ABSTRACT
The author's studies in several alluvial and fractured-rock aquifers point to several useful results of general application. 1. The construction of large dams in arid river basins provides an isotope dating tool specific to the basin downstream of the dams, owing to the O and H isotope effect of evaporation of the impounded water. 2. Ancient fluvial sediments continue to act as preferential flow paths long after surface flow has been diverted elsewhere. This effect can lead to the separation of recharge and surface flow by many kilometers. 3. Two distinctive patterns of O and H isotope data are found in mountain-system aquifers, one yielding a linear data array parallel to the Global Meteoric Water Line; the other yielding a linear array of slope near 5. Topography, geology and recharge seasonality may all be implicated in differentiating the two kinds of data trend. 4. S isotopes commonly exhibit three-way mixing with end-members corresponding to rain/dust, Permian marine sulfate and igneous sulfide. The marine/igneous sulfur distinction is useful in basins supplied with surface water from streams draining different rock types.