Geology and Hydrology of the Shallow Alluvial Aquifer, West Sharrard Gulch, Colorado

A hydrogeologic investigation was conducted during the winter and spring of 1987 by Oak Ridge National Laboratory (ORNL) in West Sharrard Gulch adjacent to the former site of the Anvil Points Oil Shale Processing Facility (APF). The purpose of the investigation was to evaluate potential environmental impacts from past waste disposal operations. Complex relationships exist between the surface water, groundwater, alluvium, and bedrock along a small intermittent tributary of the Colorado River in western Colorado. Interactions between the alluvial groundwater and surface water is West Sharrard Creek were studied during a series of investigations prompted by concerns over former waste disposal sites along the drainage. The investigations involved well installations, groundwater monitoring and surface water studies. The studies revealed that surface water and groundwater along West Sharrard Gulch are linked by a series of alternating recharge and discharge zones. These zones are in turn directly related to the gradients controlled by the differential erosion of various bedrock layers. Groundwater seeps were found at predictable locations related to the intersection of alluvial groundwater at streambed nickpoints. The nickpoints result when streambed erosion exposes sandstone lenses in the underlying Wasatch Formation. Information from well logs, groundwater monitoring, and topographic maps was combined more » to form a conceptual model of the flow relationships. « less