ATLANTIC COASTAL PLAIN HYDROSTRATIGRAPHY FOR WATER SUPPLY

The water resources and ecosystems of the Atlantic Coastal Plain, especially coastal North Carolina, continue to be stressed by industrial activities, agricultural development, and population growth in the lower reaches of the Roanoke River watershed. Current descriptions of the regional aquifer system are inadequate for accurately assessing the effects of existing and future water withdrawals. In response to such environmental stresses, the U.S. Geological Survey (USGS) is conducting ongoing interdisciplinary investigations to gain a better understanding of the hydrostratigraphy of the Atlantic Coastal Plain and to develop a large-scale definition of the hydrology.

During March and April 2004, USGS scientists used a wireline continuous-core drill rig to complete a deep (1,094.5-foot) stratigraphic corehole to basement (Triassic basin) at the Hope Plantation in Bertie County, North Carolina. This study area in northeast North Carolina is of special interest because it lies slightly southeast of an anomalous pattern of rapid eastward drop-off in the geologic layers of the Coastal Plain. The possibility of faults, which would significantly complicate the geologic and hydrologic interpretation of the subsurface geology, is being investigated.

A suite of borehole geophysical surveys was obtained, in the open borehole, and a ground-water monitoring piezometer also was installed at the Hope Plantation site. The core samples and supportive data were used to determine the thickness of the aquifers and confining units at this site. Scientists collected geologic and paleontologic information sufficient to define the stratigraphic units underlying the site. The joint hydrologic and geologic analyses provide a hydrostratigraphic anchor point and a detailed snapshot of the regional aquifers and confining units. Increased understanding of the geologic controls in the Coastal Plain will ultimately help assess the effects of existing and future withdrawals from the system.