By Hillel Aron
By Joseph Tsidulko
By Patrick Range McDonald
By David Futch
By Hillel Aron
By Dennis Romero
By Jill Stewart
By Dennis Romero
What is dangerous about the Belmont site?
What is methane (CH4 )?
Why is methane dangerous?
How much methane is there at the Belmont site and where?
What is hydrogen sulfide (H2S)?
Why is hydrogen sulfide dangerous?
How much hydrogen sulfide is at the Belmont site and where?
How great a danger is hydrogen sulfide at the Belmont site?
Is methane an issue only at the Belmont site?
What makes the Belmont site different from other former oil fields that have been built on?
Why can’t the Belmont site just be cleaned up?
In brief, what are the upsides of trying to make the Belmont site work?
In brief, what are the downsides of trying to make the Belmont site work? What is dangerous about the Belmont site?
Much of the Belmont Learning Complex site rests atop a shallow oil formation, the Los Angeles City Oil Field (see map), which stretches across a swath of Los Angeles from east of downtown to past Vermont Avenue. The underground oil deposits are a constant source of methane and hydrogen sulfide.
The greatest concentrations of these oil-field gases are in the northeastern section, near the intersection of Temple and Boylston streets, where the most oil drilling historically occurred. Construction also uncovered oil-stained soil in the site’s northwestern corner, when a hill was graded down. Methane gas is present along First Street, suggesting that hazards associated with oil fields affect the entire site.Return to top. What is methane (CH4 )?
Methane is a colorless, odorless hydrocarbon, the lighter-than-air "natural gas" that heats your water and lights your stove — and blew up a Los Angeles department store in 1985.
Methane forms underground two different ways: either deep underground under immense pressure, or as a byproduct released when subsurface bacteria chomp on decomposing biomass — which can include oil residue.
This first method of methane production — pressure deep below the surface — is the same process that creates crude oil. Oil drilling can allow methane to migrate up to the surface.Return to top. Why is methane dangerous?
Methane is flammable and explosive. When the amount of methane reaches 5 to 15 percent of the air in an enclosed space, any spark from electrical equipment, a match or a cigarette can literally set the air on fire. Methane isn’t known to be carcinogenic or otherwise toxic. Pure methane is odorless; the gas company adds a smelling agent, mercaptan, as a safety precaution.Return to top. How much methane is there at the Belmont site and where?
Comprehensive soil-vapor testing of all 35 acres at once was not attempted until March 1999. Although that report calls for additional testing, the 1999 figures remain the most current. The numbers represent snapshots of gas levels that fluctuate naturally.
Every soil probe recorded methane; concentrations approaching or surpassing explosive levels were measured in 12 of 57 soil-vapor probes. Of the 12, two found methane concentrations up to 16 times above the explosive threshold five feet below ground level in the baseball field. Similar readings up to 18 times the limit also were recorded in that area from five probes thrust to depths between 40 and 78 feet below ground, mostly along the Boylston Street edge, where the heaviest oil drilling occurred. In the football field, a soil probe (27 feet underground) near midfield measured eight times the explosive level (see map).Return to top. What is hydrogen sulfide (H2S)?
A noxious rotten-egg odor is the signature of this toxic, combustible, heavier-than-air gas, which is formed either at great depth under pressure or by sulfur-eating bacteria. Methane and hydrogen sulfide are often found together in oil fields.Return to top. Why is hydrogen sulfide dangerous?
The consequences of breathing hydrogen sulfide include headaches, eye irritation, pulmonary damage and, in concentrations heavy enough, neural damage or death. The permissible exposure limit of hydrogen sulfide under state law is .03 parts per million per hour, although workplace standards allow exposure up to 50 parts per million for short periods of time. Prolonged exposure to 50 ppm can cause upper respiratory tract damage; exposure up to 150 ppm temporarily paralyzes the sense of smell after only a few minutes, while a few lungfuls of 500 ppm can cause unconsciousness. Minute exposure to 1,000 ppm can cause coma, neural damage and death. The cumulative effects over time of small doses are unknown and the subject of much debate. It’s almost certain that children are at greater risk of harm than adults.Return to top. How much hydrogen sulfide is at the Belmont site and where?
Tests in April 1999 twice found levels up to 3,300 parts per million of hydrogen sulfide around 30 feet underground in the baseball outfield and 6 parts per million five feet down. Otherwise, one probe found barely detectable levels underneath the Administrative Center, and nothing elsewhere. March 1998 testing found around 33 ppm of hydrogen sulfide under the Administrative Center and 192 ppm under the planned Community Center. (see map)Return to top. How great a danger is hydrogen sulfide at the Belmont site?
Some experts minimize the need for special protection against hydrogen sulfide at Belmont. Widespread hydrogen sulfide was not found, and they downplay the possibility that this heavier-than-air gas would migrate to the surface in a damaging quantity.