USE OF FLUORESCEIN DYE TRACING TO DETERMINE GROUND-WATER FLOW IN A GLACIATED, ALPINE VALLEY, SYLVAN PASS, YELLOWSTONE NATIONAL PARK, WYOMING

Sylvan Pass is located at an altitude of 2600 m in eastern Yellowstone National Park and serves as a major road corridor connecting Yellowstone to Cody, Wyoming. Ice from the Yellowstone ice cap carved this high alpine pass into the Absaroka andesitic bedrock during the Pinedale glaciation. Following glaciation, talus from the over-steepened valley filled the pass with an unknown volume of talus.

The east entrance road to Yellowstone is undergoing a major reconstruction. In August 2004, more than 8 km of Middle Creek located below Sylvan Pass had become milky white color as a result of turbidity. Turbidity and temperature data from Mammoth Crystal Spring, a large spring about 1.5 km east of the pass, indicates that gravel mining associated with road construction may be affecting the water quality of the spring. A turbidity of 1,536 NTU was measured at the spring during September 2004. Permafrost and local debris flows from severe storms add complexity to the assessment.

In June 2005, a dye-tracer injection was conducted at Sylvan Pass. Fluorescein dye was injected on the west side of the pass where an unnamed stream is lost into talus. Activated charcoal samplers were deployed on the east and west sides of the pass, and an auto sampler was deployed at Mammoth Crystal Spring. Grab samples also were collected when the area was visited. Visible dye was observed in Mammoth Crystal Spring about 22.5 hours after the injection. The distance from the injection site to the spring is 2.25 km, which results in a ground-water velocity of about 0.1 km per hour. Results of the dye trace indicate that the ground-water divide is located to the west of the topographic divide. Ground-water travel times are very rapid from the dye-injection site to the spring, and surface disturbances could quickly affect water discharging from the springs. Dye-tracer injections are uncommonly used in subalpine settings with this type of aquifer but might be a valuable tool in investigating ground-water flow paths in mountainous alpine and subalpine terrains.