HR: 0800h
AN: H21C-1366    [Abstracts]
TI: Environmental investigations at the Amchitka Island nuclear test site with magnetotelluric exploration
AU: * Unsworth, M
EM: unsworth@phys.ualberta.ca
AF: University of Alberta, Department of Physics, Edmonton, T6G 0B9 Canada
AU: Soyer, W
EM: wsoyer@phys.ualberta.ca
AF: University of Alberta, Department of Physics, Edmonton, T6G 0B9 Canada
AU: Tuncer, V
EM: vtuncer@phys.ualberta.ca
AF: University of Alberta, Department of Physics, Edmonton, T6G 0B9 Canada
AB: Amchitka Island is located in the western Aleutian Islands of Alaska and was used as an underground nuclear test site from 1965 to 1971. Three underground nuclear tests were conducted on the island and included the 5 megaton Cannikin shot, the largest underground explosion conducted by the United States. Since nuclear testing was completed in 1971, there have been concerns about the potential release of radionuclides into the marine environment. The hydrogeology of islands such as Amchitka is characterized by a fresh water layer overlying a layer of rock that is saturated with seawater. Hydrogeological modeling has provided some constraints on transport times from the shot cavities to the marine environment, but are limited by the lack of information about the porosity and salinity structure. In June 2004 magnetotelluric (MT) data were collected as part of the CRESP (Consortium for Risk Evaluation with Stakeholder Participation) Amchitka Island expedition to give constraints for groundwater flow modeling. MT data were collected on profiles that passed through the Longshot, Milrow and Cannikin test sites with a spacing of 500 m. Detailed data analysis was used to determine resistivity models of the subsurface structure on each profile. The resistivity models were interpreted in terms of porosity and salinity and showed that: (1)All three nuclear tests were located in the zone of transition from fresh to saline groundwater. This implies shorter transit times for radionuclide transport into the ocean than if the explosions had been located in the salt water layer. (2)Effective porosity in the upper 3 km are the region 1-20% and imply slower transit times than inferred in previous hydrogeological modeling. (3)There is no evidence for near surface faults influencing the ground water flow or for faults providing high permeability pathways to the marine environment.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1834 Human impacts
DE: 1855 Remote sensing (1640)
SC: Hydrology [H]
MN: Fall Meeting 2005