Effect of iron and carbonation on the diffusion of iodine and rhenium in waste encasement concrete and soil fill material under hydraulically unsaturated conditions

Assessing long-term performance of Category 3 cement wasteforms and accurate prediction for radionuclide encasement requires knowledge of the radionuclide–cement interactions and mechanisms of retention (i.e. sorption or precipitation). A set of sediment-concrete half-cell diffusion experiments was conducted under unsaturated conditions (4% and 7% by weight moisture content) using carbonated and non-carbonated concrete–soil half cells. Results indicate the behavior of Re and I release was comparable within a given half-cell test. Diffusivity in soil is a function of moisture content; a 3% increase in moisture content affords a one to two order of magnitude increase in diffusivity. Release of I and Re was 1–3 orders of magnitude less from non-carbonated, relative to carbonated, concrete monoliths. Inclusion of Fe in non-carbonate monoliths resulted in the lowest concrete diffusivity values for both I and Re. This suggests that in the presence of Fe, I and Re are converted to reduced species, which are less soluble and better retained within the concrete monolith. The release of I and Re was greatest from Fe-bearing, carbonated concrete monoliths, suggesting carbonation negates the effect of Fe on the retention of I and Re within concrete monoliths. This is likely due to enhanced formation of microcracks in the presence of Fe, which provide preferential paths for contaminant migration. Although the release of I and Re were greatest from carbonated concrete monoliths containing Fe, the migration of I and Re within a given half cell is dependent on the moisture content, soil diffusivity, and diffusing species.     

Predicting Formation Pore-Pressure from Well-Log Data with Hybrid Machine-Learning Optimization Algorithms

Natural Resources Research - Accurate prediction of pore-pressures in the subsurface is paramount for successful planning and drilling of oil and gas wellbores. It saves cost and time and helps to...     

Sporormiella as a proxy for non-mammalian herbivores in island ecosystems

Spores of the dung-fungi Sporormiella are routinely used as a proxy for past megaherbivore biomass and to pinpoint the timing of extinctions. Further ecological insight can also be gained into the impacts that followed initial human arrival in a region through correlation of spore abundance with other proxies (e.g. pollen, charcoal). Currently, the use of Sporormiella as a palaeoecological proxy has been restricted to landmasses where large-herbivore guilds are dominated by mammals. Here, we use New Zealand as a case study to show that the method can also be applied effectively to islands dominated by large avian herbivores. We examine 44 dung samples from 7 localities to show that Sporormiella spores were widely distributed in the dung of endemic avian herbivores (South Island takahe (Porphyrio hochstetteri), kakapo (Strigops habroptilus), and several species of extinct moa, identified by ancient DNA analysis). In addition, we show that Sporormiella spores in a forest soil core from the Murchison Mountains, South Island, accurately trace the post-settlement decline of native avian herbivores, and combined with high-resolution radiocarbon dating reveal severely reduced local herbivore populations by the late 17th Century AD. The spores also trace the subsequent spread of Red deer (Cervus elaphus) introduced to the area in the early 20th Century AD. Our results suggest Sporormiella spores may provide a useful new tool for examining extinctions on numerous islands where terrestrial herbivore guilds were dominated by birds or reptiles. Our findings also highlight the need to consider entire herbivore communities (including birds and reptiles) when examining Late Pleistocene continental Sporormiella records, where the focus has often been tracing the decline of populations of large mammals.     

World's Largest In Situ Thermal Desorption Project: Challenges and Solutions

This paper presents the largest In Situ Thermal Desorption (ISTD) project completed to date. The redevelopment of a former aerospace manufacturing facility adjacent to a commercial airport was the main driver, requiring relatively rapid reduction of several chlorinated volatile organic compounds (CVOC) in a 3.2‐acre source zone. The source zone was divided into four quadrants with differing treatment depths, heated simultaneously using a total of 907 thermal conduction heater wells. Five different depths were selected across the area, according to the depth of contaminant impact. Prior to implementation, a risk and optimization study led to placement of a vertical sheet‐pile wall around the treatment zone to minimize groundwater flow, and a pilot test of a novel direct‐drive method for installation of the heater casings. Because of a shallow water table, a layer of clean fill was placed over the treatment zone, and partial dewatering was necessary prior to heating. A network of vertical multiphase extraction wells and horizontal vapor extraction wells was used to establish hydraulic and pneumatic control and to capture the contaminants. The site was split into four decision units, each with a rigorous soil sampling program which included collecting a total of 270 confirmatory soil samples from locations with the highest pretreatment CVOC concentrations requiring reduction to below 1 mg/kg for each contaminant. Temperature monitoring and mass removal trends were used to trigger the sampling events. Eventually, a small area near the center of the site required the installation of four additional heaters before the soil goals were reached after 238 days of heating. The total energy usage for heating and treating the source area was 23 million kWh—slightly lower than the estimated 26.5 million kWh. Actual energy losses and the energy removal associated with the extracted steam were lower than anticipated. An estimated 13,400 kg (29,800 lbs) of CVOC mass was removed, and all soil goals were met. This paper presents the challenges associated with a project of this scale and describes the solutions to successfully complete the ISTD remedy.     

Using Sealed Wells to Measure Water Levels Beneath Streams and Floodplains

The design of wells beneath streams and floodplains has often employed with tall standpipes to prevent incursion of surface water into the well during flood events. Here, an approach has been presented to minimise the infrastructure demands in these environments by sealing the well top (e.g., prevent water entering the well) and monitor the total pressure in the water column using an absolute (non‐vented) pressure transducer. The sealed well design was tested using a laboratory experiment where the total pressure responses were monitored in both an unsealed and sealed well, while the water level was varied. It is observed that, whether the well is sealed or not, the total pressure at a given depth in the aquifer will be equal to that within the well. This indicates that the sealed well design is a viable alternative to tall standpipes and also facilitates installation of wells beneath streams and floodplains.