Contrasts between apparent high resistivity of the saturated freshwater zones and apparent low resistivity of the saturated saltwater zone are recorded on ill Schlumberger sounding field curves. The field measurements are inverted to subsurface layers. Generally, resistivity decreases with depth from the high value of the unsaturated zone near the surface to the low values of the saltwater saturated zone at depth of 30 to 130 m. Contour maps are constructed for variations of resistivity at depths of 3, 5, 10, 20, 30, 40, 50, 60, 70, 100 and 130 m. Resistivity contours of less than 30 Omega m, are indicated at depths of 5-20 m near the narrow bands of Chesapeake Bay and the Atlantic Ocean in the coastal regions of Accomack County. Within the area covered by the cities of Onancock, Accomac, and Wachapreaque, low-resistivity contours of less than 30 Omega m are observed from 30 to 60 m depth. In 70 to 130 m depth range, a major part of Accomack County is covered by low-resistivity contours of 10 to 30 Omega m which connect the Chesapeake Bay to the Atlantic Ocean. Vertical profiles of the contour maps indicate the shape of the saltwater plumes. The interface appears to be as shallow as 30 m where intrusion has occurred, and extends downward to a depth of 130 m where the saltwater of the Atlantic ocean and Chesapeake Bay are connected. (C) 1999 Elsevier Science B.V. All rights reserved.
