ABSTRACT:

This is a modified version of GEOSIM, which generates multi-scale fluvial heterogeneous facies. This code does not need the same number of cores as the number of compound bars generated. To compile these codes, the Intel fortran and openmpi compilers are both needed. The post-process codes, which are written in Python, are also included here.

ABSTRACT:

Numerical models have been extensively used to understand and predict flow and reactive transport processes in the hyporheic zone. However, most models focus on fully saturated riverbeds without accounting for surface water stage fluctuations related to precipitation and flooding. To capture the complete picture of hyporheic processes in riverbeds and riverbanks, we developed a fully-coupled multiphase reactive transport solver using the Open Source Field Operation And Manipulation (OpenFOAM) platform. This solver captures surface water stage fluctuations and partially-saturated flow in fluvial sediment using VoF two-phase flow and extended-Darcy's Law two-phase flow models for surface and subsurface domains, respectively. The transport models designed for partially saturated conditions in both domains are implemented. A geochemical reaction module, PhreeqcRM, is integrated into the solver to facilitate complex geochemical reaction networks. A two-way conservative flux boundary condition is implemented at the surface-subsurface interface to realistically map fluxes. The solver's capability is illustrated through a variety of hyporheic-related problems across spatial scales. These include laboratory experiments and reactive transport in two and three dimensions, from the bedform scale to multiscale riverbeds and riverbanks with fluctuating surface water flow. This novel solver allows for quantifying dynamics in the hyporheic zone with fewer simplifications. Based on the code structure and parallel design of OpenFOAM, the solver can simulate large, three-dimensional (3D) multiscale cases. The code, examples, and pre- and post-processing scripts are all open source, providing community access to use and modify them as desired.

ABSTRACT:

Per- and polyfluoroalkyl substances (PFAS) are surface-active contaminants, which are detected in groundwater globally presenting serious health concerns. The vadose zone and surface water are recognized as primary sources of PFAS contamination. Previous studies have explored PFAS transport and retention mechanisms in the vadose zone, revealing that adsorption at interfaces and soil/sediment heterogeneity significantly influences PFAS retention. However, our understanding of how surface water-groundwater interactions along river corridors impact PFAS transport remains limited. To analyze PFAS transport during surface water-groundwater interactions, we performed saturated-unsaturated flow and reactive transport simulations in heterogeneous riparian sediments. Incorporating uncertainty quantification and sensitivity analysis, we identified key physical and geochemical sediment properties influencing PFAS transport. Our models considered aqueous phase transport and adsorption both at the air-water interface (AWI) and the solid phase surface. We tested different cases of heterogeneous sediments with varying volume proportions of higher permeability sediments, conducting 2,000 simulations for each case, followed by global sensitivity and response surface analyses. Results indicate that sediment porosities, which are correlated to permeabilities, are crucial for PFAS transport in riparian sediments during river stage fluctuations. High permeable sediment (e.g., sandy gravel, sand) is the preferential path for the PFAS transport and the low permeable sediment (e.g., silt, clay) is where PFAS is retained. Additionally, the results show adsorption at interfaces (AWI \& solid phase) have small impact on the PFAS retention in riparian environments. This study offers insights into factors influencing PFAS transport in riparian sediments, potentially aiding the development of strategies to reduce the risk of PFAS contamination in groundwater from surface water.