HR: 0830h
AN: H11G-0916    [PDF]
TI: Evaluation of the Effects of Potash Mining in the Region of the Waste Isolation Pilot Plant, Carlsbad, New Mexico
AU: * Lowry, T S
EM: tslowry@sandia.gov
AF: Sandia National Laboratory, P.O. Box 5800 MS 0735, Albuquerque, NM 87185-0735 United States
AU: Beauheim, R L
EM: rlbeauh@sandia.gov
AF: Sandia National Laboratory, 4100 National Parks Hwy., Carlsbad, NM 88220 United States
AB: The Waste Isolation Pilot Plant (WIPP) in southeast New Mexico has been developed for underground disposal of transuranic waste in halite beds of the Permian Salado Formation. Managed by the Department of Energy (DOE), the WIPP has been operational since March 1999. Regulatory requirements call for the DOE to submit a Compliance Recertification Application (CRA) every five years, the first of which is due to the Environmental Protection Agency in 2004. In support of the CRA, performance assessment (PA) analysis is being conducted. PA is a series of linked models that make probabilistic assessments of possible future states of the WIPP and its performance under each of those states. One possible future state involves human intrusion into the repository creating pathways for upward migration of radionuclides into the Culebra dolomite aquifer. The Culebra is about 200 m below ground surface and 400 m above the repository. Current and future potash mining in the upper Salado Formation, within and outside the WIPP boundary, will likely cause subsidence of the Culebra, resulting in higher transmissivities that may change regional groundwater flow patterns. This analysis evaluates the impact of potash mining on the Culebra flow patterns and the resulting influence on repository performance. The impacts are modeled by creating 100 calibrated transmissivity (T) fields through stochastic inverse modeling using the parameter estimation code, PEST. Transmissivities in each field are then scaled in areas deemed to contain extractable potash by a random mining factor between 1 and 1000. Two mining scenarios are modeled: mining in all extractable areas within the WIPP boundary and across the entire region and mining everywhere except within the WIPP boundary. Three random mining factors are applied to each calibrated T-field for both mining scenarios, creating 600 instances of modified T-fields. Steady-state flow models are run for each instance and particle tracking is used to determine the flow path and travel time from the center of the WIPP to the site boundary. Cumulative probability distribution functions of travel time are produced for each mining scenario and compared to the undisturbed case. Particle pathways are also examined. Results show that the median travel times for the mining cases are 2.3 to 2.5 times longer than for the undisturbed case. This is due to increased transmissivity in the mining zones creating preferential flow routes around most of the WIPP site. Flow path changes are also apparent between the mining and undisturbed cases. No correlation is found between the travel times and the random mining factor, meaning small values of this factor are enough to shift the flow field from a non-mining pattern to a mining pattern.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2003 Fall Meeting