The Science of Making Belmont Safe
RIVERSIDE COUNTY Under a hot, humid March sky, down the road from a cow shed, another subdivision is on the rise at the end of a featureless cul-de-sac. But theres one complication. These four houses under construction are located atop ground that contains methane gas a natural byproduct of decaying biomass, in this case, cow manure from a dairy. Methane disperses harmlessly in open areas, but it can accumulate to explosive concentrations in enclosed spaces. Unless something is done, methane could eventually collect in these homes and become a fire hazard. Light a match in a room full of methane and poof.
A similar challenge confronts the Los Angeles Unified School District at the half-finished Belmont Learning Complex. Belmont, like these houses and like thousands of other Southern California properties, sits on property that emits methane gas. At Belmont, the gas comes from the oil field below, a common situation in Los Angeles. But methane also is a problem for contractors building on wetlands, land that used to be swampy or former agricultural sites, especially dairies.
Francesco Fonseca knows exactly what to do. Hes handled this problem many times before for GeoKenetics Inc. "Were making a burrito," he explains. More precisely, hes building a system that will draw in methane from under the house and then vent it harmlessly into the open air (see "How to Make a Methane Burrito").
Fonseca and two coworkers have dug a series of trenches and lined them with a synthetic, woven fabric. The trenches snake under where the living room, the bathroom and the garage will be.
Plastic pipes slotted with vents trace the same path, inside the trenches. These pipes connect to a vertical joint that will soon lead an exhaust pipe above roof level. Gravel from a backhoe is then shoveled in by the workers. At this point the system more resembles a taco than a burrito. But then the ends of the synthetic fabric are folded over, and fastened together with duct tape. Theres your methane burrito.
Methane, which is lighter than air, follows the path of least resistance. So before it can find a crack in the floor slab, it will encounter the open vents in the pipes and begin its journey to the atmosphere.
Day and night cyclical variations in barometric pressure, says GeoKenetics principal engineer Glenn Tofani, will ensure that methane is drawn out and fresh air brought back into the pipes. This "passive" way of evacuating methane is by far the most common method. But it can be made "active" by installing a suction fan.
But theres more. A week later, Tofani is on site to supervise as workers spray on over the filled-in trenches a membrane called Liquid Boot, which dries quickly to a thin white coating. The job of the Liquid Boot is to act as a barrier keeping methane from the house. If all works as planned, the Liquid Boot coating will, in effect, route the methane toward the vented pipes.
For this job, Tofani has decided to add another barrier too a layer of plastic called high-density polyethelyne.
Installing safety systems to protect against methane has become a cottage industry in Los Angeles in the wake of a 1985 methane explosion that injured about two dozen people in the Fairfax District. The technology was originally developed for the petroleum industry and landfills, which can emit methane and other gases. Barrier-and-venting systems are underneath, among thousands of places, just about everything new built in the Fairfax District as well as L.A.s Central Library, a Wells Fargo bank on Beverly Boulevard, housing tracts in Orange County and a Marriott hotel in El Segundo. Whole hillside developments in Brea are planned on former oil fields.
At Belmont, theres an additional challenge. The ground also contains spot concentrations of hydrogen sulfide, which is toxic. Though not as pervasive as methane, hydrogen sulfide too can be found in parts of the L.A. basin that are fully developed with homes, schools and businesses. It can be dealt with through machinery that separates hydrogen sulfide from methane, so that the hydrogen sulfide can be collected in a tank.
Such a system is in place in Newport Beach at Hoag Hospital, which has higher concentrations of underground hydrogen sulfide than the Belmont site. Hoag uses its "cleaned" methane to heat the building.
The safety system at Hoag incorporates a network of wells and trench collectors that pump soil gases to a central unit, where air scrubbers remove the toxic hydrogen sulfide. The hospital also has backup measures: A pipe-and-barrier system underneath the building slab serves as extra guard against gas leaking through the buildings foundation. Inside the hospital, there are air pumps that pull in fresh air at a rate faster than the gas can come through the foundation should gas sensors detect seeping methane.
A similar layering of fail-safe systems would most likely be the plan at Belmont. For instance, contractors could install a plastic lining under the buildings, and below this, a venting system to pull out soil gases. Hydrogen sulfide could be collected in a tank, as at Hoag. Methane alarms could be installed below the barrier, above the barrier, or both, as could an alarm signaling a malfunction in the venting system. The setup sounds complex to a layman, but its relatively simple, established technology, according to engineers interviewed by the Weekly.
In fact, several engineers said that the anticipated Belmont fix was overkill, noting that they have been installing "lesser" systems all over the L.A. basin without incident. But at Belmont, it would be hard to justify anything but the strictest safety standards.
The quality of these systems has improved since the mid-1970s, when state engineers and contractors were installing methane mitigation for the first time. The process was also new to city and fire-department inspectors who had to sign off on the work after the Fairfax explosion. There is no degree program in vapor-barrier science.
Inevitably, some things went wrong. A faulty barrier system underneath an office building on Wilshire Boulevard has created an ongoing potentially hazardous nuisance.
"Oil was oozing through the walls, and the building had methane sensors that were continually going off," says Louis Pandolfi, whose firm GeoScience Analytical monitors the building for methane accumulation. Even today, he says, "youll just see the oil coming through the walls of the subterranean walls. Gas is in the building at all times in the lower levels." As a result, a venting fan must run 24 hours a day, and the encroaching oil must be removed.
Litigation over the failed system eventually led to a $4 million settlement paid to the buildings owners by contractors, subcontractors or their insurers. No one admitted any wrongdoing.
At Belmont, a Hoag-like extraction system would run about $10 million to design and install, according to Pandolfi. Another methane specialist, John Sepich, says a simpler pipe-and-barrier setup would suffice, at a cost of about $2 million.
Sepich designed the barrier system under the Central Library, among other places, as well as the original safety system intended for Belmont. Belmont opponents criticize Sepich because his final design did not protect all of the buildings at Belmont. Critics regard him as overly cost-conscious and more "pro-contractor" than "pro-safety." Sepich vigorously disputes this contention, and insists that the dangers at Belmont have been considerably overrated. The entire site does not need protection, he says, because gas was not detected everywhere and "when you dont find gas you dont need a membrane."
District officials incline toward a more conservative view. Despite the added expense, any safety system at Belmont is likely to include all the buildings and the playing fields as well.
Last month, the school district formally invited contractors to submit plans for finishing Belmont. These plans would have to include a safety fix. For Belmont, its unlikely that a "passive" system like the one used by Tofanis company in Riverside would be approved by oversight agencies. Instead, the state Department of Toxic Substances Control has indicated its preference for an "active" venting system, one that uses suction to pull methane into its pipes.
A safety system at Belmont also must address the schools playing fields. In open air, methane poses no danger, but even minuscule amounts of hydrogen sulfide pose health risks. One way to deal with hydrogen sulfide is to install a layer of sand or gravel to disperse the gas to harmless concentrations. This strategy can be combined with laying down venting pipes, which lead into gas-collection tanks.
In Riverside, back underneath the March sky, Fonseca is pushing his crew to hurry up; itll get dark soon. "I dont finish, I dont go home," he says.
Californias rapid growth is beginning to make scenes like this commonplace. Any open land, it seems, is game for building. At the very least, the boom isnt going to stop in its tracks because of oil deposits or cow feces a message brought home by the vista at the Riverside County construction site. The blocks all around are filled with houses that have tell-tale black piping poking above the roofs.
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