PNNL

Abstract

Numerical simulation has been applied in support of the U.S. Department of Energy’s (DOE’s) efforts to characterize the nature and distribution of carbon tetrachloride in the deep vadose zone at the Hanford site, near Richland, Washington. Three-dimensional computational domains were used, with layered and heterogeneous distributions of soil properties, in this numerical investigation into the vertical and lateral distribution of carbon tetrachloride beneath it release point (216-Z-9 trench) and the effects of soil vapor extraction process. The complexity of the modeled physical processes, namely, the nonlinearities associated with multifluid subsurface flow, including phase transitions and hysteresis in the relative permeability-saturation-capillary pressure functions, limits the grid resolution when executed using single processor computers. To achieve higher grid resolutions and acceptable detail in the subsurface distribution and remediation of carbon tetrachloride, execution on multiple processors was required. This paper describes and demonstrates a scalable implementation of a multifluid subsurface flow and transport with capabilities for volatile organic compounds, residual nonaqueous phase liquid formation in the vadose zone, and soil vapor extraction, using multiple wells. Developing scientific software for execution on parallel computers has unique challenges. The guiding objectives for developing this scalable code were to keep the source coding readable and modifiable by subsurface scientists, allow for both sequential and scalable processing, depend on domain scientists for code parallelization and scalable linear system solvers.