Phillips 66 has not responded to requests for comment on its delay in contacting the county.
The odor that sent dozens to the hospital and prompted the investigation was first reported at 7:15 p.m. on Sept. 20, according to Joanna Altman, an assistant to Vallejo's city manager.
Callers to the city's communications operators complained of an unknown odor in South Vallejo, areas just north of the Carquinez Strait and on the eastern shore of San Pablo Bay.
The city issued a shelter in place order, and city crews and PG&E representatives tried to find the source of the odor.
Shortly after 8 p.m. that night, Vallejo city officials were told that Phillips 66 had shut down some of its operations, but they were not told why, Altman said.
Crews on two San Francisco Bay ferryboats returning to Vallejo then reported an oil sheen to the U.S. Coast Guard.
Sawyer said that crews unloading crude from the Yamuna Spirit noticed a sheen in San Pablo Bay at 1 a.m. the following Wednesday.
At daybreak, the Coast Guard confirmed the presence of a sheen that was 1 mile long and 40 feet wide. The agency later learned that there were two oil sheens in the water, one of them close to the Phillips 66 terminal.
The refinery told the California State Warning Center shortly before 9 a.m., according to Shawn Boyd, a spokesman for the Governor's Office of Emergency Services.
The company told Contra Costa's hazardous materials program at 11 a.m., Sawyer said.
The Coast Guard and the state Office of Spill Prevention and Response (OSPR) have been testing the liquid found in the sheens to determine what the substance was and where it came from.
Results of those tests are pending and the investigation is ongoing, said OSPR spokeswoman Amy Norris.
The lack of answers frustrates at least one Vallejo city official.
Councilwoman Katy Miessner said the possibility that an oil spill may have sickened some of the city's residents is cause for concern.