Todd R. Brown, staff writer | Feb. 6, 2007 at 2:39am
SOUTH SAN FRANCISCO — One generation's trash is another's environmental headache. Case-in-point: a 57-acre landfill at Oyster Point that may be leaking methane.
A rise in the amount of the hazardous gas found there prompted the city to grant $94,000 to a consulting firm to test whether the methane is migrating from the landfill and where it is heading.
"One of our biggest concerns with methane is that it's going to get into a building, build up and then explode," said Dean Peterson, director of environmental health for the county. "The requirement is that no methane or no gas should go off the site."
According to a city staff report, tests in April and May of gas monitoring wells at the site by Terra Engineers — the same firm that will assess the possible leak — found higher-than-allowed levels of methane.
"There's no imminent public safety or public health risk," Peterson said, adding that the gas exposure is "affecting neither the day care nor any of the businesses down at the marina."
The Peninsula Family YMCA Gateway Child Care Center on Gateway Boulevard is less than a mile west of the landfill area.
Methane is explosive and can displace oxygen and cause asphyxiation the same way carbon monoxide can. It also is a greenhouse gas that contributes to climate change.
Methane is easy to measure, Peterson said, but other gases produced by decomposition in landfills pose dangers, including vinyl chloride, a known carcinogen used to make PVC.
Terra Engineers will look at whether the methane is creeping along utility trenches that are lined with gravel and connect to buildings, Peterson said, because they can serve as easy pathways for the lighter-than-air gas to travel along.
The firm also will be installing another monitoring well once it examines the methane source, according to City Engineer Ray Razavi.
"Some of their wells were getting filled with water," he said. "They'd like to have an extra well, just to be on the safe side."
Although Razavi said no buildingsare in the immediate vicinity of the elevated methane, construction of a hotel and conference center there has been under discussion for years.
"There's some proposals to build stuff right on top of Oyster Point, but nothing has been planned or accepted yet," he said.
The landfill, which was closed in 1975 and capped with clay, runs along Gull Drive and is now home to Oyster Point Marina. More than 4,000 cubic yards of liquid and solid waste, including steel drums, were removed and the cap extended during construction of Gull Drive in 1995, according to a city staff report.
The state required that gas monitoring wells be installed as part of the closure plan, and Terra Engineers (then called Gabewell) was hired for the job, which includes quarterly monitoring.
The county has 15 closed landfills, Peterson said, and several vent and burn off accumulated methane, including Colma's landfill beneath the Home Depot store and Brisbane's Baylands.
Peterson said handling a possible leak at the Oyster Point landfill requires plenty of study. He said while the city has known about the problem since last year's tests, engineers have been putting together a plan for how to deal with the unlined material.
"Often times we don't have an exact landfill boundary," Peterson said. "They weren't managed so well in the old days as they are now."
Staff writer Todd R. Brown covers the North County. Reach him at (650) 348-4473 or firstname.lastname@example.org.