An Overview of the Exxon Valdez Oil Spill, Prince William Sound, Alaska
David S. Page, Bowdoin College, Brunswick, ME      
Paul D. Boehm, Exponent, Maynard, MA 
John S. Brown, Exponent, Maynard, MA
Jerry M. Neff, Neff & Associates, LLC, Duxbury, MA

Where and Why do Remnants of the Exxon Valdez Oil Spill Persist?
David S. Page, Bowdoin College, Brunswick, ME   
Paul D. Boehm, Exponent, Maynard, MA 
John S. Brown, Exponent, Maynard, MA
Jerry M. Neff, Neff & Associates, LLC, Duxbury, MA

What are the Form, Chemical Composition, and Location of Remnants of the Exxon Valdez Oil Spill after 18 years?
Paul D. Boehm, Exponent, Inc., Maynard, MA       
David S. Page, Bowdoin College, Brunswick, ME
Jerry M. Neff, Neff & Associates LLC, Duxbury, MA
John S. Brown, Exponent, Maynard, MA
James A. Bragg, Creative Petroleum Solutions, LLC, Houston, TX
Ronald M. Atlas, University of Louisville, Louisville, KY  

Would Bioremediation be Effective on 20 Year Old Exxon Valdez Spill Remnants?
Ronald M. Atlas, University of Louisville, Louisville, KY
James R. Bragg, Creative Petroleum Solutions LLC, Houston, TX 

Are Wildlife and their Prey Exposed to Exxon Valdez Spill Remnants After 18 Years?
Jerry M. Neff, Neff & Associates LLC, Duxbury, MA                 David S. Page, Bowdoin College, Brunswick, ME
Paul D. Boehm, Exponent, Maynard, MA

What are the Problems in Using Passive Samplers in Oil Spill Studies of Contaminated Sediments?           
Paul D. Boehm, Exponent, Inc., Maynard, MA
David S. Page, Bowdoin College, Brunswick, ME
Jerry M. Neff, Neff & Associates LLC, Duxbury, MA

An Overview of the Exxon Valdez Oil Spill, Prince William Sound, Alaska

David S. Page, Chemistry Department, Bowdoin College, 6600 College station, Brunswick, ME 04011-8466
Paul D. Boehm, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA  01754
John S. Brown, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754
Jerry M. Neff, Neff & Associates, LLC. 20 Templewood Dr., Duxbury, MA 02332  

As an introduction to the following papers, this presentation provides an overview of the major facts of the oil spill, the important features of the environments affected, the shoreline surveys conducted, the cleanup, and the post-spill scientific studies of the fates and effects of the spilled oil.  

The March 24, 1989 grounding of the Exxon Valdez and the release of 37,000 tons of Alaska North Slope crude oil into the PWS marine environment was followed an unprecedented cleanup operation that continued through the fall of 1992 when it was terminated by order of the Federal On-Scene Coordinator.  The Exxon Valdez oil spill was undoubtedly the most thoroughly surveyed spill ever and the mapping of surface and subsurface oil (SSO) deposits throughout the spill zone provided a basis for subsequent scientific studies of spill effects. Many scientific studies were conducted by ExxonMobil-supported scientists and by government-supported scientists beginning in 1989 to assess the fate and effects of the spill. Additionally, a number of shoreline surveys were performed after 1999 to map remnants of the spill and assess their form and location. 

The surveys showed that much of the oil disappeared rapidly from the shore by a combination the cleanup and natural processes, showing loss rates consistent with those following other well-studied spills.  There is no longer any credible pathway by which spill remnants can pose a risk to wildlife.  By 2000, intertidal mussels collected from even the most heavily oiled sites contained low background range concentrations of polycyclic aromatic hydrocarbons (PAH), indicating low bioavailability of PAH from SSO residues on the shore and low risk of exposure to spill remnants for intertidal invertebrates and the wildlife the forage on them.  Despite active cleanup and natural removal of oil residues in the 20 years after the spill, the current scientific controversy focuses on the remaining oil residues, where they are and whether they represent a risk to wildlife. This series of papers will address those questions.

Where and Why do Remnants of the Exxon Valdez Oil Spill Persist? 

David S. Page, Chemistry Department, Bowdoin College, 6600 College station, Brunswick, ME 04011-8466 USA
Paul D. Boehm, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA  01754
John S. Brown, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754
Jerry M. Neff, Neff & Associates, LLC. 20 Templewood Dr., Duxbury, MA 02332

The long term (>10 yr) persistence of shoreline deposits of surface (SO) and subsurface oil (SSO) is a well-known phenomenon for a number of major marine oil spills where there are geomorphologic features that can contribute to the sequestration of SSO residues.  In the case of the 1989 Exxon Valdez oil spill, numerous shoreline surveys done since 2000 demonstrate the relationship between shoreline type and the SSO residues. SO residues persisting past 2001 are sporadically scattered in small weathered asphaltic patches in the upper shore, have a low accessibility and are not considered to pose an environmental risk.  Remaining SSO deposits mapped after 2000 occur at specific locations that represent a minute fraction (<0.1%) of the 783 km of Prince William Sound shoreline originally impacted by the spill. These locations are primarily exposed boulder/cobble and sheltered boulder/cobble/gravel shorelines.  Over 78% of the total heavy and moderate SSO deposits mapped in 2001 by NOAA occur at exposed boulder/cobble shoreline sites, with 70% at 6 specific locations.  Subsequent surveys done by NOAA in 2003 and by us in 2002, 2004, 2007 and 2008 demonstrate that natural degradation and oil removal processes are continuing, although at rates slower than reported by NOAA in 2001. Patchy SSO residues persist at these sites because they are (1) sequestered in low porosity finer-grained sediments between subsurface boulders and cobbles and (2) protected by surface boulder/cobble armor. These features inhibit the tidal flushing needed to promote natural oil loss, making SSO deposits more persistent but less bioavailable.  The cumulative results of these surveys show that SSO deposits persist primarily at locations associated with specific shoreline types that promote SSO sequestration, consistent with findings from other major oil spills.

What are the Form, Chemical Composition, and Location of Remnants of the Exxon Valdez Oil Spill after 18 years?

Paul D. Boehm, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754
David S. Page, Bowdoin College, 6600 College Station, Brunswick, ME 04011   
Jerry M. Neff, Neff & Associates LLC, 20 Templewood Dr., Duxbury, MA 02332 
John S. Brown, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754
James A. Bragg, Creative Petroleum Solutions, LLC, Houston, TX 77030
Ronald M. Atlas, University of Louisville, Louisville, KY 40292

As a continuation of an extensive series of shoreline surveys undertaken since 1989, we conducted a systematic survey in 2007 to evaluate the form, chemical composition, and locations of remaining subsurface oil (SSO) residues of Exxon Valdez oil (EVO) at scattered locations on some Prince William Sound (PWS) shorelines.  678 subsurface sediment samples were collected from 22 sites that were heavily oiled in 1989 and known to contain SSO deposits, based on multiple studies conducted since 2001.  All samples were analyzed for total extractable hydrocarbons (TEH), and 25% of samples were also analyzed for saturated and aromatic hydrocarbon weathering parameters.  Over 90% of the samples from all sites contained low levels of TEH, similar to background levels.  Of samples containing total polycyclic aromatic hydrocarbon (TPAH) concentrations greater than 500ng/g, 81% had TPAH loss greater than 70% (calculated using the saturate biomarker ethylcholestane as the conserved species), relative to the cargo oil, with most having >80% loss.  SSO residues were located in isolated patches sequestered by boulder and cobble armoring.  Samples showing the lowest TPAH loss correlated strongly with higher elevations in the intertidal zone.  Of the six atypical, less weathered samples having less than 60% TPAH loss, only two were found sequestered in the lower intertidal zone, both at a single site. Most of the EVO in PWS has been eliminated due to natural weathering.   Some isolated SSO residues remain scattered along the 783 km of shoreline originally oiled because they are sequestered and largely isolated from the natural weathering processes that would bring about their rapid removal.  However, of the SSO residues that remain, most are highly weathered and sporadically distributed at a small number of sites that are characterized by boulder-cobble armoring which serve to sequester the SSO. These beaches are distinctly different from those that support sea otter foraging. In addition, the SSO occurs primarily in the middle and upper tide zones and at specific locations, which are widely separated from biologically productive lower tide zones where most foraging by wildlife occurs.

Would Bioremediation be Effective on 20 Year Old Exxon Valdez Spill Remnants?

Ronald M. Atlas, University of Louisville, Louisville, KY 40292 USA, Tel: 502-852-0873, Email: r.atlas@louisville.edu
James R. Bragg, Creative Petroleum Solutions LLC, 2119 Goldsmith St., Houston, TX 77030 USA, Tel: 713-828-0326, Email: JRBragg@aol.com

Studies in Prince William Sound over the 19 years since the spill provide valuable lessons about the applicability of bioremediation for oil spill cleanup. Initially the oil coating the shores contained significant amounts of alkanes as well as aromatics that were readily biodegradable. The concentrations of available nitrogen nutrients, though, were insufficient to support rapid biodegradation. Fertilizer was applied extensively to oiled shorelines from 1989-1991, where fertilizer addition was found to increase the rate of polycyclic-aromatic hydrocarbon (PAH) degradation by a factor of 2, and the degradation rate of total GC-detectable hydrocarbons by a factor of 5 relative to the controls. Since 1991, natural weathering and biodegradation have continued. Extensive field studies were conducted between 2002 and 2008 involving systematic shoreline sampling. In 2007 alone 744 sediment samples were collected and extracted to determine the amount of remaining subsurface oil and its weathering state. Gravimetric analyses show that most sites that were heavily oiled by the spill and physically cleaned and bioremediated between 1989 and 1991 have no remaining subsurface oil above background concentration.  Detailed GC-MS analyses of over 350 samples show that where subsurface oil residue does remain, it is for the most part highly weathered.  For 2007 oil samples, 97% of samples analyzed had depletion of total resolvable alkanes of > 90%, and 81% had depletion of total PAH of > 70% relative to the spilled oil. Most of this oil residue is sequestered together with fine-grained sediments in patchy deposits under boulder/cobble armor, where both the armor and the low-porosity fine sediments severely limit contact of oil residue by flowing water and nutrients. The relatively high nutrient concentrations relative to remaining biodegradable oil that now exists at these sites, and the very patchy distribution, advanced weathering state and sequestration of the remaining subsurface oil suggest that it is in a form and location where any further bioremediation would likely be ineffective at increasing the rate of ongoing natural hydrocarbon removal.

Are Wildlife and their Prey Exposed to Exxon Valdez Spill Remnants After 18 Years?

Jerry M. Neff, Neff & Associates LLC, 20 Templewood Dr., Duxbury, MA 02332
David S. Page, Chemistry Dept., Bowdoin College, 6600 College Station, Brunswick, ME 04011
Paul D. Boehm, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754

Small, widely scattered patches of weathered oil have persisted for more than 18 years on some shores in western Prince William Sound (PWS) where oil came ashore after the March 1989 Exxon Valdez oil spill (EVOS). There is a large body of data pertaining to the PAH residues in the water column, intertidal sediments, and marine invertebrate prey species such as mussels and clams. We have used these data to examine the risk of exposure of sea otters and harlequin ducks, both of which forage on intertidal invertebrates, to polycyclic aromatic hydrocarbons (PAH) from EVOS residues. Three exposure pathways were evaluated: water column, prey, and direct contact with oil residues in sediments. Median water column PAH concentrations after 2001 are at background levels ranging from 1 to 5 ng/L (parts per trillion), orders of magnitude below potentially toxic concentrations.  Concentrations of total PAH in invertebrate prey on oiled shores where sea otters and harlequin ducks are known to forage are orders of magnitude below levels that might be toxicologically significant. Therefore the risk of water column and dietary exposure to EVOS residues is negligible. Although sea otters and harlequin ducks occupy near-shore habitats in western PWS that were heavily oiled in 1989, there is little overlap at the local level between areas on the shore where weathered oil persists and areas where these animals forage. Most subsurface oil (SSO) residues are located in the middle and upper intertidal zones under boulder/cobble armor, while sea otters dig pits exclusively in the subtidal and in the lower intertidal zone in sand/gravel substrates where clams are abundant. Thus, there is a very low risk that an otter would be physically exposed to SSO while digging for prey.  Harlequin ducks are not at risk of exposure to SSO because they do not dig pits, but rather forage on surface biota. There is negligible risk that harlequin ducks will encounter bioavailable PAH from any weathered oil on the sediment surface during foraging on the shore. Surface oil residues found since 2001 are highly weathered asphalt patches, located almost exclusively in the upper intertidal and supratidal zones, where harlequin ducks do not forage. 

What Are the Problems in Using Passive Samplers in Oil Spill Studies of Contaminated Sediments?

Paul D. Boehm, Exponent, 3 Clock Tower Place, Suite 205, Maynard, MA 01754
David S. Page, Bowdoin College, 6600 College Station, Brunswick, ME 04011 
Jerry M. Neff, Neff & Associates LLC, 20 Templewood Dr., Duxbury, MA 02332

Attempts have been made to use passive samplers to evaluate the natural bioavailability of residual oil remaining on and buried in shorelines affected by oil spills. While the use of passive samplers has potential to yield useful monitoring data in this context, there are two important questions relating to both the deployment of these devices and the interpretation of data obtained. First, is it appropriate and necessary to use passive samplers to measure bioavailability of oil residues in field situations where indigenous sentinel organisms (e.g., mussels; clams, worms, etc.) are available? Second, is it appropriate to deploy passive samplers in pits dug beneath the surface of the shoreline, such that they come in direct contact with buried oiled sediments? In recent studies at four sites in Prince William Sound, Alaska, we made side-by-side comparisons of polycyclic aromatic hydrocarbon (PAH) concentrations in resident blue mussels (Mytilus trossulus) and in SPMDs, deployed both at the surface and in pits dug in the beach. Total PAH (TPAH) concentrations in mussels and in SPMDs deployed on the sediment surface were correlated, but the PAH compositions were different. The lower molecular weight 2- and 3-ringed PAH were relatively more abundant in the SPMDs than in the mussels. TPAH concentrations in SPMDs deployed in pits dug into the beaches and mussels collected at the time of SPMD retrieval adjacent to those pits at oiled sites were much higher than in SPMDs and mussels from similar non-pitted SPMD locations.  Deployment of SPMDs in subsurface pits allowed physical contact of the SPMD with the SSO deposits and resulted in high PAH levels in the SPMDs caused by direct transfer of oil and its PAHs to the SPMD’s triolein.  SPMDs deployed in this manner do not serve as surrogates for local biota because they overestimate the natural bioavailability of sequestered subsurface oil residues.  Our results explain the observations of recent published studies conducted in PWS based upon the deployment of SPMDs in pits dug into deposits of subsurface oil residues. These studies erroneously imply that PAH concentrations obtained using this method are bioavailable, ignoring the effect of sequestration. We conclude that where available, indigenous sentinel organisms should be used to assess the bioavailability of buried oil residues sequestered in intertidal sediments following an oil spill. Indigenous biota (e.g., mussels) sampling is the preferred monitoring tool for this purpose, especially when the assessments involve food-chain effects. At locations where the absence of biota necessitates the use of SPMDs or other passive sampling devices, their limitations need to be carefully considered. When passive samplers are used to assess bioavailability, they should be deployed at the intertidal sediment surface. If the intent is to duplicate natural conditions relevant to biologic exposure, there is no justification for deploying them in pits so as to bring them in direct contact with oil residues, a process which creates obvious sampling artifacts. 

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