High levels of methane-based hydrocarbons have been discovered underground near the Manhattan Village development, site of the Manhattan Village Mall and more than 160 homes and condominiums in Manhattan Beach.
The tests, ironically, were begun in mid-February to assuage the fears of owners, residents and city officials that hydrocarbon vapors discovered in El Porto last month had migrated farther south to Manhattan Village, which sits atop a former Chevron USA Inc. fuel storage farm.
At that time, Chevron Land and Development Co. spokesman Gary Luque said, "We don't expect to find anything. We're doing this mainly to alleviate any concerns the city or residents may have."
But independent consultants for Chevron Land, which owns the site, said that in preliminary testing they have discovered readings of 10,000 parts per million of mostly methane gas on a proposed golf course near the residential portion of the development. Methane is explosive at 53,000 ppm.
Highest Reading on Monitor
Those levels, found 50 feet below the surface near the center of the proposed golf course, are the highest that the monitoring equipment used can register. Another well, closer to the homes, measured 3,200 ppm. No significant levels were found on the residential development itself.
Luque said that in addition to the vapors, consultants discovered "oily black material" in an area about 50 feet wide, indicating, he said, an on-site source.
"My guess is these are coming from somewhere on the site," Luque said. "I don't think they have any connection with the (El Segundo) refinery."
Chevron USA spokesman Norman R. LeRoy said that the high methane levels found essentially rule out gasoline as a source.
"We are looking at the chemical breakdown of some other material that could very likely be heavy oil," he speculated. "When toxic organic material such as heavy oil is covered with dirt, as it was here, it undergoes biodegradation, which results in methane."
Luque said that the proposed golf course lies "right in the middle of the sump area," where Chevron once stored crude oil and other heavy fuel-oil compounds. The liquids, he said, were stored in concrete-lined reservoirs "the size of football fields" until the 1960s. Testing conducted in the late 1970s, before construction of the project, Luque said, showed no soil or water contamination.
Worry About Drinking Water
While the current readings are still far below the explosive level for methane, a senior engineer for the Regional Water Quality Control Board, Raymond K. Delacourt, says he is concerned that the fumes might endanger the ground water that supplies about 15% of Manhattan Beach's drinking water.
Delacourt explained that on the west side of Sepulveda Boulevard, where gasoline-based hydrocarbon vapors have been found in El Porto and El Segundo, ground water has long since been rendered unusable for drinking because of salt-water intrusion. Fresh-water injection wells along Sepulveda act as a barrier to prevent intrusion farther inland.
But because these vapors have been found on the east side of the street, he said, they could be mixing with drinkable ground water. Delacourt added, however, that the vapors have been found only at shallow levels, and noted that the Silverado Aquifer, which supplies drinking water, is 600 feet below the surface. But, he said, "the potential is there."
Monitoring the ground water, Delacourt said, "is definitely the next step."
According to Chevron Land project manager Luque, the company this week will be proposing a full-scale investigation of the vapors, including additional vapor wells, testing to define the extent and severity of the vapors, and speciation tests (special tests to determine the chemical makeup of the vapors and their exact levels). The last time vapors peaked at 10,000 ppm on standard monitoring equipment in El Porto, speciation tests showed the vapors were actually at 95,000 ppm in spots.
Delacourt emphasized that his agency will be monitoring the investigation--and particularly the speciation tests--closely.
"The speciation results we've gotten so far from Chevron in El Porto and El Segundo have been less than adequate, considering the amount of time they've had," Delacourt said. "We expect more rapid progress on this one."
Chevron USA has been conducting extensive investigations in both El Porto and El Segundo since the January disclosure that a large pool of liquid hydrocarbons had leaked off the refinery into El Segundo's manufacturing district.
In February, potentially explosive levels of hydrocarbon vapors were discovered along The Strand in the El Porto section of Manhattan Beach. Those vapors have not been directly linked to the refinery. Speciation tests on the El Porto vapors so far have shown only that they are so-called light-end petroleum products with a gasoline base.
Delacourt said that he particularly wants to know whether there are "priority pollutants" in the ground water at all three areas. Those pollutants, he said, are among the most hazardous that the state watches for, and include carcinogenic substances such as benzene, toluene and chlorinated hydrocarbons.