Expanded testing for potentially explosive hydrocarbon vapors has been initiated by Chevron USA Inc. after the discovery of high levels of the vapors in this city's El Porto section.
The new survey area extends from The Strand east to Ardmore Avenue and from 45th Street south to approximately 27th Street.
The survey, which was to begin this weekend, includes testing of homes along The Strand to determine whether vapors are leaking in through sewer or utility lines or cracks in foundations.
Other measures include digging vapor and observation wells, testing sewers and monitoring air quality.
Chevron, whose El Segundo refinery lies along Manhattan Beach's northern border, began conducting studies about two weeks ago after a large pool of liquid hydrocarbons was found to have migrated off the refinery into El Segundo's manufacturing district. The vapors from the pool, which until then were assumed to be incapable of migration, have traveled an undetermined distance into El Segundo.
The El Porto discovery was made in connection with surveying done to determine the extent of El Segundo hydrocarbon migration. But Chevron officials say they do not yet know whether the refinery is the source of the Manhattan Beach vapors.
Chevron spokesman Jim Edmisson said the nearest hydrocarbon pool is 500 feet from the El Porto site and that there may be "multiple sources" of the problem.
One possible source is an abandoned sewer line running along that strip of The Strand, he said. "We took sewer readings at 45th and The Strand that registered 8,000 parts per million. That's very high for a sewer, which normally runs about 200 ppm."
That sewer line, which runs up to the Scattergood generating plant, "would be a perfect conduit" for the hydrocarbon pool located beneath the plant, Edmisson said. Chevron has been recovering hydrocarbons from that pool since the late 1970s.
Another possible source may be a Chevron service station at 45th Street and Highland Avenue where 25-year-old tanks were replaced last year, he said.
May Enlarge Survey
"Those may have leaked without our knowing it," he said, "although so far tests there have uncovered nothing."
While officials are most concerned about the 15 to 20 homes located on The Strand, Edmisson said the survey may include hundreds of homes in that area.
"We want to make darn sure that area is safe," he said at a press conference Thursday. "There is a problem. There's no question about that. We don't know what has happened out there."
Initial readings at 45th Street and Highland Avenue registered hydrocarbon vapor levels of at least 10,000 ppm, Edmisson said, the level at which such fumes become explosive. Those readings were taken from shallow, hand-dug wells at sites extending in a narrow strip along The Strand to 39th Street.
Because the instruments used in earlier tests do not register levels above 10,000 ppm, other tests are being conducted with instruments that register up to 40,000 ppm.
Edmisson said Chevron does not believe the area affected extends past 41st Street, because readings dropped off drastically there, to about 5 ppm.
"However, we've already been shown how unpredictable these vapors can be," he said, "and we will continue to survey the area extensively."
The discovery of the vapors in El Segundo and El Porto has prompted Chevron officials to plan new tests for a shopping center and housing development that sit on an old Chevron tank farm in Manhattan Beach.
The tank farm, used to store fuel oil and heavy oil until the late 1960s, is now the site of the Manhattan Village Mall and about 186 new homes and condominiums.
Gary Luque, project manager for Chevron Land and Development Co. in Huntington Beach, said Thursday that Chevron will begin vapor tests on Feb. 18 to determine whether vapors are present at the Manhattan Village site.
Independent consultants for Chevron conducted extensive tests in 1979 when the project was built and found nothing, Luque said, "and we don't expect to find anything now. We're doing this mainly to alleviate any concerns the city or residents may have."
Testing will continue for a week, he said, with results available by the end of the month.