As federal leaders in oil spill response science, NOAA’s Office of Response and Restoration is grateful for each oil spill which does not take place, which was fortunately the case on July 24, 2014 in Seattle, Washington, near our west coast office. A train passing through the city ran off the tracks, derailing three of its 100 tank cars carrying Bakken crude oil from North Dakota to a refinery in the port town of Anacortes, Washington. No oil spilled or ignited in the accident.
However, that was not the case in five high-profile oil train derailments and explosions in the last year, occurring in places such as Casselton, North Dakota, when a train carrying grain derailed into an oil train, causing several oil tank cars to explode in December 2013.
Oil production continues to grow in North America, in large part due to new extraction technologies such as hydraulic fracturing (fracking) opening up massive new oil fields in the Bakken region of North Dakota and Montana. The Bakken region lacks the capacity to transport this increased oil production by the most common methods: pipeline or tanker. Instead, railroads are filling this gap, with the number of tank cars carrying crude oil in the United States rising more than 4,000 percent between 2009 (9,500 carloads) and 2013 (407,761).
Just a day before this derailment, Seattle City Council signed a letter to the U.S. Secretary of Transportation, urging him to issue an emergency stop to shipping Bakken crude oil in older model tank train cars (DOT-111), which are considered less safe for shipping flammable materials. (However, some of the proposed safer tank car models have also been involved in oil train explosions.) According to the Council’s press release, “BNSF Railway reports moving 8-13 oil trains per week through Seattle, all containing 1,000,000 or more gallons of Bakken crude.” The same day as the Council’s letter, the Department of Transportation proposed rules to phase out the older DOT-111 model train cars for carrying flammable materials, including Bakken crude, over a two-year period.
NOAA’s Office of Response and Restoration is examining these changing dynamics in the way oil is moved around the country, and we recently partnered with the University of Washington to research this issue. These changes have implications for how we prepare our scientific toolbox for responding to oil spills, in order to protect responders, the public, and the environment.
For example, based on our knowledge of oil chemistry, we make recommendations to responders about potential risks during spill cleanup along coasts and waterways. We need to know whether a particular type of oil, such as Bakken crude, will easily ignite and pose a danger of fire or explosion, and whether chemical components of the oil will dissolve into the water, potentially damaging sensitive fish populations.
Our office responded to a spill of Bakken crude oil earlier this year on the Mississippi River. On February 22, 2014, the barge E2MS 303 carrying 25,000 barrels of Bakken crude collided with a towboat 154 miles north of the river’s mouth. A tank of oil broke open, spilling approximately 31,500 gallons (750 barrels) of its contents into this busy waterway, closing it down for several days. NOAA provided scientific support to the response, for example, by having our modeling team estimate the projected path of the spilled oil.
We also worked with our partners at Louisiana State University to analyze samples of the Bakken crude oil. We found the oil to have a low viscosity (flows easily) and to be highly volatile, meaning it readily changes from liquid to gas at moderate temperatures. It also contains a high concentration of the toxic components known as polycyclic aromatic hydrocarbons (PAHs) that easily dissolve into the water column. For more information about NOAA’s involvement in this incident, visit IncidentNews.
At the Trans Alaska Pipeline’s Start, Where 200 Million Barrels of Oil Begin their Journey Each Year
A couple years ago I visited the southern end of the 800-mile-long Trans Alaska Pipeline in Valdez, Alaska. As the northernmost port that remains free of ice, the Valdez Marine Terminal is where crude oil from the North Slope oil fields is loaded on tankers destined for refineries on the west coast of the United States. Last month I got to visit the northern end of the pipeline in Deadhorse, Alaska, where on average 17,001 gallons of oil enter the pipeline each minute and more than 200,000,000 barrels each year [PDF].
I was in Deadhorse to meet with Alaska Clean Seas, the primary Oil Spill Response Organization (OSRO) for all of the oil exploration and production operations in Prudhoe Bay and the other nearby oil fields.
The flight from Anchorage was right on time, boarded quickly, and was full of jackets and hats with every industry logo in the oilfield servicing business. Safety is a big concern in a place that is so remote, and the safety policy starts at Anchorage. Nobody is allowed on the plane without appropriate clothing.
The scenery in Deadhorse is difficult to describe. It has a flat, sprawling industrial footprint surrounded by vast tundra, shallow braided rivers, and innumerable shallow ponds and lakes. All of the infrastructure is built on large gravel pads: living quarters, warehouses, huge drilling rigs, and other equipment, with multiple racks of elevated pipelines running every direction. Unheated structures sit on the ground, but heated buildings are constructed on concrete stilts to prevent thawing of the permafrost.
Deadhorse is home to the beginning of the Trans Alaska Pipeline, combining oil from five major feeder pipelines that originate in the different oil fields that comprise the North Slope. Oil takes about 15 days to get to Valdez, moving about five miles per hour. Since its construction in 1977, the Trans Alaska Pipeline System has transported nearly 17 billion barrels of oil.
While in Deadhorse, I also got to see the Beaufort Sea. Although it was close to the summer solstice (the last sunset was about a month ago), the ocean was still mostly frozen. Response boats remained staged on land, waiting for open water.
As you can gather from these descriptions and the pictures that follow, the Arctic is not a place that easily lends itself to the type and speed of oil spill cleanup possible in warmer and more accessible areas. Learn more about NOAA’s ongoing Arctic efforts in a series of reports released in April 2014.
Despite improved navigation aids, including charts and Global Positioning Systems (GPS), ships still have accidents in our nation’s waterways, and I regularly review notification reports of these accidents from the National Response Center. Sometimes I need to consult the old nautical dictionary I inherited from my grandfather (a lawyer and U.S. Navy captain) to figure out what they mean.
The U.S. Coast Guard investigates ship accidents, but they use the terms “marine casualty or accident” interchangeably [PDF]. Mariners are required to report any occurrence involving a vessel that results in:
- Reduction or loss of a vessel’s electrical power, propulsion, or steering capabilities
- Failures or occurrences, regardless of cause, which impair any aspect of a vessel’s operation, components, or cargo
- Any other circumstance that might affect or impair a vessel’s seaworthiness, efficiency, or fitness for service or route
- Any incident involving significant harm to the environment
Some of those terms are pretty straightforward, but what is the difference between grounding and stranding? Or foundering and flooding? And my favorite, collision and allision?
Here is my basic understanding of these terms, but I am sure that some of these could fill an admiralty law textbook.
Groundings and strandings are probably the most common types of marine casualties. A grounding is when a ship strikes the seabed, while a stranding is when the ship then remains there for some length of time. Both can damage a vessel and result in oil spills depending on the ocean bottom type (rocky, sandy, muddy?), sea conditions, and severity of the event (is the ship a little scraped or did it break open?).
Flooding means taking on excessive water in one or more of the spaces on a ship (e.g., the engine room), while foundering is basically taking on water to the point where the vessel becomes unstable and begins to sink or capsize. Note that “foundering” is different than “floundering,” which is to struggle or move aimlessly.
And collision and allision … These terms are sometimes used interchangeably, but technically, a collision is when two vessels strike each other, while an allision occurs when a vessel strikes a stationary object, such as a bridge or dock.
No matter the proper terminology, all of these incidents can result in spills, keeping us pollution responders on our toes because of the potential impacts to coasts, marine life, and habitats such as coral reefs and seagrass beds. But understanding these various nautical terms helps us understand the circumstances we’re dealing with in an emergency and better adapt our science-based recommendations as a result. And as my grandfather used to say, a collision at sea can ruin your entire day …
With Lobster Poacher Caught, NOAA Fishes out Illegal Traps from Florida Keys National Marine Sanctuary
This is a post by Katie Wagner of the Office of Response and Restoration’s Assessment and Restoration Division.
On June 26, 2014, metal sheets, cinder blocks, and pieces of lumber began rising to the ocean’s surface in the Florida Keys National Marine Sanctuary. This unusual activity marked the beginning of a project to remove materials used as illegal lobster fishing devices called “casitas” from sanctuary waters. Over the course of two months, the NOAA-led restoration team plans to visit 297 locations to recover and destroy an estimated 300 casitas.
NOAA’s Restoration Center is leading the project with the help of two contractors, Tetra Tech and Adventure Environmental, Inc. The removal effort is part of a criminal case against a commercial diver who for years used casitas to poach spiny lobsters from sanctuary waters. An organized industry, the illegal use of casitas to catch lobsters in the Florida Keys not only impacts the commercial lobster fishery but also injures seafloor habitat and marine life.
Casitas—Spanish for “little houses”—do not resemble traditional spiny lobster traps made of wooden slats and frames. “Casitas look like six-inch-high coffee tables and can be made of various materials,” explains NOAA marine habitat restoration specialist Sean Meehan, who is overseeing the removal effort.
The legs of the casitas can be made of treated lumber, parking blocks, or cinder blocks. Their roofs often are made of corrugated tin, plastic, quarter-inch steel, cement, dumpster walls, or other panel-like structures.
Poachers place casitas on the seafloor to attract spiny lobsters to a known location, where divers can return to quite the illegal catch.
“Casitas speak to the ecology and behavior of these lobsters,” says Meehan. “Lobsters feed at night and look for places to hide during the day. They are gregarious and like to assemble in groups under these structures.” When the lobsters are grouped under these casitas, divers can poach as many as 1,500 in one day, exceeding the daily catch limit of 250.
In addition to providing an unfair advantage to the few criminal divers using this method, the illegal use of casitas can harm the seafloor environment. A Natural Resource Damage Assessment, led by NOAA’s Restoration Center in 2008, concluded that the casitas injured seagrass and hard bottom areas, where marine life such as corals and sponges made their home. The structures can smother corals, sea fans, sponges, and seagrass, as well as the habitat that supports spiny lobster, fish, and other bottom-dwelling creatures.
Casitas are also considered marine debris and potentially can harm other habitats and organisms. When left on the ocean bottom, casitas can cause damage to a wider area when strong currents and storms move them across the seafloor, scraping across seagrass and smothering marine life.
“We know these casitas, as they are currently being built, move during storm events and also can be moved by divers to new areas,” says Meehan. However, simply removing the casitas will allow the seafloor to recover and support the many marine species in the sanctuary.
There are an estimated 1,500 casitas in Florida Keys National Marine Sanctuary waters, only a portion of which will be removed in the current effort. In this case, a judge ordered the convicted diver to sell two of his residences to cover the cost of removing hundreds of casitas from the sanctuary.
To identify the locations of the casitas, NOAA’s Hydrographic Systems and Technology Program partnered with the Restoration Center and the Florida Keys National Marine Sanctuary. In a coordinated effort, the NOAA team used Autonomous Underwater Vehicles (underwater robots) to conduct side scan sonar surveys, creating a picture of the sanctuary’s seafloor. The team also had help finding casitas from a GPS device confiscated from the convicted fisherman who placed them in the sanctuary.
After the casitas have been located, divers remove them by fastening each part of a casita’s structure to a rope and pulley mechanism or an inflatable lift bag used to float the materials to the surface. Surface crews then haul them out of the water and transport them to shore where they can be recycled or disposed.
For more information about the program behind this restoration effort, visit NOAA’s Damage Assessment, Remediation, and Restoration Program.
Katie Wagner is a communications specialist in the Assessment and Restoration Division of NOAA’s Office of Response and Restoration. Her work raises the visibility of NOAA’s effort to protect and restore coastal and marine resources following oil spills, releases of hazardous substances, and vessel groundings.
When NOAA environmental scientist Alyce Fritz talks about her first visit to the Metal Bank Superfund Site back in 1986, she always mentions the orphanage next door. St. Vincent’s Orphans Asylum, as it was named when it was opened by the Catholic Archdiocese of Philadelphia in 1857, is separated from the Metal Bank site by a stormwater outfall that drains into the Delaware River just north of the former orphanage.
The Metal Bank Superfund Site and St. Vincent’s are located several miles north of the center of Philadelphia, Pennsylvania, on the banks of the Delaware River in an industrial district that is part of the historic Tacony neighborhood. Located on 29 acres along the river, St. Vincent’s looks like a beautiful old park. What Fritz remembers clearly on that first visit was the children’s playground equipment placed near the river’s edge.
On the adjacent 10 acre Metal Bank site, a company called Metal Bank of America, Inc., owned and operated a salvage facility where scrap metal and electric transformers were recycled for over 60 years. Part of the recycling process used by Metal Bank of America, Inc. involved draining oil—loaded with toxic compounds including PCBs—from the used transformers to reclaim copper parts. PCBs are considered a probable cause of cancer in humans and are harmful to clams and fish found in the mudflats and river next to the site.
In the 1970s the U.S. Coast Guard discovered oil releases in the Delaware River and traced them back to the site. Throughout the 1980s, the Metal Bank site’s owners used an oil recovery system to clear the groundwater of PCB-laced oil. However, oil continued to seep from an underground tank at the site. As a result, PCBs and other hazardous substances were left in the soil, groundwater, and river bed sediments at the Metal Bank site and adjacent to St. Vincent’s.
In 1983 the Metal Bank site was placed on the National Priorities List (the Superfund program) and slated for federal cleanup. During the course of the federal cleanup process, various parties were identified as being liable for the contamination at the site, including a number of utility companies that transported their used electrical transformers to the Metal Bank site for disposal or otherwise arranged to dispose of their used electrical transformers at the Metal Bank site.
Federal and local agencies collaborated on a design for cleanup of multiple contaminants of concern at the Metal Bank site. Found in the soil, sediment, groundwater, and surface water, these contaminants included but were not limited to:
- polynuclear aromatic hydrocarbons (a toxic component of oil).
- semi-volatile organic compounds.
The cleanup, which began in 2008, included excavating soils and river sediments contaminated with PCBs, capping some areas of river sediment, installing a retaining wall near the river, and removing an old transformer oil storage tank. Most of this work was completed in 2010.
As part of the required 5-year review period, monitoring of the Metal Bank site continues. This is to ensure the cleanup is still protecting human health and the environment, including endangered Atlantic Sturgeon and Shortnose Sturgeon. Through successful coordination among the EPA, other federal and state agencies, and some of the potentially responsible parties (PRPs) during the Superfund process, the cleanup has reduced the threat to natural resources in the river and enhanced the recovery of the habitat along the site and St. Vincent’s property.
Over the years, the role of St. Vincent’s has evolved too, from serving as a long-term home for orphans toward one of providing short-term shelter and care to abused and neglected children. Prior to the early 1990s, children who came to St. Vincent’s spent a significant part of their childhood as residents of the institution. In a 1992 article in the Philadelphia Daily News, Sister Kathleen Reilly explained that the children currently cared for by St. Vincent’s range in age from two to 12 years of age and are placed at the home temporarily through an arrangement between the City of Philadelphia Department of Human Services and Catholic Social Services. Today St. Vincent’s serves young people mostly through day programs. One thing hasn’t changed though—the lush grounds along the river are still beautiful.
The federal and state co-trustees for the ongoing Natural Resource Damage Assessment at the Metal Bank site include NOAA’s Damage Assessment, Remediation, and Restoration Program; the U.S. Fish and Wildlife Service; and multiple Pennsylvania state agencies. Collectively, the trustees are working together to further engage with the potentially responsible parties and build upon what has been accomplished at the site by the cleanup.
The trustees have invited the potentially responsible parties to join them in a cooperative effort to improve habitat for the injured natural resources (such as habitat along the river and wetlands) that support the clams, fish, and birds using the Delaware River. In addition, there is the potential for a trail to be routed through the property to a scenic view of St. Vincent’s and the river (an area which is now safe for recreational use). The trustees hope that the natural resources at the Metal Bank site can evolve to become a vibrant part of the historic Tacony neighborhood once again too.
This is a post by LTJG Kyle Jellison, NOAA Scientific Support Coordinator.
“Every day is a new adventure.” I came to believe this phrase while sailing on the high seas, but it proves true as a NOAA Scientific Support Coordinator as well. There have been many adventures in my time working in the Gulf of Mexico doing emergency response for oil spills and hazardous materials releases.
The most recent oil spill—a pipeline leak in a Louisiana marsh—didn’t seem out of the ordinary, that is, until the Unified Command in charge of the response turned to alternative approaches to quicken and improve the effectiveness of the cleanup.The Spill and Our Options
On May 28, 2014 a plane hired by Texas Petroleum Investment Company was performing a routine aerial survey of their inland oilfield and noticed a slight oil sheen and a dead clump of roseau cane (phragmites). This sparked further investigation and the discovery of 100 barrels (4,200 gallons) of crude oil, which had leaked out of a breach in their pipeline passing through the Delta National Wildlife Refuge, outside of Venice, Louisiana. Pipelines like this one are routinely inspected, but as they age the potential for corrosion and spills increases.
Roseau cane is a tall, woody plant, similar to bamboo, reaching heights of up to 20 feet. The stalks grow very close together and in water depths between two and 30 inches. This creates a complex situation which is very hard to clean oil out from.
The least invasive method for oil cleanup is to flush out the oil with high volumes of water at low pressure, but this is a long process with low amounts of oil recovered each day. Another common practice is to flush with water while cutting lanes into the vegetation, creating pathways for the oil to migrate along for recovery. Though more aggressive and with higher amounts of oil recovered each day, it still would likely take many weeks or months to clean up this particular oil spill using this method.An Unconventional Solution
What about doing a controlled burn of the oil where it is, a strategy known as in situ burning? It removes a large amount of oil in a matter of days, and when performed properly, in situ burning can help marsh vegetation recover in five years or less for more than 75 percent of cases in one study.
In situ burning, Latin for burning in place, is considered an “alternative” response technology, rather than part of the regular suite of cleanup options, and is only employed under the right set of circumstances. More information about this can be found in the NOAA report “Oil Spills in Marshes,” which details research and guidelines for in situ burning in chapter 3, Response.
To help determine if burning was appropriate in this case, the Unified Command brought in the NOAA Scientific Support Team, U.S. Fish and Wildlife Service Fire Management Team, U.S. Coast Guard Gulf Strike Team, and T&T Marine Firefighting and Salvage. After considering the situation, gaining consensus, developing a burn plan, and earning the support of Regional Response Team 6, it was time to light it up!Where There’s Smoke …
On June 3, 2014, we burned the oil for two hours, with flames reaching 40 feet. The next day, we burned for another six hours. There was a lot of oil to be burned, with pockets of oil spread throughout three acres of impacted marsh. The fire remained contained to the area where enough oil was present to support the burn, extinguishing once it reached the edge of the oiled marsh.
We have an ongoing study to evaluate the impacts of the burn, and preliminary results indicate that there was minimal collateral damage. More than 70 percent of the oil was burned over the two-day period. We considered this to be a very successful controlled burn. The much less remaining oil will be recovered by mechanical methods within a few weeks, instead of months.
Texas Petroleum Investment Company, as the responsible party in this case, will be responsible for all costs incurred for this incident, including cleanup and monitoring (and restoration, if necessary).
To help ensure we learn something from this incident, an assessment team entered the impacted marsh before the burns to collect oil, water, and sediment samples. The team also collected samples after each day of burning and returned a week after the burn to assess the condition of the vegetation and collect samples. This multi-agency team will return to the site in August for more sampling and monitoring.
The long-term monitoring and sampling project is being managed by NOAA, Louisiana Department of Environmental Quality, Fish and Wildlife Service, and Texas Petroleum Investment Company. We are conducting the study under the umbrella of the Response Science and Technology Subcommittee of the New Orleans Area Committee, a standing body of response scientists. Jeff Dauzat of Louisiana Department of Environmental Quality and I co-chair this subcommittee and are looking forward to the results of this ongoing scientific project.
Was burning the right move? The science will speak for itself in time.
For more information:
- U.S. Fish and Wildlife Service, Coast Guard, and Responsible Party Responds to 50-Barrel Oil Spill on Delta National Wildlife Refuge with Controlled Burn
- When Setting Fire to an Oil Spill in a Flooded Louisiana Swamp is a Good Thing | February 2013
- In Situ Burning | NOAA’s Office of Response and Restoration
LT Kyle Jellison is a Scientific Support Coordinator for NOAA’s Office of Response and Restoration. He supports Federal On-Scene Coordinators throughout the Gulf of Mexico by providing mission critical scientific information for response and planning to oil and hazardous material releases.
This is a post by Vicki Loe and Jill Petersen of NOAA’s Office of Response and Restoration.
They say that imitation is the sincerest form of flattery, which is why we were thrilled to hear about recent efforts in India to mirror one of NOAA’s key oil spill planning tools, Environmental Sensitivity Index maps. A recent Times of India article alerted us to a pilot study led by scientists at the National Institute of Oceanography in India, which used our Environmental Sensitivity Index (ESI) shoreline classifications to map seven talukas, or coastal administrative divisions in India. Amid the estuaries mapped along India’s west coast, one of the dominant shoreline types is mangroves, which are a preferred habitat for many migratory birds as well as other species sensitive to oil.
Traditional ESI data categorize both the marine and coastal environments as well as their wildlife based on sensitivity to spilled oil. There are three main components: shoreline habitats (as was mapped in the Indian project), sensitive animals and plants, and human-use resources. The shoreline and intertidal zones are ranked based on their vulnerability to oil, which is determined by:
- Shoreline type (such as fine-grained sandy beach or tidal flats).
- Exposure to wave and tidal energy (protected vs. exposed to waves).
- Biological productivity and sensitivity (How many plants and animals live there? Which ones?).
- Ease of cleanup after a spill (For example, are there roads to access the area?).
The biology data available in ESI maps focus on threatened and endangered species, areas of high concentration, and areas where sensitive life stages (such as when nesting) may occur. Human use resources mapped include managed areas (parks, refuges, critical habitats, etc.) and resources that may be impacted by oiling or clean-up, such as beaches, archaeological sites, or marinas.
Many countries have adapted the ESI data standards developed and published by NOAA. India developed their ESI product independently, based on these standards. In other cases, researchers from around the world have come across ESI products and contacted NOAA for advice in developing their own ESI maps and data. In the recent past, Jill Petersen, the NOAA ESI Program Manager, has worked with scientists who have visited from Spain, Portugal, and Italy.
By publishing our data standards, we share information which enables states and countries to develop ESI maps and data independently while adhering to formats that have evolved and stood the test of time over many years. In addition to mapping the entire U.S. coast and territories, NOAA has conducted some of our own international mapping of ESIs. In the wake of Hurricane Mitch in 1998, we mapped the coastal natural resources in the affected areas of Nicaragua, Honduras, and Ecuador.
Currently, we are developing new ESI products for the north and mid-Atlantic coasts of the United States, many areas of which were altered by Hurricane Sandy in 2012. The new maps will provide a comprehensive and up-to-date picture of vulnerable shorelines, wildlife habitats, and key resources humans use. Having this information readily available will enable responders and planners to quickly make informed decisions in the event of a future oil spill or natural disaster.
For further information on NOAA’s ESI shoreline classification, see our past blog posts: Mapping How Sensitive the Coasts Are to Oil Spills and After Sandy, Adapting NOAA’s Tools for a Changing Shoreline.
I’ve seen a lot of firsts in the past four years.
During that time, I have been investigating the environmental impacts, through the Natural Resource Damage Assessment process, of the Enbridge pipeline spill in Michigan. In late summer of 2010, a break in an underground pipeline spilled approximately 1 million gallons of diluted bitumen into a wetland, a creek, and the Kalamazoo River. Diluted bitumen (“dilbit”) is thick, heavy crude oil from the Alberta tar sands (also known as oil sands), which is mixed with a thinner type of oil (the diluent) to allow it to flow through a pipeline.A Whole New Experience
This was my first and NOAA’s first major experience with damage assessment for a dilbit spill, and was also a first for nearly everyone working on the cleanup and damage assessment. Dilbit production and shipping is increasing. As a result, NOAA and our colleagues in the field of spill response and damage assessment are interested in learning more about dilbit:
- How does it behave when spilled into rivers or the ocean?
- What kinds of effects does it have on animals, plants, and habitats?
- Is it similar to other types of oil we’re more familiar with, or does it have unique properties?
While it’s just one case study, the Enbridge oil spill can help us answer some of those questions. My NOAA colleague Robert Haddad and I recently presented a scientific paper on this case study at Environment Canada’s Arctic and Marine Oil Spill Program conference.
In addition, the Canadian government and oil pipeline industry researchers Witt O’Brien’s, Polaris, and Western Canada Marine Response Corporation [PDF] and SL Ross [PDF] have been studying dilbit behavior as background research related to several proposed dilbit pipeline projects in the United States and Canada. Those experiments, along with the Enbridge spill case study, currently make up the state of the science on dilbit behavior and ecological impacts.How Is Diluted Bitumen Different from Other Heavy Oils?
Dilbit is in the range of other dense, heavy oils, with a density of 920 to 940 kg/m3, which is close to the density of freshwater (1,000 kg/m3). (In general when something is denser than water, it will sink. If it is less dense, it will float.) Many experts have analyzed the behavior of heavy oils in the environment and observed that if oil sinks below the surface of the water, it becomes much harder to detect and recover. One example of how difficult this can be comes from a barge spill in the Gulf of Mexico, which left thick oil coating the bottom of the ocean.
What makes dilbit different from many other heavy oils, though, is that it includes diluent. Dilbit is composed of about 70 percent bitumen, consisting of very large, heavy molecules, and 30 percent diluent, consisting of very small, light molecules, which can evaporate much more easily than heavy ones. Other heavy oils typically have almost no light components at all. Therefore, we would expect evaporation to occur differently for dilbit compared to other heavy oils.
Environment Canada confirmed this to be the case. About four to five times as much of the dilbits evaporated compared to intermediate fuel oil (a heavy oil with no diluent), and the evaporation occurred much faster for dilbit than for intermediate fuel oil in their study. Evaporation transports toxic components of the dilbit into the air, creating a short-term exposure hazard for spill responders and assessment scientists at the site of the spill, which was the case at the 2010 Enbridge spill.
Since the light molecules evaporate after dilbit spills, the leftover residue is even denser than what was spilled initially. Environment Canada, Witt O’Brien’s/Polaris/WCMRC, and SL Ross measured the increase in dilbit density over time as it weathered, finding dilbit density increased over time and eventually reached approximately the same density as freshwater.
These studies also found most of the increase in density takes place in the first day or two. What this tells us is that the early hours and days of a dilbit spill are extremely important, and there is only a short window of time before the oil becomes heavier and may become harder to clean up as it sinks below the water surface.
Unfortunately, there can be substantial confusion in the early hours and days of a spill. Was the spilled material dilbit or conventional heavy crude oil? Universal definitions do not exist for these oil product categories. Different entities sometimes categorize the same products differently. Because of these discrepancies, spill responders and scientists evaluating environmental impacts may get conflicting or hard-to-interpret information in the first few days following a spill.Lessons from the Enbridge Oil Spill
Initially at the Enbridge oil spill, responders used traditional methods to clean up oil floating on the river’s surface, such as booms, skimmers, and vacuum equipment (see statistics on recovered oil in EPA’s Situation Reports [PDF]).
After responders discovered the dilbit had sunk to the sediment at the river’s bottom, they developed a variety of tactics to collect the oil: spraying the sediments with water, dragging chains through the sediments, agitating sediments by hand with a rake, and driving back and forth with a tracked vehicle to stir up the sediments and release oil trapped in the mud.
These tactics resulted in submerged oil working its way back up to the water surface, where it could then be collected using sorbent materials to mop up the oily sheen.
While these tactics removed some oil from the environment, they might also cause collateral damage, so the Natural Resource Damage Assessment trustees assessed impacts from the cleanup tactics as well as from the oil itself. This case is still ongoing, and trustees’ assessment of those impacts will be described in a Damage Assessment and Restoration Plan after the assessment is complete.
For now, we can learn from the Enbridge spill and help predict some potential environmental impacts of future dilbit spills. We can predict that dilbit will weather (undergo physical and chemical changes) rapidly, becoming very dense and possibly sinking in a matter of days. If the dilbit reaches the sediment bed, it can be very difficult to get it out, and bringing in responders and heavy equipment to recover the oil from the sediments can injure the plants and animals living there.
To plan the cleanup and response and predict the impacts of future dilbit spills, we need more information on dilbit toxicity and on how quickly plants and animals can recover from disturbance. Knowing this information will help us balance the potential impacts of cleanup with the short- and long-term effects of leaving the sunken dilbit in place.