Ground-water hydrology and subsurface migration of radionuclides at a commercial radioactive-waste burial site, West Valley, Cattaraugus County, New York

Low-level radioactive wastes were buried from 1963-75 in trenches excavated in a clay-rich till about 28 meters thick. Beneath the till is a lacustrine sequence that is unsaturated in its upper part and acts as a drain to the till. The till is nearly isotropic; hydraulic conductivity ranges between 2 times 10 to the minus 8th power and 6 times 10 to the minus 8th power centimeters/sec. Fractures with oxidized walls extend as much as 5 meters below the original land surface. The fractured till is 5 to 10 times more permeable than the deeper unfractured till, as determined from computer simulations. The direction of groundwater flow in the till is predominantly downward, with an average linear pore velocity of 1 to 8 centimeters/year. Tritium migrated less than 3 meters from three trenches in the 7 to 11 years after they were completed. Carbon-14 migrated less than 1 meter, and migration of other radionuclides is apparently even less. The migration of tritium and carbon-14 occurs chiefly by diffusion. Radionuclides are far less likely to reach the surface environment by subsurface flow through the till than by seepage of trench water through the trench covers, which can occur whenever trenches become filled with water from recharge entering through cracks that form in the cover. (USGS)