Suggested fix at Grand County landfill would cost $6.6 million
July 28, 2011
The landslide at the Grand County-owned Granby Landfill is not going to stop without further costly human intervention.
This year’s heavy precipitation has accelerated and complicated the landfill landslide, which was first addressed in 2007 with a $4 million engineered berm to stop the uphill mass of the slide.
That upper portion has since remained sound, according to county officials, but about 30 acres of a lower land mass that includes solid waste is moving as one unit atop a slippery layer of clay material and water deep underground.
The slide has been moving at a rate of about 1 foot per month, and this spring, according to Grand County Road and Bridge Assistant Superintendent Bill Clark, the slide has reached a record rate of 1.5 feet per month.
“It has speeded up this year over last year,” Clark said.
The “fastest” part of the sliding land mass is about 50 feet to 75 feet from Coyote Creek, which feeds into the Colorado River, but the solid waste portion of the mass is much farther away.
County Road and Bridge personnel have been working to keep a 3- to 4-foot crack in the solid-waste portion of the land constantly filled with dirt to prevent surface water from penetrating into the groundwater table. The county has been heavily monitoring the groundwater to ensure there has not been a contaminated breach, according to County Manager Lurline Underbrink Curran.
The Granby Landfill has been closed to the public, but the problem of the landslide must be solved in order to gain state approval for closure of the site, at which point continued landfill monitoring and remediation for a period of 30 years would begin as the landfill is restored to a natural state.
But any solution in stopping the sliding land mass is likely to entail a substantial engineering feat.
County officials met with a panel of engineers on Tuesday, July 26, to learn about the county’s options for stopping the slide – options with estimated costs ranging from $6.6 million to $59 million.
Engineers KRW Consulting of Lakewood, Ground Engineering of Commerce City and oversight engineers from the Colorado School of Mines, Dr. Mike Mooney and Dr. Paul Santi, said the Granby Landfill is a “strong candidate” for a $6.6 million “tieback system,” deemed the best solution for having “a high probability of success with the least cost,” according to engineers.
The tieback system has been used several times in the Rocky Mountains, engineers said, and offers a 95 percent chance at success.
It involves 500 permanent ground anchors used to stabilize the landslide. At the surface are rows of 10-foot by 10-foot concrete bearing pads each attached to a steel cable that is drilled deep into the ground through the slip plane and into the bedrock below.
This system in effect locks the land in place, allowing it to settle over time, according to engineers.
The process would be relatively simple, they said, and would likely stop the slide upon completion.
All the exposed concrete pads could be buried to hide them from plain view and allow for the slope to be re-seeded.
Other options considered but not recommended to county officials are: Do nothing; relocate the landfill at a cost of $43 million with a success rate of 100 percent; incinerate waste at a cost of $59 million with 100 percent success rate; create a much larger buttress than what was completed in 2007 at a cost of $20 million with a 95 percent success rate; and dewater the landslide with vertical wells at a cost of $7.6 million with a 75 percent success rate.
But each of those options has its own share of negatives, according to engineers. Relocating the waste to another county landfill would be expensive, would take nine years to complete and likely would generate strong public opposition.
Incinerating the waste, with some used to generate electricity, is the most expensive option and may not even be permitted due to the landfill’s proximity to a wilderness “class one airshed.”
Creating an earthen buttress four times the size of the one constructed in 2007 may require relocating portions of Coyote Creek, CR 125 and power lines.
Dewatering the site may take at least three years, may not be feasible beyond 600 feet, may require drilling wells through landfill waste, and could impact emergent wetlands near Coyote Creek.
In engineering analyses, the tieback system was deemed to have zero cons.
Commissioners intend to make a decision on a future date.
Tonya Bina can be reached at 970-887-3334 ext. 19603