ASSESSMENT OF METHODS AND CONDITIONS TO LOCATE BOUNDARIES .1. ONE OR 2 STRAIGHT IMPERVIOUS BOUNDARIES

A straight impervious boundary within an ideal confined aquifer may be detected in the semilog drawdown graph of an observation well. This p aper gives and assesses two known and one proposed equations that may help to determine the location and orientation of an impervious bounda ry. Then the two conditions for an adequate detection are established. First, if the distance of the pumping well to the boundary is called ''a,'' only those observation wells at a distance smaller than a/5 fro m the pumping well can detect the boundary. Second, data must be colle cted for approximately two time log cycles after the slope has changed in the drawdown graph. Similar equations, and time or distance condit ions, are given for the case of two intersecting straight impervious b oundaries. Frequently, the two conditions are not met. In this case, t he drawdown graphs give incorrect estimates of aquifer parameters. In most field conditions, a combination of drawdown data, geophysical sur veys, and exploratory boreholes is mandatory to locate one or two impe rvious boundaries. Available methods and a proposed one for recharge b oundaries are assessed in a companion paper.