Friday, September 27, 2013

Friday, September 27, 2013

When Exxon's Pegasus oil pipeline ruptured in Mayflower, Arkansas on March 29, it flooded streets and homes in a pretty suburban subdivision with dilbit -- that's "diluted bitumen." Bitumen is a sticky, heavy precursor to oil; it's the stuff that is being extracted from the vast tar sands mining operations up in Alberta, Canada.  The bitumen is diluted with lighter hydrocarbon liquids that essentially act as solvents so it can flow through the pipeline. 

A similar pipeline rupture in Michigan in 2010 flooded the Kalamazoo River with dilbit, a substance that -- unlike crude oil -- sinks rather than floats, making the cleanup significantly more difficult and expensive.  

The Mayflower cleanup has also been a prolonged and contentious operation, with local residents reporting illnesses in the aftermath, and disagreement about exactly what areas have been impacted.

This series of before-and-after pairs of high-resolution images of the Mayflower area yields some clues.  The "before" imagery is aerial survey photography from Google Earth that was taken on September 4, 2010.  The "after" imagery was shot from DigitalGlobe's Worldview-2 satellite on July 31, 2013, four months after the spill. Some changes are easy to see: large light brown areas of bare soil show where excavation and soil removal occurred; and a notable loss of aquatic vegetation in a cove that empties into Lake Conway.  

Before: overview, September 2010, showing area of March 2013 pipeline spill in Mayflower, Arkansas.
After: overview, July 2013.
Before: Detail 1, September 2010, showing subdivision at lower left (next to SkyTruth logo) that was flooded with dilbit during March 2013 spill.  Pegasus pipeline right-of-way cuts diagonally across the left (west) side of the image; two long driveways at the end of the cul-de-sac at the northwest corner of the subdivision lie directly on top of the pipeline.
After:  Detail 1, July 2013, showing subdivision.  Light brown patches on north side of the subdivision probably shows area of soil that was excavated and removed as part of the cleanup operations.  Oil flowed from west to east, toward Lake Conway.
Before:  Detail 2, September 2010, showing end of cove and wetlands where spill apparently entered Lake Conway.
After:  Detail 2, July 2013.  Floating booms (thin, pale light lines) are strung across the cove in attempt to intercept the dilbit. Turbid, open water and very pale green area (newly planted grass?) suggest impact to wetlands and aquatic vegetation in this area.
Before: Detail 3, September 2010, showing area where cove meets main body of Lake Conway (upper right).
After: Detail 3, July 2013. More booms are apparent, as are distinct changes in water color that can indicate variations in the presence of turbidity, algae, or other substances.

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