Paper No. 70-1
Presentation Time: 1:45 PM
HIGH RATES OF TRACER GAS TRANSPORT IN A DEEP FRACTURED BASALT (Invited Presentation)
In the phenomenon known as barometric pumping, atmospheric pressure fluctuations contribute to the motion of gases in the vadose zone. While the resulting gas transport is often negligible in homogeneous media, rates of transport in fractured media can be significant. We present results from a tracer test that was conducted to characterize deep subsurface fractured basalt and investigate the effects of barometric pumping on gaseous contaminant mobility. The tracer testing provided data to constrain permeability, porosity, and diffusivity in a numerical representation of the experiment. The numerical model was then used to simulate gas flow and transport under fluctuating pressure conditions. Results from the tracer test and simulations suggest that barometric pumping induces 10x to 100x more mixing in the basalt than standard diffusive theory would predict. Further, within the basalt fractures, estimates of average linear velocity reach maximums of nearly 1000 m/day.