Fayette County, Kentucky


Sinkhole and Karst Issues

 

Limestone terrain provides subsidence hazards that usually can be overcome by prior planning and site evaluation. "A" shows construction above an open cavern which later collapses. This is one of the most difficult situations to detect, and the possibility of this situation beneath a structure warrants insurance protection for homes built on karst terrain.

 

 

"B" is a situation where a heavy structure presumed to lie above solid bedrock actually is partially supported on soft, residual clay soils that produce very gradual subsidence and damage to the structure. This occurs where inadequate site evaluation can be traced to lack of geophysical studies and inadequate core sampling.

"C" and "D" show the close relationship between hydrology and subsidence hazards in limestone terrain. In "C", the house is situated on porous fill (light shading) at a site where surface and groundwater drainage move supporting soil (darker shading) into voids in limestone (blocks) below. The natural process is then accelerated by infiltration through fill around the home.

"D" shows a karst site where normal rainfall is absorbed by subsurface conduits, but water from an infrequent heavy storm cannot be carried away quickly enough to prevent flooding of low-lying areas (American Institute of Professional Geologists, 1993).

About karst

More about karst

 

Flooding in a large karst basin. Sinkhole swallets and solution channels are not large enough to carry off the water from this large storm. The problem is exacerbated by development. Often the only solution is to relocate the homes out of the karst flood plain. (photo courtesy of Jim Currens)

Sinkhole cover collapse. After perhaps years of slow settlement, soils over bedrock solution channels collapse rapidly and wash out, leaving sinkholes such as this. This phenomenon occurs throughout the Inner Bluegrass karst landscape. (photo courtesy of Jim Currens)

Attempt to fill in a cover-collapse sinkhole in Fayette County.

(photo courtesy of Leslie Russo)

 


Soil Moisture and Drainage

An uplifting experience that will not be appreciated! LEFT - All is well in this newly built home until water from percolation, drains, lawn sprinklers, leaking sewers or water mains soaks swelling soil beneath foundation. RIGHT - With time, expanding soils exert several tons per square foot of pressure on foundation and shallow pilings. Without remedial measures, the house will actually deform out-of-plumb and shatter masonry and windows. Remedies vary from mere maintenance that keeps drainage away from the house to expensive reconstruction of foundations. Prior site planning that takes geology into account is always preferable to dealing with problems after a structure is built (American Institute of Professional Geologists, 1993).

 


Seepage and Geology

Seepage at the boundary between overlying permeable and underlying impermeable rocks. Often not evident during dry weather construction, it can produce a variety of problems, including foundation disturbance, flooding, soil movement, wet basements, and failure of onsite wastewater treatment systems. (photo by Paul Howell)

 


Pond Construction and Geology

Seepage at the interface of evenly-bedded limestone above shale and limestone, permeable rock overlying relatively impermeable rock. Successful ponds are often located below this seepage zone, as shown on the map below.

(Photo by Paul Howell)

Geologic map showing existing ponds located below the seepage zone in the photo above. Ponds should be constructed so that the springs or seeps will always be above the level of the pond surface.

(Illustration by Paul Howell)

 

Successful pond construction must prevent water from seeping through structured soils into limestone solution channels below. A compacted clay liner, or artificial liner, may prevent pond failure. Getting the basin filled with water as soon as possible after construction prevents drying and cracking, and possible leakage, of the clayey soil liner. Ponds constructed in dry weather are more apt to leak than ponds constructed in wet weather.

(Illustration by Paul Howell)

 

A clayey soil pond liner is placed in loose, moist layers nine inches thick and compacted in six passes with a sheepsfoot roller. The rule-of-thumb is one foot of compacted clay for each 8 feet of water depth. (Photo by Paul Howell)

Other leakage prevention measures include synthetic liners, bentonite, and asphaltic emulsions. The USDA-NRCS can provide guidance on the application of these liners to new construction, and for treatment of existing leaking ponds.

Dams should be constructed of compacted clayey soils at slopes flatter than 3 units horizontal to 1 unit vertical. Ponds with dam heights exceeding 25 feet, or pond volumes exceeding 50 acre-feet require permits. Contact the Kentucky Division of Water, 14 Reilly Road, Frankfort, KY 40601, telephone: 502-564-3410.


Radon

Radon gas, although not widely distributed in Kentucky in amounts above the Environmental Protection Agency's maximum recommended limit of 8 picocuries per liter, can be a local problem. Unit 6 on the map, the Tanglewood limestone, may contain high levels of uranium or radium, parent materials for radon gas. The Tanglewood, and several other limestones in the state, locally contain the phosphate mineral apatite. Uranium is sometimes part of the apatite structure, and when the limestone weathers away the phosphates containing uranium become concentrated in the soil and ultimately can give rise to high levels of radon. A few areas of high radon concentrations have been recorded in the Bluegrass region. Homes in these areas should be tested for radon, but the homeowner should keep in mind that the health threat results from relatively high levels of exposure over long periods of time, and the remedy may simply be additional ventilation of the home.


Mapped Surface Faults

Faults are common geologic structures across Kentucky, and have been mapped in many of the commonwealth's counties. The faults shown on this map represent seismic activity which occurred several million years ago at the latest. There has been no activity along these faults in recorded history. Seismic risk associated with these faults is very low. Faults may be associated with increased fracturing of bedrock in the area immediately adjacent to the fault. This fracturing may influence slope stability and groundwater flow in these limited areas.


References

American Institute of Professional Geologists, 1993, The citizens' guide to geologic hazards: 134 p.

Carey, D.I., and Stickney, J.F., 2001, Ground-water resources of Fayette County, Kentucky: Kentucky Geological Survey Open-File Report OF-01-34, 27 p.

Currens, J.C., and Ray, J.A., 1996, Karst Groundwater basins in the Lexington 30 x 60 Minute Quadrangle: Kentucky Geological Survey, ser. 11, Map and Chart 10, scale 1:100,000.

Johnson, C.G., and Hopkins, H.T., 1966, Engineering geology of Lexington and Fayette County, Kentucky and water resources of the Fayette County area, Kentucky: U.S. Geological Survey Open-File Report, 32 p., 5 plates.

Paylor, R.L., Florea, L.J., Caudill, M.J., and Currens, J.C., 2003, A GIS coverage of sinkholes in karst areas of Kentucky, in preparation, metadata and shapefiles of highest elevation closed contours, 1 CDROM.

Sims, R.P., Preston, D.G., Richardson, A.J., Newton, J.H., Isgrig, D., and Blevins, R.L., 1968, Soil survey of Fayette County, Kentucky: U.S. Department of Agriculture, Soil Conservation Service, 62 p.

Sparks, T.N., Dever, G.R., Jr., and Anderson, W.H., 2001a, Geologic map of the Harrodsburg 30 x 60 minute quadrangle, central Kentucky: Kentucky Geological Survey, ser. 12, Geologic Map 1, scale 1:100,000.

Sparks, T.N., Dever, G.R., Jr., and Anderson, W.H., 2001b, Geologic map of the Lexington 30 x 60 minute quadrangle, central Kentucky: Kentucky Geological Survey, ser. 12, Geologic Map 2, scale 1:100,000.


Copyright 2003 by the University of Kentucky, Kentucky Geological Survey. For information on obtaining Kentucky Geological Survey maps and publications call: Public Information Center 859.257.3896. 877.778.7827 (toll free). View the KGS World Wide Web site at: www.uky.edu/kgs