Crews are removing contaminated soil from a remote area west of Tracy after a pipeline spilled 21,000 gallons of oil into the ground near Patterson Pass and Midway roads early Friday.
The oil came from a 24-inch underground line belonging to Shell Pipeline Co. that stretches from Martinez to Coalinga, according to Garrett Backus, lead senior registered health specialist at the San Joaquin County Environmental Health Department. Backus estimated that the pipeline is buried 10 feet deep.
He said the leak was discovered when Shell officials noticed a loss of pressure in the pipeline and shut down pumping.
The leak was reported to the county’s environmental health department at 2:20 a.m., and the department sent crews out at first light to assess the damage.
“The release is in a remote area away from population. It did not get into any surface water, but there is potentially groundwater,” Backus said. “There is no immediate threat right now, and Shell is conducting a cleanup.”
An estimated 500 barrels of crude — unrefined oil — spilled into the soil.
Backus characterized the area of the leak as cattle grazing land near windmills — roughly bordered by Patterson Pass and Midway roads and Interstate 580 — 900 feet west of the San Joaquin-Alameda county border.
Backus said that as of Wednesday afternoon, cleanup crews under the supervision of the Central Valley Regional Water Quality Control Board had filled 218 bins holding 18 cubic yards each with contaminated soil. He did not have an estimate of when the work would be completed.
“The cleanup is ongoing,” he said. “The state fire marshal is overseeing pipeline safety and pipeline repair.”
The Central Valley water board is overseeing the cleanup because of the possibility of oil contaminating groundwater near the spill area.
Lynne Tolmachoff, a spokeswoman for Cal Fire, said the fire marshal would also investigate to find the root cause of Friday’s spill.
“They will try to determine what caused the failure and what has potential for the same type of failure down the line,” she said.
Tolmachoff said the safety investigation could span the entire length of the pipeline. Any sections that are found to have similar problems could be dug up and fixed before the line is put back into service.
The history of the pipeline, including any previous leaks, could also come into question.
In September, an estimated 500 barrels of crude spilled from the same Shell pipeline in the same general area, as documented by the California Emergency Management Agency in the Office of Emergency Services. The document lists Tracy as the area of the hazardous material spill.