PNNL

Abstract

Water resources, including groundwater and prominent rivers worldwide, are un-der extreme duress because of various chemicals present in the environment including contaminants and nutrients. The Department of Energy (DOE) has supported research and cleanup associated with challenging subsurface problems since the late 1980s, such as treating subsurface radioactive waste, heavy metals, and metalloids (e.g., U, Hg, As). Research efforts have provided insights into detailed ground-water biogeochemistry and resulting geochemical exports of metals and nutrients to the environment. Recently, an increased focus has been placed on constraining the exchanges and fates of carbon and nitrogen within and across bedrock to canopy compartments of a watershed and in river floodplain settings because of their important role in driving biogeochemical interactions with contaminants and the potential of increased fluxes under changing precipitation regimes, including extreme events. While reviewing the extensive research that has been conducted at DOE's representative sites and testbeds such as the Oyster Site in Virginia, Savannah River Site in South Carolina, Oak Ridge Reservation in Tennessee, Hanford in Washington, Nevada National Security in Nevada, Riverton in Wyoming, and Rifle and East River in Colorado, this review paper explores the nature and distribution of contamination and their coupled interactions with carbon and nitrogen dynamics. We summarize several important constructs developed at these representative sites toward enhancing a predictive understanding of contaminants and nutrient cycling and their transport in the environment. We also describe state-of- the-art, scale-aware characterization approaches and models developed to predict contaminant fate and transport. The models take advantage of DOE leadership-class high-performance computers and are beginning to incorporate artificial intelligence approaches to help confront the extreme diversity of hydro-biogeochemical processes and measurements. Recognizing that the insights and capability developments are potentially transferable to many other sites, we also explore the scientific implications of these advances and recommend future research directions.