HR: 0800h
AN: H41B-0299    [Abstracts]
TI: Utilizing Tritium and CFC-12 to Determine Groundwater Sources in an Unconfined Aquifer Within the Abalone Cove Landslide, Palos Verdes, California
AU: * DiFilippo, E L
EM: edifilip@usc.edu
AF: University of Southern California, Department of Earth Sciences 3651 Trousdale Pkwy, SCI 117, Los Angeles, CA 90089 United States
AU: Hammond, D E
EM: dhammond@usc.edu
AF: University of Southern California, Department of Earth Sciences 3651 Trousdale Pkwy, SCI 117, Los Angeles, CA 90089 United States
AU: Douglas, R
EM: rdouglas@usc.edu
AF: University of Southern California, Department of Earth Sciences 3651 Trousdale Pkwy, SCI 117, Los Angeles, CA 90089 United States
AU: Clark, J F
EM: jfclark@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, Building 526, Santa Barbara, CA 93106 United States
AU: Avisar, D
EM: dror@crustal.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, Building 526, Santa Barbara, CA 93106 United States
AU: Dunker, R
EM: dunkroy@isu.edu
AF: Idaho State University, Department of Physics-EML, Campus Box 8106, Pocatello, ID 83209 United States
AB: The Abalone Cove landslide occupies 80 acres of an ancient landslide complex on the Palos Verdes peninsula, and was re-activated in 1979. The uphill portion of the ancient landslide complex has remained stable in historic times. Water infiltration into the slide is a short term catalyst for mass movement in the area, so it is important to determine the sources of groundwater throughout the slide mass. Water may enter the slide mass through direct percolation of recent precipitation, inflow along the head scarp of the ancient landslide or by rising through the slide plane from a deeper aquifer. The objective of this contribution is to use geochemical tracers (tritium and CFC-12) in combination with numerical modeling to constrain the importance of each of these sources. Numerical models were constructed to predict geochemical tracer concentrations throughout the basin, assuming that the only source of water to the slide mass is percolation of recent precipitation. Predicted concentrations were then compared to measured tracer values. In the ancient landslide, predicted and measured tracer concentrations are in good agreement, indicating that most of the water in this area is recent precipitation falling within the basin. Groundwater recharged uphill of the ancient landslide contributes minor flow into the complex through the head scarp, with the majority of this water flowing beneath the ancient slide plane. However, predicted tracer concentrations in the toe of the Abalone Cove landslide are not consistent with measured values. Both CFC-12 and tritium concentrations indicate that water is older than predicted and communication between the slide mass and the aquifer beneath the slide plane must occur in this area. Infiltration of this deep circulating water may exert upward hydraulic pressure on the landslide slip surface, increasing the potential for movement. This hypothesis is consistent with the observation that current movement is only occurring in the area in which tracers indicate communication with the deeper aquifer.
DE: 1829 Groundwater hydrology
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting