AbstractEstimates can be made of the distances to hydrologic boundaries by using water‐level measurements from pumping wells and by assuming in each case the possible range of the coefficient of storage. Interpretation of pumping test data from Well 6 (J‐13) at the Nevada Test Site implies that a fault 1200 feet from the well acts as the closest of the impermeable boundaries. In a case where no boundary has been felt the areal extent or volume of rocks affecting the drawdown pattern of a well can be estimated by assuming that a hypothetical boundary is just about to be felt at the time pumping stop