A mixed groundwater system at Midway, UT:: discriminating superimposed local and regional discharge

Mixed thermal and cold water groundwater occurs in the Midway area, UT. Midway is located in the western Heber Valley, an alluvial-filled intermontane basin behind the crest of the Wasatch Mountains. In addition to streams and thermal springs, groundwater discharges from alluvium, bedrock, and karstified tufa. Evaluation of the thermal system reveals that it has been circulated to depths of similar to 2 km and temperatures of similar to 150degreesC. Most groundwater characteristics of the area can be explained by subsurface mixing between isotopically depleted, Pleistocene-aged thermal water and isotopically enriched, cold, modem, low TDS groundwater. Because the entire system exhibits evidence of mixing, it is possible to define the regional extent of upwelling of thermal water, as well as mixing fractions between the two end-members. The subsurface mixing of thermal and non-thermal waters is highly controlled by the superimposition of local irrigation recharge. (C) 2003 Elsevier Science B.V. All rights reserved.