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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.

Ammonium and nitrate were used as nitrogen sources to support microbial biodegradation of crude oil in continuous-flow beach microcosms to determine whether either nutrient was more effective in open systems, such as intertidal shorelines. No differences in the rate or extent of oil biodegradation were observed, regardless of whether these nutrients were provided continuously or intermittently. Nutrients were provided once every two weeks to intermittent-input microcosms and washed out within four to five days. In continuous-input microcosms, ammonium and nitrate were assimilated as quickly as they were provided during the first week, but both accumulated to greater than 10 mg N/L thereafter. The sensitivity of the oil mineralization rate to nutrient input decreased rapidly as the extent of oil degradation increased, and after about two weeks the rate of oil-mineralization appeared to be independent of nutrient input. Therefore, there may be little value in maintaining a long-term supply of nutrients in contact with oil-contaminated sediments. The rates of microbial assimilation of ammonium and nitrate followed similar trends. Both compounds were assimilated more slowly as the extent of oil biodegradation increased, and the nitrate uptake rates approached zero after about two weeks. Ammonium assimilation continued at a low rate throughout the six-week experiment, but this did not appear to affect the rate of oil mineralization. Assimilation of ammonium resulted in a sharp decrease in the pH of the synthetic seawater that was pumped continuously through the microcosms, but nitrate had a much smaller effect on pH. The magnitude of the ammonium-associated pH change was never as large as was observed in previous studies involving oil biodegradation in batch reactors, however, and did not affect the oil-biodegradation rate. CE Database subject headings: Crude oil; Biodegradation; Oil spills; Nutrients; Kinetics; Shore protection.

The current U.S. Environmental Protection Agency protocol for testing the effectiveness of dispersants, the swirling flask test, has been found to give widely varying results in the hands of different testing laboratories. The sources of the ambiguities in the test were determined by considering several options in a rigorous systematic fashion. Options considered were variability among three operators and the variability and limitations of three analytical instruments in establishing a calibration curve for oil/dispersant mixtures. Other options included flask type, impact of operational variables (rotational speed, mixing time, settling time, and oil:dispersant ratio), development of a revised procedure for dispersant effectiveness, reproducibility and repeatability of the revised procedure, and development of selection criteria for screening of dispersants. A redesign of the test flask, which is characterized by having baffles with a stopcock at the bottom for sample collection, was deemed necessary to accomplish reproducibility within operator and between operators. The results indicated that the baffled flask provided a total coefficient of variation (variations within operator and between operators) less than 11% compared to above 100% in some cases for the swirling flask. CE Database subject headings: Oil spills; Crude oil; Dispersion; Screening; Sea water; Protocols.

The current U.S. Environmental Protection Agency (EPA) protocol for testing the effectiveness of dispersants for use in treating oil spills on the open water, the swirling flask test (SFT), has been found to give widely varying results in the hands of different testing laboratories. Part I addressed the sources of the ambiguities in the EPA SFT and the development of a new test referred to as the baffled flask test (BFT). In this part of the series, further experiments were conducted for estimating the repeatability of three operators in determining the effectiveness of 18 dispersants by both the EPA SFT and the BFT methods. Overall statistical analysis of the results indicated that the coefficient of variation by the BFF was only 7.8% compared to 21.9% for the EPA SFT. The mean percent effectiveness of the EPA SFF was only 19.7% as compared to 64.6% for the BFT. Proposed selection criteria for screening of dispersants for listing on the National Contingency Plan Product Schedule have been developed. CE Database subject headings: Oil spills; Crude oil; Dispersion; Screening; Sea Water; Protocols.

A response alternative for floating vegetable oil spills based on sedimentation of negatively buoyant oil-mineral aggregates followed by anaerobic biodegradation in the sediments is under investigation. Sedimentation of floating canola oil by interaction with montmorillonite was demonstrated, and the oil-binding capacity of wet and dry clay was determined. Only two of the four factors that were investigated produced statistically significant effects on the sedimentation of floating oil: Clay was required for oil sedimentation to occur, and high mixing energy during the initial contact between oil and clay reduced the amount of oil that could be transported to the sediment compartment. The addition of ferric chloride as a coagulant and the mixing energy imparted during the flocculation period did not significantly affect the extent to which oil was transported to the sediment compartment. The maximum oil-binding capacity of dry high-surface-area (220-270 [m.sup.2]/g) clay was about three times higher than for wet clay (1 g oil/g dry clay versus 0.3 g oil/g wet clay). The oil-binding capacity of low-surface-area (20-40 [m.sup.2]/g) clay was less affected by prior interaction with water (0.7 g oil/g dry clay versus 0.6 g oil/g wet clay), but it was much less effective in promoting sedimentation of floating oil. The differences between the oil sedimentation abilities of these two types of clay suggest that the success of this remedial alternative requires a clear understanding of the nature of the oil-mineral interactions. CE Database subject headings: Sedimentation; Oil spills; Aggregates; Biodegradation.

An ultrafiltation membrane bioreactor was evaluated for biodegradation of methyl tert-butyl ether (MTBE) in contaminated water. The system was fed 5 mg/L MTBE in granular activated carbon (GAC) treated Cincinnati tap water containing ample buffer and nutrients. Within 120 days the culture had adapted to membrane operational conditions and was consistently achieving greater than 99.95% biological removal of both MTBE and tert-butyl alcohol. This condition was steadily maintained for the next 200 days of study. Effluent dissolved organic carbon values remained at or below concentrations of the feed GAC treated tap water alone. An increase in biomass concentration as measured by volatile suspended solids was observed to correlate with an increase in MTBE removal efficiency. Some operational observations, including fouling, recovery from an accident, and overall performance, are described. CE Database keywords: Biodegradation; Aerobic processes; Biological treatment; Biomass; Ohio; Water treatment.

Methyl tert-butyl ether (MTBE) contamination in groundwater often coexists with benzene, toluene, ethylbenzene, and xylene (BTEX) near the source of the plume. Tertiary butyl alcohol (TBA) is a prevalent intermediate of MTBE degradation. Therefore, there is a significant potential for interference of MTBE and TBA degradation by the presence of BTEX whether treatment is in situ or ex situ. In this study, the effect of BTEX on the degradation of MTBE and TBA was examined using a mixed bacterial culture enriched on MTBE and BTEX. In batch studies, the presence of BTEX did not have a significant effect on MTBE degradation, but did have a slight effect on TBA degradation. Under continuous flow conditions, all compounds degraded simultaneously. Normalizing rates to the MTBE loading to the reactor indicates that BTEX may assist in the development of the biomass for TBA and overall MTBE degradation. Using denaturing gradient gel electrophoresis, several diverse organisms were identified, two of which showed very high similarity with PM1, a known MTBE degrader. CE Database keywords: Biodegradation; Ground water; Water treatment; Gasoline.

Bioremediation of oil spills is characterized by a shift in the population of microorganisms toward gram-negative bacteria from the alpha-Proteobacteria and the Flexibacter-Cytophaga-Bacteroides phylum. This was the conclusion of a study of a field experiment simulating a coastal oil spill.

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.