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This article explores the hypothesis that natural losses of light nonaqueous phase liquids (LNAPLs) through dissolution and evaporation can control the overall extent of LNAPL bodies and LNAPL fluxes observed within LNAPL bodies. First, a proof‐of‐concept sand tank experiment is presented. An LNAPL (methyl tert‐butyl ether) was injected into a sand tank at five constant injection rates that were increased stepwise. Initially, for each injection rate the LNAPL bodies expanded quickly. With time the rate of expansion of the LNAPL bodies slowed and at extended times the extent of the LNAPL became constant. Attainment of a stable LNAPL extent is attributed to rates of LNAPL addition being equal to rates of LNAPL losses through dissolution and evaporation. Secondly, analytical solutions are developed to extrapolate the processes observed in the proof‐of‐concept experiment to dimensions and time frames that are consistent with field‐scale LNAPL bodies. Three LNAPL body geometries that are representative of common field conditions are considered including one‐dimensional, circular, and oblong shapes. Using idealized conditions, the solutions describe volumetric LNAPL fluxes as a function of position in LNAPL bodies and the overall extent of LNAPL bodies as a function of time. Results from both the proof‐of‐concept experiment and the mathematical developments illustrate that natural losses of LNAPL can play an important role in governing LNAPL fluxes within LNAPL bodies and the overall extent of LNAPL bodies. 相似文献
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Mitchell R. Olson Thomas C. Sale Charles D. Shackelford Christopher Bozzini Jessica Skeean 《Ground Water Monitoring & Remediation》2012,32(3):63-74
ZVI‐Clay is an emerging remediation approach that combines zero‐valent iron (ZVI)‐mediated degradation and in situ stabilization of chlorinated solvents. Through use of in situ soil mixing to deliver reagents, reagent‐contaminant contact issues associated with natural subsurface heterogeneity are overcome. This article describes implementation, treatment performance, and reaction kinetics during the first year after application of the ZVI‐Clay remediation approach at Marine Corps Base Camp Lejeune, North Carolina. Primary contaminants included trichloroethylene, 1,1,2,2‐tetrachloroethane, and related natural degradation products. For the field application, 22,900 m3 of soils were treated to an average depth of 7.6 m with 2% ZVI and 3% sodium bentonite (dry weight basis). Performance monitoring included analysis of soil and water samples. After 1 year, total concentrations of chlorinated volatile organic compounds (CVOCs) in soil samples were decreased by site‐wide average and median values of 97% and >99%, respectively. Total CVOC concentrations in groundwater were reduced by average and median values of 81% and >99%, respectively. In several of the soil and groundwater monitoring locations, reductions in total CVOC concentrations of greater than 99.9% were apparent. Further reduction in concentrations of chlorinated solvents is expected with time. Pre‐ and post‐mixing average hydraulic conductivity values were 1.7 × 10?5 and 5.2 × 10?8 m/s, respectively, indicating a reduction of about 2.5 orders of magnitude. By achieving simultaneous contaminant mass depletion and hydraulic conductivity reduction, contaminant flux reductions of several orders of magnitude are predicted. 相似文献
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Saeed Kiaalhosseini Richard L. Johnson Richard C. Rogers Maria Irianni Renno Mark Lyverse Thomas C. Sale 《Ground Water Monitoring & Remediation》2016,36(4):41-49
We evaluated tools and methods for in situ freezing of cores in unconsolidated subsurface media. Our approach, referred to as cryogenic core collection (C3), has key aspects that include downhole circulation of liquid nitrogen (LN) via a cooling system, strategic use of thermal insulation to focus cooling into the core, and controlling LN back pressure to optimize cooling. Two cooling systems (copper coil and dual‐wall cylinder) are described. For both systems, the time to freeze a single 2.5‐foot (76‐cm) long by 2.5‐inch (63‐mm) diameter core is 5 to 7 min. Frozen core collection rates of about 30 feet/day (10 m/day) were achieved at two field sites, one impacted by petroleum‐based light nonaqueous phase liquids (LNAPLs) and the other by chlorinated solvents. Merits of C3 include (1) improved core recovery, (2) potential control of flowing sand, and (3) improved preservation of critical sediment attributes. Development of the C3 method creates novel opportunities to characterize sediment with respect to physical, chemical, and biological properties. For example, we were able to resolve water, LNAPL, and gas saturations above and below the water table. By eliminating drainage of water, gas and LNAPL saturations in the range of 6 to 23% and 1 to 3% of pore space, respectively, were measured in LNAPL‐impacted intervals below the water table. 相似文献
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Stuart E. Sale J. E. Drew Y. C. Unruh M.J. Irwin C. Knigge S. Phillipps A. A. Zijlstra B. T. Gänsicke R. Greimel P. J. Groot A. Mampaso R. A. H. Morris R. Napiwotzki D. Steeghs N. A. Walton 《Monthly notices of the Royal Astronomical Society》2009,392(2):497-513
We present an algorithm (MEAD, for 'Mapping Extinction Against Distance') which will determine intrinsic ( r '− i ') colour, extinction, and distance for early-A to K4 stars extracted from the IPHAS r '/ i '/Hα photometric data base. These data can be binned up to map extinction in three dimensions across the northern Galactic plane. The large size of the IPHAS data base (∼200 million unique objects), the accuracy of the digital photometry it contains and its faint limiting magnitude ( r '∼ 20) allow extinction to be mapped with fine angular (∼10 arcmin) and distance (∼ 0.1 kpc) resolution to distances of up to 10 kpc, outside the solar circle. High reddening within the solar circle on occasion brings this range down to ∼2 kpc. The resolution achieved, both in angle and depth, greatly exceeds that of previous empirical 3D extinction maps, enabling the structure of the Galactic Plane to be studied in increased detail. MEAD accounts for the effect of the survey magnitude limits, photometric errors, unresolved interstellar medium (ISM) substructure and binarity. The impact of metallicity variations, within the range typical of the Galactic disc is small. The accuracy and reliability of MEAD are tested through the use of simulated photometry created with Monte Carlo sampling techniques. The success of this algorithm is demonstrated on a selection of fields and the results are compared to the literature. 相似文献
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We investigated whether the otolith chemistry ofHaemulon flavolineatum (French grunt), a nocturnally active fish, could be used as a means to differentiate individuals occupying mangrove and coral reef habitats. In 2003, adults were collected from 9 mangrove and 10 coral reef sites throughout Turneffe Atoll, Belize. Concentrations of trace elements were measured at the edge of sagittal otoliths by laser ablated inductively coupled plasma mass spectrometry. Results of a two-factor nested MANCOVA (sites nested within habitat and covariate of fish size), used to investigate whether significant differences in otolith elemental concentrations existed between habitats (i.e., mangrove versus reef) and among sites, indicated significant differences between habitats, in terms of lithium, magnesium, zinc, and rubidium (fish from mangroves had greater concentrations than those from coral reefs), as well as among sites (for several elements). Because elemental variability existed between habitats and among sites, we asked whether this variability was sufficient to differentiate habitats and sites using separate linear discriminant function analyses (LDFA). LDFA indicated that fish were classified to the habitat (mangrove or reef) from which they were collected with a moderate degree of accuracy (correct classification of 74% and 79% for mangrove and coral reef fish, respectively), but were poorly classified to the site from which they were collected (average correct classification of 46% with a range of 0–89%). Otolith microchemical investigations ofH. flavolineatum at Turneffe Atoll can be used to identify movement between habitats, yet due to the lack of unique site-specific chemical signatures likely caused by the nocturnal movement of individuals, it will not be possible to identify specific sites from which reef fish originated. 相似文献
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The stability of subsurface Light Nonaqueous Phase Liquids (LNAPLs) is a key factor driving expectations for remedial measures at LNAPL sites. The conventional approach to resolving LNAPL stability has been to apply Darcy's Equation. This paper explores an alternative approach wherein single‐well tracer dilution tests with intermittent mixing are used to resolve LNAPL stability. As a first step, an implicit solution for single‐well intermittent mixing tracer dilution tests is derived. This includes key assumptions and limits on the allowable time between intermittent mixing events. Second, single‐well tracer dilution tests with intermittent mixing are conducted under conditions of known LNAPL flux. This includes a laboratory sand tank study and two field tests at active LNAPL recovery wells. Results from the sand tank studies indicate that LNAPL fluxes in wells can be transformed into formation fluxes using corrections for (1) LNAPL thicknesses in the well and formation and (2) convergence of flow to the well. Using the apparent convergence factor from the sand tank experiment, the average error between the known and measured LNAPL fluxes is 4%. Results from the field studies show nearly identical known and measured LNAPL fluxes at one well. At the second well the measured fluxes appear to exceed the known value by a factor of two. Agreement between the known and measured LNAPL fluxes, within a factor of two, indicates that single‐well tracer dilution tests with intermittent mixing can be a viable means of resolving LNAPL stability. 相似文献
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Saeed Kiaalhosseini Benjamin Kohn A. Ted Watson Tom C. Sale Jens Blotevogel 《Ground Water Monitoring & Remediation》2019,39(2):71-75
Organic contaminants present as nonaqueous phase liquids (NAPLs) in the subsurface often pose a long-term risk to human health and the environment. Investigating the distribution of NAPLs in porous media remains a major challenge in risk assessment and management of contaminated sites. Conventional soil coring and monitoring wells have been widely used over past decades as the primary means of subsurface investigation to determine NAPL extent. Known limitations of conventional approaches have led us to explore an alternative or a complementary technique to provide high-quality information of NAPL source zone architecture. This work advances an imaging tool for a variety of organic NAPL contaminants in unconsolidated soils through magnetic resonance imaging (MRI) of frozen cores. Using trichloroethylene (TCE) and o-xylene as model species, we illustrate that discriminatory freezing of water, while keeping the NAPL in a liquid state, enables high-resolution qualitative delineation of NAPL distribution within porous media. This novel approach may help improve site conceptual models and consequentially lead to highly tailored, more efficient remedial measures. 相似文献
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Micrometeorites provide a large range of samples sourced from a wide variety of planetary materials, thereby providing a scope for expanding the known inventory of solar system materials. Here we report the micrometeorite AAS62‐34‐P117 having the assemblage of corundum, hibonite, unknown Al‐rich phases, FeNi metal blebs, sulfide, and phosphate embedded in Al‐rich silicate composition, and Pt‐group element nuggets dispersed throughout the micrometeorite. Here, we report the presence of corundum in micrometeorites as a major refractory phase with sizes greater than ~10 μm. The Al‐rich phases have Al2O3 ~50–70%, such high Al phases are not known from meteoritic components either in chondrules or refractory inclusions. In addition, the Ca content is extremely poor to relate it directly to known refractory inclusions, but is very high in Al. The presence of corundum in Al‐rich phases indicates the micrometeorite to be early condensate from solar nebula that later got incorporated into Si‐rich materials leading to a transformation that produced the unusual Al‐rich and Ca‐poor phases different from the average solar composition. The observed texture and mineralogy of the micrometeorite appears to have evolved in a nebular setting that has compositional reservoirs different from those of any known components of meteorites. 相似文献