The Lower Cretaceous Aquifer of Southeastern Virginia is simulated in this study. The aquifer is only a few feet thick along the Fall Line, where it is near or at the surface, but it thickens and dips to the east. At Franklin where the top of the aquifer is 220 feet (67 metres) below sea level, it is about 600 feet (180 metres) thick. Thirty five miles (56 kilometres) east of Franklin, along the eastern boundary of the model area, the top is about 900 feet (270 metres) below sea level, and the thickness is estimated to be 2,000 feet (610 metres). The aquifer consists of an alternating series of permeable and semipermeable beds, which contain various mixtures of sand, gravel, silt and clay. The sediments are continental stream deposits in the western and central parts of the area, but grade to marine deposits in the eastern part. Transmissivity is zero at or near the Fall Line, and increases eastward to 19,000 cubic feet per day per foot (1,800 cubic metres per day per metre) at Franklin. Further eastward, transmissivity probably increases slightly, but then decreases as the marine phase is reached. The aquifer is overlain by a semipermeable confining layer and is underlain by relatively impermeable rocks of the pre-Cretaceous basement.
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A predictive computer model of the Lower Cretaceous aquifer, Franklin area, southeastern Virginia