About 20 Buellton residents called the fire department Sunday night into Monday morning complaining of a gas smell.
They said it was nauseating and burned their eyes.
The fire department found out Plains All American Pipeline company is replacing a pipeline in west Buellton that runs under Highway 246.
The needed to flush out the section first to prevent oil spills and contamination.
The sent out a letter in February telling residents they would perform a routine replacement of the 15-year-old pipeline.
Residents are upset the letter didn't mention the possible rotten-egg odor.
The fire captain said the smell is hydrogen sulfide that is present in crude oil, and the chilly morning air forced the gas to sit in the neighborhood.
An air quality monitor said there were low levels of gas in the air, which the fire department believes to be harmless.
The company says the flushing is complete but residents may still smell some odors from the remaining work they have to do to replace the section of the pipeline.
The pipeline runs from the Central Coast to Bakersfield.
The fire department says to call 9-1-1 if anyone feel sick from the gas.