89
characterizing shoreline oiling, SCAT (Owens and Sergy 2003), and the first welldocumented use of bioremediation to cleanse oiled shorelines (Bragg et al. 1994).
While the water column aspects of the spill were relatively short-lived, the focus of
longer-term fate and degradation studies turned to the shorelines where oil weathering and biodegradation (Boehm et al. 2008) and bioavailability (Neff et al. 2006) of
buried oil residues dominated investigations for almost two decades after the spill.
In 2010, a large and complex set of investigations drove multiple field sampling
efforts immediately following the DWH wellhead blowout in the Gulf of Mexico
(GoM) and continued for many months after the well was capped. The DWH well
blowout at Mississippi Canyon Lease Block 252 (MC252) occurred on April 20,
2010, at approximately 1500 m water depth and approximately 103 km from
Southwest Pass on the Louisiana coast. Over an 87-day period, until the well was
capped on July 15, 2010, large volumes of natural gas and oil (API gravity 37 (SL
Ross Environmental Research 2010)) were released into the waters of the GoM. To
lessen the ecological impact from surface oiling and prevent the fouling of shorelines, Corexit 9500, a chemical dispersant, was injected into the oil stream at the
release point at depth and applied aerially to surface slicks (Houma ICP Aerial
Dispersant Group 2010; U.S. Senate 2010). The chemical dispersion at depth, combined with the physical dispersion resulting from the force of the gas and oil escaping from the well, resulted in the formation of oil droplets in a range of sizes. The
larger droplets of oil rose to the surface, while finer droplets remained suspended
within the water column where they were neutrally buoyant (Camilli et al. 2010). In
the water column, soluble components of the oil dissolved and were degraded by
microbial populations (Atlas and Hazen 2011; Hazen et al. 2010). At the ocean
surface, the oil was also subjected to evaporation and photodegradation of susceptible components. The overall magnitude and duration of the DWH incident
Table 6.1 (continued)
Process
Subsurface blowout
Surface release
Timeframe
Notes
Timeframe
Notes
Biodegradation
Begins within
the first hours
Can occur within the
water column,
sediment, or at the
surface. Rates are
dependent on site
conditions
Begins within
the first hours
Can occur
within the water
column,
sediment, or at
the surface
Sedimentation
Time scale
dependent on
mechanism
Oil may sink after loss
of lighter compounds or
due to interactions with
organic or inorganic
particles Deepwater
blowouts may be distant
from shoreline, but
interactions with
particulate plumes near
the continental shelf or
at shorelines may occur
Time scale
dependent on
mechanism
Oil may sink
after loss of
lighter
compounds or
due to
interactions with
organic or
inorganic
particles
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…
characterizing shoreline oiling, SCAT (Owens and Sergy 2003), and the first welldocumented use of bioremediation to cleanse oiled shorelines (Bragg et al. 1994).
While the water column aspects of the spill were relatively short-lived, the focus of
longer-term fate and degradation studies turned to the shorelines where oil weathering and biodegradation (Boehm et al. 2008) and bioavailability (Neff et al. 2006) of
buried oil residues dominated investigations for almost two decades after the spill.
In 2010, a large and complex set of investigations drove multiple field sampling
efforts immediately following the DWH wellhead blowout in the Gulf of Mexico
(GoM) and continued for many months after the well was capped. The DWH well
blowout at Mississippi Canyon Lease Block 252 (MC252) occurred on April 20,
2010, at approximately 1500 m water depth and approximately 103 km from
Southwest Pass on the Louisiana coast. Over an 87-day period, until the well was
capped on July 15, 2010, large volumes of natural gas and oil (API gravity 37 (SL
Ross Environmental Research 2010)) were released into the waters of the GoM. To
lessen the ecological impact from surface oiling and prevent the fouling of shorelines, Corexit 9500, a chemical dispersant, was injected into the oil stream at the
release point at depth and applied aerially to surface slicks (Houma ICP Aerial
Dispersant Group 2010; U.S. Senate 2010). The chemical dispersion at depth, combined with the physical dispersion resulting from the force of the gas and oil escaping from the well, resulted in the formation of oil droplets in a range of sizes. The
larger droplets of oil rose to the surface, while finer droplets remained suspended
within the water column where they were neutrally buoyant (Camilli et al. 2010). In
the water column, soluble components of the oil dissolved and were degraded by
microbial populations (Atlas and Hazen 2011; Hazen et al. 2010). At the ocean
surface, the oil was also subjected to evaporation and photodegradation of susceptible components. The overall magnitude and duration of the DWH incident
Table 6.1 (continued)
Process
Subsurface blowout
Surface release
Timeframe
Notes
Timeframe
Notes
Biodegradation
Begins within
the first hours
Can occur within the
water column,
sediment, or at the
surface. Rates are
dependent on site
conditions
Begins within
the first hours
Can occur
within the water
column,
sediment, or at
the surface
Sedimentation
Time scale
dependent on
mechanism
Oil may sink after loss
of lighter compounds or
due to interactions with
organic or inorganic
particles Deepwater
blowouts may be distant
from shoreline, but
interactions with
particulate plumes near
the continental shelf or
at shorelines may occur
Time scale
dependent on
mechanism
Oil may sink
after loss of
lighter
compounds or
due to
interactions with
organic or
inorganic
particles
6 The Importance of Understanding Transport and Degradation of Oil and Gasses…