Reports
Well yields in the bedrock aquifers of Maryland
1974, Nutter, L.J.
Information Circular 16
Abstract
Well yields from the bedrock aquifers west of the Fall Line in Maryland are extremely variable and difficult to predict at specific sites because the ground water is transmitted mainly through a complex and variable fracture system in the rocks. Conclusions regarding the yield of wells necessarily reflect the data used in an analysis. At least 80 percent of the well records published in Maryland groundwater reports are of domestic and farm wells which in many cases are located on ridgetops or upland areas where there is little probability of obtaining high-yielding wells. Furthermore, in the construction of domestic wells there is seldom an effort made to obtain the maximum yield. In contrast to domestic wells, municipal and industrial wells are usually drilled for maximum yields, and in many cases only the most productive of several test wells are used for the water supply.
In this report an estimate of optimum well yields in generalized groups of bedrock aquifers was made using cumulative-frequency graphs of specific-capacity based on available well records. On the basis of this analysis, the estimated average yields of wells drilled under optimum conditions for generalized groups of bedrock aquifers range from 40 gallons per minute (151 liters per minute) for granite and gneiss to 195 gallons per minute (738 liters per minute) for limestone and dolomite.
In some areas, where obtaining adequate yields for individual domestic wells is difficult, it may be feasible to have a central groundwater supply. Ideally well sites for a central supply would be carefully selected before construction begins, several test wells planned, and the wells spaced several hundred feet apart to minimize well interference.
