The rationale for chemical time-series sampling has its roots in the same fundamental relationships as govern well hydraulics. Samples of ground water are collected as a function of increasing time of pumpage. The most efficient pattern of collection consists of logarithmically spaced sampling intervals, analagous to the collection of drawdown data during pumping tests. The analogy extends further because simultaneous collection of drawdown values, flow rates, and chemical time-series samples yields a set of data which can be used to determine not only the distance from which specific levels of contaminants were drawn, but also the direction from whence they came. The potential power of this technique in locating contaminant sources is obvious and is enhanced by analysis of the patterns of concentrations of contaminants drawn into the well.