Ground-water flow near two radioactive-waste-disposal areas at the Western New York Nuclear Service Center, Cattaraugus County, New York: Results of flow simulation

Abstract

Two adjacent burial areas are excavated in a clay-rich till at a radioactive-waste-disposal site near West Valley in Cattaraugus County, N.Y. One of the burial grounds, which contains mainly low-level radioactive wastes generated onsite by a nuclear-fuel-reprocessing plant, has been in operation since 1966. The other, which contains commercial low-level-radioactive wastes, was operated during 1963-75. Ground water below the upper 3 meters of till generally moves downward through a 20to 30-meter-thick sequence of tills underlain by lacustrine and kame-delta deposits of fine sand and silt. Ground water in the weathered, upper 3 meters of till can move laterally for several meters before either moving downward into the kame-delta deposits or discharging to land surface. A two-dimensional finite-element model that simulates two vertical sections was used to evaluate hydrologic factors that control ground-water flow in the till. Conditions observed during March 1983 were reproduced accurately in steady-state simulations that used four isotropic units of differing hydraulic conductivity to represent two fractured and weathered till units near land surface, an intermediate group of isolated till zones that contain significant amounts of fine sand and silt, and a sequence of till units at depth that have been consolidated by overburden pressure. Recharge rates used in the best-fit simulation ranged from 1.4 centimeters per year along smooth, sloping or compacted surfaces to 3.8 centimeters per year near swampy areas. Values of hydraulic conductivity and infiltration used in the calibrated best-fit model were nearly identical to values used in a previous model analysis of the nearby commercial-waste burial area. Results of model simulations of a burial pit assumed to be filled with water indicate that water near the bottom of the burial pit would migrate laterally in the shallow, weathered till for 5 to 6 meters before moving downward into the unweathered till, and water near the top of the pit would move laterally less than 20 meters before moving downward into the unweathered till. These results indicate that subsurface migration of radionuclides in ground water to points of dishcarge to land surface is unlikely as long as the water level does not rise into the reworked cover material. INTRODUCTION The Western New York Nuclear Service Center occupies 13.5 km2 ±n northern Cattaraugus County, about 50 km south of Buffalo, N.Y. (fig. 1). A fuelreprocessing plant and related waste-management facilities occupy about 1 within the center on a fairly level plateau on the west flank of the Buttermilk Creek valley (fig. 2). These facilities include an area for receiving and storage of irradiated fuel before reprocessing, an underground storage-tank complex for liquid high-level radioactive wastes generated by the reprocessing, and a low-level radioactive wastewater storage plant (fig. 2). The center contains two separate burial areas for disposal of radioactive waste. One is a 2.2-hectare area previously licensed by the U.S. Nuclear Regulatory Commission for disposal of waste generated on site by the nuclearfuel-reprocessing plant, hereafter referred to as the facility's disposal area. The other, just east of the facility's disposal area, is a 7-hectare area that was licensed by the State of New York for burial of commercial low-level radioactive waste and was operated from 1963-75, hereafter referred to as the State-licensed waste-disposal area. 79° OO'OO 78° 30'00 La*!.____ Buffalo NEW YORK f-4Cattaraugus Co WESTERN NEW YORKNUCLEAR SERVICE CENTER (See inspt, fig. 2) >'WEST VALLEY Connoisarau/ey Creek FRANKLINVILLE Boundary of Cattaraugus Creek basin