The Lower Cretaceous aquifer is the principal source of water in Southeastern Virginia. Synoptic water-level measurements made since 1970 have been used to verify a digital model of the aquifer. Measurements made in December 1973, August and December 1974 were used to further verify the model, using updated pumpage for those periods. The close agreement of the potentiometric maps based on measured and simulated water levels indicates that the model is simulating hydrologic conditions satisfactorily. (Woodard-USGS)