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 North Carolina, and contains areas where it has eroded or pinches out. The Gordon confining unit is located in southern South Carolina and southeastern Georgia.

Spatial dataset pp1773_layer7_extent represents the extent of the Beaufort/Gordon aquifer unit. The Beaufort aquifer, in northeastern North Carolina and southeastern Virginia, and the Gordon aquifer, in southeastern South Carolina and southeastern Georgia, are not continuous or hydraulically connected.

Spatial dataset pp1773_layer8_extent represents the extent of the Peedee/Crouch Branch confining unit. The Peedee/Crouch Branch confining unit is positioned stratigraphically near the contact of the Paleocene Beaufort and Late Cretaceous Peedee Formations in the eastern North Carolina Coastal Plain, from southeastern North Carolina down to southern Georgia.

Spatial dataset pp1773_layer9_extent represents the extent of the Peedee/Crouch Branch aquifer. The Peedee/Crouch Branch aquifer is positioned in southeastern North Carolina, encompasses all of the Atlantic Coastal Plain in South Carolina, and parts of southeastern Georgia.

Spatial dataset pp1773_layer10_extent represents the extent of the Black Creek/McQueen Branch confining unit. The areal extent of this unit includes much of North Carolina within the Atlantic Coastal Plain, all of South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain.

Spatial dataset pp1773_layer11_extent represents the extent of the Black Creek/McQueen Branch aquifer. The areal extent of this unit includes northeastern parts of North Carolina within the Atlantic Coastal Plain, most South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain. Black Creek and McQueen Branch aquifers are hydraulically connected.

Spatial dataset pp1773_layer12_extent represents the extent of the Upper Cape Fear/Charleston confining unit. The areal extent of this unit includes a small area in southeastern Virginia, much of North Carolina within the Atlantic Coastal Plain, part of South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain.

Spatial dataset pp1773_layer13_extent represents the extent of the Upper Cape Fear/Charleston aquifer unit. The areal extent of this unit includes a small area in southeastern Virginia, much of North Carolina within the Atlantic Coastal Plain, part of South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain. Upper Cape Fear and Charleston aquifer units are hydraulically connected.

Spatial dataset pp1773_layer14_extent represents the extent of the Lower Cape Fear/Gramling confining unit. The areal extent of this unit includes a small area in southeastern Virginia, much of North Carolina within the Atlantic Coastal Plain, part of South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain.

Spatial dataset pp1773_layer15_extent represents the extent of the Lower Cape Fear/Gramling aquifer unit. The areal extent of this unit includes a small area in southeastern Virginia, much of North Carolina within the Atlantic Coastal Plain, part of South Carolina within the Atlantic Coastal Plain, and a region in southeast Georgia within the Atlantic Coastal Plain. Lower Cape Fear/Gramling aquifer units are hydraulically connected.

Spatial dataset pp1773_layer16_extent represents the extent of the Lower Cretaceous aquifer unit. The areal extent of this unit includes a small area in southeastern Virginia and northeastern North Carolina within the Atlantic Coastal Plain. Based on available information, it is not possible to determine the position and extent of an intervening confining unit between the Lower Cape Fear and Lower Cretaceous aquifers.