2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
Paper No. 330-8
Presentation Time: 9:45 AM-10:00 AM

Factoring Uncertainty into Restoration Modeling of In-Situ Leach Uranium Mines

JOHNSON, Raymond H. and FRIEDEL, Michael J., Geologic Discipline, Crustal Imaging and Characterization Team, USGS, Denver Federal Center, PO Box 25046, MS 964, Denver, CO 80225, rhjohnso@usgs.gov

Post-mining restoration is one of the greatest concerns for uranium in-situ leach (ISL) mining operations. The ISL-affected aquifer needs to be returned to conditions specified in the mining permit (either pre-mining or other specified conditions). When uranium ISL operations are completed, post-mining restoration is usually achieved by injecting reducing agents into the mined zone. The objective of this process is to restore the aquifer to pre-mining conditions by reducing the solubility of uranium and other metals in the ground water.

Reactive transport modeling is a potentially useful method for simulating the effectiveness of proposed restoration techniques. While reactive transport models can be useful, they are a simplification of reality that introduces uncertainty through the model conceptualization, parameterization, and calibration processes. For this reason, quantifying the uncertainty in simulated temporal and spatial hydrogeochemistry is important for post-remedial risk evaluation of metal concentrations and mobility. Quantifying the range of uncertainty in key predictions (such as uranium concentrations at a specific location) can be achieved using forward Monte Carlo or other inverse modeling techniques (trial-and-error parameter sensitivity, calibration constrained Monte-Carlo, Markov-chain, and Null-Space Monte Carlo). These techniques provide simulated values of metal concentrations at specified locations that can be presented as nonlinear uncertainty limits or probability density functions. Decision makers can use these results to better evaluate environmental risk as future metal concentrations with a limited range of possibilities, based on a scientific evaluation of uncertainty.

2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
General Information for this Meeting
Session No. 330
Hydrogeology III - Uranium, Metals, and Other Contaminants in Groundwater
George R. Brown Convention Center: 342BE
8:00 AM-12:00 PM, Thursday, 9 October 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 6, p. 528

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