Beach geomorphic factors for the persistence of subsurface oil from the Exxon Valdez spill in Alaska

Abstract

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.

Geomorphic Factors Related to the Persistence of Subsurface Oil from the Exxon Valdez Oil Spill

“…The nearly anoxic conditions in this low-permeability layer negatively affected the ability of microbes to degrade the oil. In another study, Xia and Boufadel (2011) identified beach slope as a geomorphic factor that influenced hydrologie flushing rates locally within a beach. It is particularly challenging to characterize subsurface hydrology in the extremely heterogeneous shoreline environments of PWS without subsurface investigation, and our results indicate almost no difference between the rates of occurrence of heavier subsurface oil at sites with and the rates at those without stream mouths or evidence of signiflcant groundwater flow.…”

“…Lastly, hydrologie processes such as wave backwash, groundwater flow, and surface-water runoff are generally more energetic on a steeper intertidal slope. In studies of a highly exposed gravel beach with heavy remaining subsurface oil, the findings of Xia and Boufadel (2011) imply that hydrologie processes are more efflcient at oil flushing and nutrient replenishment on steep gravel beaches. A steep nearshore zone, with its accompanying deeper water, allows waves to break near the shore or on the intertidal zone.…”

Petroleum hydrocarbon contaminations in the intertidal seawater after the Hebei Spirit oil spill – Effect of tidal cycle on the TPH concentrations and the chromatographic characterization of seawater extracts

“…Boufadel (2010, 2011) and reported that subsurface oil persisted in the beach with two hydraulically different layers and small fresh groundwater flow. Xia and Boufadel (2011) found that mild beach slop and armoring of beach surface were the major elements for oil persistence. Oil persistent in beaches are possibly re-dissolved or dispersed into the water column and may be potential threat to marine organisms (Michel et al, 2009;Peterson et al, 2003;Short et al, 2006).…”

Evaluation of the biodegradation of Alaska North Slope oil in microcosms using the biodegradation model BIOB

“…To check for the possible limitation of interfacial area, the specific surface area per unit mass was evaluated for each of the islands by using the grain size distribution obtained from the literature. The average diameter of the sediment was 4.2 mm (Li and Boufadel, 2010), 7 mm (Xia et al, 2010), and 9.4 mm (Xia and Boufadel, 2011) for Eleanor Island (EL056C), Knight Island (KN114A), and Smith Island (SM006B), respectively. The grain size distribution of Eleanor Island presented in this study is not from a same beach as was used in the Venosa et al (2010) study.…”