DISCHARGE MONITORING, CHEMICAL CHARACTERIZATION, AND SOURCE IDENTIFICATION OF SPRINGS ALONG THE EAST SIDE OF SOUTHERN CACHE VALLEY, UTAH

Discharge monitoring and water sampling of springs in the southeastern portion of Cache Valley, Utah has been performed in order to determine their sources of recharge and the cause of decreasing flows for some springs. The discharges of 43 springs have been measured monthly since May of 2005. Water samples from 36 of these springs plus an additional ten were analyzed for major ions and trace metals. Twenty of the springs sampled were analyzed for deuterium and oxygen-18 and ten of these were also analyzed for tritium.

Nearly all of the 43 springs flowed continuously throughout the year, suggesting that the shallow, unconfined aquifer supplies a major portion of their recharge. Thirteen springs had peak discharges during the summer, indicating that irrigation water, river water and/or canal water contribute substantially to their recharge, and six had peak discharges in the spring, demonstrating that precipitation is likely the source of much of their recharge. However, eight springs had peak discharges during the winter, which is difficult to explain. The remaining 16 springs had nearly constant discharges throughout the year, indicating shallow ground water was their primary source of recharge, since fluctuations in irrigation and precipitation did not directly affect their discharges.

The chemical data were compared with data from previous studies for potential spring sources, including: shallow groundwater, deep groundwater, irrigation (river/canal) water, and precipitation. Spring water is characterized by calcium, magnesium and bicarbonate, similar to deep ground water and river water. However, most of the 20 springs analyzed for deuterium and oxygen-18 displayed an evaporative signature; thus, chemically, these springs appear to be recharged at least in part by excess irrigation water.

Because of the evaporative signature, it seems unlikely that the springs are directly connected hydraulically with the deep, confined aquifer, which most of the wells in the valley withdraw their water from. Thus, the recent drought, rather than increased pumping, probably has been responsible for decreases in spring discharges.