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Indiana Department of Environmental Management

Proper Investigative Techniques in Karst

Mitchell E. Daniels, Jr. Thomas W. Easterly

Governor Commissioner

100 N. Senate Ave., Indianapolis, IN 46204

Toll Free: (800) 451-6027

Guidance Created/Revised: June 30, 2011

The implementation of a karst assessment can provide data needed to evaluate exposure pathways in areas where karst is present. The methods and procedures presented in this document were gathered from both published materials and staff experiences. These methods may not be the only way to assess exposure pathways in karst, but they are widely used.
Karst is defined by the United States Geological Survey (USGS) as:
“A terrain generally underlain by limestone or dolomite in which the topography is chiefly formed by the dissolving of rock, and which may be characterized by sinkholes, sinking streams, closed depressions, subterranean drainage, and caves. [1] The term karst unites specific morphological and hydrological features in soluble (mostly carbonate) rocks. Morphological features (see the karst term glossary for definitions) include; sinkholes, caves, caverns, etc. Hydrological features include; basins of closed drainage, lost rivers, springs, submarine springs, more or less individualized underground streams, and incongruity of surface and underground divides. Karst is understood to be the result of natural processes in and on the earth’s crust caused by the solution and leaching of limestones, dolomites, gypsum, halite, and other soluble rocks”[2]
Environmental investigations in karst areas present unique problems. The conventional site investigation methods and installation of monitoring wells usually do not provide an accurate picture of how contaminants behave in a karst aquifer. Because of the very different morphological and hydrological features, investigations in karst do not typically employ the same techniques used in site characterizations conducted in non-karst environments. The guidance in this document will assist the proper characterization of a site located in a karst area.

Table of contents

Karst Overview 3

  1. Limestone or other types of carbonate rock may form karst 4

  2. How sinkholes form 4

  3. Karst is not stable 4

  4. Groundwater in karst does not flow in a consistent manner 4

  5. Vapors, free product, and dissolved phase contamination 5

  6. Soil sampling may not reveal a groundwater problem 5

  7. Karst Aquifers may not have a surface expression 5

  8. Suspended load may transport contamination 6

  9. Contaminant concentrations and flow rates 6

  10. Direction of groundwater flow can change 6

  11. Monitoring wells are of limited use 6

    1. Placement of wells 7

    2. Accurate well logs 7

    3. Soil bedrock interface 7

    4. Additional tests 7

Elements of a Karst Investigation 8

  1. Identification of karst in the study area 8

    1. Visit the site 8

    2. Conduct a literature search 8

    3. Consult map contained in this document 8

  2. Soil Bedrock Interface Study 8

    1. Map the bedrock surface 9

    2. Sample the epikarstic water 9

  3. Karst Drainage Basin Study 10

    1. Locate all springs located within the karst basin 11

    2. If there are a limited number of springs, sample them 12

  4. Qualitative Dye Trace 13

    1. Spring Locations 13

    2. Spring Descriptions 13

    3. Background Sample Collection 14

    4. Directions for conducting the test 14

  5. Conduct a Quantitative Dye Trace 15

  6. Vapor Intrusion Investigations in karst 16

  7. Sampling Schedule and Frequency 16

  8. Design of Remedial Measures 16

    1. Soils 16

    2. Groundwater 16

    3. Vapors 17

Figures and References

Figure 1 3

References 18

Information Links 18

Agencies and organizations 18

Karst Papers, Publications, and Proceedings 19

In Indiana, areas with limestone and dolomite bedrock are susceptible to karst formation should be determined. Karst terrains are not confined to one area of Indiana. Karst can be found at or near the surface in at least 28 Indiana counties. Figure 1 is a map with the shaded counties affected by karst.

The 28 Indiana Counties are:

  1. Allen

  2. Huntington

  3. Randolph

  4. Delaware

  5. Fayette

  6. Union

  7. Franklin

  8. Dearborn

  9. Ohio

  10. Switzerland

  11. Jefferson

  12. Ripley

  13. Decatur

  14. Bartholomew

  15. Jennings

  16. Jefferson

  17. Scott

  18. Clark

  19. Floyd

  20. Harrison

  21. Washington

  22. Jackson

  23. Putnam

  24. Owen

  25. Monroe

  26. Lawrence

  27. Orange

  28. Crawford

Figure 1

A karst study should begin with a review of the basic concepts of karst formation:

  1. If the bedrock material is made of limestone or other types of carbonate rock; there is the possibility that a karst aquifer could be present.

Even if a significant thickness of unconsolidated material exists above the

carbonate rock, a karst conduit aquifer could still exist.

  1. The openings (i.e. sinkholes) and conduits are not formed from the

disintegration of rocks, but as a result of the dissolution of carbonate bedrock.
This process occurs when groundwater that is slightly acidic flows down through fractures or along bedding planes in the bedrock and dissolves it. There is a common misconception that if a sample of bedrock is tested for its hydrologic properties, the properties of the aquifer will be known. This is not true. The primary porosity (pores in the rock itself) is not important, but the secondary porosity (the fractures and bedding planes) is important in the formation of a karst aquifer.

  1. The dissolution of carbonate rocks is an ongoing process and needs to factor into any the determination of long term risk.

There have been numerous attempts to classify karst areas as stable. This is not acceptable since karst by nature is unstable, because the carbonate rock is in a constant state of dissolution. Any risk calculations cannot assume that karst will remain stable. This is one of the main reasons why new landfills and treatment storage and disposal facilities should not be located in karst areas.

  1. Groundwater in a karst terrain does not behave in the same manner as groundwater in a porous medium.

Flow in karst aquifers is based on conduit or fracture flow, therefore Darcy’s Law does not apply. Darcy’s Law is an equation used to predict flow velocity through a porous material, given a hydraulic conductivity for that material. Since water in karst flows through fractures and/or conduits in the bedrock, the use of the hydraulic conductivity of the rock will not accurately predict the flow velocity for the karst aquifer. The fractures may plug with clay and close, or suddenly open; the drainage system is constantly changing. There are also possibilities that fractures and sinkholes from the surface make a direct conduit to the aquifer. If this is the case, contaminants could enter the aquifer at full strength and not leach through soils and unsaturated materials. However, when fractures and sinkholes are filled with soil and a release occurs that drains into them, the soils will adsorb most of the contamination and then act as a continuing source. Over time the soils erode away and enter the karst system along with the contamination.

The most common way to measure groundwater movement is with the use of a slug test. Comparisons between slug tests and dye tracer tests in karst aquifers have shown that slug tests are not a valid way to find groundwater velocity in karst. Results show that groundwater flow is as much as five orders of magnitude greater than slug tests results would have predicted.

  1. Vapors, in addition to free phase liquids (product) and dissolved phase contamination, occur in karst aquifers. The potential for vapors needs consideration when calculating the risk.

If contamination (i.e. free product, vapors, or contamination adhered to colloids) enters the karst system, it is possible that a vapor or gas phase of contamination could develop (much in the same way a release to a sewer system behaves). This is possible because most conduits in karst systems are not completely filled with water. As the water cuts deeper into the bedrock it will leave behind stranded channels that will be dry and may only be wet during storm events. Vapors and gases from contamination can migrate to these areas. If there is an outlet to the surface these vapors or gases may migrate to a receptor. Sometimes the vapors will enter structures. There are documented instances of homes exploding in the City of Bowling Green, Kentucky as a result of vapors migrating out of karst. Even if explosive vapors are not present in the karst system, there is still an inhalation hazard associated with the groundwater contamination. The inhalation routes of contaminants are assumed to be complete in karst areas, unless proven otherwise.

  1. Low contaminant levels in soils do not necessarily mean that low

contaminant levels are present in the groundwater.
Since it is possible that soil macropores exist, and that soil sampling may

miss these features, groundwater is assumed (until proven otherwise) to be contaminated.

  1. Lack of surface expression does not mean the area in question is not in karst.

There are areas in Indiana where, at the surface, there does not appear to be any karst development. This is usually due to a thick soil cover or the area was filled for redevelopment. Over time, sinkholes can become filled in with soils and sediments. Even when a sinkhole is apparently filled in, water can still flow through and leach out or directly carry surface or sub-surface soil contamination into the karst aquifer. Even worse, a sinkhole could suddenly open, swallowing all above.

  1. Karst systems can carry suspended solids with attached contamination.

When springs are tested, this major contaminant transport mechanism is

usually overlooked. Most investigations do not consider the suspended solids in water exiting springs. This can be a major problem when analyzing for contaminants that prefer to stay attached to suspended solids. Metals and PCBs are two examples of contaminants that will stay attached to the particles in the suspended load. When field filtering is conducted on a sample, the suspended soils are removed, and with them a major portion of the contaminant. Field filtering of groundwater or spring water samples in karst areas is not recommended.

  1. Contaminant concentrations can vary greatly depending on flow rates and rainfall amounts.

Unlike granular aquifers, there is an almost immediate response to rainfall in karst aquifers. Most karst aquifers do not usually have a defined plume at a consistent concentration level. For example a spring may have a normal discharge rate of 20 gallons per minute (gpm) and a contaminant concentration of 2 parts per billion (ppb). However, after a rain fall event the discharge rate may be increased to 200 gpm and the contaminant concentration to 400 ppb.

  1. Groundwater flow directions may not be apparent and can change direction during storm conditions.

During precipitation events, conduits fill with water and could enter areas that are normally dry. These dry conduits may drain to springs and seeps that do not flow during low flow conditions (these types of springs are called over-flow springs). It is also possible that water could fill up the conduit system enough to cross drainage basin boundaries. Therefore when evaluating karst, both base flow and storm flow conditions need to be studied.

11) Monitoring wells are of limited use in karst areas.
It is quite possible that contamination will not be detected unless the right conduit is intersected at the right location by a monitoring well. For this reason, sites in karst areas are investigated in a different way (i.e. by sampling the outflows). If precautions are taken, it is possible to install useful monitoring wells in karst areas. However, without extensive knowledge of the karst aquifer, it may not be possible to place wells to take representative samples of the potentially contaminated aquifer.
If monitoring wells are to be installed, follow the listed procedures below:
  1. Placement of Monitoring Wells

Monitoring wells installed in karst need to be able to monitor the wide range in fluctuations in water levels that occur in karst aquifers. The fluctuations are the result of water entering the system through discrete high-permeable zones. Monitoring wells in karst need to monitor all of these zones. Since most of the high-permeable zones occur along bedding planes, knowledge of the local stratigraphy is helpful. In addition to knowledge of the area stratigraphy, video logging of borings (done prior to installation of the well) can be useful. Wells installed in un-weathered bedrock usually have casing installed through the unconsolidated material and weathered bedrock but are left open through the un-weathered bedrock. This makes it possible to monitor discrete water producing fractures in bedrock. This is usually done with a packer.

  1. Accurate Well Logs

A detailed record of each boring is needed. This should include at a minimum:

1. The location of zones where circulation (if drilling fluids were used) or air pressure (if air was used) was lost;

2. Where enhanced volumes were obtained during well development; and

3. Where open or mud-filled cavities were encountered.

  1. Soil Bedrock Interface

The area at the soil/bedrock interface (epikarst) is important in the

transport of contaminants. The investigation should include wells which straddle this zone. The epikarst may be dry most of the time. Wells should be gauged and sampled after rain events. Monitoring this zone is important. The epikarst wells are best utilized in the source area of contamination. A well-planned and executed site investigation should provide enough information to place these wells.

  1. Additional Tests

Once the monitoring wells are installed at the site, the hydraulic connection between the wells, source area, and the identified springs is determined. This can be done in two ways:

1. Hydraulic tests; or

2. Dye traces.

A karst investigation is usually conducted in phases (listed below). The sections provide the iterative steps in the process. It may be possible to collect the data needed without completing all of the steps:
1) Identification of karst in the study area

  1. Direct observations may be used to determine if a karst system exists beneath the site.

  1. A literature search is needed to determine if any information exists about the subsurface conditions. Information commonly available includes:

1. Stratigraphic cross sections from previous studies (site specific or regional);

2. Geologic Maps (U.S.G.S. or State Geologic Surveys);

3. Topographic maps; Consult U.S.G.S. geologic and topographic maps for the area (site map plus maps surrounding the site map.) to determine if any surface expressions of karst are located at or near the site. Karst will not form in all limestones and dolomites. Field investigations

are usually necessary to determine if karst is present.

4. Potentiometric surface maps;

5. Geophysical logs/maps/or local studies;

6. Cave maps (U.S.G.S., State Survey, or privately produced);

7. IDNR Water Well Records.

  1. The location of the site is checked against the list of counties found earlier in this document (Fig 1, Page 3).

2) Soil Bedrock Interface Study
Once the site is known to be located in an area susceptible to the development of karst, an investigation of the interface between the soil and bedrock is needed to determine if contaminated groundwater may enter the karst aquifer. There are several tests to conduct to determine if the karst aquifer needs further study:

  1. Mapping the bedrock surface.

Mapping the bedrock surface is a simple way of determining how water is draining through the subsurface materials beneath the site. Usually, a series of probe points are advanced (on a grid pattern) until refusal (collect soil samples in a subset of these “borings”). The depths of refusal and the contaminant levels are mapped and, if possible, the “low spot” on the bedrock surface is located. If high levels of soil contamination are identified in the “low spot”, there is a high probability the contamination is entering the karst aquifer. However, prior to investigating the bedrock aquifer, confirm if water draining from the site is contaminated (i.e. sample the water flowing through the epikarst).

  1. Sampling the soil and epikarstic water, to determine if the karst aquifer is contaminated.

  1. Soil Sampling:

Soil sampling in karst settings should be conducted both above and below the water table. Since soils in karst settings can become entrained in water flowing through the karst system, migration of contaminated soil particles is a concern.

  1. Epikarstic Groundwater Sampling:

Once the bedrock mapping is completed, and “low

spots” are identified; several monitoring wells, installed so that the screens intersect the interface between the unconsolidated materials and the bedrock surface, are needed. At least one monitoring well should be installed in each of the “low spots” identified on the bedrock surface map. These wells are installed to monitor water flowing along the bedrock surface. One of the most difficult aspects of sampling this type of groundwater is knowing when to sample.
Sampling groundwater at the soil-bedrock interface is

dependent on rainfall. Sampling needs to occur soon (6 to

12 hours) after a rain event, otherwise, contamination (or

even water) could be missed. The best way to determine

when to sample is to install data loggers (used to monitor

water levels) in several of the wells to monitor responses to

multiple rain events. Optimal sampling times can then be

determined. If possible, automatic samplers should be used

to collect the groundwater samples. These samplers can be

programmed to collect samples at predetermined intervals.

3) Karst Drainage Basin Study
Once contamination has reached a karst aquifer, a dye trace may be needed to find the discharge point. At this point, the investigator should make a more detailed survey or the karst features of the area. Without this information, the investigation cannot successfully find the contaminant pathways.

  1. A field investigation of the surrounding area is needed to

locate all of the springs within the karst drainage basin.
To determine where the water is going without using a dye trace, water samples are collected at the spring locations to see if contaminated water is discharging to surface water. To determine possible locations where contamination from the site may be going, conduct a field investigation of the karst drainage basin. The exact boundaries of the basin are unknown until a dye trace is conducted, but this investigation will give the investigator an idea of the size of the karst drainage basin. Prior to any sampling or the commencement of a dye trace investigation, identify and locate the following karst features:

              1. Springs

              2. Blue Holes (springs in streams)

              3. Karst Windows

              4. Caves

              5. Soil Springs (seeps)

              6. Sinkholes

              7. Swallets (openings to the conduit system not

associated with sinkholes)
These features can initially be located by using maps and through literature searches, however, all karst features need to be field verified.

  1. Obvious contaminant discharge pathways need to be sampled first.

If the drainage basin investigation has identified only a limited number of springs, or other features, it may be simpler to evaluate the discharge points first. This will save the expense and time of a dye trace. If contamination is found at any of those locations, a qualitative dye trace may be needed. In addition to the dye trace, investigation of the surface activities between the site and the contaminated feature is needed to determine if any other sources (in addition to the site) may be present that could account for the contamination.

4) Qualitative Dye Trace
If groundwater flow pathways are unknown, a qualitative dye trace (basic trace designed to find out where the water is going) is needed. In order to implement a dye trace study, a survey of the karst groundwater basin(s) is needed to locate springs beyond the facility boundary. All of the features listed in item 3A should be inventoried, described, and located on a map. The spring survey should include the following:

  1. Spring Locations

All springs need be located accurately on a topographic map (springs are surveyed for a quantitative dye trace).

  1. Spring Descriptions

Collect the following information for each spring:

              1. A physical description of each spring site;

              2. The nature of discharge (i.e. type of spring; bedrock

or soil);

              1. Record the number of spring output locations;

              2. Record the characteristics of the discharge;

              3. Record the conductivity of the spring waters and the total suspended solids;

              4. Record the pH of the spring water;

              5. Take discharge measurements should be taken at each spring where possible, and;

              6. Specify the method used for obtaining the stream discharge rate(s)

A report with all the above information should be submitted to IDEM prior to conducting the dye trace. The report needs to include a map of the hypothesized groundwater basins.

Discharge measurements are needed for each measurable spring within the karst groundwater basin(s) where contamination may exist. Spring discharge measurements are collected during conditions when all springs are flowing. The investigator should submit any justification regarding the method selected for spring discharge measurements.
C. Background Sample Collection.
Background sampling is needed to determine if any of the commonly used dyes are already present in the environment (this test is usually run for four weeks).

  1. Assign each spring an inventory number or name and accurately located on a U.S.G.S topographic map;

  2. Construct a set of dye receptors for each spring. Each dye receptor is tagged and assigned an inventory number;

  3. Station two sets of background dye receptors, each consisting of different dye sorbents (cotton and charcoal) for multiple dyes, in each spring;

    1. Dye receptors are usually made of coconut grade charcoal and surgical cotton for receiving corresponding types of dyes;

    2. Dye receptor sets are stationed apart from each other and hidden to avoid vandalism or theft;

  4. Take a grab sample of the spring water for background determination once a week for four weeks prior to dye injection;

  5. Use a black-light and dye elutriants to test dye receptors for background levels of dye or fluorescent chemicals;

  6. Test grab-samples on a Model 10 Turner Designs Fluorometer, Spectroflourometer, or similar device;

  7. Install new dye receptors at all previous locations and steps 1 through 6 are repeated until the four week period is completed;

  8. Once the background dye concentrations are known, select the proper dyes for the tracer study.

D. Conducting a Qualitative Dye Trace.
A qualitative dye trace is the first type of dye trace conducted at a site. A qualitative dye trace does not provide travel times or concentrations at the receptor points. It is used to determine which springs are or are not contaminated by the site in question. This is necessary because the next step (quantitative dye trace) can be expensive. The following steps are needed to conduct a qualitative dye trace:

  1. Select multiple dye injection locations. Several possible locations may include the soil bedrock interface (will require trenching), sinkholes, swallow holes, or losing streams;

  2. Select dye such as water soluble sodium fluorescein or optical brightener. There are other types of dyes but fluorescein and optical brightener are the most common;

    1. Dye receptors made of coconut grade charcoal or surgical cotton capable of receiving the types of dyes used in the test are placed at all springs in the drainage basin, if monitoring wells have already been installed, dye receptors are also placed in them;

    2. Dye is flushed into the system with a large volume of water, ten parts water to one part dye is a standard ratio;

  3. Replace the dye receptors weekly until dye is recovered;

  4. Analyze the dye receptors, and;

  5. Show the path or route of groundwater flow from dye injection point to dye recovery point on a map.

The qualitative dye trace is used to determine the general path of conduit flow between the points of dye injection and dye recovery. Provide quality control protocol for handling dye and dye receptors to insure the prevention of dye receptor contamination.

Once the qualitative dye trace is concluded, identify all springs and wells connected to the karst system. The springs and wells are then analyzed to determine if contamination is present in groundwater and sediment discharging from the springs (the values recorded may or may not represent the maximum concentrations that can be discharged from the spring).

  1. Quantitative Dye Trace.

Once the previous investigations have determined where the water is going, and have verified that COCs from the site are discharging from the springs, The investigator should evaluate whether a quantitative dye trace (used to design remedial measures at the springs) would be appropriate and valuable.

A quantitative dye trace is used to determine the direction and rate of groundwater flow as well as contaminant transport routes. In addition to the dye tracer study, a potentiometric survey is needed. Once the survey has identified all domestic, municipal, industry and livestock wells and springs, a potentiometric contour map of the karst groundwater basin(s) is developed. Documentation for the map should include:

    1. A map showing the location of all active and inactive water wells within three miles of the facility;

    2. Depth to the water surface in each well;

    3. Depth of the well;

    4. Activity of the well (i.e., human and or livestock use, and in use or abandoned);

    5. Any construction details or well logs;

    6. Surface elevation of the well from a known datum point (National

    7. Geodetic Vertical Datum). Use elevation datum from mean sea level for each well;

    8. Elevation and location of springs and blue holes; and

    9. Last precipitation event at time wells were measured.

Once hydrologic outputs and flow paths are established, a quantitative dye trace is constructed and the dye recovery curves are used to better understand the time of travel, peak concentration, and flow duration of the dye.

Conducting quantitative dye traces during varying discharge conditions provides an understanding of aquifer response to storm events and is a useful predictive tool to determine groundwater discharge, apparent groundwater flow velocity, and solute characteristics. Normalized peak-solute concentration, mean travel time, and standard deviation of time of travel are applied to simulate solute-transport characteristics for selected discharges. The analysis of recovery curves is used, in conjunction with discharge measurements, to estimate arrival time, peak concentration, duration or persistence, and dispersion of a soluble conservative contaminant at a spring.
The time of travel, peak concentration, and flow duration results are used to directly describe general fate and transport characteristics of contaminants released into the groundwater. Predicting the contaminant concentration maxima, relative to storm hydrographs, should provide information on optimal conditions for sampling at springs, seeps, cave streams, and relevant groundwater monitoring wells. Automatic water sampling equipment is used to record this information. The equipment needs to be capable of measuring, temperature, conductivity, pH, and flow rates. Equipment capable of collecting samples that can be sent to a laboratory for analyses of the contaminants of concern for that site are utilized, as well as the tracer dye.
Once the dye trace identifies spring or springs and determines the optimal time for sampling, that information is incorporated into a groundwater sampling plan. The plan is designed to sample groundwater hourly, before, during and after a significant storm event. A significant storm event is defined as: “A storm event of sufficient magnitude to yield an appreciable increase in spring discharge or rise in the storm hydrograph.” While a quantitative dye trace may provide a cost effective fate and transport model, compare the model to actual concentrations in the groundwater conducted before, during and shortly after a heavy rain. Groundwater samples collected from monitoring wells should coincide with samples collected at the springs are sampled. The method of collection should be the same for both monitoring well and springs.
A hydrograph is used to continuously monitor peaks in flow. This may indicate multiple slugs of contaminant are passing through the aquifer. Design of an efficient groundwater treatment system requires an understanding of the contaminant concentrations with respect to characteristics of the storm hydrograph of the springs.
6) Vapor Intrusion Study
Karst systems are natural preferential pathways composed of caves and bedrock fractures enlarged by dissolution. The assumptions made to evaluate vapor intrusion for sites in non-karst areas are not the same as those in karst areas.
When human activities intersect karst areas, additional preferential pathways are created. These pathways can be underground utility lines, basements, sump pumps or any subsurface alteration that provides vapors a path of least resistance into a structure.
It is important to investigate both the natural pathways and those created by human activity. Either one, both, or some combination, may be the path of least resistance into a structure. Vapor intrusion in karst areas is not necessarily linear; therefore the processes for investigation are somewhat different than for non-karst situations.
Many of the assumptions from the vapor intrusion guidance cannot be applied in karst settings:

    1. The default attenuation factors are not applicable because there is often a direct connection between the contaminant source and the receptor.

    2. The groundwater screening values do not consider open conduit flow.

    3. Soil gas sampling is not representative, because the soil porosity may not be homogeneous due to open conduits or soil fractures.

    4. Vapors may not be derived solely from the groundwater contaminant plume. In karst, vapors can originate from the contaminated groundwater, traveling as a separate phase, or contaminated sediments. The investigation needs to account for all phases of contamination.

A comprehensive vapor investigation will only be successful if the karst drainage basin is indentified. Default distance assumptions do not apply, because the open conduits can allow vapors to travel much greater distances without attenuating. Conduct vapor sampling in the same way as in investigations conducted in non-karst areas but, base locations on the drainage basin and not linear distances from the source. Each karst vapor investigation is site specific, consult with Geological Services when developing a work plan.

Do not apply attenuation factors developed for non-chlorinated compound exposure concentrations in karst settings. Both chlorinated and non-chlorinated compounds are treated the same way unless the investigation demonstrates that ample oxygen is present to biodegrade the non-chlorinated contaminants. However, it is also possible that non-chlorinated vapors could be displacing oxygen. If this has happened, biodegradation of non-chlorinated contaminants may not occur.
7) Sampling Schedule and Frequency
Water flow in karst aquifers is not the same as in granular aquifers. Therefore a sampling frequency based on pre-specified fixed intervals may not yield representative samples of aquifer conditions. Sampling is based on recharge and discharge rates (determined during the dye trace study) of the springs and wells that are connected to the contaminant source area. Measurements of both high and low rates of discharge are needed. Measure low rates (also known as base flow) of discharge on fixed time intervals.
Sampling for vapors follows the same pattern. In most cases vapor concentrations will be higher when water levels are low (base flow). However, it is also possible that sudden increases in water levels can force vapors into structures and utilities. Therefore, measurements of both high and low water levels are needed. Low water level vapor samples can be collected on fixed time intervals. If the location of a conduit is known, a soil gas sample of the air within the conduit could help with the investigation.

  1. Design of Remedial Measures

    1. Soils

Soil excavation is the best way to deal with contamination above the

soil/bedrock interface. In addition to removing source material, there is also a reduction in the amount of soil present that could become mobile in the karst aquifer.

    1. Groundwater

It is necessary to treat water at all of the known discharge points (i.e. springs and seeps) to be successful in remediating groundwater at a site containing a karst aquifer. Attempting to treat water up-gradient of the discharge point may mean that some contaminated groundwater is not treated and will be discharged to surface water. In addition to treating the discharge from a karst aquifer, it is necessary to control the infiltration of surface water. This is done in a variety of ways:

  1. Use of a surface impoundment to allow water to slowly infiltrate into the aquifer. If the velocity of the water flowing through the karst conduits is controlled, the erosion of contaminated sediments are minimized. This will also reduce the peak concentrations seen during storm events.

  2. Construction of surface water diversion structures. If the amount of surface water entering the karst system is reduced, less water will need treatment. In addition, if the conduits are not allowed to fill, leaching of contaminants in upper portions of the system is minimized.

  3. The system(s) is modified to operate only during peak flow (storm events) or only run during low flow conditions. Depending on the results of the dye trace and the types of contaminants of concern it is possible to design a remediation system that only runs part of the time.

  4. Use the karst investigations to properly design the capacity of the remediation system. Systems more often fail as a result of being undersized and cannot treat the necessary volume of water.

  5. Use information gathered during the karst investigation to determine the type of equipment needed to properly treat the groundwater.

(modified from State of Minnesota draft guidelines for investigation of

groundwater contamination at petroleum release sites in karst areas;

Fact Sheet #3.42; April 1996)

    1. Vapors

The use of mitigation systems to remove vapors from the subsurface or from the sub-slab of structures is the same regardless if karst is present or not. The most common method of controlling and removing vapors is to block the migration at the point where vapors enter the building by installing a vapor mitigation system, sometimes called a “Radon System”. The most common type of vapor mitigation system, called a sub-slab depressurization system or a sub-slab ventilation system, has been used for years to prevent radon from infiltrating from soils into buildings, and is also effective for preventing contaminant vapors from

entering buildings. The USEPA has developed a number of publications

that describe the proper design, installation, and operation of sub-slab depressurization systems.

1. Monroe, W.H. (Compiler). 1970. A Glossary of Karst Terminology, USGS Water Supply Paper 1899-K. U.S.G.S. U.S. Government Printing Office. Washington, D.C. 26 pp.
2. UNESCO. 1972. Glossary and Multilingual Equivalents of Karst Terms.

United Nations Educational. Scientific. And Cultural Organization. Paris. France. 72 pp.

3. State of Minnesota. 1986. Draft Guidelines for Investigation og Groundwater Contamination at Petroleum Sites in Karst Areas, fact sheet #3.42. State of Minnesota. Minneapolis, MN.
4. State of Indiana. 2006. Draft Vapor Intrusion Pilot Program Guidance Document, State of Indiana, Indianapolis IN.

Information Links
Agencies and organizations
Below is a list of several agencies and organizations that work in karst that may be of use when reviewing and designing a karst investigation. This is not an exhaustive list and additional agencies and organizations may be out there.

  • Speleogenesis. An international website the provides links to the latest papers and publication on karst hydrogeology.

Web Site:

  • USGS Karst Website. Provides information on karst in the United States. Web Site:

  • National Cave and Karst Research Institute A research organization based out of Carlsbad NM and partnered with the national park service conducts research around the US and world

Web Site:

  • The Karst Waters Institute: A research organization based out of Baton Rouge, Louisiana and partnered with Louisiana State University conducts research around the US and world.

Web Site:

  • The Karst Information Portal: A website that provides information not only on karst but also information on the formation of carbonate rocks. This site is run by the University of South Florida.

Web Site:

  • International Association of Hydrogeologists: International Group of Hydrogeologists who specialize in karst hydrogeology.

Web Site

  • Western Kentucky University Karst Studies Group: A research organization based out of Bowling Green, Kentucky and partnered with Western Kentucky University conducts research around the US.

Web Site:

Karst Papers, Publications, and Proceedings

Below is a list of several karst publications that may be of use when reviewing and designing a karst investigation. This is not an exhaustive list and more up-to-date papers may be out there.

  • Geophysical Choices For Karst and Mine Investigations

Rick A. Hoover1, P.G.,

1 Senior Geophysicist, Science Applications International Corporation, 6310 Allentown Boulevard, Harrisburg, Pennsylvania 17112

Web Site:

  • Geotechnical/Geophysical Evaluation of karst Limestone Sites – A Case History

Gregory B. Byer, Mundell & Associates, Inc., Indianapolis, IN

John A. Mundell, Mundell & Associates, Inc., Indianapolis, IN

John H. M. Vanderlaan, Mundell & Associates, Inc., Indianapolis, IN

Web Site:

Web Site:

  • Karst Characterization Using Geophysics, Part 1:

Effective Geophysical Methods for Karst”

Kochanov, William E., DCNR, Bureau of Topographic and Geologic Survey, 3240 Schoolhouse Road, Middletown, PA 17057-3534.

Web Site:

  • Geophysical Choices For Karst Investigations

Rick A. Hoover, P.G.,

Web Site:

  • U.S. Geological Survey Karst Interest Group Proceedings, Shepherdstown, West Virginia, August 20-22, 2002

Eve L. Kuniansky, editor U.S. Geological Survey Water-Resources Investigations Report 02-4174

Web Site:

  • Ground water Investigations in Karst Areas

Guidance Document 4-09

Petroleum Remediation Program Minnesota Pollution Control Agency

Web Site:,com_docman/task,doc_view/gid,3033
Further Information
If you have any additional information regarding this technology or any questions about the evaluation, please contact Geological Services at (317)234-0991 or This technical guidance document will be updated periodically or if new information is acquired.

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