Redefining Surface Area: Understanding Reactive Interfaces in Heterogeneous Porous Media

Redefining Surface Area: Understanding Reactive Interfaces in Heterogeneous Porous Media

Biogeochemical reaction rates in the natural subsurface are typically controlled by those at the 'hot' reactive interfaces where fluids and solids of different properties and conditions meet. These interfaces are often restricted to relatively small, sharp zones with rates orders of magnitude higher than those at the rest of the domain. The research outcomes from this project will be important for a broad spectrum of applications at the nexus of energy, water, and environment. In particular, they will advance understanding and predicting of physical, chemical, and biological processes important for shale gas development, acid mine drainage, nuclear waste disposal, geological CO2 sequestration, geothermal energy, and contaminant transport. Fundamental understanding of the earth systems, including the Critical Zone where humans live, is also essential for soil fertility and productivity, water sustainability, and energy security, all of which are subject to climate change and intense human activities in the Anthropocene.

In this study the investigator hypothesizes that the emergence and nature of reactive interfaces are dictated by spatial heterogeneities, the spatial variations in porous medium properties and conditions. These reactive interfaces ultimately govern large scale processes and system functioning. Whereas hydrologists have documented significant impacts of physical heterogeneities on fluid flow and solute transport in the past decades, present understanding on the role of physical and geochemical heterogeneities in determining (bio)geochemical processes has not kept pace. The investigator proposes to understand fundamental principles that govern the occurrence and functioning of reactive interfaces. The ultimate goal is to develop conceptual and predictive framework for geochemical processes in natural, heterogeneous subsurface. The proposed work will integrate two-dimensional flow-through experiments and multi-scale reactive transport modeling. The 2D flow cells will be packed using calcite, chlorite, and quartz-minerals that differ drastically in reactivity and are ubiquitous in natural systems. Understanding reactive interfaces will enable a significant step toward unifying observations across scales. The goal of the education and outreach plan is to empower the science community and general public with tools and education in ways that transcend limits of time, space, and individual disciplines. The investigator proposes to (1) develop an online module with a 'heterogeneity' focus as part of a much-needed online reactive transport modeling (RTM) course for delivery through Penn State's World Campus; (2) develop a repository website that organizes the online teaching materials for free access to the public; (3) promote diversity and environmental awareness by offering underrepresented high school students a summer research opportunity on 'Water flow through rocks'. The plan will equip the community with knowledge and predictive tools for environmental stewardship, water management, as well as protection and sustainable use of natural resources.