UTAH'S ONLY DOCUMENTED PERIODIC SPRING: CHARACTERIZING KARST IN SOUTHERN CACHE COUNTY, UTAH

Continuous flow measurements captured a rare instance of periodic or intermittent spring flow that effectively doubled the discharge from about 1.5 cubic feet per second to about 3 cubic feet per second every 71 to 87 hours in Wellsville Creek. Based on peak recession analysis the rise in discharge likely represents siphon draining of a subterranean karst chamber or void that has a volume of approximately 66,500 gallons. Duration of the pulse of increased flow ranged from 165 to 210 minutes.

The hydrogeology of the area is characterized by broadly folded Paleozoic carbonate aquifers spanning a drainage divide in the Powder Mountain area. Relatively impermeable Cambrian quartzite underlies the carbonate rocks. Semi- to unconsolidated Tertiary Wasatch Formation and late Quaternary colluvium and alluvium overly large areas of the carbonate aquifers. The extent of the carbonate aquifers is limited by folding along a broad, north-plunging syncline and erosion.

The Paleozoic carbonate rocks are the source of major springs and baseflow in the area as well as culinary water supply to wells. Carbonate-sourced springs and baseflow contribute two-thirds of the total flow to the tributaries on the south side of the mountain, and nearly all the spring and baseflow to the Wellsville Creek drainage in Cache County.

Chemistry of all groundwater samples is dilute calcium-bicarbonate (Ca-HCO3) type water. Specific conductivity is lowest for water sourced from quartzite, the Wasatch Formation, and basin fill, and higher for carbonate or covered carbonate rocks. Water from carbonate aquifers has distinct chemistry with low dissolved silica and characteristic calcium and magnesium concentrations. Stable isotope ratios of hydrogen and oxygen in water samples across the Powder Mountain area generally are similar, likely indicating a common source of local snow melt. Some water samples from basin fill and quartzite, however, have distinct isotopic concentrations indicating different sources of recharge.