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Groundwater mixing dynamics play a crucial role in the biogeochemical cycling of shallow wetlands. In this paper, we conducted groundwater simulations to investigate the combined effects of evaporation and local heterogeneity on mixing dynamics in shallow wetland sediments. The results show that evaporation causes groundwater and solutes to upwell from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology reveals that local heterogeneity generates spatially varied mixing patterns mainly along preferential flow pathways. The upwelling of groundwater induced by surface evaporation through heterogeneous sediments is likely to create distinct mixing hotspots that differ spatially from those generated by lateral preferential flows driven by large‐scale hydraulic gradients, which enhances the overall mixing in the subsurface. These findings have strong implications for biogeochemical processing in wetlands. Plain Language Summary: In shallow wetlands, groundwater mixing and exchange have been identified as critical factors affecting biogeochemical cycling and transformation in sediments. Our results for the first time demonstrate evaporation causes a significant upwelling of groundwater and solutes from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology, including the Okubo‐Weiss parameter and dilution index, reveals that evaporation and local heterogeneity generates dynamic mixing patterns along preferential flow pathways. Such mixing mechanisms would strongly affect biogeochemical conditions in near‐surface sediments of shallow wetlands, which have strong implications for wetland ecosystems. Key Points: Evaporation causes groundwater and solutes to upwell from deep sediments to the surface, resulting in near‐surface solute accumulationHeterogeneity causes strain‐dominated and vorticity‐dominated flow regions to coexist at small spatial scales along preferential flow pathsUpwelling groundwater creates distinct mixing hotspots that differ spatially from those generated by large‐scale hydraulic gradients [ABSTRACT FROM AUTHOR]

Nonaqueous phase liquids (NAPL) tend to be trapped within aquifers. The review first covers conventional technologies that rely on pumping water, hot water, and/or air sparging with vapor extraction. The review then addresses polymer and foam delivery, which are intended to directly add solutions to low-permeability zones, where NAPL resides. Based on data from the literature, the removal of hydrocarbons by any of the flushing techniques, including polymer and foams apply well for porous media whose hydraulic conductivity is greater than 10−4 m/s , excluding silt and clay materials. For those lower permeability soils, electrokinetics (EK) appears appropriate. EK relies on imposing a voltage of DC current across the soil, which would engender three types of flows: electromigration, which causes ions to move to the electrode of opposite sign; electrophoresis, which causes charged particles, such as negatively charged clay particles or bacteria (mostly negatively charged but also some positively charged) to the electrode of the opposite sign; and electroosmosis, which occurs only when a zeta potential exists in the soil (typical of clay and silt) that would cause the movement of water and potentially NAPL. EK could be used to deliver anionic surfactants through electromigration or nonionic surfactants through electroosmosis (in clay or silt). An emerging hydraulic technique is chaotic advection, and it maximizes the contact between the delivered solution and the soil region of interest. The main challenge of applying EK in field studies is the familiarity of operators and scalability, as the electrodes cannot be more than 15–20 m apart. [ABSTRACT FROM AUTHOR]

Jets and plumes have been the focus of quantitative investigations since the mid-1950s. These investigations intensified following the Deepwater Horizon oil spill, in which thousands of tons of oil and natural gas were released into the Gulf of Mexico. This review focuses on plume dynamics that apply to both single-phase and multiphase liquid-in-liquid and liquid plus gas into liquid plumes, including bubble and droplet formation, and heat and mass transfer. Broadly, our work highlights several previously unknown or overlooked aspects of multiphase flow in the deep oceans. Upstream of the jet release, multiphase hydraulics can significantly affect the turbulence, for instance, through churn flow that enhances the turbulence in the free jet, affecting the conditions where bubbles and droplets are formed. Droplet formation was a major focus recently, with experiments covering a range of scales and flow rates of oil and gas at low and high pressure. Detailed observations of droplet formation at the jet-water boundary reveal the formation of compound droplets, which are emulsions of oil and water with implications for mass conservation and mass transfer. At the plume scale, integral models have been adapted to include the complex thermodynamics and chemistry of oil and gas plumes. In parallel, significant advances were made in numerical simulations of multiphase plumes through large eddy simulations by treating the oil and gas either a continuous or discrete phase. Through this work, a vivid picture of the complex droplet, chemical, and hydrodynamic behavior of multiphase plumes in the ocean is emerging. [ABSTRACT FROM AUTHOR]

Subsurface heterogeneity could influence groundwater flow with implications on structure and productivity of aquifer ecosystems. Here we investigate effects of multifractal heterogeneity on topology of groundwater flow through MODFLOW simulations within a Monte Carlo framework. The results show that heterogeneity leads to focused groundwater advection and the creation of hotspots of bending‐type vortex flow in the fields. We demonstrate for the first time that the vortex structures characterized by Q criterion are 3‐D distributed and greatly deform surrounding pore‐water flow. The structures exhibit scale‐invariant features in multifractal fields and in stationary fields below the correlation scale, indicating that such vortex flow might be widely present with no characteristic scale. Complex spatial patterns of kinetic energy dissipation rate are identified for pore water flowing through heterogeneous porous media and correlate strongly with preferential flows. These findings are important for understanding solute fate and transport in aquifer systems. Plain Language Summary: The findings of this study provide insight into influences of heterogeneity on groundwater flow and solute transport processes in aquifers. Our results reveal that multifractal heterogeneity leads to focused regions of groundwater advection and creates hotspots of bending‐type vortex flow that are 3‐D and greatly deform surrounding pore water. It has strong implications for groundwater contamination and associated implementation of effective bioremediation strategies. This is because solutes/contaminants would be spun around these structures and therefore have less interaction with the soil matrix in the inner part of the vortices. We also demonstrate that the structures of the vortex flow are scale invariant in multifractal K fields and below the correlation scale of stationary K fields. It indicates that these vortex flow structures may be widely present in the field with no characteristic scale. Substantial energy dissipation along the high‐velocity zones also has strong implications for understanding activity, diversity, and the distribution of subterranean microorganisms. Key Points: Deformation and rotation of pore‐water flow occur near high vorticity zones, formed as blobs and correlated strongly to preferential flowsVorticity‐dominated blobs exhibit scale invariance in both multifractal K fields and up to the correlation scale in variogram K fieldsHeterogeneity dissipates substantial kinetic energy within large pore‐water velocity zones [ABSTRACT FROM AUTHOR]

Abstract: Improved understanding of the character of an uncontrolled pipeline flow is critical for the estimation of the oil discharge and droplet size distribution both essential for evaluating oil spill impact. Measured oil and gas properties at the wellhead of the Macondo255 and detailed numerical modeling suggested that the flow within the pipe could have been “churn,” whereby oil and gas tumble violently within the pipe and is different from the bubbly flow commonly assumed for that release. The churn flow would have produced 5 times the energy loss in the pipe compared to bubbly flow, and its plume would have entrained 35% more water than that of the bubbly flow. Both findings suggest that the oil discharge in Deepwater Horizon could have been overestimated, by up to 200%. The resulting oil droplet size distribution of churn flow is likely smaller than that of bubbly flow. [ABSTRACT FROM AUTHOR]

The interaction of oil and sediment in the environment determines, to a large extent, the trajectory and fate of oil. Using confocal microscope imaging techniques to obtain detailed 3D structures of oil-particle aggregates (OPAs) formed in turbulent flows, we elucidated a new mechanism of particle attachment, whereby the particles behave as projectiles penetrating the oil droplets to depths varying from ~2 to 10 µm due to the hydrodynamic forces in the water. This mechanism results in a higher attachment of particles on oil in comparison with adsorption, as commonly assumed. The projectile hypothesis also explains the fragmentation of oil droplets with time, which occurred after long hours of mixing, leading to the formation of massive OPA clusters. Various lines of inquiry strongly suggested that protruding particles get torn from oil droplets and carry oil with them, causing the torn particles to be amphiphillic so that they contribute to the formation of massive OPAs of smaller oil droplets (<~5-10 µm). Low particle concentration resulted in large, irregularly shaped oil blobs over time, the deformation of which without fragmentation could be due to partial coverage of the oil droplet surface by particles. The findings herein revealed a new pathway for the fate of oil in environments containing nonnegligible sediment concentrations. [ABSTRACT FROM AUTHOR]

A numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach. The simulations were conducted by using a numerical model BIOMARUN, which coupled a multi-Monod kinetic model BIOB to a density-dependent variably saturated groundwater flow model MARUN. The fate and transport of the contaminant plume were characterized by computing its centroid trajectory, spreading area and percentage of biodegradation in beach saturated and unsaturated zone, respectively. Key factors likely affecting this process were investigated, including tide amplitude, capillarity and hydraulic conductivity. It was found that aerobic biodegradation was the major fate of the contaminant plume in the beach. Tidal action twisted the centroid of the contaminant plume during its migration in the beach, which increased the residence time of the plume in the beach. High tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach. In contrast, the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach. The increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone, up to 40%, which is comparable to that in the saturated zone. Hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach. Higher hydraulic conductivity induced faster contaminant biodegradation in the beach. [ABSTRACT FROM AUTHOR]

Summary A numerical study, based on a density-dependent variably saturated groundwater flow model MARUN, was conducted to investigate subsurface flow and salt transport in bare saline aquifers subjected to evaporation, which was simulated using the bulk aerodynamic formulation. As evaporation was assumed to depend on the pore moisture, the evaporation flux evolved gradually causing a gradual increase in the pore salinity. This is in contrast to prior studies where the high salinity was imposed instantaneously on the ground surface. Key factors likely affecting subsurface hydrodynamics were investigated, including saturated hydraulic conductivity, capillary drive, relative humidity in the air, and surrounding groundwater replenishment. The simulations showed two temporal regimes where the first consists of rapid evaporation for a duration of hours followed by slow evaporation, until evaporation ceases. In the absence of surrounding groundwater replenishment, evaporation-induced density gradient generated an upward water flow initially, and then the flow decreased at which time a high density salt “finger” formed and propagated downwards. Capillary properties and atmospheric condition had significant impacts on subsurface moisture distribution and salt migration in response to the evaporation. The results also suggested that the presence of subsurface water replenishment to the evaporation zone tended to produce a steady evaporation rate at the ground surface. [ABSTRACT FROM AUTHOR]

A numerical study was undertaken to investigate the effects of waves on groundwater flow and associated inland-released solute transport based on tracer experiments in a laboratory beach. The MARUN model was used to simulate the density-dependent groundwater flow and subsurface solute transport in the saturated and unsaturated regions of the beach subjected to waves. The Computational Fluid Dynamics (CFD) software, Fluent, was used to simulate waves, which were the seaward boundary condition for MARUN. A no-wave case was also simulated for comparison. Simulation results matched the observed water table and concentration at numerous locations. The results revealed that waves generated seawater-groundwater circulations in the swash and surf zones of the beach, which induced a large seawater-groundwater exchange across the beach face. In comparison to the no-wave case, waves significantly increased the residence time and spreading of inland-applied solutes in the beach. Waves also altered solute pathways and shifted the solute discharge zone further seaward. Residence Time Maps (RTM) revealed that the wave-induced residence time of the inland-applied solutes was largest near the solute exit zone to the sea. Sensitivity analyses suggested that the change in the permeability in the beach altered solute transport properties in a nonlinear way. Due to the slow movement of solutes in the unsaturated zone, the mass of the solute in the unsaturated zone, which reached up to 10% of the total mass in some cases, constituted a continuous slow release of solutes to the saturated zone of the beach. This means of control was not addressed in prior studies. [ABSTRACT FROM AUTHOR]

We conducted simulations of oil transport from the footprint of the Macondo Well on the water surface throughout the Gulf of Mexico, including deposition on the shorelines. We used the U.S. National Oceanic Atmospheric Administration (NOAA) model General NOAA Operational Modeling Environment (GNOME) and the same parameter values and input adopted by NOAA following the Deepwater Horizon (DWH) blowout. We found that the disappearance rate of oil off the water surface was most likely around 20% per day based on satellite-based observations of the disappearance rate of oil detected on the sea surface after the DWH wellhead was capped. The simulations and oil mass estimates suggest that the mass of oil that reached the shorelines was between 10 000 and 30 000 tons, with an expected value of 22 000 tons. More than 90% of the oil deposition occurred on the Louisiana shorelines, and it occurred in two batches. Simulations revealed that capping the well after 2 weeks would have resulted in only 30% of the total oil depositing on the shorelines, while capping after 3 weeks would have resulted in 60% deposition. Additional delay in capping after 3 weeks would have averted little additional shoreline oiling over the ensuing 4 weeks. [ABSTRACT FROM AUTHOR]

Abstract: This paper explored numerical techniques to simulate the movement of an applied tracer plume in a laboratory beach subjected to tide. The MARUN model () was used. The movement of the tracer plume in the beach and the development of a transient seepage on the beach surface were modeled. By calibrating the results of the numerical model against the observed data, the laboratory beach was found to have two different zones: a top layer (thickness 9–17cm) with a saturated hydraulic conductivity, K 0, of 0.2cm/s and a lower layer with a K 0 of 0.12cm/s. The simulations revealed that the plume moved seaward during falling tides and downward during rising tides, which is consistent with previous studies. It was also observed that the plume developed a tail that extended in the landward direction, and a freshwater pool became entrapped between the main plume and its extended tail. A sensitivity analysis was conducted to evaluate the effects of boundary conditions, seepage face development, capillarity, and dispersivity values. It was found that a Dirichlet boundary condition landward of the beach causes the plume of applied tracer to sink deeper into the beach in comparison with a Neumann boundary condition. The suppression of the seepage face by forcing the water table to match the tide level did not have great effects on beach hydrodynamics or on the movement of the tracer, which was probably due to the small slope of the beach (10%). However, seepage flow was around half of the seaward flow leaving the beach through the submerged face. Investigation on the capillarity through the van Genuchten parameter revealed that a decrease in the pore size of the beach greatly affects solute hydrodynamics; we noted that the effects on solute transport increase with depth. Thus, we conclude that using a saturated flow model for tidally influenced beaches should be discouraged, especially for fine textured media (i.e., small α or strong capillarity). The simulations also showed that dispersivity does not affect the travel time of the peak of solute concentration at a specific location but affects its magnitude. [Copyright &y& Elsevier]

Summary: The HydroGeoSphere model is further developed and used to investigate the effects of viscosity, capillarity and grid spacing on thermal variable-density flow. Under saturated and unsaturated flow conditions, the flow dynamics significantly depends on the viscosity assumption (constant vs. variable), where downwelling regions (constant viscosity) become upwelling regions (temperature-dependent variable viscosity). Capillarity does not change the location of downwelling and upwelling regions. Capillarity can significantly alter the flow dynamics in the way that the water table acts as a “lid” to flow, and it diverts a thermal plume laterally. Significance of capillarity increases with increasing soil moisture. Thermal convective flow is highly sensitive to spatial discretization. While the flow dynamics remains to be a function of grid level, spatial discretization Δx =Δz =1m appears to be appropriate to simulate unsaturated variable-density flow and heat transfer in porous media because estimated errors have asymptotically reached a minimum. [ABSTRACT FROM AUTHOR]

Measurements of the background concentrations of nutrients, dissolved oxygen (DO), and salinity were obtained from a beach that has oil from the Exxon Valdez oil spill in 1989. Two transects were set across the beach, one passed through an oil patch while the other transect was clean. Three pits were dug in each transect, and they ranged in depth from 0.9 to 1.5 m. The DO was around 1.0 mg L-1 at oiled pits and larger than 5 mg L-1 at clean pits. The average nutrient concentrations in the beach were 0.39 mg-N L-1 and 0.020 mg-P L-1. Both concentrations are lower than optimal values for oil biodegradation (2 to 10 mg-N L-1 and 0.40 to 2.0 mg-P L-1), which suggests that they are both limiting factors for biodegradation. The lowest nitrate and DO values were found in the oiled pits, leading, to the conclusion that microbial oil consumption was probably occurring under anoxic conditions and was associated to denitrification. We present evidence that the oxygen level may be a major factor limiting oil biodegradation in the beaches. [ABSTRACT FROM AUTHOR]

Summary: Experiments were conducted to investigate the flushing of saltwater out of a laboratory aquifer (or beach) by freshwater propagating seaward. After a steady state distribution was achieved with a seaward hydraulic gradient, freshwater was introduced while keeping the total head constant at each boundary. This caused the propagation of freshwater seaward. Two initial uniform concentrations were used: Case 1: 2.0g/L (low salinity case) and Case 2: 34.0g/L (high salinity case). The observed salinity and pressure data were closely reproduced using the MARUN () numerical code. The results indicated that buoyancy plays an important role for Case 2 but is negligible for Case 1. The results also indicated that the flow in the offshore beach aquifer (submerged portion of beach) was negligible especially for Case 2. For this case, the pressure increased with time until reaching a peak and then decreased (i.e., humps were formed). This was not observed in the low salinity case. Investigations revealed that the increase in pressure is due to a combination of remnant high salinity and a rise in the water table at that location. Numerical investigations revealed that for the same difference in total head, the seaward flow of freshwater increases with a decrease in the seawater salinity. The increase, however, was nonlinear as a function of seawater density. For example, the discharge in the high salinity case was 20% lower than that in the low salinity case. [Copyright &y& Elsevier]

Numerical simulations were conducted to quantify bank storage in a variably saturated, homogenous, and anisotropic aquifer abutting a stream during rising stream stage. Seepage faces and bank slopes ranging from 1/3 to 100/3 were simulated. The initial conditions were assumed steady-state flow with water draining toward the stream. Then, the stream level rose at a constant rate to the specified elevation of the water table given by the landward boundary condition and stayed there until the system reached a new steady state. This represents a highly simplified version of a real world hydrograph. For the specific examples considered, the following conclusions can be made. The volume of surface water entering the bank increased with the rate of stream level rise, became negligible when the rate of rise was slow, and approached a positive constant when the rate was large. Also, the volume decreased with the dimensionless parameter M (the product of the anisotropy ratio and the square of the domain’s aspect ratio). When M was large (>10), bank storage was small because most pore space was initially saturated with ground water due to the presence of a significant seepage face. When M was small, the seepage face became insignificant and capillarity began to play a role. The weaker the capillary effect, the easier for surface water to enter the bank. The effect of the capillary forces on the volume of surface water entering the bank was significant and could not be neglected. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we investigated the tide-induced seawater–groundwater circulation in shallow beach aquifers using the finite element model MARUN. The numerical solutions were generalized using a dimensionless formulation. From a dimensionless tidal period and a dimensionless beach slope of 10%, we obtained results that apply to a wide range of beach permeabilities from 10−4 m/s to 10−3 m/s, beach slopes from 3.16% to 31.6%, tidal amplitude (0.3m-2m) and period (diurnal or semidiurnal). The numerical simulations demonstrated the following: The maximum Darcy velocity always occurs at the intersection of the watertable and the beach surface. The offshore beach groundwater is almost stagnant compared with the onshore groundwater flow, which may explain the previous observations that the major portion of the seaward groundwater seepage usually occurs in the shallow part of the submerged beach. The outflow from the seepage face accounts for 41–97% (average 55%) of the outflow from the intertidal zone. The amount of seawater infiltrating into the intertidal zone in a tidal cycle increases with the beach permeability and decreases when the inland recharge increases, and ranges from 35.5m3 yr−1 m−1 to 505.8m3 yr−1 m−1 for all the cases considered. Smaller beach slopes, smaller inland freshwater recharges, and/or greater beach permeability lead to larger saltwater plumes in the intertidal zone of the beach. The results are in line with the existing results of field observations and numerical simulations by previous researchers. [Copyright &y& Elsevier]

This work investigated the washout of dissolved nutrients from beaches due to waves by conducting tracer studies in a laboratory beach facility. The effects of waves were studied in the case where the beach was subjected to the tide, and that in which no tidal action was present. The following may be inferred: (1) waves created a steep hydraulic gradient in the swash zone and a mild one landward of it; (2) waves increased the residence time of a plume when they broke seaward of it. They also created additional pathways for transport of the tracer to the beach surface; and (3) in the presence of a tide that completely covered the solute plume, overall, the waves increased the washout of the tracer from the intertidal zone of the beach in comparison with the no-wave case. The residence time of the tracer plume due to waves superimposed on the tide was estimated as 75% of that resulting from the tide with no waves. Discussion on scaling up the results and implications for bioremediation are also presented. [ABSTRACT FROM AUTHOR]

Dispersed oils (i.e., oil droplets) at sea are transported by convection due to waves and buoyancy and by turbulent diffusion. This work follows the common approach in the oil community of using a Lagrangian approach instead of the Eulerian approach. Our focus was on small scale simulation of oil plumes subjected to regular waves. Stokes'' theory was used to obtain analytical expressions for wave kinematics. The velocity above the Mean Water Level was obtained using a second order Taylor''s expansion of the velocity at the MWL. Five hundred droplets were used to simulate the plume for a duration of 60 wave periods. A Monte Carlo framework (300 simulations) was used to compute theoretical mean and variance of plumes. In addition, we introduced a novel dimensionless formulation, whose main advantage was to allow one to report distances in terms of the wave length and times in terms of the wave period. We found that the Stokes'' drift was the major mechanism for horizontal transport. We also found that lighter oils propagate faster but spread less than heavier oils. Increasing turbulent diffusion caused the plume to disperse deeper in the water column and to propagate less forward. The spreading in both vertical and horizontal directions increased with an increase in turbulent diffusion. The increase in wave slope (or wave steepness) caused, in general, an increase in the downward and horizontal transport. In the context of mixing in the water column, the dimensionless formulation showed that small steepness waves with a large turbulent diffusion coefficient could result in essentially the same spreading as large steepness waves with a small turbulent diffusion coefficient. [Copyright &y& Elsevier]

A conservative solute tracer experiment was conducted in Indian Creek, a small urban stream in Philadelphia, PA, to investigate the role of subsurface properties on the exchange between streamwater and the hyporheic zone (subsurface surrounding the stream). Sodium bromide (NaBr) was used as a conservative tracer, and it was monitored in the surface water and in the bed sediments of a 15 m long pool. Subsurface sampling occurred at 12 locations in the upper layer sediments (extending from 7.5 to 10 cm below the streambed) and 13 locations in the lower layer sediments (extending from 10 to 12.5 cm below the streambed). The hydraulic conductivity (K) of the upper bed sediments and the lower bed sediments was measured in situ. Several locations within the streambed exhibited an increase in tracer concentration with depth, suggesting the presence of horizontal flow paths within this small pool. Over the entire pool, the influence of K heterogeneity on hyporheic exchange was masked by the groundwater head gradient and the morphology of the stream. Together, the groundwater head gradient and stream morphology induced a generally high tracer concentration and fast hyporheic exchange on the left side and center of the channel and low concentrations and slower exchange on the right side. Although the reach-scale effects on the surface water concentration were small, groundwater greatly influenced the local-scale hyporheic exchange in the pool. Understanding how physical stream characteristics control the location and extent of hyporheic exchange pathways will lead to a better understanding of bio-geochemical cycling of nutrients and contaminants. [ABSTRACT FROM AUTHOR]

Abstract: Conservative solute tracer experiments were conducted in Indian Creek, a small urban stream located in Philadelphia, Pennsylvania, USA. Estimated flow rates were between 46Ls−1 and 81Ls−1, average stream width was 5.5m and average stream depth was 0.2m. Given these dimensions, most researchers would think it reasonable to assume that the stream is completely mixed vertically and horizontally. However, we found that the stream was not vertically completely mixed in a 1.0m deep, 30m long pool. The limited mixing was demonstrated by the vertical stratification of a tracer cloud which was completely mixed both laterally and vertically across the stream prior to entering the pool. We suggest that the cause of limited mixing is due to a balance between groundwater inflow and transverse dispersion at the cross-section. We show that the unsupported assumption of complete mixing may result in a wide range, and thus increased uncertainty, of the values of stream flow and longitudinal dispersion coefficient estimated from these data. We conclude that the assumption of complete mixing and one-dimensional modeling must be checked against actual field conditions, even in small streams. [Copyright &y& Elsevier]

Bioremediation of oil spills on tidally influenced beaches commonly involves the addition of a nutrient solution to the contaminated region of the beach at low tide to stimulate the growth of indigenous oil-degrading bacteria. Maximizing the residence time of nutrients in the beach and subsequently their contact time with microorganisms is a main goal for successful bioremediation. Therefore, understanding the effects of the tide on water flow and solute transport in a beach is an essential task for designing a nutrient application strategy. We investigated these effects by conducting a tracer study in a laboratory beach simulating nutrient application on natural beaches. The study consisted of applying, at low tide, a conservative tracer solution onto the beach surface near the high-tide line and monitoring its movement in the beach subsurface. The tidal motion caused the applied plume to move downward and seaward. The downward movement occurred during rising tides, while the seaward movement occurred mainly during falling tides. The results indicate that nutrients should be applied at the high-tide line during low tides. Guidelines for scaling up the results to natural beaches are provided along with an example. [ABSTRACT FROM AUTHOR]

Abstract: We used two stream tracer studies to address issues related to using the transient storage model (TSM) in simulating solute transport in streams containing riffle-pools and step-pools. The injection durations were short such that one may consider the storage zones to consist mainly of surface water storage zones. We found that the TSM was not able to reproduce the high portion (near the peak) of the breakthrough curve in the first subreach (85m) regardless of the functional form of the objective function. We attributed this to the presence of a large pool 35m downstream of the injection location that caused segregation of solute flow that was completely mixed across the stream upstream of the pool. The model was able to closely fit the breakthrough curves at x=185 and 323m, most likely because the signature of the pool diminished downstream. The fitting method did not always ensure that the parameter values represented physical reality, and we believe that physical measurements should be made and incorporated into the parameter estimation procedure utilizing Bayesian estimation. Our findings indicate that the representative values of TSM parameters in a reach do not generally fall between the representative values of its subreaches. Hence, the expression ‘reach-averaged’ should be used cautiously. The results indicated that it is more reliable to extrapolate (going downstream) than to interpolate. We believe this is due to local physical controls that could not be accounted for with parameters estimated far downstream from the controls. [Copyright &y& Elsevier]

The evaluation of dispersant effectiveness used for oil spills is commonly done using tests conducted in laboratory flasks. The success of a test relies on replication of the conditions at sea. We used a hot wire anemometer to characterize the turbulence characteristics in the swirling flask (SF) and the baffled flask (BF), the latter is being considered by the Environmental Protection Agency to replace the prior. We used the measurements to compute the velocity gradient, G and the energy dissipation rate per unit mass, [variant_greek_epsilon]. The study shows that the mixing in the BF is more uniformly distributed than that in the SF. Flask average energy dissipation rates in the SF were about 2 orders of magnitude smaller than those in the BF. The sizes of the microscales in the BF were found to be much smaller than that in the SF. Also, in the BF, the sizes of the microscales approached the size of oil droplets observed at sea (50–400 μm), which means that the turbulence in the BF closely resembles the turbulence occurring at sea during breaking waves. Hence, the BF is preferable for dispersant testing in the laboratory. [ABSTRACT FROM AUTHOR]

Scaling analyses on geophysical measurements of electrical conductivity, gamma radiation, and magnetic fields, at the Oak Ridge Reservation were conducted. The electrical conductivity and magnetic data exhibited multifractality in the north-south and east-west directions. The radiation data were observed to be non-scaling; a variogram with a sill was found to be more appropriate. The scaling of the EC and magnetic was generally within a range smaller than the maximum distance selected, as periodicity dominated at the larger distances. The electrical conductivity had anisotropy in the scaling of their variograms. But the magnetic data appear to have an isotropic scaling. The underlying statistics of the fields were near Gaussian for the electrical conductivity, but essentially Gaussian for the magnetic data. In environmental hydrogeology, knowledge of the spatial distribution of the intrinsic permeability, K, is very helpful in understanding the transport and spreading of contaminant plumes. Our previous studies have shown that the subsurface permeability, K, is multifractal. Detailed measurement of K is costly. Hence, large data sets of value collected both on a fine scale and over large distances are rare. In this study, we hypothesize that geophysical data could be used indirectly as a surrogate measurement for K, for obtaining statistical information on scale limited K data, and perhaps, directly at sites where K and electrical conductivity are correlated. [ABSTRACT FROM AUTHOR]

Focuses on the role of capillarity in transient seepage situations. Equations for water flow in variably saturated media in dimensionless form; Information on soil moisture and hydraulic conductivity; Definition of seepage face.

Provides information on the investigation of steady seepage of water from two-dimensional domains. Properties of three dimensionless parameters; Interpretation of results of the mathematical modeling; Presentation of nomographs for simulating trenches and dams.

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

With the increase in transport of oil by rail, the probability of oil spills in rivers has increased. Traditionally, focus has been placed on oil slicks moving on the water surface. However, the density of bitumen oil carried by rail within and from Canada to the United States can exceed that of freshwater, causing this oil to get submerged in the water column. This also has the potential of forming oil particle aggregates (OPAs) upon interaction with suspended sediments. The energy-dissipation rate is a key parameter for predicting the formation of oil droplets, and for this purpose, expressions are developed to estimate the energy-dissipation rate at various depths in the river using easily measured quantities such as water depth, streambed slope, and streambed roughness. The formulation showed that for a stream 30 m wide with a natural slope of 1/1,000 and roughness height of 1.0 cm, the average and maximum energy-dissipation rates are 0.01 and 0.22 W/kg , respectively. The average value is comparable to spilling breakers of height around 0.3 m, and the maximum value is comparable to those obtained from plunging breakers of 0.30-m-high waves. The large average value suggests that breakup of droplets in streams is higher than in the open sea under regular waves. [ABSTRACT FROM AUTHOR]

Intertidal aquifers are hotspots of biogeochemical cycling where nutrients and contaminants are processed prior to discharge to the ocean. The nature of the dynamic subsurface mixing zone is a critical control on mitigating reactions. Simulation of density‐dependent, variably saturated flow and salt transport incorporating realistic representations of aquifer heterogeneity was conducted within a Monte Carlo framework to investigate influence of nonuniform permeability on intertidal groundwater flow and salt transport dynamics. Results show that heterogeneity coupled with tides creates transient preferential flow paths within the intertidal zone, evolving multiple circulation cells and fingering‐type salinity distributions. Due to heterogeneity, strain‐dominated (intense mixing) and vorticity‐dominated (low mixing) flow regions coexist at small spatial scales, and their spatial extent reaches peaks at high tide and low tide. Such topological characteristics reveal complex tempo‐spatial mixing patterns for intertidal flow with localized areas of high and low mixing intensities, which have implications for intertidal biogeochemical processing. Plain Language Summary: In marine coastal environments, groundwater‐seawater mixing and exchange have been identified as critical factors affecting biogeochemical cycles and nutrient loads from aquifers to coastal waters. Our results for the first time demonstrate a dynamic response of intertidal flow topology and preferential flow paths to tides in the presence of aquifer heterogeneity. Heterogeneity coupled with tides results in different types of mixing than homogeneous or nontidal systems, which is important for geochemical reactions in the beach. These results highlight the importance of considering geologic heterogeneity in studies of groundwater flow and solute transport processes in tidally influenced beach aquifers. Key Points: Heterogeneity coupled with tides creates transient preferential flows within the intertidal zone, altering salinity distributionStrain‐dominated and vorticity‐dominated intertidal flow regions coexist at small spatial scales due to geologic heterogeneityHeterogeneity increases spatial variability of mixing of pore water flowing through the intertidal zone [ABSTRACT FROM AUTHOR]

Competing time scales involved in rapid rising micro-droplets in comparison to substantially slower biodegradation processes at oil-water interfaces highlights a perplexing question: how do biotic processes occur and alter the fates of oil micro-droplets (<500 μm) in the 400 m thick Deepwater Horizon deep-sea plume? For instance, a 200 μm droplet traverses the plume in ~48 h, while known biodegradation processes require weeks to complete. Using a microfluidic platform allowing microcosm observations of a droplet passing through a bacterial suspension at ecologically relevant length and time scales, we discover that within minutes bacteria attach onto an oil droplet and extrude polymeric streamers that rapidly bundle into an elongated aggregate, drastically increasing drag that consequently slows droplet rising velocity. Results provide a key mechanism bridging competing scales and establish a potential pathway to biodegradation and sedimentations as well as substantially alter physical transport of droplets during a deep-sea oil spill with dispersant. [ABSTRACT FROM AUTHOR]

Tides have been recognized as a major driving forcing affecting coastal aquifer system, and deterministic modeling has been very effective in elucidating mechanisms caused by tides. However, such modeling does not lend itself to capture embedded information in the signal, and rather focuses on the primary processes. Here, using yearlong data sets measured at beaches in Alaska Prince William Sound, we performed spectral and correlation analyses to identify temporal behavior of pore-water pressure, temperature and salinity. We found that the response of the beach system was characterized by fluctuations of embedded diurnal, semidiurnal, terdiurnal and quarterdiurnal tidal components. Hydrodynamic dispersion of salinity and temperature, and the thermal conductivity greatly affected pore water signals. Spectral analyses revealed a faster dissipation of the semi-diurnal component with respect to the diurnal components. Correlation functions showed that salinity had a relatively short memory of the tidal signal when inland freshwater recharge was large. In contrast, the signature of the tidal signal on pore-water temperature persisted for longer times, up to a week. We also found that heterogeneity greatly affected beach response. The response varied from a simple linear mapping in the frequency domain to complete modulation and masking of the input frequencies. [ABSTRACT FROM AUTHOR]

The effects of mixing time and energy on Alaska Northern Slope (ANS) and diluted bitumen Cold Lake Blend (CLB) were investigated using EPA baffled flask test. Dispersion effectiveness and droplet size distribution were measured after 5–120 min. A modeling method to predict the mean droplet size was introduced for the first time to tentatively elucidate the droplet size breakup mechanism. The ANS dispersion effectiveness greatly increased with dispersant and mixing energy. However, little CLB dispersion was noted at small energy input ( ε = 0.02 Watt/kg). With dispersant, the ANS droplet size distribution reached quasi-equilibrium within 10 min, but that of CLB seems to reach quasi-equilibrium after 120 min. Dispersants are assumed ineffective on high viscosity oils because dispersants do not penetrate them. We provide an alternative explanation based on the elongation time of the droplets and its residence in high intensity zones. When mixing energy is small, CLB did not disperse after 120 min, long enough to allow the surfactant penetration. Our findings suggest that dispersants may disperse high viscosity oils at a rougher sea state and a longer time. The latter could determine how far offshore one can intervene for effective responses to a high viscosity oil spill offshore. [ABSTRACT FROM AUTHOR]

Knowledge of the droplet size distribution (DSD) of spilled oil is essential for accurate prediction of oil dissolution and biodegradation. To predict DSD in turbulent flow, understanding the two resisting forces to droplet breakup are important: oil-water interfacial tension (IFT) and oil viscosity. Most existing predictive models consider only resisting force to droplet breakup due to IFT. However, in situations (e.g., high oil viscosity or low IFT) when oil viscosity becomes important, neglecting the resistance to breakup due to oil viscosity overestimates the extent of droplet breakage, and produces erroneously droplets of smaller size than reality. For these reason, we introduced a comprehensive conceptual-numerical model, VDROP, capable of simulating the transient droplet size distribution (DSD) in turbulent regimes while accounting for both oil viscosity and the oil-water IFT in resisting breakup. The residence time of high viscosity (and/or small IFT) oils in systems is more important than that of the low viscosity (and/or large IFT) oils. An expedient formulation was introduced to account for the residence time of high viscosity oils. Results showed that the model was able to reproduce the transient droplet size distribution of both low and high viscosity oils. VDROP was then used to provide the DSD of oils in breaking waves, and various IFT (due to usage of surfactant) and oil viscosities were considered. The results show that the transient DSD of high viscosity oils was bimodal and converged to unimodal when approaching steady state, which occurred within 2 h for considered case. [ABSTRACT FROM AUTHOR]

There is considerable interest in addressing soils contaminated with per- and polyfluoroalkyl substances (PFAS) because of the PFAS in the environment and associated health risks. The neutralization of PFAS in situ is challenging. Consequently, mobilizing the PFAS from the contaminated soils into an aqueous solution for subsequent handling has been pursued. Nonetheless, the efficiency of mobilization methods for removing PFAS can vary depending on site-specific factors, including the types and concentrations of PFAS compounds, soil characteristics. In the present study, the removal of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) from artificially contaminated soils was investigated in a 2D laboratory setup using electrokinetic (EK) remediation and hydraulic flushing by applying a hydraulic gradient (HG) for a duration of 15 days. The percent removal of PFOA by EK was consistent (∼80%) after a 15-day treatment for all soils. The removal efficiency of PFOS by EK significantly varied with the OM content, where the PFOS removal increased from 14% at 5% OM to 60% at 50% OM. With HG, the percent removal increased for both PFOA and PFOS from about 20% at 5% OM up to 80% at 75% OM. Based on the results, the mobilization of PFAS from organic soil would be appropriate using both hydraulic flushing and EK considering their applicability and advantages over each other for site-specific factors and requirements. [Display omitted] • PFAS mobilization from soils with different organic matter contents was investigated. • The organic matter content in soils substantially affects the mobilization efficiency of PFAS. • PFAS removal from soils by electrokinetics and hydraulic flushing increases with higher organic content. • Hydraulic flushing worked better for mobilizing PFAS from highly organic soils. [ABSTRACT FROM AUTHOR]

Summary: The submarine outlet of a coastal confined aquifer is usually covered by less-permeable material such as silt and fine sand which forms a sloping or almost flat seabed. Previous analytical studies of the tide-induced head fluctuation usually assumed a vertical interface between the outlet-capping and the seawater and neglected the effects of the outlet-capping’s slope. Here we conducted a series of numerical simulations to investigate the effect of the slope of the outlet-capping on the tide-induced head fluctuations in a coastal confined aquifer. The numerical simulations demonstrated that when the hydraulic diffusivity, slope and/or the outlet-capping leakance are large, the tidal loading effect is relatively weak and the leakance dominates. In this case the analytical solution applies. In general, the joint actions of the outlet-capping leakance and the tidal loading effects result in complicated, 2-dimensional flow in the aquifer near the shoreline. For aquifers with small hydraulic diffusivity, small slope and/or small outlet-capping leakance, the outlet acts approximately as a no-flow boundary condition and the tidal loading dominates. In this case, negative phase shifts (time–advance) may occur near the coastline. The study provides potential guide to infer the aquifer’s submarine structure and parameter from tidal head fluctuation observations in inland wells. [Copyright &y& Elsevier]

Summary: This paper investigated the tide-induced head fluctuation in a coastal confined aquifer with an infinitely-extending semipermeable roof. The roof is overlain by an unconfined aquifer terminating at the coastline. Previous analytical studies ignored the effect of the elastic storage of the semipermeable roof. Our model incorporated this effect. The analytical solution indicated that the increase of the elastic storage of the offshore semipermeable roof may significantly enhance the tidal head fluctuation in the confined aquifer at the coastline. A threshold leakance exists in the sense that when the leakance is less than the threshold, the head fluctuation at the coastline will become insensitive to leakance and the roof can be regarded as impermeable. The threshold strongly depends on the roof’s elastic storage and decreases as the roof’s elastic storage increases, indicating that the roof’s leakage effect is significantly enhanced by the increase of the roof’s elastic storage. [Copyright &y& Elsevier]

Abstract: This paper considered the tide-induced head fluctuations in two coastal multi-layered aquifer systems. Model I comprises two semi-permeable layers and a confined aquifer between them. Model II is a four-layered aquifer system including an unconfined aquifer, an upper semi-permeable layer, a confined aquifer and a lower semi-permeable layer. In each model, the submarine outlet of the confined aquifer is covered with a skin layer (“outlet-capping”). Analytical solutions of the two models are derived. In both models, leakages of the semi-permeable layers decrease the tidal head fluctuations. The outlet-capping reduces the aquifer’s head fluctuation by a constant factor and shifts the phase by a positive constant. The solution to Model II explains the inconsistency between the relatively small lag time and the strong amplitude damping effect of the tidal head fluctuations reported by Trefry and Johnston [Ground Water 1998;36:427–33] near the Port Adelaide River, Australia. [Copyright &y& Elsevier]

Summary: This paper considers a leaky aquifer system comprising an unconfined aquifer, a confined aquifer, and a confining layer (the aquifer’s roof). The unconfined aquifer terminates at the coastline, the confined aquifer and its roof extend under the sea for a certain distance. The aquifer’s submarine outlet is covered by a thin layer of sediment (referred to as the “outlet-capping” hereafter) with properties dissimilar to the aquifer. Previous studies either neglected the leakage through the aquifer’s roof or the outlet-capping. This paper considers both effects and gives an analytical solution to describe the tide-induced head fluctuation in the aquifer system. For aquifers with zero or infinite offshore length, or with impermeable roof or outlet-capping, or without the outlet-capping, existing solutions in the literature are obtained. We defined the threshold value for the offshore aquifer length, which was found to be less than 5km for typical coastal aquifer systems. For an aquifer with its offshore length greater than the threshold, the inland head fluctuation becomes insensitive to variations of this length and the outlet-capping’s leakance. The leakage through the offshore roof decreases the threshold value. When the offshore confined aquifer is short, the inland head fluctuation increases with the outlet-capping’s leakance. In this case negative phase shift occurs near the coastline only for aquifers with small leakages through the offshore roof and the outlet-capping. In general, the combined actions of the tidal loading, the leakage and length of the offshore roof, and the leakage of the outlet-capping lead to complex, non-monotonic dependency of the inland head fluctuation on the aquifer parameters. [Copyright &y& Elsevier]

We used multifractals to analyze the Lebanese topography focusing on Mount Lebanon. The elevation data were obtained from NASA STRM Global Digital Elevation of Earth Land, spaced at 80 m in the East-West direction, and at 90 m in the North-South direction. After transforming the grid to be perpendicular and parallel to the range, we found anisotropic scaling from 500 m to 10,000 m, and it reflected the fact that the Lebanese topography was more correlated in the direction perpendicular to the mountain range, probably due to occurrence of valleys and ridges in that direction. We estimated the parameters of the Universal Multifractal (UM) model and found α = 1. 4 5 and c 1 = 0. 0 5 , consistent with values reported for topography. The UM parameter H was found to be 0.72 across the range and 0.57 along the range, the latter value agrees with prior observations. However, the larger value across the range is consistent with the higher spatial correlation in that direction. We introduced a new expression for the 2D power spectral density, and we showed that it can decently capture the anisotropic scaling. We also generated multiple realizations and we showed that the generation of anisotropic scaling did not alter the underlying parameter values α and c 1 of the UM model. We also proposed an approximate method for generating conditional simulations, and we showed that through a judicious selection of values, one may reproduce approximately the observed field values at the desired locations. We believe such an approach could be used to generate realistic simulations of fields that are time-invariants, such as topography and soil properties. [ABSTRACT FROM AUTHOR]

The tempo-spatial patterns of Covid-19 infections are a result of nested personal, societal, and political decisions that involve complicated epidemiological dynamics across overlapping spatial scales. High infection "hotspots" interspersed within regions where infections remained sporadic were ubiquitous early in the outbreak, but the spatial signature of the infection evolved to affect most regions equally, albeit with distinct temporal patterns. The sparseness of Covid-19 infections in the United States was analyzed at scales spanning from 10 to 2,600 km (county to continental scale). Spatial evolution of Covid-19 cases in the United States followed multifractal scaling. A rapid increase in the spatial correlation was identified early in the outbreak (March to April). Then, the increase continued at a slower rate and approached the spatial correlation of human population. Instead of adopting agent-based models that require tracking of individuals, a kernel-modulated approach is developed to characterize the dynamic spreading of disease in a multifractal distributed susceptible population. Multiphase Covid-19 epidemics were reasonably reproduced by the proposed kernel-modulated susceptible-infectious-recovered (SIR) model. The work explained the fact that while the reproduction number was reduced due to nonpharmaceutical interventions (e.g., masks, social distancing, etc.), subsequent multiple epidemic waves still occurred; this was due to an increase in susceptible population flow following a relaxation of travel restrictions and corollary stay-at-home orders. This study provides an original interpretation of Covid-19 spread together with a pragmatic approach that can be imminently used to capture the spatial intermittency at all epidemiologically relevant scales while preserving the "disordered" spatial pattern of infectious cases. [ABSTRACT FROM AUTHOR]

A numerical framework was developed to study oil-particle aggregate (OPA) formation by incorporating NEMO3D code and the A-DROP model into an open-source platform, OpenFOAM. The developed framework was then used to study oil transport and OPA formation in a two-dimensional (2D) hypothetical river at a depth of 3.0 m. The river's hydrodynamic profile was used in conjunction with the A-DROP model to simulate OPA formation, whereas the NEMO3D model was used to track the movement of the oil droplets and OPAs. Results suggest that an increase in buoyancy results in a decrease in the streamwise variance and spreading coefficient. The small (i.e., 50 μm) droplets became entrained in the deep water column at high-energy dissipation rates, which enhanced OPA formation. The large (i.e., 200 μm) droplets aggregated much more rapidly than the small ones in the same turbulence environment owing to differential sedimentation. In general, OPA formation in the upper rivers was dominated by collisions caused by differential sedimentation, while in the deep water column, collision caused by turbulence shear plays a more critical role. The aggregation rates of the formed OPAs were less than 60% within a short period (20 min) in a river with relatively mild turbulence (ε<5×10−4 W/kg). [ABSTRACT FROM AUTHOR]

Understanding the trajectory of oil droplets in crossflow jets is important to estimate the pathways of hydrocarbons and to plan countermeasures. We report experimental results of an oil jet with release velocity around 1.5 m/s in a crossflow of 0.3 m/s. The hydrodynamics of the jet obtained with the Large Eddy Simulation (LES) were used to predict the migration of the oil droplets. Two Lagrangian techniques were explored, one with the inertia of the droplet is considered and the other that treats the droplets as massless particles with rising velocities corresponding to their size. We did not note a large difference between the two approaches. The droplets showed stronger segregation in the vertical direction, which renders the usage of a Gaussian distribution approximation in the vertical inapplicable. The dispersion coefficient at each direction was computed for different-sized droplets. The eddy diffusivity computed based on Boussinesq gradient approximation using the LES data was compared with the dispersion coefficients obtained based on Lagrangian tracking. We also found that droplets 500 μ m and larger escape the vortex while smaller ones get trapped within the vortex. A similar outcome was observed using a vortex trapping function based on inward–outward force balancing at the elevation of the vortex core. The counter-rotating vortex pair (CVP) altered the distribution of droplets of 1 mm and smaller significantly, and bimodal concentration distributions with peaks near the CVP vortex cores and minimum concentration near the center plane were obtained in the lateral–horizontal​ direction. Therefore, measurements of the oil droplet size distribution (DSD) in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume. • Oil droplet transport with Lagrangian techniques using the hydrodynamics obtained through large eddy simulation. • Larger droplets were observed near the top boundary of the plume in our experiments. • Eddy diffusivity based on Boussinesq approximation using LES and the dispersion coefficients based on Lagrangian tracking. • Trapping of 400 μ m and smaller droplets in the counter rotating vortex pair. • Droplet size distribution in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume. [ABSTRACT FROM AUTHOR]

The dispersion of oil droplets in rivers was numerically investigated for uniform flow in a hypothetical wide river with a depth of 3.0 m. The river hydrodynamics profile was used in conjunction with the VDROP model to produce the oil droplet size distribution (DSD), whereas the NEMO3D model was used to track the movement of the oil droplets. Results suggest that the gradient of eddy diffusivity significantly affected the upward-normal (i.e., quasi-vertical) transport of the droplets, and caused them to mix rapidly through the depth. We also found that an increase in buoyancy resulted in a decrease in the streamwise variance and spreading coefficient. Oil droplets broke up due to the relatively large energy dissipation rates in the river at approximately 1.0 m below the surface and deeper. The droplet breakup varies DSD in the river water column, which may subsequently affect other chemo-physical processes (e.g., oil-particle aggregation). The breakup efficiency is affected by a system-dependent parameter Kb , which reflects the uncertainty of a system. The steady-state DSD was bimodal for the case Kb=0.05 , whereas it was unimodal for larger Kb values (i.e., Kb=1.0 and 0.25), respectively. More small-sized droplets were generated and persisted in the deep-water column with larger Kb values. The droplet breakup also enhanced the streamwise spreading of the plume. The effect of droplet entrainment on oil dispersion was studied by assuming constant entrainment probabilities of surface oil droplets. The oil DSD varied with different droplet entrainment probabilities, and the number of oil droplets generated in the water column decreased significantly with a decrease in the entrainment probability of the oil droplets. [ABSTRACT FROM AUTHOR]

• Multiphase large eddy simulation of an oil jet in crossflow was conducted. • Oil trajectory and dilution rate were compared to experiments and integral model. • Multiphase model was modified to include the transport term due to the rise velocity of oil droplets. • Jet and crossflow interference created small-sized eddies near the upper edge of the plume. • Counter rotating vortex pair is likely to enhance the mixing of chemicals and droplets within the plume. Experimental results were presented for the release of diesel oil from a one-inch (2.5 cm) vertical pipe in a crossflow at 0.27 m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7.1 × 10 3. In the experiments, the plume shape was photographed, and the oil droplets were measured at two vertical locations on the center axis of the plume. Acoustic Doppler velocimetry (ADV) data was also obtained and compared to numerical predictions. The plume was simulated using large eddy simulation (LES), and the mixture multiphase model. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. Using the rise velocity based on d 50 (volume-median) droplet size in the lower part of the plume allowed us to capture the lower boundary of the plume, but the estimated upper boundary of the plume penetrated less into the crossflow as compared to the experimental findings. However, using the rise velocity of the d 50 at the upper part of the plume allowed one to estimate the upper boundary of the plume. As the droplets are too small to be resolved by the LES, we could not use a systematic approach to allow the multiphase plume to spread to mimic the observations. Based on the simulation results, the interaction between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume. [ABSTRACT FROM AUTHOR]

• Beach stratification and inland recharge affect the oil persistence in PWS beaches. • Inland recharge prevents oil from infiltrating into lower low-permeability layer. • High seaward flow in upper high-permeability layer causes washout of oil to the sea. • Depth (and slope) of bedrock greatly alters hydrodynamics in the lower beach layer. A combined field and numerical study of water flow and solute transport was conducted along a clean transect of a tidal gravel beach in Smith Island, Prince William Sound (PWS) that was heavily polluted after the Exxon Valdez oil spill. Water table and pore water salinity were directly measured in the field. The numerical model MARUN, validated with the field observations, was used to simulate subsurface flow and dissolved salt transport processes. Our study identified a two-layer hydraulic structure in the beach, a high-permeability upper layer and a low-permeability layer at the bottom. Numerical simulations indicated that the density gradient between the saltwater and freshwater strongly affects solute transport in the intertidal zone of the beach. A sensitivity study indicated that depth to and slope of the bedrock had major effects on solute transport in the lower layer, but minor effects in the upper layer. A deep bedrock caused the water particles travelling in the lower layer to penetrate deeper in the beach. Our study revealed high terrestrial freshwater recharge to the transect which promotes the removal of oil in two-layer beaches by maintaining the water table at or above the interface of the two layers. The study presented in this paper has strong implications on the oil persistence and associated removal strategies along the Alaskan coastline polluted with oil. Findings from this work in relation to oiled beaches include: 1) oil tends to persist at locations of small freshwater recharge and 2) Prior to oil arriving to the shoreline, one could minimize oil penetration into the beach by releasing water onto the beach at the high tide line during low tides. [ABSTRACT FROM AUTHOR]

Oil weathering models are essential for predicting the behavior of spilled oil in the environment. Most models use a "Pseudo Component" (PC) approach to represent the wide range of compounds found in petroleum products. Within the approach, rather than modeling each individual compound in an oil, a manageable number of PCs are developed that represent whole classes of compounds. However, previous studies focused mainly on traditional crude oils and did not develop a generic approach to create an optimal set of PCs for a variety of oils. In developing the updates to the NOAA oil weathering model, we propose herein a generic approach to construct PCs using oil distillation data to capture the complexity of oil evaporative weathering. We validated our approach with 899 oils from the Automated Data Inquiry for Oil Spills (ADIOS) oil library and found that an optimal set of sixteen PCs should be used. These PCs include two with low boiling point (below 144 °C), one with a high boiling point (above 400 °C), and thirteen constructed within a middle range of boiling points with a temperature resolution of 20 °C. Our simulation tests suggested that this set of sixteen PCs adequately characterizes oil evaporation processes for a wide variety of oils. [Display omitted] • A pseudo-component approach is developed for modeling oil evaporative weathering. • 16 pseudo-components constructed to model oil evaporation are tested with 899 oils. • Empirical formulas are derived to estimate pseudo-components' density and viscosity. [ABSTRACT FROM AUTHOR]

The microbial degradation of crude oil stranded on seashores is usually much slower than that of dispersed oil at sea. This is usually attributed to nutrient limitation and higher oil concentrations on beaches than in dispersed plumes, in addition to the low moisture content and transient hypersaline conditions of the upper intertidal and supratidal zones. Here, we investigated the effect of hypersaline conditions, oil concentration, and nutrient limitation on the hydrocarbonoclastic activity. Beach sand, with oil concentrations of 1 and 10 mL/kg, was infiltrated with seawater at salinities of 30, 90, and 160 g/L to 20% saturation, with and without the addition of nutrients. Oil chemistry, 16 S rRNA gene amplicon, and metagenomic sequencing analyses were conducted every 30 days for 180 days. The biodegradation of aromatic hydrocarbons was much slower at higher salinities, while that of alkanes was not noticeably affected, and the addition of nutrients only marginally enhanced the biodegradation of hydrocarbons. The relative abundance and diversity of genera varied substantially with the increase in pore water salinity, whereby halophilic hydrocarbon-degrading microorganisms, particularly in the Marinobacter genus, were significantly abundant only under hypersaline conditions. The enzymes were considerably less abundant at high salinities, mainly for those associated to aromatic hydrocarbon degradation pathways. Consequently, occasional inundation of the upper parts of oiled sandy beaches with seawater to decrease the pore water salinity and reseed the contaminated region with indigenous hydrocarbon degraders, along with the concomitant addition of fertilizers, could be a suitable, non-destructive, and inexpensive response tool for enhancing the biodegradation of beached crude oil, particularly that of the aromatic fraction. [Display omitted] • Hydrocarbonoclastic activity is much slower in beaches relative to dispersed plumes. • Biodegradation of aromatics in sandy beaches is noticeably slower at higher salinity. • Biodegradation of alkanes in sandy beaches is not affected by salinity. • Marinobacter genus were significantly abundant only under hypersaline conditions. • Enzymes associated to aromatic degradation pathways were much less abundant at high salinities. [ABSTRACT FROM AUTHOR]