Transport and biogeochemical reaction of metals in a physically and chemically heterogeneous aquifer (original) (raw)

Integrating Variable Aquifer Geochemistry and Sediment Properties into Models of Uranium Retention at the Nuclear Metals Incorporated Superfund Site

2016

The EPA-designated Superfund site Nuclear Metals, Inc. of Concord, Massachusetts, is contaminated by depleted uranium, a byproduct of defense-related uranium metals processing. Uranium retention in the solid phase, either by adsorption or precipitation, impedes its transport and dissemination from the contamination source. Geochemical parameters including pH, Ca content and alkalinity influence uranium speciation and phase partitioning and thus its transport properties. Understanding these effects is essential to the formulation of an informed remediation strategy. This research examines and attempts to model uranium adsorption in contaminated and uncontaminated sediments in a range of synthetic ground waters with compositions similar to those found at the site. Surface area and particle size were the dominant sediment characteristics that influenced the extent of uranyl adsorption. Uranyl hydroxycarbonate complexes are the dominant form of adsorbed uranium in neutral solutions; dis...

Reactive transport modeling at uranium in situ recovery sites: uncertainties in uranium sorption on iron hydroxides

2013

Geochemical changes that can occur down gradient from uranium in situ recovery (ISR) sites are important for various stakeholders to understand when evaluating potential effects on surrounding groundwater quality. If down gradient solid-phase material consists of sandstone with iron hydroxide coatings (no pyrite or organic carbon), sorption of uranium on iron hydroxides can control uranium mobility. Using one-dimensional reactive transport models with PHREEQC, two di2erent geochemical databases, and various geochemical parameters, the uncertainties in uranium sorption on iron hydroxides are evaluated, because these oxidized zones create a greater risk for future uranium transport than fully reduced zones where uranium generally precipitates.