That sinking feeling
Geological hazards can wreak havoc in parts of Colorado
Rick Moore had never heard of the geological term “evaporite” before he bought a home in the Ironbridge golf course development in the Roaring Fork Valley south of Glenwood Springs.
He’s been learning about it the hard way, since his house began sliding downhill.
“Right now the garage is sinking, the driveway is sinking and basically the house is moving, too,” said Moore.
Blame goes to evaporative minerals that were deposited in Colorado millions of years ago. In a lawsuit, Moore and several other Ironbridge homeowners also blame those involved with the development, where dissolution of underlying evaporite also was responsible for a large sinkhole that swallowed up two golf carts in 2005.
That sinkhole is pictured in a report that accompanies a new Colorado Geological Survey map aimed at boosting awareness about areas of Colorado where sinkholes, subsidence, near-surface cavern formation and other effects of evaporite dissolution pose potential hazards for development, and even to life and limb.
Ted Swain, 63, can attest to the latter. He lives on his family’s ranch between Paradox and Bedrock in Montrose County. The new CGS report, principally authored and researched by senior engineering geologist Jonathan White, includes photos of the Swain family rescuing a calf that had fallen into a sinkhole on the ranch in 2005.
Swain said the family had covered the hole with cedar posts to divert cows around it while moving them during branding.
“After branding I was up there checking calves and I heard this bawling and this one calf had spilled through the cedar posts and fallen in there,” he said.
He used a ladder to enter the hole, which widened inside to 8 or 10 feet in diameter, and rigged up a rope harness. A tree skidder with a winch was used to pull out the calf, which recovered after having become hypothermic from water in the hole bottom.
This wasn’t the first time a sinkhole had trapped an animal on the family’s ranch. When Swain was young, his dad took him and others to see a bobcat that had fallen in one.
“Dad threw in a cedar post to give that cat a ladder to get out. I remember that vividly,” Swain said.
He also remembers his dad once inadvertently dropping the front wheels of a John Deere tractor into a sinkhole and having to use another piece of equipment to pull it out.
Something to think about
Evaporite problems also can pose threats to development, as in the Roaring Fork and Eagle valleys, where in recent decades ranchlands have rapidly been converted to often-pricey residential subdivisions. The new CGS map is meant to serve “as a guide for landowners, planners, government land-use regulators, and the geotechnical and civil engineering community,” White’s report reads.
In an interview, he said the hope is that people will take evaporite issues into consideration in areas identified by the map. In most cases it’s likely the hazard will be determined to be low, but if it isn’t, that allows for steps such as engineering that addresses the issue.
“We’re trying to promote a level of investigation that wouldn’t necessarily be done otherwise,” White said.
Swain said evaporite and related issues such as sinkholes are more of a curiosity and occasional nuisance than anything else in what he calls the “gyp hills” where he lives. (Gypsum is a kind of evaporite.)
Development is less common there, but he said when Paradox built a fire station in the early 1980s, it took the proper precautions with the foundation and hasn’t had problems.
According to White’s report, investigative borings for a condominium complex at the Beaver Creek ski resort in Eagle County revealed gypsum caverns up to 13 feet wide and 80 feet deep. As a result, holes for pier foundations were drilled to below the voids, and the caverns were cased off and isolated before pouring concrete into the drill shaft.
Another technique used in Colorado is grouting to plug the throat of sinkholes.
Due to evaporite’s solubility, proper drainage and water management are important in developments.
“Several re-activations of sinkholes have been the result of proximity to irrigation or irrigation ditches,” White’s report notes.
One piece of agricultural land in the Buford area east of Meeker is so sinkhole-prone it became known as Pot Hole Ranch. When former Goldman Sachs co-president Jon Winkelried bought the ranch and planned to build a large horse arena there, he hired a geophysics team to shoot electrical currents to determine where sinkholes existed or were absent down to bedrock, according to 2003 Rio Blanco County commissioner minutes.
“An investment of this nature requires that it be completed carefully and correctly,” the minutes paraphrase Winkelried as telling commissioners.
A sinkhole-ridden valley
White believes similar precautions are worth considering in areas such as the Roaring Fork Valley between Glenwood Springs and Carbondale.
Sinkholes are common in undeveloped areas along the valley floor. In addition, in 2003 a 25-by-20-foot sinkhole opened on the soccer field at the Colorado Mountain College campus in the Spring Valley area above the valley. It was backfilled but reopened and further enlarged in 2004, according to White’s report. Also in 2003, a sinkhole opened along the newly built Midland Avenue near the large Glenwood Meadows retail development then being built in Glenwood Springs.
At Ironbridge, Moore said the backsplash on his kitchen counter has pulled about an inch away from the wall and a crack in the wall runs from a window to the floor. He said he lives in a beautiful place, but the assessed value of his home has dropped sharply and it’s hard to know how much is due to the recession versus the foundation problems. While the house is still livable, it would be hard to sell without doing major foundation work, he said.
Affected homeowners at Ironbridge are suing parties including the builders, soils experts and developer, trying to determine who might be responsible for their problems. The development is still owned by the holding company that emerged from the Lehman Brothers bankruptcy.
Moore said the whole ordeal, which has been further complicated by the bankruptcy, has been draining for him. He doesn’t know if developers were given bad information about how to build proper foundations in the area, or ignored it. But he’s not an expert on evaporite problems and had reason to assume the house was built the correct way, he said.
“I run a lodge. If I tell someone it’s going to be a clean room with a queen bed and it’s a dirty room with two twin beds, then it’s my fault, not the (fault of the) people who come into the room,” he said.
Knowing versus doing
Fred Jarman, Garfield County’s building and planning director, said the Ironbridge developers knew from the start that they faced issues related to evaporite.
“To that end, the question is can you engineer around these issues,” he said.
He said there was “upfront and ongoing engineering” occurring at Ironbridge related to the evaporite.
Construction in such areas occurs all the time, he said.
“Whether it’s done correctly … that’s a different issue,” he said.
White said sometimes geotechnical reports aren’t followed or are forgotten. Or drainage isn’t dealt with properly, or landscapers or homeowners do something that improperly wets soils and creates problems.
He said sometimes such geological hazards are addressed at a preliminary level, but once a development is approved “people tend to stop remembering that stuff.”
“It’s deep in a file and people don’t see it,” he said.
Jarman said there are evaporite areas in Garfield County that may simply be too risky to be developed, and county commissioners have the authority to prevent such development.
Otherwise, he said, it’s important that the issues receive a proper review, mitigations occur if warranted, and then documentation occurs in places such as plats and covenants so people can take the matter into consideration when deciding whether to buy a property.
White hopes the new state map will help put everyone on notice where potential problems may exist. That way the risk can be evaluated, site-specific investigation can occur where warranted, and proper mitigation steps can be considered.
He said if he was going to spend a half-million dollars on a house and was considering building in an area with a history of sinkholes, he would want to make sure there weren’t potential issues. If that cost $15,000 or $20,000 to do, he would either spend the money or look elsewhere, he said.
“People need to understand ground movement is not covered by basic homeowners insurance,” he said.