Stanislaus County will try a new groundwater treatment system to keep the former Geer Road landfill from polluting the Tuolumne River and nearby wells.
The county will pay a Southern California contractor $1.74 million to build the groundwater extraction and treatment equipment at the old landfill on the north side of the Tuolumne River, about a mile northeast of Hughson.
It will replace an original treatment system that’s inefficient and unable to contain the tainted groundwater within the boundaries of the former dump, said Jami Aggers, director of county environmental resources.
The underlying groundwater is polluted with volatile organic compounds including vinyl chloride, which is classified as a known carcinogen by the Environmental Protection Agency.
The 168-acre landfill, jointly owned by the county and Modesto, was in operation next to the river from 1970 until it was closed in 1991. The dump with no bottom liner received 4.5 million tons of garbage from the county unincorporated area, Modesto and other cities.
Saying the county had conducted a remedial program on the cheap for 20 years, state officials issued a stern cease-and-desist order in 2011, demanding more aggressive cleanup measures. The order threatened the county with harsh penalties.
Tests showed that a toxic plume – created by landfill wastes leaching into the groundwater -- had spread underneath the Tuolumne River and could possibly move toward Hughson’s drinking water.
Recent tests show the contamination has not been detected in groundwater on the Hughson side of the river.
“It has not gone past the river,” Aggers said. ”We are required to sample the river several months each year and we have not identified any contamination in the river.”
To keep the plume from moving farther, the county has used a system to pump water from the ground and filter out contaminants. The county doubled the number of extraction wells in recent years to comply with the state’s requirements. Now, a more powerful extraction system will be installed and should be in operation in spring of 2018.
Other equipment at the former landfill removes and burns the gas that is emitted into the soil by rotting garbage.
“We are pretty confident that this will work,” said Andrew Altevogt, assistant executive officer for the Central Valley Regional Water Quality Control Board in Sacramento. “Our general order stays in effect until the problem is alleviated or they can show they are well on the road to alleviating it.”
The county’s progress in reducing the groundwater pollution will be reported to the state agency.
Aggers recommended hiring Innovative Construction Solutions of Santa Ana after two other firms, ETIC Engineering and Environmental Construction, Inc., submitted bids of $2.1 million and $2.68 million, respectively.
The county has spent millions of dollars on environmental cleanups at the former Geer landfill. Money from fees collected at Fink Road Landfill will pay for the latest project because of insufficient funds in a Geer Road cleanup account, a county report said.
Ken Carlson: 209-578-2321, @KenCarlson16