Modeling Ground-water Flow in Cedar Valley, Utah County, Utah, USA

Abstract

The population of Utah County’s Cedar Valley, including the city of Eagle Mountain, has grown from less than 1000 residents in 1990 to over 23,000 today, drastically increasing the need for potable water. This need is being met primarily by installing new wells and converting agricultural supply wells to municipal use, since the few natural streams and springs are fully appropriated. Over the past 5 years, the UGS has performed pumping tests, collected water levels and water-quality samples, and created a three dimensional (3D) computer ground-water flow model to provide water users and regulators with a better understanding of the ground-water flow system. Cedar Valley occupies a closed surface-water drainage basin west of Utah Lake and the Provo– Orem metropolitan area. Ground water is present in the unconsolidated sediments that fill the basin and in bedrock that underlies the basin fill and forms the surrounding Oquirrh, Traverse, Lake, and East Tintic Mountains. The unconsolidated sediments are as much as 2100 feet thick and are generally silt and clay mixed with small amounts of gravel, except near the mountains where sand and gravel dominate. A clay unit as much as 240 feet thick covers two-thirds of the surface of the valley and creates confined ground-water flow conditions beneath it. On average, the basin fill is slightly less permeable to ground water than the fractured Paleozoic carbonate bedrock, which is atypical compared to most ground-water basins. Ground water generally flows from west to east across the valley but then encounters a northsouth-trending normal fault on the eastern margin of the valley. The fault is a conduit for ground-water flow parallel to the fault, but acts as a barrier to ground-water flow across the fault. As a result, ground-water flow is directed around the Lake Mountains to exit the valley through bedrock at Cedar Pass and the Mosida Hills on the north and south ends of the Lake Mountains, respectively.