Reports
Water resources of Dorchester and Talbot Counties, Maryland, with special emphasis on the ground-water potential of the Cambridge and Easton areas
1971, Mack, F.K., Webb, W.E., and Gardner, R.A.
Report of Investigations 17
Abstract
The available ground water in Dorchester and Talbot Counties exceeds by many times the present consumption. However, the supply of fresh surface water is small.
The two counties occupy a low-lying plain along the eastern shore of Chesapeake Bay. Drainage is by two large tidal rivers, the Choptank and the Nanticoke, and by many small creeks directly tributary to Chesapeake Bay. Much of the two-county area is poorly drained and coastal swamps are common.
A thick section of Coastal Plain sediments including sands, silts, clays, and minor gravel beds overlies the crystalline basement rocks, which are found at depths of 2,200 to 4,200 feet. To date, only the upper 1,500 feet of sediment have been explored. The known aquifers include the Patapsco Formation, upper Cretaceous sands (primarily the Magothy Formation), the Aquia, Pine Point, and Calvert Formations, which are Tertiary in age, and the Pleistocene deposits. The most important artesian aquifer, the Piney Point Formation, has a transmissibility of 30,000 to 45,000 gpd per foot (gallons per day per foot) in the Cambridge area, but does not exist in some parts of Talbot County. The Pleistocene deposits form a very productive water-table aquifer in northeastern Dorchester County, where the transmissibility is very high (95,000 to 175,000 gpd per foot) and where many wells are capable of yielding more than 1,000 gpm (gallons per minute).
Water use, excluding withdrawals for cooling electric power generators, averaged 11 mgd (million gallons per day) in 1960, of which 10 mgd was ground water and 1 mgd was surface water. Ground water is used for public water supplies at the cities of Cambridge and Easton and at five villages. It is also used by several small industries, mainly food processing plants. Cambridge obtains over 80 percent of its average supply of 3.5 mgd from the Piney Point Formation and the remainder from the Magothy Formation. Easton obtains most of its average supply of about 0.9 mgd from Cretaceous sands and the remainder from the Aquia and Calvert Formations.
Estimates, made of the long-term yield of individual aquifers by using field-determined values for the coefficients of transmissibility and storage, indicate that large additional quantities of water are available from the aquifers currently being pumped. The additional water would be obtained by lowering pumping levels to greater depths, a practice which will increase pumping costs and may cause subsidence of the land surface. The theoretical estimates show that a total of 11 mgd could be obtained from the Piney Point and Magothy aquifers at Cambridge and that a total of 5 mgd could be obtained from the Cretaceous and Aquia aquifers in the Easton area.
The development of surface-water supplies is limited by the low relief, which precludes the construction of reservoirs, and by the high salinity of water in the major streams, all of which are estuaries of Chesapeake Bay. At present, surface water is used for cooling at a thermal power plant on the Nanticoke River and for a small amount of irrigation.
The quality of water ranges from water with low mineral content, satisfactory for most uses without treatment, to the moderately saline water (specific conductance greater than 5,000 micomhos) in the major streams and Chesapeake Bay. Water in the small streams in the topographically high areas and most ground water are characterized by low concentrations of dissolved solids – less than 500 mg/l (milligrams per liter). Ground water from the Piney Point and Aquia Formations is hard (hardness averages 142 mg/l) in the northwestern part of the area but is softer (hardness averages about 30 mg/l) and higher in dissolved solids towards the southeast.
