The Yucca Mountain Project

Ambient Testing: The El Nino Effect (Alcoves 1 and 7 Testing)

Large-scale infiltration studies have been conducted by the USGS and Berkeley Lab in Alcoves 1 and 7. Moisture monitoring networks have been installed to identify and measure the location, timing, and quantities of infiltration and deep percolation resulting from the heavy rainfall expected under El Nino conditions. The results of these studies will be used to refine our understanding of the conceptual model of future climate change. These studies will also provide the opportunity to evaluate the role of open surface fractures and their influence on infiltration rates.

An active infiltration experiment will be initiated at the surface directly above the end of Alcove 1 to introduce controlled volumes of water above the alcove, providing the most likely conditions under which fracture flow and seepage might occur. A percentage of the water introduced at the surface is expected to seep into Alcove 1, which lies approximately 30 meters beneath the land surface. If there is limited seepage into Alcove 1 during the current El Nino event, in combination with artificial introduction of water at the surface, the study will strengthen confidence that seepage into drifts under normal conditions will be minimal. The UZ site-scale and drift-scale models will be used to predict potential seepage, and then after testing they will be refined using the final test data.

The experience from Alcove 1, together with existing data from Alcove 7 walls, cores, and boreholes, will be used to construct models for deep infiltration and percolation through the Ghost Dance Fault zones and in the neighboring nonfaulted rock zones. The amount of percolation required to initiate deep seepage into Alcove 7 (approximately 200 meters beneath the surface) will be evaluated. After completion of testing by USGS, Berkeley Lab will compare the simulated results of seepage with the measured influx in Alcove 7. The presence or absence of measurable seepage in Alcove 7 will be used to evaluate whether surface infiltration can be correlated with percolation at the repository level, and whether drift seepage can be quantified from surface infiltration data. The findings can be used to calibrate models for the unsaturated zone at Yucca Mountain.

For more information, please contact:
Joe Wang
Ph: 510-486-6753

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