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08-15-2006 06:52 AM |
Swallowed Up
http://www.news-leader.com/apps/pbcs...WS01/608150380
As a sinkhole swallowed more of a house in Nixa, researchers worked Monday to determine how the void formed and whether it will continue growing.
Shortly before noon, the north side of the house hanging over the sinkhole's edge collapsed into the hole, breaking the house's spine.
The sight stunned people like longtime Nixa resident Charles Green, who with his wife, Karen, joined dozens of people watching in yards across the street from the roped-off area.
There are plenty of sinkholes around Nixa, but not in the downtown neighborhood where the sinkhole appeared Sunday, Green said.
"It's weird, it's weird," he said of the appearance of a sinkhole where there had been no sign of the geological formations. "I think the drought had something to do with it."
That's a possibility, said Missouri State University assistant professor of geology Doug Gouzie.
"I don't know of any evidence, but it wouldn't surprise me it played a role," he said.
Nixa officials might want to act to stop its progress before its walls collapse and it consumes a section of Delaware Street and another home to the north of the sinkhole, said Peter Price, environmental geology section chief with the Missouri Department of Natural Resources' Division of Geology and Land Survey.
Price and two colleagues surveyed the sinkhole that appeared Sunday morning and devoured Norm Scrivener's garage and car.
"It may be best to provide some remediation as soon as possible to prevent additional collapse," Price said of handling a sinkhole originally estimated to be nearly 70 feet across and 75 feet deep Sunday. By Monday, it had grown in width about 5 feet but became shallower as dirt fell from its walls.
Sinkholes shouldn't be converted to ponds or stormwater detention basins, or filled in for construction, hydrogeologist Tom Aley said.
And sinkholes shouldn't be filled with trash or debris, which along with impeding water flow can cause groundwater pollution, the owner of Ozark Underground Laboratory at Protem said.
"It's a part of the (natural) plumbing," he said of sinkholes. "You play with the plumbing, and it's going to change the plumbing somewhere else."
Sinkholes pock much of southwest Missouri. Greene County, considered the only county in Missouri to conduct a full-scale sinkhole survey, has recorded over 2,500.
Nixa has hired a consulting engineer to provide advice on what to do and is forming a plan on how to fill the sinkhole, City Administrator Brian Bingle said as firefighters and police stood by while researchers checked the sinkhole Monday.
The city's initial concern is to make sure the public is safe by fencing the site and to get ready to move a high-voltage electric line located just to the west of Scrivener's home if necessary, Bingle said.
The subdivision where Scrivener's home is located was platted in the 1950s, decades before Nixa enacted regulations that require developers to have geologists check for sinkholes and leave no-build areas around them.
Filling the sinkhole immediately might backfire, so determining the size of the "throat," or the passage leading underground, is important, engineer Gary Pendergrass said.
Pendergrass, environmental compliance officer with Springfield City Utilities, said he's working for Nixa as a consultant.
"We're looking for the throat, where the soil is actually dropping into bedrock," he said.
Once that's done, it might be possible to put stone of varying size into the sinkhole to fill it, yet allow the natural flow of water, he said.
But it's too early to determine how large the sinkhole might become, Pendergrass said.
If the sinkhole grows until it stabilizes, it could be 150 feet across, he said.
Efforts to use an underground camera on loan from Springfield Public Works to probe the sinkhole's depths were frustrated because debris from the collapsing house filled the bottom, Gouzie said after an attempt to lower him into the sinkhole was canceled.
Having firefighters spray 2,000 gallons of water into the hole to dislodge debris to get a look at the sinkhole throat didn't work, he said.
Enough dirt had fallen into the sinkhole from its vertical dirt walls to hide the remains of Scrivener's garage and Chevy Cavalier, Gouzie said.
Monday afternoon, as a half-dozen firetrucks left the scene, geologist Price remained with two colleagues to gather information that might provide a view of what's happening underground.
That work took the form of hammering a line of steel stakes into the ground near Scrivener's home, then stringing electric cables used to send impulses into the ground in an effort to determine the depth of bedrock and whether there are undetected voids.
But the testing method is susceptible to interference from water lines and other materials, he said.
"There always is a certain amount of uncertainty," he said.
Uncertainty is just as disturbing as seeing a sinkhole appear just down the street, nearby neighbor Casey Cays said.
"It's just amazing," she said. "You would never think a sinkhole."
As researchers spent Monday trying to uncover what caused the sinkhole to appear and how large it will become, people like Cays made their own discoveries that prompted concern.
While relieved Scrivener's insurance will cover his losses, she found her insurance policy doesn't have a provision for sinkhole collapses, Cays said.
"We're selling," she said. "High taxes, and it's not worth falling into a sinkhole."
Rep. Jay Wasson, while talking to constituents he represents in the 141st District, said state legislators may consider enacting a provision making sinkhole collapse insurance available.
"Certainly, it's something that ought to be considered," he said. "Yes. It's something we'd want to look at."
Living in a Karst region can really bite. Pictures at web site.
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