From legacy contamination to watershed systems science: a review of scientific insights and technologies developed through DOE-supported research in water and energy security

Abstract

Water resources, including groundwater and prominent rivers worldwide, are under duress because of excessive contaminant and nutrient loads. To help mitigate this problem, the United States Department of Energy (DOE) has supported research since the late 1980s to improve our fundamental knowledge of processes that could be used to help clean up challenging subsurface problems. Problems of interest have included subsurface radioactive waste, heavy metals, and metalloids (e.g., uranium, mercury, arsenic). Research efforts have provided insights into detailed groundwater biogeochemical process coupling and the resulting geochemical exports of metals and nutrients to surrounding environments. 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 contaminants in the surface and shallow subsurface (i.e., the critical zone) and their interactions with carbon and nitrogen dynamics. 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 tackle 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.

Sulfidation and Reoxidation of U(VI)-Incorporated Goethite: Implications for U Retention during Sub-Surface Redox Cycling

“…Globally, U is considered a key environmental contaminant, prevalent in the sub-surface at numerous nuclear legacy and mining sites (e.g., Hanford/Rifle/Oak Ridge, USA). − U is also significant in higher activity radioactive wastes that are destined for disposal in a deep underground geological disposal facility (GDF) . To aid long-term containment, any GDF design will contain multiple barriers to limit radionuclide migration from the facility over geological timescales. ,, In addition to naturally occurring minerals from the surrounding host rock of the GDF, the corrosion of engineering iron and steel structures will lead to iron (oxyhydr)­oxide phases (e.g., magnetite, goethite, and green rust) being ubiquitous in and around the facility. − Previous studies have shown that iron (oxyhydr)­oxides can readily incorporate U species into their crystal structure and may therefore act as a further barrier to U migration in the environment over timescales relevant to a GDF. − However, the sub-surface biogeochemistry of both contaminated land and GDF environments will evolve over time, and this may include redox cycling induced by the onset of sulfate-reducing conditions and/or by oxygen ingress. ,− Consequently, U-associated iron (oxyhydr)­oxide phases may react with aqueous sulfide via a sulfidation reaction. , Potential reoxidation of this sulfidized system may then occur over the longer term, with cycling likely between reduced and oxidized states. , Given the potential for these fluctuating biogeochemical cycles in the sub-surface (e.g., effects of redox cycling, organic matter, carbonates, etc), , the long-term fate of incorporated radionuclides (including U) is unclear.…”

Impact of a Biological Chelator, Lanmodulin, on Minor Actinide Aqueous Speciation and Transport in the Environment

“…Spent fuel reprocessing, nuclear waste management, and risk assessment studies over the past few decades have resulted in a large body of literature on plutonium and minor actinide chemistry with aqueous chelators, for both inorganic and organic molecules. [6][7][8][9]11,43 Several speciation studies have been performed to determine the stoichiometry, formation constants, and spectroscopic signatures of actinide complexes, including those with Am(III) and Cm(III). These studies include soluble complexes formed with carbonate-bicarbonate ions, 44−46 phosphates, 47,48 chlorides, small natural chelators like carboxylic acids, 49,50 ATP, 51 hydroxamic acids, 52,53 siderophore ligands, 54−56 humic and fulvic acids, 57−62 and also unidentified natural dissolved organic matter.…”

“…While the waste packages are designed to initially isolate the radioactive materials when they are the most radioactive, those engineered barriers will ultimately fail due to underground mechanical forces and natural alteration processes. In this context, contact between radionuclides and the underground natural environment (e.g., minerals, groundwater, metal chelators, as well as microorganisms) is expected to take place, and thus, studying the chemistry of radioelements under environmentally relevant conditions is critical to assess the long-term behavior of nuclear waste. − …”

From Soils to Streams: Connecting Terrestrial Carbon Transformation, Chemical Weathering, and Solute Export Across Hydrological Regimes

“…Here we begin to address this knowledge gap by asking the question: How and to what extent do subsurface carbon transformation, chemical weathering, and solute export differ across hydrological and subsurface structure regimes? To answer this question, we draw upon the rich foundation of reactive transport modeling (RTM) that has been widely used to understand hydrological and biogeochemical coupling (Ackerer et al., 2021; Dwivedi et al., 2022; Jung & Navarre‐Sitchler, 2018; Li, Bao, et al., 2017; Wen et al., 2020). Here we first developed a hillslope‐scale RTM using soil CO 2 and soil water chemistry data from the Fitch Forest, a temperate forest at the ecotone boundary of the Eastern temperate forest and mid‐continent grasslands in Kansas (Fitch, 2006).…”