Two large oil sheens on San Pablo Bay Wednesday morning, after a mysterious odor prompted shelter-in-place orders in Vallejo Tuesday night, appear to have come from a Phillips refinery tanker in Rodeo, authorities said.

A spokesperson for the Phillips 66 Rodeo Refinery Marine Terminal in Rodeo said a tanker berthed at the marine terminal might have released the crude oil. A light, oily sheen was discovered near the refinery around 8 a.m. Wednesday. The refinery notified the National Response Center and the U.S. Coast Guard and temporarily shut down operations.

The Rodeo refinery supplies gas and diesel throughout California at Phillips 66 gas stations.

By Wednesday night, Coast Guard officials could no longer detect the sheens on the water.

"It may have sunk, we don't know," said Coast Guard Lt. Megan Mervar. "There are a lot of unknowns. But dissipation is one possibility. If it was a lighter oil, it could've just evaporated."

Officials have not said whether the oil sheen is linked to the mysterious odor that sickened dozens of people in Vallejo on Tuesday night.

Meanwhile, Coast Guard crews earlier Wednesday laid down a thousand-foot boom to contain oil surrounding the Yamuna Spirit tanker.

Scientist Ian Wren of the San Francisco Baykeeper said his environmental advocacy group is working closely with the Coast Guard.

"The community is watching, and the local environmental watchdog is kind of making sure that adequate cleanups are proceeding," Wren said. "But they are reluctant to actually prescribe blame at this point."

It's unclear what caused the spill or how much has spread, but Wren says there will be an impact.

"Yeah, fish, wildlife, sea birds, as well as marine mammals might be affected," he said. "We don't know if it's crude oil versus bunker fuel from the vessel."

The exact volume of material released is being determined and the incident remains under investigation, the refinery spokesperson said. According to the spokesperson, there have been no injuries associated with the release so far and health impacts to the community are not anticipated.

The NBC Bay Area Investigative Unit searched through Environmental Protection Agency records and found the Phillips 66 refinery in Rodeo did not comply with federal standards for the disposal of solid and hazardous waste for the past three years. An inspection report from March reveals the refinery was operating in significant violation, which is the agency’s most serious designation and shows the refinery poses a severe level of environmental threat.

The shelter-in-place in Vallejo was lifted around 6 a.m. Wednesday after reports of a strong smell sent multiple people to hospitals in Vallejo and Fairfield Tuesday night.

Late Tuesday night, Coast Guard Lt. Steven Dross said a sheen had been confirmed on the water in a number of mostly connected locations in and around Vallejo as well as San Pablo Bay and the Carquinez Straits.

Ferry service between Vallejo and San Francisco was delayed Wednesday morning because of the oil spill investigation in San Francisco Bay.

The Vallejo Fire Department said it received more than 500 calls reporting a strong odor in the Glen Cove and Beverly Hills Park neighborhoods in South Vallejo Tuesday night. Firefighters reportedly were able to rule out natural gas and refinery emissions as the source of the odor.

Michelle Norris sheltered in place at her Crockett home, a few hundred yards from the ship and refinery. She said at her house, strong odors are not unusual.

"Quite often, I smell strange things," Norris said. "I never know what to worry about and what's just normal."

Vallejo fire officials said local hospitals reported multiple patients as a result of the mysterious odor. Patients complaining of burning in their throats and noses arrived at Sutter Solano Medical Center in Vallejo, Kaiser Vallejo Medical Center and Northbay Medical Center in Fairfield.

Crews have been utilizing portable 4gas monitors throughout the area and have not picked up any abnormal readings. — Vallejo Firefighters Association (@VallejoFire) September 21, 2016

NBC Bay Area's Elyce Kirchner, Terry McSweeney and Rachel Witte contributed to this report.