At approximately 0600 on December 15, 1976,
the Liberian tanker Argo Merchant went aground on Fishing Rip (Nantucket Shoals),
29 nautical miles southeast of Nantucket Island, Massachusetts in high winds and ten foot seas.
The vessel was carrying approximately 183,000 barrels of No. 6 Fuel Oil (80%) and cutter stock (20%).
The master of the Argo Merchant requested permission to dump cargo
in an effort to control draft and re-float the vessel.
Permission was denied and attempts to lighter and re-float the vessel
using emergency pumps and an Air Deliverable Anti-Pollution Transfer System (ADAPTS) were unsuccessful.
The following day the weather worsened and the crew of the Argo Merchant was evacuated.
On December 17 the vessel began to pivot clockwise and buckle.
On December 21 the vessel broke in two aft of the king post,
spilling approximately 36,000 barrels of cargo.
The bow section split forward of the bridge and capsized on December 22,
resulting in the loss of the remaining cargo.
The bow section floated 400-500 yards to the southeast
and was eventually sunk by the USCG while the stern section remained aground.
Prevailing currents carried the spilled oil away from the shorelines and beaches of Nantucket.
Weather conditions and uncharted depths surrounding the wreck made salvage attempts difficult.
No. 6 fuel oil is a heavy product with an API gravity that ranges from 7 to 14.
The bulk of the spill formed large pancakes (largest observed was 240 feet by 760 feet)
and sheens on the surface.
Inspection of the pancakes by divers revealed flat bottoms.
Fresh oil formed pancakes 1-1.5 inches thick with tiered edges.
The pancakes thickened as the oil aged, some heavily weathered pancakes up to 10 inches thick were observed.
The weathered pancakes lacked tiered edges and associated sheens.
The cutter stock, which was mixed with the fuel oil to improve handling, entered the water column.
Levels as high as 250 parts per billion were measured beneath areas of fresh oil.
Extensive efforts were made to monitor and track the spill.
Detailed mapping was undertaken due to the level of concern, potential impacts,
and to help develop more accurate trajectory models for future spills.
Multiple trajectory models were utilized and evaluated during the incident.
Accurate measurements of the speed of the spill revealed i
that oil in pancakes traveled at an average speed of about 1.1% of the wind speed,
and the sheens somewhat slower.
The spill moved to the south-southeast of the wreck site, out over the continental shelf,
and into the prevailing North Atlantic circulation pattern.
As the oil moved further offshore, wind direction and weather conditions became less of a concern. i
Six thousand drift cards were deployed between the spill and the coast i
in an attempt to give advance warning at locations of imminent shoreline impacts.
Large tar balls (up to 70 pounds) came ashore in the Nantucket area during March of 1977. i
Analysis of the oil confirmed that it was No. 6 Fuel Oil,
but it could not be directly identified as product from the Argo Merchant.
Some impacts to the bottom sediments were observed in the area of the sunken bow section of the vessel.
In addition to this localized area,
one sediment sample taken from the area of the spill showed oil contamination.
In-situ burning was attempted on two occasions.
The material used was composed of fine grained, fumed silica particles
treated with silane to render the material hydrophobic.
Originally marketed as CAB-O-SIL ST-2-0,
the product was later marketed under the trade name Tullanox 500.
In the first burning attempt, conducted on December 27,
a USCG helicopter dropped isolated boxes of Tullanox 500 charged with JP-4 jet fuel onto the oil
and ignited the boxes using a timed grenade.
The isolated boxes burned, but the flame failed to spread.
It was believed that the wicking agent was not sufficiently dispersed to allow spreading of the flames.
The second attempt was conducted on December 31.
The USCG vessel Spar, aided by aircraft, located a 90 foot by 120 foot elliptically shaped slick
that was of a heavy, tarry consistency, and 6 to 8 feet thick.
The slick broke into smaller pancakes as the Spar maneuvered alongside.
Sixty-six pounds of Tullanox 500, in 11 pound bags,
were thrown near the center of a 30 foot by 60 foot slick.
The bags were torn open and much of the material was blown off of the slick.
Another application of six bags was applied along the edge of the slick and charged with JP-4.
The experiment was terminated after attempts to ignite the slick failed to sustain a burn.