Balboa Park Standing at the tee pad of hole 15, a Frisbee player on Morley Field’s Disc Golf Course can’t see the basket he’s aiming for. It’s hidden in a thicket of trees 246 feet away. Players searching for their errant neon-colored discs amble down a hill, then up a slope, toward a chain-link fence and adjoining cinder-block wall. The fence and wall enclose a maintenance yard, and rising above the wall is a stack from which issues a deep, low roar.
Frisbee golfers familiar with the course know the basket is 15 feet below and just to the right of the stack. Serious players gauge the wind’s direction by checking the heat waves emanating from the top of the stack. Most people have no idea what’s burning inside.
Brandon L. and Eric Stanger, both 26 years old, often play the course. “Everybody’s always wondered, like, what’s coming out of it and if it is hazardous,” says Brandon. “It’s obviously heat and chemicals. You can see the waves coming off of it.”
“It’s used for burning something,” suggests an employee at the course’s pro shop. “Some people have said it’s used for burning eucalyptus trees, because sometimes if the wind blows in the right direction, it smells weird.”
At one time this southeast corner of Balboa Park was called the Arizona Landfill. Open between 1952 and 1974, the 139-acre landfill was one of three city-operated dumps. Approximately 90 percent of the landfill’s waste came from regular household trash; the other 10 percent came from construction demolition. A portion of the disc golf course — as well as the archery course, the city nursery, the outfield for the college-sized baseball field, and the walking/mountain-biking trail — sit atop an estimated 1.9 million tons of trash.
Decomposing trash creates landfill gas. The composition of landfill gas varies but is approximately 40 percent methane, 40 percent carbon dioxide, nitrogen, water vapor, and hundreds of trace gases. The trace gases originate from all sorts of sources, from PVC to concrete to decomposing plastics. If no gas-collection system is in place, over 90 percent of the methane, a greenhouse gas, is released into the environment.
Methane can also cause an explosion. In 1987, the City began grading the Arizona Landfill and extending a storm drain system. During the project, a laborer removed a piece of plywood that was covering a storm drain inlet. A short time later, he lit a cigarette. The spark ignited the accumulating gases, causing an explosion that left the worker with third-degree burns over 35 percent of his body.
Ray Purtee works for the City of San Diego’s Environmental Services Department. “In the late ’80s, new air pollution regulations weren’t allowing the methane to just waft out into the environment,” he says.
So in 1990, the City began installing a vacuum and flare system. The original plan called for 23 gas extraction wells to be spread throughout the old landfill, but after further testing, 51 more wells had to be installed.
Methane wells are made by drilling a hole into the landfill and inserting a perforated pipe. The pipes are then backfilled with gravel and sediment and are connected to an underground vacuum collection system that pumps the gases to the stack, called, in this case, a “shrouded flare.” An initial spark from a propane tank starts the combustion process.
Although primitive looking, the shrouded flare — an enclosed, insulated cylinder — is precisely engineered. The stack is 16 feet 2 inches tall and 5 feet 11 inches in diameter. “It’s that tall for a number of reasons,” says Purtee. “The height of the flame of combustion and what we call the ‘residence time.’ The residence time holds the landfill gas at 1600 degrees at a minimum of .3 seconds. That is how it is designed to destroy the constituents of the landfill gas.
“The manufacturer of the flare claims 99.5 percent destruction efficiency,” Purtee says, “so there is that .5 percent that is not being destroyed, and that .5 percent are the compounds considered toxic, like hydrogen sulfide, PVC monomer, and xylene. In high quantities you wouldn’t want to be breathing it, and it would be toxic.”
At the time the Arizona Landfill was open, people threw hazardous waste into their trashcans, things like paint, pesticides, and photochemicals. Depending on what’s buried in the landfill and what gases are being released, dioxin, among the most dangerous toxins, can be created in the stack and released into the air.
The flare system runs 24 hours a day, except for once a month when it’s shut down for maintenance. If a malfunction is detected, an automated system is alerted and places a call to Purtee’s cell phone.
Some landfills around the country, rather than flaring their methane, use it as an energy source, employing either gas-fired boilers, internal combustion engines, or gas-fired turbines. In San Diego, the City-owned Miramar Landfill and privately owned Sycamore Landfill both use methane to produce electricity in gas-fired turbines.
Mirat Gurol, a professor of environmental engineering at San Diego State University, is unsure of the overall benefit of using landfill gas as an energy source. “The gases can be collected and treated by methods such as activated carbon adsorption or washing of gases before or after burning. These are costly alternatives to flaring. Although methane has a heating value, typically old landfills do not generate sufficient concentrated gases to justify collecting the gases to produce energy.”
Purtee says the City and civic groups “have been looking at alternatives for this site for beneficial use of the landfill gases other than flaring it. This system will remain the system even if there would be another method to reuse some of the gas. We just have too much capital invested to throw this system away, and the amount of gas this site produces, though significant, is rather small in comparison to larger landfills like Miramar.” The City has spent “easily $1.5 million so far at this site, just in gas collection and flaring,” Purtee says. But he can think of uses for the electricity created by the methane, for instance, to light the nearby tennis courts. “There’s a huge lighting load at the tennis courts at night,” he says.