Tuesday, November 8, 2011

Two Kansas Sinkholes of Interest

Crawford Sink, Kansas
The two-lane Highway 24 used to be the East/West travel route through NW Kansas from Kansas City to Denver.  But in the mid 1960's a new 4-lane, Interstate I-70, was finally under construction. As with all highway construction in Kansas, it began with a geology survey.  As the records have it, the geology survey found a fairly large pond sitting just on the South side of the interstate right-of-way about six miles West of Russell, KS.  Asking around, the highway geologists were told that the pond had always been there - at least as long as the oldest oldtimers in the areas could remember.  So the construction continued by filling in the pond, final grading of the roadbed and constructing an overpass just to the West of the pond.

Immediately thereafter the subgrade kept sinking right where the old pond had been.  Engineers thought this was just fill material settling but soon discovered they were building the interstate right over an active sinkhole. While this discovery was being further considered and evaluated, paving continued.  Just afterwards, geologists checked older aerial photos from the early 1950's and found no such pond.  It was now confirmed that it was a very problematic sinkhole having been caused by an improperly plugged oil well - part of the very active Gorham Oil Field.  This is when it gets named the Crawford Sinkhole, for the oil lease name causing the problem.  Through significant study, it was determined that fresh and brackish groundwater contained in the Dakota, Cheyenne and Cedar Hills sandstones was moving down the abandoned oil well and dissolving the subsurface Hutchinson Salt Member as oil operations continuously remove oil and salt water from the deeper target zone - the Lansing-Kansas City oil member. As the 270 feet thick Hutchinson Salt dissolves, cavities are created and the overburden slumps in, eventually translating the slump all the way to the surface.

Through much work, the entities involved determined there was no risk of a catastrophic collapse, so to date Interstate 70 gets built up 5-6 feet whenever it needs it.  In the 1970's there was thought to re-routing I-70, but the Gorham Oil Field goes several miles in each direction with no assurances that other sinkholes wouldn't be discovered later.  And then the Witt Sinkhole showed up just 1/2 mile to the West.  It too  begun to sink - actually a bit faster than the Crawford Sink - and by now the overpass bridge between these two holes was being affected as well - being torqued a couple of feet with the East curb being 2 feet lower than the West curb.

By 1984 attention was being applied to the Witt Sink and an attempt to stop the subsidence was launched.  A hole was drilled next to the old suspected abandoned well and drillers pumped 30 cubic yards of cement down the new hole, until pressure built up, hoping to plug the mess and stop the flow of water.  It worked for about 6 months, but then water got around the plug and the highway quickly resumed its pre-plugging subsidence rate of 5 to 6 inches a year.  In 1988 they tried again, this time pumping 200 sacks of bentonite mud and 100 cubic yards of cement into the problem.  This attempt also stopped the sinking for another short period of time before it resumed.  Is it prophetic that rearranging the letters in "Crawford Sinkhole" yields the phrase:  "A cork hinders flow"?

For now the plan is to continue re-grading the Witt Sink as needed to make it safe for traffic, but the Crawford sinkhole may be getting too deep to continue this plan much longer.  The good news is that the overpass was removed about 5 years ago, so it no longer is interfering with the possibilities.  Meanwhile, the oil production from the Gorham Field continues with everyone aware that until it ceases, the sink will continue to work it's magic.  I've been driving over these two sinkholes about 20 times a year for the past 35 years, and I still try not to drive through them when a semi or two are down there with me!   Fair warning, if I suddenly stop blogging it's possible one of these two sinks finally got me!  And is it also coincidence that another anagram for "Crawford Sinkhole" happens to be:  "Drain. Flow. Shocker!"

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