Stanislaus County will expand an environmental cleanup system at the former Geer Road landfill in an effort to keep a toxic groundwater plume from spreading.
Consultants advised the county to improve and expand a system that removes and burns the landfill gas that’s a source of the groundwater pollution. A project will add 28 landfill gas extraction wells, close some of the current wells, upgrade sumps and make other improvements.
The Geer Road landfill received garbage from 1970 until it was closed in early 1991 after local agencies discovered that water underneath the dump site was polluted with toxic compounds. The county and Modesto own the site, and the county has managed the cleanup over the years.
An April 2011 order from the state’s Regional Water Quality Control Board called for more aggressive cleanup measures after tests showed the toxic plume had spread underneath the Tuolumne River, about a mile north of Hughson.
A contractor replaced wellheads and made repairs to the gas collection system, which removes and burns the gas that’s emitted into the soil by rotting garbage.
Jami Aggers, county environmental resources director, said the repairs made the equipment work better while plans for expanding the system were submitted for state approval.
County supervisors approved designs for the new gas extraction wells Tuesday. The county expects to receive bids from contractors by July 16; the work should be completed in January. Aggers declined to release a cost estimate for the six-figure project.
Another system at the 168-acre Geer Road site pumps water from the ground and removes the toxic compounds, but stronger gas collection will serve to limit the contamination, Aggers said.
The additional wells will pull more of the gases from the decaying waste material in the ground, she explained.
Since the dump was closed 23 years ago, the county has spent $7.4 million on corrective actions and about $2.2 million to settle lawsuits from neighbors whose wells were contaminated. That was before supervisors approved a $3 million contract in December 2012 with Tetra Tech BAS Inc. for professional design services, monitoring and testing at the Geer Road site.
The cleanup is funded by disposal fees collected at the Fink Road landfill. The plume emanating from the Geer Road site is tainted with volatile organic compounds including vinyl chloride, 1,2-dichloroethane and dichlorodifluoreo-methane.
Landfill cleanups often take 30 years or more, and the county is obligated to continue until the site is clean, Aggers said.