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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. DOI: 10.1061/(ASCE)0733-9372(2007)133:7(722) CE Database subject headings: Waves; Tides; Beaches; Tracers; Nutrients; Laboratory tests; Biological treatment.

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. DOI:10.1061/(ASCE)0733-9372(2006)132:6(616) CE Database subject headings: Oil spills; Nutrients; Biological treatment; Beaches.

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, [epsilon]. The study shows that the mixing in the BF is more uniformly distributed than that in the SE Flask average energy dissipation rates in the SF were about 2 orders of magnitude smaller than those in the BE The sizes of the microscales in the BF were found to be much smaller than that in the SE Also, in the BF, the sizes of the microscales approached the size of oil droplets observed at sea (50-400 [micro]m), 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. CE Database subject headings: Oil spills; Turbulence; Anemometers; Energy dissipation; Velocity; Time series analysis; Data collection.

Steady seepage from two-dimensional domains is investigated using a dimensionless formulation for variably saturated media that depends on three dimensionless parameters, M, n, and [Alpha]. The parameter M is the product of the anisotropy ratio and the squared ratio of the vertical length scale to the horizontal length scale. The parameter n increases with the uniformity of the pore sizes, and a represents the ratio of the domain height to the height of the capillary fringe. Our modeling results show that the seepage face height in rectangular domains is always larger than the seepage face height computed from saturated flow models. The results also show that the seepage face height increases with increasing M, increasing n, and/or decreasing [Alpha]. The outflows computed from the present model are always larger than the outflows computed by the Dupuit assumption. Nomographs for rectangular and trapezoidal domains simulating trenches and dams are presented.

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]

Self-designed electrokinetic setups were constructed to examine the differences in electromigration and electroosmotic rates in both sand and clay. Two dyes were analyzed separately to measure these phenomena within these two media types. The dyes used were a red food coloring (primary compound Allura Red) and a green food coloring (referred to as a "blue dye," as its migrating component was C-phycocyanin (C-PC) via SpirulinaBlue extract). The power supply had a 30 Voutput with ameasured 9.36±0.04 mAcurrent (0.054 mA/cm²) output. Electromigrationwas readily apparent for the red dye in both sand (9.12±1.57 cm/d) and clay (0.93±0.16) cm/d. It was also observed for the blue dye (C-PC) in sand (7.28±0.57 cm/d) but not in clay. A confirmation experiment for the blue dye in sand was performed at an identical voltage but a slightly lower current output (0.040 mA/cm²), and the migration rate was found to be similar, at 6.60±0.20 cm/d. For the blue dye in clay, the migration rate proceeded toward the cathode at 0.17 cm/d. Calculations indicate this phenomenon to be due to electroosmosis but may be due to a weak electromigration of the dye in protonated form. [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]

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]

The baffled flask test (BFT) has been proposed by United States Environmental Protection Agency to be adopted as the official standard protocol for testing dispersant effectiveness. The mixing energy in the baffled flask is investigated in this paper. Particle image velocimetry (PIV) was used to measure the water velocity in the flask placed at an orbital shaker that was rotated at seven rotation speeds: 100, 125, 150, 160, 170, 200, and 250 rpm. Two dimensional velocity fields in large and small vertical cross sections of the flask for each rotation speed were obtained. The one-dimensional (1D) energy spectra indicates the existence of inertial subrange. The estimated average energy dissipation rates were in the range 7.65 x 10-3 to 4 W=kg for rotation speeds of Ω = 100-250 rpm, of which it is larger than the one estimated by prior studies using single-point velocity measurement techniques for Ω = 100 and 200 rpm. Factors such as instruments used, velocity components measured, and different analysis methods could contribute to the discrepancies in the results. The Kolmogorov scale estimated in this study for all seven rotation speeds approached the size of oil droplets observed at sea, which is 50-400 µm. The average energy dissipation rate, ε and Kolmogorov microscale, η, in the flasks were correlated to the rotation speed, and it was found that ε = 9.0 x 10-5 Exp(0.043Ω) with R² = 0.97 and 77 = 1,463 Exp(-0.015Ω) with R² = 0.98. [ABSTRACT FROM AUTHOR]

The hydraulics of a gravel beach on Eleanor Island in Prince William Sound (PWS), Alaska, was investigated by measurements of the water table and by numerical simulations using the software SUTRA. Sediment samples were obtained from six wells at the approximate three depths: 0.30, 0.60, and 0.90 m, and they were sieved in the lab to generate the grain size distribution, and subsequently the saturated hydraulic conductivity, K0. The results indicated that the beach consisted of two layers: an upper layer with a high K0 and a lower layer with a low K0. In the landward portion of the intertidal zone, K0 was around 10-2 m/s and 10-5 m/s for the upper and lower layers, respectively. In the seaward portion of the intertidal zone, the K0 values were 10-4 m/s and 10-6 m/s in the upper and lower layers, respectively. The agreement of the model with the observed water table data was very good. A decrease in the slope of the beach in the seaward direction caused water to flow out from the lower layer and propagate seaward within the upper layer. This ensured that the water table seaward of the exit point was replenished and remained above the interface of the layers. The results suggest that the porosity of the beach decreases from 0.33 at the surface to around 0.05 at 1.0 m deep. The absence of oil on this beach is probably because the beach water table remained above the layers' interface during low tides. Using the calibrated model, it was found that the flow from land into the beach is around 6 m3/day (per meter parallel to the shoreline) and that the flow out of the lower layer varied with time reaching a maximum of 13 m3/(day·m) at low tide. The beach exchanges up to 7 m3/(day·m) with the sea. [ABSTRACT FROM AUTHOR]

A novel dimensionless formulation for water flow in two-dimensional variably saturated media is presented. It shows that scaling physical systems requires conservation of the ratio between capillary forces and gravity forces. A direct result of this finding is that for two physical systems to be hydraulically similar, the soil in the smaller system has to be coarser than the soil in the larger system. The new formulation is implemented in a finite-element model that compared favorably with published numerical results with a minimal mass balance error. Bayesian estimation using prior physical information was used to fit the model to experimental data that simulated tidal action in a laboratory beach. Results show that the model is not sensitive to the residual soil moisture or the parameter n in the van Genuchten model, but is sensitive to variation in the saturated hydraulic conductivity and the parameter α in the van Genuchten model. Nomographs based on the dimensionless formulation were used to scale the results of the laboratory beach to the range of natural beaches. [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]