Groundwater Issues in the Karst Terrane of Kentucky
Gregory Eck
Applied Hydrology
Karst terrane is a problematic area for groundwater, wellhead and aquifer
contamination. Typical karst hazards also include sinkhole flooding and sinkhole
formation.1 In Kentucky as elsewhere the country side is being impacted by
continued urbanization, as population increases and former rural areas are
domesticated.2 Just over 30% of Kentucky drinking water is from groundwater
sources.3
Karst terrane is usually identified as having carbonate bedrock such as
limestone or dolomite.4 Approximately 55 percent of Kentucky has carbonate
karst forming rock, of which 25% is mature karst. A terrane is a landscape or a
region that is under laid by similar rocks or sediment to those on surface. Mature
karst terrane is identified as land with little or no above ground drainage which
typically has exposed outcroppings of carbonate rock, sinkholes, springs and
caves. Karst terrane includes integrated groundwater conduits which are joints
and fissures in the rock or sediment which have been enlarged due to dissolution
of carbonate rocks. Carbonate rocks are dissolved via the interaction of these
carbonate rocks with carbon dioxide, the more CO2 the more carbonate reaction.
5
In the karst environments the carbonate rock is continuously changing as the
groundwater moves through it. Over time the flow patterns and the rock porosity
are also being modified.6 Carbonate rock permeability has three sources: the
primary porosity of limestone, the permeability due to the formation of
dissolution joints and conduit formation.7 These conduits and solution cavities
that rapidly transport groundwater are what make karst aquifers different from
others. The conduits result in rapid and turbulent flow.8
Within karst terrane there are two types of recharge, autogenic when
precipitation falls directly on a karst region and allogenic when water drains via
streams and overland flow into karst aquifers.9 The location of caves or enlarged
dissolution openings via sampling is often required to verify that a region
includes karst. However, this definition is far too simplified and takes into
account only part of the karst terrane definition. One article suggested this was
equivalent to someone purchasing a large number of lottery tickets (large sample
size) but failing to win concluding that no ‘jackpot” exists.10 The most reliable
method requires groundwater tracing to establish where the flow pattern of water
in karst areas. The reliable and time tested calculations that provide accurate
data in confined aquifers can not be used in the karst terrane.11 Non toxic
fluorescent dyes which are highly detectable and low cost of analysis are the most
common methods of tracing.12 There are five tests for defining the bounds of
groundwater source protection areas distance, drawdown, time of travel, flow
boundaries and assimilative capacity. All except flow boundaries which have been
established via dye tracing are invalid in karst areas. Karst areas are by definition
unconfined or partially unconfined aquifers and do not meet the assumptions of
the Darcy equation.13 For example, in a karst area water and contaminants time
of travel t over a x distance may be made of traveling through 1% of x made of
soil and non-carbonate rock in 99% of t, then encountering a carbonate fissure or
stream in a cave and traveling 99% of x in 1% of t.14 The result can be that
contaminates could slowly filter through a locally existing matrix taking far
longer than the assumed time in a karst area and perhaps well after monitoring is
ended, then “rocket” through a conduit under turbulent flow conditions to a
groundwater source days, weeks, months after the initial event.15 Conversely,
using typical distance tests that work well in non karst areas involving a 300m
distance may be traveled in a few hours in a karst area. Drawdown, pumping
influence and pumping rate calculations are based on assumptions that are
invalid in the unconfined, turbulent flow of a karst terrane conduit.
Discharge springs are usually identified are being the result of either
conduit flow ie underground streams or diffuse flow ie ground water seepage
through the primary permeability of the rock. In karst regions variation in flow
and water quality are more readily explainable by examining the recharge area
rather than the discharge flow.16 Normalized Base Flow (NBF) is measured by
dividing the base flow of a spring by the area of the drainage basin the result is
flow measured in cubic feet/second/square mile. Discharge spring NBF can then
be used to estimate the size, characteristics and boundaries of a recharge area, as
well as study their hydrogeology.17
The Fort Knox Military Reservation is over 100,000 acres in size.
Numerous hazardous materials are used and stored throughout the base. As a
result there was a need for a through understanding of the groundwater flow
patterns and baseline measurement of the groundwater quality. An important
goal was the creation of a groundwater monitoring program for the base.18 The
groundwater basins at the base were studied using dye injection into monitoring
wells, sinkholes and sinking streams.19 The Fort Knox studies used eight
different dyes which were collected in automatic water samplers. These tracings
were conduced in both wet and dry periods. During the study daily and weekly
flow rate measurements, ph measurements and temperature were used in the
calculation of normalized base flow. The dye tracings indicated that groundwater
flow is controlled by geologic structure and stratigraphy.20 The geologic structure
limits the formation of conduit, which follows the path of least resistance. 21
These controls can then be used to develop a model of the groundwater flow. At
Fort Knox the springs typically occurred were the soluble St Louis limestone
made contact with one below it known as the Salem Limestone that acted as an
aquitard. This forced the groundwater to flow horizontally because vertical
movement was highly limited. The horizontal flow resulted in the creation of
conduit as well as addition springs. In the eastern section of the military
reservation these conduits resulted in dye traces being recovered 4 kilometers to
the west of a injection site rather than at a spring less than half a km away.22 The
Fort Knox study incorporated geologic study, spring identification, dye tracing to
determine groundwater flow and direction. This allowed the determination of
groundwater basin boundaries. When normalized base flow calculations were
added to the model the extent of the groundwater basins could be determined.
The NBF indicated that the basin was recharged visa autogenic means. Having
estimated the recharge basins, areas of concern for groundwater contamination
could be matched with maps of known hazardous waste site, allowing for the
better groundwater management. 23
The Safe Water Drinking Act mandates that all states have a
wellhead protection plan in order to safeguard water supply wells and springs.
Kentucky’s EPA approved plan requires that recharge areas for groundwater
basins be determined and potential hazards within the recharge areas
identified.24 As a result of this type of study the Kentucky Geological Survey has
undertaken the development of a statewide atlas of groundwater basins to be
available as a GIS database. The data collected is from 50 years of dye tracing.
These dye tracing records were studied to determine groundwater flow patterns
and watershed boundaries. The watershed boundaries are difficult to determine
in karst areas because the majority of surface drainage drops into underground
conduits and caves. Existing databases from geological and water agencies were
used to locate springs and karst features.25 Dye tracing also establishes
groundwater flow so that the source of pollution in a discharge spring can be
more readily located. The maps created were 30 x 60 minute quadrangles. The
basin maps are key to the state of Kentucky being able to understand and protect
groundwater resources. The atlas includes a series of maps identifying karst
areas that are likely to flood. The majority of these are sinkholes which fill and
flood during heavy of frequent storms, damaging structures in and around the
sinkhole plain26 These maps are created by using GIS analysis comparing aerial
and satellite images taken during dry and flood conditions in order to identify the
areas of change 27
The karst atlas will also map places were sinkhole collapses have occurred.
When used in conjunction with land use and groundwater flow map areas of
concern can be identified. The purpose of the atlas does not include any sinkhole
prediction, just the identification of sinkhole prone areas. Roads and buildings
that lie within these areas can then be identified for continued monitoring.28 The
following page is a map of the Karst Groundwater Basin for the Bowling Green 30
x 60 quadrangle from the atlas.
For example the Mammoth Cave area includes a large sink hole plain
recharge area. Here thousands of sinkholes recharge the aquifer almost
immediately and directly from precipitation. 29 In areas with sandstone caprock,
streams run along the surface and then upon reaching the karst edge drop into
the aquifer via vertical shafts. These sinking streams usually have fast infiltration
into the groundwater 30 this can result in flood conditions when sinkholes can not
take in the volume of water in the recharge area. Flood waters pond and build up
in the vadose zone, resulting in increased hydraulic head. These flood conditions
result in the deposit of both sediments and contaminants in the floodplain.
Sinkholes form in places were there is depression in the underlying
bedrock which is covered by soil or unconsolidated material, and finally a vertical
drain path for the groundwater. As the carbonate rock is dissolved the bedrock
collapses and the materials are carried away in the conduit. The resulting dome
works its way up until the surface collapses into the dome.31 Sinkholes force
water into the aquifer at localized points, increasing head and resulting in
conduit formation along resistant aquitard formations.32 As groundwater
conduits and springs form the potentiometric surface is lowered in places,
resulting in little or no water and the resulting caverns which karst terrane is so
well known for.33
The hydrology of the karst terrane is unique. The techniques and
methodologies used elsewhere often do not provide adequate basis for the study
of this unique environment.
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology of
Sinkholes and Karst- 1999, p.85.
2
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology of
Sinkholes and Karst- 1999, p.88.
3
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 527
4
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 526
5
Hess, John W; Wells and White, William B. “Chemical Hydrology”. Karst Hydology p 156
6
Hess, John W; Wells and White, William B. “Chemical Hydrology”. Karst Hydology p 145
7
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 47
8
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 47
9
Quinlan, James F, Ray, Joseph E ”Normalized base-flow discharge of groundwater basins: Auseful
parameter for estimating recharge areas of springs and for recognizing drainage anomalies in karst
terranes” Karst Geohazards p151
10
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 526
11
Quinlan, James F, , Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 530
12
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 527
13
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 527
14
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 528
15
Quinlan, James F, Ray, Joseph E, Schindel, Geary M. “Intrinsic limitations of standard criteria and
methods for groundwater-source areas in carbonate terrranes:Critical review, technically sound resolution
of limitations and case study in Kentucky Karst” Karst Geohazards, p 528
16
Quinlan, James F, Ray, Joseph E ”Normalized base-flow discharge of groundwater basins: Auseful
parameter for estimating recharge areas of springs and for recognizing drainage anomalies in karst
terranes” Karst Geohazards p151
17
Quinlan, James F, Ray, Joseph E ”Normalized base-flow discharge of groundwater basins: Auseful
parameter for estimating recharge areas of springs and for recognizing drainage anomalies in karst
terranes” Karst Geohazards p151
18
Conner,Dennis, Engel,Sott and Murrary, Brain S. “Karst groundwater basin delineation in Fort Knox
Kentucky”, Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999, p.287
19
Conner,Dennis, Engel,Sott and Murrary, Brain S. “Karst groundwater basin delineation in Fort Knox
Kentucky”, Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999, p.288
20
Conner,Dennis, Engel,Sott and Murrary, Brain S. “Karst groundwater basin delineation in Fort Knox
Kentucky”, Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999, p.288
21
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 49
22
Conner,Dennis, Engel,Sott and Murrary, Brain S. “Karst groundwater basin delineation in Fort Knox
Kentucky”, Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999, p.288
1
Conner,Dennis, Engel,Sott and Murrary, Brain S. “Karst groundwater basin delineation in Fort Knox
Kentucky”, Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999, p.291
24
Harker, Kay and Ray, Joseph E ”Status of Kentucky’s regulatory programs that address karst” Karst
Geohazards p507
25
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology
of Sinkholes and Karst- 1999, p.86
26
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology
of Sinkholes and Karst- 1999, p 87.
27
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology
of Sinkholes and Karst- 1999, p.88.
28
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology
of Sinkholes and Karst- 1999, p.88.
29
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 29
30
Currans, James and Ray, Joseph, “Karst Atlas for Kentucky”, Hydrogeology and Engineering Geology
of Sinkholes and Karst- 1999, p.85.
31
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 34
32
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 50
33
Hess, John W; Wells, Stephen; Quinlan, James F.; White, William B. “Hydrogeology of the SouthCentral Kentucky Karst”. Karst Hydology p 51
23
Source Works:
Hydrogeology and Engineering Geology of Sinkholes and Karst- 1999 edited by Barry F. Beck, Aurthur J
Pettit, J. Gayle Herring. AA Balkema Rotterdam, Netherlands, 1999.
Karst Geohazards edited by Barry F. Beck. AA Balkema Rotterdam, Netherlands, 1995.
Karst Hydrology edited by William B White, Elizabeth L White. Van Nostrand Reinhold, New York, 1989