Abstract

Insights into the ground-water chemistry of Salt Lake and Cache Valleys can be gleaned from water samples collected from wells, springs, streams and snow that have been analyzed for stable and radioactive isotopes. Each valley has the same general hydrostratigraphy, with a principal aquifer consisting of a confined portion in the center of the valley that is overlain by Lake Bonneville deposits and an unconfined portion around the periphery of the valley, and an unconfined aquifer of recent alluvial material overlying the Lake Bonneville deposits.

Oxygen-18 (¹⁸O) and deuterium (D) analyses of ground-water samples in the Salt Lake Valley suggest that most of the recharge to the principal aquifer originates from a laterally distant area rather than from the ground surface or the shallow, unconfined aquifer. However, ¹⁸O and D analyses of samples in Cache Valley suggest that water from streams, rather than precipitation, recharges the principal aquifer.

Tritium (³H) values for ground-water samples in the Salt Lake Valley indicate that a significant portion of the water was recharged after 1952. Tritium values for well and spring samples in Cache Valley also indicate recharge is less than 50 years old.

Carbon-14 (¹⁴C) dating of a water sample from one well in the Salt Lake Valley that is completed in the principal aquifer and had pre-1952 ³H values, yielded age estimates of between 1,300 and 5,900 years. The ¹⁴C-age difference between water in four wells in Cache Valley, two completed in the principal aquifer (younger) and two west of the principal aquifer (older), is on the order of tens of thousands of years.