Slope movement impacted land near Colorado Springs housing development
A 2015 slope failure affected land near a plot that’s now slated for development at Gold Hill Mesa, representatives of the developer acknowledged.
Stephanie Edwards, executive vice president for the developer, Gold Hill Neighborhood LLC, said in a statement that the land movement happened on an adjoining property and “affected a small portion” of the developer’s property in 2015. The effects were subsequently mitigated, and there were no impacts to Gold Hill Mesa homeowners, Edwards said.
State geologists last fall questioned the current stability of the northeast slope at the plot, known as Filing 10, atop the century-old mine tailings pile.
Colorado Springs city planners and engineers have put on hold construction at Filing 10 and another plot, called Filing 11, amid the Colorado Geological Survey’s concerns, including the potential for settlement and liquefaction, which is a form of destabilization that could be triggered by seismic activity from nearby faults.
Soils at Filing 10 are highly saturated, wrote Jonathan Lovekin, a senior engineering geologist for the Colorado Geological Survey, in an Oct. 19 letter to city planners outlining the State Survey’s concerns about the plot.
One boring from 1999 showed a water content of 73.2% in deep silts. Above a certain saturation level, soils behave like liquids and become unstable, Lovekin has said. And further developing Filing 10 could weigh down those soils and increase that saturation level, which could cause slope failure, he wrote.
The developer’s representatives have asserted that a slope analysis, along with other work, has shown the Filing 10 site is safe and stable for construction.
But the developer has commissioned further testing on Plot 10 in order to address the Geological Survey’s concerns about slope stability. The plot sits on the northeast side of the development, visible from U.S. 24.
The area of the slope failure in May 2015 is roughly 770 feet southeast of Filing 10’s boundary, according to an annotated map provided to The Gazette by the developer.
The failure, which occurred on a section of the east mesa slope, was “a result of an historic, prolonged precipitation period,” according to a 2018 geologic hazards evaluation update by CTL Thompson that the developer provided to The Gazette.
“Our investigation concluded this was a reactivation of the west end of a 30+ year old slope creep failure that exists along the south side of the mobile home park that lays east of Gold Hill Mesa along Gardner Street,” states the update report, which also covers two other Filings and includes site grading recommendations.
Gold Hill’s Edwards noted in a recent statement that the old tailings dam face will be capped with non-tailings material and planted with a mix of native seeds “to help with long-term stability and sustainability.”
The developer has not released an evaluation of the 2015 slope failure that was written by CTL Thompson, a regional engineering firm that the developer has hired to conduct some of the additional testing on Filings 10 and 11. The Colorado Geological Survey requested the slope failure evaluation last fall; the developer plans to submit that report to the city with the new Filing 10 analysis, Edwards said in a statement.
She declined to provide the slope failure evaluation to The Gazette, saying it isn’t applicable to the current analysis or the most recent Filing 10 submission.
Looking out over Gold Hill Mesa, a housing development in Colorado Springs.