Hydrochemical facies is used in this paper to denote the diagnostic chemical aspect of ground-water solutions occurring in hydrologic systems. They reflect the chemical response of the interrelated effects of the lithology and the pattern of ground-water flow. The facies and their distribution are shown on trilinear diagrams, isometric panel diagrams, and maps showing isopleths of chemical constituents within certain formations. The occurrence of the various facies within one formation or group of formations in which the mineralogy is uniform indicates that the flow of characteristics of the aquifer systems controls the distribution of the hydrochemical facies. By use of available head data, flow patterns of the fresh ground water are shown on maps and cross sections. The e patterns are controlled in part by the distribution of higher landmasses and the depth to bedrock or to the salt-water interface. Mapping of the hydrochemical facies shows that at shallow depths (less than about 200 feet) the calcium-magnesium cation facies generally predominates in the northern Atlantic Coastal Plain. The bicarbonate anion facies occurs more widely in the shallow deposits of the Coastal Plain than does the sulphate or chloride

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facies. In the deeper deposits the sodium chloride facies predominates. The lower total dissolved solids in the ground water in New Jersey indicates that less upward vertical leakage occurs there than in Maryland and Virginia where the shallow deposits contain more concentrated solutions.

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