Permeability of covers over low-level radioactive-waste burial trenches, West Valley, Cattaraugus County, New York

Among the facilities at the Western New York Nuclear Service Center, near the hamlet of West Valley in the northern part of Cattaraugus County, N.Y., is a State-licensed burial ground for commercial low-level radioactive wastes. The 11-acre burial ground contains a series of trenches excavated in a silty-clay till of low permeability that contains scattered pods of silt, sand, and gravel. Gas pressure in the unsaturated parts of radioactive waste burial trenches responds to fluctuations in atmospheric pressure. Measurements of atmospheric pressure and the differential pressure between the trench gas and the atmosphere on several dates in 1977-78 were used to calculate hydraulic conductivity of the reworked silty-clay till that covers the trenches. Generally the hydraulic conductivity of covers over trenches that had a history of rapidly rising water levels are higher, at least seasonally, than covers over trenches in which the water level remained low. This supports the hypothesis that recharge occurs through the cover, presumably through fractures caused by desiccation and (or) subsidence. Hydraulic conductivities of the cover as calculated from gas- and air-pressure measurements at several trenches were 100 to 1,000 times greater than those calculated from the increase in water levels in the trenches. This difference suggests that the values obtained from the air- and gas-pressure measurements need to be adjusted and at present are not directly usable in ground-water flux calculations. The difference in magnitude of values may be caused by rapidly decreasing hydraulic conductivity during periods of recharge or by the clogging of fractures with sediment washed in by runoff. (USGS)