A Product of the Groundwater Resources Program Prepared in 

Cooperation with the National Cave and Karst Research Institute

U.S. Geological Survey Karst Interest Group 

Proceedings, Carlsbad, New Mexico,

April 29 – May 2, 2014

Scientific Investigations Report 2014-5035

U.S. Department of the Interior

U.S. Geological Survey

i

A Product of the Groundwater Resources Program Prepared in

Cooperation with the National Cave and Karst Research Institute

U.S. Geological Survey Karst Interest Group 

Proceedings, Carlsbad, New Mexico, 

April 29 – May 2, 2014

Edited by Eve L. Kuniansky and Lawrence E. Spangler

Scientific Investigations Report 2014-5035

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Kuniansky, E.L., and Spangler, L.E., 2014, U.S. Geological Survey Karst Interest Group Proceedings, Carlsbad, New 

Mexico, April 29–May 2, 2014: U.S. Geological Survey Scientific Investigations Report 2014-5035, 155 p.,

http://dx.doi.org/10.3133/sir20145035.

ISSN 2328-0328 (online)

ISSN 2328-031X (print)

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Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

INTRODUCTION AND ACKNOWLEDGMENTS ........................................................................ 1

AGENDA U.S. GEOLOGICAL SURVEY KARST INTEREST GROUP WORKSHOP ................. 3

KEYNOTE.................................................................................................................................. 7

Speleotrek: The Cutting Edges of Karst into the 21st Century..................................................... 7

PROGRAMS AND KARST AQUIFERS.....................................................................................19

A Preview of “Karst in the United States of America: A Digital Map Compilation and Database”

.................................................................................................................................................19

Groundwater Availability of the Floridan Aquifer System ...........................................................28

Assessing Potential Impacts from a Proposed Phosphate Mine on Ashley Spring, a Unique 

Karst Public Water Supply in the Uinta Mountains, Uintah County, Utah...................................30

TRACERS.................................................................................................................................39

Groundwater Tracing in Arid Karst Aquifers: Concepts and Considerations ..............................39

Challenges to a Karst Dye-Tracing Investigation in an Urban Brownfields Area, Springfield, 

Missouri ....................................................................................................................................44

SPELEOGENESIS, GEOLOGIC FRAMEWORK, GEOPHYSICS, AND GEOLOGIC HAZARDS

.................................................................................................................................................54

The Role of Spongework in the Speleogenesis of Hypogenic Caves in the Guadalupe 

Mountains, New Mexico ............................................................................................................54

Geologic Framework, Structure, and Hydrogeologic Characteristics of the Knippa Gap Area in 

Eastern Uvalde and Western Medina Counties, Texas .............................................................65

A Hypothesis for Carbonate Island Karst Aquifer Evolution from Analysis of Field Observations 

in Northern Guam, Mariana Islands...........................................................................................66

Using Borehole and Surface Geophysics to Develop a Conceptual Model of Hydrostratigraphic 

Layers, Pecos County Region, Texas, 2012 .............................................................................67

Perils of a Dissolving State—Florida .........................................................................................68

MODELING KARST AQUIFERS...............................................................................................69

Taking the Mystery Out of Mathematical Model Applications to Karst Aquifers—A Primer ........69

Refined Hydrostratigraphic Framework and Model of the Edwards Aquifer, Texas ...................82

Simulation of Groundwater Flow in the Edwards-Trinity and Related Aquifers in the Pecos 

County Region, Texas...............................................................................................................83

Automatic Methods of Groundwater Flow Model Construction of the Ozark Plateaus Aquifer 

System......................................................................................................................................85

CHEMICAL FATE AND TRANSPORT ......................................................................................86

Transport of Salt, Trace Metals, and Organic Chemicals from Parking Lot and Road Surfaces 

into Mammoth Cave..................................................................................................................86
iv

CAFOs on Karst—Meaningful Data Collection to Adequately Define Environmental Risk, with a 

Specific Application from the Southern Ozarks of Northern Arkansas .......................................87

An Initial Investigation of Hydrogeology and Water Quality of Big Creek in the Buffalo River 

Watershed near a Major Concentrated Animal Feeding Operation............................................97

A Method to Investigate Karst Groundwater Flow in Nash Draw, Eddy County, New Mexico, to 

Delineate Potential Impacts of Potash Industry Discharge and Runoff ......................................98

Use of A Dual Continuum Model to Describe Solute Transport in Karst ..................................108

GEOCHEMISTRY...................................................................................................................109

Geochemical Evidence for Denitrification in the Epikarst at the Savoy Experimental Watershed, 

Northwest Arkansas................................................................................................................109

Geochemistry of Paleokarst Aquifers of the Knox Group in Tennessee and Kentucky ............121

Integration of Geochemical and Isotopic Data to Assess Sources of Discharge at a Major Spring 

in the Edwards Aquifer, South-Central Texas..........................................................................125

MICROBIAL ECOLOGY AND KARST ECOSYSTEMS...........................................................126

Linking Climate Change and Karst Hydrology to Evaluate Species Vulnerability: The Edwards 

and Madison Aquifers .............................................................................................................126

Response of Cave-Stream Bacteria to Sub-Lethal Concentrations of Antibiotics ....................127

Role of Surface Water Dissolved Organic Carbon in the Survival, Growth, and Transport of 

Escherichia coli in a Deep Limestone Aquifer in South Florida................................................129

Cave Bacteria and Crystal Formation in the Laboratory ..........................................................133

Non-Target Bacterial Response to White-Nose Syndrome Treatment: Quaternary Ammonia 

Compounds and Linear Alkylbenzene Sulfonate.....................................................................134

THURSDAY, MAY 1, 2014, FIELD TRIP GUIDE.....................................................................135

Evaporite Karst of the Lower Pecos Valley, New Mexico ........................................................135
1

INTRODUCTION AND ACKNOWLEDGMENTS

Karst aquifer systems are present throughout parts of the United States and some of its territories, and 

have developed in carbonate rocks (primarily limestone and dolomite) that span an interval of time 

encompassing more than 550 million years. The depositional environments, diagenetic processes, postdepositional tectonic events, and geochemical weathering processes that form karst aquifers are varied 

and complex, and involve biological, chemical, and physical changes. These factors, combined with the 

diverse climatic regimes under which karst development in these rocks has taken place, result in the 

unique dual- or triple-porosity nature of karst aquifers. These complex hydrogeologic systems typically 

represent challenging and unique conditions to scientists attempting to study groundwater flow and 

contaminant transport in these terrains.

The dissolution of carbonate rocks and the subsequent development of distinct and beautiful 

landscapes, caverns, and springs has resulted in the most exceptional karst areas of the United States 

being designated as national or state parks; commercial caverns and known privately owned caves 

number in the tens of thousands. Both public and private properties provide access for scientists to study 

the flow of groundwater in situ. Likewise, the range and complexity of landforms and groundwater flow 

systems associated with karst terrains are enormous, perhaps more than for any other aquifer type. Karst 

aquifers and landscapes that form in tropical areas, such as the cockpit karst along the north coast of 

Puerto Rico, differ greatly from karst landforms in more arid climates, such as the Edwards Plateau in 

west-central Texas or the Guadalupe Mountains near Carlsbad, New Mexico, where hypogenic processes 

have played a major role in speleogenesis. Many of these public and private lands also contain unique 

flora and fauna associated with these karst hydrogeologic systems. As a result, numerous federal, state, 

and local agencies have a strong interest in the study of karst terrains.

Many of the major springs and aquifers in the United States have developed in carbonate rocks, such 

as the Floridan aquifer system in Florida and parts of Alabama, Georgia, and South Carolina; the Ozark 

Plateaus aquifer system in parts of Arkansas, Kansas, Missouri, and Oklahoma; and the Edwards-Trinity 

aquifer system in west-central Texas. These aquifers, and the springs that discharge from them, serve as 

major water-supply sources and as unique ecological habitats. Competition for the water resources of 

karst aquifers is common, and urban development and the lack of attenuation of contaminants in karst 

areas can impact the ecosystem and water quality of these aquifers.

The concept for developing a platform for interaction among scientists within the U.S. Geological 

Survey (USGS) working on karst-related studies evolved from the November 1999 National GroundWater Meeting of the USGS. As a result, the Karst Interest Group (KIG) was formed in 2000. The KIG is 

a loose-knit, grass-roots organization of USGS and non-USGS scientists and researchers devoted to 

fostering better communication among scientists working on, or interested in, karst science. The primary 

mission of the KIG is to encourage and support interdisciplinary collaboration and technology transfer 

among scientists working in karst areas. Additionally, the KIG encourages collaborative studies between 

the different mission areas of the USGS as well as other federal and state agencies, and with researchers 

from academia and institutes. The KIG also encourages younger scientists by participation of students in 

the poster and oral sessions.

To accomplish its mission, the KIG has organized a series of workshops that are held near nationally 

important karst areas. To date (2014) six KIG workshops, including the workshop documented in this 

report, have been held. The workshops typically include oral and poster sessions on selected karst-related 

topics and research, as well as field trips to local karst features. Proceedings of the workshops are 

published by the USGS and are available online at http://water.usgs.gov/ogw/karst/kig.
2

The first KIG workshop was held in St. Petersburg, Florida, February 13–16, 2001, in the vicinity of 

the large springs and other karst features of the Floridan aquifer system. The second KIG workshop was 

held August 20–22, 2002, in Shepherdstown, West Virginia, in proximity to the carbonate aquifers of the 

northern Shenandoah Valley and highlighted an invited presentation on karst literature by the late Barry 

F. Beck of P.E. LaMoreaux and Associates. The third KIG workshop was held September 12–15, 2005, in 

Rapid City, South Dakota, nearby to karst features in evaporites and limestones of the Madison Group in 

the Black Hills of South Dakota, including Wind Cave National Park and Jewel Cave National 

Monument. The workshop also included a featured presentation by Thomas Casadevall, Central Region

Director, USGS, on the status of earth science at the USGS and evening trips to Jewel Cave led by Mike 

Wiles, National Park Service (NPS) and Wind Cave led by Rod Horrocks, NPS. The fourth KIG 

workshop was held May 27–29, 2008, and hosted by the Hoffman Environmental Research Institute and 

Center for Cave and Karst Studies at Western Kentucky University in Bowling Green, Kentucky, near 

Mammoth Cave National Park and karst features of the Chester Upland and Pennyroyal Plateau. The 

workshop featured a late-night field trip into Mammoth Cave with Rickard Toomey and Rick Olsen, NPS. 

The fifth workshop was held April 26–29, 2011, and was a joint meeting of the USGS KIG and 

University of Arkansas HydroDays, hosted by the Department of Geosciences at the University of 

Arkansas in Fayetteville. The workshop featured an outstanding field trip to the unique karst terrain along 

the Buffalo National River of the southern Ozarks and a keynote presentation on paleokarst in the United 

States by Art and Peggy Palmer.

This sixth and current 2014 KIG workshop is hosted by the National Cave and Karst Research 

Institute (NCKRI) in Carlsbad, New Mexico, with Director of NCKRI, George Veni, serving as co-chair 

of the workshop with Eve Kuniansky, USGS. The session planning committee for this sixth workshop 

includes Van Brahana, USGS retired and University of Arkansas Professor Emeritus; Tom Byl, USGS 

and Tennessee State University; Zelda Bailey, former Director of NCKRI and retired Director, National 

Institute of Standards and Technology, Boulder Laboratory, Colorado; Patrick Tucci, USGS retired; and 

Mike Bradley, Allan Clark, Geoff Delin, Daniel Doctor, James Kaufmann, Eve Kuniansky, Randy 

Orndorff, Larry Spangler, and Dave Weary of the USGS. The karst hydrology field trip on Thursday will 

be led by Lewis Land (NCKRI karst hydrologist) and the optional Friday field trip on the geology of 

Carlsbad Caverns National Park will be led by George Veni. The keynote speaker is Dr. Penelope Boston, 

Director of Cave and Karst Studies at New Mexico Tech, Socorro, and Academic Director at NCKRI,

who will address the future of karst research. Additionally, there is a featured presentation “Irish karst and 

its management,” by Caoimhe Hickey, The Geological Survey of Ireland, preceding a panel discussion on 

“Collaboration During Times of Limited Resources.”

The extended abstracts of USGS authors were peer reviewed and approved for publication by the U.S. 

Geological Survey. Articles submitted by university researchers and other federal and state agencies did 

not go through the formal USGS peer review and approval process, and therefore may not adhere to our 

editorial standards or stratigraphic nomenclature and is not research conducted or data collected by the 

USGS. However, all articles had at a minimum of two peer reviews, and all articles were edited for 

consistency of appearance in the published Proceedings. The use of trade, firm or product names in any 

article is for descriptive purposes only and does not imply endorsement by the U.S. Government. The 

USGS, Office of Groundwater, provides technical support for the Karst Interest Group website and public 

availability of the Proceedings from these workshops, and the USGS Groundwater Resources Program 

funds the publication costs. Finally, the cover illustration is the work of Ann Tihansky, USGS, used since 

the first KIG workshop in 2000.

Eve L. Kuniansky

USGS Karst Interest Group Coordinator
3

AGENDA U.S. GEOLOGICAL SURVEY KARST INTEREST GROUP WORKSHOP

April 29–May 2, 2014 Carlsbad, New Mexico

Hosted by the National Cave and Karst Research Institute

TUESDAY, APRIL 29

Registration 

Start at 8:00 am-- All day – pick up name tags and Proceedings

Welcome and Introductions

8:20 – 8:40 Eve Kuniansky, U.S. Geological Survey, Karst Interest Group Coordinator and 

George Veni, Director of National Cave and Karst Research Institute

Programs and Karst Aquifers (Randall Orndorff, moderator)

8:40 – 9:00 A preview of “Karst in the United States of America: A digital map compilation 

and database” by David Weary and Dan Doctor

9:00 – 9:20 Groundwater availability of the Floridan aquifer system by Andrew O’Reilly and 

Eve Kuniansky (presenter)

9:20 – 9:40 An overview of the Ashley Spring groundwater system - a unique public watersupply karst spring in northeastern Utah, and potential impacts from a proposed 

phosphate mine by Lawrence Spangler

9:40 – 10:20 BREAK

KEYNOTE (Zelda Chapman Bailey, moderator)

10:20 – 10:40 Speleotrek: Cutting edge karst into the 21st century by Penelope Boston, Director 

of Cave and Karst Studies, New Mexico Tech and Academic Director, National 

Cave and Karst Research Institute

Tracers (Zelda Chapman Bailey, moderator)

10:40 – 11:00 Groundwater tracing in arid karst aquifers: Concepts and considerations by 

George Veni

11:00 – 11:20 Challenges to a karst dye-tracing investigation in an urban Brownfields area by 

Douglas Gouzie, Kevin Mickus, and Micah Mayle

11:20 – 1:20 LUNCH ON YOUR OWN

Modeling Karst Aquifers (J. Van Brahana, moderator)

1:20 – 1:40 Taking the mystery out of mathematical model applications to karst aquifers—A 

primer by Eve Kuniansky

1:40 – 2:00 Refined hydrostratigraphic framework and model of the Edwards aquifer, Texas

by Beth Fratesi, Ron Green, Ronald McGinnis, Hakan Basagaoglu, Leslie 

Gergen, Jim Winterle, Marques Miller, and Paul Bertetti

2:00 – 2:20 Simulation of groundwater flow in the Edwards-Trinity aquifer in the Pecos 

County region, Texas by Brian Clark, Jonathan Bumgarner, and Natalie Houston

2:20 – 3:00 BREAK
4

Chemical Fate and Transport (Michael Bradley, moderator)

3:00 – 3:20 Transport of salt, trace metals, and organic chemicals from parking lot and road 

surfaces into Mammoth Cave by David Solomon, Irucka Embry, Bobby Carson, 

Roger Painter, Lonnie Sharpe, Rick Toomey, and Tom Byl (presenter)

3:20 – 3:40 CAFOs on karst—Meaningful data collection to adequately define environmental 

risk, with a specific application from the southern Ozarks of northern Arkansas 

by Van Brahana, Joe Nix, Carol Bitting, Chuck Bitting, Ray Quick, John 

Murdoch, Amie West, Sarah Robertson, Grant Scarsdale, and Vanya North 

3:40 – 4:00 A method to investigate karst groundwater flow in Nash Draw, Eddy County, 

New Mexico, to delineate potential impacts of potash industry discharge and 

runoff by Jim Goodbar and Andrea Goodbar

4:00 – 6:00 Poster Session at National Cave and Karst Research Institute

WEDNESDAY, APRIL 30

Geochemistry, Fate and Transport, Microbial Ecology and Karst Ecosystems (Patrick Tucci, 

moderator)

8:20 – 8:40 Geochemical evidence for denitrification in the epikarst at the Savoy 

Experimental Watershed, northwest Arkansas by Jozef Laincz and Phillip D. 

Hays

8:40 – 9:00 Geochemistry in paleokarst aquifers of the Knox Group in Tennessee and 

Kentucky by Michael Bradley and Marty Parris

9:00 – 9:20 Linking climate change and karst hydrology to evaluate species vulnerability: 

The Edwards and Madison aquifers by Barbara Mahler, Andrew Long, John 

Stamm, Mary Poteet, and Amy Symstad

9:20 – 9:40 Response of cave–stream bacteria to sub-lethal concentrations of antibiotics by 

Tom Byl, Petra Byl, and Rickard Toomey

9:40 – 10:20 BREAK

Modeling Karst Aquifers (David Weary, moderator)

10:20 – 10:40 Automatic methods of groundwater flow model construction of the Ozark 

Plateaus aquifer system by Brian Clark and Joseph Richards

10:40 – 11:00 A hypothesis for carbonate island karst aquifer evolution from analysis of field 

observations in northern Guam, Mariana Islands by John Jenson, Danko 

Taboroŝi, Kolja Rotzoll, John Mylroie, and Stephen Gingerich (presenter)

Speleogenesis (David Weary, moderator)

11:00 – 11:20 The role of spongework in the speleogenesis of hypogenic caves in the 

Guadalupe Mountains, New Mexico by Mark Joop

11:20 – 1:20 LUNCH ON YOUR OWN

Featured Presentation

1:20 – 1:40 Irish karst and its management by Caoimhe Hickey, The Geological Survey of 

Ireland
5

PANEL DISCUSSION: Collaboration During Times of Limited Resources (Eve Kuniansky, 

moderator)

1:40 – 3:00 U.S. Department of the Interior panelists:

James Goodbar, Bureau of Land Management,

Randy Orndorff, U.S. Geological Survey, and 

Dale Pate, National Park Service

University Perspective: 

Doug Gouzie, Missouri State University

Institute Perspective: 

George Veni, National Cave and Karst Research Institute

Other Federal Agency with Stewardship Responsibilities: 

Johanna Kovarik, U.S. Department of Agriculture-Forest Service

3:00 – 3:40 BREAK

Karst Interest Group Business 

3:40 – 4:00 Discuss proposals for location of next KIG workshop in 2017

4:00 – 4:20 Thursday Field Trip overview and logistics by Lewis Land

THURSDAY, MAY 1

7:45AM – 5:30PM Field Trip Day 1—Evaporite karst of the Lower Pecos Valley, New Mexico

 by Lewis Land

FRIDAY, MAY 2

7:45AM – 5:30PM Field Trip Day 2—Geology tour of Carlsbad Cavern by George Veni

POSTERS

Geologic Framework, Geophysics, and Geologic Hazards

Geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern 

Uvalde and western Medina Counties, Texas by Allan K. Clark (presenter), Diana E. Pedraza, 

and Robert R. Morris

Three-dimensional model of the hydrostratigraphy and structure in and around the Camp Stanley storage 

facility, northern Bexar County, Texas by Michael P. Pantea and Allan K. Clark (presenter)

Using borehole and surface geophysics to develop a conceptual model of hydrostratigraphic layers, Pecos 

County region, Texas, 2012 by Jonathan V. Thomas, Johnathan R. Bumgarner, Gregory P. 

Stanton, Andrew P. Teeple, and Jason D. Payne

Perils of a dissolving State—Florida by Clint Kromhout

Geochemistry, Fate and Transport, Microbial Ecology, and Karst Ecosystems

Role of surface-water dissolved organic carbon in the survival, growth, and transport of Escherichia coli

in a deep limestone aquifer in south Florida by Ronald W. Harvey, Jen Underwood, John Lisle, 

David W. Metge, and George Aiken

Integration of geochemical and isotopic data to assess sources of discharge at a major spring in the 

Edwards aquifer, south-central Texas by MaryLynn Musgrove and Cassi L. Crow

Cave bacteria and crystal formation in the laboratory by Petra Byl, Aaron Covey, Jessica Oster, Tasneem 

Siddiquee, and Tom Byl (presenter)
6

Non-target bacterial response to white-nose syndrome treatment: Quaternary ammonia and linear alkyl 

sulfonate compounds by JeTara Brown, Zheer Ahmed, and Tom Byl (presenter)

Flowable fill for subsurface cavity remediation by Chase Kicker (Carlsbad High School, accepted at New 

Mexico Tech for fall, 2014)

Chemical Transport and Contamination in Karst 

Use of a dual continuum model to describe solute transport in karst by Justin Harris, Roger Painter, 

Lonnie Sharpe and Tom Byl (presenter)

An initial investigation of hydrogeology and water quality of Big Creek in the Buffalo River watershed 

near a major concentrated animal feeding operation By Victor L. Roland II, Phillip Hays, Van 

Brahana, and Erik Pollock

Demonstration

The National Karst Map by David Weary
7

KEYNOTE

Speleotrek: The Cutting Edges of Karst into the 21st Century

By Penelope J. Boston1,2

1

New Mexico Tech, 801 Leroy Place, Socorro, NM 87801

2

National Cave and Karst Research Institute (NCKRI), 1400-1 Cascades Ave., Carlsbad, NM 88222

Abstract

Exploration and study of Earth’s subsurface has been the delight of some but a blank slate to many 

within the mainstream geoscience and biology communities until perhaps the past several decades. 

Especially in the United States, many aspects of cave and karst studies have been marginalized but this 

picture is now changing. Increasing awareness of karstic processes include the classic areas of cave 

origins and development (speleogenesis) and karst geohydrology, but now include such fields as 

geomicrobiological influences on karst, the role of karst and cave environments in biogeochemical 

cycling, and caves as repositories of several types of important climate proxy data. A dawning 

appreciation of the subsurface habitat connection with surface habitats is upon us, especially with regard 

to material and energy transfers. Even apparent examples of karstic phenomena beyond Earth have begun 

to seep into the larger scientific landscape. Such contemplation can provide a new basis for comparative 

studies enabling us to test our ideas in more than one planetary context. Finally, new technology and 

methodologies emerging now will help to advance karstic studies into the future and bring karst science 

into the mainstream of the 21st century science portfolio. Implications of karst in matters of human 

welfare, and opportunities for applications of new arenas of research are numerous. Concerns range from 

geohazards associated with karst and special issues unique to karst aquifer management, to the potential 

for unique compounds of pharmaceutical and industrial uses derived from subsurface sources. The 21st

century is shaping up to be a productive time for karst understanding and utilization.

KARST IN THE BROAD CONTEXT 

The existing body of work on karst and 

related topics is an important source of 

understanding of fundamental processes, not 

only in relation to the particulars of dissolvable 

landforms, but also in the greater context of the 

Earth sciences writ broadly. Shallow crustal and 

surficial processes involving aqueous 

dissolution, consequences for hydrological 

drainage, modification of the landforms 

overlying and underlying soluble rock facies, 

and the properties of caves as environments for 

microbial and macroscopic biota are already 

acknowledged arenas of speleology. In a highly 

interdisciplinary 2007 workshop organized by 

the Karst Waters Institute (KWI), a number of 

major research directions for the future of karst 

were identified (Martin and White, 2008). 

However, since that assessment was completed 

there are a handful of developments of particular 

note that are newly emerging or are undergoing 

major development and these constitute the topic 

of this paper. By its very nature, speleology is a 

place-based, highly interdisciplinary field. 

Where karst geohydrology overlaps with 

speleology, research also benefits from 

interdisciplinary synthesis. Some cutting edge 

research fits within the geoscience framework 

and some is clearly biological in nature. Often 

these broad disciplines overlap, and all research 

approaches will be enhanced by new 

technologies that can allow us to better detect, 

access, and study caves and the karstic terrains 

that house them. Furthermore, any ways in 

which karst studies can fruitfully interact with 

other scientific research areas will enhance both 

the broader picture and in turn feed back into 

further invigorating karst science itself.

CUTTING-EDGE SCIENCE DIRECTIONS

Although numerous questions remain to be 

answered and understood in detail, many aspects 

of classical karst science are relatively mature 

fields, with suites of major fundamental 

principles currently understood and 

implementable in field, laboratory, and modeling 

efforts (Palmer 2007; Ford and Williams, 2007). 

However, several aspects of karst studies that 

have been little explored are now gaining 

attention and are discussed below.
8

More Than Just CaCO3! 

The classic conception of karst dates from as 

far back as the mid-17th century (Larsen, 2003) 

and was described originally for the Dinaric 

carbonate karst of Slovenia and surrounding 

areas. Jovan Cvijić, the famous Serbian scientist 

and polymath of the late 19th century, also made 

seminal contributions to the early concepts of 

carbonate karst, publishing a major work on the 

subject in 1895. This early work firmly planted 

the notion of karst in carbonate lithology.

Arguments have raged in the past over 

whether the term karst should be reserved only 

for terrains in calcium carbonate rock types (see 

Monroe (1970) for a typical version of such a 

definition of karst.) Perhaps most modern 

thinkers on the subject have broadened the scope 

of karst to encompass any geomorphic terrain 

type that relies on dissolution of soluble rock as 

its primary driving mechanism (e.g. Ford, 1980). 

Surface and subsurface characteristics typically 

associated with many karst terrains can be 

helpfully diagnostic in assessing the karst status 

of a particular area but should not be required as 

definitive because of the great complexity of 

features that can be considered as karst. The 

trend to broaden the lithologies under the karst 

umbrella is very handy because there are a 

number of compelling examples in a variety of 

rock types around the world!

Gypsum and other evaporite minerals are an 

important additional type of dissolvable rock 

with wide global distribution of resulting 

landforms and caves. Many speleologists 

already refer to these lithologies as karst (see 

Klimchouk and others (1996) for a review of the 

state of the art at that time.) Powerful 

comparisons of gypsum karst with carbonate

karst can yield a refined partitioning of the 

relative roles of physical and chemical processes 

that govern solubility of bedrock in the natural 

environment. For example, the major influence 

of pH that we see in carbonate karst is irrelevant 

to gypsum dissolution, and of course, the 

intrinsically high solubility of calcium sulfate is 

itself a critical factor in the origin and 

development of gypsum karst. Truly enormous 

and spectacular examples of gypsum caves and 

karstification exist in western Ukraine and

Moldova (e.g. Andrejchuk, 1996; Klimchouk 

and Andrejchuk, 2002). Smaller scale but 

scientifically important examples occur in many 

other parts of the world.

Also associated with many evaporite rocks 

are halite (NaCl) deposits. Such salt deposits 

may house caves and related karst drainage 

features. Seminal work by a relatively small 

number of investigators (e.g. Frumkin, 1994; 

Bosak and others, 1999) has enabled 

understanding of the basic behaviors of such 

systems but much remains to be done to extend 

understanding. Halite karst is uncommon but 

widely distributed, occurring in Iran, Israel, 

Algeria, Chile, Romania, Spain, Syria, 

Tadjikistan, and Tunisia (Chabert and Courbon, 

1997).

Even more exotic karstic processes occur in 

quartzite, most notably in massifs in South 

America (Gibbs and Barron, 1993; Piccini, 

1995). Wray (1997) has argued convincingly 

that caves in South American quartzite massifs 

qualify as true dissolutional karst. Further, he 

points to a number of other quartzite karst 

occurrences in Chad and Australia. Quartzite 

karst is one instance among a growing number 

of cases that implicates biological processes in 

the alteration, modification, or even inception of 

a karstic phenomenon. In this case, 

microbiologically enhanced silica dissolution 

and mobilization appears to be significant in the 

development of karst in siliceous materials like 

quartzite (e.g. Chalcraft and Pye, 1984; Zhou 

and others, 2011). 

Further comparative study of soluble rock 

processes can be extremely fruitful, allowing us 

to explore along a gradient from extremely 

soluble and needing only the presence of water 

(halite and gypsum), to the classical pHdependent karst in limestone, dolomite, and 

marble, to extremely refractory siliceous rock 

like quartzite that requires the presence of 

significant microbial (and perhaps plant) 

chemical mobilization.

Caves as Key Interface Systems in the 

Critical Zone 

The Critical Zone (CZ), that part of the 

Earth that houses the interactions of the 

atmosphere, hydrosphere, biosphere, and near 

surface lithosphere, was invented as a defined 

phrase over a decade ago in a largely ecological 

context (National Research Council, 2001). The 
9

intent was to capture the essence of the thin 

outer envelope of our planet within which all life 

resides, and where we conduct the vast majority 

of our human activities. Caves are discrete 

systems uniquely positioned to capture these 

dynamic interactions that collectively describe 

the Critical Zone. Indeed, caves may represent 

the single best example of the terrestrial Critical 

Zone in miniature since they contain some 

combination of atmosphere, fluid, rock, often 

sediment, a huge array of microorganisms, and 

often macroscopic animal life. 

There are several key properties of caves 

that come together to enable us to take a systems 

approach to cave study and place it within the 

Critical Zone context: 1) all three common 

phases of matter come together in caves, 2) 

caves are separated from the surface by 

significant boundary conditions, and 3) they are 

partly open systems vis a vis energy and 

materials, but over short timescales they can act 

as discrete closed systems! 

Ideally, subsurface cavities as Critical Zone 

examples can capture the attention of non-karst 

scientists as well as speleologists to further the 

understanding of interfaces between the various 

compartments of the Earth system both in caves 

and as applicable to the wider surface 

environment. A recent major assessment of 

Critical Zone science and applications in 

response to various global environmental 

challenges set forth a broad plan for research 

and applications and did mention karst in 

connection with hydrogeology. However, the 

paper did not mention caves a single time in the 

course of a rather lengthy document, in spite of 

the unique nature of karst habitats (Banwart and 

others, 2013). More work on the part of the karst 

community is necessary to sensitize the broad 

scientific community to the importance of karst 

systems on Earth and their properties 

specifically in the Critical Zone context.

Caves in the Era of Geomicrobiology 

A major new research thrust over the past 20 

years or so has been subsurface 

geomicrobiology studied at depths ranging from 

shallow caves and lava tubes to extremely deep 

mines and deep within the ocean floors. While 

there is still much to be learned about the 

unusual and often unique species of 

subterranean animals that inhabit caves and 

cavities within limestone aquifers and other 

types of caves, it is in the realm of microbiology 

that many new research directions are 

particularly coming to the fore. 

The awareness of microbial interactions 

with rocks and minerals has developed from the 

surface down, with an important early attempt to 

classify organisms on the basis of how they were 

positioned within, over, or under rocks (Golubic 

and others, 1981). Since that seminal attempt, 

our grasp of the degree to which Earth’s 

terrestrial and marine crust is thoroughly 

infested with tiny life forms has greatly 

expanded. We now know that there is a vast 

global subsurface rock fracture habitat that 

houses countless strains of microorganisms, and 

that aquifers, caves, and even volcanic terrains, 

and the immense ocean floor with a mix of 

young and very aged rocks are part of the rock 

fracture wilderness (Boston and others, 2001, 

2009a; Cowan and others, 2003; Frederickson 

and Balkwill, 2006; Gihring, 2006; Lin and 

others, 2006; Northup and Lavoie, 2001). 

Clearly caves and karst systems are vital and 

important parts of this hidden microbial 

wilderness because they can provide us windows 

into that terra incognita.

In our research team’s experience in caves, 

we see unique features of subsurface microbial 

communities that often include extremely high 

biodiversity and a large degree of habitat 

partitioning at a very fine spatial scale on the 

order of centimeters to meters (Boston and 

others, 2009b). In contrast, those working in the 

deep subsurface may be seeing a much reduced 

biodiversity, perhaps even as little as a single 

species (Chivian and others, 2008)! The pace of 

growth can be very slow in the typically energylimited subsurface (Kieft and Phelps, 1997; 

Boston and others, 2009b) and opportunities for 

transport around such systems can be severely 

limited by lithologic and hydrologic barriers. 

Coupled with the growing understanding of 

the vertical extent of the rock fracture habitat, 

the awareness of the role of organisms in 

precipitation of minerals has been occurring at 

the same time (e.g. Banfield and Nealson, 1997; 

Newman and Banfield, 2002). This has been a 

critical development in interpreting how many 

subterranean microbes make their living 
10

chemolithotrophically, that is, by transforming 

inorganic materials like minerals into energy 

rather than relying for energy on utilization of 

organic compounds derived from the aboveground biosphere. Oxidation of metal-containing 

minerals is a very common energy-acquisition 

mechanism, and the proximity to the waste 

products of those transformations make 

subterranean microbes inclined to auto-fossilize 

as they are growing, thus providing a 

mechanism for exquisite preservation of 

biotextures and even microbial body fossils (e.g. 

Boston and others, 2001, 2009b; Curry and 

others, 2009; Melim and others, 2001, 2009). 

Additionally, the ubiquity of biofilms that the 

organisms make for protection and manipulation 

of the chemistry of their environments, also 

contributes to the production and preservation of 

distinctive biosignatures including biomineral 

textures. Battin and colleagues (2007) have 

exhorted us to view biofilms as miniature 

landscapes and those who study these materials 

are well–acquainted with the clear parallels to 

the larger scale landscapes we see in nature.

Very small cell sizes (100-500 nm diameter) 

and very slow growth rates are common in 

subsurface microbial communities and 

presumably are an adaptation to stringently 

limited energy sources to be found there (Kieft, 

2000, 2002). Energy limitation is also coupled 

with the absence of grazing by animals or 

protists in many of the deeper systems that 

allows organisms to prosper without having to 

“outgrow” the rate at which they are being 

consumed by other organisms (Boston and 

others, 2009b). 

A further outgrowth of the work of a number 

of investigators is beginning to point to the role 

of microorganisms in low temperature 

hydrothermal ores (e.g. Southam and Saunders, 

2005), and particularly copper (Enders and 

others, 2006), and gold (Karthikeyan and 

Beveridge, 2002; Lengke and Southam, 2006; 

Southam and others, 2009). Carbonate systems 

that host emplacement of such ores as a result of 

a granitic intrusion are known as skarn deposits 

(Einaudi and Burt, 1982). The potential for use 

of organisms from these environments is great 

and could be used for biomining, 

bioremediation, and biobeneficiation (Shannon 

and Unterman, 1993; Rawlings and others, 

2007). 

Importantly for purposes of human use, 

many subsurface microbes produce a wealth of 

unusual chemical compounds of potential use to 

the pharmaceutical, industrial, and remediation 

communities, thus providing a major new 

application for speleology (Poulson and others, 

1986). Much of the work that has been done on 

these compounds has not yet been published in 

the open literature for a variety of reasons, one 

of which is the uncertain legal framework under 

which potentially commercially important 

compounds coming from organisms within the 

purview of a national land management agency 

should be handled (e.g. Northup and others, 

Boston and others, and Mallory and others, 

unpublished data).

Besides the microorganisms that we can 

understand well enough to at least study, an

extraordinary biological morphology has come 

to our research group’s attention that we are still 

at a loss to explain after 15 years of finding 

variants of this morphology in a variety of caves 

around the world in all lithologies (Melim and 

others, 2008; Northup, Boston, and Spilde, 

unpublished data). Very tiny hexagonal mesh 

tubes, ~0.5 μm in diameter and up to several 

tens of μm in length appear draped across the 

micro-landscape in scanning electron 

micrographs. They display a host of 

mineralogical characteristics indicating that they 

are covered by compounds in their environment. 

We do not know who or what these structures 

are; we have so far not succeeded in growing 

them, and the long dance cards of DNA strains 

that we obtain cannot be matched up to a single 

morphology seen only in electron micrographs. 

Are they some sort of cellular skeletons? Are 

they microstructures belonging to a higher life 

form? Are they organisms in their own right? 

So far we are stumped.

However tantalizing it is to study the

peculiar and exotic as with our reticulated 

filaments described above, Northup and Lavoie 

(2001) have pointed out that, “Caves should be 

used as experimental study systems for 

geomicrobiology, not because they are strange, 

but because they are simple and often locally 

abundant, allowing for replicate studies....”
11

This is an important observation which means 

that we do not necessarily need to seek out the 

most extreme and extraordinary caves or 

bizarre-appearing life forms in order to study the 

geomicrobiology. All caves can offer important 

insights into bio-diversity, functional diversity, 

critical metabolic pathways, and metabolic 

products that may be of use for human concerns. 

Subsurface Biodiversity as a 

Hydrological Proxy 

Patterns of microbial and functional gene 

biodiversity are on the threshold of emerging 

from phylogenetic studies of well samples, 

borehole cuttings, natural caves, active and 

abandoned mines, deep ocean drilling cores, and 

from beneath glaciers and ice fields. As the 

databases swell with entries at an ever greater 

pace due to continuous improvements in the 

technology and lower analytical cost per sample, 

it is now possible to suggest that the emerging 

patterns may provide useful proxies for 

hydrological connectivity in fractured aquifers 

that are difficult to measure directly. I have 

expressed this as karst-controlled biogeography 

of subsurface life (Boston, 2002). The essence of 

the idea is that organisms move very slowly 

through a connected fracture system in the 

subsurface. Transport mechanisms include fluid 

flow, which can be extremely slow, and active 

motion by organisms with independent motility, 

also typically slow. The patterns of propagation 

of organisms through the subsurface and their 

relationships to one another will eventually be 

able to provide insights into connectivity in 

subsurface systems that may be difficult to infer 

by direct physical evidence.

Besides the inherently slow nature of the 

two transport mechanisms mentioned above, 

there are a number of other roadblocks to

microbial movement through a karst system, 

ranging from geological barriers like 

impermeable facies, to microbiologicallyinduced blockage of porosity and permeability 

by biofilms and biominerals that the organisms 

may produce. The biofilm lifestyle is ubiquitous 

in nature and its antiquity dates to some of the 

earliest evidences of life on Earth, some 3.25 

billion years ago (Hall-Stoodley and others, 

2004). Thus, organisms may well have been 

influencing porosity and permeability of rock 

masses in the crust for the vast majority of 

Earth’s geological history and are still doing that 

today.

Climate Proxies in Caves

Several decades ago, calcite in caves was 

identified as important material for investigating 

climate records, particularly during non-glacial 

times (e.g. Gascoyne, 1992; Bar-Matthews and 

others, 1996). Of the many potential data types 

that calcite speleothems may supply, stable 

isotope ratios have gained ascendency and are 

being used extensively to reconstruct ancient 

climates (Ghosh and Brand, 2003). As those 

authors point out in the paleoclimate context, 

“Atmospheric CO2 provides a link between 

biological, physical and anthropogenic processes 

in ecosystems.” As we well know, CO2 is an 

intrinsic part of karst mechanisms and thus, the 

use of speleothem stable isotopes as one of the 

climate proxy data sets has become very popular 

(Fairchild, 2006). In concert with stable isotopic 

fractionation, recent work (Woodhead and 

others, 2010) has extended the radiometric 

dating timeline back to ancient speleothems in 

paleokarst systems as far back as the Permian, 

which makes such studies even more useful. 

Speleothem climate study using stable isotopes 

is thus, a tremendously exciting and promising 

field of research. However, what has not yet 

been addressed is the potential for microbial 

interference in these signals. Microorganisms 

are not known to alter the fractionation of 

oxygen, so the O16/O18 ratio used to indicate 

evaporation and indirectly temperature is 

probably safe from microbial effects. However, 

carbon is highly fractionated between C13 and 

C12 isotopes on the basis of photoautotrophy or 

chemolithotrophy, both of which slightly favor 

the lighter isotope and can be used to define 

carbon sources and sinks (see Ghosh and Brand, 

2003, for a nice explanation of these 

complicated interactions.) Organic carbon 

received from above-ground, coupled with 

chemolithotrophic carbon fixation by 

microorganisms in-cave, complicated further by 

reports of direct excavation of solid carbonate by 

microorganisms (Garcia-Pichel and others, 

2010), means that the straightforward 

interpretation of carbon in the climate context is 

not always possible and certainly presents 

caveats to be considered.
12

Caves and rock shelters have been identified 

as excellent sediment traps in the archaeological 

context (Colcutt, 1979) and this also applies to 

their role as sediment traps in general. Further, 

vegetation indicators in sediments are often well 

preserved in caves. Primarily, pollen has been 

studied in this context although not exploited as 

much as it can be (McGarry and Caseldine, 

2004) but plant biominerals (known as 

phytoliths) and diatoms (photosynthetic algae 

with silica tests) are equally promising and often 

the most abundant botanical remains recovered 

from cave sites. For several good examples of 

combining these data types see Martínez and 

others (2013) and Trombold and IsradeAlcantara (2005). The use of phytoliths in 

climate reconstruction has now been applied to 

very recent climate and vegetation change of 

only several hundred years in the past (Morris 

and others, 2009). 

The partitioning of trace elements in 

speleothems as indicators of ancient conditions 

has also been explored, although to a far lesser 

degree than the other proxy data sets. This 

includes laboratory simulations of uptake of 

trace elements as well as field observations of 

natural systems (Huang and others, 2001a, b; 

Treble and others, 2005; Johnson and others, 

2006, Day and Henderson, 2004). There is 

additional potential for applying this approach to 

cave climate records.

Broadly viewed, all of the proxy indicators 

of climate discussed above can be combined 

fruitfully in cave studies (Couchard, 2008). For 

an excellent example of vegetation bioindicators 

combined with isotopic data, see Scott (2002). In 

the future, studies which attempt to crosscorrelate all possible climate data sets contained 

within caves could be immensely valuable in 

helping us to unravel Earth’s past climates in 

non-marine and low- to mid-latitude 

environments.

Extraterrestrial Karst? 

The tantalizing prospect of extraterrestrial 

caves ranges from lava tubes, pit crater shafts, 

and other collapse features first speculated about 

and then observed on the Moon (Oberbeck and 

others, 1969; Greeley, 1971; Sakimoto and 

others, 1997; Haruyama and others, 2009), and 

Mars (Wyrick and others, 2004; Cushing and 

others, 2007; Cushing, 2012) to hypothetical 

exotic true karst in radically different planetary 

settings (Boston, 2004; Grin and others, 1998, 

1999). Within this context, we include water ice 

"bedrock", liquid methane rain, and derived 

organic surface “soil” on Titan (Mitchell and 

Malaska, 2011; Malaska and others, 2011). The 

epistemological power of comparative planetary 

studies can now be extended into speleology. 

Can we take what we believe we understand 

about karstic processes on Earth and validly 

translate that to another planetary body and vice 

versa? Such a rigorous test bed could play an 

important role in providing new perspectives 

and potentially new insights.

In order to handle the concept of karstic 

phenomena on other planetary bodies, a new 

conceptual framework is needed. A number of 

speleologists have devised schemes for karst or 

cave classification that are of great utility for 

Earth applications (e.g. Cams, 1989; Dreybrodt, 

1988; Ford and Williams, 1989; Self and 

Mullan, 1996). However, most may not fit some 

of the more unusual processes that we can 

anticipate seeing on other bodies. Table 1 shows 

an ongoing attempt to reduce the complexity of 

karst and cave processes that may be seen on 

other planets to basic physical and chemical 

processes (modified from Boston, 2004). As a 

work in progress, this is hardly definitive but a 

start in attempting to rethink the issues involved 

in radically different gravitational environments.

CUTTING-EDGE TECHNOLOGIES 

New non-invasive or less invasive 

methodologies can reveal the subsurface in new 

ways or allow us to directly explore them using 

robotic proxies. Application of well known 

techniques to the cave environment is one 

important direction and exemplified by the 

development of a prototype mass spectrometer 

for in-situ analysis of cave atmospheres working 

toward a better understanding of the gases that 

make up cave air (Patrick and others, 2012). 

Other well known instruments could also be 

tailored for the rigorous challenges of using high 

precision instrumentation in a dirty and difficult 

environment. However, entirely new approaches 

to karst research are being tried and discussed 

below.
13

Thermographic Mapping 

Mapping relative degrees of heat to show 

contrasts potentially indicating subsurface 

cavities has been shown to be feasible in 

ground-based infrared camera trials on Earth 

conducted in New Mexico, West Virginia, 

Missouri, Greece, and the Atacama Desert, 

Chile, and balloon-borne trials conducted in the 

Mojave Desert, CA (Thompson and Marvin, 

2006). Modeling efforts have been mounted to 

study the Martian thermal environment to 

determine suitability of this method in the much 

colder temperatures of Mars with lower 

temperature contrast between inside and outside 

cavities (Wynne and others, 2008). Applicability 

to ultra low-temperature bodies with minimal 

thermal contrast remains to be demonstrated: 

Titan, which has a very dense atmosphere, or 

Enceladus and Europa, both of which have 

virtually no atmospheres.

Imaging 

Miyamoto and colleagues (2005) have been 

developing a ground penetrating radar (GPR) 

system with shielded antennas and steppedfrequency capability (50-500 MHz) that will 

enable both significant penetration depth (>10 

m) and high spatial resolution (< 1 m) at the 

same time. They field tested the instrument in a 

lava tube (Koumoriana, Aokigahara lava flow, 

Japan), and is also applicable to karst as well.

Recently a team from the NASA Jet 

Propulsion Laboratory analyzed interferometric 

synthetic aperture radar (InSAR) imagery of the 

area around a giant sinkhole that opened up in 

Bayou Corne, LA, in 2011 (Jones and Blom, 

2014). Uninhabited Airborne Vehicle Synthetic 

Aperture Radar (UAVSAR) is mounted on a C20A jet. The InSAR instrument can measure tiny 

deformations in a planet’s surface, and very 

small horizontal surface irregularities have now 

been shown to precede the development of a 

sinkhole far in advance of its collapse, 

potentially providing a predictive capability for 

Earth applications and possibly a detection 

method for other planets.

Radar imaging of gigantic frigid Titan, 

orbiting Saturn, suggests both cryovolcanism 

(e.g. Wall and others, 2009) and subsurface 

structures (Burr and others, 2009). Can 

processes on a body of water-ice bedrock and a 

surface of a bizarre mixture of organic 

compounds awash with alkane lakes and rain 

possibly produce structures like caves and 

karstic terrain familiar to us on Earth and other 

rocky terrestrial bodies? A plausibility argument 

can be made and tested using orbital radar 

imaging data and modeling. 

Even more futuristically, muon imaging may 

provide ultra-deep penetration (~1 km). The 

technique, which relies on the production of 

muons by collision of galactic cosmic rays with 

the atmosphere has already been tested for 

volcanology, archeology, and national security 

applications, and has recently been suggested for 

imaging the interior of small solar system bodies 

like asteroids or comets (Prettyman, 2013). A 

preliminary (Phase I) study has been funded by

NASA to explore the possibilities. While the 

muon production rate is slow, meaning long 

signal collection times of days to weeks, caves 

are usually not moving targets and so may be 

perfect for such a leisurely approach!

Robotics for Cave Access

Successful robotic access to caves, rock 

shelters, and other rugged and unpredictable 

surface terrain is essential to allow exploration 

of other planets and even for some extreme 

Earth sites. Concepts like hopping, selfdeploying microbots with high energy-density 

power and polymer “muscle” actuated motion 

for subsurface sensing and telemetering 

networks have been suggested and developed to 

an early stage (Dubowsky and others, 2004). 

Unique clinging and climbing mechanisms also 

are being developed (Parness, 2010). A field 

demonstration with Jet Propulsion Laboratory 

colleagues during 2014 tested gravityindependent inverted clinging robots in lava 

caves in New Mexico and California and will 

continue into mid-2016 to investigate methods 

of advanced mobility.

SUMMARY 

In summary, speleology is a place-based 

field of tremendous depth that has often been 

marginalized from mainstream science, 

especially in the United States. Over a decade 

ago, I wrote of the then-new National Cave and 

Karst Research Institute (NCKRI) and its 

aspirations for the future (Boston, 2003). Five 

years later, at the 2008 Karst Interest Group 
14

meeting, I attempted to further expand on our 

grasp of how we can be useful to the karst 

community and the directions to follow in 

accomplishing our mission. It is now time to 

reassess and possibly to reposition ourselves to 

proactively advocate for the cutting edge areas 

of research and application that will matter the 

most to the future of the field and applications. 

The past decade has seen emergence of a suite of 

research directions that map an exciting future in 

karst studies as we go into the next century of 

science and exploration. NCKRI stands ready to 

assist in the development of this future.

Table 1. Fundamental physical and chemical process classification of caves including karst, karst-like processes, and 

non-karst mechanisms for karst formation. Revised and updated from Boston, 2004.

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19

PROGRAMS AND KARST AQUIFERS

A Preview of “Karst in the United States of America: A Digital Map 

Compilation and Database”

By David J. Weary and Daniel H. Doctor

U.S. Geological Survey, 12201 Sunrise Valley Drive, MS926A, Reston, VA 20192

Abstract

A series of new digital maps delineating areas of known and potential karst and pseudokarst 

development in the United States, including Puerto Rico and the U.S. Virgin Islands, have been compiled 

and are being released as a U.S. Geological Survey Open-File Report (OFR). These maps show areas 

underlain by soluble rocks with potential for karst development as well as volcanic rocks, sedimentary 

deposits, and permafrost with potential for pseudokarst development. Data indicate that all 50 States 

contain areas with potential for karst development. About 18 percent of the area of the United States is 

underlain by karst or soluble rocks that have the potential for karst development. The mapped areas of 

soluble rocks, containing significant amounts of carbonate or evaporite minerals, are primarily based on 

their distribution shown on state geologic maps. Areas underlain by soluble rocks are further classified by 

general climate setting, induration, and exposure. Areas with potential for volcanic pseudokarst are those 

chiefly underlain by basaltic extrusive rocks no older than Miocene in age. Potential pseudokarstic 

features in unconsolidated sedimentary rocks include piping caves. Areas with potential for development 

of thermokarst subsidence features in Alaska contain permafrost mantled by various thicknesses of 

sediment. The OFR includes a GIS database with links from the map unit polygons to online geologic 

unit descriptions. This paper is an interim product, and a formal publication and print edition, with 

revisions and additions, is planned for the near future.

INTRODUCTION

A new digital national karst map will be 

published as an Open-File Report (OFR) (Weary 

and Doctor, in press). The OFR contains 

extensive discussion and detailed descriptions of 

the processes used to compile and classify the 

karst data that it contains. In addition, the maps 

included in the OFR are both more complex and 

of higher resolution than the figures shown in 

this paper.

Because the development of karst is 

primarily dependent on the presence of soluble 

rocks, the delineation of karst was based on 

compiling areas of soluble rocks from geologic 

maps (e.g. Williams and Ford, 2006). We 

compiled regions of known and potential karst in 

the United States using the latest, most detailed 

published digital geologic map information. 

While this approach is representative of karst 

potential, a complex interaction of many factors 

determines the formation, localization, and 

intensity of karst development. These factors 

include the rock type, structural setting, climate, 

sedimentary cover, vegetation, local hydrologic 

conditions, and time. Because very sparse karst 

features evident at the land surface can indicate 

important groundwater flow processes in the 

subsurface, we have included all areas 

containing soluble bedrock types as potentially 

hosting karst features. 

Pseudokarst (Halliday, 2007) discussed in 

the OFR includes areas with features analogous 

to karst that arise from processes other than rock 

solution. Potential pseudokarst includes areas 

underlain by geologic materials susceptible to 

formation of voids produced in lava flows and 

by erosion of fine-grained sediments by piping 

(stoping), and melting of permafrost. Examples 

include lava tubes in Miocene and younger 

volcanic flow rocks (primarily basalts), piping 

features within unconsolidated sediments in 

semiarid to arid regions, as well as areas of 

piping in sediments affected by intermittently or 

progressively thawing permafrost in Alaska. 

Pseudokarst in permafrost areas is also known as 

thermokarst (Sweeting, 1973). Large karst-like 

integrated groundwater flow systems that 

resurge at large springs occur in some areas of 
20

layered volcanic rocks in the western United 

States. Examples include the Columbia Plateau 

aquifer system in Oregon and Washington, and 

the Snake River Plain aquifer system in Idaho. 

Five thematic maps in the report include 1) 

karst and potential karst areas of relatively 

soluble rocks (e.g. limestone, dolomite, gypsum, 

anhydrite, halite, etc.) exposed at the surface or 

buried at depths up to 300 feet in the contiguous 

United States, 2) karst and potential karst areas 

of relatively soluble rocks (e.g. limestone and 

dolomite) in Alaska, Hawaii, Puerto Rico, and 

the U.S. Virgin Islands, 3) areas underlain by 

evaporite rocks at varying depths up to 7,000 

feet, 4) areas with potential for pseudokarst in 

the contiguous United States, and 5) areas with 

potential for pseudokarst in Alaska and Hawaii.

The extent of outcrop of soluble rocks 

provides a good first-approximation of the 

distribution of karst and potential karst areas, 

particularly in parts of the United States with a 

humid climate. Criteria for further refinement of 

the karst map units includes 1) climate of 

regions based on annual precipitation and Level 

III ecoregion designation, 2) degree of burial 

and nature of the overlying sediments, and 3) 

degree of consolidation of the lithostratigraphic 

unit.

The geographic information system (GIS) 

data that accompany the OFR represent karst 

areas as spatially registered polygons containing 

multiple attributes that allow the user to perform 

selection and analysis on the data. Certain 

attributes also allow linking back to the original 

lithostratigraphic unit descriptions and ecoregion 

descriptions. 

DATA SOURCES 

Most of the spatial data compiled in this 

project originated as lithologic map units on 

geologic maps produced by various state 

geological surveys. Versions of the original 

source maps are available for purchase or 

download from the respective state geological 

surveys. Much of the digital map data was 

compiled from a series of integrated geologic 

map databases for the United States produced by 

the United States Geological Survey (USGS) 

Mineral Resources Program, National Surveys 

and Analysis (NSA) Project (available at 

http://mrdata.usgs.gov/geology/state/, accessed 

02/10/2014). Use of the USGS digital geologic 

data provided a consistent data structure within 

which a derivative database of areas with 

potential for karst could be constructed. Edits, 

deletions, and additions to this database were 

made based on 1) comparison to other published 

karst maps (principally Davies and others, 1984; 

Veni, 2000), 2) comments and contributions by 

other cave and karst researchers having local 

knowledge of particular areas, and assisted by 

the comprehensive compilation in Palmer and 

Palmer (2009), and 3) the personal knowledge of 

the authors. Further characterization of the karst 

areas was also accomplished via overlay 

analyses with other data including distribution of 

glacially-derived sediments (Soller and others, 

2012), permanently frozen ground (Brown and 

others, 2002), and Level III Ecoregions (U.S. 

Environmental Protection Agency, 2013).

MAPS

The maps shown in figures 1-5 were 

generated from GIS data derived from various 

original geologic map sets that ranged from 

1:24,000 to 1:500,000 scale. The graphic files 

provided in the OFR are designed for display at 

1:6,000,000 scale for the contiguous United 

States and Alaska, and 1:3,000,000 scale for 

Hawaii, Puerto Rico, and the U.S. Virgin 

Islands. They will print at these scales at 100 

percent resolution. The geographic data for all of 

these maps is in Albers projection using the 

North American Horizontal Datum of 1983.

Map of Karst in Soluble Rocks in the 

Contiguous United States

The distribution of karst and potential karst 

areas of soluble rocks in the contiguous United 

States is shown on figure 1. Because of space 

limitations, this is a greatly simplified version of 

the map that will be available in the OFR. 

Distribution of mature surface karst areas in 

the contiguous United States is primarily 

dependent on the presence of soluble rocks at or 

near the land surface and where the mean annual 

precipitation above approximately 30 inches 

(in.) (76 centimeters (cm)). In the humid parts of 

the United States, most karst features such as 

caves and sinkholes (dolines) occur in carbonate 
21

(limestone and dolomite) rocks; evaporite rocks 

are rarely found at or near the surface in these 

areas. Most of the eastern United States and the 

Pacific coastal zone are considered to be humid. 

Local areas of the Rocky Mountains and the 

Sierra Nevada are also classified as humid 

regions in this paper because of higher 

precipitation totals mostly due to orogenic 

effects. All areas of Alaska, Hawaii, Puerto Rico 

and the Virgin Islands are considered humid at 

the resolution of this study. In the semi-arid and 

arid regions of the western United States less 

soluble carbonate rocks are more resistant to 

erosion while the more soluble evaporite rocks 

that can exist at or near the surface in those 

environments, exhibit the most prominent karst 

features. Karst features created by hypogenic 

processes tend to be better preserved in arid and 

semi-arid areas as these features are less likely 

to be modified by epigenic processes in drier 

climates (Palmer, 2000; Auler and Smart, 2003).

Potential karst areas shown on figure 1 are 

grouped by areas of humid climate and areas of 

dry (semi-arid to arid) climates. In addition to 

carbonate and evaporite rocks, an area of quartz 

sandstone in Minnesota with documented 

solution karst is also shown (Shade, 2002). 

Other areas of anomalous solution, in what are 

normally considered insoluble rocks, may exist 

elsewhere in the United States and are yet to be 

documented.

For figures 1 and 3, the boundaries between 

dry and humid regions were delineated by 

comparing the average annual precipitation map 

for the years 1961-1990 with descriptions of 

North American Level III Ecoregions (Daley 

and Taylor, 2000; U.S. Environmental 

Protection Agency, 2013). These boundaries are 

coincident with the Level III Ecoregion 

boundaries and they approximate the 30 in. (76 

cm) per year annual average precipitation 

isohyet (Daley and Taylor, 2000). These 

boundaries, although shown as hard lines on 

figures 1 and 3, are actually diffuse and 

approximate. The principal boundary separating 

the eastern from the western areas of the United 

States also approximates the southern part of the 

annual average precipitation isohyet used by 

Epstein and Johnson (2003). There is some 

divergence of the humid and dry region

Figure 1. Simplified map of the distribution of karst and potential karst areas of soluble rocks, as well as arid, semi-arid, and 

humid climate regions. Thick white line indicates approximate maximum southern extent of Pleistocene ice.
22

boundaries from the principal 30-inch 

precipitation line at both north and south 

latitudes, as the effective regional humidity is 

also a function of the regional evapotranspiration rate, which itself is affected by 

temperature. 

Effects of late Cenozoic glaciations have a 

profound influence on the development and 

preservation of karst features in the northern and 

eastern parts of the contiguous United States. 

The line of demarcation approximating the 

greatest extent of the last glaciation is shown on 

figure 1, and the thickness of glacially-derived 

sediments overlying areas of soluble rocks is 

also integrated into the classification of map 

units in the OFR. The glacial data are derived 

from Soller and others (2012).

Karst Map Units

Space limitations preclude a detailed 

description of the 11 map units shown on the 

OFR map (not shown separately on figure 1 in 

this paper). Map units occurring in either a 

humid or arid climate regime include 

• Carbonate rocks at or near the land 

surface

• Carbonate rocks buried beneath 

<300 feet of insoluble sediments

• Carbonate rocks buried beneath <50 

feet of glacially-derived insoluble 

sediments

• Carbonate rocks buried beneath >50 

feet of glacially-derived insoluble 

sediments

• Calcareous sediments at or near the 

land surface

• Unconsolidated calcareous 

sediments buried beneath <300 feet 

of insoluble sediments

• Evaporite rocks exposed at or near 

the land surface

• Evaporite rocks buried beneath <50 

feet of glacially-derived insoluble 

sediments

• Evaporite rocks buried beneath >50 

feet of glacially-derived insoluble 

sediments

• Quartz sandstone buried beneath 

<50 feet of glacially-derived 

insoluble sediments

• Quartz sandstone buried beneath 

>50 feet of glacially-derived 

insoluble sediments

Map of Karst in Soluble Rocks in Alaska, 

Hawaii, Puerto Rico, and the U.S. Virgin 

Islands

The distribution of potentially karstic areas 

of soluble rocks in Alaska, Hawaii, Puerto Rico, 

and the U.S. Virgin Islands is shown on figure 2. 

All of these areas have relatively humid 

climates, so evaporite rocks rarely occur at or 

near the surface. Areas of carbonate rocks 

occurring at or near the surface are shown as a 

single map unit on figure 2.
23

Figure 2. Simplified map of karst and potential karst areas of soluble rocks in A, Alaska; B, Hawaii; and C, Puerto Rico and the 

U.S. Virgin Islands.

Map of Areas Extensively Underlain by 

Evaporite Rocks at Depths up to 7,000 

Feet Below the Surface

In addition to areas of outcropping and nearsurface evaporite rocks, figure 3 shows the 

extent of subsurface evaporite basins and the 

greater extent of commonly occurring evaporite 

rocks in the subsurface. The evaporite basins 

contain soluble rocks buried to depths of up to 

about 7,000 feet, but generally much less. 

Because of the physical properties and very high 

solubility of evaporite rocks, human activities 

such as fluid injection or leaking well casings 

can induce large solution voids. Collapses of 

these voids are known to propagate up to the 

surface from depths of more than 1,000 feet.

Map of Pseudokarst Areas in the 

Contiguous United States

Two different pseudokarst units are 

portrayed on the map of the contiguous United 

States (fig. 4). The first unit represents areas of 

poorly consolidated sedimentary rock units 

known, at least locally, to contain piping 

features (tubes, caves, and subsidence features). 

Most of the areas of piping potential are 

commonly characterized by fine-grained 

sedimentary rocks. These units are known to

contain pseudokarst features; however, areas 

with potential for such features are probably 

more widespread. The second unit represents 

areas of volcanic rock that may contain lava 

tubes (vulcanokarst) and/or layered volcanic 

rocks with integrated fast groundwater flow 

systems.
24

Figure 3. Simplified map of areas underlain by evaporite rocks at depths up to 7,000 feet. Arid regions receive less than about 30 

inches of annual precipitation. 

Map of Pseudokarst Areas in Alaska and 

Hawaii

Because of the relatively recent and ongoing 

volcanism in both Alaska and Hawaii, they 

contain widespread, relatively young (Miocene 

age or younger) lava flow deposits that contain 

lava tubes and other pseudokarst features (fig. 

5A, B). Lava tubes form most readily and 

extensively in low-viscosity lava flows, 

generally of basaltic composition. Lava tube 

caves are relatively short-lived geologic features 

as they are 1) either filled by succeeding 

eruptive lavas, or 2) as near surface features they 

are susceptible to erosion and collapse of the 

overlying rocks. Lava tubes are generally not 

found in rocks older than Miocene age, and this 

age was used as a cutoff for selecting volcanic 

flow units for this map. 

The cold climate of Alaska results in 

extensive regions of permafrost, or permanently 

frozen ground (Brown and others, 2002) (fig. 

5A). As the climate warms and these areas 

experience melting, landforms and hydrologic 

conditions that are analogous to karst terrains, 

such as sinkholes and sinking streams result. 

Because this phenomenon is related to melting 

of ice rather than solution of bedrock, these 

permafrost features are considered a category of 

pseudokarst (Halliday, 2007) and termed 

thermokarst (Sweeting, 1973, p. 308).

The OFR describes several classes of 

thermokarst terrain, on the basis of ice quality 

and overlying sediment thickness. 
25

Figure 4. Areas of known pseudokarst features in the contiguous United States.

SPATIAL STATISTICS

Simple spatial statistics were used to calculate 

the percentage area of the United States that is 

underlain by the areas of karst and pseudokarst 

defined in the OFR. These statistics are 

exclusive of Puerto Rico and the U.S. Virgin 

Islands. The results are shown on figure 6. In 

summary, about 25 percent of the United States 

is underlain by rocks or sediments, as previously 

described, with a potential for karst or 

pseudokarst features. About 18 percent of the 

United States is underlain by soluble rocks, of 

which 16 percent consists of carbonate rocks and 

the remaining 2 percent are evaporite rocks. The 

area of the nation underlain by basins where 

evaporite rocks may be encountered by deep 

drilling is not included in these statistics. These 

values underestimate the area of the United 

States underlain by karst aquifers, a major 

source of potable water for the nation. About 2 

percent of the United States is underlain by 

sedimentary rocks prone to pseudokarst features 

developed primarily by piping. Almost 4 percent 

of the country, and entirely restricted to Alaska, 

is underlain by sediments and permafrost prone 

to development of thermokarst. Lastly, about 1.5 

percent of the total area of the United States, 

which includes areas in the western part of the 

contiguous United States, Alaska, and Hawaii, 

are underlain by volcanic rocks with potential

for lava tubes.
26

Figure 5. Simplified map of areas that may contain lava tubes or thermokarst pseudokarst features, A, Alaska; and B, Hawaii.

Figure 6. Chart showing proportion of the area of the 50 United States underlain by potentially karstic and pseudokarstic rocks.
27

REFERENCES

Auler, A.S., and Smart, P.L., 2003, The influence of 

bedrock-derived acidity in the development of 

surface and underground karst: Evidence from the 

Precambrian carbonates of semi-arid northeastern 

Brazil: Earth Surface Processes and Landforms, 

v. 28, p. 157-168.

Brown, J., Ferrians, O.J., Jr., Heginbottom, J.A., and 

Melnikov, E.S., 2002, Circum-Arctic map of 

permafrost and ground-ice conditions, version 2: 

Boulder, Colorado USA, National Snow and Ice 

Data Center.

Daley, C., and Taylor, G., 2000, United States 

average annual precipitation, 1961-1990: Spatial 

Climate Analysis Service, Oregon State 

University, accessed 5/22/2013 at 

http://www.prism.oregonstate.edu/pub/prism/map

s/Precipitation/Total/U.S./us.gif

Davies, W.E., Simpson, J.H., Ohlmacher, G.C., Kirk, 

W.S., and Newton, E.G., 1984, Engineering 

aspects of karst: U.S. Geological Survey, 

National Atlas of the United States of America, 

scale 1:7,500,000.

Epstein, J.B., and Johnson, K.S., 2003, The need for 

a national evaporite-karst map, in Johnson, K.S., 

and Neal, J.T., eds., Evaporite karst and 

engineering/environmental problems in the 

United States: Oklahoma Geological Survey 

Circular 109, p. 21-30.

Halliday, W.R., 2007, Pseudokarst in the 21st 

century: Journal of Cave and Karst Studies, v. 

69, no. 1, p. 103–113.

Palmer, A.N., 2000, Hydrogeologic control of cave 

patterns, in Klimchouk, A.B., and others, eds., 

Speleogenesis—evolution of karst aquifers: 

National Speleological Society, Huntsville, 

Alabama, p. 77-90.

Palmer, A.N., and Palmer, M.V., eds., 2009, Caves 

and karst of the USA: National Speleological 

Society, Huntsville, Alabama, 446 p.

Shade, B.L., 2002, The genesis and hydrology of a 

sandstone karst in Pine County, Minnesota: 

Minneapolis, University of Minnesota, M.S. 

thesis, 131 p., 8 tables.

Soller, D.R., Packard, P.H., and Garrity, C.P., 2012, 

Database for U.S. Geological Survey Map I-1970 

-- Map showing the thickness and character of 

Quaternary sediments in the glaciated United 

States east of the Rocky Mountains: U.S. 

Geological Survey Data Series 656, available at 

http://pubs.usgs.gov/ds/656/.

Sweeting, M.M., 1973, Karst landforms: Columbia 

University Press, New York, 362 p.

U.S. Environmental Protection Agency, 2013, Level 

III ecoregions of the conterminous United States: 

Office of Research and Development (ORD) -

National Health and Environmental Effects 

Research Laboratory (NHEERL), accessed 

8/08/2013 at 

http://www.epa.gov/wed/pages/ecoregions/level_i

ii_iv.htm#Level%20III

U.S. Geological Survey, National Surveys and 

Analysis (NSA) Project, Geologic maps of U.S. 

states: Mineral Resources Program, U.S. 

Geological Survey, Reston, VA., accessed 

02/010/2014, at 

http://mrdata.usgs.gov/geology/state/

Veni, G., 2000, Revising the karst map of the United 

States: Journal of Cave and Karst Studies, v. 64, 

p. 45-50.

Weary, D.J., and Doctor, D.H., in press, Karst in the 

United States of America: A digital map 

compilation and database: U.S. Geological

Survey Open-File Report.

Williams, P.W., and Ford, D.C., 2006, Global 

distribution of carbonate rocks: Zeitschrift für 

Geomorphologie, Supplement, v. 147, p. 1-2.
28

Groundwater Availability of the Floridan Aquifer System

By Andrew M. O’Reilly1 and Eve L. Kuniansky2

1

U.S. Geological Survey, Florida Water Science Center, 12703 Research Parkway, Orlando, FL 32826

2

U.S. Geological Survey, Water Mission Area, 1770 Corporate Drive, Suite 500, Norcross, GA 30093

Abstract

The Floridan aquifer system is one of the most productive aquifers in the world and extends 

throughout 100,000 square miles of the southeastern United States in Florida and parts of Georgia, 

Alabama, South Carolina, and Mississippi. The Floridan aquifer system has been used since the late 

1800s and currently is the primary source of water for almost 10 million people (in 2000) in parts of 

Florida, Georgia, Alabama, and South Carolina. Water from the Floridan aquifer system is used for 

public, domestic, and industrial water supply, and almost 50 percent of withdrawals are used for 

irrigation. Where water in the Floridan aquifer system is not potable, shallower aquifers generally are 

used for water supply, most notably the Biscayne aquifer, which is the sole source of fresh groundwater in 

southeast Florida.

The U.S. Geological Survey (USGS) Groundwater Resources Program 

(http://water.usgs.gov/ogw/gwrp/) is assessing groundwater availability in areas of critical importance 

across the Nation. The objectives of the current study on the Floridan aquifer system are to quantify 

current groundwater resources, evaluate possible groundwater resource changes over time, and provide 

tools to better understand aquifer system responses to future human and environmental stresses. This 

regional study of the Floridan aquifer system will provide numerous benefits, including an updated 

hydrogeologic framework incorporating new data available since the USGS Regional Aquifer-System 

Analysis study completed in the 1980s, regional and subregional water budgets, and a modern, systemwide groundwater flow model that can be used to assess the effects of human and environmental stresses 

on the aquifer system. Further information on the approach and current products of the study are available 

at http://fl.water.usgs.gov/FASWAM/.

The Floridan aquifer system is a sequence of carbonate rocks more than 3,000 feet (ft) thick in 

southern Florida, thinning to less than 200 ft at the northern extent in southern Alabama, southeast 

Georgia, and southern South Carolina where it grades into clastic coastal plain sediments. A thick 

sequence of sand, silt, and clay confine the Floridan aquifer system over much of its extent; in these areas 

recharge to the aquifer system generally is less than 1 inch per year (in/yr). Where the Floridan aquifer 

system is thinly confined (less than 100 ft thick), karst terrain is common, leading to semiconfined to 

unconfined conditions and recharge rates generally ranging from 10 to 25 in/yr. The karst geologic 

characteristics contribute to specific aquifer vulnerabilities, including groundwater/surface-water linkage 

and saline-water encroachment in some areas.
29

Stresses on the Floridan aquifer system include land-use change and associated groundwater 

withdrawals, climate change, and sea-level rise; the effects of these stresses may be magnified by the 

vulnerabilities of the aquifer system in certain areas. For example, increased irrigation of crops in the 

Dougherty Plain (southwest Georgia, southeast Alabama, and adjacent areas of northern Florida) have led 

to streamflow and water-level decreases in the ecologically sensitive Apalachicola-Chattahoochee-Flint 

River Basin. Reduction or cessation of flow at some springs, sinkhole collapse and lake drainage, and 

reduced lake and wetland levels have occurred in central and northern Florida since the 1950s while total 

groundwater withdrawals from the Floridan aquifer system increased nearly fourfold. In central Florida,

developed land area has increased 160 percent, and cropland/pasture has decreased 40 percent from 1977 

to 2006. Such land-use changes may influence the partitioning of rainfall into evapotranspiration, runoff, 

and infiltration, thus affecting short-term and long-term groundwater levels and flows. Also, changing 

land-use practices have led to degraded water quality, particularly elevated nitrate concentrations in 

groundwater (wells) and springs. Saline water encroachment has occurred in localized coastal areas of 

South Carolina, Georgia, and northeast Florida, where groundwater movement is largely controlled by 

geologic features, such as paleochannels, fractures, solution-enlarged joints, or paleocollapse structures.

Climate change and sea-level rise may affect the future quantity of available groundwater in the 

Floridan aquifer system. Water budget analysis indicates the system is largely meteorologically driven. 

Water demands are likewise substantially influenced by weather owing to the prevalence of groundwater 

withdrawals for irrigation. Predevelopment conditions consisted of 53 in/yr of rainfall, 37 in/yr of 

evapotranspiration, 16 in/yr of runoff, and less than 0.5 in/yr of offshore discharge. In 2000, groundwater 

withdrawals totaled nearly 4 billion gallons or 0.9 in/yr, representing 2 and 6 percent of predevelopment 

evapotranspiration and runoff, respectively. Therefore, the Floridan aquifer system likely will be sensitive 

to future weather extremes and climate change, while sea-level rise may affect coastward hydraulic 

gradients. Even though total groundwater withdrawals are a relatively small component of the water 

budget, these withdrawals may be sufficient to reduce the frequency at which the system is “filled and 

reset,” thus causing long-term declines in water levels and flows in certain areas.
30

Assessing Potential Impacts from a Proposed Phosphate Mine on 

Ashley Spring, a Unique Karst Public Water Supply in the Uinta 

Mountains, Uintah County, Utah

By Lawrence E. Spangler

U.S. Geological Survey, 2329 Orton Circle, Salt Lake City, Utah 84119

Abstract

Ashley Spring is one of the largest springs in Utah, with a reported discharge that ranges from about 

15 cubic feet per second (ft3/s) at low flow (base flow) to at least 80 ft3/s during the snowmelt runoff 

period in May and June. The spring rises from the Weber Sandstone alongside the channel of Ashley 

Creek in the bottom of Ashley Gorge near its outlet along the southeast flank of the Uinta Mountains. 

Water from the spring is a public supply for the nearby city of Vernal and residents in several rural 

communities in Ashley Valley, as well as for irrigation. In 2010, an estimated 3,800 acre-feet or about 3.4 

million gallons per day were withdrawn from the spring for municipal use. 

Previous studies of the hydrology of Ashley Spring and adjacent springs have shown a complex 

groundwater flow system along the southeast flank of the Uinta Mountains. Dye-tracer tests carried out 

primarily in the late 1960s and late 1970s indicate that most of the flow discharging from Ashley Spring 

originates from the Dry Fork watershed more than 10 miles to the west and also from a losing reach in 

Ashley Creek about 7 miles upstream of the spring. Water losses in the Dry Fork and Ashley Creek 

drainages occur through glacial and alluvial deposits that overlie the Madison Limestone. Fractures in the 

Weber Sandstone, which overlies the Madison Limestone, allow upward movement of water back to the 

surface at Ashley and other springs. 

Proposed mining of the Park City Formation near Ashley Spring has raised concerns among county 

leaders and local citizens that mining may impact the quality and discharge of the spring water. Possible 

impacts of the mining operation on the hydrologic system include effects on the water quality of the 

spring by downward movement of water from the Park City Formation through the Weber Sandstone with 

constituents related to mining activities, such as phosphate and selected trace elements; possible effects 

on the water quality of the Madison Limestone aquifer, from which the spring discharges; and the effects 

of blasting on the groundwater flow system. This study expands upon previous studies and is conducting 

additional investigations to improve our understanding of the recharge (contributing) area for Ashley 

Spring, and the relation between groundwater movement in the Madison Limestone aquifer and the 

overlying Weber Sandstone, to evaluate the potential impacts of the proposed phosphate mine on the 

groundwater system.

INTRODUCTION

Proposed mining of the Park City 

(Phosphoria) Formation near Ashley Spring, 

about 12 miles north of Vernal, Utah, has raised 

concerns among county leaders and local 

citizens of the effects that the mining may have 

on the quality and discharge of the spring water. 

Groundwater travel times of only a few days 

have been documented through the Madison 

Limestone aquifer that supplies water to the 

spring (Maxwell and others, 1971), but 

relatively little data are available with respect to 

groundwater movement in the overlying units in 

this area, particularly the Weber Sandstone. 

Although previous studies have documented the 

general boundaries of the Ashley Spring 

groundwater system to the west and northwest, 

additional studies are needed to further identify 

sources of water to the spring and better define 

groundwater basin boundaries between Ashley 

and adjacent groundwater basins, particularly 

the Brush Creek Spring basin to the northeast. 

An understanding of the directions and rates of 

groundwater flow in this area would allow a 

better assessment of the potential for the 

proposed mining operation to affect the 

groundwater system supplying Ashley Spring. 

Further, Uintah County is in the process of 
31

updating the groundwater source-protection area 

for Ashley Spring, and this study will provide 

additional information to help fulfill the 

recommendations outlined in the sourceprotection management plan for the spring. 

To address these concerns, the U.S. 

Geological Survey in cooperation with Uintah 

County, is conducting a 3-year study that began 

in the spring of 2013, to evaluate the 

vulnerability of the Ashley Spring groundwater 

flow system and the potential effects of the 

proposed phosphate mining operation on the 

spring. The objectives of this study are to 1) 

refine the contributing area of the groundwater 

flow system for Ashley Spring and to understand 

its relation/connection to adjacent basins and 

downgradient areas along the southeast flank of 

the Uinta Mountains, 2) evaluate groundwater 

movement in the Madison Limestone aquifer 

and overlying geologic units in the vicinity of 

the spring, particularly the Weber Sandstone, 

and the potential for downward movement of 

water from the Park City Formation through the 

Weber Sandstone, and 3) assess the potential for 

blasting and other mining activities to affect the 

groundwater system that supplies water to 

Ashley Spring. This paper provides an overview 

of the hydrogeology along the southeast flank of 

the Uinta Mountains in the vicinity of Ashley 

Spring and discusses the multi-phased approach 

that will be used to fulfill the objectives outlined 

above. 

GEOLOGY AND KARST DEVELOPMENT

The Uinta Mountains (Uintas) are part of the 

Middle Rocky Mountains physiographic 

province and are an east-west trending anticlinal 

structure. The range was initiated in the early 

Tertiary Period (Paleocene) and intermittently 

uplifted into the Miocene (Untermann and 

Untermann, 1969). Rocks making up the Uintas 

are Precambrian to Tertiary in age, with a 

distinct absence of Ordovician- and Silurian-age 

rocks; outcrops of Devonian-age rocks are found 

only on the western edge of the mountain range. 

Unlike most other mountain ranges that have 

cores of igneous and metamorphic rocks, the 

core of the Uintas is composed of reddish 

conglomeratic, quartzitic sandstones and 

interbedded shales of the billion-year old Uinta 

Mountain Group (Stokes, 1988). Late Paleozoicand Mesozoic-age rocks unconformably overlie 

the Uinta Mountain Group along the flanks of 

the uplift and generally dip away from the core 

in all directions. Rocks along the southeast flank 

of the uplift, including the Ashley Creek-Brush 

Creek area, generally dip about 10 to 20 degrees 

to the south-southeast, except in areas of faults 

and folds, where they can be considerably 

steeper (Kinney, 1955). 

Superimposed on the larger Uinta Mountain 

Anticline are regional faults and fractures that 

generally trend from west to east, and from 

northwest to southeast (Maxwell and others, 

1971). The South Flank fault between Dry Fork 

and Ashley Creek trends generally north 70 

degrees east and forms a boundary between the 

quartzitic rocks of the higher Uintas and 

overlying Paleozoic rocks (Sprinkel, 2006). 

Water flowing off the quartzitic rocks and onto 

carbonate rocks typically loses to the subsurface 

within a short distance of this boundary (fig. 1). 

The Deep Creek fault zone between Mosby Sink 

and Dry Fork (not shown on figure 1) consists of 

a series of parallel faults that trend generally 

northwest at about 60 degrees (Maxwell and 

others, 1971). North-northwest trending 

fractures are also present throughout the area, 

often associated with localized anticlinal 

structures, such as those present in both the 

Ashley Creek and Big Brush Creek drainages. 

The trend of many of the major surface 

drainages in the southeastern part of the Uintas, 

as well as the location of large springs such as 

Ashley and Brush Creek, have been influenced 

by regional fault and fracture systems (Maxwell 

and others, 1971). 

The principal carbonate and cave-forming 

units in the Uinta Mountains are Mississippian 

in age and include the Madison and Deseret 

Limestones, and the Humbug Formation 

(Sprinkel, 2006). In the study area, the Madison 

Limestone is the predominant unit. These 

formations typically consist of light to dark gray,
32

Figure 1. Location of major springs along the southeast flank of the Uinta Mountains near Vernal, Utah, results of dye tracing, 

and location of proposed phosphate mine.

thin- to thick-bedded, cherty (siliceous), and 

locally brecciated, dolomitic limestones. 

Average thickness of the Mississippian-age 

limestones is about 900 to 1,200 feet. The 

overlying Pennsylvanian-age Weber Sandstone 

is a very prominent rock unit in the eastern 

Uintas, forming many of the canyon walls in the 

major drainages, such as in Ashley Gorge and 

Big Brush Gorge (fig. 2). The formation ranges 

from about 1,000 to 1,275 feet in thickness in 

the study area and consists of predominantly 

massive, tan to white cross-bedded sandstone 

with minor amounts of sandy limestone (Haddox 

and others, 2010). Many of the large springs in 

the region, including Ashley and Brush Creek, 

discharge upward through fractures in the Weber 

Sandstone (fig. 3). Overlying the Weber 

Sandstone in the vicinity of Ashley Spring is the 

Permian-age Park City Formation. The 

formation is quite variable in lithology and 

consists of light gray to brown sandy dolostone 

interbedded with reddish-orange siltstone and 

dark gray phosphatic shale (basal 20 feet) 

(Haddox and others, 2010). Thickness of the 

Park City Formation ranges from 50 to 145 feet. 

Karst features are sporadically developed in 

the eastern Uintas, largely because of the limited 

exposure of carbonate rocks. Losing or sinking 

streams can be found in many drainages, 

particularly where surface streams originating on 

the quartzitic core of the mountains at higher 

elevations cross the band of limestones that 

flank the core, a transition zone roughly defined
33

Figure 2. Outcrop of the Weber Sandstone in Big Brush 

Gorge. Fractures in the sandstone allow water to discharge 

at the surface at Brush Creek Spring, located in the bottom 

of the canyon at lower right.

by the South Flank fault (fig. 1). Both Big Brush 

Creek and Little Brush Creek Caves were 

formed by entrenchment of surface streams 

flowing off the insoluble core of the Uintas onto 

the soluble limestones, which has resulted in the 

development of blind valleys at the entrances of 

both caves (fig. 1). Streamsinks or “sinks” also 

have formed in the drainages of Dry Fork and its 

tributaries, and in the upper reaches of Ashley 

Creek (fig. 4), where they are capable of 

swallowing the entire streamflow except during 

periods of snowmelt runoff and possibly during 

locally intense rainfall events. In the Dry Fork 

drainage, glacial moraines appear to have 

impounded or otherwise influenced the location 

and development of the streamsinks (Godfrey, 

1985). The largest springs in the southeastern 

part of the Uintas also discharge within or along 

the principal drainages. On the basis of average 

discharge, Ashley and Brush Creek Springs are 

considered second magnitude springs (10 to 100 

cubic feet per second [ft3

/s]) (Meinzer, 1927).

HYDROLOGY

Groundwater movement along the southeast 

flank of the Uintas is generally to the south and 

southeast, following the geologic structure. 

Direction of movement is influenced in large 

part by structural dip of the rocks, regional 

fractures and faults, and localized breccia zones. 

Water generally moves down dip or along faults 

in the Mississippian-age limestones to lower 

Figure 3. Near-vertical northwest-trending fractures in the 

Weber Sandstone. Fractures such as these likely serve as 

pathways for upward movement of water from the Madison 

Limestone to the surface at Ashley Spring.

Figure 4. Ashley Creek Sink. All flow in streambed, 

estimated to be at least 10 ft3

/s, abruptly sinks through 

boulders into the underlying Madison Limestone, which 

then conducts water along solution-enlarged fractures and 

(or) down dip along bedding planes to Ashley Spring, 7 

miles to the south. 

elevations where it discharges at large springs 

along the major drainages. Because the aquifer 

is generally confined (under artesian pressure) 

near the springs, groundwater movement is 

typically upward from the Madison Limestone 

aquifer along fractures and faults in the 

overlying Pennsylvanian-age rocks, particularly 

the Weber Sandstone. White (1979) calculated 

the depth to the top of the Madison Limestone in 

the vicinity of Ashley and Brush Creek Springs 

to be as much as 2,000 feet by extrapolating the 

structural dip of the rocks. On the basis of dyetracer tests carried out in the mid-1940s and 

mid-1950s, and in the late 1960s and 1970s
34

(table 1), at least five major groundwater basins 

have been delineated along the southeast flank 

of the Uintas. A brief summary of the hydrology 

of four of these basins is as follows.

Ashley Spring

Ashley Spring rises from boulder alluvium 

on the east side of Ashley Creek in the bottom of 

Ashley Gorge near its outlet. The main spring is 

covered and partly diverted to two water 

treatment plants for drinking-water and other 

public-supply uses in the city of Vernal as well 

as several smaller communities in the region. 

Water not diverted for public supply is 

discharged from the springhouse and rejoins 

Ashley Creek downstream (fig. 5). Several other 

springs discharge directly from bedrock outlets 

on the west side of the channel, and 

subsequently flow into Ashley Creek (fig. 6). 

Water discharging from the west side of the 

channel is not used for public supply but is 

withdrawn from the channel farther downstream 

for use in irrigation. Total discharge of all 

springflow is reported to range from about 15 

cubic feet per second (ft3

/s) at base flow to about 

80 ft3

/s following snowmelt runoff (Mundorff, 

1971). Historic dye tracing (Maxwell and others, 

1971) indicates that a large part of the flow 

discharging from Ashley Spring originates from 

the Dry Fork Canyon watershed, which also 

supplies water to Dry Fork Springs (see next 

section) (table 1). During periods when Dry 

Fork Springs do not flow, all flow from the sinks 

in the Main Fork of Dry Fork is assumed to 

discharge at Ashley Spring. Water losing in Dry 

Fork and its tributaries appears to move through 

glacial and alluvial deposits into the underlying 

Madison Limestone aquifer to Ashley Spring 

where fractures in the overlying Weber 

Sandstone allow upward movement of water 

back to the surface. These fractures are probably 

related to an anticlinal structure in this area, 

which has likely influenced the discharge point 

of the spring. Part of the flow path to Ashley 

Spring from Dry Fork may be along segments of 

the Deep Creek fault zone. Results of dye 

tracing have also shown that an additional 

source of water to Ashley Spring originates from 

a losing reach in Ashley Creek about 7 miles 

upstream of the spring (Godfrey, 1985).

Figure 5. Overflow from Ashley Spring. Water not 

diverted for public supply is discharged from springhouse 

back into Ashley Creek.

Figure 6. Ashley Spring discharges from the west and east 

sides of Ashley Creek (foreground). Flow from the west 

side (shown here) discharges from at least four major and 

several smaller outlets.

Dry Fork Springs

Dry Fork Springs rise in the bed of Dry Fork 

about 2 miles upstream of the community of Dry 

Fork (fig. 1). The springs discharge from the 

Weber Sandstone upward through alluvium at 

several locations in the channel. Discharge of 

the springs normally is zero, but during 

snowmelt runoff is estimated to be as much as 

80 ft3

/s (Mundorff, 1971). Estimates of flow 

from current meter measurements indicate that 

springflow generally begins once surface flow in 

the three principal tributaries of Dry Fork 

upstream of the springs exceeds about 40 ft3

/s 

(Maxwell and others, 1971). Because water from 
35

Table 1. Results of dye-tracer tests for selected karst springs in the southeastern Uinta Mountains.

[BOR, Bureau of Reclamation; SCS, Soil Conservation Service; USGS, U.S. Geological Survey; USFS, U.S. Forest Service]

Date of 

test

Agency 

conducting test

Input site Altitude

(feet) Output(s) site(s) Altitude 

(feet)

Relief

(feet)

Linear 

distance

(miles)

Travel 

time1

(days)

6/1968 BOR, SCS Little Brush 

Creek at cave

8,100 Brush Creek at 

phosphate mine

6,120 1,980 5.6 2.2

8/1967 BOR, SCS Big Brush Creek 

above cave

8,180 Brush Creek at

phosphate mine

6,120 2,060 5.9 2.6

2/1956 USGS Mosby Sink 9,160 Deep Creek Spring 7,160 2,000 6.4 14

mid1940s?BOR Dry Fork Sinks 8,080 Dry Fork Springs 6,860 1,220 6.7 No

data

8/1967 BOR, SCS Dry Fork Sinks2 8,080 Ashley Spring

(Merkeley Park)

6,260 1,820 10.5 2.8

10/1967 BOR, SCS Main Dry Fork3

(Blanchett Park)

8,080 Ashley Spring

(Merkeley Park)

6,260 1,820 10.5 3.3

8,080 Deep Creek Spring 7,160 920 46 20

5/1979 USFS Dry Fork Sinks 8,080 Brush Creek Spring5 6,120 1,960 15.8 14

8/1978 USFS Ashley Creek 7,800 Ashley Spring 6,260 1,540 7.0 9

(Red Pine) Brush Creek Spring 6,120 1,680 8.1 9

1

Groundwater travel time based on first appearance of dye, whether detected in water samples or on activated charcoal.

2

Dye was injected into Main Fork, North Fork, and Brownie Canyon simultaneously. Calculations based on Main Fork Sinks. 3

Dye was injected upstream of Main Fork Sinks and initially traveled on surface for 8.3 miles (17 hours) before losing at sinks. 4

Distance uncertain; losing reach between Mosby Sink and Dry (Main) Fork Sinks. 5

Tracer test conducted during high-flow conditions.

Dry Fork Sinks and its tributaries also 

discharges at Ashley Spring, Dry Fork Springs 

may represent a high-level or overflow point 

within the Ashley Spring groundwater flow 

system. Detailed studies by Maxwell and others 

(1971) indicate that water losing from Dry Fork 

and its tributaries, between 5 and 7 miles 

upstream of the springs, flows through conduits 

in the underlying Madison Limestone aquifer 

and thence upward along fractures in the 

overlying rocks to discharge at the surface, 

rather than through the fluvioglacial channel 

deposits (sub-channel flow) to the springs. The 

flow system feeding Dry Fork Springs is likely 

developed along segments of the Deep Creek 

fault zone (Maxwell and others, 1971, fig. 2). 

Deep Creek Spring

Deep Creek Spring rises along a hillside 

from the base of the Triassic-age Moenkopi 

Formation on the upthrown side of a northwesttrending fault (Maxwell and others, 1971). 

Discharge of the spring is reported to range from 

3 to 15 ft3

/s, with higher flows during snowmelt 

runoff (Mundorff, 1971). Results of dye tracing 

indicate that water diverted into Mosby Sink, 

located along a tributary to the Main Fork of the 

Dry Fork drainage, resurges at Deep Creek 

Spring 6 miles southeast of the sink (fig. 1). 

Actual travel time of groundwater from Mosby 

Sink to Deep Creek Spring was about 14 days 

(table 1). Because water discharging from the 

spring is confined, however, an increase in 

springflow was observed in only 3 hours, in 

response to a pressure wave generated by the 

diverted water. Some of the base flow of Deep 

Creek Spring also appears to originate directly 

from the Main Fork of Dry Fork (fig.1). 

Groundwater flow from Mosby Sink and Dry 

Fork to Deep Creek Spring is probably along 

northwest-trending faults that are associated 

with the Deep Creek fault zone. These faults 

also serve as pathways for upward movement of 

water from the underlying Madison aquifer.
36

Brush Creek Spring

Brush Creek Spring rises in the bottom of 

Big Brush Gorge near its outlet. The spring 

discharges from the lower part of the Weber 

Sandstone where localized fracturing along the 

axis of an anticline has permitted upward 

movement of water from the underlying 

Madison Limestone aquifer back to the surface. 

Groundwater movement to Brush Creek Spring 

is likely down the structural dip of the Madison 

Limestone to the spring. Estimated discharge of 

Brush Creek Spring ranges from 3 to about 200 

ft3

/s (Mundorff, 1971), making this one of the 

largest springs in Utah. Results of dye tracing 

during the summers of 1967 (Big Brush Creek) 

and 1968 (Little Brush Creek) indicate that 

much of the water discharging from the spring 

originates from both of these creeks via Big and 

Little Brush Creek Caves (fig. 1, table 1). These 

dye tests confirmed previous indications of this 

relation when reservoir releases upstream of 

Little Brush Creek Cave resulted in substantial 

increases in the discharge of Brush Creek Spring 

(Maxwell and others, 1971). Dye travel time 

from Big Brush Creek at the Red Cloud Loop 

Road above the entrance to Big Brush Creek 

Cave, to Highway 191 where it crosses over 

Brush Creek, about 3.5 miles downstream from 

the spring, was about 63 hours. Dye travel time 

from Little Brush Creek Cave to Brush Creek at 

Highway 191 was about 52 hours. Although the 

majority of flow from Brush Creek Spring 

appears to originate from the Brush Creek 

drainage basin, additional dye tracing also has 

indicated apparent hydrologic connections 

between Dry Fork Sinks (at high flow) and 

Brush Creek Spring, and Ashley Creek Sink and 

Brush Creek Spring (Godfrey, 1985) (fig. 1).

DISCUSSION

During the 3-year study beginning in April 

2013, a multi-phased approach will be used to 

further our understanding of the hydrology of 

Ashley Spring and the hydrology of overlying 

geologic units in the vicinity of the spring. The 

approach includes dye tracing, water sample 

collection and analysis, discharge measurements, water-level measurements, and analysis 

of seismic data.

Fluorescent dye tracing will be used to 

establish hydrologic connections between 

focused points of recharge (surface-water inputs) 

and Ashley Spring, particularly in areas where 

data are sparse with regard to groundwater 

movement, and also will be used to determine 

better estimates of groundwater travel time. If 

possible, tracer tests also will be used to refine 

the boundary between groundwater movement to 

Ashley and Brush Creek Springs. A dye-tracer 

study was carried out in September 2013 to 

verify a previous tracer test that was done 

indicating a hydrologic connection between 

Ashley Creek Sink and Ashley and Brush Creek 

Springs (fig. 1, table 1). Results of this test are 

currently being evaluated. 

Ten water samples were collected from 

selected springs and wells in bedrock aquifers in 

the study area in 2013 and analyzed for major 

ions, nutrients, and a suite of trace elements that 

are often associated with phosphate mining in 

other areas. These include aluminum, barium, 

strontium, arsenic, selenium, uranium, cadmium, 

chromium, lead, copper, nickel, and zinc. Water 

samples also will be collected from Ashley 

Spring during base flow, moderate flow, and 

spring (peak) runoff, and analyzed for major 

ions and trace elements to establish baseline 

conditions for the natural system prior to 

potential mining. Nitrate, orthophosphate, and 

phosphorus samples will be analyzed to 

determine background (native) concentrations 

for comparison with natural concentrations of 

these constituents in the Park City Formation, 

the lower part from which phosphate ore would 

be mined. Historic chemical data for Ashley 

Spring will be examined to evaluate trends or 

variations in water quality over time. In addition, 

water-quality data will be compiled and water 

samples collected from other springs and wells 

in the Weber Sandstone, Park City Formation, 

and other potential water-bearing units in the 

vicinity of Ashley Spring and analyzed for the 

same suite of constituents to characterize 

groundwater in these formations. The chemistry 

of groundwater from these units will then be 

compared to the water chemistry of the Madison 

Limestone aquifer. Samples for selected isotope 

analyses may be collected to further assist in 

determining source areas for water discharging 
37

from Ashley Spring (deuterium/oxygen-18) and 

for possible dating of the groundwater in the 

Madison Limestone, Weber Sandstone, and 

other aquifers in the study area (tritium/helium, 

sulfur-35, and chlorofluorocarbons).

Preliminary data indicate that dissolvedsolids concentrations in water from Ashley and 

Brush Creek Springs (Madison Limestone 

aquifer) during base-flow conditions is low (less 

than 150 milligrams per liter [mg/L]) compared 

to water from the overlying Weber Sandstone 

and other bedrock units in the area, which tends 

to be noticeably higher (greater than 200 mg/L). 

The source waters for these springs, which 

originate on the quartzitic core of the mountain 

range, can be very low in dissolved solids (less 

than 50 mg/L). Concentrations of trace elements 

and nutrients from these springs were also very 

low during base-flow conditions and below state 

drinking-water standards. In addition, 

continuous (1- and 2-hour intervals) 

measurements of temperature and specific 

conductance have been made at Ashley and 

Brush Creek Springs since April and November

2013, respectively, to document changes in these 

parameters with changes in discharge and to 

further assess groundwater travel times to the 

springs in response to precipitation events. 

Between May 2013 and March 2014, specific 

conductance and temperature of water from 

Ashley Spring was quite variable, and ranged 

from 94 microSiemens per centimeter (μS/cm) 

at 25 o

C to 168 μS/cm, while temperature ranged 

from about 6.8 to 8.7 o

C.

Discharge measurements of Ashley Spring 

will be used to evaluate response of the 

groundwater system to surface events such as 

snowmelt runoff and rainfall and to help with 

determining the potential size of the drainage 

basin needed to supply the discharge of the 

spring. Because of the numerous outlets and 

diversions for Ashley Spring, an accurate 

discharge measurement of the spring had not 

been determined previously. Therefore, a 

streamflow gage was installed for the study on 

Ashley Creek upstream of Ashley Spring and its 

outlets on the west side of the channel. 

Downstream of the outflow from Ashley Spring, 

a long-term streamflow gage records discharge 

that can be used in conjunction with the 

upstream gage to determine only the flow from 

Ashley Spring, in addition to withdrawals for 

public supply. A continuous record of discharge 

from the spring over the study period will also 

establish a baseline to which future changes in 

flow from natural and human-induced activities 

can be compared. 

Water levels in all bedrock aquifers in the 

vicinity of Ashley Spring will be measured 

during the spring and fall to assess the 

magnitude of water-level changes and for 

evaluating hydraulic-head relations between the 

aquifers. In particular, water-level data will be 

collected from wells completed in the Weber 

Sandstone aquifer and compared to water levels 

in the underlying Madison Limestone aquifer to 

determine hydraulic-head relations (differences 

in water levels) between the units. These data 

would help to assess the potential for vertical 

movement of water between the formations, 

especially in the confined portions of the 

aquifers. An evaluation of the potential for 

downward movement of water from the Park 

City Formation into and through the Weber 

Sandstone, and thus, the ability for selected 

constituents from phosphate mining to move 

downward into the discharge zone of the spring 

within the Weber Sandstone or the underlying 

Madison Limestone also will be done. As part of 

this assessment, data on fracture trends and 

fracture density will be compiled for the Weber 

Sandstone to evaluate potential pathways along 

which downward moving groundwater could 

occur. 

Finally, water-quality and hydrologic data 

from the adjacent Brush Creek Spring basin will 

be compiled for comparison to that from the 

Ashley Spring basin. The geologic and 

hydrologic setting of Brush Creek Spring is very 

similar to that of Ashley Spring, and the location 

of Brush Creek Spring in proximity to the 

Simplot phosphate mining operation about 6 

miles northeast of Ashley Spring (fig. 1), could 

provide a useful comparison (analog) with 

regard to the hydrologic relation between the 

Madison Limestone and the overlying Weber 

Sandstone in this area. This relation could also 

allow a better assessment of the potential for 
38

downward movement of water from the Park 

City Formation through the Weber Sandstone 

and thus, the potential for the proposed mine to 

affect water quality in the area near Ashley 

Spring. In addition, to evaluate the potential 

effects of blasting on the hydrologic system 

supplying Ashley Spring, records from 

seismograph stations located near the Simplot 

phosphate mine along with blasting records from 

the mine, will be compared to discharge records 

and continuous water-quality data for Brush 

Creek Spring. Identifying changes or 

fluctuations in these parameters with minerelated activities could then be used to evaluate 

the potential for mining-induced disturbances at 

the proposed mine site to affect the hydrologic 

system within the Madison Limestone or the 

fracture network within the Weber Sandstone at 

Ashley Spring.

REFERENCES

Godfrey, A.E., 1985, Karst hydrology of the south 

slope of the Uinta Mountains, Utah, in Picard, 

M.D., ed., Geology and energy resources, Uinta 

Basin of Utah: Utah Geological Association 

Publication 12, p. 277–293.

Haddox, D.A., Kowallis, B.J., and Sprinkel, D.A., 

2010, Geologic map of the Steinaker Reservoir 

quadrangle, Uintah County, Utah: Utah 

Geological Survey Miscellaneous Publication 10-

3, 2 pl.

Kinney, D.M., 1955, Geology of the Uinta River–

Brush Creek area, Duchesne and Uintah Counties, 

Utah: U.S. Geological Survey Bulletin 1007, 185 

p., 6 pl.

Maxwell, J.D., Bridges, B.L., Barker, D.A., and 

Moore, L.G., 1971, Hydrogeology of the eastern 

portion of the south slopes of the Uinta 

Mountains, Utah: Utah Department of Natural 

Resources Information Bulletin 21, 54 p.

Meinzer, O.E., 1927, Large springs in the United 

States: U.S. Geological Survey Water-Supply 

Paper 557, 94 p.

Mundorff, J.C., 1971, Nonthermal springs of Utah: 

Utah Geological and Mineralogical Survey, 

Water-Resources Bulletin 16, 70 p.

Sprinkel, D.A., 2006, Interim geologic map of the 

Dutch John 30’ x 60’ quadrangle, Daggett and 

Uintah Counties, Utah, Moffat County, Colorado, 

and Sweetwater County, Wyoming: Utah 

Geological Survey Open-File Report 491 DM, 3 

pl. 

Stokes, W.L., 1988, Geology of Utah: Utah Museum 

of Natural History Occasional Paper No. 6, 307 p.

White, W.B., 1979, Karst landforms in the Wasatch 

and Uinta Mountains, Utah, in Alpine karst 

symposium: National Speleological Society 

Bulletin, v. 41, no. 3, p. 80-88.

Untermann, G.E., and Untermann, B.R., 1969, 

Geology of the Uinta Mountain area, Utah–

Colorado, in Lindsay, J.B., ed., Geologic 

guidebook of the Uinta Mountains–Utah’s 

maverick range: Intermountain Association of 

Geologists and Utah Geological Society 16th

Annual Field Conference, p. 79-86.
39

TRACERS

Groundwater Tracing in Arid Karst Aquifers: Concepts and 

Considerations

By George Veni

National Cave and Karst Research Institute, 400-1 Cascades Avenue, Carlsbad, New Mexico 88220

Abstract

Few groundwater tracing studies have been conducted in karst aquifers located in arid landscapes. 

This paper conceptually evaluates the effects of arid conditions on the injection and detection of tracers, 

and the interpretation of the results. Tracer injection is primarily challenged by the absence of a constant 

source of flowing water to flush the tracer into and through the aquifer. Artificial recharge is often 

needed, with the amounts best determined by examining typical conduit volume, flow, and morphological 

conditions of caves in the area. The tracer mass should be calculated based not only on the volume of 

discharge from the target spring or well, but also on the volume of discharge in the conduit into which the 

tracer is injected. Tracer detection is challenged mostly by the paucity of monitoring sites and factors that 

may compromise tracer detection, such as alluviation of springs and adsorption/filtration of the tracer, and 

the potentially very slow flow velocities in these aquifers. Interpretation of the results is challenged by 

distinguishing hydrologic behavior resulting from low hydraulic gradients/velocities, and ponded and 

perched conditions, from inherently different conditions in arid karst such as poorly developed vadose 

permeability and sedimentation within the conduit system.

INTRODUCTION

By the time the Karst Interest Group holds 

its 2014 workshop at the Headquarters of the 

National Cave and Karst Research Institute 

(NCKRI), construction should be underway or 

soon-to-begin on NCKRI’s lab. Adjoining, but 

distinctly separate from the lab, will be a room 

specially designed to store dyes for groundwater 

tracing. While those of us at NCKRI look 

forward to starting a tracer program to study a 

variety of karst aquifers, our location in 

Carlsbad, New Mexico, also opens another 

research opportunity.

Few tracer studies have been conducted in 

arid karst regions. This raises some important 

questions that this paper conceptually discusses 

as three major categories: consideration for 

tracer injection and detection, and the 

implications on hydrological interpretation of 

the results. This paper does not distinguish 

between fluorescent dyes, which are most 

commonly used in karst groundwater tracing, 

and other tracers, although dye traces are often 

used as examples. NCKRI plans on conducting 

tracer studies in all climatic settings, but its 

home base in an arid karst landscape will 

provide ample opportunity to test the methods 

and concepts presented below.

CONSIDERATIONS FOR TRACER 

INJECTION 

Tracer studies were developed in humid 

climates where many streams sink perennially 

into karst landscapes. Pouring some substance 

into the water as it disappeared underground was 

an intuitive and easy action to find where the 

flow reappeared, especially when many springs 

were also present.

In arid karst, springs are few and perennial 

sinking streams are rare to non-existent. The 

absence of a constant source of water that is 

assured to carry the tracer to the water table and 

through the aquifer significantly complicates 

tracing efforts. Two main factors must be 

considered when injecting tracers in such 

regions: tracer mass and water volume.

Worthington and Smart (2003) examined the 

results of 185 dye-tracing tests in carbonate 

aquifers. They derived the following empirical 

regression equations for calculating the mass of 

dye needed and the peak recovery 

concentrations:
40

m = 0.73 (tQc)0.97 (eq. 1)

m = 19 (LQc)0.95 (eq. 2)

where:

m is the mass of dye injected, in grams, 

t is the time elapsed between injection and 

peak recovery in seconds, 

Q is the output discharge, in cubic meters 

per second (m3

/s), 

c is the peak recovery dye concentration for 

optimum detection, in grams per cubic meter 

(g/m3

), and 

L is the distance in meters between injection 

and recovery points. 

Equation 1 is used where t is known, such as 

from previous tracer tests, and Equation 2 is 

used when a particular flow route is traced for 

the first time.

Numerous subsequent studies have shown 

these equations work effectively, but they were 

not derived from data primarily collected in arid 

karst aquifers and have been rarely tested in 

such conditions. Inherent in the equations is the 

fact that groundwater conduits in karst aquifers 

are parts of tributary systems and tracers will be 

diluted by inflows from other conduits. 

However, in arid karst aquifers, Q needs to be 

considered as a percentage of the volume of 

flow in the conduit where the tracer was injected 

(Qin). If Q = Qin, or is similar in volume, there is 

little or no dilution of the tracer. This may result 

in the discoloration of water supplies and higher 

costs in materials for no additional benefit. 

While this problem is conceptually easy to state, 

in many cases Qin will not be observable and 

may need to be estimated based on tracing 

experience in the aquifer and from other data, 

which often may not exist.

Human population in a region generally 

correlates to the amount of precipitation. While 

there are concentrated population centers in arid 

climates, regional populations are usually sparse 

and so too are groundwater data and monitoring 

wells and springs. Consequently, water table 

maps and aquifer models, if even available, are 

based on relatively few data points and thus, 

have lower precision compared to maps and 

models of aquifers where data and monitoring 

locations are abundant.

The second major factor for tracer injections 

in arid conditions is water volume, both for 

injection and within the aquifer. Without a 

constant source of water flowing into the aquifer 

from the surface, two methods are available to 

deliver the tracer to the water table. The first is 

to place the tracer into the recharge feature and 

wait for rain. While such a strategy can be 

effective for qualitative tracing, quantitative 

tracing is impossible and even accurate 

groundwater velocities cannot be assured if 

multiple storms occur before the tracer is 

detected.

The second water delivery method involves 

artificially injecting water into a recharge feature 

or well. If the injection site is near a spigot or 

fire hydrant, a constant source of water can flush 

the tracer until it is detected. If no constant water 

source is available nearby, water tankers can be 

used to flush the tracer if the terrain allows. For 

either method to be effective, the morphology 

and hydrology of caves in the area should be 

evaluated to estimate the likely volume of water 

necessary to wash the tracer into the aquifer. 

That volume should be at least tripled, 

depending on the level of confidence in the 

estimate and the depth to the water table. 

Additionally, a minimum of two estimated 

volumes should be injected as a pre-flush, to 

saturate the pores in cave sediments and 

maximize the speed and volume of tracer 

transmission to the aquifer. These methods have 

proven effective in karst aquifers in semi-arid 

climates (e.g., Johnson and others, 2010).

The volume of water within the aquifer must 

also be considered when injecting a tracer—not 

total groundwater storage but the volume within 

the flow path being traced. In karst aquifers, 

tracers are not dispersed throughout a substantial 

section of the aquifer, but through the far more

limited volume of the conduits between the 

injection site and where the tracer is likely to 

discharge. The most effective means of 

evaluating that volume is by studying the 

aquifer’s springs. 
41

White (1988), for example, describes how 

aquifer and conduit storage may be determined 

from spring hydrographs. In the most simplistic 

sense, a non-flowing spring indicates that a 

tracer will not be detected until groundwater 

levels rise and springflow resumes; artificial 

recharge is unlikely to result in spring discharge 

in most cases. If springflow is seasonal or 

episodic, springflow should be monitored and 

aquifer behavior quantified prior to conducting a 

tracer test to better plan the study and predict the 

likely tracer dilution (for calculating the tracer 

mass for injection) and time until tracer 

detection. Without such monitoring, there is a 

much greater chance that the tracer will be 

missed by not waiting long enough to detect it.

CONSIDERATIONS FOR TRACER 

DETECTION 

Too often tracer novices have concluded that 

a trace “didn’t work” when in fact they didn’t 

look in the right place for the tracer and/or didn’t 

wait long enough for the tracer to arrive. These 

factors are especially problematic in arid karst 

aquifers.

Tracing in humid climates often poses the 

challenge of selecting which, of an abundance of 

springs, are most important to monitor within 

the time, cost, and logistical constraints of the 

study. The challenge in arid climates is finding 

any spring to monitor. Not only are springs 

fewer due to less water, be it by natural causes 

or exacerbated by groundwater pumping, but the 

dry climate promotes sedimentation of stream 

channels where springs are most likely to occur. 

Alluviated springs are common, but with 

comparatively little hydraulic head, fewer 

distinctly identifiable springs form in thick 

alluvium. Many provide underflow through 

sediments beneath valley floors, which may 

emerge as surface flow kilometers from the 

buried spring outlets. The flow of many other 

springs never rises in ways that can be 

connected to the individual springs, and the 

presence of some is only vaguely reflected by 

areas of more lush vegetation in the dry 

landscape.

Some arid springs are poorly known and 

unidentified in hydrogeologic surveys because 

they flow short distances before the water 

evaporates or sinks into the stream channel. The 

easy availability of aerial photos through Google 

Earth now makes it simpler to find such 

locations for monitoring. 

Where individual springs cannot be 

identified, tracer detectors can be placed at 

regular intervals along flowing streams. If no 

tracer is recovered, repeating the trace by 

injecting a greater tracer mass may be warranted 

if the springs emerge below thick alluvial 

deposits that could adsorb or otherwise filter the 

tracer.

The discrete conduit flow paths in karst 

aquifers often make it impractical to trace to 

wells, but in arid karst aquifers where few 

springs are available for monitoring, wells 

should be considered important parts of the 

tracer detection program whenever possible. If 

all wells within the likely flow paths cannot be 

monitored, wells with indications of intersecting 

groundwater conduits should be selected (e.g., 

bit drops, rapid changes in water levels, turbid 

flows, large volume discharge, etc.). By 

intersecting high-permeability conduits, these 

wells monitor groundwater that has converged 

from broader areas, increasing the likelihood of 

tracer detection.

Perhaps the greatest challenge and 

uncertainty in tracing arid karst groundwater is 

determining how long to wait for a tracer to 

appear. Tracing experience in the area is helpful 

but there is probably more variability in arid 

karst than in humid karst to offer reliable 

predictability. Hydrograph and other directly 

related hydrogeologic data should be collected 

and interpreted in advance whenever possible to 

estimate the probable time frame of tracer 

arrival. It is important that such estimates be 

based on karstic, not Darcian flow conditions. 

As indicated previously, conduit storage is an 

important consideration but so are antecedent 

conditions, lag time between recharge events 

and spring response, and the degree of spring 

response to variable precipitation rates and 

volumes.
42

IMPLICATIONS FOR HYDROLOGICAL 

INTERPRETATION 

Once a tracer has been detected at a well or 

spring, what does it mean about the hydrology of 

the aquifer? In general, groundwater velocities 

are slower in arid climates due to less hydraulic 

head, but is that the sole consideration?

Jim Nepstad and Paul Burger (personal 

communication, 2014) respectively conducted 

tracer tests from above Wind Cave, South 

Dakota, in 1993-1996, and Carlsbad Cavern, 

New Mexico, in 2005. Mean rainfall in those 

areas is 44 and 33 cm/year, respectively. Both 

traces exhibited mostly slow and variable 

groundwater velocities and long storage times. 

Dye appeared in Wind Cave in as little as 1 day 

to as long as 5 years. Dye in Carlsbad Cavern 

first appeared in 21-40 days and persisted for at 

least 1.5 years. These slow velocities, at least 

when compared to many karst aquifers, is at 

least partly the result of poor saturation of 

vadose zone fractures. However, other factors 

must also be considered.

Both Wind Cave and Carlsbad Cavern are 

hypogenic caves formed independently of 

immediately overlying recharge features. While 

overprinting of vadose, epigenic morphologies 

occurs in many hypogene caves (for examples, 

see Klimchouk, 2007), the semi-arid climate at 

these caves has minimized their development. 

Hypogene factors aside, are arid karst aquifers 

recharged at a quantifiably lower rate due to less 

water and carbon dioxide (from less vegetation) 

available to enhance vadose permeability? 

Additional future tracer studies may help answer 

this question.

Goodbar (2009) also reported apparently 

slow groundwater velocities in the Carlsbad area 

but within the phreatic zone. Do phreatic 

conditions in arid climates fundamentally affect 

aquifer hydrology? Surface streams in arid 

regions form anastamosed and braided patterns. 

Related patterns occur in bedrock conduits of 

caves due to flooding, where groundwater is 

injected into bedding planes and fractures, where 

it is stored and dissolves a multitude of conduits 

until the floodwaters drain away. Could similar 

patterns significantly form in caves by lowgradient to ponded water? The water chemistry 

would be less aggressive in dissolving the 

bedrock, which could potentially be overcome 

with sufficient time, but it is not currently 

suggested by maps and observations of most arid 

climate caves beyond typical storage and flow 

from fractures and bedding planes that surround 

cave passages.

Alternatively, sediment deposition in lowgradient conditions could create other 

restrictions to groundwater flow. Travel times 

could be reduced and, as with alluviated surface 

streams, large volumes of saturated sediment 

could adsorb or filter tracers to reduce their 

detectability.

Perched and pooled groundwater in conduits 

is potentially more common in arid versus 

humid karst, which will affect tracer detection. 

Intermittent appearance of a tracer may reflect 

intermittent flushing of a tracer out of a pool or 

perched zone by multiple recharge events. It 

could also result from a single recharge event 

converging at and flushing the tracer from the 

pool or perched zone at different times. Residual 

tracer that is trapped within a pool or in perched 

groundwater may reappear during subsequent 

trace studies and result in misleading data and 

faulty conclusions if its source is not correctly 

recognized.

Where groundwater is shallow, roots from 

trees occasionally extend into conduits and 

withdraw water. Groundwater is not subject to 

evaporation, but potentially substantial 

transpirational losses may occur. Calculations of 

conduit groundwater storage from tracer and 

hydrograph data may show exceptional 

variability and inaccuracy as a result of such 

losses.

Anthropogenic factors must also be 

considered in arid regions, more so than in 

humid climates. Groundwater mining 

(unsustainable groundwater withdrawals) is 

more common in arid regions where pumping 

water wells have a proportionally greater impact 

on aquifer hydrology. As a result, the influence 

of wells on groundwater movement should 

increasingly be considered in planning tracer 

tests at potential major detection sites and in 

interpreting the time, direction, and volume of 

flow.
43

CONCLUSIONS

Tracer studies in arid karst aquifers pose a 

variety of challenges and uncertainties not found 

in humid climates. This paper presents some of 

these factors, which are present throughout all 

aspects of a tracer study: injection, detection, 

and interpretation. Presently, relatively few 

tracer investigations have occurred in arid karst 

areas, but future research will refine the 

observations of this paper, answer its questions, 

and probably provide hydrogeological insights 

not currently considered.

REFERENCES

Goodbar, J.R., 2009, Dye tracing oil and gas drilling 

fluid migration through karst terrain: A pilot 

study to determine potential impacts to critical 

groundwater supplies in southeast New Mexico, 

USA, in White, W.B., ed.: Proceedings of the 15th

International Congress of Speleology, p. 1507-

1510.

Johnson, Steve, Schindel, Geary, and Veni, George, 

2010, Tracing groundwater flowpaths in the 

Edwards aquifer recharge zone, Panther Springs 

Creek Basin, northern Bexar County, Texas: 

Edwards Aquifer Authority Report No. 10-01: 

112.

Klimchouk, Alexander, 2007, Hypogene 

speleogenesis: Hydrogeological and morphogenetic 

perspective: National Cave and Karst Research 

Institute Special Paper No. 1, 106 p.

White, W.B., 1988, Geomorphology and hydrology of 

karst terrains: New York, Oxford University Press, 

464 p.

Worthington, S.R.H., and Smart, C.C., 2003, 

Empirical determination of tracer mass for sink to 

spring tests in karst, in Beck, B.F., ed., Sinkholes 

and the engineering and environmental impacts of 

karst, Proceedings of the ninth multidisciplinary 

conference: American Society of Civil Engineers, 

Geotechnical Special Publication, No. 122, p. 

287-295.
44

Challenges to a Karst Dye-Tracing Investigation in an Urban 

Brownfields Area, Springfield, Missouri

By Douglas R. Gouzie1, Kevin L. Mickus1, and Micah V. Mayle1

1

Department of Geography, Geology, and Planning, Missouri State University, 901 S. National Ave., 

Springfield, MO 65897 

Abstract

Urban karst areas seldom lend themselves well to traditional karst investigation methods such as dye 

tracing. Often the impetus for an urban karst investigation is the detection of chemicals at a specific 

location, such as a spring, leading landowners or regulators to seek for the source area feeding that spring. 

If historic dye traces have not been done or recorded and disseminated in an accessible database, new 

studies may be hampered by limited access to obvious surficial karst features such as sinkholes and 

springs, many of which may have been covered over with engineering projects. Dye tracing may also be 

impacted by urban stormwater management, which may direct excess water into tracing routes and thus 

interfere with estimates of appropriate dye-injection amounts. Other tools more recently added to the karst 

toolbox, such as shallow geophysics, may also be hampered by urban infrastructure, such as electrical 

interference from utility lines.

A recent investigation to determine the source of water to a hydrocarbon-contaminated spring 

uncovered during Brownfields remediation activities at an urban karst site in Springfield, Missouri, 

encountered numerous practical problems. A combination of dye-tracing and shallow geophysical 

methods was used to determine possible subsurface flow paths contributing flow to the spring. Urban 

issues posed challenges for the project, including high-discharge stormflows related to urban pavement 

runoff, limited dye input locations due to urban cover and past landscape alteration, timeline pressures of 

a remedial project, and contaminant interference with dye detection. The issues encountered and efforts to 

address those issues and arrive at a successful end result of the karst investigation are presented.

INTRODUCTION 

Traditional karst investigations often involve 

the study of water movement in a region 

underlain by carbonate rocks. Such studies may 

include drainage basin delineation, specific 

recharge/discharge areas, groundwater flow 

paths and velocities, or similar issues (Luhmann 

and others, 2012). Often these studies have no 

specific timetable and only follow the workload 

of the investigators and the climate conditions at 

the site (Brahana, 2011). Investigations in urban 

karst areas tend to have similar strategies, 

although there are some notable differences. For 

example, in urban areas, surface karst features 

such as sinkholes, may have been covered over 

by buildings or infrastructure. Equally troubling, 

disruption to the routines of local citizens may 

impose shortened timelines for investigations 

than are typically experienced in regional 

studies. In addition, issues such as industrial 

pollution tend to be more common in urban 

areas. This report discusses an investigation 

attempting to determine the source of 

hydrocarbon contamination to a spring 

discovered during remediation of an urban 

Brownfields site.

Site Background

The study site is an urban Brownfields 

project in the city of Springfield, Missouri. 

Springfield is located in the Ozarks Plateaus 

physiographic region. The study area consists of 

an east-west-trending valley containing a 

channelized urban stream, Jordan Creek. Jordan 

Creek flows roughly east to west for 

approximately 4 miles through the central 

business district of Springfield before emptying 

into Wilsons Creek, a major stream running 

southward along the western edge of the city. 

The study area, shown in figure 1, was 

primarily occupied for many years by the 

Springfield railway station and multiple railyard 

sidings, freight docks, and rail maintenance 

facilities. In the mid 20th century, the main 

railyard operations moved farther north toward 

the edge of the city, and the site area reverted to 
45

mostly abandoned or under-used buildings and 

rail sidings. The Brownfields Program is a 

means by which the U.S. Environmental 

Protection Agency (EPA) can accelerate the 

typical superfund remedial process in order to 

facilitate urban renewal and development.

Geologic Setting

Springfield has a four-season climate with 

warm, humid summers and winter temperatures 

cold enough for snow. Average annual 

precipitation is 45 inches spread across the year 

(Springfield Business Development Corp, 2013).

The geologic setting of Springfield is 

dominated by nearly flat-lying carbonate rocks 

with dips of 0 to 2 degrees. The surficial unit 

across the entire project area is the 

Mississippian-age Burlington-Keokuk

Limestone, which is in excess of 200-feet thick 

in most of the Springfield area. The Burlington 

and a few thinner underlying carbonate units 

(Pierson, Elsey, and Reeds Spring Formations) 

compose the Springfield Plateau aquifer. 

Underlying these units, the Northview 

Formation is a shaly unit that acts as a leaky 

confining layer overlying the Ozark aquifer 

(Imes and Emmett, 1994). The Ozark aquifer 

includes greater than 1,000 feet of Ordovicianage dolostones and limestones.

Figure 1. Brownfields study site and area features within Springfield city limits. Point BS is Brewery Spring, point DS is Diesel 

Spring, point VS is Vich Spring, and point WC is a monitoring location on Wilsons Creek. Letters A through E are sinkhole 

locations discussed in the text. The shaded area is the outline of figure 2, the study site. The dashed lines are potential fracture 

trends. Springfield’s downtown square is at Boonville Avenue and College Street.
46

Both the Springfield Plateau and Ozark 

aquifers exhibit numerous features and flow 

patterns consistent with karst conduit flow. 

Recent studies in the area surrounding 

Springfield have indicated that much of the 

shallow groundwater flow system is controlled 

by hydraulically conductive vertical joints and 

relatively horizontal conduits congruent with 

bedding planes (Gouzie and others, 2010; 

Berglund and Gouzie, 2012; Berglund and 

others, 2012). 

Site History

The city of Springfield was founded in the 

1830s along the banks of Jordan Creek and near 

a spring on the Fulbright homestead. By the start 

of the 20th century, the central business portion 

of Springfield extended from about 0.75 mile 

south of Jordan Creek to1 mile north of Jordan 

Creek. The original railway station was located 

on or near the old Fulbright homestead. As 

Springfield grew, the growing railway moved 

toward the northern edge of the city (near the 

town of North Springfield), merging the two, 

and the original downtown railyard became 

essentially unused. Recent investigations 

indicate that roughly 75percent of the site study 

area was contaminated by industrial and railyard 

operations prior to the railroad transferring the 

property to the city (City of Springfield, 2013). 

A spring located on the south bank of Jordan 

Creek discharged hydrocarbons, earning the 

local nickname of “Diesel Spring” owing to the 

strong hydrocarbon odors common at the site. 

Subsequently, the city of Springfield began a 

Brownfields project to investigate and remediate 

the site area as part of an urban development 

project to create a greenway park corridor 

running along Jordan Creek through the urban 

core of Springfield.

PROJECT ACTIVITIES 

Project activities at the Brownfields site 

included a preliminary investigation, 

contaminated soil removal, revegetation, and a 

number of other remedial actions by the city and 

its Brownfields Program contractors. During 

these efforts, some of the soil-removal activities 

uncovered a spring buried beneath the bed of a 

(usually) dry drainage tributary to Jordan Creek. 

Backhoe activities breached what apparently 

was a confining bed within the Burlington 

Limestone and allowed a rise pool spring to 

form. As this rise pool flowed, globules of 

discolored and odoriferous hydrocarbon 

contamination issued regularly from within the 

pool at intervals spaced from a few seconds to a 

few minutes apart. These globules dispersed as 

an oily sheen on the surface of the spring water 

as it flowed approximately 200 feet down the 

tributary reach and into Jordan Creek. Also of 

note was that the previously existing Diesel 

Spring located offsite, on the south bank of 

Jordan Creek and approximately 125 feet 

upstream, had been experiencing the same 

intermittent hydrocarbon contamination. A few 

days after the onsite spring was uncovered by 

the backhoe, Diesel Spring ceased flowing and 

was not observed to flow during the remainder 

of the project. For the purpose of this report, the 

new onsite spring will be called Brewery Spring.

After discovering Brewery Spring, the city 

and its contractors sought someone with 

expertise to conduct a dye trace to determine the 

source of the spring water and the likely location 

of the hydrocarbon contamination source. 

Geophysical studies were proposed by the 

authors to aid in focusing the dye-trace 

investigation.

Sub-Contractor Status

The authors were selected as sub-contractors 

to the city’s primary remedial contractor for this 

portion of the Brownfields project. That decision 

relegated dye tracing and geophysical tasks to a 

secondary status compared to other site activities 

and timelines already established for site 

investigation and remediation. It also allowed 

access to the otherwise closed site, which was 

permitted through agreements already negotiated 

by the remedial contractor.

Field Reconnaissance

Field reconnaissance was conducted during 

the first calendar quarter of 2013. In addition to 

meeting the primary remedial contractor and 

going over their site procedures, a brief 

reconnaissance of the prospective geophysical

study area was conducted and the timing of 

geophysical fieldwork was planned. Following 

these initial activities, topographic maps were 

reviewed and a cursory driving assessment was 
47

conducted of areas north and south of the site to 

investigate the suitability of local sinkholes for 

the dye injection. Suitability was defined as 1) 

property access, and 2) documented stream 

losses or a clear indication that water could 

disappear underground if conditions were wet. 

Site Geophysical Study

After site reconnaissance was completed, it 

was determined that direct current (DC) 

electrical resistivity profiles would likely offer 

the most useful results and that electromagnetic 

(EM) surveying would also be used in order to 

offer a more robust interpretation than one 

method alone would offer. The resistivity and 

EM surveys were conducted in the second 

calendar quarter of 2013 and a geophysical 

report was prepared in early May 2013. Results 

and interpreted fracture or joint orientations 

from the resistivity data are shown in figure 2. 

Using the geophysical report, a meeting was 

held with the primary remedial contractor to 

discuss the results and implications for dye 

tracing and the selection of appropriate 

sinkholes for dye injection. 

As can be seen on figure 2, the most 

promising trend for fractures running through 

the new onsite spring appeared to be along an 

azimuth trending between about 320 and 340 

degrees. This trend also correlated well with the 

trend between the old (now dry) contaminated 

Diesel Spring offsite on the south bank of Jordan 

Creek and a line projected from that spring 

through the new onsite Brewery Spring, a line 

that would trend at an azimuth of approximately 

305 degrees.

Dye-Tracing Study

As is usually the case with any dye-tracing 

study, the initial tasks were to identify potential 

tracer-injection locations and, in the case of 

unknown conditions, to identify all potential

dye-resurgence locations surrounding the 

injection point. 

Dye-Injection Point Locations

Using both topographic maps and driving 

tours of the area (and walking possible sites 

where property access allowed), five potential 

sites were considered, and these sites were 

identified by letters A through E on figure 1.

Figure 2. Electrical conductivity map of the Brownfields site as determined from the electromagnetic survey. White lines 

indicate the possible location of fractures determined from electrical resistivity profiles. Numbers 1 and 2 represent high 

conductivity regions on the electromagnetic profiles. Dark blue areas represent areas of site debris. Small rows of circles are the 

locations of the resistivity lines (each circle represents an electrode location.) This figure is the shaded area in figure 1 with north 

oriented toward top of page.
48

A. small sink in field north of Calhoun 

Street (private property), 

B. small sink in unused residential lot on 

northeast end of Scott Street, 

C. sink used as city stormwater drain on 

northwest corner of West Avenue and 

Calhoun Street,

D. small sink immediately west of Kansas 

and Nichols Streets, and

E. sink mapped at west end of railyard 

north of Division Street.

Possible sinkholes south of the site were also 

evaluated, but no apparent sinkholes near any of 

the projected azimuths were identified from 

topographic maps to the south of the site, 

probably due to the more developed or 

urbanized grading south of College Street.

Based on preliminary reconnaissance, the 

lack of any discernible physical openings 

(swallow holes or sinkhole depressions with 

open “throats”) removed two of the sites (B and 

D) from further consideration. The inability to 

gain access to the Division Street railyard 

eliminated the sink at location E from 

consideration. Of the two remaining sites, the 

corner of West Avenue and Calhoun Street 

(location C) was selected as the preferred dyeinjection location based on closest linear 

distance to the Brownfields site and also based 

on its current use as a stormwater drainage 

structure for the city of Springfield’s stormwater 

drainage system. A photograph of this site and 

the stormwater inlet structure, a slotted pipe 

made of welded steel approximately 3 feet in 

diameter and surrounded by coarse gravel, is 

shown in figure 3.

Dye-Monitoring Point Locations

Five monitoring locations were selected for 

the dye trace. These monitoring locations were: 

1) Jordan Creek on the West Meadows site, 

upstream (east) of the confluence with the 

Brewery Spring tributary, 

Figure 3. Dye-injection site at West Avenue and Calhoun 

Street.

2) BS-The new onsite Brewery Spring (the 

anticipated resurgent location for the dye), 

3) VS-An unnamed drainage northeast of the 

dye-injection point (this drainage was the 

approximate location of “Vich Spring” 

where historical dye traces from north of the 

Division Street railyard had been detected), 

4) WC-A wet portion of the north branch of 

Wilsons Creek to the west of the injection 

point, and 

5) Rader Spring, on the banks of Wilsons 

Creek several miles south of site WC (a 

“catch all” location in the southwestern part 

of the metropolitan area). 

This array of monitoring points was 

designed to cover streams north, west, and south 

of the site, in addition to the onsite Brewery 

Spring, and one upstream Jordan Creek site 

designed to detect any dye resurging east of the 

site. Charcoal packets (which adsorb the dye) 

were placed at each of these locations and an 

automated water sampler (Hach 900) was also 

utilized at the Brewery Spring site. All 

monitoring sites were sampled either with 

charcoal packets or grab sample bottles (or both) 

for analysis of the natural background 

fluorescence prior to selection of a dye for the 

trace. Based upon the background sample 

analyses, no interferences were found within the 

spectral wavelengths associated with Rhodamine 

WT dye (RWT), and it was selected for the test. 
49

Dye-Trace Injection Details—Problems 

and Challenges

Based partly on contractor schedules, it was 

decided to inject the RWT as promptly as 

possible. Groundwater tracers in Missouri are 

regulated so that only those trained in proper use 

of photochemical dyes should be injecting 

suitable amounts of dye into the state’s waters. 

The regulatory program also requires prenotification of the Missouri Department of 

Natural Resources before injecting any dye to 

prevent interference with any existing dye traces 

already underway. These steps delayed the first 

trace until after a rainfall event on Monday, May 

20. Based on weather forecasts of no other 

rainfall for that week, arrangements were made 

to use city water from a nearby fire hydrant for 

the actual dye injection. On Thursday, May 23, 

starting at approximately 2:30 pm, approximately 500 gallons of city water were flushed 

into the stormwater inlet, followed by 2 gallons 

of RWT dye (Koch Industries, 20% solution). 

This was followed by approximately another 

400 additional gallons of city water to continue 

flushing the dye into the stormwater structure, 

and into the shallow aquifer. 

Based on past experience in the region and 

map distance from the stormwater injection site 

to the Brewery Spring, an estimated dye 

(groundwater) travel time of approximately 30-

36 hours was expected. Therefore, the 

automated sampler was programmed to collect a 

sample every hour for the first 24 hours, 

beginning at 6 pm Thursday, May 23; the unit 

was refilled with clean bottles and reset at 24-

hour intervals after that. 

Unfortunately, the unit experienced a 

malfunction (battery, timer, or programming 

issue) at the beginning of the second 24-hour 

interval (i.e., the first 24 hourly samples were 

collected, then the unit failed to collect samples 

for hours 27–42 after dye injection before the 

malfunction was discovered.) An identical 

(substitute) Hach unit with an alternate battery 

was placed onsite approximately 44 hours after 

dye injection, and the second unit operated 

properly for the following week. The onsite 

charcoal packet placed next to Brewery Spring 

was expected to serve as a backup for any 

issues, such as the autosampler failure. 

The charcoal packets for the first 2 weeks 

onsite displayed significant interference with the 

detection (or more likely the sorption) of RWT. 

Although background interference samples were 

collected prior to the traces, the project timeline 

was met by evaluating potential interference 

with grab-sample bottles of water from the 

monitoring locations rather than waiting for 

charcoal packets to be retrieved from the field, 

dried, and processed. No interference was 

observed with detection of RWT in any of the 

background grab samples. 

When the charcoal packets were analyzed, it 

appeared that the organic contamination at the 

site either preferentially adsorbed to the charcoal 

or otherwise had such a strong signal when 

eluted from the charcoal as to significantly 

obscure any RWT signal. Given the nature of the 

hydrocarbon contamination (almost certainly 

hydrophobic based on the globules and oily 

sheen onsite), it is reasonable to believe that the 

contamination preferentially sorbed on the 

charcoal and limited the sorption of the 

hydrophilic RWT on the charcoal. An example 

fluorometric scan of the analysis of a charcoal 

sample with detectable RWT is shown in 

figure 4.

450 500 550 600

Nanometers

0

10

20

30

40

50

60

Figure 4. Fluorometric synchronous scan of sample 

charcoal packet elutant from Brewery Spring, showing a 

notable RWT peak at about 545 nm of excitation, and a 

much stronger but unknown peak around 440 nm 

excitation. The Y-axis of the figure is in fluorescence 

intensity units recorded by the fluorometer.
50

Due to the autosampler malfunction, the 

Brewery Spring charcoal packet was changed on 

the morning of May 24, as scheduled, and then 

again late in the day on May 25, to cover the 

specific period of autosampler malfunction. 

As shown in figure 4, it appears the charcoal 

sample from the Brewery Spring site collected 

on May 25 does show the presence of RWT. 

However, the amount of fluorescence is well 

below the threshold used in our lab of at least 

three times the fluorescence value of a pre-trace 

background sample in order to declare the 

sample a positive dye recovery. After 

discovering this interference, the charcoal packet 

monitoring location for Brewery Spring was 

moved approximately 100 feet downstream on 

Jordan Creek (to the underpass of Fort Avenue) 

in an attempt to allow site contaminants to dilute 

or disperse more before encountering the 

charcoal, and thus allowing the RWT dye to 

have a greater chance of sorbing on the charcoal.

Because dye concentration and duration did 

not match our lab requirements of a positive 

trace during the first 48 hours, the autosampler 

was re-stocked with clean bottles and 

programmed to continue sampling on a regular 

basis. The charcoal packets were also removed 

and replaced on a weekly schedule.

On May 30, approximately 1 week after 

sampling began, an intense storm event 

(approximately 2 inches of rain in less than 4 

hours) occurred in the Springfield area, causing 

a significant flooding event in the onsite northsouth tributary where Brewery Spring is located. 

The flooding during this event was so extensive 

that the autosampler, secured about 5 feet above 

normal spring stage, was apparently floated 

downstream and overtopped by flood water. 

The chain securing the autosampler in place 

apparently caused the unit to be submerged in 

enough water to flood and short-out the main 

circuit board. As a result, no spring water 

samples were collected from May 30–June 14. 

However, throughout this time period, charcoal 

packets were maintained at all locations 

(including Brewery Spring) and continued to be 

changed and analyzed on a regular basis. With 

the exception of the one possible interferencemasked detection noted above during the first 48 

hours after injection, at no point in time did 

elutant from any charcoal packet at any 

monitoring location show a positive detection 

for RWT.

After the first major storm event and 

replacement of the failed autosampler with a 

functional unit, plans were made to re-introduce 

more of the same RWT dye into the same 

sinkhole. Although a second injection of the 

same dye would add a level of uncertainty to the 

actual travel time (as it would not be possible to 

prove which injection was being detected), it 

was more expedient than the delay which would 

have ensued in using a second dye such as 

fluorescein (an alternate dye would have 

required additional approval of the Missouri 

Department of Natural Resources.) This 

expedient use of RWT for the second trace 

attempt was deemed acceptable because the 

primary purpose of the project (for the 

Brownfields site work) was to identify a 

connection between a sinkhole and the Brewery 

Spring. 

This second dye injection was planned to 

coincide with an anticipated storm event in midJune. On the morning of June 15, 2 gallons of 

RWT were injected into the same West and 

Calhoun Streets stormwater sinkhole (location 

C) on the leading edge of a storm hydrograph, 

during the first 30 minutes of storm runoff. 

After injecting the dye, the authors travelled to 

the onsite Brewery Spring to check the 

autosampler unit. Upon arrival at the site, a 

visual discharge estimate of approximately 35 to 

40 cubic feet per second (ft3

/s) was made. The 

approximate discharge was calculated by 

multiplying the average of width times depth 

times velocity, with velocity determined by 

measuring the time it took a floating object on 

the water surface to move downstream a known 

distance. Because previous estimates of 

discharge from Brewery Spring typically had 

been in the range of 3 to 6 ft3

/s or less using the 

same visual estimation method, it appears that 

the urban runoff from the rain event of June 15 

may have diluted the dye recovery to a point 

where once again it would be undetectable. 

After the June 15 injection, monitoring was 

continued with both the autosampler and 
51

charcoal packets and in the surrounding area, 

although the West Bypass charcoal packet site 

went dry approximately June 21, which 

indicated no dye could resurge along that 

segment of stream. Monitoring was continuedfor 

8 weeks after the initial dye injection on July 17, 

at which time the primary remedial contractor 

for the site chose to cease all further tracing 

activities. Using the criteria of the Missouri 

State University Cave and Karst Lab, no dye 

was ever definitively detected from either 

injection. Plans were made for another trace at a 

future time during wetter weather; however, the 

contractor’s work plan and site access ended 

before any additional traces were attempted.

DISCUSSION OF CHALLENGES 

Below is a brief summary of the challenges 

encountered beyond the normal issues found in 

dye tracing and field work. Also offered are 

some possible causes or major contributing 

factors to the challenges and possible ways to 

mitigate the issues.

Urban Stormwater Issues

One key issue was the unseasonal weather 

combined with the flow regimes of urban 

stormwater runoff. As noted above in the dyetracing section, both attempts at a successful 

trace were hampered by unusual and unexpected 

rainfall runoff. The first dye-injection event was 

impacted by a small but intense rainstorm 

which, based on water levels at the Brewery 

Spring, probably generated stormwater runoff at 

the site that was at least 10 times greater than 

typical baseflow at the site. Visual discharge 

estimates shortly after the second dye injection 

suggested that runoff in the site tributary 

containing Brewery Spring was in the range of 

40 ft3

/s. The stage associated with this discharge 

was below the elevation of the onsite 

autosampler, so water levels high enough to 

float and flood the autosampler would need to 

have been in excess of 40 ft3

/s. Such large 

variations in flow were particularly challenging 

in determining amounts of dye to inject. 

Groundwater tracers in Missouri are 

regulated, therefore, it is expected that registered 

dye-tracing professionals will limit the amount 

of dye injected to an amount that would not be 

expected to discolor any waters of the state. 

Flashy urban runoff poses the challenge of 

diluting a normal injection amount to become so 

dilute as to no longer be detectable. The easiest 

way to overcome this challenge is to find a 

losing stream rather than an existing storm 

drainage structure, which may lead to 

groundwater but where the current groundwater 

connection cannot be observed or determined. 

A recently located segment of losing stream 

northeast of the Brewery Spring site shows 

promise for a future dye-tracing attempt. 

Contract Limitations on Study Timeline

As noted, this work was performed under a 

sub-contract to the city’s primary remedial 

activity contractor for the site. Because the 

Brownfields Program is intended to accelerate 

redevelopment of urban lands, the project 

already was on a strict timeline before the 

authors were contacted for involvement. 

The applied approach of determining the 

source area for a springfed stream created a 

challenge because typical tracing approaches 

using a point of known, ongoing flow into the 

subsurface were hampered by the desire to keep 

the tracer test moving forward on the established 

timeline. Adding the seasonal nature of study 

activities (pre-leafout being preferred for 

geophysics activities and post-freezing, wetseason weather preferred for dye tracing) to the 

already existing schedule posed challenges for a 

successful completion.

The ability to perform site geophysical 

studies quickly after study approval by the 

primary remedial contractor was a positive item 

– all parties were pleased to see activity onsite 

soon after approval of the proposed workplan, 

and the ability to perform the geophysical 

surveys during winter plant dormancy was 

fortunate. However, the additional insight 

offered by the geophysics and the time 

consumed by geophysical tasks did add 

increased pressure to the timeline and success of 

the dye trace. The desire to establish a successful 

dye trace led the authors to offer to conduct 

another trace after the project had officially 

ended. 

Although such a tracer test is still planned, 

the added challenges of negotiating site access 
52

after the primary remedial activity contract has 

ended have delayed any new dye-trace attempts. 

Although site access was relatively easy under 

the umbrella of a site contractor, reaching an

agreement on liability that satisfies the city’s 

normal contract for property access and which is 

acceptable to the university (as a state agency 

limited in liability waivers to which it can agree) 

requires time-consuming negotiations between 

attorneys with more pressing legal issues on 

their schedules.

Contaminant Interference with Dye 

Discovered during the first dye injection, the 

hydrocarbon contamination that prompted the 

investigation may also have interfered with 

detection of the dye by preventing sorption of 

the dye on the activated charcoal in the packets. 

Although fluorescence in the narrow wavelength 

range of RWT was detectable using a modern 

scanning spectrofluorometer, the intensity and 

recurrence was not enough to meet the Missouri 

State University Cave and Karst Lab criteria for 

a definitive detection. It appears that moving the 

Brewery Spring charcoal detector packet slightly 

downstream from the contamination source may 

have adequately overcome the challenge of 

contaminant interference, but this remains to be 

tested. The use of larger amounts of dye is also 

planned for future efforts, as the existing 

contamination of the site makes the issue of 

discoloration of the water less offensive during 

the remedial project. Local residents are already 

offended by the strong hydrocarbon odors and 

the oily sheen, so a brief period of slightly tinted 

water would likely be tolerated in order to 

achieve a definitive trace and move the remedial 

efforts forward. 

Geophysics – Guidance or Misguidance?

Perhaps the most puzzling challenge 

encountered is the utility of using geophysical 

data in guiding or shaping the dye-tracing 

efforts. Although geophysics as used on the site 

have become very useful in other parts of the 

metropolitan Springfield area (Berglund and 

others, 2012; Gerson and others, 2012), it is 

unclear whether the geophysics contributed to a 

better understanding of the site subsurface or if 

it led investigators down a “primrose path.”

Given the reasonable prediction of a 

groundwater feature trending at azimuth 305 

degrees (based on the Diesel Spring going dry 

soon after the onsite Brewery Spring was 

uncovered), a reasonable interpretation of the 

geophysics data indicates linear features 

trending in azimuths ranging from 320 to 340 

degrees and in general agreement with the 305-

degree azimuth trend. However, none of the 

discovered sinkhole features were actually in the 

geophysics-predicted range. The closest sinkhole 

discovered during the initial study, the urban 

stormwater drain at West and Calhoun Streets, is 

roughly on a 305-degree azimuth from the site, 

but there has not yet been a successful dye trace 

from this location. A newly discovered sinking 

stream segment that shows great promise is 

actually slightly northeast of the site and is in the 

upper reaches of the stormwater channel 

tributary running onto the site.

Given the location of the newly discovered 

sinking stream segment, it seems worth 

revisiting the geophysical data and considering 

the other low-resistivity features (marked as 

areas 1 and 2 on figure 2). It is possible that 

these features represent contamination that may 

be closer to a trend between the sinking stream 

segment and Brewery Spring. It also is possible 

that Jordan Creek itself is losing flow 

underground on the eastern edge of the 

downtown area, and that the lost flow is 

resurfacing at Brewery Spring after picking up 

some contamination in the east-west-trending 

alluvial fill in the Jordan Creek valley. 

Understanding that the historical Jordan Creek 

meandered across the east-west-trending valley 

through downtown, but is now channelized on 

the southern margin of the valley due to urban 

development, may open up new interpretations 

of site geophysics related to groundwater (and 

contaminant) movement. Hopefully a successful 

dye trace conducted in the near future will offer 

more data for a combined geophysical –

hydrogeologic interpretation.

CONCLUSIONS 

Based on the challenges encountered, much 

was learned about modifying a traditional dyetracing research project into an applied site 
53

investigation and remedial effort under the U.S. 

EPA Brownfields Program. 

Lessons learned for future studies include 

the following:

• Be flexible in using the entire karst toolset to 

adapt to schedule pressures of commercial 

contracts and timelines. Being able to use 

additional methods such as geophysics 

during weather conditions not conducive to 

dye tracing was helpful to the overall 

success of the project.

• Remember that the site is already 

contaminated and undesirable side effects of 

the current tasks may be more tolerated than 

they would be at undisturbed research sites. 

The hydrocarbon contamination driving this 

project may have interfered with the 

sorption of dye at the part-per-billion levels 

typically used in modern tracing, whereas 

higher levels up to a few hundred parts-perbillion for brief periods might have been 

tolerated as the cost of moving site 

remediation forward.

• Maintain the fundamental principles of the 

simplest research approach. Staying true to 

traditional dye tracing under “normal” 

conditions of existing streamflow losing to 

the subsurface and re-surfacing at a spring 

would have led to increased searching to 

locate losing stream segments in the urban 

area, or more searching for city employees 

familiar with past use, now covered, of the 

natural karst drainage features incorporated 

into the city’s stormwater system. 

Knowledge gained after the unsuccessful 

traces were reported has provided at least 

two additional potential dye-injection 

locations that are anticipated to yield more 

successful traces in the near future. 

Overall, the interaction with remedial and 

urban managers was a satisfying experience and 

one that is encouraged for all researchers. 

However, those used to research projects 

designed and conducted with few, or no, 

external pressures or timelines, should be 

prepared for the challenges involved in applied 

urban studies in karst areas.

REFERENCES

Berglund, J., and Gouzie, D., 2012, Conceptualizing 

flow interaction and conduit geometry in nearsurface karst using a quantitative dye tracing 

method: Geological Society of America 

Abstracts with Programs, v. 44, no. 5, p. 20.

Berglund, J., Mickus, K., and Gouzie, D., 2012, 

Studying urban karst features using near-surface 

geophysics in Springfield, Missouri: Geological 

Society of America Abstracts with Programs, v. 

44, no. 5, p. 27.

Brahana, V., 2011, Ten relevant karst hydrogeologic 

insights gained from 15 years of in situ field 

studies at the Savoy Experimental Watershed, in

Kuniansky, E., ed., U.S. Geological Survey Karst 

Interest Group Proceedings, Fayetteville, AR, 

April 26-29, 2011: U.S. Geological Survey 

Scientific Investigations Report 2011-5031, p. 

132–141. 

City of Springfield, Missouri, 2013, Jordan Valley 

West Meadows Project Fact Sheet, accessed at 

www.springfieldmo.gov/brownfields

Gerson, L., Mickus, K., and Gouzie, D., 2012, An 

urban karst geophysical study in Springfield, 

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Abstracts with Programs, v. 44, no. 7, p. 78.

Gouzie, D., Dodd, R., and White, D., 2010, Dye 

tracing studies in southwestern Missouri, USA: 

Indication of stratigraphic flow control in the 

Burlington Limestone: Hydrogeology Journal, v. 

18, no. 4, p. 1043–1052.

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the Ozark Plateaus aquifer system in parts of 

Missouri, Arkansas, Oklahoma, and Kansas: U.S. 

Geological Survey Professional Paper 1414-D, 

127 p.

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Schwartz, B., Groten, J., and Alexander, E., Jr., 

2012, Comparing conservative and 

nonconservative tracers in karst and using them to 

estimate flow path geometry: Journal of 

Hydrology, v. 448-449, p. 201–211.

Springfield Business Development Corporation, 

2013, Springfield area Chamber of Commerce 

website, Live in Springfield, Climate in 

Springfield, accessible at 

http://www.liveinspringfieldmo.com/live/climate
54

SPELEOGENESIS, GEOLOGIC FRAMEWORK, GEOPHYSICS, AND GEOLOGIC HAZARDS

The Role of Spongework in the Speleogenesis of Hypogenic Caves in 

the Guadalupe Mountains, New Mexico

By Mark Joop

New Mexico State University, Carlsbad, New Mexico 88220

Abstract

Recent studies of the few active sulfuric acid caves in the world have shed some light on the 

interpretation of relic sulfuric acid caves in the Guadalupe Mountains, New Mexico. The Guadalupe 

caves share most of the common features, including spongework morphology. The spongework clearly 

predates the hypogenic speleogenesis in the Guadalupe caves and provided the cavernous porosity needed 

to form the sulfuric acid subaerially. The generation of sulfuric acid requires an abundant supply of sulfur 

and oxygen. It is argued that the hydrogen sulfide came from microbial reduction of the abundant sulfate 

in the brine water, and that the oxygen came from the atmosphere in the spongework above the water 

table. A modern analog of how sulfuric acid is produced in caves may be found in concrete wastewater 

pipes and tanks.

INTRODUCTION

Spongework has been recognized in the 

caves of the Guadalupe Mountains as far back as 

1949, when Bretz wrote, “Carlsbad’s 

magnificent display of spongework is to be seen 

from the highest to the lowest levels of the 

cave,” and “the spongework of the [Left Hand] 

Tunnel is unsurpassed in any cave that the writer 

has ever seen” (Bretz, 1949). It is clear from 

Bretz’s statements that he had seen spongework 

in caves in other areas (e.g., Meramec Cave in 

Missouri and Wind Cave in South Dakota). In 

fact, Bretz studied over 100 caves in 50 states, 

including Carlsbad Cavern, and coined the term 

“spongework” for the cave morphology 

discussed here (Bretz, 1942). Thus, while the 

spongework in Carlsbad Cavern was not cited as 

the type locality (White, 1988), it is definitely an 

excellent example of the relation between 

spongework and hypogene speleogenesis. 

The purpose of this paper is to re-examine 

the spongework in Carlsbad Cavern and Spider 

Cave, as type localities in the Guadalupe 

Mountains, in light of more recent work, to 

determine its role in the speleogenesis of these 

caves.

DEFINITION OF SPONGEWORK

Spongework is defined in the Lexicon of 

Cave and Karst Terminology as “Randomly 

shaped cavities created by undirected phreatic 

dissolution in a massive, essentially 

homogeneous limestone” (USEPA, 2002). 

Earlier definitions focused on the morphology of 

spongework, and did not include its genesis. 

Palmer (1991) defined spongework as 

“interconnected solution cavities of varied size 

in a seemingly random three-dimensional pattern 

like the pores of a sponge.” White (1988) had 

earlier defined spongework as “interconnected, 

nontubular solution cavities of varied size and 

irregular geometry arranged in an apparently 

random, three-dimensional pattern,” but added 

that it “appears in caves formed in young, 

porous, and poorly jointed limestones.” Both 

Palmer (1975, 2005, 2007) and White (1988) 

categorize spongework as a feature of maze 

caves. While there are some divergent 

hypotheses on the genesis of spongework, most 

speleologists agree with Bretz that spongework 

is produced in the phreatic zone under slow, 

diffuse, hydraulic conditions (Klimchouk, and 

others, 2000). This is indicated by the smooth, 

rounded, irregular speleogens such as cupolas, 

holes, pendants and bridges, the lack of scallops 

and channels, and the irregular floors and 

ceilings. Bretz deduced that spongework is “the 

solutional work of water without definite 

current, without surface gradient, without air 

above it.” 

Modern investigations of spongework caves 

not associated with hypogenic speleogenesis 
55

have determined that this morphology formed by 

corrosion at the fresh/salt water mixing zone of 

coastal aquifers; such caves are now called 

flank-margin caves (Mylroie and Carew, 1990). 

The mixing can be explained by the hydraulic 

action of tides, penetrating into the bedrock as 

far as the hydraulic conductivity of fractures, 

joints, and bedding planes allow, which would 

increase with time as porosity and transmissivity 

increased due to corrosion. Constant mixing is 

essential to maintain aggressiveness, which is 

initially most active close to the coastline. The 

mixed water is corrosive to limestone because it 

is undersaturated with respect to calcite 

(Plummer, 1975; Bogli, 1980). Spongework 

caves are found in a wide variety of carbonate 

lithologies (Klimchouk and others, 2000), 

though primary porosity is believed to be 

important (Palmer, 2005, 2007). The large 

chambers of flank-margin caves appear to be 

due to the coalescing of cupolas and holes, often 

leaving remnants of the rock in between as 

pendants protruding from the ceiling, walls, and 

floor (Mylroie and Carew, 1990). Spongework is 

not a common cave morphology (White, 1988), 

yet with so many relic and active spongework 

caves associated with emergent limestone in 

contact with seawater, perhaps the flank-margin 

environment, as opposed to being a special case 

(Klimchouk, 2000), is the common, or at least 

primary, geologic setting required to produce 

spongework caves. In other words, it is not 

mixing corrosion alone which best explains most 

occurrences of this phreatic morphology 

(Palmer, 2005), but this type of dissolution in 

combination with the low-velocity, turbulent, 

swirling, back and forth flow pattern associated 

with tidal action.

NATURE OF SPONGEWORK IN 

CARLSBAD CAVERNS NATIONAL PARK

The spongework in Carlsbad Cavern is 

variable in size, from walking passages to small 

holes that only a finger can pass through. This 

cave morphology is found around the perimeter 

and in between the large chambers (fig. 1). A 

nearly vertical fracture is typically observed in 

the center of the ceiling of the “trunk” passages, 

indicating that the spongework developed along 

this secondary porosity, and spread laterally on 

both sides of the fracture (fig. 2). Usually, the 

lateral development is not far from the fracture 

unless there are intersecting or parallel fractures, 

and is characterized by small interconnected 

pockets that dead-end. Even the trunk passages 

come to a dead-end, though the fracture usually 

continues. In Spider Cave, the spongework 

developed along a bedding plane contact 

between a sandstone member of the Yates 

Formation and the underlying dolomite. The 

natural floors of the spongework are not flat 

unless they have been filled in and leveled with 

secondary clay or sediment deposits (e.g., Big 

Room, Kings Palace/Lower Cave), which 

represent water table stands. Most of the 

spongework in Carlsbad Cavern is located at the 

Big Room level – the northeast ends (the Zoo, 

the Underground Lunchroom and all along Left 

Hand Tunnel), and the Boneyard (above Lower 

Cave spongework); at the Lower Cave level –

the northeast side; and at the Main Corridor 

level – the north side (the New Section). 

Figure 1. Typical spongework in Carlsbad Cavern.

In addition to pendants, rock bridges are 

another common speleogen found throughout 

the spongework, where the bedrock between 

holes is left suspended, with air space on all 

sides of the bridge (fig. 2). Some of these rock 

bridges are only a couple of centimeters in 

diameter at the thinnest spot. Typical of 

spongework in this and other caves, primary 

flow features such as scallops are absent 

(Klimchouk, and others, 2000).

The vertical extent of the spongework in 

Carlsbad Cavern is from the bottom of the lower 

sandstone unit in the Triplet Member of the 

Yates Formation, as can be seen in the Main 

Corridor and in the route to Hall of the White 
56

Giant, to at least the floor of Lower Cave in the 

Capitan Reef. Spider Cave formed at the same 

upper limit. This 5-meter thick sandstone unit 

may have been a groundwater confining layer. 

The vertical extent represents about 207 meters.

Figure 2. Fracture in the ceiling, with spongework on both 

sides. Note the rock bridge spanning across the fracture, as 

well as the one in the upper left corner of the picture.

GEOLOGIC TIMING OF SPONGEWORK

Because the spongework occurs around the 

perimeter and in between the large chambers of 

Carlsbad Cavern, Hill (1996, 2006) recognized 

that it pre-dates the sulfuric acid hypogene 

speleogenesis that occurred during the Miocene. 

The spongework represents the first stage of 

dissolution in the Guadalupe Mountains. Hill 

suggested that the timing of the spongework 

started no later than after the Permian and 

extended through the Mesozoic into the early 

Cenozoic, when the Delaware Basin was 

emerging (Hill, 1996). A date of early Jurassic 

(188 ± 7 ma) was provided by a speculative 

40K/40Ar date for montmorillonite clay found 

in the spongework. Hill recognized that the reef 

complex had to be emergent for a freshwater 

lens to be present to create spongework, and 

with no Triassic- or Jurassic-age deposits in the 

Delaware Basin, this date made sense. But is the 

end of the Permian the first emergence of the 

reef complex? Most early workers agreed that 

the Delaware Basin was first tilted eastward at 

the end of the Permian, but there is strong 

evidence that this tilting occurred earlier (Hill, 

1996).

The spongework developed along preexisting, near vertical fractures, the major ones 

being the same two sets on which most of the 

caves in the Guadalupe Mountains developed: 

one set parallel to the reef escarpment, and one 

set almost perpendicular to the reef escarpment. 

Strong evidence indicates that the earliest of 

these fractures are syndepositional with the reef, 

and Capitanian in age (Hunt and others, 2002; 

Kosa and others, 2006). Basin and Range 

extensional stress most likely reactivated these 

pre-existing fractures. When this evidence is 

coupled with the fact that the Ochoan-age 

evaporite deposits in the basin are wedgeshaped, thickening to the east, unlike the 

underlying Delaware Mountain Group, it seems 

reasonable to deduce that some eastward tilting 

of the Delaware Basin occurred at the end of the 

Guadalupian (Hill, 1996). Saller (1996) 

concluded that the reef complex had tilted 10o 

basinward after deposition due to compactioninduced differential subsidence (the backreef 

deposits thicken toward the reef margin). Hunt 

and others (2002) refined this tilt to a 2o 

depositional dip of the Yates Formation with an 

additional 6-8o syndepositional tilting due to 

subsidence, which was believed to be 

responsible for the progradation of the Capitan 

shelf. However, during and/or after the 

deposition of the Tansill Formation, an 

additional 4-6o basinward tilt occurred (Hunt 

and others 2002), which perhaps was due to 

tilting of the basin itself. Because the evaporites 

are the result of the Delaware Basin being cut 

off from the ocean to the west, then perhaps this 

cutoff was due to eastward tilting of the basin, as 

opposed to a drop in sea level. 

Hill (1996) summarizes evidence supporting 

a strong case that the Castile sea did not cover 

the reef or forereef on the western side of the 

Delaware Basin, from the Guadalupe Mountains 

to the Apache Mountains, indicating that it was 
57

emergent during Castile time, and perhaps even 

during Salado time. If this is the case, then the 

freshwater lens required to create the mixing 

corrosion that produced the spongework was 

present as early as the Capitanian/Ochoan 

boundary (260 ma). Kirkland and others (2000) 

agree that the basin was closed off from the 

ocean during deposition of the 260,000 laterally 

correlative, varved lamina of the Castile 

evaporites due to the western reef complex being 

emergent. They show that the parent brine water 

of the Castile evaporites was predominantly 

marine, and that the source of the marine water 

kept pace with evaporation, such that desiccation 

never occurred. They conclude that the brine 

water entered the basin by seepage through the 

Capitan Formation, and the brine water level 

remained close to sea level.

ROLE OF SPONGEWORK IN HYPOGENE 

SPELEOGENESIS

That sulfuric acid hypogene speleogenesis 

was involved in the formation of the large 

chambers and passages that make the Guadalupe 

caves world famous is well accepted and 

supported today (Palmer, 2006). However, how 

this process works is still being studied. A recent 

comparison of active sulfidic karst systems in 

the world (Hose and Macalady, 2006) has found 

some common features: 1) thermal groundwater 

rich in sulfate, 2) sulfate-reducing and sulfuroxidizing chemoautotrophic bacteria, 3) the 

release of sulfides from the aquifer into the 

atmosphere of pre-existing caves/cavities, 4) the 

subaerial formation of sulfuric acid in the 

condensate on the walls, 5) gypsum rinds on the 

walls from limestone replacement, 6) massive 

gypsum floor deposits from stoped rinds, and 7) 

spongework cave morphology. The sulfuric acid 

production in the Guadalupe Mountains ceased 

long ago, which makes these caves relict. Even 

in Lechuguilla Cave, which intersects the 

groundwater table 488 meters below the surface, 

there is no sulfuric acid in the water or in the 

cave. Therefore, if the present is the key to the 

past, then observations made at active sulfuric 

acid caves would indeed aid in our understanding of the speleogenesis of Guadalupe 

caves.

As discussed above, the spongework in 

Guadalupe caves clearly pre-dates the sulfuricacid dissolution phase by at least 240 million 

years (the caves are believed to be 2-12 million 

years old, as determined by 40Ar/39Ar dating of 

alunite, a potassium-clay mineral that can only 

form in acidic environments; Polyak and others, 

1998). Therefore, the age of the spongework, its 

existence along the perimeter and in between the 

large chambers having developed along the 

same fracture sets as the large chambers and 

passages, and that spongework remnants such as 

pendants and cupolas are seen in the bedrock of 

the large chambers, all suggest that the large 

chambers could be the result of enlargement of 

pre-existing spongework by sulfuric acid. The 

fact that most active sulfuric acid caves have 

spongework morphology has led some writers to 

think the relation is causal (e.g., Palmer, 2007). 

There are several reasons to believe otherwise: 

1) sulfuric acid is very corrosive, so there is no 

reason to believe that it would dissolve 

limestone preferentially, creating sculpted 

interconnecting holes as opposed to uniform 

dissolution, 2) it would be hard to explain how 

so many rock bridges remain, when they can be 

attacked from all sides, 3) the gypsum rinds 

conform uniformly to the morphology of the 

spongework (fig. 3), as opposed to producing it, 

and the rinds are not found in the interior of the 

peripheral spongework, where they would be 

expected to survive, and 4) this morphology is 

produced phreatically, which would require the 

sulfuric acid to be created subaqueously, which 

is not observed in active sulfuric acid caves.

Figure 3. Gypsum rind on spongework. Note how the rind 

conforms to the shape of the spongework, even inside the 

hole.
58

The relation between spongework and 

sulfuric acid appears to be related to the question 

of whether sulfuric acid forms subaqueously or 

subaerially, or both. Sulfuric acid in active caves 

is formed subaerially within the condensate on 

the walls. However, do the active sulfuric acid 

caves represent a late stage of development that 

is different from the initial stage, or are the 

observed processes consistent throughout the 

speleogenesis of these caves? This question is 

best answered by determining whether sulfuric 

acid can be formed subaqueously. 

Hill never included spongework as one of 

the controlling factors in cave development. This 

was because she believed that the hypogenic 

caves cut across the previous stage, and because 

she believed the sulfuric acid was in solution 

below the top of the water table, where hydrogen 

sulfide (H2S) gas rising through the brine water 

encountered oxygenated meteoric water and 

reacted with dissolved oxygen. But a review of 

the abiotic origin of sulfuric acid outside of 

caves and in the manufacturing process revealed 

that in each case, the acid forms in the 

atmosphere, not subaqueously. Sulfuric acid in 

its anhydrous form does not occur in nature 

because the hydration reaction is 

thermodynamically favorable (Ka1 = 2.4 x 106

), 

and so it has a strong affinity for water. Sulfuric 

acid is even used as a desiccant because of this 

property. The reaction is highly exothermic, and 

produces hydronium and sulfate according to the 

equations: H2SO4 + H2O → H3O + HSO4, and 

HSO4 reacts with water to form H3O + SO4 (Ka2

= 1.2 x 10-2

). Therefore, sulfuric acid would not 

form in a medium that strongly forces it to 

dissociate. 

Hill’s concept of H2S gas, produced by 

sulfate-reducing bacteria (SRB) thriving on the 

petroleum hydrocarbons that migrated up dip 

when the Delaware Basin tilted eastward during 

the Miocene uplift, bubbles up through brine 

water and reacts with dissolved oxygen in 

oxygenated meteoric water below the water 

table, is problematic on many accounts. The H2S 

would not degas at pressures greater than a 

meter or two below the water table (Palmer and 

Palmer, 2000), so a transport mechanism would 

be required to move aqueous H2S from deep in 

the basin where the petroleum deposits exist, to 

the water table within the shelf.

Hydrogen sulfide, which is only slightly 

soluble, reacts with water to form hydronium 

and HS: H2S + H2O → H3O + HS. At the pH 

range of seawater (7.5-8.4), most available H2S 

dissociates to HS (pK1 = 7 in pure water at 

25oC), and this occurs at lower pH with 

increasing salinity and temperature; HS is stable 

(pK2 = 17 at 25oC). Therefore, H2S would have 

dissociated in the saline groundwater before it 

could reach meteoric water, especially if the 

water was above 25oC.

Why would the meteoric water come to have 

such high levels of dissolved oxygen, which is 

usually low in mountainous areas due to a lack 

of soil (Palmer and Palmer, 2000)? This could 

only occur if the water was aerated as it traveled 

down epigenic conduits, which are not observed 

in Guadalupe caves, or there were air-filled 

cavities above the water table. 

The abiotic oxidation of H2S is very slow 

due to the lack of dissolved oxygen in 

groundwater and to kinetic constraints (Luther 

and others, 2011), but when it occurs in 

freshwater, it produces sulfur according to the 

equations: 2H2S(aq) + O2(aq) → 2H2O + 2S, or 

H2S(aq) + O2(aq) → H2O2 + S, not sulfuric acid. 

Biotic oxidation enhances the rate by three or 

more orders of magnitude, but the outcome is 

the same. This reaction most likely explains the 

occurrence of elemental sulfur found in sulfuric 

acid caves (e.g., Cueva de Villa Luz; Hose and 

Pisarowicz, 1999). If the source of H2S is the 

petroleum deposits in the basin, why has the 

sulfuric acid process ceased, as there is still 

plenty of oil, and the Delaware Mountain Group 

formations still contain “sulfur water”?

All abiotic occurrences of sulfuric acid (acid 

rain) do not start with H2S, but with oxidized 

sulfur, usually sulfur dioxide (SO2), which is 

oxidized in air (producing sulfur trioxide, SO3) 

in the presence of water vapor to form sulfuric 

acid. Sulfuric acid is the world’s most important 

industrial chemical, and the manufacturing 

process also starts with SO2, which is obtained 

by either burning sulfur, or as an alternative, 

incinerating H2S gas (2H2S + 3O2 → 2H2O + 

2SO2). In other words, the production of SO2 by 
59

the oxidation of H2S cannot occur abiotically in 

water, nor is it going to occur in air (heat of 

formation = -1,036 kilo Joules per mole 

[kJ/mol]; compare to S + O2 → SO2 = -297 

kJ/mol). The chemical equation that Hill used, 

H2S + 2O2 → H+ + HSO4 → 2H+ + SO4, while 

thermodynamically feasible (ΔG = -760.88 

kJ/mole for the first product), does not occur 

abiotically in water because of the kinetic 

constraints of three molecules of low concentrations due to low solubilities coming together 

at the same place at the same time to react. But 

can this reaction occur biotically in air? 

Gypsum rinds are a common feature of 

active sulfuric acid caves, including Carlsbad 

Cavern and other Guadalupe caves, and they are 

best explained by subaerial replacement of 

limestone by sulfuric acid in the condensate 

(Hose and Pisarowicz, 1999). In fact, this 

subaerial process is believed to account for the 

greatest volume of carbonate dissolution in 

Guadalupe caves and in the Frasassi caves in 

Italy (Palmer and Palmer, 2012, and Galdenzi 

and Maruoka, 2003, respectively). The domed 

cross-sectional shape of Carlsbad Cavern, with 

its flat floors representing the water table, 

suggests that this cave formed subaerially 

(Palmer and Palmer, 2012). For sulfuric acid to 

be generated at the water table, as what appears 

to be the case for the Guadalupe caves, a 

constant supply of sulfur and oxygen is required, 

as both are consumed with the dissolution of 

limestone. If sulfuric acid is formed subaerially, 

then subterranean, humid air space directly 

above the water table, large enough for 

condensation to occur and have air flow (oxygen 

has to be replenished), is required. The preexisting spongework would have provided such 

an environment, and would have provided the 

necessary supply of oxygen, especially if the 

spongework had small connections (fractures) to 

the outside. But what was the source of sulfur to 

create the sulfuric acid? 

The reason that Hill turned to H2S as the 

source of sulfur is because the δ34S isotopic 

values for the cave gypsum and sulfur are 

isotopically light (mean = -16.8 permil for 22 

samples), which she could only ascribe to the 

fractionation that occurs by reduction of sulfate 

in the evaporites in contact with petroleum by 

SRB. However, isotopically light δ34S values 

appear to be common in active sulfuric acid 

caves that are not near petroleum reservoirs 

(Hose and others, 2000; Galdenzi and Maruoka, 

2003). Another common feature of sulfuric acid 

caves is thermal, sulfate-rich, saline water. The 

main sulfur compound in seawater is sulfate; it 

is the third most abundant component of 

seawater by weight. H2S is a negligible 

dissolved-gas component (outside of microbial 

action) because it quickly dissociates. The 

isotopically light δ34S values can be explained 

by the fractionation due to SRB thriving in the 

thermal water near the aerobic/ anaerobic 

interface (water table). Perhaps the source of the 

high H2S content in the water of active sulfuric 

acid caves is due to sulfate reduction by SRB in 

the caves, rather than a possible source 

upgradient of the caves. The biofilms in the 

streams in the Frasassi cave system were found 

to include predominantly gamma- and deltaproteobacteria (Macalady and others, 2006).

A SULFURIC ACID SPELEOGENESIS

MODEL FOR GUADALUPE CAVES

The following model is based on studies of 

previous workers (Kirkland, 1982; Palmer and 

Palmer, 2000; Hose and others, 2000; Palmer, 

2006; Hose and Macalady, 2006), combined 

with the author’s own observations in the 4.5 

years working at Carlsbad Caverns National 

Park.

The cave morphology of typical flankmargin caves includes a large chamber with 

spongework along the perimeter, the chamber 

being the result of the holes coalescing in an 

area of more aggressive dissolution. The 

spongework extends inland into the limestone 

via fractures or other secondary porosity. The 

spongework is the result of mixing corrosion at 

the freshwater lens/seawater boundary, and near 

the coastline where the freshwater lens is 

thinnest and the tidal action is more aggressive 

(Mylroie and Carew, 1990). This scenario is 

easily superimposed onto the geologic setting of 

the Guadalupe Mountains, an emergent reef 

complex due to the closure of the Delaware Sea 

260 ma. Basinward tilting of the reef complex 

by syndepositional subsidence caused tensional 

fractures to develop parallel to the reef 

escarpment, as well as a nearly perpendicular 
60

conjugate set. These fractures, along with the 

vuggy porosity of the Capitan Reef massive, 

provided the avenues for both the infiltration of 

meteoric water and the horizontal penetration of 

seawater. At the fresh/salt water boundary, 

mixing corrosion occurred initially along these 

fractures, especially at intersections, but spread 

laterally as the fractures were enlarged, 

producing spongework caves at sea level. The 

vertical extent of the spongework indicates that 

either sea level dropped 207 meters after the 

Capitanian, or the western side of the basin was 

being tilted. Many of the caves in the Guadalupe 

Mountains occur near the escarpment, the late 

Permian coastline (Palmer and Palmer, 2000, 

fig. 2). Once the mixing zone intersected the 

backreef formations, spongework also began to 

develop along bedding planes (e.g., Spider 

Cave). 

During Miocene Basin and Range tensional 

faulting, three western sections of the buried reef 

ring were in the path of the north-northwesttrending uplift. The section now known as the 

Guadalupe Mountains broke perpendicular to the 

reef at the Border Fault and was thrust upward at 

the fault about 1,500 meters from its late 

Permian position, analogous to pulling on a tire 

buried in the sand, where the tire was cut in two. 

The uplift was episodic, as evidenced by the flat 

cave floors at different levels, which represent 

long stands of the water table. This period was 

accompanied by rifting, flood basalts, igneous 

intrusions, and heating of the crust to over 50oC 

(Barker and Pawlewicz, 1987). This paleogeothermal gradient would have heated the 

groundwater as well, producing thermal 

convection upwelling. In Carlsbad Cavern, this 

upwelling may have occurred as a thermal 

spring at the Bottomless Pit, which is currently 

18 meters deeper than Lower Cave (the lowest 

water table stand within the cave), the floor of 

which is very sandy, with stoped breakdown 

blocks. Another possible thermal spring may 

have occurred at Lake of the Clouds (63 meters 

deeper). The potentiometric surface for both 

springs was at the level of the Big Room floor at 

the time this chamber was enlarging. Bottomless 

Pit, which is on the same fracture as the large 

chambers of Lower Cave, was most likely the 

spring that also fed Lower Cave when the 

potentiometric surface was at that level, but the 

breakdown floor at the southwest end of the Big 

Room is covering the connection. Devil’s Den 

may have been a thermal spring when the Main 

Corridor was enlarging, with the current bottom 

of the pit, where a gypsum block and rinds 

remain, being the potentiometric surface. 

SRB, most likely thermophiles (40-70o

C 

temperature range, with 50o

C optimum), were 

thriving near the air/water interface in this 

warm, anaerobic, sulfate-rich brine water, with 

the densest colonies (biofilms and mats) at the 

spring orifices. The sulfate reduction produced 

H2S, most of which was released as a gas to the 

air-filled spongework above the water table. 

Some of the H2S dissolved in the brine water 

could have oxidized abiotically to SO3 (as well 

as to sulfur; Zhang and Millero, 1993), which 

then hydrated in the humid atmosphere to create 

sulfuric acid vapor that would eventually 

condense on the cooler walls and ceilings, but 

could travel away from the spring. The H2S gas 

would have adsorbed onto the film of condensed 

and/or seeped water on the walls, where abiotic 

and biotic oxidation occurs using the oxygen in 

the cave atmosphere; this oxidation produces 

elemental sulfur. The sulfur is further oxidized 

by aerobic sulfur-oxidizing bacteria (SOB), such 

as Acidithiobacillus sp., to form sulfuric acid 

(Hose and others, 2000). The sulfur folia on the 

walls of sulfuric acid caves may be a remnant of 

this process. 

Sulfuric acid generation would not have 

extended far from a thermal spring, due to the 

water becoming cooler with distance–not a 

conducive environment for mesophilic or 

thermophilic bacteria. The sulfuric acid caused 

the outer layer of limestone to be replaced with 

gypsum as a rind. This replacement could only 

penetrate into the limestone a limited depth, 

usually 5-15 centimeters, due to the rind acting 

as a barrier. The rinds allowed the H2S gas and 

acid vapor to travel farther down passage in the 

direction of air flow. The ceiling height in the 

Big Room, which decreases from about 60 

meters at the southwest end to about 6 meters at 

the northeast end, indicates that the acid was 

generated at the southwest end, and that the air 

flow was toward the Main Corridor at the 

northeast end. Once the cave system opened to 
61

the atmosphere by breaching the surface, H2S, 

which is heavier than air, would rise higher in 

the cave due to barometric convection and 

thermal gradients. This breach must have 

already occurred by the time the water table was 

at the level of the Big Room, as the rillenkarren 

on the limestone breakdown blocks of Appetite 

Hill (in the borehole passage between the Main 

Corridor and the Big Room) indicates that 

sulfuric acid condensate was still dripping at the 

point of ascension after the collapse. Original 

spongework is extant in the areas peripheral to 

the main path of air flow, as evidenced by the 

absence of gypsum rinds in the interior of the 

spongework.

The weight of a rind would cause it to peel 

off of inclined surfaces. As each rind fell off the 

walls and ceiling, a new layer of limestone 

became exposed to the acid, and the process 

would repeat itself, enlarging the spongework 

into the huge chambers we see today. The 

spongework provided greater surface area and 

less rock to dissolve. The height of the chambers 

and passages appears to have been controlled by 

both the vertical extent of the spongework (it 

does not continue above the ceilings) and the 

horizontal distance from the acid source. Above 

the Bottomless Pit spring orifice, the ceiling was 

under constant acid attack and a dome was 

created (Liberty Dome). Subsequent stoping 

increased the ceiling height where closely 

spaced vertical fractures occurred (e.g., southwest end of the Big Room and Appetite Hill). 

The fallen rinds dissolved in the water, 

causing the water table to become saturated in 

gypsum, which eventually precipitated out as a 

blanket that covered the floor wall-to-wall as 

much as 10 meters thick (Hill, 1996). Much of 

this gypsum blanket is now gone due to 

dissolution by dripping meteoric water, and left 

the cave system as the water table lowered. 

There is a very close, modern analog to this 

model of sulfuric acid speleogenesis, which has 

been studied since the mid-1940s (Parker, 1951), 

decades before the concept was applied to caves. 

It is called biogenic sulfide corrosion, and 

occurs in concrete sanitary wastewater pipes and 

tanks (USEPA, 1992). When the wastewater 

flow is sluggish and there is air space above it, 

SRB thrive in the anaerobic, sulfate-rich water 

as a biofilm that coats the wall of the submerged 

portion of the pipe. The produced H2S that 

volatilizes into the humid air space diffuses into 

the condensate on the pipe wall. SOB thriving in 

that water oxidize the H2S through a series of 

steps via sulfur to produce sulfuric acid. Abiotic 

oxidation also occurs, but the reaction is slow 

and proceeds via thiosulfate (S2O3) (Okabe and 

others, 2005). The acid corrodes the pipe wall, 

most intensely at the crown (where drips 

accumulate) and just above the water line, by 

converting the calcium carbonate in the concrete 

into gypsum rinds. The gypsum is usually 

dissolved away by high wastewater flow, 

leaving pitted walls of reduced thickness. 

Unreacted acid runs down the pipe wall, 

producing rills.

When this scenario is compared to an active 

sulfuric acid cave like Cueva de Villa Luz, the 

similarities seem to outweigh the differences. In 

both scenarios, sulfuric acid is generated 

subaerially and biotically by oxidizing elemental 

sulfur.

CONCLUSIONS

Not all the caves in the Guadalupe 

Mountains were formed by spongework 

enlargement, especially for those caves that 

developed above and beyond the reaches of tidal 

mixing, where no mixing corrosion occurred. 

Based on a comparison of Carlsbad Cavern with 

active sulfuric acid caves, it appears that the 

geologic setting must include three features for 

sulfuric acid hypogene speleogenesis to occur: 

1) Pre-existing cavernous porosity 

(sufficient air space for condensation and air 

flow) in the carbonate rock to allow sulfuric acid 

to form above the water table as a vapor and 

within condensate. In the Guadalupe Mountains, 

and perhaps in many sulfuric acid caves, this 

pre-existing porosity appears to have been 

spongework, not phreatic conduits.

2) Subterranean springs of sulfate-rich 

groundwater (seawater or brine water) to allow 

SRB to flourish near the top of the water table 

and produce H2S as a byproduct.

3) A geothermal heat source to heat the 

groundwater to cause upwelling, creating an 
62

environment where meso- and/or thermophilic 

SRB can thrive, and a thermal gradient between 

the groundwater and the walls above the water 

table to promote condensation and an 

environment for SOB to thrive.

A geologic setting where all three features 

combine to produce sulfuric acid caves is 

relatively rare, but includes proximity to a sea or 

a former sea basin with evaporites. This would 

explain the common combination of 

spongework and sulfate-rich groundwater. The 

relation between petroleum reservoirs and 

sulfuric acid caves is a shared geologic setting–

basins. However, the relation ends there. That 

minor quantities of oil can migrate up from the 

basin via fractures and seep into sulfuric acid 

caves on the edge of the platform is not 

surprising, but it is not a forgone conclusion that 

the petroleum is the source of the H2S. That H2S 

is being produced by SRB in connection with 

high petroleum deposits in the Delaware Basin 

is not doubted. However, petroleum-derived 

H2S(aq) in the brine water would remain 

undissociated under lithostatic pressure, 

allowing it to oxidize abiotically to sulfur upon 

mixing with meteoric water, as is found in the 

Ochoan evaporites (Davis and Kirkland, 1970), 

or dissociate as it approaches the water table. 

Only when H2S is produced near the water table 

can it be expected to enter air-filled cavities as a 

gas.

An excellent example of how a sulfuric acid 

cave can transition from active to relic by the 

removal of requirements 2 and 3 outlined above 

can be observed by comparing the difference 

between Upper and Lower Kane Caves in Big 

Horn Basin, Wyoming. Upper Kane Cave is 

believed to be a relic sulfuric acid cave directly 

above (about 30 meters) and air-connected to 

Lower Kane Cave, an active sulfuric acid cave 

(Hose and Macalady, 2006). The reason that 

Upper Kane Cave is relic is because base level 

lowered and the thermal, sulfate-bearing stream 

now runs through Lower Kane Cave. SOB 

cannot thrive in a dry environment.

Spongework is not a common cave 

speleogen, so any theory of its origin must take 

this into account (a single process is more likely 

than two unrelated processes). Outside of 

sulfuric acid caves, spongework is believed to be 

the result of phreatic mixing corrosion at the 

freshwater/seawater interface of a coastal 

aquifer. The speleogens that are the product of 

sulfuric acid dissolution include walls that are 

pitted and have upward-pointing scallops from 

convective air currents. The absence of these 

speleogens and gypsum rinds in the peripheral 

spongework indicates that it was outside the 

reaches of sulfuric acid dissolution and is 

original. Both chemistry and modern analogs 

indicate that sulfuric acid is not generated 

subaqueously. Therefore, the pre-existing 

spongework provided the necessary air space 

above the water table for sulfuric acid to form 

subaerially, mostly by SOB. Without the preexisting spongework, sulfuric acid would never 

have formed. Sulfuric acid forms abiotically 

from sulfur oxides, so the sulfuric acid equation 

commonly used, H2S + 2O2 → H2SO4, is 

actually shorthand for a two to four step process 

of oxidation, which is greatly enhanced by SOB. 

The process of sulfuric acid enlargement of preexisting porosity (spongework) only lasted as 

long as the high heat flow from the Basin and 

Range crustal thinning and igneous intrusions 

(about 20-0 ma), which provided a warm, saline 

water environment for thermophilic SRB to 

thrive in and produce abundant H2S. Perhaps an 

active sulfuric acid cave like Cueva de Villa Luz 

is more of a modern analog to the relic caves of 

the Guadalupe Mountains than initially 

perceived, the only significant difference being 

that Guadalupe caves were not resurgent caves.

REFERENCES

Barker, C.E., and Pawlewicz, M.J., 1987, The effects 

of igneous intrusions and higher heat flow on the 

thermal maturity of Leonardian and younger 

rocks, western Delaware Basin, Texas, in

Cromwell, Dave, and Mazzullo, L.J., eds., The 

Leonardian facies in west Texas and southeast 

New Mexico and guidebook to the Glass 

Mountains, West Texas: SEPM-Permian Basin 

Section, Publication No. 87-27, p. 69-84.

Bogli, Alfred, 1980, Karst hydrology and physical 

speleology: New York, Springer-Verlag, 284 p.

Bretz, J.H., 1942, Vadose and phreatic features of 

limestone caverns: Journal of Geology, v. 50, no. 

6, p. 675-811.
63

Bretz, J.H., 1949, Carlsbad Caverns and other caves 

of the Guadalupe block, New Mexico: Journal of 

Geology, v. 57, no. 5, p. 447-463.

Davis, J.B., and Kirkland, D.W., 1970, Native sulfur 

deposition in the Castile Formation, Culberson 

County, Texas: Economic Geology, v. 65, p. 

107-121.

Galdenzi, Sandro, and Maruoka, Teruyuki, 2003, 

Gypsum deposits in the Frasassi Caves, central 

Italy: Journal of Cave and Karst Studies, v. 65, 

no. 2, p. 111-125.

Hill, C.A., 1996, Geology of the Delaware Basin -

Guadalupe, Apache, and Glass Mountains, New 

Mexico and west Texas: SEPM-Permian Basin 

Section, Publication No. 96-39, 480 p.

Hill, C.A., 2006, Geology of the Guadalupe 

Mountains: An overview of recent ideas, in

Land, Lewis, and others (eds.), Caves and karst 

of southeastern New Mexico: New Mexico 

Geological Society, 57th Annual Field 

Conference, Socorro, September 21-24, 2006, p. 

145-150.

Hose, L.D., and Macalady, J.L., 2006, Observations 

from active sulfidic karst systems: Is the present 

the key to understanding Guadalupe Mountain 

speleogenesis?, in Land, Lewis, and others 

(eds.), Caves and karst of southeastern New 

Mexico: New Mexico Geological Society, 57th

Annual Field Conference, Socorro, September 

21-24, 2006, p. 185-194.

Hose, L.D., Palmer, A.N., Palmer, M.V., Northup, 

D.E., Boston, P.J., and Duchene, H.R., 2000, 

Microbiology and geochemistry in a hydrogensulphide-rich karst environment: Chemical 

Geology, v. 169, p. 399-423.

Hose, L.D., and Pisarowicz, J.A., 1999, Cueva de 

Villa Luz, Tabasco, Mexico: Reconnaissance 

study of an active sulfur spring cave and 

ecosystem: Journal of Cave and Karst Studies, v. 

61, no. 1, p. 13-21.

Hunt, D.W., Fitchen, W.M, and Kosa, Eduard, 2002, 

Syndepositional deformation of the Permian 

Capitan reef carbonate platform, Guadalupe 

Mountains, New Mexico, USA: Sedimentary 

Geology, v. 154, p. 80-126.

Kirkland, D.W., 1982, Origin of gypsum deposits in 

Carlsbad Caverns, New Mexico: New Mexico 

Geology, v. 4, p. 20-21.

Klimchouk, A.B., Ford, D.C., Palmer, A.N., and 

Dreybrodt, Wolfgang, (eds.), 2000, 

Speleogenesis: Evolution of karst aquifers: 

Huntsville, Alabama, National Speleological 

Society, 527 p.

Kosa, Eduard, and Hunt, D.W., 2006, Heterogeneity 

in fill and properties of karst-modified 

syndepositional faults and fractures: Upper 

Permian Capitan platform, New Mexico, USA: 

Journal of Sedimentary Research, v. 76, p. 131-

151.

Luther, G.W., III, Findlay, A.J., MacDonald, D.J., 

Owings, S.H., Hanson, T.E., Beinart, R.A., and 

Girguis, P.R., 2011, Thermodynamics and 

kinetics of sulfide oxidation by oxygen: A look 

at inorganically controlled reactions and 

biologically mediated processes in the 

environment: Frontiers in Microbiology, v. 2, 62.

Macalady, J.L., Lyon, E.H., Koffman, Bess, 

Albertson, L.K., Meyer, Katja, Galdenzi, Sandro, 

and Mariani, Sandro, 2006, Dominant microbial 

populations in limestone-corroding stream 

biofilms, Frasassi Cave system, Italy: Applied 

and Environmental Microbiology, v. 72, no. 8, p. 

5596-5609.

Mylroie, J.E., and Carew, J.L., 1990, The flank 

margin model for dissolution cave development 

in carbonate platforms: Earth Surface Processes 

and Landforms, v. 15, p. 413-424.

Okabe, Satoshi, Ito, Tsukasa, Sugita, Kenichi, and 

Satoh, Hisashi, 2005, Succession of internal 

sulfur cycles and sulfur-oxidizing bacteria 

communities in microaerophilic wastewater 

biofilms: Applied and Environmental 

Microbiology, v. 71, no. 5, p. 2520-29.

Palmer, A.N., 1975, The origin of maze caves: 

National Speleological Society Bulletin, v. 37, p. 

56-76.

Palmer, A.N., 1991, Origin and morphology of 

limestone caves: Geological Society of America 

Bulletin, v. 103, p. 1-21.

Palmer, A.N., 2005, Passage growth and 

development, in Culver, David C., and White, 

William B. (eds.): Encyclopedia of Caves, p. 

440-444.

Palmer, A.N., 2006, Support for a sulfuric acid origin 

for caves in the Guadalupe Mountains, New 

Mexico, in Land, Lewis, and others (eds.), Caves 

and karst of southeastern New Mexico: New 

Mexico Geological Society, 57th Annual Field 

Conference, Socorro, September 21-24, 2006, p. 

195-202.

Palmer, A.N., 2007, Cave geology: Dayton, OH, 

Cave Books, 454 p.
64

Palmer, A.N., and Palmer, M.V., 2000, 

Hydrochemical interpretation of cave patterns in 

the Guadalupe Mountains, New Mexico: Journal 

of Cave and Karst Studies, v. 62, no. 2, p. 91-

108.

Palmer, A.N., and Palmer, M.V., 2012, Petrographic 

and isotopic evidence for late-stage processes in 

sulfuric acid caves of the Guadalupe Mountains, 

New Mexico, USA: International Journal of 

Speleology, v. 41, no. 2, p. 231-250.

Parker, C.D., 1951, Mechanics of corrosion of

concrete sewers by hydrogen sulfide: Sewage 

and Industrial Wastes, v. 23, no. 12, p. 1477-

1485.

Plummer, L.N., 1975, Mixing of sea water with 

calcium carbonate ground water: Geological 

Society of America Memoir 142, p. 219-236.

Polyak, V.J., McIntosh, W.C., Guven, N., and 

Provencio, P., 1998, Age and origin of Carlsbad 

Caverns and related caves from 40Ar/39Ar of 

alunite: Science, v. 279, p. 1919-1922.

Saller, A.H., 1996, Differential compaction and 

basinward tilting of the prograding Capitan Reef, 

Permian, west Texas and southeast New Mexico, 

USA: Sedimentary Geology, v. 101, p. 21-30.

U.S. Environmental Protection Agency (USEPA), 

1992, Detection, control, and correction of 

hydrogen sulfide corrosion in existing 

wastewater systems: EPA No. 832R92001, 162 

p.

U.S. Environmental Protection Agency (USEPA), 

2002, Lexicon of cave and karst terminology: 

http://www.karstwaters.org/files/glossary.pdf.

White, W.B., 1988, Geomorphology and hydrology 

of karst terrains: New York, Oxford University 

Press, 464 p.

Zhang, Jia-Zhong, and Millero, F.J., 1993, The 

products from the oxidation of H2S in seawater: 

Geochimica et Cosmochimica Acta, v. 57, p. 

1705-1718.
65

Geologic Framework, Structure, and Hydrogeologic Characteristics of 

the Knippa Gap Area in Eastern Uvalde and Western Medina Counties, 

Texas

By Allan K. Clark, Diana E. Pedraza, and Robert R. Morris 

U.S. Geological Survey, 5563 De Zavala Rd., San Antonio, TX, 78249

Abstract

The Edwards aquifer is the primary source of potable water for the San Antonio area in south-central 

Texas. The Knippa Gap area was postulated to channel or restrict flow in the Edwards aquifer in eastern 

Uvalde County, and its existence was based on a series of numerical simulations of groundwater flow in 

the aquifer. To better understand the function of the area known as the Knippa Gap as it pertains to its 

geology and structure, the geologic framework, structure, and hydrogeologic characteristics of the area 

were evaluated by the U.S. Geological Survey in cooperation with the U.S. Army Corps of Engineers Fort 

Worth District. The principal structural feature in the San Antonio area is the Balcones Fault Zone, which 

is the result of Miocene-age faulting. Groundwater flow paths in the Edwards aquifer are influenced by 

faulting and geologic structure. Some faults act as barriers to groundwater flow where the aquifer is offset 

by 50 percent or more and result in flow moving parallel to the fault. The effectiveness of a fault as a 

barrier to flow changes as the amount of fault displacement changes. 

The structurally complex area of the Balcones Fault Zone contains relay ramps, which form in 

extensional fault systems to allow for deformation changes along the fault block. In Medina County, the 

faulting of the Balcones Fault Zone has produced a relay ramp that dips to the southwest from the 

Edwards aquifer recharge zone and extends westward and below land surface from Seco Creek. In the 

northern part of the county, groundwater moves downgradient (downdip) to the southwest along this relay 

ramp towards a structural low (trough). In Uvalde County, groundwater also moves downdip from a 

structural high known as the Uvalde Salient towards a structural low (trough) to the northeast. These two 

opposing structural dips result in a subsurface structural low locally referred to as the Knippa Gap. This 

trough is located in eastern Uvalde County beneath the towns of Knippa and Sabinal. By using data that 

were compiled and collected for this study and previous studies, a revised map was constructed depicting 

the geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern 

Uvalde and western Medina Counties, Texas. The map also shows the interpreted structural dip directions 

and interpreted location of the structural low in the area known as the Knippa Gap.

REFERENCE

Clark, A.K., Pedraza, D.E., and Morris, R.R., 2013, Geologic framework, structure, and hydrogeologic 

characteristics of the Knippa Gap area in eastern Uvalde and western Medina Counties, Texas: U.S. Geological 

Survey Scientific Investigations Report 2013–5149, 35 p., 1 pl., http://pubs.usgs.gov/sir/2013/5149/.
66

A Hypothesis for Carbonate Island Karst Aquifer Evolution from 

Analysis of Field Observations in Northern Guam, Mariana Islands 

By John W. Jenson1, Danko Taboroši1, Kolja Rotzoll2, John E. Mylroie3, and Stephen B. 

Gingerich4

1

Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, GU 

96923

2

Water Resources Research Center, University of Hawaii, Honolulu, HI 96822

3

Department of Geosciences, Mississippi State University, Mississippi State, MS 39762

4

Pacific Islands Water Science Center, U.S. Geological Survey, Honolulu, HI 96813

Abstract

Field studies of coastal discharge and aquifer properties on northern Guam, an uplifted eogenetic 

karst plateau, suggest carbonate island karst aquifers undergo profound reorganization of porosity and 

permeability and develop complex but predictable patterns of hydraulic conductivity, internal transport, 

and coastal discharge. Discharge features along the coast can be classified into four geomorphic 

categories: beach seeps and springs, reef seeps and springs, fracture springs, and cave springs. The styles 

and distribution of discharge among these four categories suggest that in aquifers composed of uplifted 

geologically young limestone, matrix, fracture, and conduit porosity each play significant but varying 

roles. Analyses of tidal attenuation in wells across the plateau indicate that hydraulic conductivity near the 

periphery is two orders of magnitude lower than in the interior: 20-800 meters/day, compared to 2,000-

90,000 meters/day. We propose a conceptual framework that relates the four categories of coastal 

discharge to the evolution and reorganization of porosities in the aquifer, and offer a hypothesis for the 

general distribution of hydraulic conductivity on uplifted carbonate island aquifers, in particular the 

juxtaposition of high conductivity in the interior against lower conductivity on the periphery: (1) 

dissolutional enhancement of horizontal hydraulic conductivity in the interior, (2) concurrent reduction of 

local hydraulic conductivity in the cliffs and steeply inclined rocks on the periphery by case hardening 

and perhaps other karst processes that promote occlusion of primary porosity on and inland of the 

rampart, and (3) development of the stronger influence of higher conductivity regional-scale features in 

the interior relative to the periphery. Complexity is further increased by glacioeustasy and tectonic 

fluctuations that moved the freshwater lens vertically through the bedrock column and forced 

reorganization of porosities within horizontal planes at different levels.

REFERENCES

Gingerich, S.B., 2013, The effects of withdrawals and drought on groundwater availability in the northern Guam 

Lens aquifer, Guam: U.S. Geological Survey Scientific Investigations Report 2013–5216, 76 p., 

http://dx.doi.org/10.3133/sir20135216.

Rotzoll, Kolja, Gingerich, S.B., Jenson, J.W., and El-Kadi, A.I., 2013, Estimating hydraulic properties from tidal 

attenuation in the northern Guam Lens aquifer, territory of Guam, USA: Hydrogeology Journal, v. 21, p. 643–

654, DOI 10.1007/s10040-012-0949-9.
67

Using Borehole and Surface Geophysics to Develop a Conceptual 

Model of Hydrostratigraphic Layers, Pecos County Region, Texas, 

2012 

By Jonathan V. Thomas, Johnathan R. Bumgarner, Gregory P. Stanton, Andrew P. 

Teeple, and Jason D. Payne

U.S. Geological Survey, 2775 Altamesa Blvd., Fort Worth, TX 76133 

Abstract

Future groundwater availability is a concern in the Pecos County region of west Texas, where the 

Edwards-Trinity aquifer is an important water resource. The U.S. Geological Survey (USGS), in 

cooperation with the Middle Pecos Groundwater Conservation District, Pecos County, City of Fort 

Stockton, Brewster County, and Pecos County Water Control and Improvement District No. 1, developed 

a conceptual model of the Edwards-Trinity aquifer as part of a multi-phase study of the Pecos County 

region. Interpreting the hydrostratigraphic layer contacts from historic and newly collected borehole 

geophysical logs, surface geophysical soundings, and geologic data was a major part of model 

development. Approximately 200 borehole geophysical logs and 300 well reports, along with 4 timedomain electromagnetic soundings, and 13 audio-magnetotelluric soundings were correlated to determine 

tops and bases of the aquifer (hydrostratigraphic) layers. Data collected by the USGS during 2009-11 and 

historical data from 1930-2011 collected by various state and local agencies were used in the model. 

Previous studies in this region indicate that groundwater flow is largely controlled by collapse structures 

and associated faulting. Multiple north-south and east-west geologic sections were constructed from 

hydrostratigraphic surface grids across the Pecos County region to analyze fault zones and local structural 

features. Updated grids were created to reflect the fault displacement associated with fault zones, in many 

cases showing units juxtaposed across the fault zone. The resulting hydrostratigraphic grids were used 

along with geochemistry and hydraulic-property data to develop the conceptual model, which aids in 

understanding the hydrogeologic framework, geochemistry, and groundwater-flow system. This 

information will be used to construct a groundwater flow model of the region. Additional information on 

this study can be found online at http://pubs.usgs.gov/sir/2012/5124/pdf/SIR12-5124.pdf.
68

Perils of a Dissolving State—Florida

By Clint Kromhout

Florida Geological Survey, Department of Environmental Protection, 903 West Tennessee Street, 

Tallahassee, Florida 32304

Abstract

Florida is no stranger to tropical storms or sinkholes, and for many who live in the state their primary 

worry is focused on the state’s annual hurricane season. Sinkholes, however, have become a storm of 

their own in recent years. In June 2012, Tropical Storm Debby dropped record amounts of rain upon 

Florida during a time of extended drought, which triggered hundreds of sinkholes that resulted in property 

damage across a wide swath of the state. Several subsequent well-publicized sinkhole events in Florida, 

combined with pervasive insurance industry financial troubles, have brought these natural karst features 

to main stage. The Florida Division of Emergency Management (DEM), a first responder to many of 

these sinkhole incidents, sought a science-based solution to assessing regional sinkhole vulnerability. In 

September 2013, the DEM’s Mitigation Section contracted with the Florida Geological Survey to produce 

a statewide map depicting relative vulnerability to sinkhole formation.
69

MODELING KARST AQUIFERS

Taking the Mystery Out of Mathematical Model Applications to Karst 

Aquifers—A Primer

By Eve L. Kuniansky

U.S. Geological Survey, 1770 Corporate Drive, Suite 500, Norcross, GA 30093

Abstract

Advances in mathematical model applications toward the understanding of the complex flow, 

characterization, and water-supply management issues for karst aquifers have occurred in recent years. 

Different types of mathematical models can be applied successfully if appropriate information is available 

and the problems are adequately identified. The mathematical approaches discussed in this paper are 

divided into three major categories: 1) distributed parameter models, 2) lumped parameter models, and 3) 

fitting models. The modeling approaches are described conceptually with examples (but without 

equations) to help non-mathematicians understand the applications.

INTRODUCTION 

Understanding the nature of karst aquifers, 

including their management and protection, 

poses unique challenges. Advances have been 

made in the development (codes developed in 

late 1970s through 90s) and use of mathematical 

model applications (late 1980s to present) to

improve the understanding of dual flow 

processes as well as characterization and 

management of karst aquifers. 

Several different types of mathematical 

models can be applied to problems in complex 

dual or triple porosity karst aquifers. Depending 

on the types of data available and the problems 

that are identified, different mathematical 

techniques can be applied appropriately. The 

naming of the types of mathematical models that 

have been applied has become somewhat 

confusing because terminology has not been 

used consistently among all authors. This paper 

groups the different mathematical approaches 

into three major categories: 1) distributed

parameter models, 2) lumped parameter models, 

and 3) fitting models. The three categories were 

chosen based on the general mathematical 

methods applied in the calculations. The 

modeling approaches are described conceptually

with examples (but without equations) to help 

non-mathematicians understand the applications. 

The first category, distributed parameter or 

deterministic numerical models, includes models 

derived for physical processes defined by partial 

differential equations, which are solved 

numerically. This first category of mathematical 

models is used to simulate flow in a karst aquifer 

as inferred from hydrogeologic investigations of 

all types. The second category, lumped 

parameter models, is based on mathematical 

methods that combine a physically based 

equation (ordinary differential equation) with 

control theory or operations research techniques 

(Hillier and Lieberman, 1967; Takahashi and 

others, 1972; U.S. Department of Agriculture, 

1973). This second category has some physical 

basis, but generally lumps the karst aquifer into 

large basins and is not meant to simulate details 

of the flow system. This type of model also is 

incapable of distinguishing between different 

system compartments and different flow 

processes. Many of the hydrogeochemical 

mixing models used for estimating the average 

age of water (binary mixing, piston flow, 

exponential, and dispersion) fall into this 

category (Maloszewski, 2000; Katz, 2004). The 

third category, fitting models, refers to 

mathematical methods that involve either 

statistical regression, fitting shape functions, 

statistical transfer functions, or use of pattern 

recognition functions, such as artificial neural 

networks to recreate observations (Long and 

Putnam, 2002, 2007; Hu and others, 2007). 

There is some overlap in the mathematical 

methods employed in the categories of lumped 

parameter models and fitting models, because

both categories involve mathematical techniques 
70

that come from the fields of control theory 

(sometimes called operations research) or linear 

systems theory (U.S. Department of Agriculture, 

1973). 

DISTRIBUTED PARAMETER MODELS

Distributed parameter models, also called 

deterministic numerical models, are frequently 

applied to karst aquifer systems (Teutsch and 

Sauter, 1998; Scanlon and others, 2003). 

Distributed parameter models are process 

oriented: equation(s) are derived that include the 

important physical process (es) that result in a 

partial differential equation(s) that can be solved

numerically. In general, the physical processes 

involved in the flow of water through an aquifer 

are simplified in order to develop an equation 

that can be solved by a numerical method, such 

as finite element or finite difference. Because 

distributed parameter models require dividing 

(discretizing) the system into smaller volumes, 

such as finite-difference cells or finite elements, 

representation of the karst aquifer is greatly 

simplified, but the physical parameters, such as 

storage, hydraulic conductivity, or transmissivity 

are distributed spatially and allowed to vary in 

each cell or element. 

Several types of deterministic models have 

been applied to karst aquifers (fig. 1). The 

simplest method is called the single continuum 

porous equivalent, potential flow,

Figure 1. Approaches to karst modeling with deterministic 

numerical models and some stochastic methods for 

developing fracture networks, where the networks are 

simulated with flow equations for pipes or fractures (from 

Teutsch and Sauter, 1998).

heterogeneous continuum, distributed parameter, 

or smeared conduit approach. Another method is

called the dual continuum porous equivalent 

approach (DCPE), which links two flow regimes 

at each cell or element with an exchange term. 

The hybrid model (HM) couples a single 

continuum porous equivalent model with a 

discrete one-dimensional pipe network. The last 

two examples are the discrete single-fracture set 

(DSFS) and the discrete multiple fracture set 

(DMFS) models, which may involve the 

stochastic generation of fracture networks;

however, the networks once generated are 

simulated with equations for pipe or fracture 

flow. Each approach has advantages and 

disadvantages, described below (fig. 1).

Single Continuum or Porous Equivalent 

Models

A single continuum porous equivalent 

approach using the groundwater flow equation 

based on laminar flow is the simplest to apply. 

Generally, this approach has been applied for 

regional flow problems because the investigation 

scale is much greater than the scale of the 

heterogeneities (conduits), and for waterresources investigations in which the models can 

be calibrated to flow and head information and 

only water budgets are desired (Kuniansky and 

Holligan, 1994; Davis, 1996; Teutsch and 

Sauter, 1998; Kuniansky and others, 2001; 

Svensson, 2001; Scanlon and others, 2003; 

Davis and Katz, 2007; Davis and others, 2010). 

In general, this approach can simulate transient 

springflow for monthly or annual averages, but 

may not reproduce detailed storm event 

hydrographs as well as other model types as a 

result of the onset of turbulence during storms 

(Hill and others, 2010; Kuniansky and others, 

2011; Gallegos and others, 2013; Saller and 

others, 2013). However, simulations of 

advective transport using a single continuum 

model are frequently performed and are able to 

match geochemical age estimates and tracer-test 

times of travel when using a porosity of less than 

5 percent (Knochenmus and Robinson, 1996; 

Kuniansky and others, 2001; Renken and others, 

2005; Davis and others, 2010). The flow in these 

studies was mainly determined by the model cell 

hydraulic conductivity and total model layer 

thickness. In some cases where conduit locations 

are known, the finite-difference cells with 

conduits are assigned much greater hydraulicconductivity values than surrounding cells and 

have been successful in reproducing transient 

spring discharge and matching tracer tests in part 

of the Floridan aquifer system (Davis and others, 
71

2010). A similar attempt was not successful 

within the Edwards aquifer system (Lindgren 

and others, 2009). 

Both finite difference and finite element 

methods have been widely applied. Finite 

element methods allow for greater variation in 

element size, and streams, wells, and springs can 

be more accurately located. Finite elements 

readily accommodate sites where geologic 

structure results in preferential directions of 

dissolution that can create anisotropy varying in 

direction over the aquifer domain (Kuniansky 

and Lowther, 1993). However, developing 

model datasets for a finite-element model is 

more complex than a block-centered finitedifference scheme, and a graphic-user interface 

(GUI) is essential. As computer speeds have 

increased, so has the simulation speed of larger 

finite-difference model grids with smaller grid 

spacing. Additionally, packages such as the 

horizontal flow barrier package for MODFLOW 

(Hsieh and Freckleton, 1993) have been used to 

help incorporate geologic structure that reflects 

anisotropy rather than direct incorporation of 

anisotropy into the flow equation (Lindgren and 

others, 2004). The new code for MODFLOW 

that allows unstructured grids has many of the 

advantages of finite elements, but also requires a 

sophisticated GUI (Panday and others, 2013).

Most single-continuum applications 

described above involve simulating laminar 

flow. The most commonly used computer code 

is MODFLOW 

(http://water.usgs.gov/ogw/modflow/). However, 

turbulent flow for large-pore aquifers, where 

flow becomes turbulent at low Reynolds 

numbers, has been incorporated as an option into 

MODFLOW-2005, called the conduit flow 

process mode 2 (MODFLOW-CFP mode 2; 

Shoemaker and others, 2008; Kuniansky and 

others, 2008). Reimann and others (2011a) 

derived a general form for incorporation of 

turbulence into MODFLOW-CFP mode 2, 

which can simulate turbulence for porous media 

or conduits, employing a single continuum 

approach.

Dual Continuum or Porous Equivalent 

Models

Dual continuum models link two single 

continuum models via a hydraulic headdependent flux term between each model cell. 

One continuum has high hydraulic conductivity 

and low storage, representing conduits, and the 

other continuum has low hydraulic conductivity 

and high storage, representing the primary 

porosity of the rock matrix. The main advantage 

of the dual continuum approach is that the 

detailed geometry of the conduits is not required 

(Teutsch, 1993; Sauter, 1993; Lang, 1995), and 

dual continuum models have been applied 

successfully when the geometry of conduits is 

not known (Teutsch and Sauter, 1991; Teutsch, 

1993; Sauter, 1993; Teutsch and Sauter, 1998; 

Painter and others, 2007). Dual continuum 

models can simulate rapid variations in 

discharge and head change following recharge 

events and can accommodate the variable 

contributions of conduit and rock matrix flow 

with time. The data demand of the model is 

relatively modest and the parameterization effort 

is manageable for general field studies. The dual 

continuum model, however, is not always 

capable of simulating transport processes on a 

small scale (Mohrlok, 1996).

Hybrid Models

A hybrid model is the coupling of a single 

continuum model with a discrete conduit or pipe 

network model (Kiraly, 1998; Teutsch and 

Sauter, 1998). The approach allows the 

integration of detailed information about the 

conduits in areas where the geometry of the 

conduits may be known, thus providing a more 

physically representative model. They are 

considered hybrid models because they link a 

single continuum model for groundwater flow in 

3 dimensions with a 1-dimensional pipe network 

model. The two models exchange water via 

hydraulic head-dependent flux terms and iterate 

calculations between the two models until both 

converge, similar to the dual continuum model.

The 2008 distribution of the conduit flow 

process (CFP) for MODFLOW-2005 (Harbaugh, 

2005; Shoemaker and others, 2008) takes the 

hybrid modeling approach developed in the 

Conduit Aquifer Void Evolution (CAVE) code 
72

(Clemens and others, 1996; Bauer and others, 

2003; Liedl and others, 2003) from a research 

code to a tool that can be used by a wider group 

of practitioners. The main advantage of this 

modeling approach is that it allows simulation of 

the high transport velocities observed in karst 

systems, while continuing to represent the 

presence of a lower hydraulic conductivity 

matrix, representing the storage component of 

the karst aquifer. Limitations of this approach 

are the lack of geometric data for the conduit 

system (i.e., effective properties have to be 

assumed). The first release of CFP has 

limitations in that the pipe network is intended 

for full pipes (flow controlled by difference in 

pressure gradient - no free surface) and does not 

account for free surface flow (open channel 

flow-flow is under atmospheric pressure and 

flow is dominated by gravity.) 

Several models originally intended for 

surface-water systems have been applied to karst 

aquifers. The Storm Water Management Model 

(SWMM) (Metcalf and Eddy Inc., 1971),

designed for simulation of sewer systems, was 

applied by Peterson and Wicks (2006) to 

simulate conduits, but no interchange with the 

rock matrix was simulated. The MODBRANCH 

code (Swain and Wexler, 1996) was modified 

for simulation of karst systems by Zhang and 

Lerner (2000). MODBRANCH was originally 

developed by coupling a 1-dimensional freesurface open channel flow model with the top 

layer of a 3-dimensional groundwater flow 

model for simulation of groundwater/surfacewater interactions. Reimann and others (2011b) 

developed the ModBraC version of a hybrid 

model that couples the single continuum model 

with a pipe network model capable of simulating 

storage in the conduit system, including full 

flowing pipes as well as cave streams in the 

conduits. An accurate representation of conduit 

storage is essential in order to be able to 

simulate the lag time between discharge changes 

and the transport signal (for example, 

temperature or conductivity) after recharge 

events.

Discrete Single and Multiple Fracture 

Network Models

The discrete fracture approach has been 

proposed for problems where transient solutetransport responses are desired for a system 

dominated by conduits (Adams and Parkin, 

2002). Knowledge of the fracture network 

geometry, however, is required for this model. 

Generally, there are limited data for mapping the 

fracture network(s); therefore, stochastic 

methods are often used to generate the single- or 

multiple-fracture network for deterministic 

numerical simulations of flow. The 

disadvantages of discrete multiple fracture 

networks are the requirements of detailed 

knowledge of a fracture network at multiple 

scales and the application of computationally 

intensive codes that have long computer 

simulation time and memory requirements 

(Lang, 1995). Application of this approach to 

field scale problems is not common, and no 

examples can be provided.

Application of Deterministic Numerical 

Models – Example Comparisons of 

Single Continuum and Hybrid Models

The karst drainage system of the Wakulla 

Springs-Leon Sinks, Florida, submerged conduit 

system is moderately well characterized as a 

result of pioneering work accomplished over the 

past 20 years by cave divers of the Global 

Underwater Explorers as part of their Woodville 

Karst Plain Project (WKPP). The Woodville 

karst plain containing the Wakulla Springs-Leon 

Sinks system covers an area of 450 mi2

. Wakulla 

Springs is one of the largest first magnitude 

springs in Florida with an average flow of 

approximately 400 ft3

/s and issues from a large 

opening forming the headwaters of the Wakulla 

River at Edward Ball Wakulla Springs State 

Park, Florida. 

The WKPP maps served as the basis for 

three model approaches used for simulation of 

the groundwater-conduit system: (1) single 

continuum laminar flow only (equivalent porous 

media approach documented in Davis and 

others, 2010), (2) a hybrid model that consists of 

a single continuum model coupled to a 1-

dimensional pipe-flow network capable of both 

turbulent and laminar flow (Gallegos and others, 
73

2013), which is an evaluation of the CFP mode l 

(Shoemaker and others, 2008), and (3) simulated

turbulence within the model layer with large 

hydraulic-conductivity values assigned to cells 

with conduits using the single continuum model 

(Davis and others, 2010; Kuniansky and others, 

2011), which is an application of CFP mode 2 

(Shoemaker and others, 2008, with modification 

to mode 2 documented in Reimann and others, 

2011a). Large hydraulic-conductivity values 

were assigned to cells that represent mapped 

conduits (fig. 2) in approaches 1 and 3. For the 

hybrid model, the single continuum model of 

Davis and others (2010) was modified by 

removing the large hydraulic-conductivity cells 

and replacing them with a pipe network using 

MODFLOW-CFP mode 1 (Shoemaker and 

others, 2008) and recalibrated to a steady-state 

average condition (Gallegos and others, 2013). 

Figure 2. Simulated hydraulic conductivity in model layer 

2 with large hydraulic conductivity located at mapped 

submerged conduits (modified from Davis and others,

2010, fig. 27).

The field applications of MODFLOW-2005 

(Harbaugh, 2005) and the CFP (Shoemaker and 

others, 2008) examined spring discharge under 

various time discretization and flow conditions. 

Model approach 1, the subregional model of 

Davis and others (2010), was a single continuum 

transient simulation from January 1, 1966, when 

spray field (irrigation using treated wastewater 

as part of municipal wastewater treatment 

processing) operations began, through 2018, 

when effects of system upgrades will occur. The 

stress periods were mostly annual. Calibration 

data for water levels and spring discharge were 

available for November 1991, and May to early 

June 2006. Additional hydrologic information 

was provided by tracer tests conducted in 2006 

and 2007 by Hazlett-Kincaid, Inc. (listed in 

Davis and others, 2010). The hybrid model 

(approach 2) was calibrated to steady-state 

conditions for the same calibration datasets as in 

approach 1 (Gallegos and others, 2013). The 

third approach, single continuum with 

turbulence turned on for layer 2, yielded almost 

identical heads and flows as in Davis and others 

(2010) for the original monthly to annual 

average transient simulation. All three model 

approaches simulated observed average spring 

discharge at Wakulla and Spring Creek Springs 

within 10 percent, and head residuals were 

within the calibration criteria of plus or minus 5 

feet. Thus, for average spring discharge and 

tracer test time of travel, the models produce 

similar results and all are considered acceptable 

calibrations (Davis and others, 2010; Kuniansky 

and others, 2011; Gallegos and others, 2013).

To observe differences between the single 

continuum and hybrid model approaches, a 

transient period with daily spring-flow 

observations and a storm event (rising and 

falling springflow, no recalibration) was 

simulated (Kuniansky and others, 2011; 

Gallegos and others, 2013). For the 52-day 

storm event, which was simulated with daily 

time steps, none of the models simulated the 

observed peak discharge accurately (within 10 

percent of observed) (fig. 3). The shape of the 

storm hydrograph for Wakulla Springs is best 

matched by the single continuum with 

turbulence (approach 3, labeled CFP mode 2 in 

Reimann and others (2011a), fig. 3), and the 

peak discharge at about day 15 is matched 

within 10 percent; however, neither approach 1 

(labeled MODFLOW, fig. 3) nor approach 2 

(labeled CFP mode 1 hybrid, fig. 3) matched
74

peak discharge within 30 percent. If the total 

volumes of measured and simulated discharge 

for the 52-day period at Wakulla Springs are

compared, approach 1 matched observed within 

23 percent, approach 2 within 16 percent and 

approach 3 within 0.01 percent of total volume 

of discharge under the 52-day hydrograph. 

Model 1 overestimated and model 2 

underestimated peak discharge at Wakulla 

Springs. The computation time required by the 

hybrid model approach 2 (over 72 hours on a 

personal computer) was more than 100 times 

longer than the time required for the single 

continuum approaches 1 and 3. This test using

hybrid models is perhaps the largest ever 

undertaken, with more than 1,000 pipes and 

nodes simulated. The hybrid approach requires 

that two models are iteratively solved until both 

converge for each 1-day stress period, resulting 

in very slow convergence. The greater than 72-

hour simulation time precludes using parameter 

estimation to improve model fit for the hybrid 

model and thus, no attempt was made to

recalibrate all three models to both annual or

monthly average and the daily storm 

hydrographs (Kuniansky and others, 2011).

Figure 3. Simulated and observed springflow at Wakulla 

Springs (modified from Gallegos and others, 2013).

A recent study (Hill and others, 2010), 

comparing the hybrid model approach with the 

single continuum model approach for two other 

spring systems in Florida concluded that the 

hybrid model more closely simulated observed 

transient spring discharge. Another recent study 

(Saller and others, 2013) converted a single 

continuum model to a hybrid model for a 

watershed in the Madison aquifer in South 

Dakota and found that although the hybrid 

model matched observation well heads better, 

both models simulated spring discharge 

accurately. The Wakulla Springs example 

indicates that, for simulation of average 

conditions, none of the three model approaches 

is distinctly better (hybrid model calibrated with 

steady-state). For the simulation of a transient 

52-day storm hydrograph, the single continuum 

with turbulence model (approach 3) matched 

peak spring discharge within 10 percent at 

Wakulla Springs, and the hybrid model 

(approach 2) matched the total volume of 

springflow. Improved calibration with parameter 

estimation techniques was not possible for the 

hybrid model approach as a result of the long 

simulation time. Thus, it is unclear if the extra 

effort required to use a hybrid model, both in 

data preparation and computation time, is 

justified for large submerged conduit networks 

(over 100 pipes and nodes in Kuniansky and 

others, 2011). The change in temporal 

discretization appeared to result in the need for 

recalibration of the models for storm events if 

the desired accuracy between the model 

simulation and observed data was 10 percent or 

less. However, as computer speeds increase, it 

likely will be feasible to fully calibrate the 

hybrid models using parameter estimation,

resulting in more physically realistic models. An 

additional test of model capabilities could be 

comparison of residence times of rapid (event) 

flow components or slow flow matrix 

components, derived from use of geochemical 

mixing models with hydrograph separation 

techniques given time series datasets of 

chemistry and flow information. Unfortunately, 

no such data were available at the time of 

publication.

LUMPED PARAMETER MODELS

The control theory approach has been 

successfully applied to simulate karst aquifers 

using mathematical methods for solving sets of 

ordinary differential equations, as for example, 

filling and mixing of water in a tank or a 

network of tanks. Coefficients (or lumped 

parameters) for each tank are developed by

calibrating a system of equations (Wanakule and 

Anaya, 1993; Barret and Charbeneau, 1997). 
75

Data preparation for lumped parameter models 

is simpler than that used in deterministic 

numerical models, and computational times are 

faster. However, detailed representation of the 

aquifer is not possible using this approach. 

Groundwater withdrawals and recharge are 

summed together for each tank, which represents 

a geographic area (or spring basin), rather than 

being placed at actual locations. In addition, 

withdrawals and recharge may be used as input 

to simulate spring discharge. This method may 

be adequate for providing gross estimates of the 

effects of hypothetical pumpage and recharge 

rates on spring discharge as well as for 

providing better estimates of recharge given 

natural discharge and pumpage. Mathematical 

filters can be applied to some of the input data, 

such as development of filters to distribute the 

annual basin recharge to each month, to gain a 

better fit of observed versus simulated spring 

discharge (Dreiss, 1982; Wanakule and Anaya, 

1993). 

Application of Lumped Parameter 

Models

The lumped parameter modeling method is 

demonstrated in a simulation of springflow at 

Comal and San Marcos Springs, Texas. The 

model input and calibration data were based on 

annual estimates of recharge and pumpage in 

nine surface-water basins and an index water 

level in each basin of the Edwards aquifer 

(Wanakule and Anaya, 1993). The lumped 

parameter mathematical relation was developed 

much like a statistical regression model where 

recharge and pumpage in each lumped 

parameter block (conceptually, these are nine 

interconnected tanks as described above) were 

treated as input to a set of linked tanks that 

transport water to the major springs. The 

mathematical description of each tank was 

formulated with an ordinary differential 

equation. Figure 4 shows the Edwards aquifer 

and catchment area and how the tanks are 

arranged. Surface runoff from the catchment 

area infiltrates the Edwards aquifer across its 

outcrop area. Wanakule and Anaya (1993) used 

the recharge and pumpage data as inputs to the 

system. They developed filters to disaggregate 

the annual estimates of recharge into monthly 

estimates using streamgage data and annual 

recharge estimates. Additionally, the monthly 

pumpage by county was reapportioned to each 

watershed (Wanakule and Anaya, 1993). These 

values were then matched to monthly 

groundwater levels in each basin and to the 

historical spring discharge at Comal and San 

Marcos Springs by calibrating storage and 

transmissivity parameters for each tank. The 

filtering methods for the disaggregation of 

recharge fall into category 3 (fitting models), 

which includes time series techniques. 

Wanakule and Anaya (1993) were successful in 

refining estimates of monthly recharge and 

pumpage for each basin and simulating the 

spring discharge at Comal and San Marcos 

Springs (fig. 4c) along with water levels in each 

basin (not shown herein, refer to Wanakule and 

Anaya, 1993).

Schulman and others (1995) developed 

equations for stochastically generating recharge 

for the watershed basins (generated recharge has 

the same statistical properties as the historical 

data--recharge estimates available since 1934.) 

Endangered species at the springs are at issue, 

and the courts have required minimum 

discharges to be maintained at both springs. 

Groundwater use frequently is restricted during 

the summer months even as the population 

continues to grow. Thus, water-resources 

planners recognize that water may need to be 

imported to maintain discharge at the springs. 

Because of its computational speed and 

simplicity, the calibrated lumped parameter 

model of Wanakule and Anaya (1993), 

combined with the generated recharge scenarios, 

were used in an attempt to screen water-supply 

options for the Edwards aquifer (Watkins and 

McKinney, 1999).
76

Figure 4. A) Map of the Edwards aquifer and its recharge 

area, B) Schematic diagram of the lumped parameter 

model, and C) Comparison of observed and simulated 

spring discharge (modified from Wanakule and Anaya, 

1993).

FITTING MODELS

Fitting or statistical models have long been 

used in the field of hydrology. For this 

discussion, statistical models involve the 

matching of field data to either a statistical 

distribution or the development of a single- or 

multiple-linear regression equation. 

Additionally, the broad category includes other 

forms of linear systems modeling in which the 

karst aquifer is treated as a filter, and complex 

mathematical functions (linear kernels) are used 

to process inputs like recharge and pumpage to 

generate an output of springflow. The simplest 

application of linear systems in hydrology has 

been in rainfall-runoff models that employ what 

is called the unit hydrograph method (Sherman, 

1932). These and similar techniques have 

recently been applied to karst aquifers (Neuman 

and de Marsily, 1976; Dreiss, 1982; Wicks and 

Hoke, 2000). To some extent, these are 

considered “black box” methods because 

detailed knowledge about the physical system 

(locations of conduits, transmissivity, or storage 

properties) is not required. These methods have 

advantages and disadvantages that are similar to 

the lumped parameter models. In fact, statistical 

models are similar to the lumped parameter 

approach described earlier, except that they lack 

any physically-based differential equation to 

describe the physical aquifer. Instead, complex 

mathematical functions sometimes based on 

statistical or probability distributions are used as 

transfer functions, with time offsets and shape 

terms used to take an input(s) and create an 

output (response) that mimics the desired output 

(response) signal. Another fitting model would 

be the application of artificial neural networks, a 

form of pattern recognition, to karst aquifers (Hu 

and others, 2007; Trichakis and others, 2009). A

physical understanding of how the karst aquifer 

system works is required to select an appropriate 

input, such as recharge and pumpage that is 

physically related to the output, such as 

springflow or water level. 

Simple regression analysis has been used to 

predict spring discharge from the water level of 

a nearby well by developing a linear regression 

equation using historical data. This technique 

has also been used for tidally affected springs by 

developing a multiple linear regression using 

both water levels at a nearby well and stage data 

to estimate spring discharge (Wanakule, 1988; 

Knochenmus and Yobbi, 2001). Development of 

the regressions requires numerous discharge 

measurements over the full range of conditions 

anticipated, but does not involve time-series 

analysis.

More complex auto-correlation analysis has 

been used with time-series data to predict 

springflow from precipitation data (Eisenlohr 

and others, 1997). Time-series analysis has also 

been used with isotope data to estimate travel 

times and the diffuse versus conduit flow nature 

of karst aquifers as demonstrated with the 

following case study.
77

The advantage of fitting models is that they 

are easy to apply and to calibrate. The 

disadvantage is that these models are specific to 

the respective catchment, and model results are 

highly uncertain if prediction simulations require 

input or output variables that exceed those of the 

historic calibration period.

Application of Fitting Model 

Stable-isotope samples were collected at 

about 6-week intervals over a 6-year period at a 

streamflow-loss zone that recharges the karstic 

Madison aquifer in South Dakota and at a 

nearby well located close to or within a main 

groundwater flow path (fig. 5a) (Long and 

Putnam, 2002, 2007). Time-series analysis of the 

isotope data indicates that the well responds 

rapidly to recharge from a sinking stream during 

wet periods. The hydraulic connection between 

the stream’s loss zone and the well primarily 

results from flow along conduits. During dry

periods when streamflow is low, isotopic values

in the well samples primarily were influenced by 

aquifer-matrix water that has been in storage for 

many months or years. 

Data were analyzed by correlation and 

linear-systems analysis for a 34-month period of 

high recharge. Figure 5b shows the original data 

that were used to develop the model. Figure 5c 

shows the final model and the log-normal 

distribution used as the transfer function for 

estimating the oxygen-18 isotope value in the 

spring discharge from the streamflow 

concentration as the input data.

The stable-isotope and water-level datasets 

correlate most closely when the data from the 

losing stream reach and the well are lagged 22 

days, which may approximate the travel time 

from the loss zone to the well. Linear-systems 

analysis results in an estimated travel time to the 

well of about 15 days and a system memory of 2

to 3 years, resulting from diffuse matrix flow. 

Based on these analyses, the conduit-flow 

velocity was estimated at 380 to 800 feet/day

(120 to 240 meters/day). A log-normal 

distribution approximates the distribution of 

travel times of a plume for conduit flow.

A) Location of the study area.

B) δ18O data and streamflow recharge to the Madison 

aquifer from Spring Creek for 1996 through 2001. The 

curved line through the δ18O data points was interpolated 

by a cubic spline. The A sections indicate periods of nearmaximum recharge, whereas B sections indicate periods of 

lower recharge. The streamflow recharge has a maximum 

estimated rate of 21 ft3

/s (Hortness and Driscoll, 1998).

C) Results of linear-systems analysis including the 

computed δ18O data for the sampled well and the transfer 

function used in the analysis. The curved line through the 

δ18O data points was interpolated by a cubic spline.

Figure 5. Statistical regression model of stable isotope

values for springs in the Madison Limestone aquifer. A) 

Location of study area, B) Isotope and streamflow data, and 

C) Linear-systems analysis model (from Long and Putnam, 

2002).
78

CONCLUSIONS

The mathematical methods for simulation of 

karst aquifers are well developed. All of the 

methods require an understanding of each karst 

aquifer and its unique hydrogeologic setting.

The main difficulty in application of the 

methods relates to the difficulty of mapping the 

conduit networks, or having high-quality 

datasets to calibrate the models. Advances in 

geophysics, tracer testing, geochemistry, cave 

exploration, streamflow measurement, and 

recharge estimation will further improve 

application of the mathematical models. 

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82

Refined Hydrostratigraphic Framework and Model of the Edwards 

Aquifer, Texas

By S. Beth Fratesi1, Ronald T. Green1, Ronald M. McGinnis1, Hakan Basagaoglu1, 

Leslie Gergen1, Jim Winterle2, Marques Miller1, and F. Paul Bertetti1

1

Southwest Research Institute®, 6220 Culebra, San Antonio, Texas 78238 (www.swri.edu) 

2

Edwards Aquifer Authority, 900 E. Quincy, San Antonio, Texas 78215 (www.edwardsaquifer.org)

Abstract

A refined conceptual and numerical groundwater flow model is being developed for the karstic 

Edwards aquifer in central Texas. Improved understanding of the Edwards aquifer, its extent, boundary 

conditions, recharge, and internal hydraulics warrants development of this new conceptualization and 

model. The refined conceptualization is predicated on an enhanced hydrostratigraphic framework model. 

The framework has as many as nine separate units, although not all units are pervasive across the model 

domain. Over 100 faults are explicitly incorporated into the model. The framework was developed to be 

consistent with hydraulic characteristics of the Edwards aquifer to facilitate calibration of a new 

numerical model. The ensuing hydrostratigraphic framework and numerical model have resulted in 

significant refinements to the existing Edwards aquifer geologic framework and groundwater flow model. 

These refinements provide enhanced opportunity to replicate and predict the hydraulic response of the 

aquifer.
83

Simulation of Groundwater Flow in the Edwards-Trinity and Related 

Aquifers in the Pecos County Region, Texas

By Brian R. Clark1, Johnathan R. Bumgarner2, Natalie R. Houston3, and Adam L.Foster3

1

U.S. Geological Survey, 700 W. Research Blvd., Fayetteville, AR, 72701

2

U.S. Geological Survey, 5563 De Zavala Rd., San Antonio, TX, 78249

3

U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX, 78754

Abstract

The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and public 

supply uses in the Pecos County region of western Texas. The U.S. Geological Survey completed a 

comprehensive, integrated analysis of available hydrogeologic data to develop a numerical groundwaterflow model of the Edwards-Trinity and related aquifers in the study area in parts of Brewster, Jeff Davis, 

Pecos, and Reeves Counties. The active model area covers about 3,400 square miles of the Pecos County 

region of Texas west of the Pecos River, and its boundaries were defined to include the saturated areas of 

the Edwards-Trinity aquifer. The model is a five-layer representation of the Pecos Valley, EdwardsTrinity, Dockum, and Rustler aquifers. The Pecos Valley aquifer is referred to as the alluvial layer, and 

the Edwards-Trinity aquifer is divided into layers representing the Edwards part of the Edwards-Trinity 

aquifer and the Trinity part of the Edwards-Trinity aquifer, respectively. The calibration period of the 

simulation extends from 1940 to 2010. Simulated hydraulic heads generally were in good agreement with 

observed values; 1,833 out of 2,929 (63 percent) of the simulated values were within 25 feet of the 

observed value. The average root mean square error value of hydraulic head for the Edwards-Trinity 

aquifer was 33.61 feet, which was approximately 4 percent of the average total observed change in 

groundwater-level altitude (groundwater level). Simulated springflow representing Comanche Springs 

indicates a similar pattern as compared to the observed springflow. Independent geochemical modeling 

corroborates results of simulated groundwater flow that indicates groundwater in the Edwards-Trinity 

aquifer in the Leon-Belding and Fort Stockton areas is a mixture of recharge from the Barilla and Davis 

Mountains and groundwater that has upwelled from the Rustler aquifer.

The model was used to simulate groundwater-level altitudes resulting from prolonged pumping to 

evaluate sustainability of current and projected water-use demands. Each of three scenarios utilized a 

continuation of the calibrated model. Scenario 1 extended recent (2008) irrigation and nonirrigation 

pumping values for a 30-year period from 2010 to 2040. The results of scenario 1 indicate widespread 

declines in groundwater levels ranging from 5.0 to 15.0 feet. Projected groundwater-level declines in and 

around the Leon-Belding area and the Fort Stockton area are almost nonexistent apart from a small area 

of decline in the southwestern part of the Leon-Belding area. Scenario 2 evaluated the effects of extended 

recent (2008) pumping rates as assigned in scenario 1, with year-round permitted values in the Belding 

area. Results of scenario 2 reflect the modification of year-round pumping in the Belding area through 

increased declines in groundwater levels (maximum decline of approximately 27.3 feet). The extent of the 

projected groundwater-level decline in the Leon-Belding area expanded from that of scenario 1 to include 

much of the central and southern part of the irrigation area. Scenario 3 evaluated the effects of periodic 

increases in pumping rates over the 30-year extended period. Results of scenario 3 are similar to the 

results of scenario 2 in terms of the areas of groundwater-level decline. The maximum projected 

groundwater-level decline increased to approximately 32.7 feet in the Leon-Belding area and the extent of 

the decline is larger areally than that of scenario 2, joining with an existing area of decline to the north. 

The localized nature of the projected groundwater-level declines is a reflection of the highly fractured 

nature of the Edwards-Trinity aquifer. Additionally, the finding that simulated springflow is highly 

contingent on the transient nature of the underlying hydraulic heads indicates the importance of 

adequately understanding and characterizing the entire groundwater system.
84

REFERENCES

Bumgarner, J.R., Stanton, G.P., Teeple, A.P., Thomas, J.V., Houston, N.A., Payne, J.D., and Musgrove, Marylynn, 

2012, A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of 

the Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S. Geological Survey Scientific 

Investigations Report 2012-5124 (revised July 10, 2012), 74 p., available at http://pubs.usgs.gov/ds/678/.

Clark, B.R., Bumgarner, J.R., Houston, N.A., and Foster, A.L., 2014, Simulation of groundwater flow in the 

Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S. Geological Survey Scientific 

Investigations Report 2013-5228, 56 p., available at http://pubs.usgs.gov/sir/2013/5228/.

Pearson, D.K., Bumgarner, J.R., Houston, N.A., Stanton, G.P., Teeple, A.P. and Thomas, J.V., 2012, Data collection 

and compilation for a geodatabase of groundwater, surface-water, water-quality, geophysical, and geologic 

data, Pecos County region, Texas, 1930–2011: U.S. Geological Survey Data Series 678, 67 p., available at

http://pubs.usgs.gov/ds/678/.

Thomas, J.V., Stanton, G.P., Bumgarner, J.B., Pearson, D.K., Teeple, A.P., Houston, N.A., Payne, J.P., and 

Musgrove, MaryLynn, 2012, A conceptual model of the hydrogeologic framework, geochemistry, and 

groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S. 

Geological Survey Fact Sheet 2013-3024, 6 p., available at http://pubs.usgs.gov/fs/2013/3024/.
85

Automatic Methods of Groundwater Flow Model Construction of the 

Ozark Plateaus Aquifer System

By Brian R. Clark1 and Joseph M. Richards2

1

U.S. Geological Survey, 700 West Research Blvd., Fayetteville, AR 72701 

2

U.S. Geological Survey, 1400 Independence, Rolla, MO 65401

Abstract

As computational speeds increase, highly parameterized groundwater flow models are becoming 

more common. A typical model may include thousands or tens of thousands of parameters representing 

components of hydraulic properties, recharge, boundary conditions, and stresses. Often these parameters 

are estimated or include measured values that include a certain degree of error. The sensitivity of 

simulation results to the accuracy of these parameters or to variability in these parameters is evaluated by 

comparing changes in parameter values to the resultant effect on simulated water levels and flows. The 

scale of horizontal and vertical discretization used to develop the model grid may introduce structural 

noise into the simulation, however, and changes in grid dimensions can directly affect calibrated 

parameters. Despite this recognized dependence of model parameters on the underlying grid, grid 

dimensions typically are developed early in the model construction process and are based on a quick 

computation of potentially active cells with some regard to the resolution of existing data and the purpose 

of the simulation. The grid dimensions are then held constant throughout the modeling process. Using 

automated scripting methods to dynamically rediscretize a model grid allows the grid dimensions to 

become parameters that also can be evaluated by using sensitivity analysis to optimize the cell sizes and 

layering, and minimize the structural noise. 

The challenge of including grid dimensions as a parameter of the model is that the model grid is the 

basis of all model inputs (layer, row, and column is the typical method to reference the location of all 

features in a model), and changes to the dimensions of the grid affect how all simulated features are 

represented. Therefore, the automated scripting methods must be capable of intersecting each feature 

within the model grid and creating appropriate model files. The Python® scripting language provides 

robust methods to interface with database structures, text-based files, and spatial data files. Initial tests of 

the scripts applied to information about the Ozark Plateaus aquifer system indicate potential in evaluating 

the sensitivity of grid dimensions to groundwater-level altitude. The scripts are used to create the grid 

(with associated layer elevations), split layers if desired, assign hydraulic parameter zones, create 

observation files, and create preliminary river and drain files. Post-processing scripts are included as final 

steps in the process. These scripts calculate residual statistics and produce plots for comparison to other 

simulations using various grid dimensions.

REFERENCE

U.S. Geological Survey, 2014, Ozark Plateaus groundwater availability study, accessed February 20, 2014, at 

http://ar.water.usgs.gov/ozarks/.
86

CHEMICAL FATE AND TRANSPORT

Transport of Salt, Trace Metals, and Organic Chemicals from Parking 

Lot and Road Surfaces into Mammoth Cave 

By David Solomon1, Irucka Embry2*, Bobby Carson3, Larry Johnson3, Roger Painter1, 

Lonnie Sharpe1, Rickard Toomey, III3, and Thomas D. Byl1,2

1

Tennessee State University, College of Engineering, 3500 John A Merritt Blvd., Nashville, TN 37209

2

U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*contract employee) 3

Mammoth Cave International Center for Science and Learning, Science & Resource Management, 

Mammoth Cave National Park, KY 42259

Abstract

Mammoth Cave National Park in south-central Kentucky is the world’s longest known cave system 

and is host to many unique and threatened species including the Kentucky cave shrimp. The National 

Park Service operates Mammoth Cave National Park to educate tourists while still protecting the unique 

and fragile ecosystem in the cave. The Park in partnership with Tennessee State University and the U.S. 

Geological Survey has established a monitoring system to characterize selected chemicals transported 

from parking lots and dissolved salt from winter-treated roads. The project was initiated, in part, because 

of the high volume of traffic into and through the Park, and because the Park has begun phasing in the 

application of brine and rock salt to melt ice on primary roads through the Park. The scope of this 

investigation included six surface monitoring stations and two cave streams for the winter road-runoff 

study, and seven surface drains and six cave sites for the parking lot segment of the project. Chemical 

analysis of road runoff included grab samples between and during storms, and continuous measurement 

of specific conductance as a surrogate measure of salt concentration. Chemical analysis of parking lot 

runoff included quaternary ammonia compounds, anionic surfactants, nitrate, ammonia, zinc, and copper. 

The road-runoff monitoring sites were selected based on their location with respect to primary roads 

targeted for salt treatment, traffic volume, drainage qualities, and drainage to critical cave shrimp habitat. 

This project began in 2011 prior to any road treatments in the Park, and continued through the winter of 

2013. Specific conductance meters and autosamplers were used to monitor the runoff waters. There were 

three brining events in January 2013. The specific conductance of road runoff during the January 2013 

storms ranged from 50 to 400 microSiemens per centimeter (μS/cm) at 25 degrees Celsius. Specific 

conductance of road storm runoff during winter storms with no brine or salt applications ranged from 50 

to 300 μS/cm. Analysis of the specific conductance pattern on the surface and in the corresponding cave 

found that it took from 0.5 to 3 hours for road runoff to reach the mid-level of the cave.

The parking lot sampling sites were associated with storm filters. First-flush storm samplers and 

random grab samples were collected from 2011-2014. Concentrations of quaternary ammonia compounds 

ranged from below detection (<0.1 milligrams per liter (mg/L)) to a high of 22 mg/L in storm runoff from 

an RV waste transfer station. Quaternary ammonia compound concentrations in Annette’s Dome (in the 

cave below the RV waste transfer station) exceeded 0.5 mg/L two times in the summer of 2012 (5.4 and 

2.5 mg/L). Copper and zinc concentrations were less than 1 mg/L in all monitored events. Nitrate (as N) 

and ammonia concentrations spiked as high as 29 and 22 mg/L, respectively, in parking lot runoff from 

areas frequented by grazing deer. The concentration of ammonia in most surface runoff was less than 1 

mg/L, and nitrate (as N) rarely exceeded 5 mg/L. Concentrations of ammonia and nitrate in the cave were 

generally less than half the surface concentrations. The anionic surfactant concentrations in the surface 

runoff samples were generally less than 10 micrograms per liter (μg/L) with an occasional spike as high 

as 100 μg/L in runoff draining the biosecurity mats. Trace concentrations (<5 μg/L) of anionic surfactants 

were detected at all the cave sampling sites and probably represent natural surfactants. The results of the 

investigation indicate that concentrations are diluted as water moves from the land surface into the cave.
87

CAFOs on Karst—Meaningful Data Collection to Adequately Define 

Environmental Risk, with a Specific Application from the Southern 

Ozarks of Northern Arkansas

By Van Brahana1, Joe Nix2, Carol Bitting3, Chuck Bitting4, Ray Quick5, John Murdoch6, 

Victor Roland7, Amie West7, Sarah Robertson8, Grant Scarsdale9, and Vanya North5

1

Department of Geosciences, 20 Ozark Hall, University of Arkansas, Fayetteville, AR 72701 

2

Ouachita Baptist University Water Lab, Arkadelphia, AR 71988 

3

HC 73, Box 182 A, Marble Falls, AR 72648

4

National Park Service, Harrison, AR, 72601

5

Department of Geosciences, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701

6

11908 Elk Ridge Rd., Wesley, AR 72773 7

Program of Environmental Dynamics, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701 8

243 South Gregg Ave., Fayetteville, AR 72701 9

303 Oxford, Harrison, AR 72601

Abstract

Karst typically contains a noticeably larger percentage of groundwater in its hydrologic budget than 

insoluble lithologies. Because subsurface flow is not directly observable, flow quantity, flow direction, 

flow velocity, water quality, groundwater basin delineation, and hydrologic variation with changing water 

levels are key components essential to characterizing the hydrogeology and assessing contaminant risk in 

karst aquifers. Concentrated animal feeding operations (CAFOs) are but one of the many sources of 

contamination that have been documented in karst, and owing to the large concentration of animal wastes 

generated by these factory farms and their potential for allowing pollution to enter nearby waters, these 

nonpoint sources require thorough and careful study prior to permitting by state and federal 

environmental agencies. Environmental impact statements and preconstruction studies are essential to 

preserve the environmental and ecological integrity of karst basins. Remediation is typically much more 

expensive and commonly requires more time to mitigate the damage.

The state environmental protection agency (Arkansas Department of Environmental Quality [ADEQ]) 

approved the construction of a 6,500-head swine CAFO in accordance with existing regulations on karst 

terrain in the area of Big Creek basin in Newton County, Arkansas. The CAFO lies less than 10 

kilometers from the confluence of Big Creek with the Buffalo National River, a National Park Service 

facility that is the main drain from this karst drainage basin. The Buffalo National River is one of the few 

free-flowing rivers remaining in the contiguous 48 states, hosting various recreational activities, including 

canoeing, fishing, and swimming, in addition to ecosystems for a large number of unique aquatic and 

endangered bat species. This CAFO was permitted under a General Permit which did not require 

appropriate investigations, including a hydrogeologic study, a karst study, and an evaluation of 

groundwater/surface water interaction. Newton County is characterized by karst hydrogeology, containing 

more known caves than any other county in Arkansas. Operation of the CAFO has been the subject of 

much debate and has pitted the landowners and small family farms against big-agriculture factory 

farming. This paper describes the resulting pro bono research that was undertaken to fill in essential data 

originally missing (hydrogeology, karst inventory, dye tracing, water quality), and the continuing effort to 

educate the local landowners about a resource that moves unseen beneath the ground. It has strong 

technical components, but more importantly, has a direct relevance to the human impacts of our science 

on environmental justice and policy.
88

INTRODUCTION 

Karst regions typically are considered to be 

vulnerable with respect to various anthropogenic 

land-use activities, owing to the intimate 

association of surface and groundwater. 

Inasmuch as the soluble rocks of the karst 

landscape can be dissolved to create large, rapidflow zones that compete successfully with 

surface streams, groundwater and subsurface 

flow represent a much larger component of the 

hydrologic budget in karst regions than in areas 

where non-soluble rocks predominate. Karst 

areas typically are distinguished by being unique, 

but some general approaches can be applied to 

characterize the hydrology of the area. These 

approaches include an evaluation of the degree of 

karstification, the hydrologic attributes of the 

groundwater flow system, the baseline water 

quality, the time-of-travel through the karst flow 

system, and the general flux moving through the 

system. The nature of potential contaminants and 

their total mass and range of concentrations are 

critical to understanding the potential 

environmental risk. Using these approaches, it is 

possible to represent a minimum level of 

hydrogeologic characterization to assess 

environmental risk in a karst area. Wellestablished, fast-flow systems with structural 

deformation likely will demand more complete 

study, but lacking the aforementioned minima, 

the cost of remediating contamination is typically 

increased many fold.

CAFOs are but one of many industrial 

activities that pose a threat to the environmental 

integrity of a karst basin. The typically large 

number of animals (from hundreds to more than a 

hundred thousand animals—most commonly 

cattle, pigs, chickens and turkeys) generate 

wastes in solid, liquid, and gaseous phases. Our 

focus in this paper is limited to nitrate and total 

phosphorus, major dissolved constituents, 

organics, sediment, and pathogens.

The objectives of this paper are threefold. 

The first is to describe minimal requirements for 

siting any facility on karst.

Figure 1. General area of major physiographic regions of 

the Ozark Plateaus, including the Buffalo National River and 

the Ozark National Scenic Riverways, two unique and 

Extraordinary Resource Waters that are part of the National 

Park Service. The karst area discussed in this study is 

restricted to the Springfield Plateau in the area of the Buffalo 

National River. Figure from Adamski and others (1995).

From a hydrogeologic standpoint, much of this 

objective is a reiteration of commonly wellknown sampling requirements in karst (Quinlan, 

1989; Alexander, 1989). The second objective is 

to provide an abbreviated case study from the 

southern Ozarks in northern Arkansas, in the 

drainage basin of the Buffalo National River (fig. 

1), which shows that implementation of 

meaningful environmental impact studies for 

potentially risky industrial activities on karstlands 

is fraught with politics and emotion. The third 

objective is to propose a scientifically-sound, 

thorough, fair approach for the ultimate 

achievement of environmental justice for the 

greatest number of stakeholders.

MINIMAL STUDY REQUIREMENTS FOR 

INDUSTRIAL ACTIVITIES PROPOSED ON 

KARSTLANDS

Based on the seminal work of Quinlan 

(1989), we have modified his original assessment 

of required study components to include what we 

believe are minimum questions that should be 

answered prior to siting CAFOs on karst.

1. Compile, study and interpret topographic, 

soils, and geologic maps, and all related 

previous hydrogeologic studies of the 

area. Fully document this in a list of 

selected references. 
89

2. Conduct a complete karst inventory, 

including input, flow through, and 

discharge features accurately plotted on 

topographic and geologic maps of 

appropriate scale.

3. Determine groundwater-flow directions, 

flow type, velocities, and water budgets, 

and estimate groundwater basin 

boundaries using the principle of 

normalized base flow (Brahana, 1997).

4. Characterize the baseline water quality of 

the shallow karst aquifer and overlying 

and underlying aquifers to assess

interaquifer transfer of flow and 

contaminants, including dissolved major 

constituents, original contaminants and 

their breakdown products from the 

industrial operation, and in the case of 

CAFOs, key nutrients, pathogens, 

sediments, and other unique waterquality indicator parameters.

5. Conduct dye-tracing studies concurrently 

with items 3 and 4, using study results to 

answer questions raised in item 2.

6. Integrate items 1 through 5 into a report 

that synthesizes groundwater hydrologic 

characteristics in the karst aquifer, 

proposes a defensible conceptual model, 

and accurately assesses the background 

water quality prior to the permitting of 

the industrial operation. Insofar as the 

complexity of the karst is not well 

understood by disciplines outside 

geology, this study should be conducted 

only by a registered professional 

geologist.

CASE STUDY OF THE INDUSTRIAL HOG 

CAFO ON THE KARST OF BIG CREEK 

BASIN, NEWTON COUNTY, ARKANSAS 

The approval by the Arkansas Department of 

Environmental Quality (ADEQ) of a 6,500-head 

swine facility on Big Creek less than 10 

kilometers upstream from the Buffalo National 

River (fig. 2) was approved on August 3, 2012. 

This approval came as a surprise to almost all 

stakeholders in the region, not the least of whom 

was the National Park Service (NPS), the agency 

responsible for maintaining the environmental 

quality of the Buffalo River, which is classified 

as an Extraordinary Resource Water. The 

resulting furor brought deeply held emotions to 

the surface. Unfortunately, space constraints for 

this paper limit discussion to only key elements 

of the controversy, but the interested reader is 

directed to the following websites, each of which 

offers disparate views of the facts. These sources 

represent web pages of some of the major 

participants, and additional information can be 

acquired from pointers on each webpage, or web 

searches using examples such as the Buffalo 

National River, Big Creek Hog Farm, or Newton 

County, Arkansas Hog Farm, to name a few. 

Some specific connections with those involved 

and shown in parentheses are: 

http://www.arfb.com/ (Arkansas Farm 

Bureau); 

http://www.adeq.state.ar.us/ (ADEQ); 

http://www.cfra.org/news/140127/corporatefarming-notes-industrial-hog-operation-dividescommunity (Center for Rural Affairs); 

http://www.npca.org/news/mediacenter/press-releases/2013/groups-go-to-court-toprotect (National Parks Conservation 

Association); 

http://www.ozarksociety.net/2013/03/conserv

ation-issue-hog-farm-near-big-creek/ (Ozark 

Society); 

http://buffaloriveralliance.org/Default.aspx?p

ageId=1547312 (Buffalo River Alliance); 

http://www.npca.org/news/mediacenter/press-releases/2013/groups-go-to-court-toprotect.html. 

It should be noted that these sources reflect 

the bias of each support group, and that 

misrepresentations or inaccuracies may be 

present on non-peer-reviewed web pages. These 

are provided to assist the reader and to show how 

distinctly different interpretations are possible 

from the same data set. The difference lies in the 

filters, the fears, the politics, and the emotional 

reactions of each stakeholder. 
90

Selected Components of the Permitting 

Process

As previously mentioned, the permit for the 

CAFO was granted by ADEQ according to 

existing regulations, which did not include a 

through characterization of the site. The geology, 

hydrology, and unique karst terrain were not 

adequately considered. Additionally, no 

predevelopment characterization was made to 

evaluate the true effects of the CAFO on the 

watershed. 

Site Geology, Hydrogeology, Karst, and 

Hydrology

Big Creek is one of the two largest tributaries 

to the Buffalo National River, encompassing 

about 8 percent of the total drainage of the entire 

Buffalo River watershed. Physiographically, 

tributaries head in uplands of the Boston 

Mountains Plateau (fig. 1) on terrigenous 

sediments of Pennsylvanian age and flow 

generally toward the north with relatively steep 

gradients. The stratigraphic units of concern are 

within the Boone Formation (Braden and 

Ausbrooks, 2003), an impure limestone that 

contains as much as 70 percent chert, much of 

which was thought to have formed through 

geochemical alteration of volcanic ash from 

atmospheric deposition from the island arcs south 

of the Ouachita Orogeny, approximately 150 

kilometers south of study area. The upper and 

lower units of the Boone Formation have much 

less chert (typically less than 5 percent) than the 

middle part of the Boone. Structurally, the Boone 

is near-horizontal; owing to the high 

concentration of brittle chert, it has been 

subjected to extensional faulting and jointing. 

The upper and lower parts of the Boone 

Formation host significant caves (fig. 4) in the 

region (Mott and others, 2000). Intervening 

layers of limestone are karstified by smaller 

dissolution features (fig. 5), with the chert acting 

as confining units above and below.

The geologic unit underlying the CAFO is 

the Boone Formation, and all formations in Big 

Creek basin are shown in figure 3. Approximately 50 meters of the middle Boone 

limestone/chert lithology is exposed in a cliff face 

about 2 kilometers downstream from the CAFO 

(fig. 6). Big Creek is characterized by both 

gaining and losing reaches where it crosses the 

Boone Formation, and during low flow there are 

entire reaches that are completely dry 

downstream of flowing reaches.

Figure 2. Aerial view of 6,500-head industrial hog CAFO, 

including waste lagoons. The facility is sited on the Boone 

Formation, a karst aquifer less than 10 km upstream from the 

confluence of Big Creek with the Buffalo National River.

Figure 3. Stratigraphic column of most of Big Creek basin 

in the vicinity of the CAFO, from the Mt. Judea 7.5-minute 

quadrangle (Braden and Ausbrooks, 2003).
91

Big Creek and its major tributary, Left Fork, 

flow in alluviated valleys composed of 

nonindurated sediments, primarily chert and 

terrigenous rock fragments from younger, 

topographically higher formations (fig. 3). The 

alluvium in these valleys varies in thickness from 

a feather-edge to about 8 meters. Outcrops of the 

Boone Formation are common in the streambed. 

Springs are common along the entire reach of Big 

Creek, ranging from relatively small discharges 

in the tens of liters per minute range to large 

discharges of tens of liters per second. These 

larger discharges resurge from relatively pure 

limestone lithologies (Mott and others, 2000).

Figure 4. Newton County, where Big Creek occurs, has the 

largest number of recorded caves of all counties in the state. 

Most of these, such as this cave just north of Big Creek basin 

on the Buffalo River, are concentrated in the upper and 

lower parts of the Boone and St. Joe Formations, which 

include more pure limestone. Photo by Carol Bitting.

Figure 5. Karst dissolution features in limestone interbedded 

with chert from the middle Boone Formation. The chert acts 

as an insoluble confining unit for the karst. The scale of 

these voids typically ranges from 2 to more than 5 cm.

The existence of well-developed karst near a 

NPS facility designated as an Extraordinary 

Resource Water, increases vulnerability to 

anthropogenic sources of contaminants that can 

move through the hydrologic cycle with little 

attenuation of contaminants. The concentrated 

wastes of the CAFO and the calculated allowable 

leakage through the clay of the lagoon liner (fig. 

7) and the waste-spreading fields (fig. 8) are 

perceived as being a risk, not only to the ecology 

and environmental integrity of Big Creek, but to 

the Buffalo National River, with the extensive 

direct contact of its waters with the many tourists 

who canoe and swim there. The lack of any 

geologic, hydrogeologic, or karst studies do not 

allay fears related to assessing the overall risk 

this CAFO poses.

Figure 6. Erosional bluff face showing approximately 50 m 

of interbedded limestone and chert in the middle part of the 

Boone Formation near the confluence of Big Creek with its 

major tributary, Left Fork. The differential weathering 

suggests that this landscape reflects the solubility of the 

limestone facies. Photo courtesy of John Murdoch.
92

In response to the lack of appropriate 

hydrogeologic and karst studies of the basin 

associated with the CAFO, a diverse group of 

volunteers (the authors) proposed a pro bono

investigation of several unstudied elements that 

would minimally describe 1) the karst inventory 

in Big Creek basin, and its relation to the 

geology; 2) the baseline groundwater quality, 

including an assessment of expected capability of 

the soil/regolith/bedrock flow system to 

accommodate additional wastes; and 3) the 

general flow directions, rates of flow, quantities 

of flow, and water budgets based on dye tracing. 

The interpretation of these field data are expected 

to be shared with all stakeholders in a report. 

Geologic, hydrologic, and karst inventories 

which were outlined earlier under minimal study 

requirements were conducted. These were 

accomplished by an intensive map and previously 

published reports study, intensive field work to 

identify gaining and losing reaches, caves, 

springs, sinkholes and visible karst landforms, 

low-level aerial surveillance, and canvassing of 

the local farmers and landowners.

Strict baseline water-quality (pre-CAFO) 

sampling was not possible, but the slow startup of 

the CAFO in the summer of 2013 allowed 

sampling approximately 40 wells, springs, and

Figure 7. The clay liner shown here is the sole confining 

entity separating the hog waste in the lagoons from the 

underlying Boone Formation. This photo, taken after 

construction of the liner, indicates that it has numerous chert 

fragments up to fist size within the clay, and dessication 

cracks, and that erosion rills have eroded some of the 

thickness. These features reduce its ability to confine. The 

liner was required to be 30 cm thick, but the owners of the 

CAFO increased that to 45 cm. Photo courtesy of Tony 

Morris (ADEQ).

Figure 8. Fields permitted for spreading hog waste along 

Big Creek by the CAFO (white color) granted by ADEQ. 

Most of the permitted fields are on alluvium and regolith that 

directly overlie the Boone Formation at thicknesses ranging 

from a feather edge to about 8 m. The proximity to Mt. 

Judea school (magenta color) to the spreading fields is 

shown in the upper right-hand corner of the figure.

streams for field parameters, major dissolved 

constituents, nutrients, and pathogens prior to the 

major CAFO activity. Nutrients and pathogens 

were analyzed by the Arkansas Water Quality 

Lab on the campus of the University of Arkansas 

owing to the short holding-time requirements, 

and dissolved major and selected trace 

constituents were analyzed by the Water Quality 

Lab of Ouachita Baptist University in 

Arkadelphia.

The dye-tracing study has yet to be 

undertaken, because permission to inject nontoxic fluorescent dyes was just granted in midMarch 2014. 
93

Figure 9. Conceptual model showing surface and groundwater interaction in a cross-sectional view in the area of Big Creek near 

the hog CAFO. Red arrows identify potential karst flow pathways that were not characterized or previously studied.

Preliminary Results 

Description of the geology and karst of Big 

Creek basin in the area of the CAFO support the 

observation that the Boone Formation is a 

mantled karst with numerous springs and a high 

degree of surface and groundwater interaction. 

Sinkholes are typically not common in the middle 

part of the Boone, but springs and secondary 

zones of limestone dissolution between chert 

layers are. The large number of caves in the basin 

(fig. 10) provides additional support for large 

discharge, rapid-flow systems with turbulent flow 

that have the ability to transport not only 

conservative solutes, but nutrients, sediment, and 

pathogens. At this time, the shallow karst aquifer 

is dominated by bicarbonate water type,

Figure 10. Locations of selected reference points, sampling sites, spreading fields permitted for the CAFO, caves, and springs in 

Big Creek and contiguous basins. Spreading fields are yellow, springs are blue, caves are green, surface-water sampling sites are 

red, major roads are in white, forested regions are dark green, and cemeteries are brown. Locations are from GPS measurements 

plotted on Google Earth.

Big Creek

permeable voids created by secondary dissolution in karstified limestone of the 

Boone Formation transmit hog waste and related contaminants to Big Creek

land surface

spraying waste on fields adds additional contaminants 

that drain downward into the underlying karst

West

East

lagoon with 45-cm “liner”
94

dissolved solids generally less than 400 

milligrams per liter (mg/L), groundwater 

temperatures consistent with shallow karst flow 

(summer temperatures in the 16-19 o

C range, 

winter temperatures in the 12 to 14 o

C range), 

nutrients elevated above background levels (e.g. 

nitrates in the range of 2 to >10 mg/L), 

reflecting effects of anthropogenic land uses, 

and pathogens, some as high as tens to hundreds 

of thousands of colony forming units (cfu) per 

100 mL, indicating little or no attenuation. 

Recent groundwater analyses show no 

contamination from the CAFO; however, these 

data are from select locations. Therefore, some 

monitoring points may not be included due to 

the diverse nature of the karst system and the 

inability to get permission to sample locations 

on private property.

PROPOSAL FOR OPTIMIZING THE 

INCORPORATION OF SCIENCE, POLICY, 

AND TRANSPARENCY INTO FUTURE 

STUDIES OF PERMITTING INDUSTRIAL 

ACTIVITIES ON KARST

1. Include all stakeholders at the table, 

exclude no one.

2. Promote an environment of openness, 

wherein no favored or powerful group 

dominates other stakeholders.

3. Verify and document all facts and aspects 

of potential problems, especially if it 

appears that this is a karst system.

4. If disinformation or deceit are evident, 

confront these.

5. Be respectful.

6. Use a holistic approach to the proposed 

activity, including scientific and human 

considerations that are relevant.

7. Reframe the discussion to avoid words or 

terms that are incendiary, and allow 

reasonable options.

8. Above all else, base decisions and 

regulations on science and on treating 

others the way you would like to be 

treated.

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97

An Initial Investigation of Hydrogeology and Water Quality of Big 

Creek in the Buffalo River Watershed near a Major Concentrated

Animal Feeding Operation

By Victor L. Roland II1, Tyler Wright1, J. Van Brahana1, and Phil D. Hays1,2

1

University of Arkansas, Department of Geosciences, Ozark Hall 216, Fayetteville, AR 72701 

2

U.S. Geological Survey, Arkansas Water Science Center, 401 Hardin Rd., Little Rock, AR 72211

Abstract

A swine concentrated animal feeding operation (CAFO) in Newton County, Arkansas near the 

Buffalo River was approved, permitted, and constructed in 2012. The CAFO is adjacent to Big Creek, 

which is a major tributary of the Buffalo River. The region has a mature karst landscape, which provides 

rapid recharge to groundwater. Groundwater and surface-water interaction within the Big Creek 

watershed is extensive, raising concerns over potential contamination of surface water or groundwater. 

Contamination pathways associated with CAFOs include leakage and lagoon overflow, preferential flow 

paths through the soil, and nutrient-rich runoff from manure application fields. Contaminants of concern 

are nutrients, pathogens, sediment, and trace metals. The objective of this project was to provide 

preliminary data on water-quality conditions in the Big Creek basin associated with the CAFO drainage 

area. Water samples were collected from Big Creek, natural springs, and private wells during base-flow 

conditions in July and August 2013. Sampling was conducted before initial application of CAFO waste 

effluent to fields in the watershed designated for manure application. Analyses of dissolved solutes 

indicated calcium-bicarbonate as the predominant water type in the study area. Calcium-bicarbonate-type 

water is indicative of dissolution of Boone Formation limestone, which crops out in the study area. 

Biological data show Escherichia coli and total coliform concentrations ranged from <1.0–980 Most 

Probable Number counts per 100 milliliters (MPN/100mL) and from <1.0–241,900 MPN/100mL, 

respectively. The wide range of Escherichia coli and total coliform concentrations may result from smallscale CAFOs, wildlife, and anthropogenic sources in the water; however, more data are necessary to 

elucidate sources of bacteria in groundwater and surface water. Nutrient concentrations varied spatially 

with no discernible trend; however, phosphorus and nitrate concentrations were elevated in groundwater 

samples relative to surface-water samples. Preliminary data from this study show the variability in 

chemical and biological water quality in the study area, and provide background information necessary 

for future assessments of potential changes in water quality in the Big Creek watershed as the CAFO 

becomes fully operational.
98

A Method to Investigate Karst Groundwater Flow in Nash Draw, Eddy 

County, New Mexico, to Delineate Potential Impacts of Potash 

Industry Discharge and Runoff 

By James Goodbar1, and Andrea Goodbar2

1

Bureau of Land Management, 620 E. Greene St., Carlsbad, NM 88220

2

Central New Mexico Community College, 3027 Derrick Rd., Carlsbad, NM 88220

Abstract

Nash Draw is a karst valley approximately 15 miles east of Carlsbad, New Mexico. It is the site of 

several potash mines – one has been operating since the early 1930s. During that time a significant 

amount of refining brine waste has been disposed of into the valley. The geology and hydrology of Nash 

Draw have been studied extensively in relation to the potash industry, the Gnome Project, and the Waste 

Isolation Pilot Plant. All studies agree that the karst nature of Nash Draw plays an important role in the 

overall hydrology of the area. Specific studies suggest that the brine effluent of the potash industry may 

be causing dramatic changes in the ecosystem associated with the draw. To date, there have been no 

quantitative (or qualitative) studies to delineate specific flow paths in this complex hydrologic system. A 

quantitative water-tracing study may supply a critical piece of information in understanding the 

complexities and flow paths of the karst groundwater system in Nash Draw. It would also provide useful 

information for environmental assessments and impact statements necessary in making responsible 

resource management decisions related to the potash industry and the Nash Draw ecosystem.

SETTING AND BACKGROUND

Nash Draw is a karst subsidence valley in 

southeastern New Mexico that is 4 to 6 miles 

wide, 22 to 23 miles long, and covering about 

128 square miles (fig. 1). The average depth 

ranges from 100 to 200 feet. It generally runs 

from the north-northeast to the south-southwest, 

and is bound on the north by the Maroon Cliffs, 

on the west by Quahada Ridge, on the east by 

Livingston Ridge, and on the south by the Pecos 

River. More than 100 collapsed sinks and cave 

entrances have been documented in the bottom 

of the valley. Dissolution takes place primarily 

in the Rustler and the Salado Formations of 

Permian age. At Nash Draw, the Rustler consists

of interbedded sulfates, dolomites, and 

mudstones while the Salado is primarily halite 

with minor sulfate beds. At the lower end of 

Nash Draw are a series of seven shallow lakes or 

playas. The presumed base level of the Nash 

Draw hydrologic system is the Pecos River due 

to the increased salt content in the Pecos River 

below Nash Draw at Malaga Bend (fig. 1).

Potash mining has been operating along the 

flanks of Nash Draw since the early 1930s 

(Brokaw and others, 1972). Tailings ponds were 

established in the margins of the draw and 

mining fluids have been intermittently 

discharged into the karst valley as a result of 

dike breaches and/or releases of brine fluids to 

avoid catastrophic dike failure. Sinkholes have 

formed in the bottom of tailings ponds draining

the brine tailings into the subsurface. Large 

sinkholes have developed in salt tailings piles, 

suggesting a direct release of at least some of the 

waste directly to the subsurface conduits with 

eventual discharge at downstream locations. 

Several of the natural playas on the south end of 

Nash Draw have progressively become more 

and more salty over the decades. This has 

resulted in some of the playas becoming 

unsuitable for certain species of plants and 

wildlife that previously inhabited them.

Previous Studies

Geologic and hydrologic studies conducted 

in Nash Draw over the decades have attempted 

to accurately describe the geology and 

characterize groundwater flow. Most of the 

studies acknowledge that the solution activity 

and associated collapse, subsidence, and 

fracturing have increased the permeability of the 

overlying rock members and increased the 

hydrologic communication between formations. 

The earliest of these works by Willis T. Lee 
99

(1925) describes “erosion by solution and fill.” 

After the discovery of potash in the area, 

Robinson and Lang (1938) published an early 

paper on the geology and hydrology of Nash 

Draw. This study identified the brine aquifer at 

the top of the Salado running down the 

Figure 1. Nash Draw boundary and potentiometric surface at the top of the brine aquifer.
100

length of Nash Draw to the Pecos River. 

Hendrickson and Jones (1952) also noted that 

the brine aquifer moves under the Salt Lake and 

discharges into the Pecos River near Malaga 

Bend. A landmark report was written by James 

Vine on behalf of the Atomic Energy 

Commission to study the surface geology of 

Nash Draw in preparation for the Gnome 

Project, the detonation of a nuclear device for 

peaceful purposes (Vine, 1962). His report was 

one of the first comprehensive works on the 

geology of Nash Draw and included the first 

detailed geologic map of Nash Draw. He 

describes Nash Draw and the lakes on the south 

end as having no external surface drainages or 

outlets. Brokaw and others (1972) reported 

comprehensively on the geology and hydrology 

of the Carlsbad potash area as background for 

siting a repository for nuclear waste. 

Geohydrology Associates (1978) was contracted 

by the Bureau of Land Management (BLM) to 

specifically study the effects of potash industry 

brine disposal on the limited quantities of fresh 

water in the area. They were asked to address 

three questions: 1) is fresh water in the Carlsbad 

potash area in danger of contamination from 

expanded potash mining activities, 2) is the 

brackishness of the Pecos River below Malaga 

Bend due to mining activity, and 3) is the 

amount of leakage from brine-disposal ponds 

significant compared to the volumes of naturally 

occurring brine? This study was followed up by 

a second study by the same company 

(Geohydrology Associates, 1979) to address 

other objectives: 1) establish the depth and 

configuration of the water table in the potash 

area, 2) measure aquifer parameters in the 

potash area, 3) refine the hydrologic parameters 

used in water-budget studies in order to establish 

more accurate inflow-outflow relations at 

various plant sites, and 4) evaluate the suitability 

of several natural salt lakes as brine-disposal 

sites. Geohydrology Associates (1979, p. 86) 

concluded that leakage from the Salt Lake “may 

discharge into the Pecos River” and that 

groundwater quality and levels have been 

affected by potash-refinery waste disposal. 

Bachman (1981, 1987) postulates that Nash 

Draw has taken its present form as a result of the 

coalescing of collapse sinkholes. Powers and 

Owsley (2003) identified numerous cave and 

karst features during a study along the 

realignment of Highway 128 where it crosses 

Nash Draw, concluding that karst processes are 

still active in that area. Powers and others (2006) 

brought many of these studies together in their 

paper on Nash Draw evaporite karst features and 

processes. They also suggest that brine water of 

Laguna Grande may be infiltrating sediments in 

a low divide known as Scoggin Flat. Powers and 

others (2006) also cite the lack of quantifiable 

data in being able to differentiate springflows 

into the lagunas and calculate storage capacities 

in the karst hydrologic system.

All authors agree that karst processes are at 

work in Nash Draw and acknowledge that the 

underground transport of water and subsequent 

solution and collapse of the evaporite 

formations, with attendant erosion, is 

responsible for the development of the karst 

valley. The extent of influence that karst conduit 

flow has on the system and the potential impacts 

to the downstream ecosystems are still not 

understood.

This is an abbreviated account of geological 

and hydrological studies of Nash Draw. A few 

additional background references include 

Bachman and Johnson (1973), Hale and others 

(1954), Cooper and Glansman (1971), and 

Mercer (1983). Numerous more detailed articles 

and documents have been produced for Project 

Gnome, the Waste Isolation Pilot Plant (WIPP), 

and industrial interests in the area.

Climate

The area has an arid to semiarid climate. 

The average rainfall is between 25 and 35 

centimeters (9-12 inches) per year. The average 

monthly maximum temperatures in July range 

from 34.5 to 36.5 o

C (94 to 98 oF) with average 

monthly minimums of -2 to -1 o

C (28 to 31 oF) 

in December and January. Average annual 

potential evaporation rates far exceed average 

annual precipitation. Evaporation rates approach 

13,400 cubicmeters per hectare (4.4 acre-feet 

per year) in the brine ponds of this area, 

resulting in a large moisture deficit. Lesser 

evaporation rates can be attributed to spoil piles, 

mud flats, bare soil, and plant transpiration 

(Geohydrology and Associates, 1978, p. 60).
101

GEOHYDROLOGY

The Nash Draw area contains Permian-age 

evaporites of the Rustler and Salado Formations. 

In this area, the Rustler is primarily made up of 

interbedded sulfates, dolomites, and 

mudstone/siltstones while the Salado is 

composed of 75 percent halite (fig. 2). A 

potentiometric surface map on top of the brine 

aquifer (fig. 1) was developed by Geohydrology 

Associates (1979), but it contains uncertainties 

inherent in all such maps regarding specific flow 

paths in karst terrain such as Nash Draw.

Within the Rustler Formation from the top 

units to the bottom (fig. 2), the members are the 

Forty-niner, the Magenta Dolomite, the 

Tamarisk, the Culebra Dolomite, and the Los 

Medaños, an interbedded unit of sandstone, 

siltstone, and sulfate.

The Forty-niner is 12-19 meters (40-65 feet) 

thick and is composed primarily of sulfate with 

lesser amounts of mudstone. Where exposed the 

Forty-niner also contains well developed cave 

systems that, at times, reach the Magenta 

(Goodbar, 2013).

The Magenta is 6-9 meters (20-30 feet) 

thick, composed of dolomite and sulfate, and can 

be identified in outcrop by its color, weathering 

to a pink to pale-red. The dolomite is alternately 

laminated with yellowish-green anhydrite or 

gypsum. The Magenta is water-bearing in the 

Nash Draw area, with generally very low 

production.

The Tamarisk in Nash Draw is 35 meters 

(115 feet) thick and largely composed of sulfate 

(gypsum in Nash Draw) that can be coarsely 

crystalline where exposed at the surface; these 

sulfate beds are laterally continuous downdip to 

the east out of Nash Draw where they are 

anhydrite. The Tamarisk also contains caves and 

swallets in the floor of Nash Draw where water 

can be channeled into subsurface conduits (fig. 

3) or sink slowly into them where sinkholes are 

covered by soil layers (fig. 4). The two sulfate 

beds of the Tamarisk (A-2 and A-3, fig. 2) are 

separated by a mudstone unit (M-3) in Nash 

Draw and nearby surrounding areas.

Figure 2. Basic stratigraphic units in Nash Draw (modified 

from Powers and others, 2006). Each of the 

mudstone/siltstone units has halite or halitic facies 

equivalents east of Nash Draw.

The Culebra is a microcrystalline gray 

dolomite approximately 9 meters (30 feet) thick,

containing numerous small spherical cavities 

and having high porosity (Vines, 1963, p. 13-

18). The Culebra also contains the lower aquifer 

of the Rustler.

Below the Culebra Dolomite is the Los 

Medaños Member (Powers and Holt, 1999). It is 

composed of mainly siltstone and mudstone, but 

also includes sulfate beds as well as halitic to 

halite intervals to the east of Nash Draw. 
102

Figure 3. Cave entrances in the bottom of Nash Draw 

create point sources for aquifer recharge.

The Salado Formation is composed of thick 

beds of halite and thinner beds of sulfate 

(commonly anhydrite with lesser amounts of 

polyhalite). At Nash Draw, the upper section 

consists of variably consolidated clay and 

reddish-gray to brown silt with varying amounts 

of gypsum that may be brecciated. This layer is 

thought to be the insoluble residue left over from 

the solution of halite in the upper part of the 

Salado. It is through this breccia, resting on top 

of undissolved Salado halite, that the brine 

aquifer flows (Vine, 1963, p.7-8).

The two primary aquifers in Nash Draw are 

the brine aquifer in the solution breccia at the 

top of the Salado and the Culebra Dolomite. 

Other upper members of the Rustler, such as the 

Magenta and Forty-Niner, may also contribute to 

the overall water input and can be considered as 

hydrologically connected over parts of Nash 

Draw due to extensive dissolution and 

associated collapse, subsidence, and fracturing 

(Brokaw and others, 1972, p. 54).

WATER TRACING

The purpose of conducting a water tracing 

project in Nash Draw would be to determine 1) 

where water goes once it enters the subsurface, 

2) what the water budget is for the hydraulic 

system when factoring in the potash mining 

discharge rates, 3) the extent conduit flow 

contributes to the overall groundwater flow in 

Nash Draw, and (4) the residence times and flow 

rates within the system. The concerns prompting 

such a study are the same as those identified in 

the 1970s; do salts from potash operations enter 

the natural lakes and depressions in Nash Draw 

and the Pecos River in sufficient quantities to 

create undesirable impacts to the ecosystem?

Conventional hydrologic and hydrogeologic 

methods of groundwater modeling often do not 

provide accurate results when applied to karst. 

Karst-specific methods are needed to more 

accurately characterize flow and transport in 

conduit networks (International Association of 

Hydrogeologists, 2013).

Figure 4. Alluviated sinkholes provide slow infiltration of 

runoff into the subsurface.

Groundwater tracing has long provided the 

detailed point-to-point connection information in 

complex hydrologic systems where the exact 

nature of interactions between the hydrologic 

and geologic settings is difficult to determine. 

This is particularly the case in karst terrains. A 

groundwater trace would provide a more 

empirical and definitive study needed to identify 

point-to-point connections in the Nash Draw 

karst groundwater system. This will help 

managers better understand the dynamics and 

interactions of that complex system and the

potential impacts to a properly functioning 
103

ecosystem. Figure 5 shows a generalized cross 

section of Nash Draw and the relation between 

geologic members and the hydrologic system.

It is widely held that in order to obtain the 

most useful information, it is much more 

effective to conduct a quantitative trace than a 

qualitative trace. Field (2002) showed that 

quantitative tracing studies provide detailed 

information about flow dynamics. This is done 

by developing a tracer budget and plotting the 

amount of tracer injected with the amount of 

tracer recovered over time while factoring in 

groundwater discharge. This is referred to as a 

breakthrough curve. The use of qualitative 

tracing methods is good to establish positive 

connections between input sources and 

monitoring points. Qualitative methods may also 

be used to estimate flow rates. They are not 

designed to determine how much of the tracer 

material is escaping past the monitoring 

locations and into other parts of the hydrologic 

system. Using a quantitative tracing method can 

give a better idea of how significant an amount 

of tracer is moving into unmonitored locations. 

Quantitative tracer studies can also provide 

better data about mean residence time, flow 

rates, and dispersion. This information allows 

for better analysis and evaluation of the 

hydrologic system’s divergence, convergence, 

dilution, and storage properties.

Figure 5. Generalized cross section of Nash Draw showing geologic and hydrologic relations (From Geohydrology Associates, 

1979). There are no current “fresh water springs” along the margins of Nash Draw at the Magenta outcrops.

The first phase of the project would begin in 

the lower reaches of Nash Draw at its terminus 

near the Pecos River and include the Mosaic 

potash mine tailings piles/discharge points. The 

second phase would move up Nash Draw to its 

northern reaches and include the Intrepid potash 

mine tailings piles/discharge points (fig. 6).

There are several factors to consider when 

initiating a water-tracing project. These include 

1) using the appropriate tracer for the 

environment, 2) using a sufficient amount of 

tracer, 3) how the tracer will be introduced into 

the hydrologic system, 4) sampling techniques 

and locations, and 5) the analysis and 

interpretation of the data.
104

The first of these factors is using the 

appropriate tracer for the environment at hand, 

as some tracers may not perform well or give the 

desired results due to specific water chemistry, 

geologic conditions, and other variables.

Another factor is using a sufficient amount 

of tracer to ensure that the trace will be 

successful, which requires understanding the 

potential water quantities in the aquifer and the 

potential for loss of the tracer.

The next factor is how the tracer will be 

introduced into the hydrologic system. In karst 

terrains, entry points may be natural sinkholes, 

swallets, cave entrances, or other surface 

features such as lakes or other man-made 

impoundments. Input point sources may also 

occur from collapse of closed depressions into 

conduits below.

 

Figure 6. Proposed dye traces and boundaries: Phase 1 and Phase 2 showing cave and karst features.
105

This can be a relatively common occurrence 

in the natural world but may be exacerbated 

when closed depressions are used for solid or 

fluid storage. Tracers can be introduced in liquid 

form or as a solid (powder). In areas where 

rainfall is low and water flow is limited, tracers 

may need to be flushed into the system using 

large water tankers, although this may be 

impractical in some situations.

A forth factor is that of selecting the 

appropriate techniques and locations, which 

become a critical part of tracer project design. 

Sampling locations should be selected carefully. 

Multiple background samples should be 

taken prior to the introduction of any tracer into 

the system. Background concentrations can 

adversely affect tracer analysis if not recognized 

and taken into account. There are a large number 

of both naturally occurring and man-made 

materials and substances that can affect accurate 

tracer analysis. Due to this, it becomes critically 

important to be able to subtract those 

background concentrations from subsequent 

samples to obtain more accurate tracer results 

(Field, 2011). This ensures there is no cross 

contamination from other sources that may give 

false data. The method(s) of sampling are also 

critical to the success of a tracer test. The use of 

continuous autosamplers, activated carbon 

receptors or intermittent grab samples makes a 

difference in the quality of data gathered and the 

reliability of the test.

A final and critical point is having proper 

analysis and interpretation of the data. A poor or 

inadequate analysis can taint the results of the 

test and cause the trace to lose credibility. 

Choosing a laboratory that maintains high 

standards and reliability can make the difference 

between a successful trace or not (Aley, 2002). 

A proper analysis requires both experience in 

interpreting tracer tests and modeling 

breakthrough curves. Multiple peaks on 

breakthrough curves may indicate multiple flow 

channels or conduits that have been partially 

constricted, forcing flow to diverge into 

auxiliary channels. It could also mean that there 

were some areas in which the flow was held in 

detention pools or in waterfall plunge pools. In 

such cases the use of a multi-dispersion model 

and dual-advection dispersion equations may 

provide for a more accurate interpretation (Field, 

2012). Together the collective data will provide 

a much more detailed picture of the hydrologic 

system. 

APPLIED SCIENCE AND ADAPTIVE

MANAGEMENT

Once a water trace has been conducted and 

the data analyzed and interpreted it should 

provide a much clearer understanding of the 

hydrologic system from which to make resource 

management decisions. Options and alternatives 

for proposed actions involving mine operations 

can be analyzed from a knowledge-based 

standpoint and potential outcomes can be more 

accurately predicted. Through a better 

understanding of this complex hydrologic 

system the BLM in conjunction with the potash 

industry can develop better mitigation and 

monitoring plans and reach a finer balance 

between resource use and resource protection. 

With a clearer picture of the groundwater flow 

system in Nash Draw, adaptive management 

strategies can be generated to react to 

undesirable events and changes in mine 

operations. Knowing the point-to-point flow 

paths and probable impacts downgradient should 

help guide management decisions and avoid 

future adverse impacts to the environment. In 

the long term, higher quality water flowing 

through the system will provide better water 

quality and habitat for the collective ecosystems.

The BLM Carlsbad Field Office maintains 

and manages geographic information system 

(GIS) data used within the land management 

agency. Data generated through the course of an 

investigation such as this could be maintained 

and managed for ease of retrieval for further 

analysis. It could be combined with existing 

spatial data as well as analytical data such as 

land use, well pumping and recharge, 

evapotranspiration, surface-water flow, stream 

networks, digital elevation models (DEMs) and 

geology. This will allow the BLM to create new 

groundwater models and information for 

environmental assessments.

Resource management issues could be 

addressed using 3-D hydrogeological models, 

groundwater level and quality spatial 
106

information products that show the area of 

critical interest, and animations that show 

groundwater changes and movement through 

time.

SUMMARY

Nash Draw is a karst valley approximately 

15 miles east of Carlsbad, New Mexico. It is 

formed in the Rustler Formation of Permian age 

as a result of dissolution and collapse of 

dolomite and sulfate beds within the formation. 

There are two aquifers within the system. One 

aquifer is in the Culebra Dolomite and the other 

is a brine aquifer at the base of the Rustler and in 

the top of the Salado Formations. Nash Draw 

has been the site of several potash mines since 

the 1930s. Three tailings piles and brine ponds 

are located along the edges of Nash Draw. Brine 

pond leakage has been an acknowledged 

occurrence since the industry began their 

disposal operations. There have been multiple 

events over the decades where brine ponds have 

breached and sinkholes have opened up in 

tailings piles and brine ponds, diverting their 

contents into subsurface conduits. The natural 

playas at the lower end of Nash Draw have been 

getting more and more salty. Species of plants 

and wildlife can no longer survive the salt 

concentrations. There have been no conclusive 

studies to determine where water or potash 

industry discharge goes once it enters the karst 

conduit system. There is speculation that fluids 

entering the aquifer may go into the natural 

playas and the Pecos River.

A primary method of determining 

subsurface connections and transport rates, 

particularly in karst areas, is through the use of 

water-tracing techniques. The use of water 

tracers has been used very successfully for 

decades and has proven to give reliable results. 

The most efficient way to gather sufficient data 

to answer the critical questions needed to make 

informed management decisions regarding 

future discharge and retention of potash 

industrial discharge would be to conduct a 

quantitative water trace rather than a qualitative 

trace. This would provide the BLM with the 

information needed to make decisions and 

develop best management practices based on the 

best available science and verifiable results.

The use of GIS as a method of tracking and 

analyzing data would provide a long-term rapid 

retrieval system for the data. It could also be 

used as a groundwater modeling tool for future 

studies and in developing future adaptive 

management strategies.

ACKNOWLEDGMENTS

The authors thank Dr. Malcolm Field and 

Dr. Dennis Powers for their constructive reviews 

and comments, which greatly improved the 

manuscript. The authors also thank Shiva Achet, 

David Herrell, and Ruben Rodriguez for their 

reviews, comments, and GIS assistance.

The views expressed in this paper are solely 

those of the authors and do not necessarily 

reflect the views or policies of the BLM.

REFERENCES

Aley, Thomas, 2002, Groundwater tracing handbook: 

Ozark Underground Laboratory, Protem, 

Missouri, USA, 44 p.

Bachman, G.O., 1981, Geology of Nash Draw, Eddy 

County, New Mexico: U.S. Geological Survey 

Open-File Report 81-31, 10 p., 4 pl.

Bachman, G.O., 1987, Karst in evaporites in 

southeastern New Mexico: Sandia National 

Laboratories, SAND84-7178, p. 38-41.

Bachman, G.O., and Johnson, R.B., 1973, Stability of 

salt in the Permian Salt Basin of Kansas, 

Oklahoma, Texas, and New Mexico: U.S. 

Geological Survey Open-File Report 73-14, 

62 p.

Brokaw, A.L., Jones, C.L., Cooley, M.E., and Hays, 

W.H., 1972, Geology and hydrology of the 

Carlsbad potash area, Eddy and Lea Counties, 

New Mexico: U.S. Geological Survey Open-File 

Report 72-49, 86 p.

Cooper, J.B., and Glanzman, V.M., 1971, 

Geohydrology of project Gnome site, Eddy 

County, New Mexico: U.S. Geological Survey 

Professional Paper 712-A, 24 p.

Field, M.S., 2002, The QTRACER2 program for 

tracer-breakthrough curve analysis for tracer 

tests in karst aquifers and other hydrologic 

systems: U.S. Environmental Protection Agency 

/600/R-02/001, 179 p.

Field, M.S., 2011, Application of robust statistical 

methods to background tracer data characterized 
107

by outliers and left-censored data: Water 

Research, v. 45, p. 3107-3118.

Field, M.S., and Feike, J.L, 2012, Solute transport in 

solution conduits exhibiting multi-peaked 

breakthrough curves: Journal of Hydrology, v. 

440-441, p. 26-35.

Geohydrology Associates, 1978, Ground-water study 

related to proposed expansion of potash mining 

near Carlsbad, New Mexico: Bureau of Land 

Management, Contract YA-512-CT7-217, p. 1-2. 

Geohydrology Associates, 1979, Water-resources 

study of the Carlsbad potash area, New Mexico: 

Bureau of Land Management, Contract YA-512-

CT8-195, 86 p.

Goodbar, J.R., 2013, Solution mining and the 

protection of karst groundwater supplies in 

Burton Flats, southeast New Mexico, USA, in

Land, L., ed., Proceedings of the 20th National 

Cave and Karst Management Symposium, p. 13-

17.

Hale, W.E., Hughes, L.S., and Cox, E.R., 1954, 

Possible improvement of quality of water of the 

Pecos River by diversion of brine at Malaga 

Bend, Eddy County, New Mexico: Pecos River 

Commission, 43 p., 8 pl.

Hendrickson, G.E., and Jones, R.S., 1952, Geology 

and ground-water resources of Eddy County, 

New Mexico: New Mexico Bureau of Mines and 

Mineral Resources Ground-Water Report 3, 

73 p. 

International Association of Hydrogeologists, 2013, 

available online at 

http://karst.iah.org/karst_hydrogeology.html

Lee, W.T., 1925, Erosion by solution and fill, in

Contributions to the geology of the United 

States: U.S. Geological Survey Bulletin 760-C, 

107 p.

Mercer, J.W., 1983, Geology of the proposed waste 

isolation pilot plant site, Los Medanos area, 

southeastern New Mexico: U.S. Geological 

Survey Water-Resources Investigations Report 

83-4016, 121 p.

Powers, D.W., Beauheim, R.L., Holt, R.M., and 

Hughes, D.L., 2006, Evaporite karst features and 

processes at Nash Draw, Eddy County, New 

Mexico, in Land, L., Lueth, V., Raatz, W., 

Boston, P., and Love, D., eds., Caves and karst 

of southeastern New Mexico: New Mexico 

Geological Society Fifty-seventh Annual Field 

Conference, p. 253-264.

Powers, D.W., and Holt, R.M., 1999, The Los 

Medanos Member of the Permian Rustler 

Formation: New Mexico Geology, v. 21, no. 4, 

p. 97-103.

Powers, D.W., and Owsley, D., 2003, Field survey of 

evaporite karst along New Mexico Highway 128 

realignment routes, in Johnson, K.S., and Neal, 

J.T., eds, Evaporite karst and 

engineering/environmental problems in the 

United States: Oklahoma Geological Survey 

Circular 109, p. 233-240.

Robinson, T.W., and Lang, W.B., 1938, Geology and 

ground-water conditions of the Pecos River 

Valley in the vicinity of Laguna Grande de Sal, 

New Mexico: New Mexico State Engineer 12th

and 13th Biennial Report, 89 p.

Vine, J.D., 1963, Surface geology of the Nash Draw 

quadrangle, Eddy County, New Mexico, in

Contributions to general geology: U.S. 

Geological Survey Bulletin 1141-B, 46 p.
108

Use of A Dual Continuum Model to Describe Solute Transport in Karst 

By Roger Painter, Justin Harris, and Lonnie Sharpe

Tennessee State University, College of Engineering, 3500 John A Merritt Blvd., Nashville, TN 37209

Abstract

The advection dispersion equation (ADE) as applied to pipe flow often successfully models solute 

transport along major karst features. This approach has had success when flow within these features is 

predominantly along conduits. However, the slower solute transport associated with flow in the diffuse 

continuum may explain the tendency of tracer response concentration data to have a long upper tail 

compared to the diminishing tail predicted by the ADE. The hydraulic response of karst to a rain event 

also reflects the dual continuum for karst flow. The high permeability of the conduit network allows for a 

subsequent quick response at the spring to a rain event. A slow recession to pre-rain event springflow is 

often related to water being released from storage in the fractured media or epikarst. It is in this context 

that the case is made for a dual continuum transport model for karst. In existing double continuum models 

the matrix and the conduit network are each represented by a continuum, and the exchange of water 

between the two continua is governed by lumped exchange parameters. This paper presents a dual

continuum model for karst, which is based on the finite element solution of the rigorous model in terms of 

the Navier-Stokes and continuity equations describing conduit flow, the Forchheimer-corrected Brinkman 

equations describing the diffuse phase flow, and finally, the transient ADE describing solute 

concentration. In the model, the two adjacent continua share a common boundary. Due to the extreme 

differences in the flow regimes near the common boundary, the boundary conditions are characterized by 

very steep gradients. Furthermore, the hydraulic characteristics are independent of the concentration of 

the diluted contaminant. To facilitate validation of the computational approach, a laboratory-scale analog 

model was constructed consisting of an open channel submerged in a porous media. The analog model 

allows the conduit cross section and the hydraulic conductivity of the porous media to be varied as 

parameters. The computer code, COMSOL 4.4 Forchheimer Flow Module, was modified to provide the 

steady state solution for the system (COMSOL user’s manual, 2014), and the transient flow model with 

solute transport was developed using the FlexPDE 6.0 finite element solver (FlexPDE 6 user’s manual, 

2014). 

REFERENCES

COMSOL user’s manual, 2014, Introduction to COMSOL multiphysics: COMSOL Inc., Burlington, MA, USA, 158 

p., website accessed on 3/12/2014, also available at 

http://www.comsol.com/shared/downloads/IntroductionToCOMSOLMultiphysics.pdf 

FlexPDE user’s manual, 2014, FlexPDE 6, version 6.35, Spokane Valley, WA, website accessed on 3/12/2014, also 

available at http://www.pdesolutions.com/download/flexpde635.pdf 
109

GEOCHEMISTRY

Geochemical Evidence for Denitrification in the Epikarst at the Savoy 

Experimental Watershed, Northwest Arkansas

By Jozef Laincz1 and Phil D. Hays2,3

1

Environmental Dynamics, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701

2

University of Arkansas, Department of Geosciences, Ozark Hall 216, Fayetteville, AR 72701 

3

U.S. Geological Survey, Arkansas Water Science Center, 401 Hardin Rd, Little Rock, AR 72211

Abstract

Karst aquifers are highly vulnerable to agricultural nitrate (NO3

-

) contamination due thin soils and 

rapid conduit flow characteristic of karst geology. Many karst regions contain epikarst, an upper 

weathered layer of carbonate bedrock, which could support a higher degree of denitrification, as a result 

of physical properties that are distinctly different from the underlying karst. This study aimed to identify 

denitrification and characterize controls on denitrification in a well-delineated epikarst system in 

northwest Arkansas. Water samples were collected at an interceptor trench and at epikarst springs 

downgradient from the trench after four storm events in the spring 2011 and analyzed for NO3

-

concentration, NO3- delta-nitrogen-15 (δ15N; ratio of nitrogen-15 (15N):nitrogen14 (14N) isotopes) and 

delta-oxygen-18 (δ18O; ratio of oxygen-18 (18O):oxygen-16 (16O) isotopes), dissolved organic/inorganic 

carbon ratio (DOC/DIC) concentration and delta-carbon-13 (δ13C; ratio of carbon-13 (13C):carbon-12 

(

12C) isotopes), and dissolved gas concentration of nitrogen and oxygen (N2, O2 respectively). 

Denitrification was indicated by an average NO3- decrease of approximately fifty percent along the 

trench-spring flowpaths. For flowpaths upgradient from the trench, denitrification was indicated by 

simultaneous isotopic enrichment in NO3

-

with 15N and 18O and by the trend of increasing DIC 

concentration with decreasing δ13C of DIC detected in the trench samples. The occurrence of 

denitrification in the system was corroborated by dissolved N2 measurements which showed 

supersaturation of up to one hundred-six percent in all except for three samples. Consistent with 

environmental requirements of denitrifiers, N2 saturation negatively correlated with O2 saturation and 

positively correlated with DOC concentration at the springs, with the latter suggesting a limiting role of 

DOC on denitrification in the epikarst. The results also suggest that hydrology (epikarst saturation) plays 

an important indirect role in controlling denitrification: more saturated conditions likely deliver more 

DOC substrate and more restrict O2 diffusion into the epikarst, thus helping to create an anoxic 

environment suitable for denitrification. In conclusion, this study successfully identified denitrification 

and several of its controls in the studied epikarst system, and its findings can serve as a foundation for 

future, quantitative studies.

INTRODUCTION

High nitrate (NO3

-

) concentrations in water 

pose a risk to human health (Tenovuo, 1986) as 

well as the health of aquatic ecosystems 

(Goolsby and Battaglin, 2001; Rabalais and 

others, 1996). The problem of groundwater NO3

-

contamination is most often associated with 

agricultural activity, and one type of landscape 

especially vulnerable to such contamination is 

karst (Boyer and Pasquarell, 1996; Power and 

Schepers, 1989). Here, the typically thin or 

missing soil cover, direct point-recharge via 

sinkholes, and rapid, concentrated flow in the 

conduit network with little microbial 

remediation and high rates of dispersion offer 

little protection of aquifers from contamination 

originating at the surface. A case in point is the 

area under study, the karst region of northwest 

Arkansas, where intense animal production and 

excess nutrient generation have been linked to 

elevated NO3

- concentrations in local springs 

and wells (Adamski, 1997; Davis, Brahana, and 

Johnston, 2000; Laubhan, 2007; Steele and 

McCalister, 1990). Protection of these systems is 

paramount as karst aquifers are important 

sources of drinking water; as much as one 

quarter of the world's population obtains its 
110

drinking water from karst aquifers (Ford and 

Williams, 2007).

Many karst systems are mantled by a layer 

known as regolith or epikarst, generally defined 

as the dissolutionally weathered, typically 3-15 

m thick, upper portion of the carbonate bedrock 

(Ford and Williams, 2007). The U.S. karst map 

(Veni and others, 2001) identifies more than 

50% of U.S. karst as being buried, i.e, covered 

by the epikarst.

Epikarst hydrology is distinctly different 

from that in the underlying bedrock and could 

be conducive to significant microbial activity 

including denitrification, which is the most 

important NO3

- attenuation process removing 

NO3

- from watersheds in the form of gaseous 

nitrogen. For example, as porosity and 

permeability diminish with depth, the epikarst 

has a tendency to detain and delay recharge 

(Aquilina, Ladouche, and Dörfliger, 2006; 

Bakalowicz, 1995; Einsiedl, 2005), which 

translates into increase in residence time, an 

important factor facilitating denitrification 

(Green and others, 2009; Seitzinger and others, 

2006). The decrease in permeability also induces 

lateral flow (Klimchouk, 2004) which acts to 

route the flow away from vertical shafts and 

conduits leading to the phreatic zone in the 

deeper bedrock. Studies have documented that 

the epikarst is a chemically reactive zone 

changing the chemistry of recharging water with 

respect to Cl-, Br-, oxygen-18 and deuterium 

(Aquilina and others, 2006) as well as 

attenuating organic dye and phosphate tracers 

(Sinreich and Flynn, 2011).

At the same time, epikarst discharge has 

been found to constitute as much as 55% of the 

total discharge volume of springs or small 

catchments (Lee and Krothe, 2001). Therefore, 

the quality of waters discharging out of karst 

watersheds likely is dictated to a great degree by 

biogeochemical processes taking place in the 

epikarst, which emphasizes the importance of 

understanding of biogeochemical functioning of 

the epikarst.

While various aspects of epikarst hydrology 

have been well established, the understanding of 

its biogeochemical functioning, including the 

processes of nitrate attenuation, is lacking. A 

number of studies on this topic have 

characterized karst systems where the epikarst 

was present (Einsiedl, 2005; Lee and Krothe, 

2001; Panno, Hackley, Hwang, and Kelly, 

2001), but none focused solely on the epikarst 

itself.

The purpose of our investigation was to add 

to the knowledge of the biogeochemical 

functioning of the epikarst and, more 

specifically, to identify denitrification and its 

spatial and temporal variation as well as any 

controlling factors in an epikarst system with 

well-delineated hydrology. Study methods relied 

on a complex geochemical characterization 

involving measuring concentration and stable 

isotopes of all of the key reactants and products 

of the denitrification reaction, including nitrate, 

dissolved organic and inorganic carbon, and 

dissolved dinitrogen. The application of 

dissolved dinitrogen measurements to detect 

denitrification in an epikarst system is somewhat 

novel. While commonly applied to aquatic and 

marine systems, the technique rarely has been 

employed in unsaturated terrestrial systems due 

to challenges posed by high N2 background and 

its rapid exchange with air (Groffman and 

others, 2006), and there appears to be no study 

that has employed it specifically in the epikarst.

Site Description

The study site is located at the Savoy 

Experimental Watershed (SEW) near the town 

of Savoy in northwest Arkansas. The landscape 

of SEW is characterized by steep-sided valleys 

cut into a highly dissected plateau formed on 

impure, chert-rich limestone. Land use is 

dictated by the topography, with the steep side 

slopes and narrow ridge tops in hardwood forest 

and the broader ridge tops and valley bottoms in 

permanent pasture characteristic of the Illinois 

River Watershed. Geologically, the SEW 

represents the regolith-mantled karst setting of 

the Ozark Highlands, and is a geologic setting 

typical of approximately 15% of the eastern 

U.S., where karstified carbonate bedrock is 

overlain by a variable thickness of erosional 

residuum (regolith or epikarst) composed mainly 

of clay and rock fragments of silicic carbonate. 

The epikarst at the site is from 1 to 4 m thick. 

The soil at the top consists of up to 60% of rock 
111

fragments, which become more abundant and 

also progressively turn into more continuous and 

less weathered rock ledges with depth. A 

detailed pedologic characterization of the site 

can be found in Sauer and Logsdon (2002) and a 

structural description of the epikarst based on 

subsurface geophysics in Ernenwein and 

Kvamme (2004).

METHODOLOGY 

Denitrification was studied in a section of 

the epikarst in Basin 1 of the SEW. Samples 

were collected at two stages of the hydrologic 

gradient of the epikarst section: an interceptor 

trench located on a sloping (15%) ridge-top 

pasture and five epikarst springs (J1-J5) located 

on the side slope from 29 to 137 m 

downgradient from the trench (fig. 1). The 

trench is about 1.5 m deep, excavated down to 

relatively unweathered carbonate bedrock, and 

fitted with a French drain. The trench serves to 

intercept waters representative of epikarst 

throughflow. The springs are natural, terminal 

discharge points of the epikarst flowpaths and 

thus provide samples representing the final 

geochemical signature of waters leaving the 

epikarst. The springs were fitted with V-notch 

weirs for accurate discharge measurement. The 

hydrologic connections between the trench and 

each of the springs had previously been 

established by dye tracing (Laincz, 2007). Prior 

to sampling, chicken litter was applied at a rate 

of 5 tons per acre across the pasture area of 

about 80 x 150 m upgradient from the trench in 

March 2011 to simulate common NO3- loading 

practices in Arkansas and also to increase NO3-

signal.

Samples were collected following each of 

four consecutive storm events from May 2011 

until July 2011 in conditions of increased 

saturation and flow. Water samples were 

collected from the trench and all of the springs 

for each storm event. Samples were collected 

into appropriate containers for each type of 

chemical and isotopic analysis, and filtered and 

preserved in accordance with guidelines from 

the analyzing lab. For anion (NO3-, Cl-

) and 

NO3- stable isotope (δ15N and δ18O) analyses, 

samples were collected without filtration or 

preservation. For DOC/DIC concentration and 

13C stable isotope analysis, samples were filtered 

on-site (0.7 μm Whatman GF/F filters in a 

Millipore 47-mm syringe filter assembly), and 

samples for DOC13C isotopic analysis were 

acidified with 85% H3PO4. For dissolved-gas 

analyses, samples were collected via a portable 

sampler (Masterflex E/S, Cole-Parmer, Vernon 

Hills, IL) directly from the point of emergence 

of water from the ground to minimize contact 

with air. The pump outflow tubing was inserted 

to the bottom of a sample vial, with 234 μl of 

50% ZnCl2 preservative solution (1.2% final 

conc., v/v) pre-dosed in each vial (18 ml Kimax 

Figure 1. Conceptual model of the epikarst illustrating the lateral flow and sampling points along the flowpath. (Not to scale)
112

test tube with a ground glass stopper), and water 

was pumped at a slow rate to prevent bubble 

formation before the vial was stoppered, sealed 

with Parafilm, and carefully checked to ascertain 

that no air bubbles were present. Samples were 

placed on ice and transported into laboratory, 

where they were stored in the dark at 4°C until 

analysis. During sample collection, several field 

and environmental parameters were measured 

including pH, electrical conductivity, 

temperature, dissolved oxygen (DO), and 

barometric pressure.

Chemical Analyses

Chemical analysis of samples for major 

anions and cations was conducted at the 

Arkansas Department of Environmental Quality 

Water Quality Lab using ion chromatography 

(U.S. Environmental Protection Agency (EPA) 

method 300.0) and inductively coupled plasmaatomic emission spectrometry (EPA method 

200.7), respectively. Stable isotopes of NO3-

(δ15N and δ18O) were analyzed at the University 

of Arkansas Stable Isotope Lab using the 

denitrifier method (Casciotti, Sigman, Hastings, 

Bohlke, and Hilkert, 2002; Sigman and others, 

2001) involving the use of genetically modified 

denitrifier to quantitatively convert sample NO3

-

to N2O, with adaptations described in Winston 

(2006). The analysis was performed using a 

GasBench II system with a CO2 trap made of 

stainless steel and organics and a water trap 

consisting of isopropanol-dry ice slush, 

connected to a continuous flow isotope ratio 

mass spectrometer (XP, ThermoFinnigan, 

Bremen, Germany). The method precision for 

δ15N and δ18O was ±0.46 and ±0.49‰, 

respectively. The results are expressed in the 

text below in δ notation defined as δ X (‰) = 

(Rs/Rst – 1) * 1000, where X is 15N, 18O, or 13C, 

and R is the 15N/14N, 18O/16O, 13C/12C ratios of 

the sample (s) and reference standard (st), 

respectively. The reference standards were Air 

for δ15N, Vienna Standard Mean Ocean Water 

(VSMOW) for δ18O, and Vienna Pee Dee 

belemnite (VPDB) for 13C. DOC and DIC 

concentration and stable isotope (13C) 

composition were analyzed at the Colorado 

Plateau Stable Isotope Lab, Flagstaff, AZ, using 

an O.I. Analytical Model 1010 TOC analyzer 

(OI Analytical, College Station, TX) interfaced 

to a Finnigan Delta+ XL isotope ratio mass 

spectrometer (Finnigan-MAT, San Jose, CA) 

(St-Jean, 2003). The DIC and DOC 

measurements had an error margin of ±0.03 and 

±0.13‰, respectively. Dissolved O2 and N2

analyses were performed in the Scott 

Biogeochemistry Lab at the University of 

Arkansas Department of Crop, Soil and 

Environmental Sciences using a membrane inlet 

mass spectrometry (MIMS) setup consisting of a 

Pfeiffer Prisma mass spectrometer and a Bay 

Instruments DGA membrane inlet S-25-75. The 

MIMS setup and analysis are described in detail 

in Kana and others (1994) and Grantz and others 

(2012), respectively. The precision of the MIMS 

analysis was ±0.3%.

RESULTS

Nitrate Concentration and δ15N and δ18O

Nitrate concentrations ranged from 1.5 to 

7.6 mg/L, with an average of approximately 3 

mg/L. These concentrations are similar to those 

reported for the watershed by other authors 

(Sauer and others, 2008; Winston, 2006). The 

NO3

- concentration did not seem to have been 

significantly affected by the application of 

chicken litter two months prior to the test. The 

average NO3

- concentrations of the trench and 

spring water samples were 4.7 and 2.6 mg/L, 

respectively. The NO3

-

-δ18O values ranged 

between 1.3 and 4.6‰. The trench average was 

higher than the springs average (5.2 and 3.7‰, 

respectively). The NO3

-

-δ15N values varied 

between 2.5 and 5.8‰. The trench samples 

averaged approximately 2‰ while water from 

the springs averaged 3.6‰. The measured NO3--

δ15N and -δ18O values are consistent with NO3

-

originating from soil organic matter and animal 

waste (i.e., manure, chicken litter) (Kendall and 

McDonnell, 1998). The indicated origin is 

accurate as soil and animal waste were in fact 

the primary potential sources of NO3

- at the site.

DIC, DOC Concentration, and δ13C

DIC varied from 7.2 to 35.5 mg/L-C, with 

an average of 25.5 mg/L-C. The average DIC 

concentrations of the trench and spring samples 

were 28.6 mg/L-C and 10.1 mg/L-C, 

respectively. Isotope analyses showed the DIC 

δ13C values ranging between -13 and -21‰. The 
113

springs averaged at approximately -15‰ while 

the trench average was lower (-19‰). DOC 

concentration varied between 0.3 and 4.8 mg/LC. DOC concentration in the springs averaged 

0.8 mg/L-C, which is typical for groundwater, 

while the trench average was higher, at 3.9 

mg/L-C, possibly as a result of being situated 

closer to the organics-rich soil zone than the 

springs. DOC δ13C values were within a 

relatively narrow range of about -25 to -27‰. 

This is an expected range that accurately 

pinpoints the origin of this DOC in the local 

vegetation dominated by C-3 plants. 

Dissolved N2 and O2

Dissolved N2 concentration ranged from 

15.1 to 17.2 mg/L. The concentration data varied 

in both time and space. Spatially, on average, the 

highest concentration was in J2 (103 mg/L) 

while the lowest was in J5 samples (100.8 

mg/L). Temporally, samples collected on April 

28 had the highest average concentration (104.2 

mg/L) while the lowest average concentration 

was found in the only sample of April 15 (99.4 

mg/L). N2 saturation levels calculated from 

N2:Ar ratios and Ar concentrations ranged from 

99.4 to 105.6%, with an average of 102.2%. All 

but three samples were supersaturated with 

respect to N2, i.e., their N2 content exceeded the 

equilibrium-with-air concentration or 100% 

saturation. DO concentration ranged from 4.9 to 

8.2 mg/L and averaged 6.5 mg/L. On average, 

the highest DO concentration was in the trench 

(7.9 mg/L), the lowest in J2 (5.1 mg/L). 

Temporally, the variation in DO was small, with 

the highest value at 7.1 mg/L on 4/15 (only one 

sample from J3) and the lowest average at 6.2 

mg/L on 4/28. Calculated O2 saturation ranged 

between 46.9 and 90.5% and averaged 65.9%. 

The trends of temporal and spatial averages were 

similar to those for DO concentration. 

DISCUSSION

Nitrate Concentration and δ15N and δ18O

The NO3

- concentration data show a pattern 

of decreasing concentration between the trench 

and the springs. The concentration of the former 

was on average two times higher than of the 

latter. The processes that in subsurface situations 

can cause decreases in NO3

- concentration are 

dilution and denitrification (Clark and Fritz, 

1997). Dilution did not appear to be the cause 

since chloride concentration between these two 

points of the flowpath did not decrease. 

Consequently, the likely process responsible for 

the NO3

- depletion was denitrification.

Denitrification causes an isotopic 

enrichment in both 15N and 18O of the remnant 

NO3-

, with the 15N enrichment approximately 

twice that of 18O (Bottcher, Strebel, Voerkelius, 

and Schmidt, 1990; Mariotti, Landreau, and 

Simon, 1988). This phenomenon shows on a 

δ15N vs. δ18O plot as a line with a positive slope 

of 0.5. While all of the samples do not produce 

such trend, the trench samples δ15N and δ18O 

exhibit a strongly positive correlation with a 

slope of 0.6 (fig. 2). This is an indication of 

denitrification in the upper compartment of the 

epikarst drained by the trench. Further down the 

flowpath, the spring samples do not show any 

definite δ15N-δ18O relation. Denitrification might 

be occurring on the flow path to the springs as 

well, but the remnant NO3

- may mix with NO3-

from extraneous sources (e.g. decomposition of 

organic matter) concealing the isotopic signature 

of denitrification.

Figure 2. Isotopic composition of nitrate in trench samples 

(squares) and spring samples (triangles).

DIC Concentration and δ13C

The denitrification reaction also is known to 

increase DIC concentration (Aravena and 

Robertson, 1998) as well as to impart 13C 

depletion to the DIC through the addition of 13Cdepleted organic carbon participating in the 

reaction (Fritz, Cherry, Weyer, and Sklash, 
114

1976). The spring samples indeed had 

significantly higher DIC compared to the trench 

samples, with the average concentration in the 

springs about 3 times that in the trench. This 

DIC, however, was not depleted in 13C relative 

to the trench values. A likely reason is addition 

of DIC via carbonate dissolution along the 

flowpath. If the only DIC source was 

denitrification, DIC in the samples would have a 

δ13C in the range of its source organic matter 

(Aravena and Robertson, 1998). In this case, the 

δ13C of dissolved organic matter of all samples 

ranged 25-27‰. However, if the aquifer is a 

carbonate aquifer, dissolution of carbonate 

minerals (δ13C ~ 0‰) will buffer the input of the 

depleted 13C generated by denitrification. 

Mixing equal amounts of organic (δ13C = -26‰) 

and inorganic (δ13C = 0‰) carbon would 

generate DIC with a δ13C value of -13‰. A 

calculation using a binary mixing equation 

shows that DIC with the same δ13C value as the 

average for the springs (-15‰) would be 

produced by mixing of about 42% of inorganic 

and 58% of organic carbon. Thus, denitrification 

may have been occurring along the trench-tospring flowpaths and is responsible for the NO3-

depletion observed at the springs, but the 

expected DIC δ13C response was masked by DIC 

from calcite dissolution.

Applying the same approach as with NO3

-

isotopes and separately analyzing for trends in 

the spring samples and the trench samples, a 

positive relation was noted between DIC and 

δ13C in the trench samples, indicating 

denitrification occurring in the upper epikarst 

compartment drained by the trench (fig. 3). This 

is consistent with the NO3-

δ15N and δ18O data, 

which also indicated denitrification in the trench 

samples. The spring samples, however, 

exhibited a weakly positive trend for DIC vs. 

δ13C, which does not support an interpretation of 

denitrification; however, as shown by the above 

mixing calculation, mixing in the epikarst may 

have occurred and could be masking the effect 

of denitrification on the DIC and δ13C 

composition of the samples.

Dissolved N2 and O2

The most significant observation that can be 

made from the data is that 18 out of 21 samples 

were supersaturated with respect to N2. This 

supersaturation is most probably the footprint of 

denitrification because virtually no other process 

could feasibly occur in this system that would 

cause dissolved N2 to increase beyond saturation 

levels. The only other possible process would be 

the incorporation of excess air, i.e., the 

dissolution of air bubbles entrapped in capillarysized pore spaces by downward migrating 

waters. This mechanism, however, is only 

feasible at sufficient depth and hydrostatic 

pressure below the water table, with about 10 m 

depth required for complete dissolution of the air 

bubbles (Heaton and Vogel, 1981). The thin 

(generally <2 m) and transiently saturated 

epikarst does not offer conditions for the 

occurrence of this process. Denitrification as the 

cause of N2 supersaturation is corroborated by

multiple lines of evidence already presented –

NO3

- and DIC concentrations as well as the 

corresponding isotopic data. Hence, 

denitrification is the most plausible cause of N2

supersaturation.

Figure 3. Relationship between DIC concentration and 

δ13C in trench samples (squares) and spring samples 

(triangles).

We have not found any other denitrification 

studies that determined N2 supersaturation in the 

epikarst or in other groundwater systems, which 

precluded comparison of the data with similar 

studies. However, a few studies, which 

determined N2 supersaturation linked to 

denitrification in deep sea waters, report values 

in the range between 101% and 108% 

(Quinones-Rivera and others, 2007; Rönner and 
115

Sörensson, 1985). This range is similar to the 

values obtained in our study.

Most denitrifiers are facultative anaerobes 

and, consequently, denitrification requires 

anoxic or very low oxygen conditions –

generally below 0.2 mg/L (Tiedje, 1988). The 

measured O2 concentration, however, was in the 

range of 4.7-8.2 mg/L and therefore, any 

denitrification activity in the epikarst would 

have to be restricted to anoxic 

mircroenvironments such as those described by 

Sexstone and others (1985) or Koba and others 

(1997). Such microsites could exist in the 

studied epikarst, indeed; pockets of grayish 

colors indicative of reducing conditions were 

observed in abundance throughout the epikarst 

profile during excavation works at the site. 

Concentration of O2 within these microsites 

would probably be affected by O2 concentration 

in the surrounding matrix; the lower the latter, 

the lower the former. As a result, granted that all 

other requirements for denitrification are met, 

one could expect to see that the less O2 is in the 

system as a whole, the more denitrification will 

occur in these microsites. This phenomenon 

would then manifest itself as a negative 

correlation between the measured N2 and O2

saturation levels. While such correlation is found 

to be only negligible for the entire dataset, 

correlation is relatively strong when the highest 

O2 saturation sites – the trench and J1 site – are 

excluded from the analysis (fig. 4). The 

exclusion seems justified since the relatively 

high O2 content of waters from these two sites 

could well be due to the distinct physical 

hydrologic character of these flowpaths as 

opposed to being a reflection of some intrinsic 

biogeochemical process affecting the O2 content 

in the epikarst (i.e. aerobic or anaerobic 

respiration consuming O2 along the other 

flowpaths). This is especially true for the trench 

waters which could be oxygenated in the final, 

pipe segment of the installed collector (French 

drain) of this flowpath. The J1 flowpath, as 

suggested by discharge and specific conductance 

(this study data) as well as DOC bioavailability 

(Winston, 2006), is dominated by focused flow, 

a more turbulent type of flow characterized by 

increased potential for oxygenation. Thus, a 

combined analysis of N2 and O2 data indicates 

denitrification occurring along the J2-J5 

flowpaths of the epikarst. Dissolved O2, or lack 

thereof, appears to play a role in enabling this 

denitrification.

The effect of O2 saturation on denitrification 

suggested by the data invites the question as to 

exactly what mechanism could enable the 

further drawdown of O2 concentration, creating 

anaerobic conditions within the microsites. 

While, in general, dissolved O2 is consumed by 

aerobic or anaerobic microbial activity and 

geochemical reactions, the key mechanism 

enabling the development of anoxic conditions 

in the microsites could be the blocking of access 

of O2 by waterlogging. The phenomenon of 

waterlogging causing an increase in 

denitrification and consequently loss of soil 

nitrogen by restricting oxygen diffusion to the 

soil is widely known among agronomists and 

soil scientists. Under certain conditions, even a 

small percentage increase in soil saturation can 

initiate denitrification by sealing off a sufficient 

soil volume from diffusion of atmospheric O2

(Craswell, 1978). Similarly, according to Sylvia 

and others (1999), rates of denitrification are

Figure 4. Relationship between dissolved oxygen and 

nitrogen saturation in J2-J5 spring samples (samples from 

J1 and trench are excluded).

generally greatest in wet soils where more than 

80% of pore space is saturated and respiratory 

activity is reasonably high. The data in this study 

provide some evidence for the occurrence of this 

mechanism in the epikarst. Assuming the 

average discharge for a sampling event to be a 

measure of epikarst saturation, the highest 

epikarst saturation event (4/28) had the lowest 

average O2 saturation (and the highest average 
116

N2 saturation), the lowest epikarst saturation 

event (4/15) had the highest O2 saturation (and 

the lowest N2 saturation), and the two 

intermediate epikarst saturation events had 

proportionally inverse intermediate O2 saturation 

(and intermediate N2 saturation) (fig. 5). When 

the analysis is conducted for the sites 

individually instead of averaging the sites for 

each event, the trend of increasing discharge 

with decreasing O2 saturation is present for all 

sites except for the trench. This inconsistency 

again could be caused by aeration effects of the 

collector elevating the O2 content of trench 

waters, particularly at higher discharge rates. 

The evidence overall thus indicates that physical 

hydrology of the epikarst can control 

geochemistry, specifically, O2 concentration and 

subsequently denitrification. The analysis, 

however, relies on only four events and uses 

discharge to assess water saturation. The trend 

therefore should be confirmed with an analysis 

involving more measurements and perhaps some 

more direct method of measuring water 

saturation (e.g., the electrical resistivity method). 

DOC 

One of the reactants of denitrification is 

organic carbon, which the microbes use as an 

electron donor. Denitrifying activity has been 

found to be related to organic carbon contents in 

a wide range of environments, including 

sediments (Van Kessel, 1978), soils (Bremner 

and Shaw, 1958; Burford and Bremner, 1975), 

riparian zones (Vidon and Hill, 2005), shallow 

aquifers (Starr and Gillham, 1993) as well as 

oxic surface waters and porewaters (Sobczak 

and Findlay, 2002). The data from this study 

suggest this to also be the case in the epikarst; 

for the spring samples, N2 saturation, which can 

be taken as a proxy measure of denitrification, is 

positively correlated with DOC concentration 

(fig. 6). This correlation does not hold when the 

trench samples are included in the analysis due 

to their abnormally high DOC levels, on average 

about 5 times higher than those in the springs. 

These are suspected to be caused by 

contamination of carbon compounds leaching 

from surface-derived organic detritus 

accumulated in the French drain gravel pack and 

pipe. The trench samples, therefore, were 

excluded. In addition, the utilization of DOC by 

denitrifiers also depends on quality or 

bioavailability of this DOC. While this 

parameter was not assessed, the positive relation 

between DOC and N2 saturation suggests that 

this DOC was sufficiently labile for denitrifiers.

The relation thus indicates that carbon 

availability has a limiting effect on 

denitrification in the epikarst, and two reasons 

may explain why this perhaps should be the case 

in the epikarst even more than in other 

environments: Firstly, in general, in 

environments that are not completely anaerobic 

such as the epikarst, denitrifiers have to compete 

for carbon with obligately aerobic heterotrophs, 

which make up the bulk of the microbial 

biomass in these environments (Sylvia and 

others, 1999). Secondly, organic carbon in the 

system is already a limited resource due to the 

Figure 5. Average discharge (Q), O2 saturation, and N2

saturation for four sampling events (error bars represent 

mean +/- 1 SD).
117

fact that karst groundwater systems do not have 

significant autotrophic sources of organic carbon 

(Susan Ziegler, personal comm.).

The correlation also shows data points 

clustered according to event date, with the 

higher discharge events having higher N2

saturation and DOC concentration (fig. 6). This 

indicates that hydrology (epikarst saturation) not 

only impacts O2 concentrations and 

subsequently denitrification in the epikarst as 

noted before, but epikarst saturation also seems 

to exert control on denitrification by controlling 

DOC availability. Higher discharge events likely 

mobilize and deliver more DOC than lower 

discharge events. The greater supply of DOC 

then likely translates into a greater 

denitrification potential during storm events. 

This dynamic makes the epikarst different from 

surface systems where storm-flow events are 

typically thought of as events where more 

refractory carbon is delivered (Susan Ziegler, 

personal comm.). The lack of significant 

autotrophic sources of carbon means that the 

epikarst system depends upon the pulse of 

carbon from storm events.

Figure 6. Relationship between DOC concentration and N2 

saturation of spring samples (trench samples are excluded). 

Circles enclose datapoint clusters which correspond with 

sampling dates with varying hydrologic conditions 

(saturation) as indicated by average discharge (avg. Q).

CONCLUSIONS

The occurrence of denitrification along the 

flowpaths between the trench and the epikarst 

springs was indicated by the general trend of 

NO3

- depletion, which in the absence of dilution 

could only be caused by denitrification. 

Additional geochemical indicators, including 

relations between nitrate δ15N and δ18O as well 

as DIC concentration and DIC δ13C, did not 

corroborate this evidence, although it is possible 

that the positive signature of denitrification had 

been masked – in the case of NO3-

isotopic 

composition by mixing in of extraneous NO3-

and in the case of DIC δ13C by dissolution of 

calcite. 

Denitrification was also detected in the 

epikarst upgradient from the trench. The 

evidence includes the trend of simultaneous 

enrichment in nitrate 15N and 18O and another 

trend of increasing depletion in 13C of DIC as 

DIC concentration in the trench samples 

increased. The trench waters also had higher 

concentration of DOC relative to the epikarst 

springs, being closer to the soil zone DOC 

source, which would give the former a greater 

potential for denitrification. 

The most significant finding of this study is 

the dissolved N2 supersaturation detected in all 

except for three samples, strongly signaling 

denitrification in the epikarst. Negative 

correlation between N2 and O2 saturation 

suggested that the magnitude of denitrification is 

controlled by oxygenation levels of the epikarst 

waters. Oxygen concentration, in turn, seemed to 

have been affected by the wetness or saturation 

level of the epikarst as suggested by negative 

correlation between discharge and O2 saturation. 

Thus, as is the case in soils, hydrology 

(waterlogging) appears to be an important 

control on denitrification in the epikarst.

Further, N2 saturation was positively 

correlated with DOC concentration indicating a 

limiting role of carbon in denitrification in this 

system. Such a situation would be expected 

given the lack of autotrophic sources in karst 

and the dominant presence of obligately aerobic 

heterotrophs which compete with denitrifiers for 

carbon. As with the O2 content, hydrologic 

conditions also appear to affect DOC: higher 

discharge events tended to have higher DOC 

concentrations. The greater storm pulses likely 

are able to mobilize and deliver more C which 

then drives denitrification activity.

The suite of geochemical parameters 

measured for this study indicates denitrification 

5/29 

Av. Q = 20.3 l/min

5/4 

Av. Q = 19.3 l/min

4/28 

Av. Q = 13.4 l/min
118

occurring in this epikarst system. While the 

experimental approach did not allow for 

quantitative evaluation of denitrification or its 

controlling variables, it succeeded in identifying 

their occurrence, which is a valuable 

contribution to understanding the 

biogeochemical functioning of the epikarst. 

These findings also reaffirm the concept that 

within karst systems characterized by limited 

soil development and lack of bioremediation 

capacity, the epikarst is a potentially important 

zone of attenuation of leaching nitrate. The 

findings serve as a foundation for future, more 

quantitative investigations of these epikarst 

phenomena and of their response to specific 

nutrient management practices so that they may 

be optimized to reflect the ecological limitations 

of vulnerable karst landscapes.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Van 

Brahana of the University of Arkansas and Mr. 

Tim Kresse of the U.S. Geological Survey for 

their helpful reviews. Dr. Thad Scott of the 

University of Arkansas shared his expertise and 

equipment for dissolved gas analysis. Mr. Roger 

Miller of the Arkansas Department of 

Environmental Quality assisted with water 

chemistry analysis. Finally, this research was 

made possible in large part by funding from the 

U.S. Department of Agriculture, National 

Resources Conservation Service – National 

Water Management Center and the Arkansas 

Water Resources Center. 

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121

Geochemistry of Paleokarst Aquifers of the Knox Group in Tennessee 

and Kentucky

By Michael Bradley1, and Thomas (Marty) Parris2

1

U.S. Geological Survey, Tennessee Water Science Center, 640 Grassmere Park, Nashville, TN 37211

2

Kentucky Geological Survey, 228 Mining and Mineral Resources Building, Lexington, KY 40506

Abstract

Water-quality samples were collected from deep carbonate formations in the Cambrian- and 

Ordovician-age Knox Group in the central areas of Kentucky and Tennessee as part of an evaluation of 

the formations for carbon sequestration (Kentucky) and the geohydrology of the paleokarst aquifers 

(Tennessee). Geochemical data from the deep carbonate formations have been used to evaluate the 

chemical evolution of the groundwater, residence time, and the degree of confinement. The geochemical 

data indicate differences in groundwater evolution in the different structural settings including the 

Nashville Dome, Cincinnati Arch, and Illinois Basin (fig. 1). 

Figure 1. Major geologic structures and locations of selected wells in the Knox Group, Hancock and Scott Counties, Kentucky, 

and Hickman, Perry, and Wayne Counties, Tennessee.

Geologic units being tested include formations equivalent to the Mascot Dolomite of the upper Knox 

Group, the Chepultepec Dolomite of the middle Knox Group, and the Copper Ridge Dolomite of the 

lower Knox Group. The unconformity at the upper contact of the Knox Group is a major stratigraphic 

break between the lower-middle Ordovician Knox Group and the overlying middle Ordovician 

carbonates. Paleokarst features present in the Knox Group include secondary porosity and permeability,
122

and collapse breccia (fig. 2). Water-quality data from about 900 samples from aquifers in Precambrian- to 

Pennsylvanian-age geologic units in Kentucky and about 600 samples from aquifers in Cambrian- to 

Pennsylvanian-age geologic units in Tennessee indicate that groundwater from the Mascot Dolomite of

the Knox Group has lower dissolved-solids concentrations than would be expected based on data trends in 

other aquifers.

Water-quality and geochemical data from recently sampled Knox Group wells along the western side 

of the Cincinnati Arch in Tennessee and Kentucky indicate a mixing of formation and meteoric waters. 

Groundwater samples from a well in the Illinois Basin in Kentucky has high dissolved-solids and chloride 

concentrations that are indicative of possible connate water and long residence time rock-water 

interaction in the formation. Groundwater from three recently sampled wells in Middle Tennessee, west 

of the Cincinnati Arch, has relatively low dissolved-solids and chloride concentrations and indicates the 

presence of relatively young meteoric water in the formation. The stable-isotope (δ18O and δH) values for 

groundwater from wells in the Nashville Dome and Jessamine Dome are close to the meteoric water line, 

suggesting the presence and possible mixing with meteoric water (fig. 3). The stable-isotope values for 

groundwater from a well in Hancock County, plot along an isotopic trend line for the Illinois Basin, 

indicating rock-water interaction. 

 ____________________________________________________________

Depth below

Location land surface δ18O δ2

H

 (feet) (permil) (permil)

Illinois Basin

Hancock Co., KY 3,500 – 5,000 -5.1 to -5.5 -40.0 to -41.5

Cincinnati Arch – Jessamine Dome

Scott Co., KY 1,800 – 2,100 -7.3 to -8.1 -41 to -57

Cincinnati Arch – Nashville Dome

Hickman Co., TN 1,450 – 3,069 -6.26 to -6.35 -35.6 to -36.0

Wayne Co., TN 1,200 – 1,221 -5.26 to -5.9 -28.2 to -35

Perry Co., TN 4,727 – 4,960 -6.09 -35.53 

Chlorine-36 isotope analysis for water from two wells indicate substantially younger water in the 

Knox Group in Hickman County, Tennessee (Nashville Dome) than in water from a well in Hancock 

County, Kentucky (Illinois Basin), which is much older water (>1.5 million years). 

The occurrence of lower dissolved solids in water at depth in the Knox Group in Middle Tennessee is 

indicative of a permeable unit that has some connection with meteoric water. The indicated mixing of 

formation and meteoric waters and the potential connection with groundwater from shallower aquifers has 

implications regarding possible carbon sequestration in these formations. Potential recharge and 

movement of younger, relatively fresh water into and through the Mascot Dolomite indicates the potential 

for carbon dioxide leakage updip, or possible leakage through fractures in the overlying formations.
123

Core interval, in feet below Kelly bushing of drill rig 

(18.5 feet above land surface)

2,091–2,092 2,117–2,118 3,130–3,131

Photographs from E.I. DuPont, 1992

Figure 2. Core photographs from E.I. duPont GHS no. 1 well, Humphreys County, Tennessee, showing paleokarst features with 

collapse breccia, calcite mineralization, and secondary porosity in the Mascot Dolomite, Knox Group. 

Figure 3. Relation between stable isotope ratios for hydrogen (δ2H) and oxygen (δ18O), in permil (0/00), for groundwater from 

wells in the Knox Group, Kentucky and Tennessee.

Hancock Co., 

KY

Scott Co., KY

Hickman, Perry,

and Wayne Co., 

TN Illinois Basin

Nashville Dome

Jessamine 

Dome

Meteoric Water Line
124

REFERENCES

Bradley, Michael W., 2001, Geochemistry of the Upper Knox aquifer in Tennessee, in Kuniansky, E.L. (ed.), U.S. 

Geological Survey Karst Interest Group Proceedings, St. Petersburg, Florida, February 2001: U.S. Geological 

Survey Water-Resources Investigations Report 01-4011, 211 p.

Bradley, Michael W., and Parris, Thomas, 2012, Geochemistry of deep aquifers in Tennessee and implications for 

carbon sequestration: Tennessee Section-American Water Resources Association, Proceedings of the 22nd

Tennessee Water Resources Symposium, April 2012, Burns, Tennessee, p. 1C-2.

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Kentucky Water Resources Research Institute, Kentucky Water Resources Annual Symposium, March 19, 

2012, Lexington, Kentucky, p. 55-56.

Tennessee Division of Geology, 2011, Regional east-west and north-south cross sections across Tennessee from the 

eastern escarpment of the Cumberland Plateau province to the Mississippi Embayment: Tennessee Division of 

Geology, prepared for the U.S. Geological Survey National Geologic CO2 Sequestration Assessment, 1 pl. 

U.S. Department of Energy, 2013, NATCARB-National carbon sequestration database and geographic information 

system: U.S. Department of Energy, accessed February 21, 2014, at 

http://www.netl.doe.gov/research/coal/carbon-storage/carbon-storage-natcarb
125

Integration of Geochemical and Isotopic Data to Assess Sources of 

Discharge at a Major Spring in the Edwards Aquifer, South-Central 

Texas

By MaryLynn Musgrove1 and Cassi L. Crow2

1

U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX 78754 

2

U.S. Geological Survey, 5563 DeZavala Rd., Ste. 290, San Antonio, TX 78249

Abstract

The Edwards aquifer in south-central Texas is a productive and important water resource. Several 

large springs issuing from the aquifer are major discharge points, popular locations for recreational 

activities, and habitat for threatened and endangered species. Discharge amounts from Comal and San 

Marcos Springs, the first and second largest spring complexes in Texas, are used as thresholds in 

groundwater management strategies. It is generally understood that Comal Springs is predominantly 

supplied by regional groundwater flow paths; however, the hydrologic connection of San Marcos Springs 

with the regional flow system is less understood. During November 2008–December 2010, the U.S. 

Geological Survey conducted a hydrologic and geochemical investigation of San Marcos Springs to 

define and characterize its sources of discharge. During the study, hydrologic conditions transitioned from 

exceptional drought to wetter than normal, which provided the opportunity to investigate the 

hydrogeology of San Marcos Springs under a wide range of hydrologic conditions. Water samples were 

collected from streams, groundwater wells, and springs at and near San Marcos Springs, including 

periodic sampling (every 3 to 7 weeks) and sampling in response to storms. Additionally, selected 

physicochemical properties were measured continuously at several orifices of San Marcos Springs. The 

integration of geochemical and isotopic data with geochemical modeling allowed for distinguishing and 

quantifying sources of discharge at San Marcos Springs. Results indicate that discharge at San Marcos 

Springs was dominated by regional recharge sources and flow paths, and that the contribution from local 

streams was relatively minor. Different orifices of San Marcos Springs responded differently to changes 

in hydrologic conditions. Some orifices are influenced by mixing with a component of saline 

groundwater, likely from the downdip Edwards aquifer saline zone. Results of this study are useful for 

resource management strategies and for understanding geochemical and hydrologic processes that affect 

the Edwards aquifer.
126

MICROBIAL ECOLOGY AND KARST ECOSYSTEMS

Linking Climate Change and Karst Hydrology to Evaluate Species 

Vulnerability: The Edwards and Madison Aquifers

By Barbara J. Mahler1, Andrew J. Long2, John F. Stamm2, Mary F. Poteet3, and Amy J. 

Symstad4

1

U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX 78751

2

U.S. Geological Survey, 1608 Mountain View Rd., Rapid City, SD 57702 3

University of Texas at Austin, 1 University Station G2500, C0930, Austin, TX 78712 4

U.S. Geological Survey, Northern Prairie Wildlife Research Center, 8711 37th Street SE, Jamestown, ND 

58401

Abstract

Karst aquifers present an extreme case of flow along structurally variable pathways, making them 

highly dynamic systems and therefore likely to respond rapidly to climate change. In turn, many 

biological communities and ecosystems associated with karst are sensitive to hydrologic changes. We 

explored how three sites in the Edwards aquifer (Texas) and two sites in the Madison aquifer (South 

Dakota) might respond to projected climate change from 2011 to 2050. Ecosystems associated with these 

karst aquifers support federally listed endangered and threatened species and state-listed species of 

concern, including amphibians, birds, insects, and plants. The vulnerability of selected species associated 

with projected climate change was assessed.

The Advanced Research Weather and Research Forecasting (WRF) model was used to simulate

projected climate at a 36-kilometer grid spacing for three weather stations near the study sites, using 

boundary and initial conditions from the Community Climate System Model (CCSM3), a global climate 

model, and an A2 emissions scenario. Daily temperature and precipitation projections from the WRF 

model were used as input for the hydrologic Rainfall-Response Aquifer and Watershed Flow 

(RRAWFLOW) model and the Climate Change Vulnerability Index (CCVI) model. RRAWFLOW is a 

lumped-parameter model that simulates hydrologic response at a single site, combining the responses of 

quick and slow flow that commonly characterize karst aquifers. The CCVI model uses historical and 

projected climate and hydrologic metrics to determine the vulnerability of selected species on the basis of 

species exposure to climate change, sensitivity to factors associated with climate change, and capacity to 

adapt to climate change.

An upward trend in temperature was projected for 2011 to 2050 at all three weather stations; there 

was a trend (downward) in annual precipitation only for the weather station in Texas. A downward trend 

in mean annual springflow or groundwater level was projected for all of the Edwards aquifer sites, but 

there was no significant trend for the Madison aquifer sites. Of 16 Edwards aquifer species evaluated 

(four amphibians, six arthropods, one fish, one mollusk, and four plants), 12 were scored as highly or 

moderately vulnerable under the projected climate change scenario. In contrast, all of the eight Madison 

aquifer species evaluated (two mammals, one bird, one mollusk, and four plants) were scored as 

moderately vulnerable, stable, or intermediate between the two. The inclusion of hydrologic projections in 

the vulnerability assessment was essential for interpreting the effects of climate change on aquatic species 

of conservation concern, such as endemic salamanders. The linkage of climate, hydrologic, and 

vulnerability models provided a bridge to project the effects of global climate change on local karst 

aquifer and stream systems, and selected species. 
127

Response of Cave-Stream Bacteria to Sub-Lethal Concentrations of 

Antibiotics

By Thomas D. Byl1, Petra K. Byl1*, Shannon Trimboli2, and Rickard Toomey, III2

1

U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science) 2

Mammoth Cave International Center for Science and Learning, Science & Resource Management, 

Mammoth Cave National Park, KY 42259

Abstract

Mammoth Cave National Park (MACA) in central Kentucky, is a world renowned karst system that 

attracts over 500,000 tourists per year. The high volume of tourists contributes to incidental surface 

releases of soaps and disinfectants at the waste-transfer station for recreational vehicles and the 

biosecurity mats used to reduce the spread of Pseudogymnoascus destructans (formerly known as 

Geomyces destructans, the fungus that causes white nose syndrome (WNS) in bats) spores on footwear.

Multi-antibiotic resistant (MAR) bacteria were reported in high numbers around the waste-transfer station 

and WNS disinfection stations. Additionally, some disinfectant was observed in the cave streams after a 

storm. The potential problems identified by these observations led to a study by the U.S. Geological 

Survey (USGS), in partnership with MACA and Tennessee State University, to determine substrate 

utilization patterns and antibiotic resistance of microbial communities associated with cave streams at 

different levels of passages in the historic section of Mammoth Cave.

The cave streams within MACA were targeted because they represent a hydrologic connection 

between land surface and the cave system. Storm water runoff carries suspended and dissolved 

constituents from the surface or near surface into the cave. The suspended and dissolved constituents can 

either be toxic, immaterial, or serve as food for microbes and other organisms that live in the subsurface 

streams. However, very little is known about the microbial community in cave streams, the food 

preference, or the response to anti-microbial compounds by the cave-stream bacteria. Water samples were 

collected at one surface and seven cave sites in the summer of 2012 through the fall of 2013. The surface 

sampling was limited to storm events due to lack of flow between storms. The cave-stream sampling sites 

had continuous flow and were sampled during and between storms. The sampling sites were located on 

different vertical levels of the cave system: three sites in the upper mid-level passages, two in the lower 

mid-level passages, and two in the deeper levels of the cave.
128

Bacterial sensitivity to antibiotics was quantified using agar plates with 10-percent trypticase soy agar 

(10-percent TSA) augmented with 0.00, 0.01, 0.1, 1.0, and 10.0 milligrams per liter (mg/L) antibiotic 

(erythromycin, kanamycin, gentamicin, tetracycline, linear alkylbenzene sulfonates, or quaternary 

ammonia compounds). Bacteria resistant to antibiotic existed in all levels of the cave. However, the 

number of colony forming units (cfu) on the 10-percent TSA plates generally decreased as the antibiotic 

dosage increased. One exception to this pattern was erythromycin, which significantly (p < 0.05) 

increased the number of bacteria colonies in agar supplemented with 0.1 and 1.0 mg/L erythromycin in 

samples collected from Lee’s Cistern, Shaler’s Brook, and Charlotte’s Dome within the historic section of 

Mammoth Cave. Biolog EcologTM (Ecolog) plates with 31 different substrates were used to evaluate 

community substrate utilization patterns. The waters used to inoculate the Ecolog plates were 

standardized by turbidity to reduce disparity between inoculum bacteria concentrations. This 

standardization was confirmed with plate counts. Bacterial community samples collected deeper in the 

cave tended to use fewer substrates than those collected from or near the surface. Bacterial communities 

from the lower passages had a lower average well color development with the exception of Charon’s 

Cascade, located on the lowest level of the cave. It is possible that bacteria from Charon’s Cascade did 

not conform to the pattern because the lowest level of the cave floods with backwater from the Green 

River on occasion. The results of the investigation suggest that microbial communities have different 

antibiotic resistance and substrate utilization patterns associated with different locations in the cave 

stream.
129

Role of Surface Water Dissolved Organic Carbon in the Survival, 

Growth, and Transport of Escherichia coli in a Deep Limestone 

Aquifer in South Florida

By Ronald W. Harvey1, Jen Underwood1, John Lisle2, David W. Metge1, and

George Aiken1

1

U.S. Geological Survey, National Research Program, 3215 Marine St., Suite E-127, Boulder, CO 80303 

2

U.S. Geological Survey, 600 4th Street-South, St. Petersburg, FL 33701

Abstract

Much is unknown about survival and activities of bacteria within deep aquifers hydrologically 

isolated from surface-water intrusion. Groundwater about 15,000-20,000 years old was collected from 

317-482 meters below land surface in the subtropical (22 o

C) Floridan aquifer in southeast Florida. 

Dissolved organic carbon (DOC), often a major control of heterotrophic activity in shallow aquifers, had 

a low concentration (1.1 milligrams per liter). Its low specific ultraviolet (UV) absorbance (2.2) and high 

fluorescence index (1.8) indicated only modest aromaticity and a likely microbial (versus terrestrial) 

origin. Surface properties and growth of Escherichia coli (E. coli) K12 were both affected by the presence 

of the hydrophobic organic acid (HPOA) fraction of DOC in surface waters to be used in regional aquifer 

storage and recovery (ASR). Collectively, the effect of surface water DOC on the growth and surface 

properties of E. coli K12 is predicted to alter its fate in the Floridan aquifer. 

INTRODUCTION

A concern regarding deep-well injection of 

wastewater and planned expansion for aquifer 

storage and recovery (ASR) in south Florida is 

the effect of highly reactive dissolved organic 

carbon (DOC) on aquifer microbiology, 

particularly as it affects survival and transport of 

pathogenic and indicator bacteria. Plans for ASR 

involve a seasonal injection of about 6 billion 

liters per day of surface water into the upper 

Floridan aquifer. Organic-rich (17 milligrams 

per liter [mg/L] DOC) Lake Okeechobee (1,714 

km2

) is likely to be an important source of 

surface water for injection into the Floridan 

aquifer (Wedderburn and others, 2013). There 

are many factors that affect the survival of 

bacterial pathogens and indicators in 

groundwater, including levels of nutrients, 

temperature, ionic strength/salinity, redox 

conditions, presence/absence of biofilms, 

environmental microbial diversity and ecology, 

physicochemical characteristics of the solid 

phase, and the character and concentration of 

DOC. In very old, carbon-limited groundwater 

such as that present in the Floridan aquifer, 

levels and lability of the DOC can be important 

controls of growth, survival, and transport for 

non-native bacteria that are introduced during 

the ASR process.

DOC and Survival

Unfortunately, most studies of bacterial 

survival in subsurface environments involve 

very limited set(s) of conditions. Transport of 

bacteria from surface waters through a vadose 

zone into an underlying aquifer necessitates 

survival in several environments that have very 

different conditions. Consequently, survival over 

the entire transport pathway is exceedingly 

difficult to predict. 

Even when conditions favor rapid die-off of 

the bulk population of pathogens, some subpopulations can persist for long periods. Many 

bacterial pathogens and indicators, including 

Escherichia coli (E. coli) and Pseudomonas

aeruginosa, are able to enhance their survival in 

low-carbon environments by entering a pseudodormant state, termed “viable but nonculturable” 

(VBNC) (Oliver, 2010). The VBNC state, which 

can be classified as a persistent phenotype, is an 

adaptation to survival under variable 

environmental conditions (Rotem and others, 

2010) and can be triggered by environmental 

factors, such as lack of labile DOC. Cook and 

Bolster (2007) demonstrated that E. coli in

groundwater transitioned into a VBNC state 

characterized by changes in morphology and a 

reduced rate of respiration in response to 
130

starvation. Most studies involving 

environmental survival of bacterial pathogens 

use culture-based methods, which underestimate 

survival of bacterial pathogens that transition 

into and out of the VBNC state. However, Lisle 

(2014) has shown that for the Floridan aquifer, 

die-off of coliform bacteria can be considerably 

more rapid than previously believed.

The activities of indigenous subsurface 

microorganisms, which depend, in part, on the 

levels and character of the DOC, can enhance or 

inhibit the survival of bacterial pathogens and 

indicators. For example, biofilm formation has 

been shown to favor pathogen survival under 

both typical environmental conditions and under 

active disinfection (Murphy and others, 2006). 

Conversely, competition for limited DOC is 

known to inhibit pathogen survival (Crane and 

Moore, 1986). Bacteriophages are abundant and 

ubiquitous in nature (Kimura and others, 2008)

and can impact host bacterial populations by 

lysis of cells and by altering the host phenotype 

via genetic alterations (Dröge and others, 1999). 

It is likely that coliphages play an antagonistic 

role in the survival of coliform bacteria in many 

aquifers, although the roles of protozoa in the 

survival of bacterial pathogens in the subsurface 

are not well understood. However, it is known 

that the diverse communities of nanoflagellates 

in aquifers (Novarino and others, 1997) can be a 

significant sink for bacteria being advected from 

the surface environment (Kinner and others, 

1997; Kinner and others, 1998). The role of 

predation appears to increase where there are 

substantive inputs of labile DOC (Kinner and 

others, 2002), because the protozoan community 

is stimulated by the resulting bacterial growth. 

DOC and Growth

The ability of bacterial pathogens to grow in 

the environment has been a topic of considerable 

debate. The degree of growth depends upon the 

environmental conditions and the specific 

pathogen of interest. Some bacterial pathogens, 

such as Campylobacter jejuni are typical 

inhabitants of some subsurface environments 

and are expected to proliferate in-situ under 

conditions that are most favorable, i.e., optimal 

nutrients, substrates, temperature, and lack of 

competition and predation. Growth in the 

environment of non-indigenous bacterial 

pathogens is sometimes referred to as 

“regrowth” (Zaleski and others, 2005), as it is 

suspected to occur if the optimal growth 

conditions are met. 

We examined the effect of Lake 

Okeechobee DOC upon the surface properties, 

growth, and survival of E. coli K12. Although E. 

coli is generally considered incapable of 

growing outside a mammalian host (Avery and 

others, 2008), it may be able to grow in tropical 

and temperate soils (Ishii and Sadowsky, 2008). 

In this study, Lake Okeechobee DOC 

(hydrophobic organic acid [HPOA] fraction, 20 

mg/L), caused growth of E. coli K12 relative to 

unamended artificial lake water (ALW) devoid 

of DOC (fig. 1). This suggests that DOC 

introduced during ASR could affect survival of 

bacterial indicators and, possibly, certain 

bacterial pathogens.

Figure 1. Growth of Escherichia coli K12 in the absence of 

DOC (ALW) and in the presence of 20 mg/L and 40 mg/L 

of the more aromatic hydrophobic organic acid (HPOA) 

fraction of the DOC. The study was conducted using a 

laboratory microcosm with artificial lake water (ALW). 

Shaded section indicates period of observed bacterial 

growth. 

DOC and Transport

The effect of surface-water derived DOC, 

both natural organic matter (NOM) and organic 

contaminants, on transport of bacteria through 

the aquifers subject to ASR or deep-well 

wastewater injection has important public health 

Days

0 2 4 6 8 20 30 40 50 60

viable cells/mL

103

104

105

106

107

ALW

HPOA (20 mg/L)

HPOA (40 mg/L)
131

and environmental implications. Elevated levels 

of labile DOC can affect the surface 

characteristics of bacterial pathogens and, 

consequently, their transport behavior in the 

aquifer. The ability of humic material to enhance 

advective bacterial transport through aquifer 

material has been well documented (Foppen and 

others, 2008). However, to assess the role of 

DOC in bacterial transport at the field scale, it is 

useful to consider also the contributions of 

contaminant organic compounds that may also 

be present in surface waters and can affect 

bacterial attachment behavior at “trace” levels 

(Harvey and others, 2010). Although the 

majority of studies examining the roles of DOC 

on subsurface microbial transport indicate 

decreased attachment and increased transport, 

some organics have the opposite effect 

(Marshall and others, 2000). Undoubtedly, the 

extent to which DOC facilitates or inhibits 

bacterial transport is dependent upon a complex 

suite of interactions involving the nature of the 

DOC, physicochemical conditions, aqueous 

chemistry, and the surface characteristics of the 

bacteria and solid phase. Consequently, use of 

model organic compounds bacterial transport 

studies involving ASR or deep-well injection 

can lead to misleading results compared to the 

use of DOC isolated directly from the source 

water. 

We examined the role of the HPOA fraction 

of Lake Okeechobee DOC upon two important 

surface characteristics of E. coli K12 that affect 

its propensity for attachment: hydrophobicity 

and surface charge (table 1). The presence of 

surface-water derived DOC had a substantive 

effect on the net surface charge of E. coli K12, 

decreasing the zeta potential about 4-fold from 

-88 to -22 millivolts. The decrease in the surface 

charge in the presence of Lake Okeechobee 

HPOA would have the effect of making E. coli

K12 more likely to attach to aquifer surfaces 

characterized by net negative charge. This is due 

to a decreased electrostatic repulsion between 

the cell surface and the solid phase. However, 

the decreased surface charge would make E. coli

K12 less likely to attach to aquifer surfaces 

characterized by patches of net positive charge 

in the form of aluminum and iron oxides. The 

decreased hydrophobicity of E. coli K12 in the 

presence of HPOA from 26 to 18 percent should 

enhance transport in the aquifer by decreasing 

the propensity for partitioning to the solid phase. 

Results of bacterial attachment in the presence 

of aquifer material and Lake Okeechobee DOC 

were inconclusive. Clearly, the role of surface 

water DOC upon transport of indicator bacteria 

in the Floridan aquifer is complex and worthy of 

further study. However, our findings suggest 

that the effect of surface water DOC on the fate 

and transport of non-native bacteria that are 

introduced inadvertently during ASR should not 

be ignored. 

Table 1. Effect of Lake Okeechobee dissolved organic carbon on Escherichia coli K12 surface properties.

____________________________________________________________________________________________

Dissolved Organic Carbon (DOC) Hydrophobicity

(

1

MATH test)

Surface charge

(

2

zeta potential)

3

Hydrophobic Organic Acid (HPOA) fraction 18.0 ± 2.3 percent -22.0 ± 2.6 millivolts

No DOC 26.1 ± 4.9 percent -88.5 ± 2.0 millivolts

1

Microbial adhesion to hydrocarbon test.

2

Measured at ionic strength of 0.01 M (moles per liter).

3

Concentration of 40 mg/L (milligrams per liter).
132

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D.L., 2008, Survival of Escherichia coli O157:H7 

in waters from lakes, rivers, puddles and animaldrinking troughs: Science of the Total 

Environment, v. 389, p. 378-385.

Cook, K.L., and Bolster, C.H., 2007, Survival of 

Campylobacter jejuni and Escherichia coli in 

groundwater during prolonged starvation at low 

temperatures: Journal of Applied Microbiology, 

v. 103, p. 573-583.

Crane, S.R., and Moore, J.A., 1986, Modeling enteric 

bacterial die-off: A review: Water, Air, & Soil 

Pollution, v. 27, p. 411-439.

Dröge, M., Pühler, A., and Selbitschka, W., 1999, 

Horizontal gene transfer among bacteria in 

terrestrial and aquatic habitats as assessed by 

microcosm and field studies: Biology and 

Fertility of Soils, v. 29, p. 221-245.

Foppen, J.W., Liem, Y., and Schijven, J., 2008, 

Effect of humic acid on the attachment of 

Escherichia coli in columns of goethite-coated 

sand: Water Research, v. 42, p. 211-219.

Harvey, R.W., Metge, D.W., Barber, L.B., and 

Aiken, G.R., 2010, Effects of altered groundwater 

chemistry upon the pH-dependency and 

magnitude of bacterial attachment during 

transport within an organically contaminated 

sandy aquifer: Water Research, v. 44, p. 1062-

1071.

Ishii, S., and Sadowsky, M.J., 2008, Escherichia coli

in the environment: Implications for water quality 

and human health: Microbes and Environments, 

v. 23, p. 101-108.

Kimura, M., Jia, Z.J., Nakayama, N., and Asakawa, 

S., 2008, Ecology of viruses in soils: Past, present 

and future perspectives: Soil Science & Plant 

Nutrition, v. 54, p. 1-32.

Kinner, N.E., Harvey, R.W., Blakeslee, K., 

Novarino, G., and Meeker, L.D., 1998, Sizeselective predation on groundwater bacteria by 

nanoflagellates in an organic-contaminated 

aquifer: Applied and Environmental 

Microbiology, v. 64, p. 618-625. 

Kinner, N.E., Harvey, R.W., and KazmierkiewiczTabaka, M., 1997, Effect of flagellates on freeliving bacterial abundance in an organically 

contaminated aquifer: FEMS Microbiology 

Reviews, v. 20, p. 249-259. 

Kinner, N.E., Harvey, R.W., Shay, D.M., Metge, 

D.W., and Warren, A., 2002, Field evidence for a 

Protistan role in an organically-contaminated 

aquifer: Environmental Science & Technology, v. 

26, p. 4312-4318. 

Lisle, J., 2014, Survival of bacterial indicators and 

the functional diversity of native microbial 

communities in the Floridan aquifer system, south 

Florida: U.S. Geological Survey Open-File 

Report 2014-1001, 70 p. 

Marshall, S.J., House, W.A., and White, G.F., 2000, 

Role of natural organic matter in accelerating 

bacterial biodegradation of sodium dodecyl 

sulfate in rivers: Environmental Science & 

Technology, v. 34, p. 2237-2242.

Murphy, C., Carroll, C., and Jordan, K.N., 2006, 

Environmental survival mechanisms of the 

foodborne pathogen Campylobacter jejuni: 

Journal of Applied Microbiology, v. 100, p. 623-

632. 

Novarino, G., Warren, A., Kinner, N.E., and Harvey, 

R.W., 1994, Protists from a sewage-contaminated 

aquifer on Cape Cod, Massachusetts, U.S.A.: 

Geomicrobiology Journal, v. 12, p. 23-36. 

Oliver, J.D., 2010, Recent findings on the viable but 

nonculturable state in pathogenic bacteria: FEMS 

Microbiological Reviews, v. 34, p. 415-425.

Rotem, E., Loinger, A., Ronin, I., Levin-Reisman, I., 

Gabay, C., Shoresh, N., Biham, O., and Balaban, 

N.Q., 2010, Regulation of phenotypic variability 

by a threshold-based mechanism underlies 

bacterial persistence: Proceedings of the National 

Academy of Sciences, v. 107, p. 12541-12546. 

Wedderburn, L.A., Linstrom, L., Lukasiewicz, J., 

Kwiatkowski, P., Nevulis, R., Goodwin, C.R., 

Cunningham, K.J., Renken, R.A., and Reese, 

R.S., 2013, What is aquifer storage & recovery? 

http://sofia.usgs.gov/sfrsf/rooms/hydrology/ASR/ 

Zaleski, K.J., Josephson, K.L., Gerba, C.P., and 

Pepper, I.L., 2005, Potential regrowth and 

recolonization of salmonellae and indicators in 

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Environmental Microbiology, v. 71, p. 3701-

3708.
133

Cave Bacteria and Crystal Formation in the Laboratory

By Petra K. Byl1*, Aaron Covey2, Jessica Oster2, Tasneem Siddiquee3, and

Thomas D. Byl1,3

1

U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science)

2

Earth & Environmental Sciences, Vanderbilt University, Nashville, TN 37240 3

Tennessee State University, 3500 John A Merritt Blvd., Nashville, TN 37209

Abstract

Speleothems (secondary cave mineral deposits) are used as recorders of past climate change, but little 

is known about the role microbes may play in biocrystallization as well as modifying trace element 

microclimate records. This study serves to explore microbe-mineral interactions through analyzing 

bacteria endemic to Blue Spring Cave, Tennessee and Mammoth Cave, Kentucky. Microorganisms were 

swabbed from active stalagmite growth in Blue Spring and Mammoth Cave, and later suspended in a 

liquid culture media, or streaked onto the same agar media in aerobic conditions under constant 

temperature. The media were an amalgam of chitin-mineral salts media (0.04 percent chitin) and 

traditional actinomycete isolation media with 0.1 percent ammonia acetate. Bacterial exposure to the 

ammonia and phosphate salts, both present in the media, caused the biologically mediated precipitation of 

orthorhombic white crystals as evidenced by the lack of precipitates in the sterile control media. The 

crystals were identified through x-ray diffraction, energy dispersive spectroscopy, and scanning electron 

microscopy, and were determined to be struvite (NH4MgPO4 *6H2O) as well as calcite (CaCO3). The 

calcite rhombs were about 10 μm in length and appeared to form clusters within the biofilm, while the 

struvite orthorhombic crystals averaged 250 μm in length and did not appear in conglomerates. In cave

settings, struvite is naturally found in areas of high bat guano concentration, and calcite deposits over 

time form the speleothems that paleoclimatologists study. The results indicate that the microorganisms 

from active stalagmites have the potential, in the presence of ammonia and phosphate, to affect the 

precipitation and mineral composition of speleothems.
134

Non-Target Bacterial Response to White-Nose Syndrome Treatment: 

Quaternary Ammonia Compounds and Linear Alkylbenzene Sulfonate

By JeTara Brown1, Zheer Ahmed2*, and Thomas D. Byl1,2

1

Tennessee State University, 3500 John A Merritt Blvd., Nashville, TN 37209

2

U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science)

Abstract

White-Nose Syndrome (WNS) is decimating the North American bat population in many caves east 

of the Mississippi River. Tour caves, such as those in Mammoth Cave National Park in Kentucky, are 

trying to prevent the spread of this disease by requiring all visitors coming out of the caves to disinfect 

their footwear. From April 2011 through early 2013, everyone who entered the cave at Mammoth Cave 

National Park on a walking tour was required to walk across biosecurity mats soaked with the chemical 

disinfectant quaternary ammonia compounds (QAC). The National Park Service switched from a QACbased product in 2013 to a laundry detergent containing the anionic surfactant linear alkylbenzene 

sulfonate (LAS). LAS has been shown to inhibit growth of the fungus that causes WNS at regular 

strength concentrations. Both chemicals (QAC and LAS) can have a detrimental effect on other 

organisms besides WNS fungal spores. The U.S. Geological Survey (USGS) Tennessee Water Science 

Center in partnership with Mammoth Cave National Park and Tennessee State University conducted a 

study to determine the effect of QAC and LAS on non-target bacteria. 

The heavily used biosecurity mats were soon colonized by non-target bacteria that had adapted to the 

chemicals and could use the QAC or LAS as a food source. The QAC-resistant bacteria had multiple 

antibiotic resistance (MAR) to clinical concentrations of erythromycin, gentamicin, ampicillin, 

tetracycline, and kanamycin. The QAC-resistant bacteria were generally Gram-negative and rod shaped. 

Twelve liquid microcosms were established using 250 milliliters of raw liquid from the two times fullstrength QAC-soaked mats. Half the microcosms had sterile marbles added to increase the surface area 

2.6 times compared to the other microcosms. The microcosms were placed on a rotary shaker at 75 rpm 

and maintained at 25 o

C. The microcosms with higher surface area for biofilm development had a QAC 

half-life of 11 days. The microcosms with less surface area had a QAC half-life of 37 days. After 

switching to LAS, the bacteria collected from the biosecurity mats were again susceptible to antibiotics, 

with some minor resistance to gentamicin and kanamycin. The predominant LAS-associated bacteria 

were Gram-negative and cocci shaped. 

The bacteria grew on agar plates containing only LAS, indicating they readily consumed the anionic 

surfactant as a food source. The LAS-soaked mats also produced an unpleasant odor during the warm 

summer months. Additional tests focused on ways to rid the mats of these nuisance bacteria. Clean 

sponges were inoculated by placing them under the LAS-soaked mats for 4 hours during busy tour hours, 

and then exposing these sponges to different cleaning scenarios. Waters extracted from the sponges were 

then tested for culturable bacteria using 10-percent trypticase soy agar media. A 20-minute exposure to 

bleach at one-tenth the recommended laundry strength at 25 o

C eliminated the bacteria. Hydrogen 

peroxide at 0.3 percent was also effective after a 45-minute exposure. Soaking the sponges in water with 

no chemicals at 50 o

C for 45 minutes also eliminated all bacteria growth. Full strength ammonia cleaners 

at 25 o

C did not significantly reduce the number of colonies. The results of these studies help us 

understand several of the unintentional risks of using chemicals to disinfect WNS spores on footwear, and 

ways to reduce some of the detrimental side effects.
135

THURSDAY, MAY 1, 2014, FIELD TRIP GUIDE

Evaporite Karst of the Lower Pecos Valley, New Mexico

By Lewis Land

New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Pl, Socorro, New Mexico 87801

and

National Cave and Karst Research Institute, 400-1 Cascades Avenue, Carlsbad, New Mexico 88220

Overview of Mirror Lake, Bottomless Lakes State Park, Chaves Co., New Mexico; view to south. Photo 

courtesy of Lewis Land, National Cave and Karst Research Institute.
136

Figure 1. Map of field trip route. Figure 2. Stratigraphy of the lower Pecos 

region, southeastern New Mexico.

Figure 3. Stratigraphic profile showing facies relationships of Permian strata in the lower Pecos Valley.
137

Text is based in part on road logs in Land and Love (2006). Distances are given in miles for 

consistency with United States odometers.

Vehicles assemble at NCKRI headquarters, 400-1 Cascades Ave., Carlsbad, NM. Proceed to 

intersection of Cascades Ave. and Park Dr. Zero odometers and turn left onto Park Dr.

0.3 miles: Potash mines locomotive on left; Lake Carlsbad, an impounded section of the Pecos 

River, on right. Continue north through traffic circle on Riverside Dr.

0.6 miles: Bear left and continue on Riverside Dr.

1.2 miles: Crossing Canal St., bridge to right crosses Pecos River. Continue straight on 

Riverside Drive, one of the more prosperous neighborhoods in Carlsbad. Homes on the right side 

of the street have back yards facing the Pecos River.

2.4 miles: Turn left onto Landsun Drive.

2.6 miles: Turn right onto Westridge Road.

3.0 miles: Stop 1: Carlsbad Spring to right

Carlsbad spring is one of several springs that discharge into this reach of the Pecos River. 

Carlsbad spring used to discharge over 7,500 liters/min (~2000 gal/min), but its flow has been 

substantially reduced over the years due to pumping from the Capitan Reef aquifer, the principal 

source of drinking water for the City of Carlsbad. Additional discharge from the spring is derived 

from leakage from Lake Avalon and the Carlsbad Irrigation District’s South Canal, and from 

irrigation return flow (Cox, 1967). 

Carlsbad flume is visible at 12:00, ~200 m upstream from the spring. This large large 

concrete aqueduct crosses the Pecos and transports water of the Pecos River from Lakes Brantley 

and Avalon through the CID South Canal (thus, according to Ripley’s Believe It or Not, “the 

river that crosses itself”). This concrete structure was built in 1903 to replace the original 

wooden flume that was destroyed by floods. 

Return to vehicles and continue west on Westridge Rd, passing under flume.

3.2 miles: Stop sign. Turn left onto Callaway Dr.

3.4 miles: Traffic light. Turn right onto US 285.
138

4.1 miles: Roadcut to left is an exposure of the shallow marine, outer shelf facies of the Tansill 

Formation on the northeast flank of Tracy Dome, dipping ~10° east toward the Pecos River. 

Dolomites of the grapestone-grainstone facies belt indicate deposition in the subtidal 

environment of a backreef lagoon. 

Pecos River to right. Between Brantley Dam and Carlsbad Springs the Pecos River is a 

losing stream, in the process recharging near-backreef units of the Capitan Reef aquifer (Cox, 

1967).

8.7 miles: NM 524 to left leads to Happy Valley. Continue straight on US 285. The hill on the 

left is a ridge surrounding a circular depression ~1.5 km in diameter, interpreted by Motts (1962) 

as a young solution-collapse feature. Tansill dolomites on the flanks dip steeply toward the 

center of this crater-like structure, which is floored by gypsum of the Yates and Tansill 

Formations. Non-tectonic folds caused by subsurface dissolution and subsidence are widespread 

in this portion of the Pecos Valley. A well drilled to a depth of 336 m in the center of the 

depression bottomed in Seven Rivers dolomites (Kelley, 1971b).

9.9 miles: The feature superficially resembling a cinder cone on the skyline at 9:00 is Round 

Mountain, the largest of the so-called Three Twins, residual knolls formed in evaporites and 

redbeds of the Yates Formation and capped by more resistant Tansill dolomite. Such residual 

hills and ridges are common features in the carbonate-to-evaporite transitional facies belt of the 

Artesia Group.

10.0 miles: Roadcuts over the next mile expose interbedded gypsum, dolomite and redbeds of 

the Yates Formation, representing the carbonate-to-evaporite and redbed facies change within the 

Yates. Note small folds in the roadcuts, part of an arcuate fold belt called the Waterhole 

anticlinorium (Kelley, 1971a) that wraps around the west and north sides of the Carlsbad area.

12.1 miles: Cross Rocky Arroyo, a dry tributary of the Pecos River. Ridge at 10:00 is the Seven 

Rivers Hills, a southeast dipping cuesta of the Seven Rivers Formation.

12.9 miles: Turn right onto CR 30/Capitan Reef Road to Brantley Lake State Park. Brantley 

Dam to left. Driving over partially cemented terrace gravels of the Pecos River.

15.2 miles: Spillway of Brantley Dam at 9:00. Well-developed Holocene coppice dunes on both 

sides of road. Prominent bluffs on opposite bank of Pecos River at 1:00 are formed in Quaternary 

cemented terrace gravels, rotated as much as 40° due to solution-subsidence in underlying 

evaporites, redbeds and dolomites of Yates transitional facies.
139

15.4 miles: Cross Pecos River on bridge south of Brantley Dam.

17.5 miles: Road to left leads to Brantley Lake State Park and Visitors Center. Continue 

straight on CR 30.

17.7 miles: Cuesta to right is formed in redbeds and gypsum capped by dolomite of the Yates 

Formation.

18.7 miles: Cross railroad tracks. Yates gypsum exposed in railroad bed on both sides of road. 

McMillan Escarpment at 10:00. Dolomitic facies of Yates is exposed in railroad cuts ~800 m SE.

19.2 miles: T-junction with Lake Road (CR 34). Turn left onto Lake Road.

19.5 miles: Stop sign at intersection with Netherlin Road. Continue straight.

20.1 miles: Seven Rivers dolomite capping cuesta at 3:00.

20.2 miles: McMillan Dam at 12:00. Brantley Lake at 9:30. Seven Rivers Hills on horizon 

(Seven Rivers dolomite capping redbeds and gypsum).

20.3 miles: Stop 2: McMillan Dam and old Lake McMillan Lake Bed.

Park on shoulder. Breached dam straight ahead. Note man-made dike along east margin 

of lake, at base of McMillan Escarpment (Figure 4). The following discussion is based largely on 

Cox (1967), who investigated geohydrologic conditions beneath McMillan Dam and downstream 

as far as Carlsbad Springs.

Lake McMillan is located within the evaporite facies belt of the Seven Rivers Formation. 

The lake was an artificial impoundment that formerly stored water for the Carlsbad Irrigation 

District. McMillan Dam was constructed in 1893, and the reservoir almost immediately began 

experiencing leakage problems through sinkholes formed in the lake bed, particularly along the 

eastern margin of the lake. Water flowed through karst conduits in the Seven Rivers gypsum and 

returned to the Pecos River through discharge from Major Johnson Springs, ~5.6 km 

downstream at the present site of Brantley Reservoir. East and southeast of the facies change, the 

less soluble dolomite facies of the Seven Rivers retards any significant formation of solution 

channels. In 1908-09 a dike was constructed along the southeast shore of the lake, near the base 

of the McMillan Escarpment, in an attempt to isolate the areas of worst sinkhole formation. The 

dike was extended in 1953-54 along most of the eastern shore to prevent water from reaching 

exposed sinkholes during periods of high lake level. Occasionally breaks would occur in the 

dikes causing lake water to inundate the sinkholes. At these times whirlpools were reported in 

the lake, indicating that sediment cover over sinkholes in the lake bed had been disturbed. High 
140

rates of leakage would occur for short periods of time until the dikes were repaired and sediment 

cover on the floor of the lake restored.

Figure 4. Mass wasting processes indicated by gypsum fissures formed in the face of the McMillan 

Escarpment. Note man-made dike at base of escarpment.

Storage capacity of Lake McMillan steadily decreased after the dam was constructed 

because of deposition of suspended sediment, particularly during flood events, and by the early 

1940’s less than half of its original storage capacity remained. The possibility of dredging was 

considered but soon discarded when it was realized that removal of the accumulated sediment 

would considerably increase leakage through karst fissures in the gypsum bedrock underlying the 

lake. Fortunately, loss of storage capacity decreased by the mid-40’s because a stand of salt 

cedar, an invasive species, became established in bottom lands upstream from Lake McMillan, 

acting as a baffle for much of the suspended sediment carried by the Pecos River.

Consideration for construction of a new dam began as early as 1905. The U.S. Bureau of 

Reclamation began construction of Brantley Dam in 1984, and in 1991 McMillan Dam was 

breached and Lake McMillan allowed to drain into Brantley Lake. Based on recommendations 

by Cox (1967), the new reservoir is located mostly within the dolomitic facies belt of the Seven 

Rivers Formation. 

Features to note near the old damsite include small-scale non-tectonic folds, expressed as 

undulations in the Seven Rivers dolomite, almost certainly the result of subsurface dissolution of 

evaporites. Larger-scale folds exposed in the walls of the Pecos River channel on the other side 

of the dam probably have a similar origin.

Return to vehicles and proceed to Stop 3. Zero odometer, turn around and proceed southeast on 

Lake Road.

0.8 miles: Intersection with Netherlin Road (CR236). Turn left. High clearance vehicles only 

from this point on. Other vehicles park on shoulder.
141

1.4 miles: Slow down, turn left on two-track just before cattle guard. All remaining vehicles 

should have high clearance from here to stop 3. Follow fence line.

1.7 miles: Turn left away from fence line. Watch for deep ruts in two-track.

2.3 miles: Two track reaches ridge crest. Lake bed of old Lake McMillan below. Northeast end 

of Brantley Dam at 7:00.

2.4 miles: Small sinkhole to right. Vehicles should be careful of footing.

2.5 miles: Stop 3: Crest of McMillan Escarpment.

The McMillan Escarpment is a cuesta formed in gypsum and redbeds of the Seven Rivers 

Formation, capped by more resistant Seven Rivers dolomites. The carbonate-to-evaporite and 

redbeds facies change can be readily observed in a vertical sense during a partial descent down 

the face of the escarpment. Also present are large gypsum fissures and slump blocks, indicating 

continued mass wasting and evolution of the eastern margin of the lower Pecos Valley by 

undercutting of the gypsum escarpment (Figure 5). Small gypsum caves and sinkholes occur at 

the base of the cliff. These karst features began causing serious leakage shortly after construction 

of the reservoir. Attempts to isolate the worst areas of sinkhole formation by construction of a 

dike along the eastern shore of the lake were only partially successful.

Figure 5. Mass-wasting processes indicated by large gypsum fissures formed in face of McMillan 

Escarpment.

Watch your footing on unstable slopes. After stop, return to Netherlin Road.

Zero odometers and turn right onto Netherlin Road.

0.5 miles: Junction of Netherlin and Lake Roads. Turn left onto Lake Road.
142

0.8 miles: Junction with CR 30. Turn right and return to US 285.

7.1 miles: Junction of CR 30 with US 285. CR 30 is known as the Capitan Reef Road on the east 

side of the highway. The road continues across the highway toward the village of Queen in the 

high Guadalupes and is known as the Queen Highway. The Queen Highway is one of the earliest 

roads built by the Civilian Conservation Corps (CCC) in New Mexico. It connects US 285 with 

the Queen, El Paso Gap, and Dog Canyon areas of the western Guadalupe Mountains. 

Prepare to turn right onto Highway 285. Re-zero odometers as you turn onto highway.

0.0: Turn right and proceed north on US 285.

0.3 miles: mile post (MP), MP 46.

1.0 miles: Seven Rivers Hills at 10:00. Brantley Dam at 3:00.

2.7 miles: Yates dolomite at top of roadcut on left probably overlies siltstone and gypsum 

covered by dolomite riprap.

3.0 miles: Brantley Lake road and boat ramp to right.

3.8 miles: Crest of Seven Rivers Hills. Brecciated redbeds and gypsum of the Seven Rivers 

evaporite facies are exposed in roadcuts to left and right. The McMillan Escarpment can be seen 

as a low cuesta east of the Pecos River at roughly 3:00. The north-south-trending Seven Rivers 

gypsum and dolomite outcrop belt, which forms the McMillan Escarpment, swings southwest at 

this point and crosses the Pecos River, due to a northeast-trending, southeast-dipping monocline. 

The same outcrop belt forms the cuesta of the Seven Rivers Hills, which are capped by more 

resistant dolomites of the Azotea Tongue of the Seven Rivers Formation (Kelley, 1971b). The 

Seven Rivers Hills are (somewhat arbitrarily) regarded as the southern boundary of the Roswell 

Artesian Basin.

3.9 miles: Descending into alluvial lowlands formed by a confluence of the Seven Rivers 

tributaries of the Pecos River. For the past several million years, the Pecos has been migrating 

progressively eastward due to uplift of the Sacramento Mountains to the west combined with 

dissolution of gypsum bedrock to the east. Floodplain deposits of the Pecos River form a shallow 

water-table aquifer in the Roswell Artesian Basin.

5.3 miles: MP 51. About 1 km to the west the New Mexico Interstate Stream Commission has 

drilled several augmentation wells to pump water from the deep Artesian Aquifer and pipe it 

directly into the Pecos River. These augmentation wells form part of a consensus plan between 
143

the Carlsbad Irrigation District (CID) and the Pecos Valley Artesian Conservancy District 

(PVACD) to help meet our interstate compact obligation to share water resources in the Pecos 

with the state of Texas. 

5.9 miles: Crossing South Seven Rivers Arroyo. Pecan orchard to right. Pecans are an important 

cash crop in the largely agricultural economy of the Artesian Basin.

6.7 miles: Gravels capped with soil in roadcuts are Seven Rivers terrace deposits.

9.6 miles: MP 55. Junction with CR 31 to Lakewood to right. Residents of Lakewood were 

evacuated due to flooding during extreme monsoonal rains last fall, 2013. Several sinkholes 

formed in the aftermath of the flooding, one damaging a small structure in the Lakewood RV 

park. Continue straight.

10.4 miles: Crossing North Seven Rivers Arroyo. Route continues north on broad, east-sloping 

plain.

12.2 miles: Partially-cemented Quaternary gravel terrace deposits in roadcut to right.

12.6 miles: MP 58. Crossing Fourmile Draw.

14.1 miles: BP pipeline crosses under road. In 2003 several shallow fissures were discovered by 

a BP aerial survey in the vicinity of the pipeline (Figure 6). The fissures are probably associated 

with subsurface dissolution and subsidence in the Seven Rivers gypsum, which underlies the 

alluvial valley fill in this area. Depth of some of the fissures exceeds 1 m (Figure 7).
144

Figure 6. Fissure crossing pipeline access road south of Artesia, developed in alluvium overlying Seven 

Rivers evaporites.

Figure 7. Close-up of earth fissure near pipeline south of Artesia. Consultant for scale. (consultant is ~2 

m long).
145

14.4 miles: For the next several miles the route crosses a relatively nondescript terrain composed 

of pediment gravels, caliche soil and alluvial deposits of the ancestral Pecos River. The principal 

features to notice are the dense concentration of pump jacks and other oil and gas infrastructure 

on both sides of the highway. The first oil discovery in southeastern New Mexico was made in 

this area in 1924. The field trip route passes through a portion of the giant Empire Abo Field, 

which produces oil and gas from Permian strata of the Abo reef complex, Yates and Grayburg 

Formations of the Artesia Group, the San Andres limestone, Wolfcamp carbonates, as well as 

upper Pennsylvanian carbonates and lower Pennsylvanian clastic reservoirs in the Morrow and 

Atoka Formations. These multiple pay zones overlie the Artesia-Vacuum Arch, an east-west 

trending structural nose that extends to the east for ~120 km into Lea Co., New Mexico (Kelley, 

1971a). The Arch is almost completely covered by post-Permian beds; its principal surface 

manifestation is the high concentration of oil wells. Since 1960 >200 million barrels of oil have 

been produced from the Empire Abo field (Christiansen, 1989).

16.1 miles: The Slipper Gentlemen’s club on the right, one of only two adult entertainment

facilities in the lower Pecos Valley.

17.2 miles: Crossing the Rio Peñasco. The Peñasco is a perennial stream in the Sacramento 

Mountains to the west, but becomes a losing stream when it flows across the Pecos Slope west of 

Artesia, in the process recharging the underlying San Andres Artesian Aquifer.

18.2 miles: Junction with CR 65 to left. Continue straight. Sprinkler irrigation systems become 

increasingly common from this point north, as we drive farther into the Artesian Basin. Note the 

repeating image of three transformers on a utility pole and a mound of earth, indicating the 

presence of a nearby water well and pump and a pond for surface storage.

19.8 miles: Atoka Grocery on left. The village of Atoka grew along the ATSF railroad and is 

host to the Eddy County Arena. Note pecan orchards along both sides of the road.

21.8 miles: MP 67. Historic marker, showing the route of Castaño de Sosa’s 1590-91 expedition 

up the Pecos River.

22.0 miles: Halliburton service company yard to right.

22.5 miles: Entering southern Artesia. The town acquired its name in 1903 because of the 

abundant resources of artesian groundwater that were discovered in the area around the turn of 

the 20th century, making the region an agricultural oasis. Principal crops include alfalfa, 

sorghum, chiles, and pecans. In recent years dairy farming has become increasingly important to 

the agricultural economy of the lower Pecos Valley.
146

Artesia lies near the southern end of the Roswell Artesian Basin, from which 

groundwater is withdrawn from the karstic San Andres limestone aquifer to support irrigated 

agriculture. The Seven Rivers Formation in its redbed-evaporite facies serves as a leaky 

confining unit for the San Andres aquifer. Although water levels in the Artesian aquifer have 

declined substantially since development began in the early 1900s, some wells northwest of 

Artesia still display strong artesian flow.

24.1 miles: Main Street Artesia, and junction with Highway 82. Continue straight and proceed 

north through town. Navajo Refinery to right. In addition to irrigated agriculture, Artesia is also a 

local center for oil and gas activity. Yates Petroleum corporate headquarters is located 3 blocks 

to the west. The Wellhead Brewpub, owned by one of the Yates family and one of only two 

brewpubs in the lower Pecos Valley, is across the street from Yates’ offices.

24.4 miles: Crossing Eagle Draw, an east-flowing tributary of the Pecos River.

26.6 miles: Artesia adult video store to left. Bear right onto Highway 2 and continue north.

29.8 miles: MP 3. Low hills at 2:30 on east side of valley are formed in redbeds of Seven Rivers 

Formation.

32.1 miles: Bridge over Cottonwood Creek. This drainage is controlled by large levees on both 

sides of the channel for several km.

32.8 miles: Chavez County line. At this point the route crosses the NNE-trending subsurface KM 

fault. The KM fault parallels the Pecos Buckles, a series of surface faults that extend across the 

Pecos Slope to the west. Like the Buckles, the KM fault is thought to combine right-lateral 

motion with normal vertical displacement, and may be of Laramide age (Kelley, 1971a). The 

hydraulic gradient in the Artesian Aquifer increases abruptly just west of the KM fault, 

indicating that it acts as a partial barrier to down-gradient groundwater flow. Water levels are 

several tens of meters deeper in the Artesian Aquifer on the southeast side of the fault.

34.0 miles: Crossing Walnut Creek.

35.1 miles: Entering outskirts of Lake Arthur, one of several small agricultural communities of 

the lower Pecos Valley between Roswell and Artesia. In 1977, a Lake Arthur resident discovered 

an image of Jesus Christ on a flour tortilla she was preparing for her husband. By 1979, the 

Shrine of the Holy Tortilla had been visited by over 35,000 of the faithful. Images of Christ on a 

tortilla were later reported in Phoenix, AZ and Hidalgo, TX, but the Lake Arthur holy tortilla 

may be the first documented sighting in recent history.
147

36.1 miles: Lake Arthur cemetery to left. Sierra Blanca, composed of igneous intrusives and 

volcanics, on western horizon at 9:00. Capitan Mountains batholith at 10:00.

39.6 miles: El Gomez bar on left.

43.4 miles: Entering Hagerman, home of the Hagerman Bobcats. Unlike most communities in 

the Artesian Basin, Hagerman farmers derive most of their irrigation water from the Hagerman 

Canal west of town, rather than from the Artesian Aquifer, and secondarily from wells in the 

shallow alluvial aquifer. The Hagerman canal originally transported water south from the Rio 

Hondo east of Roswell. Because of intensive pumping from the Artesian Aquifer, all of the 

tributaries of the Pecos River, including the Rio Hondo, have been dry for many decades, except 

during brief flood events. For this reason, most of the “surface water” in the Hagerman canal is 

actually groundwater pumped into the canal from wells. Pumping from the shallow aquifer has 

resulted in a significant cone of depression in agricultural areas west of town.

45.0 miles: Historic bridge to right over the Rio Felix, another of the now dry tributaries of the 

Pecos River.

45.3 miles: Red bluffs east of Pecos River at 2:30 are formed in Seven Rivers redbeds and 

gypsum.

49.7 miles: Entering village of Dexter, home of the Dexter Demons. As the Pecos Slope 

descends to the east toward the river, the potentiometric surface approaches ground level. Water 

levels in wells near the river are only a meter or two deep, and many wells near Dexter still 

display strong artesian flow during winter months when irrigation is minimal.

50.3 miles: Turn right and cross railroad tracks onto First St./Shawnee Road East (NM 190).

51.1 miles: Lake Van, an artificially flooded sinkhole, is visible between houses to the right, 

south of Shawnee Road. Lake Van is one of at least nine lakes or seasonal lakes here.

51.6 miles: Dexter Fish Hatchery entrance to right. The Dexter National Fish Hatchery and 

Technology Center was established in 1931 to meet the demand for warm water game fish; its 

main focus was to supply local waterways with sport fish via rearing at the Center. After the 

Endangered Species Act was established in 1973 the hatchery mission was transformed from a 

facility that raised fish for recreational purposes to a facility that would house and protect 

endangered fish species. The Center is the only federal facility in the nation dedicated to holding, 

culturing and studying fishes facing extinction.
148

51.8 miles: Route descends low terrace of Pecos River. Agricultural activity quickly diminishes 

east of Dexter because of deteriorating water quality east of the freshwater-saltwater interface in 

the Artesian Aquifer. Groundwater near the Pecos River has a TDS content in some areas as high 

as 7,000 mg/l.

52.4 miles: Sharp bend to left onto Wichita Road.

52.7 miles: Zuber Lake Farm and artesian well to right. Rock-walled mound in front of house is 

an intermittently-flowing spring.

53.2 miles: Crossing Pecos River. Note banks 3 – 4 m high with natural levee sloping to the east. 

The banks are lined with Catclaw and Salt Cedar (Tamerisk), an invasive species. Water in this 

reach of the Pecos River is quite brackish, with TDS >2,000 ppm. Lakes along the river are a 

combination of oxbows and sinkholes.

53.5 miles: Sharp left turn to north.

54.9 miles: Bear right, staying on paved road, and begin 

ascending Seven Rivers escarpment. For the next five miles the 

route crosses extensive exposures of Seven Rivers gypsum and 

mudstone.

56.4 miles: Sacramento Mountains on western horizon; Sierra 

Blanca on skyline at 8:30. Capitan Mountains batholith at 9:30. 

City of Roswell across valley at 9:00. Reddish-brown ridge on 

far horizon to east is part of the outcrop belt of Triassic Santa 

Rosa Sandstone.

60.9 miles: Road veers left and descends into valley. Dimmitt 

Lake to right, a large sinkhole lake on private land. Lea Lake, the 

largest of the cenotes of Bottomless Lakes State Park, at 11:30.

61.3 miles: Stop sign. Turn left toward Bottomless Lakes State 

Park.

Figure 8. Digital orthophoto image of Bottomless Lakes State Park, 

showing flooded cenotes. All lakes visible in this image are formed in 

gypsum and redbeds within the Seven Rivers Escarpment, a geologic 

setting similar to that observed at Lake McMillan.
149

61.5 miles: Cross Lea Lake overflow canal; turn right into Lea Lake parking lot.

61.6 miles: Stop 4: Lea Lake sinkhole, Bottomless Lakes State Park. Bus parks in parking 

lot. Field trip participants assemble by lake shore.

Lea Lake sinkhole is the only lake in Bottomless Lakes State Park where swimming is 

permitted. Because of the clarity of the water, the lake is popular with local scuba divers. 

Bottomless Lakes is New Mexico’s first state park, established in 1933. The sinkhole lakes are 

formed in gypsum and mudstone of the Seven Rivers Formation, and are some of the larger and 

more impressive examples of the many sinkholes and other karst features that line the lower 

Pecos Valley (Figure 8). 

The Bottomless Lakes sinkholes may more properly be described as cenotes because of 

their deep, steep-walled morphology, similar to the cenotes formed in limestone bedrock on the 

Yucatan Peninsula in Mexico (Caran, 1988). The cenotes of the lower Pecos Valley are unusual 

in that they occur in a semi-arid setting, where annual evaporation rates may exceed mean annual 

precipitation by a factor of 7 or more. The lower Pecos region is also unique in that it is one of 

the few areas in the world where sinkholes are actively forming in a region of groundwater 

discharge rather than recharge (Salvati and Sasowsky, 2002).

These sinkholes, and the many others that occur in the lower Pecos Valley, are the 

product of subsurface dissolution of gypsum by upward leakage of groundwater from the karstic 

San Andres limestone, which comprises most of the artesian aquifer in the Roswell Artesian 

Basin (Figure 9) (Martinez et al., 1998). The lakes are fed by submerged springs discharging 

from the artesian aquifer, and thus represent the down gradient end of the regional hydrologic 

system in the Artesian Basin. Discharge from the springs has caused subsurface dissolution of 

evaporites within the Seven Rivers Formation, localized subsidence, and upward propagation of 

collapse
150

Figure 9. West-east hydrostratigraphic section of the artesian aquifer system in the vicinity of Bottomless 

Lakes State Park. Recharge occurs by direct infiltration from precipitation, and by runoff from 

intermittent losing streams that flow eastward across the Pecos Slope west of Roswell. Groundwater 

flows east and south, down gradient from the recharge area, then upward through leaky confining beds 

into the alluvial aquifer, and ultimately into the Pecos River. 

chimneys, which ultimately formed the cenotes (Land, 2003). Spring sapping at the base of the 

Seven Rivers escarpment has also resulted in oversteepening of the eastern walls of the sinks, 

causing occasional rockslides and other mass-wasting events, an indication of the fundamental 

role that gypsum karst processes have played in shaping the morphology of the lower Pecos 

Valley. 

The gentle (~1°) eastward regional dip of the area is locally reversed along the 

escarpment, where strata of the Seven Rivers Formation dip abruptly southwest by as much as 

40°. This local dip reversal, best viewed in the walls of Mirror Lake, is probably the result of 

subsurface dissolution of gypsum in the vicinity of the sinkholes and consequent slumping of 

overlying beds (James Quinlan1, unpublished report, 1967).

Bottomless Lakes occurs on the saline side of the fresh water/saline water transition in 

the Roswell Artesian Basin (Figure 9), thus water in all the lakes is brackish, with Total 

Dissolved Solids (TDS) content ranging from ~6000 to 38,000 mg/L. In spite of the high mineral

content, some of the lakes are periodically stocked with fish.

 

1 The late James F. Quinlan very precisely summarized the geology and hydrology of Bottomless Lakes

State Park in the text and graphics of an unpublished Christmas card he circulated among friends in 1967.
151

The Roswell Artesian Basin is one of the most intensively farmed areas in New Mexico, 

deriving virtually all of its irrigation water from groundwater stored in the artesian and alluvial 

aquifers. Since the inception of irrigated agriculture in the Artesian Basin more than a century 

ago, most of the discharge from the artesian aquifer has been from wells, although substantial 

natural discharge still occurs through fractures and solution channels in the overlying confining 

beds (Welder, 1983). Groundwater from the artesian aquifer discharges into the many springs 

and sinkhole lakes that line the Pecos River, and is manifest in the development of extensive 

wetlands above and below Roswell. These wetlands are visible along the river immediately west 

of Bottomless Lakes, and to the north at Bitter Lake National Wildlife Refuge (Land and 

Newton, 2008).

Figure 10. Rockslide in 

Seven Rivers Escarpment, 

eastern shore of Lea Lake 

cenote. 

In the early history 

of settlement in this area, 

most of the cenotes at 

Bottomless Lakes 

overflowed into wetlands 

along the eastern shore of 

the Pecos River, but the 

progressive decline in 

hydraulic head in the 

artesian aquifer (up to 70 m in some areas) caused lake levels to fall, so that now only Lea Lake 

overflows. In 1975, a catastrophic rockslide occurred on the steep eastern wall of Lea Lake 

(Figure 10), and the resulting lake surge caused significant damage to a pavilion on the opposite 

shore. No measurements of lake discharge are available prior to 1976 (probably because there 

was no discharge overflow before that date). However, the rockslide appears to have been 

associated with an increase in spring discharge and the opening of new spring outlets in the lake 

bed, as indicated by a significant post-rockslide increase in flow from the lake and the flooding 

of adjacent grazing lands with several million gallons per day of saline and alkaline water. A 

culvert was installed to convey the increased flow into wetlands west of the park, but the lake 

continued to flood an adjacent parking lot and camping area during the winter. In 2002, the park 

completed construction of a more efficient drainage canal to capture all of the discharge, 

resulting in a substantial increase in the measured flow volume from the lake. As discharge 

continued to increase, a second drain was installed in 2005. On January 14, 2006, the New 

Mexico Interstate Stream Commission measured a combined discharge of 576.2 liters/s (20.35 

cfs) from both drains.

The increased flow from Lea Lake, amounting to roughly 18 million m3

/yr (~14,600 

acre-ft/yr), has caused an expansion of wetlands to the west, which are now hydraulically 

connected to the Pecos River, and a net gain in streamflow downstream from the park, an 

interesting phenomenon in a semi-arid region that is currently experiencing an extended drought.
152

Field trip participants return to vehicles and proceed to Stop 6. Zero odometer at visitor pay 

station, exit parking lot and turn left onto loop road.

0.4 miles: Begin ascent of Seven Rivers Escarpment. Dimmit Lake to right.

1.0 miles: Turn left into scenic overlook parking lot.

Stop 5: Lea Lake scenic overlook.

We are standing on the Seven Rivers Escarpment, in a geologic setting very similar to 

that at the McMillan Escarpment farther south. As at Stop 2, large fissures are formed in the 

Seven Rivers gypsum along the upper edge of the escarpment, and large rockslides can be 

observed where they have fallen into the lake, showing the continued morphologic evolution of 

the lake margin by mass wasting. The principal difference between this location and Lake 

McMillan is the presence of active discharge of artesian groundwater at the base of the Seven 

Rivers Escarpment, enhancing mass wasting processes. At least half a dozen springs discharge 

from the lakebed in ~8 m water depth at the base of the escarpment, suggesting that spring 

sapping may have played a role in initiating the 1975 rockslide.

Field trip participants return to vehicles and proceed to Stop 6. Exit parking lot and turn left

onto loop road.

3.7 miles: Lazy Lagoon at base of escarpment to left. During winter months, when water levels 

are high due to low levels of irrigation from the Artesian Aquifer, Lazy Lagoon appears to be a 

single body of water. It is in fact three sinkholes formed in an abandoned channel of the Pecos 

River, the southernmost of which is over 25 m deep. The Lazy Lagoon sinkholes contain the 

most saline water in the park, with TDS exceeding 37,000 mg/l, greater than the salinity of 

seawater. 

3.9 miles: Bear left, and begin descent of Seven Rivers Escarpment. Over the next mile the 

route passes large gypsum slump blocks detached from the escarpment.

5.0 miles: Lazy Lagoon sinkholes to right. 

5.9 miles: Dry sinkholes in escarpment to left.

6.2 miles: Turn left into Bottomless Lakes visitors center parking lot.
153

Stop 6: Cottonwood Lake cenote, Mirror Lake, and Bottomless Lakes visitors center.

Cottonwood Lake is a small cenote containing water that in the past has been fresh 

enough to support fish, although too brackish for them to reproduce. Note rockslide on the far 

wall of the sink. The visitors center contains excellent exhibits, including air photo images and a 

3-D model of all the sinkholes in the park.

Figure 11. Mirror Lake, view to south. 

A trail along the escarpment continues south for ~300 m, crossing a dry sinkhole and 

terminating at Mirror Lake, a compound lake consisting of two cenotes that have grown together 

(Figure 11, and cover photo). A climb to the top of the escarpment reveals large gypsum fissures 

and small tectonic caves formed in the upper margin of the sinkholes. Excellent examples of 

gypsum karren are exposed in bluffs along the north margin of Mirror lake. Note the pronounced 

west dip exposed in the walls of the Mirror Lake cenote. Regional dip is about 1o to the east. This 

local dip reversal is probably the result of subsurface dissolution of gypsum along the 

escarpment.

Field trip participants return to vehicles. Zero odometer, exit visitors center parking lot, and 

turn left onto loop road.

2.0 miles: Pass Lea Lake entrance and turn right onto Wichita Road, following same route back 

to Carlsbad.
154

10.8 miles: Turn right onto Shawnee Road.

13.0 miles: In Dexter, turn left onto Highway 2 and continue south toward Hagerman.

36.4 miles: Turn left onto Highway 285, drive straight through Artesia.

58.9 miles: Begin crossing Seven Rivers Hills; Brantley Reservoir to left. 

72.0 miles: Entering city of Carlsbad; Tracy Dome/C-Hill to right. US-285 becomes W. Pierce 

St.

74.6 miles: Bear right onto South Canal St.

75.1 miles: Turn left onto Church St. 

75.6 miles: Turn right onto Park Dr. and return to NCKRI headquarters.

Figure 12. Pump jack in sinkhole, Dagger Draw oil field, Eddy Co., New Mexico.
155

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