Geohydrologic boundary envelopes

Abstract Analysis of drawdown data for an observation well in a semi-infinite aquifer gives a one-parameter family of straight lines, each of which, in the absence of supplementary geologic or hydrologic evidence, defines a possible boundary location. The curve to which all members of the family are tangent is an ellipse and is called the geohydrologic boundary envelope. This ellipse may be useful in considering the significance of nonresponsive observation wells or in using supplementary geologic data to determine the position of a boundary.