Nearly two months later, crews are working to recover the last of the oil left from a pipeline breach in California, a response team said.

Line 901, a pipeline system operated by Plains All American, ruptured May 19 in Santa Barbara, Calif. The system leaked as much as 2,500 barrels of oil and left residual contamination spread out over more than 100 miles along the state coast.

A team of state, federal and third-party scientists determined that, as of July 5, 96 percent of the beaches and shorelines soiled by the spill have met what was determined by a unified command to be clean.

"An average of 380 workers contributed to beach cleanup activities each day, which is now mostly concentrated on manually cleaning oil from the rocks and cobble," responders said in their latest update. "Work crews continued to remove the remaining oil from the large stones and cliff faces according to the cleanup plan approved by the unified command."

Preliminary findings from the federal Pipeline and Hazardous Materials Safety Administration said there was "extensive" corrosion on the pipeline system, with walls degraded by more than 70 percent of their original thickness in some locations.

Bipartisan leaders of the House Energy and Commerce Committee in June sent letters to Plains and the PHMSA seeking explanations on pipeline safety.

To Plains, the congressional leaders said they wanted details on the company's maintenance procedures.

To federal authorities, the representatives said they wanted updates on the implementation of "long overdue" safety rules spelled out in 2011 legislation. The measure, they said in their letter, is meant to prevent such tragedies from occurring.

Plains said it had conducted a system inspection two weeks before the May 19 spill, though results weren't returned until after the incident.