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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]

Abstract: Despite great efforts including bioremediation, the 1989 Exxon Valdez oil spills persist in many gravel beaches in Prince William Sound, Alaska, USA. To explore this mystery, a lithium tracer study was conducted along two transects on one of these beaches. The tracer injections and transports were successfully simulated using the 2-dimensional numerical model MARUN. The tracer stayed much longer in the oil-persisting, right transect (facing landwand) than in the clean, left transect. If the tracer is approximately regarded as oils, oils in the upper layer would have more opportunities to enter the lower layer in the right transect than in the left one. This may qualitatively explain the oil persistence within the right transect. When the tracer is regarded as nutrients, the long stay of nutrients within the right transect implies that the oil persistence along the right transect was not due to the lack of nutrients during the bioremediation. [Copyright &y& Elsevier]

Delivery of dissolved chemicals to potentially bioremediate oil from the Exxon Valdez oil spill was investigated at Smith Island, Prince William Sound, Alaska. Two transects for tracer application were installed: one at a clean area and another at an oiled area. Tracer delivery occurred under ambient pressure through manifolds. Lithium in LiBr/sea water solution was the inert tracer, and the solution (82.6 mg/L of lithium) was released at a flow rate of 0.23 L/min for 58.5 h. While maintaining the flow rate, the solution was switched to sea water (i.e., 0.0 mg/L of lithium) for 16 h. The results show that the tracer moved landward with rising tides and seaward with falling tides. The plume got deeper moving landward and shallower moving seaward of the manifold. Thus, in situations where oil biodegradation is limited by the availability of nutrients or oxygen, applying these chemicals by this technique would allow them to reach entrapped oil seaward of the manifold from below. The seaward plume traveling speed (around 2.0 m/d) suggests that this technique is logistically feasible from a hydraulic point of view. [ABSTRACT FROM AUTHOR]

Delivery of dissolved chemicals to bioremediate oil from the Exxon Valdez oil spill was investigated at Beach EL056C of Eleanor Island, Prince William Sound, Alaska. The delivery technique was high pressure injection (HPI) of an inert tracer, lithium, at the approximate depth of 1.0 m into the beach near the mid-tide line. The results revealed that the maximum injection flow rate was 3.0 L/min and the associated pressure was around 196 kPa. Therefore, exceeding any of these values would probably cause failure of the injection system. The injected tracer was monitored at multiple depths of four surrounding observation wells, and the results showed that the tracer plume occupied an area of 12 m within 24 h. The tracer plume traveled at the average speeds of 10 m/d in the seaward direction and 1.7 m/d in other directions. The rapid movement under HPI and the large diameter of influence (3.0 m) indicated that bioremediation of the Exxon Valdez oil on this beach via injection of chemicals is logistically feasible. [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]

Oil from the 1989 Exxon Valdez oil spill persists in some of the Prince William Sound (Alaska) beaches and continues to be a potential threat to the fauna. This paper reports a field investigation during the summer of 2008 of groundwater flow and solute transport in a tidal gravel beach in Smith Island, Prince William Sound. The beach contains oil on one side, the left side (facing landward). Field measurements of water table, salinity, and tracer (lithium) concentration were obtained for an approximate duration of 64 h for two transects, the oiled transect and a clean transect (the right transect). It was found that the hydraulic conductivity and the fresh groundwater recharge into the two transects were similar. It was also found that the beach slope of the mid to high tidal zone along the oiled (left) transect was ~7.4% which is considerably smaller than that of the clean (right) transect (~11.8%). This suggests a higher flushing/replenishing of the right transect with nutrients and/or oxygen, which would have enhanced biodegradation of oil on the right transect if that oil was not washed by waves. We also found that the degree of oiling at each location was inversely dependent on the armoring of the beach surface with clasts and boulders. The applied tracer concentration at the left transect was less than 2% of the source or close to the background level at all locations except a seaward well closest to the applied location, indicating that the tracer applied was diluted or washed out from the beach during the application. Thus, in situations where oil biodegradation is limited by the availability of nutrients and/or dissolved oxygen, applying the chemicals on the beach surface would most likely not enhance oil biodegradation as the applied chemicals would be greatly diluted prior to reaching the oil. Thus, deep injection of nutrients and/or dissolved oxygen is probably the only option for enhancing oil biodegradation.