Tuesday, February 16, 2016 AGS Luncheon

"Assessing Fluid Flow Characteristics and Contaminant Migration Potential in Variably- Saturated, Fractured Rock Systems: An Example from the T-Tunnel Complex, Rainier Mesa, NNSS"

Noon Luncheon 11:30-1:00 pm

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LUNCHEON ABSTRACT

This study provides a comprehensive assessment of the potential for downward radionuclide transport, released from subsurface nuclear testing at the T-tunnel complex, Nevada National Security Site, to the regional water table over a 1,000 year regulatory time period. A dual-permeability (DKM) flow model containing spatially discontinuous, poorly-connected fault networks within low-permeability, porous tuff units is utilized to simulate complex patterns of variably-saturated flow. Calibration of the DKM flow model using spatially-distributed recharge fluxes involved: reproducing direct measurements and physical observations of perched water levels in the Tertiary volcanics, with unsaturated conditions in the matrix and fractures of the Paleozoic carbonates adjacent to the volcanics and above the regional water table; a continuum of fracture saturations in the volcanics encompassing dry, partially-saturated and fully saturated fractures; and matching total discharge through the tunnel portal over an approximate 24 year transient period.

RWHet, a fully Lagrangian, random-walk particle tracking code, was modified for this project to simulate advective-dispersive particle motion in dual-permeability flow fields with diffusional mass exchange between fractures and matrix. Flow and transport simulations were run in a Monte Carlo framework that included a source term of 10 radionuclides for 6 underground tests and an additional source comprised of redistributed radionuclides in the flooded tunnel waters, and parametric uncertainty in transport parameters.

SPEAKER BIOGRAPHY

Speaker: D. Matthew Reeves, Department of Geological Sciences, University of Alaska, Anchorage

Dr. Matt Reeves received a Ph.D. in Hydrogeology from University the Nevada, Reno in 2006 and worked as a Research Professor at the Desert Research Institute for 8 years. He is currently an Associate Professor in the Geological Sciences Department at the University of Alaska, Anchorage. His primary research interests include the investigation of fluid flow, heat and solute transport through geologic media with applications to fractured rock hydrology, geothermal reservoirs, contaminant transport, and climate change.

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