Bay Area News Roundup 
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Bay City News Report 	 	Tuesday, April 3, 2001 
Breaking News Sections, Marin IJ
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(04-03) 14:00 PST -- 
The U.S. Army Corps of Engineers says building a trench around landfill at the former Hamilton Air Force Base in Novato will help curb the leaking of methane gas into a nearby housing development. 

The Army offered seven options to keep the potentially explosive gas from dispersing to a site where Shea Homes is building a 235- home subdivision in northern Marin County. 

Methane gas was found beneath the landfill at the old air force base in 1999. The gas was capped in 1995, but is reportedly spreading through soil toward the development and has forced construction on some homes to a halt. 

Readings taken last month by the developer indicate methane gas may have breached one area of the buffer zone in low level concentrations below 5 percent, according to Jim McAlister, project manager for the Corps. 

Methane gas is not harmful if inhaled but can be combustible if it collects in a contained area. The trench option provides for passive ventilation of landfill gas within the buffer zone and includes the Army's continued testing for the presence of chemicals and monitoring of methane movement within the zone. 

The Corps' report says that although the option is "highly feasible," it may not be efficient unless blowers are used. It has an estimated cost of $130,000 a year for 30 years but more information is needed regarding best placement and design of the trench. 

The source of the gas is not clear. Industrial, commercial and domestic waste was buried in the landfill until 1974, including petroleum solvents, pesticides, low level PCBs and some metals.