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).
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