SUBSURFACE CHARACTERIZATION OF UPLAND RIPARIAN MEADOWS IN CENTRAL NEVADA USING AN INNOVATIVE DIRECT-PUSH EXPLORATION RIG

The U.S. EPA and the USDA Forest Service are conducting a joint investigation to better understand the interactions between geomorphology, hydrology, and vegetation associated with riparian meadow ecosystems in upland watersheds in central Nevada. Stream incision is a major threat to these meadow ecosystems and a multidisciplinary research team is developing technical guidance and decision support tools to assist resource managers with maintaining and restoring this valuable habitat. Field work proposed as part of the EPA/Forest Service project included collecting cores to describe stratigraphic units for geomorphic and hydrogeologic interpretations, probing to bedrock to ground truth geophysical investigations of bedrock structure and thickness of valley-fill sediments, and installing monitoring wells for evaluating hydraulic heads and ground-water flow patterns and for collecting water quality samples. However, accomplishing these tasks with minimal disturbance to the fragile riparian meadow systems was a concern to local resource managers.

An innovative exploration unit, designed by EPA personnel in conjunction with equipment manufacturers, was used to successfully complete the field activities. The rig consists of a GeoProbe™ 540MTX direct-push tool mounted on a modified HydroTraxx TJ645 vehicle. The rig was designed specifically for use in conditions such as those encountered in the upland riparian meadows: saturated soils, steep slopes, and entrenched stream channels. The rig does flatten vegetation temporarily, but the path of the equipment was unnoticeable after the subsequent growing season. The unit was able to collect continuous cores to a depth of 12 m and interval specific core samples to a depth of 25 m. The rig also was able to advance a probe to almost 30 m to evaluate depth to bedrock (refusal). Monitoring wells were constructed to depths of 12 m in unconsolidated material ranging from fine-grained organic soils to poorly-sorted alluvial fan deposits. These data, unobtainable until now, are being used to support development of management and restoration strategies for Great Basin upland riparian meadow systems.

(Note: this is an abstract of a proposed presentation and does not necessarily reflect EPA policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.)