Harry Reid Center for Environmental Studies
Chemistry Division

HRC >> Chemistry >> Hydrologic Monitoring

Ground Water Level Monitoring at Yucca Mountain

Through the Cooperative Agreement with the U.S. Department of Energy, the Harry Reid Center for Environmental Studies at the University of Nevada – Las Vegas, conducts ground water level measurements at selected boreholes near Yucca Mountain, and compiles and submits generated data to the DOE Yucca Mountain Technical Data Management System. The HRC collects quarterly data from a network of 24 wells currently comprising the monitoring network. Most of these wells lie on the eastern flanks and along crest of Yucca Mountain within Areas 25 and 29 of the Nevada Test Site. There are additional wells monitored west of Yucca Mountain and east of U.S. Highway 95 on Crater Flats area and in Solitario Canyon on Bureau of Land Management public land (see map for well locations).

Ground Water Level Measurement Objectives

The objectives of the HRC ground water level monitoring program are twofold:

• Continuously monitor for seismically-induced water level fluctuations to measure the effects of earthquakes on ground water levels in selected boreholes, and
• Acquire quarterly ground water level data important to numerous site characterization activities in the unsaturated zone.

Techniques and Monitoring Frequency

As of June 2003, depth to water in 20 of these wells was measured quarterly using manual techniques such as a powered electric tape or hand-held steel tape, and 4 were monitored using downhole pressure transducers that continuously measure water level changes. Many wells are completed in one or more intervals, providing a total of 36 data sets per quarter.

Data Examples

The following figures illustrate the types of data produced by quarterly and continuous measurements, including those showing the effects of a distant earthquake.

Plot of Quarterly Ground Water Level Changes Measured Using Powered Electric Tape.

Plot of Continuously Monitored Ground Water Level Changes Using Digital Pressure Transducer Showing Effects of Earthquake.

Equipment Description

The key equipment used by the HRC to obtain measurements from the well network includes:

• A calibrated, 3,000-foot powered electric tape – this unit is used for making routine measurements across the well network with an accuracy of 0.01 foot (see photo)
• A 100-foot hand-held steel tape – this manual tape is used to make measurements in shallow, alluvial wells with an accuracy of 0.1 foot
• A 2,800-foot, calibrated, powered steel reference tape with custom spool – this unit is the reference standard used to calibrate the powered electric tape with an accuracy of 0.01 foot
• A cable deployment trailer with a gasoline-powered cable reel handler, hoist, winch, and generator. This specially designed and manufactured self-contained unit is capable of deploying water level probes to depths of up to 3,000 feet (see photo)
• In addition to the manual water-level measurement equipment which is used for routine data collection, HRC uses digital continuous monitor down hole sensors to detect important event-triggered water level changes due to seismic activity. Data are stored in an onboard microprocessor and are retrieved by laptop or hand-held computer at the well head via a communication cable (see photo).

Precipitation Monitoring at Yucca Mountain

The Harry Reid Center maintains and monitors a network of seventeen tipping bucket rain gauges at Yucca Mountain and surrounding area. The rain gauges are d

Equipment

Each gauge has a simple twin- bucket mechanism that collects a known amount of precipitation, causing the bucket to tip back and forth and close a switch as rainfall is funneled in. The switch closer sends an electronic signal to a datalogger that records the data and time of the tip.

Data

Data from the network are submitted to the US Department of Energy (DOE) annually, and are used as part of the overall work supporting the net infiltration modeling for the region.

Data shown above are preliminary and have not received final approval. Inaccuracies in the data may be present because of instrument malfunctions or physical changes at the measurement site. Subsequent review may result in significant revisions to the data.

The data indicate heavier precipitation was measured in the winter months, followed by a very dry summer and increased rainfall in autumn. This is consistent with meteorological conditions observed in the area. The average rainfall for this area is between 4 – 10 inches.