The discovery of a large tar mat on Fourchon Beach after Tropical Storm Karen prompted a renewed effort to search for buried oil in the wake of the 2010 Deepwater Horizon/BP oil disaster.

The beach is among a number of places in Louisiana still under “active response” from the oil disaster three years ago. In addition, Fourchon Beach was one of several areas this summer the U.S. Coast Guard directed the search for oil that could have been buried under the sand.

That work had largely wrapped up, then Tropical Storm Karen brought some waves and wind to state shores in early October.

Although the storm didn’t rise to the criteria mandating a post-storm search for oil, the Coast Guard federal on-scene commander for oil spill response decided it needed to be done anyway, said Petty Officer Michael Anderson, public information officer with the U.S. Coast Guard Gulf Coast Incident Management Team.

Cleanup crews found plenty of tar balls and oily material, then discovered a large and partially buried tar mat uncovered by the storm.

To understand how this tar mat remained in place and wasn’t discovered until now, more than three years after the oil disaster, means going back to 2010.

At the time of the Deepwater Horizon/BP response, the Coast Guard worked to block off natural breaches of sandy areas along Elmer’s Island and Fourchon Beach to prevent oil from migrating through these cuts and into the marsh behind them, Anderson explained. Oil would get into these cuts and stop at the barrier. Although skimming and other cleanup activities continued, a series of tropical storms later in the year pushed sand over the breaches, filling them in and burying the oil, Anderson said.

“This goes back to Louisiana’s coastline and how dynamic it is,” Anderson said.

Over the years, there has been more than just surface cleaning, where people picked up tar balls on the beaches. This summer, crews used augers to dig test holes in areas of the beach looking for oil, and other crews waded into the surf for soil samples to see if there were any oil mats just offshore.

The deepest the cleaning went into the sand was only about 3 feet to avoid disturbing the peat/clay base of the beach, Anderson said.

However, in the area of the former breaches, the natural depression meant that the oil was much deeper than 3 feet, he said.

Over the years, the natural cycle of erosion and accretion of sand meant the area around the recently discovered tar mat was starting to erode again, enabling the Tropical Storm Karen post-storm response crews to find the mat, Anderson said.

In light of the discovery, the Coast Guard took a number of steps to determine if this pattern was replicated at other former breaches along primarily Elmer’s Island and Fourchon Beach.

The Coast Guard is looking at satellite imagery from 2010 to locate the breach locations, working to determine how deep those breaches were and where potential oil could be located, and talking to property owners in the area for input.

In addition, the National Oceanic and Atmospheric Administration is working with the Coast Guard to come up with tidal currents in the area of the breaches to help find any potential collection points for the oil that would have been buried, Anderson said.

“This is a special occurrence,” Anderson said about the filled-in breaches. “But we don’t want this to happen again.”

Amy Wold covers environment for The Advocate. She can be reached at awold@ or on Twitter: @awold10.