Integrative geochronology calibrates the Middle and Late Stone Ages of Ethiopia's Afar Rift.

The Halibee member of the Upper Dawaitoli Formation of Ethiopia's Middle Awash study area features a wealth of Middle and Later Stone Age (MSA and LSA) paleoanthropological resources in a succession of Pleistocene sediments. We introduce these artifacts and fossils, and determine their chronostratigraphic placement via a combination of established radioisotopic methods and a recently developed dating method applied to ostrich eggshell (OES). We apply the recently developed Th/U burial dating of OES to bridge the temporal gap between radiocarbon (C) and Ar/Ar ages for the MSA and provide C ages to constrain the younger LSA archaeology and fauna to ∼24 to 21.

Total Recoverable Aluminum: Not Totally Relevant for Water Quality Standards.

A large water quality data set, representing more than 100 surface-water locations sampled from 2007 to 2017 in the Los Alamos area of New Mexico, USA's Pajarito Plateau, was assembled to evaluate Al concentrations in unfiltered and filtered samples. Aluminum concentrations often exceeded United States Environmental Protection Agency (USEPA) and New Mexico ambient water quality criteria (AWQC), regardless of filter size and sample location. However, AWQC are based on laboratory toxicity studies using soluble Al salts and do not reflect natural conditions in Pajarito Plateau surface waters.

Fate and transport of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its degradation products in sedimentary and volcanic rocks, Los Alamos, New Mexico.

High-explosive compounds including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were used extensively in weapons research and testing at Los Alamos National Laboratory (LANL). Liquid effluents containing RDX were released to an outfall pond that flowed to Cañon de Valle at LANL's Technical Area 16 (TA-16), resulting in the contamination of the alluvial, intermediate and regional groundwater bodies. Monitoring of groundwater within Cañon de Valle has shown persistent RDX in the intermediate perched zone located between 225 and 311 m below ground surface.

Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine.

One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. In this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA.

Isotopic Evidence for Reductive Immobilization of Uranium Across a Roll-Front Mineral Deposit.

We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area.