape Fear aquifer / Gramling aquifer L16 Lower Cretaceous confining unit and aquifer

PP1773_unit_alt_grid is a polygon shapefile of surface altitudes for 16 hydrogeologic units as described in report Professional Paper 1773. Surface altitudes were interpolated and discretized to the 2-mile by 2-mile rotated grid used to simulate groundwater flow in the Atlantic Coastal Plain of North and South Carolina. Altitudes are available for 17 surfaces, hydrogeologic unit layer 1 (top - land surface) through Layer 16 (top and bottom). Each hydrogeologic unit is referred to as its model layer number as represented in the report PP1773. For clarity, they are listed below along with the aquifer unit or confining unit name in North Carolina and its correlated name in South Carolina L1 Surficial aquifer L2 Yorktown confining unit / Upper Floridan confining unit L3 Yorktown aquifer / Upper Floridan aquifer L4 Castle Hayne - Pungo River confining unit / Middle Floridan confining unit (To be referred to as "Castle Hayne confining unit / Middle Floridan confining unit" in this document) L5 Castle Hayne - Pungo River aquifer / Middle Floridan aquifer (To be referred to as "Castle Hayne aquifer / Middle Floridan aquifer" in this document) L6 Beaufort confining unit / Gordon confining unit L7 Beaufort aquifer / Gordon aquifer L8 Peedee confining unit / Crouch Branch confining unit L9 Peedee aquifer / Crouch Branch aquifer L10 Black Creek confining unit / McQueen Branch confining unit L11 Black Creek aquifer / McQueen Branch aquifer L12 Upper Cape Fear confining unit / Charleston confining unit L13 Upper Cape Fear aquifer / Charleston aquifer L14 Lower Cape Fear confining unit / Gramling confining unit L15 Lower Cape Fear aquifer / Gramling aquifer L16 Lower Cretaceous confining unit and aquifer

This data set represents the extent of the Southeastern Coastal Plain aquifer system in Kentucky, Tennessee, Mississippi, Alabama, Georgia, and South Carolina.

This data set represents the extent of the South coast aquifer in Puerto Rico.

Digital surfaces and thicknesses of selected hydrogeologic units of the Floridan aquifer system were developed to define an updated hydrogeologic framework as part of the U.S. Geological Survey Groundwater Resources Program. This dataset contains a polygon showing the extent of the Sand and Gravel aquifer of the surficial aquifer system. This layer was extracted from the Aquifers map layer located at http://nationalatlas.gov/

Digital surfaces and thicknesses of selected hydrogeologic units of the Floridan aquifer system were developed to define an updated hydrogeologic framework as part of the U.S. Geological Survey Groundwater Resources Program. This feature class contains lines that show the boundary of permeable strata in the Intermediate aquifer system (IAS) or Intermediate confining unit (ICU).

A digital model of the sedimentary Northern Atlantic Coastal Plain aquifer system is composed of 20 rasters and hydrogeologic unit extent polygons. Rasters describe the top elevations of regional aquifers and confining units at a resolution of 2640 feet (1/2 mile). The rasters are clipped to the extent polygons, which represent the spatial extents of the hydrogeologic units onshore and several miles offshore. This three-dimensional hydrogeologic model was constructed as part of a U.S. Geological Survey Groundwater Resources Program study of groundwater availability in the Northern Atlantic Coastal Plain (NACP) aquifer system, including parts of New York, New Jersey, Delaware, Maryland, Virginia, and North Carolina. Digital elevations of major regional aquifers and confining units were compiled from published digital elevation models (DEM) of various parts of the NACP aquifer system to provide a consistent regional model of hydrogeologic unit geometries. The many studies incorporated within these data include the interpretation and analysis of thousands of well logs and other related information spanning at least a century of study. These regional units are derived from published unit-elevation contours interpreted by geologists at the state and local level, and incorporate little additional interpretation of unit elevations beyond the correlation of individual units across geographic boundaries and some extrapolation of units to the edges of the modeled area. This regionally consistent hydrogeologic framework was used as the foundation of a MODFLOW groundwater flow model of the NACP, which informed modifications to the regional hydrogeologic units that have now been incorporated into the framework data.

A digital model of the sedimentary Northern Atlantic Coastal Plain aquifer system is composed of 20 rasters and hydrogeologic unit extent polygons. Rasters describe the top elevations of regional aquifers and confining units at a resolution of 2640 feet (1/2 mile). The rasters are clipped to the extent polygons, which represent the spatial extents of the hydrogeologic units onshore and several miles offshore. This three-dimensional hydrogeologic model was constructed as part of a U.S. Geological Survey Groundwater Resources Program study of groundwater availability in the Northern Atlantic Coastal Plain (NACP) aquifer system, including parts of New York, New Jersey, Delaware, Maryland, Virginia, and North Carolina. Digital elevations of major regional aquifers and confining units were compiled from published digital elevation models (DEM) of various parts of the NACP aquifer system to provide a consistent regional model of hydrogeologic unit geometries. The many studies incorporated within these data include the interpretation and analysis of thousands of well logs and other related information spanning at least a century of study. These regional units are derived from published unit-elevation contours interpreted by geologists at the state and local level, and incorporate little additional interpretation of unit elevations beyond the correlation of individual units across geographic boundaries and some extrapolation of units to the edges of the modeled area. This regionally consistent hydrogeologic framework was used as the foundation of a MODFLOW groundwater flow model of the NACP, which informed modifications to the regional hydrogeologic units that have now been incorporated into the framework data. A related digital elevation model (DEM) for the Northern Atlantic Coastal Plain (NACP) from Long Island New York to northeastern North Carolina represents the elevation of the topographic and bathymetric surface at a uniform horizontal grid spacing of 100 feet and vertical units of 1 (integer) foot. The land-surface elevations are derived from U.S. Geological Survey 30-meter National Elevation Dataset (NED), and the bathymetric elevations are derived from 3 arc-second (90-meter-nominal) National Oceanic and Atmospheric Administration (NOAA) U.S. Coastal Relief Model (CRM).

Digital surfaces and thicknesses of selected hydrogeologic units of the Floridan aquifer system were developed to define an updated hydrogeologic framework as part of the U.S. Geological Survey Groundwater Resources Program. This dataset contains line features representing regional cross sections presented in this study.