Hydrogeochemistry and geothermal characteristics of the Tertiary White Lake basin are described in order to provide constraints on the hydrogeology and thermal regime of the basin. The basin can be divided into three flow subsystems on the basis of chemical and isotopic variations. The groundwaters evolve chemically from young Ca-Mg-HCO3 type waters in the shallow surficial sediments to Na-dominated waters in the deeper intermediate system. Surface waters and shallow groundwaters collected from wells completed in overburden have undergone extensive evaporation as evidenced by their enriched delta(18)O and delta(2)H composition. Minor evaporation identified in the isotope composition of groundwater from domestic wells completed in bedrock, as well as from springs, suggests a local to intermediate origin for these waters, and perhaps mixing with shallow evaporative waters. In contrast, the uniform isotope signatures of deep basin waters measured both spatially and vertically suggest recharge at higher elevations, and a much deeper circulation system that is essentially isolated from the shallow subsurface. Chemical geothermometry indicates that spring waters and bedrock well waters have equilibrated at temperatures of less than 20 and 60degreesC, respectively. Groundwaters encountered by deep diamond drill holes, with equilibration temperatures of less than 80degreesC, are representative of intermediate flow systems, and may serve to modify the heat flow regime in the basin. Regional groundwater flow within the basin is complex due to numerous faults that exert a strong influence on fluid circulation patterns. Transport of heat in the subsurface, which has resulted in variations in the measured thermal gradients across the basin, occurs either at depths greater than those investigated in this study or has been significantly influenced by the circulation of cooler groundwater in the central part of the basin. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved.