American Public University System
DigitalCommons@APUS
Master's Capstone Theses
11-2015
Urban Sinkholes: Are Our Communities Prepared
for Them?
Tamara L. Mann
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URBAN SINKHOLES: ARE OUR COMMUNITIES PREPARED FOR THEM?
A Master Thesis
Submitted to the Faculty
of
American Public University
by
Tamara Lynn Mann
in Partial Fulfillment of the
Requirements for the Degree
of
Master of Arts
November 2015
American Public University
Charles Town, WV
URBAN SINKHOLES
The author hereby grants the American Public University System the right to display
these contents for educational purposes.
The author assumes total responsibility for meeting the requirements set by the United
States Copyright Law for the inclusion of any materials that are not the author’s creation
or in the public domain.
Copyright © 2015 by Tammy Mann
All rights reserved.
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URBAN SINKHOLES
DEDICATION
I dedicate this paper to my family and friends. To my wonderful husband,
without his love, unwavering support, and fervent belief that I could succeed, the
completion of this work would not have been possible. To my dogs, who kept me
company while I studied and my parrots that helped me stay alert with their frequent
vocalizations. To my father-in-law who was kind enough to review and constructively
critique all of my papers, his efforts greatly enhanced my writing skills. To my friends,
who became the subjects of some of my papers, found my work informative and
interesting, and offered valuable feedback.
URBAN SINKHOLES
4
ACKNOWLEDGMENTS
I wish to thank the members of the reviewing committee for their support, and
patience. Dr. Len Clark, in particular, has been very patient with me, and throughout the
class, has provided me with numerous tips to successfully write this paper using the right
format and structure. I would not have been able to do it without his guidance. The
coursework throughout this masters program has broadened my knowledge and
theoretical understanding of Emergency and Disaster Management and has greatly
sharpened my research and analytical abilities in which to innovatively explore past and
present ideas and issues.
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URBAN SINKHOLES
ABSTRACT OF THE THESIS
URBAN SINKHOLES: ARE OUR COMMUNITIES PREPARED FOR THEM?
by
Tamara Lynn Mann
American Public University System, May 24, 2015
Charles Town, West Virginia
Professor Len Clark, Thesis Professor
The purpose of this research is to examine the theory that sinkhole events are a
common problem, are increasing in frequency within the United States and resulting in
costly damages, disrupted communities, and lost lives. Communities are ill prepared to
deal with them or their aftermath. Remediation and mitigation costs range in the
thousands, usually paid out-of-pocket as insurance coverage is not always available and,
in some cases, only covers catastrophic losses. A mixed methods approach with a
pragmatic worldview was used to evaluate data with the overarching goal to show that
communities must be knowledgeable about sinkhole hazards in order to make informed
decisions to better protect residents from their potentially devastating results. Sinkholes
are natural phenomenons that under normal circumstances take many, even hundreds of
URBAN SINKHOLES
6
years to development; human activities often accelerate that timeframe to just hours or
days. As humans trigger up to three-quarters of all sinkholes, it is largely within our
grasp to control factors that trigger the development of most sinkholes. Building longterm sustainable communities able to withstand sinkhole occurrences will require action
by governmental authorities and others to develop policies and procedures that minimize
the incidence and impact of sinkholes.
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URBAN SINKHOLES
TABLE OF CONTENTS
CHAPTER
PAGE
LIST OF FIGURES AND TABLES ……….….................……………………….…… 10
I. INTRODUCTION ………………………...…………………………......………..… 11
Problem Statement ………………………...…………………………………… 14
Research Questions ………………………...………...………………………… 14
Expected Value of the Research ………………………...…...………………… 15
II. LITERATURE REVIEW ……………………...……….………..…………….…… 16
Introduction ………………….……...….................………………………….… 16
Prevalence, Sinkhole Definitions, and Types of Sinkholes ………………….… 18
Prevalence …………………...…………………………………………. 18
Sinkhole Definitions, and Types of Sinkholes ………………………… 18
Dissolution Sinkholes ………………………………..………… 19
Cover-Subsidence Sinkholes …………………………….…….. 20
Cover-Collapse Sinkholes ……………………………………… 20
Case Studies ………………………...…...…………………………...………… 22
Bayou Corne, Louisiana ………………………....…...………………… 22
Daisetta, Texas ……………………………...........…......……………… 26
Bowling Green, Kentucky ………………………..…...…..…………… 31
Seffner, Florida ……………………………..........…...……...………… 33
URBAN SINKHOLES
8
Oveido, Spain …………………………...…...………………………… 35
III. METHODOLOGY………………………………....……...…..........………...…… 37
Introduction ……...………………………...…………………………………… 37
Data Collection ………………………...………………………….…………… 38
Scope and Limitations of the Study ……………....……………….…………… 41
IV. FINDINGS ………………………...………………..…………..……………….… 42
Introduction ……...………………………...…………………………………… 42
Prevalence ………………………...…………….……………………………… 43
State Sinkhole Maps ………………………………...…………………………. 45
Natural and Human Factors ………...…………………...…...………………… 48
Natural Factors ………...…………...………………...………………… 48
Human Factors ………...………………………...…...………………… 50
Land Use ……………………………………………..………… 50
Water Use ……………………………………………….……… 51
Hazard Risks ………………………...…………..…………….….……….…… 52
Costly Damages and Fatalities ……………………………….………… 52
Water Contamination ……………………………………….………….. 53
Intangible Hazards ………………………………………….………….. 54
V. DISCUSSION ………………………...………………………..………...………… 56
Introduction ……...………………………...…………………………………… 56
URBAN SINKHOLES
9
Emergency Response ………………….…............………………………….… 58
Detection and Identification ……………………..…...………………………... 60
Predictability …………………………………………………………………… 61
Remediation and Mitigation ………………………..….…...…….………….… 63
Remediation ……………………………………………………..…….. 63
Mitigation ……………………………………………………………… 65
Legal Framework ……………………...…...…….………..…… 66
State Hazard Mitigation Plans ……………...…….……….…… 68
Insurance ………………………...…...…………...….………… 69
FEMA ………………………...…...…………..…………..…… 71
VI. SUMMARY ………………………...……………………………………..…….… 73
Summary and Recommendations ………………....…………………………… 73
Conclusion ………………………...…………………………………………… 77
LIST OF REFERENCES ………………………...………………………………….… 81
APPENDIX ………………………………………………………….………………… 97
URBAN SINKHOLES
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LIST OF FIGURES AND TABLES
FIGURE
PAGE
1. US Map of Soluble Rock and Karst Terrane ………………...……………...……… 17
2. Dissolution Sinkhole ………………...……………………...………………………. 19
3. Cover-Subsidence Sinkhole ………………...….…………...………………………. 21
4. Cover-Collapse Sinkhole ………………...………………....………………………. 21
5. Bayou Corne Louisiana Sinkhole …………………………..………………………. 22
6. Daisetta Texas Sinkhole ………………...………...………...………………………. 26
7. National Corvette Museum Sinkhole ………………...……………..………………. 31
8. Emergency Response to Seffner Florida Sinkhole …………………………...…….. 33
9. Texas Sinkhole Map ……………………...………………...………………………. 45
10. Missouri Sinkhole Map …………………………………………………………..... 47
11. Summer Bay Resort ………………………………………………………….……. 57
12. Graded Filter System ………………………………...……………...……………. 65
TABLE
1. 1999-2011 Rising Insurance Costs in Florida …………...……….…………..……. 14
2. Natural and Human Factors ……………………………...……….…………..……. 48
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URBAN SINKHOLES
I. INTRODUCTION
Sinkholes are naturally occurring or man induced land subsidence events
that are endemic in some countries and states due to unique geological structures of the
bedrock, specifically to landscapes with water soluble, evaporative rock types, primarily
limestone and dolomite, also referred to as “karst” (USGS, n.d.). Sinkholes, cavities,
caves, springs, disappearing streams, and internally drained basins, characterize karst
terrain. Sinkholes can vary greatly in size and depth ranging from unnoticeable, tiny
depressions, to visible holes a couple of feet in diameter and under a foot in depth, to
gigantic caverns and even up to hundreds of acres, greater than 100-feet deep (USGS,
2014). One survey calculated that, on average, around 175 sinkholes developed every
year between 1950 and 1987 in the eastern United States; human activities induced nearly
all of them resulting in hundreds of millions of dollars in damages (Kemmerly, 1993,
p.1). Historically, the most damaging sinkholes in the US have occurred in the states of
“Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania,” but can
occur in other states with karst topography (USGS, 2014). Factors that can increase and
even induce the frequency of sinkholes include human activities, heavy rainfall, and
water level changes in aquifers. Recent incidences of catastrophic sinkholes have begun
to raise public awareness that sinkholes are an increasing problem worldwide.
In May this year, a large sinkhole measuring 80 feet wide and reaching the
depth of 35 feet, displaced 7,000 cubic feet of soil from a golf course in Branson,
URBAN SINKHOLES
12
Missouri (Associated Press, 2015). That region is well known for having caves, such as
the Lost Canyon Cave, and for developing sinkholes due to its karst topography. The
sinkhole appeared after a heavy rainfall, claiming vehicles, heavy equipment, and
vegetation. Last year, people were surprised when a “45-foot wide and 60-foot long
hole” sinkhole opened up at the National Corvette Museum (NCM) in Bowling Green,
Kentucky, and eight Corvettes plunged into the hole; remediation to fill the hole will cost
approximately $3.2 million (Burden, 2014). In February 2013, the public was shocked
by the headlines that a man in Seffner, Florida lost his life in a sinkhole that opened up
underneath his bedroom and swallowed the room’s contents, including the man asleep in
his bed (NOVA, 2015). Later that year another sinkhole event made the headlines when
over 30 guests at the Summer Bay Resort in Clermont Florida had to evacuate the
collapsing buildings quickly. The resort, located about 10 minutes from Walt Disney
World, is a popular location for visitors (Stapleton, 2013). In 2010, a sinkhole in Bayou
Corne, Louisiana, grew from 15 acres to 32 acres endangering nearby communities. In
May 2008, after a sinkhole in Daisetta Texas rapidly grew to around 600 by 525-feet in
diameter and 150-feet deep, the Texas Department of Transportation closed nearby
Highway 770 for several months for safety precautions (“Daisetta sinkhole,” 2008).
Karst topography and sinkholes are a common problem worldwide and cause
similar damages. The events in Guatemala and Spain demonstrated that the occurrences
of sinkholes that threaten urban populations appear to be growing. In 2010, a 65-foot
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13
wide by 100-foot deep sinkhole opened up in the “in the middle of a major urban area” in
Guatemala City (Palmer, 2010). In 1998, construction and water pumping triggered a
sudden 1-2 foot ground settlement in Oviedo, Spain that damaged two apartment
buildings, displaced occupants of 362 apartments, and cost the government around 18
million euros (Pando, Pulgar, & Gutiérrez-Claverol, 2012).
When sinkholes appear in urban areas they disrupt and pose numerous
hazards to communities including partial and complete loss of building and structures,
loss of vehicles and vegetation, contamination of local aquifers, evacuation and
displacement of residents, closure of roads and businesses, fall hazards for people and
animals, and substantial financial losses. Depending upon where a sinkhole appears,
response to sinkholes can initially require the notification and physical response from a
bevy of local, state, and federal emergency responders including the Office of Emergency
Management (OEM), police and the fire departments, American Red Cross (ARC),
search and rescue, local and US Geological Survey (USGS), and insurance companies’
adjusters. Local and government officials and departments that may need to get involved
include commissioners, mayors, governors, Department of Transportation (DOT), and
local and state Environmental Protection Agencies (EPA). Professional experts such as
geologists, structural engineers, building inspectors, land surveyors, universities,
contractors, and of course, lawyers, can be involved in the response and remediation of
sinkholes. The list seems endless and indicates the potential complexities when dealing
URBAN SINKHOLES
14
with sinkholes. While sinkholes that open up in unpopulated areas, like the one in
Missouri, can be costly to repair for the property owner, this paper will focus on those
that pose a threat to structures and people in urban areas within the US.
Problem Statement
In some states like Florida, insurance claims related to sinkholes have been
steadily increasing. According to the Florida Office of Insurance Regulation (2010, pp.
5-6) and Florida Senate (2010, p. 6), claims for sinkhole damages increased from 348 to
almost 7,000 between 1999 and 2010 respectively; costs nearly doubled in 3 years from
2006 to 2010 (see Table 1).. The purpose of this study is to examine why the incidences
of sinkholes that result in substantial property damages, disrupt communities, and take
lives, is increasing so communities can better plan for, respond to, mitigate, and recover
from future sinkhole events.
Table 1. 1999-2011 Rising Insurance Costs in Florida
Year
1999
2003
2006
2009
2010
2011
# Claims
348
1,018
2,360
7,244
6,964
Value
$22.4 Million
$65 Million
$209 Million
$406 Million
$396 Million
$468.6 Million (estimated)
Research Questions
Response to urban sinkholes can involve a multi-faceted array of city and state
officials, subject matter experts, emergency response personnel, and insurance
URBAN SINKHOLES
15
companies. While some states appear to have structures in place to help prevent and
mitigate the emergence of sinkholes, others do not. Significant and catastrophic urban
sinkholes have recently made media headlines and brought a limited amount of
awareness to the public. However, these media snapshots of events fail to reveal the
scope of the problem. This research will help provide a more comprehensive picture of
the issues associated with sinkholes and community preparedness.
1. What areas in the United States (US) are most susceptible to sinkholes?
2. How hazardous are sinkholes?
3. What factors can increase and induce the frequency of sinkholes?
4. What are the methods and costs associated with detecting sinkholes?
5. How can sinkholes be prevented and remediated?
6. Do current laws and insurance protect property owners?
Expected Value of the Research
The overarching goal of this research is to contribute to the field of emergency
and disaster management by elevating the knowledge and awareness on the hazards of
sinkholes for emergency managers, firefighters, police, and other emergency response
personnel who respond to sinkhole incidents. This research will assist and enhance local,
regional, and state disaster planning by helping to identify and analyze potential risks
associated with sinkholes. A better understanding of sinkhole risks will strengthen
emergency preparedness planning, response, and mitigation efforts. This research will
16
URBAN SINKHOLES
underscore the necessity for emergency and disaster planning to ensure communities are
prepared for sinkhole activity by demonstrating that sinkholes can pose significant risks
to communities by engulfing land and valuable property, disrupting and destroying
communities, and even taking lives.
This research will provide a clear overview of the different types of sinkholes,
their risks, how, and where they are likely to occur, how human activity can induce
sinkhole activity, and describe current mitigation and remediation procedures.
Knowledge and awareness gained by local authorities such as city planners, policy
decision makers, and government officials, will assist with efforts in developing rules,
regulations, ordinances, programs, and sustainable land use plans that address and
minimize sinkhole hazards, that will, in turn, reduce damages incurred by sinkhole
activity. Lastly, another aim of this research is to highlight deficiencies in the literature
deserving the allocation of substantial funds for further research and study from
academicians and the research community.
II. LITERATURE REVIEW
Introduction
Development and implementation of Comprehensive Emergency Management
Plans (CEMPs) prepare communities for emergencies and disasters through hazard risk
assessments, determination of vulnerabilities, and identification of response and
mitigation measures. Communities located in karst terrain are vulnerable to the
URBAN SINKHOLES
17
development of sinkholes. Planners that assess sinkhole risks and vulnerabilities,
mitigation, and remediation costs, will make informed decisions that serve to protect and
prepare communities from the hazards associated with sinkholes. “Future losses will
increase substantially unless planners recognize risks posed by sinkhole terrains and
incorporate geologically and hydrologically sensitive guidelines into approval procedures
for residential, commercial, and industrial development” (Kemmerly, 1993, p. 221). A
review of the literature provides a scientific and narrative overview of the problem. To
appreciate the diversity of the problem, it is necessary to first understand what sinkholes
are, how they develop, and what geologic terrain is most prone to sinkhole activity.
Figure 1. US Map of Soluble Rock and Karst Terrane (USGS, 2014)
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18
Prevalence, Sinkhole Definitions, and Types of Sinkholes
Prevalence. Sinkholes commonly develop in areas of karst terrain that is
characterized by sinkholes, caves, cavities, fissures, and springs that developed by the
partial dissolution of evaporative (salt, gypsum, and anhydrite) or carbonate (limestone
and dolomite) bedrock, and from exposure to water (USGS, n.d.). According to the
USGS (2014), evaporative and dissolvable bedrock comprises between 35-40 percent of
the terrain in the US (see Figure 1); about 20 percent is classified as karst. Around 40
percent of US drinking water comes from karst aquifers (USGS, n.d.). Every year since
1950, hundreds of sinkholes have been reported of which most are induced by human
activities, primarily through an inordinate removal of water and construction. The states
that tend to develop the most damaging sinkholes are “Florida, Texas, Alabama,
Missouri, Kentucky, Tennessee, and Pennsylvania,” and foreign countries with damaging
sinkholes include China, Europe, and Australia (USGS, n.d.; 2014).
Sinkhole Definition and Types of Sinkholes. In the US, the term “sinkhole”
describes “a gradual or sudden lowering of a portion of the topographical surface”
(Sauro, 2003, p. 43). Internationally, literature uses the term “doline” to describe closed
or open depressions on the topographical surface; the terms “sinkhole” and “doline” are
often both utilized at the same time. The term doline elicits a mental picture of a rounded
or shaft-like depression. In contrast, the term sinkhole brings to mind a vertical
depression in the topography as a result of a sudden collapse of surface materials in karst
URBAN SINKHOLES
19
terrain (see Figure 4). In Florida and many other states and countries, the most common
sinkholes or dolines, develop in carbonate, primarily limestone, bedrock and are
categorized as dissolution, cover-subsidence, and cover-collapse (USGS, 2014).
Figure 2. Dissolution Sinkhole (USGS, 2014)
Dissolution sinkholes. These slowly form when water causes the dissolution of
soluble, carbonate bedrock and forms cavities below the surface. Suffosion takes place
with the downward erosion of overburden materials into the cavities. As depicted in
Figure 2, they tend to develop in areas with thin, permeable overburden or surface soil
that exposes the underlying soluble bedrock to rainfall and surface water. The water
dissolves and carries away the bedrock causing subsurface cavities and fissures that
collapse resulting in depressions. The depressions become rolling hills and reservoirs
that when plugged can form ponds, wetlands, and lakes. Dissolution is the basic process
for all sinkholes; the types are different depending upon the “thickness and type of
overburden materials and local hydrology” (Tihansky, 1999, p. 126).
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20
Figure 3. Cover-Subsidence Sinkholes (USGS, 2014)
Cover-subsidence sinkholes. These gradually form in a similar fashion as
dissolution sinkholes but generally occur when the overburden consists of highly
permeable materials, such as sand, and the layer is considerably thicker as shown in
Figure 3. Like dissolution sinkholes, cover-subsidence sinkholes develop visible
depressions in the landscape. Additionally, the depressions can vary greatly in size and
depth, from inches to several feet; both types may not attract attention thus they can
remain undetected for prolonged periods (USGS, 2014).
Figure 4. Cover-Collapse Sinkhole (USGS, 2014)
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21
Cover-Collapse Sinkholes. These types of sinkholes form very similarly to
cover-subsidence sinkholes, the main difference between the two is the type of
overburden, sand versus clay as shown in Figure 4. Overburden with significant amounts
of clay is more cohesive than sand and is more likely to remain intact while a cavity
forms underneath. Eventually, as the void grows, the overburden thins until the cavity is
unable to further support the weight of the overburden thus causing a sudden and
dramatic collapse with potentially catastrophic results. Cavities often occur in karstic
aquifers filled with water that helps support the overburden; lowering the water table by
imprudent groundwater pumping can remove the supportive water creating an empty void
thereby inducing or triggering a cover-collapse sinkhole. Most new sinkholes triggered
by human activities correlate to water and land-use practices such as groundwater
pumping and urban development (USGS, 2014).
URBAN SINKHOLES
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Case Studies
Figure 5. Bayou Corne Sinkhole (Google, n.d.)
Bayou Corne, Louisiana. Assumption Parish is located near Bayou Corne and
above the Napoleonville salt dome. In 2012, over 50 manmade caverns or wells
peppered the salt domes developed mainly for the purposes of solution (brine) mining
and storage for hydrocarbons. Some of the wells date back to the 1950s, three of which
were abandoned and plugged. In 1982, owner and operator Texas Brine Company (TBC)
started operating cavern well “Oxy Geismar #3” (Oxy #3 herein) for solution mining and
operated without any issues until September 2010 when Oxy #3 failed to hold pressure.
TBC abandoned the well and plugged it with cement to a depth of 2,500 feet in June 2011
(Blue Ribbon Commission [BRC], 2013, p. 20). Although results from a vertical seismic
profile demonstrated that the base of the well was closer to the edge of the salt dome then
thought, it did not rouse concerns of a collapse.
URBAN SINKHOLES
23
All was well until a year later in May and June 2012, when community residents
reported seismic tremors and natural, non-flammable gas bubbling in the Bayou Corne
area. Investigative and monitoring efforts to determine the source of the bubbling
involved local, state, and federal resources; when the sinkhole developed on August 3,
the cause of the bubbling was still unknown. Monitors recorded hundreds of seismic
events a day for several days preceding the development of the sinkhole (BRC, 2013).
On August 3, 2012, Bayou Corne residents informed local officials of a diesel
odor in the community and of a 200-foot diameter “slurry” in the swamp in which trees
had collapsed. The local OEM issued an immediate mandatory evacuation order for a
portion of the Assumption Parish residents and coordinated with the ARC to set up
shelters (Assumption Parish Police Jury [APPJ], 2012a). The Assumption Parish
officials declared a state of emergency, as did the Governor, which allowed the
Governor’s Office of Homeland Security and Emergency Preparedness (GOHSEP) and
state agencies to respond to the incident. The GOHSEP and other state agencies
including the Department of Natural Resources (DNR), Department of Environmental
Quality (DEQ), the state National Guard (NG) and others, joined local efforts in response
to the sinkhole. The GOHSEP started coordinating efforts and information sharing
between the responding different government agencies (Governor’s Office of Homeland
Security and Emergency Preparedness [GOHSEP], 2012a).
URBAN SINKHOLES
24
The escaping, natural methane gas posed a life safety hazard to residents in the
Assumption Parish. Surveys mapped more than 50 escaping gas sites of over a two
square mile radius; Bayou Corne community residents could see gas bubbling after rain
collected on the ground (BRC, 2013, 2014). Heavy concentrations of methane gas, such
as when it collects under slabs and in crawl spaces, can be explosive; thus, the OEM
issued a mandatory evacuation order, which was still in effect in March 2014 (BRC,
2013). The slurry was near Highway 70, less than 2,000 feet from the closest bubbling
area, and around 2,500 feet from the nearest residence. The slurry prompted flyovers of
the area by Louisiana State Police and local emergency personnel to seek out the
existence of any additional slurry areas, and the OEM started 24 hours operations (APPJ,
2012a).
On August 3, 2012, the DNR issued an order for TBC to take immediate action to
suppress any further deterioration in Oxy #3; this required the drilling of an exploratory
well to assess damages and take samples (GOHSEP, 2012b). It was not until September
25, 2012, that the cause of the sinkhole was determined. DNR notified Assumption
Parish local officials that the exploratory well confirmed that TBCs brine cavern, Oxy #3
had failed creating a void; the cavern started to fill with materials which created the
sinkhole, disturbed rock layers, and freed trapped natural gas which traveled up to the
surface creating bubbles (APPJ, 2012b; Darensbourg, 2013; Wines, 2013). Parish
officials did not agree with TBC press release that blamed the collapse on local seismic
URBAN SINKHOLES
25
activity and announced their plans to hold the company accountable and ensure that the
company assisted evacuees (APPJ, 2012b).
In April 2013, Governor Jindal called for a Blue Ribbon Commission (BRC) in
order to determine or recommend conditions and/or criteria in which to lift the evacuation
order and to protect the area around the sinkhole for public safety; evacuees from 150
homes were still displaced since the original order on August 3, 2012 (BRC, 2013;
Department of Natural Resources, 2013). TBC was responsible for mitigation efforts.
Those efforts included the installation of over 50 observation relief wells to reduce gas
pressure and recover methane gas near the community, in the overlying aquitard, and
from the Mississippi River Alluvial Aquifer. Other mitigation activities included the
installation and maintenance of a berm to contain sinkhole surface waters, and
continuance of gas, seismic, and subsidence monitoring systems until governing officials
lifted the evacuation order for Assumption Parish residents (BRC, 2014).
The sinkhole first appeared in 2012 as a 2-acre slurry filled with crude oil and
debris that over time continued to grow and by March 2013 was greater than 12 acres and
by March 2014 was around 25 acres, and still growing (BRC, 2013; Howell, 2014). The
sinkhole has been financially expensive for the Parish, the state of Louisiana, and for
TBC. By March 2013, TBC was billed over 3.5 million, $480,000, and $340,000 by the
state, Assumption Parish, and Sheriff’s office, respectively (“Louisiana Governor,”
2013). Furthermore, TBC is in the process of buying out properties of residents affected
URBAN SINKHOLES
26
by the evacuation and as of January 14, 2015, 104 properties had been bought out for
around $8 million in total; “each closing also ends $875 weekly evacuation assistance
payments paid since fall 2012 at a total cost of nearly $11.8 million” (Mitchell, 2015, p.
3). By January 2015, the state of Louisiana had reputedly assumed $16 million in costs
related to the sinkhole (Mitchell, 2015). In the event the sinkhole threatens highway 70,
contingency plans estimated a cost of approximately $10 million to reroute the highway
(Kent, 2014; “Louisiana considers,” 2014). Moreover, dangers associated with the
sinkhole resulted in the displacement of over 350, a decline in property values, and the
destruction of the Assumption Parish community (“Louisiana Governor,” 2013; Wines
2013).
Figure 6. Daisetta, Texas Sinkhole (Google images, n.d.)
Daisetta, Texas. Karst terrain underlies much of central and western Texas as
shown in Figure 1, and caves and sinkholes are prominent landform features in these
URBAN SINKHOLES
27
areas. The formation of a number of sinkholes in Texas correlates with wet weather after
an extended period of dry weather. Dry spells and periodic droughts are common in
Texas; thus, the formation of sinkholes can be expected to develop. Occurrences of
sinkholes have been recorded varying in sizes from a couple of feet to greater than “2,000
feet, both in depth and diameter” (Alamo Area Council of Governments [AACOG],
2012, p. 180). Notable sinkholes include the Devil’s Sinkhole, discovered in 1867, which
is a National Natural Landmark and the Bering Sinkhole, discovered in 1987, which
served as a cemetery for local natives for over 5,500 years (AACOG, 2012). The more
recent sinkhole in Daisetta gained notoriety as it rapidly grew to the size of a small lake,
estimated to be about 6 acres, with a depth greater than 250 feet (Casselman, 2008;
KHOU Staff, 2010).
Daisetta is an old oil field town with a resident population of around one thousand
that sits atop the underground Hull Salt Dome and is surrounded by hundreds of old
wells, some of which are used to store saltwater waste. Several oil companies including
DeLoach Oil and Gas Wastewater Disposal Company own the saltwater disposal wells.
Saltwater waste, a byproduct of oil production is injected into the wells for permanent
storage as the waste must be stored underground to prevent it from contaminating water
sources and the environment (Associated Press, 2008). On 7 May 2008, the first signs of
trouble started with concentric cracks in the ground, vertical displacement followed by a
20-foot-wide sinkhole located just a block away from the high school and fire
URBAN SINKHOLES
28
department, and right next to DeLoach’s waste-water disposal facility (Dellinger, 2009;
Horswell, 2009). The circular sinkhole grew 20 feet an hour swallowing everything in its
path and quickly expanded to a diameter of around 200 meters or 656 feet filled with
debris and crude oil (Horswell, 2009; Paine, Collins, Wilson, & Buckly, 2009). Initial
tests estimated the depth of the sinkhole to be 76 meters or 249 feet; later estimates
reflected shallower depths from 21 to 24 meters or 68 to 78 feet; slumping and filling
could account for the changes in depth (Paine et al., 2012).
Simultaneous with the collapsing sinkhole, a few previously unplugged wells
purged to the surface spewing contaminated brinish water of 220,000 TDS (Total
Dissolved Solids), which created a huge kill zone in properties of nearby residents;
reputedly, three wells purged saltwater contents to the surface (Dellinger, 2009;
Horswell, 2009). In comparison, rainwater typically has a TDS of 20, brackish water is
more than 1,000 TDS, seawater TDS ranges between 35,000 to 100,000 and brine is
greater than 100,000 TDS; Acceptable TDS range for irrigation of landscapes is between
200-800 (WateReuse Foundation, 2007). The mayor was one of the residents whose land
was the recipient of a purged well, affecting more than six acres of his property and
killing 100 trees in addition to destroying vegetation; the state capped the well located on
the mayor’s property (Dellinger, 2009; Horswell, 2009, 2010).
The county’s OEM coordinated and continues to coordinate with a wide array of
other agencies to respond to, investigate, monitor, and mitigate the sinkhole, and to keep
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29
the public informed of any new developments. By closely monitoring the developing
situation, OEM was able to request the Texas DOT close a portion of Highway 770
adjacent to the sinkhole when it appeared to have subsided about five inches and did not
reopen it for several months (Liberty County Texas, 2008). The USGS also monitored
the sinkhole site for new developments. The Railroad Commission, in conjunction with
geologists from the Bureau of Economic Geology, hosted a meeting that updated
residents on the sinkhole’s status. The Texas State Senator and State Representative for
the area arranged the meeting, and attendees included a local judge, school
superintendent, and the emergency management coordinator. Scientists from the
University of Houston and Louisiana State University carried out ground testing and
daily monitoring to determine whether the site was stable and safe. The OEM received
daily updates from the Texas Railroad Commission and posted relevant information on
its website. The Liberty County Court, City of Daisetta, and Fire Department held public
workshops to “present Geological and legal options regarding the sinkhole situation”
(Liberty County Texas, 2008).
What caused the cover-collapse sinkhole? Natural causes, oil drilling, and
injected storage of saltwater waste are some of the theories about what led or caused the
cover-collapse sinkhole. The salt dome itself could have naturally dissolved and created
a sinkhole. Nearby oil drilling could have weakened the dome, resulting in its collapse.
However, some experts agree with the theory that the collapse was due to the injected
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30
storage of saltwater waste. Houston University geosciences professor Don Van
Niewenhuise thought the saltwater waste probably fractured a portion of the salt dome
and the wastewater was leaking out and geologist Robert Traylor opined that the disposal
injection of wastewater was the most probable cause (Associated Press, 2008; Horswell,
2010)
Daisetta spent almost $10,000 to fund a commission to investigate the cause of
the collapse (Railroad Commission of Texas, n.d.). The preliminary results failed to
pinpoint the exact reason for the collapse and concluded that it could have been the result
of a natural evolution of salt domes. Additionally, the commission concluded that
satellite-based Interferometric Synthetic Aperture Radar (InSAR) data did not reveal any
obvious pre-existing deformation of the ground over the salt dome (Paine et al., 2009).
However, the commission found that DeLoach’s company had been injecting nearly
double the amount of wastewater (192,000 barrel per month) than its permit allowed
(90,000 barrels per month), DeLoach’s permit was terminated and the company was fined
a $11,000 penalty (Anonymous, 2008; Casselman, 2008; Horswell, 2010). The Texas
Commission on Environmental Quality indicated saltwater could potentially infiltrate the
water and the mayor and city residents expressed concerns regarding the safety of the
town’s drinking water. Conversely, the Railroad Commission claimed that it had no
proof of saltwater migration. Yet, when an engineering company started to drill a backup
well for the town, water samples were contaminated with trace amounts of toluene and
URBAN SINKHOLES
31
naphthalene, neither of which is produced naturally; the engineering company
“recommended abandoning the $93,000 project and drilling somewhere else” (Horswell,
2010).
Figure 7. National Corvette Museum (Google images, 2014)
Bowling Green, Kentucky. The south-central region of Kentucky typically
develops large, superficial depressions that configure the surface with a mild, rolling
landscape (North, Polk, & Nedvidek, 2014). In south-central Kentucky, as in much of
the southeastern US, sinkholes are natural features that are part of the underlying geology
(see Figure 2). The number of sinkholes so numerous that the Kentucky Geological
Survey maintains a sinkhole database, storing the results of their research and work on
their occurrence, prevention, and remediation (North et al., 2014). Despite the existence
of this database providing awareness of sinkholes in the area, it was a total surprise to the
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32
owners of the NCM when in February 2014, twenty years after the museum was
completed, a large, 30-foot deep sinkhole opened up underneath the show floor in the
museum (Preston, 2014). This event gained worldwide media attention when the
sinkhole gulped down eight rare, vintage Corvettes (Bittenbender, 2015; North et al.,
2014; Preston, 2014;). The museum is located near the famous Mammoth Cave National
Park, the largest known cave system in the world with greater than 400 miles of explored
caves (Everson, 2014; National Park Service, 2015; USGS n.d.).
The incident took place early in the morning before opening hours. The
museum’s security company notified museum personnel that motion sensors were
alarming in the Sky Dome area and once on the scene, the staff discovered the sinkhole
and closed the museum for the day. The local fire department secured the site. Structural
engineers and geologists from a nearby university used remote-controlled drones to
assess the damages and stability of the Sky Dome; the assessment concluded that there
were no structural damages and that the area was stable (Everson, 2014; National
Corvette Museum, 2014). The museum opened up for business the following day.
This highly publicized event sparked the public’s interest in sinkholes and raised
concerns about insurance coverage for sinkholes. As a result, Kentucky House Bill 498
was filed which “would require insurers who offer property insurance to offer an
additional policy rider covering sinkhole damages for an additional premium,” similar to
Florida and Tennessee insurance laws for sinkhole coverage (Brandenburg, 2014).
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33
Moreover, over eight million viewers watched the security footage of the event posted on
YouTube and visitors to the museum increased by 67 percent from the previous year
leading to hiring more staff and increased revenue (Bittenbender, 2015). The increased
interest in visitors wanting to see the sinkhole led museum officials to make the decision
to delay repairs to the museum until November. Of the eight cars that plunged into the
hole, only three were salvageable; the museum plans to use the destroyed cars in a future
sinkhole exhibit. Costs to fix the sinkhole are expected to be around $3.2 million and
take up to nine months to repair; the process will include removing debris, installation of
structural supports, and filling the hole with about 4,000 tons of rock (Edelstein, 2014).
Figure 8. Emergency Response to Seffner Florida Sinkhole (Google, n.d.)
Seffner, Florida. On 28 February 2013, Jeffrey Bush lost his life while asleep in
his bed at 240 Faithway Drive when a sinkhole opened up beneath his bedroom and
URBAN SINKHOLES
34
engulfed the room’s contents, including Jeffrey Bush (Hobson, 2014). Emergency
response to the incident included a diverse array of county staff: emergency management,
police and fire rescue officials, utilities and public works, code enforcement department
and social services (Merrill, 2013). Other agencies that supported response activities
came from the private sector, including structure specialists and engineering consultants
from three different firms.
The County Fire Department’s Urban Search and Rescue team rescued Jeffrey
Bush’s brother from the sinkhole after he had jumped into the hole in an attempt to rescue
the victim. Engineering consultants deployed a listening device into the opening in order
to detect any sounds of life or movement; unfortunately no sounds were detected and the
device was subsequently lost in a secondary collapse at a depth of around 30 feet. A third
collapse occurred that same night, and the scene was deemed as too hazardous to
continue rescue attempts without additional soil sampling. Geophysical specialists and
ground testing firms were called in to ascertain the extent of the sinkhole. The team of
specialists utilized Ground Penetrating Radar (GPR), electrical resistivity, and Cone
Penetrometer Tests (CPT) to collectively detect voids, soil strength, pore water pressure,
and soil layering. As a safety precaution, and to minimize ground vibrations or
disturbance that could trigger additional collapses, testing started towards the street rather
than near the houses on either side of the affected house. Results from the tests found the
immediate area to be hazardous and signs of disturbance extended out in a 50-foot radius
URBAN SINKHOLES
35
from the sinkhole. The sinkhole itself was unstable with vertical walls that could
collapse at any time, thus, it was determined to be too dangerous to continue with
recovery activities, and the body of Jeffrey Bush was not recovered (Merrill, 2013). The
house was demolished, and the sinkhole filled in with gravel in order to stabilize the area.
Test results also indicated that the properties on either side of the impacted house
were at risk and the occupants “were told not to enter their homes again” (Merrill, 2013,
p. 2). The neighboring families were evacuated from their homes the morning after the
incident; however, they were allowed 30 minutes to return to their homes to retrieve
personal items, escorted by emergency responders. The Hillsborough County
government condemned and demolished the homes because “the cost of remediation was
greater than half the value of the home(s)” (Merrill, 2013, p. 3). The Hillsborough
County Parks, Recreation, and Conservation Department plans to formally take
possession (acquisition) of the empty lots and restore the site to its natural state with a
memorial to honor Jeffrey Bush and the loss of properties; the project is estimated to cost
$90,000 and another $2,000 in back taxes (Hillsborough County, 2014; Hobson, 2014).
Oviedo, Spain. Many foreign countries have hazard risks associated with
evaporative sediments in their topography. The most notable countries in Europe include
“England, France, Germany, Italy, Lithuania, Ukraine, Turkey, and Spain” (Pando et al.,
2012, p. 507). In 1998, a large ground settlement underneath two apartment buildings in
Oviedo Spain resulted in the displacement of 362 families with losses estimated at 18
URBAN SINKHOLES
36
million euros or approximately 28 million US dollars (Pando et al., 2012). A study of the
event that included background information, geophysical survey, borehole samples,
monitoring of water levels, and lab samples. Results of the study found two primary
factors for the settlement, building in a flood zone with a topography containing large
amounts of gypsum and subsequent excavation work.
Since the 15th century, the city of Oviedo has known of the presence of
evaporative rock in the city’s topography but was unaware of the extent of the
karstification until 1998 when the two buildings sustained damages requiring their
demolition (Pando et al., 2012). City planners had previously designated the zone for
industrial use but because the area frequently flooded, they decided to mitigate the
problem area with landfill comprised of waste materials and rechanneling of streams.
When economic hardships affected the city, city planners decided to build apartment
buildings for the socially disadvantaged, and construction of the buildings was completed
by 1965. In 1998, a parking garage project was started within close proximity of the
apartment buildings. Excavation of the area during typical construction work led to
flooding from a nearby aquifer, that in turn led to withdrawal of the water via pumping;
the deeper the excavation, the greater the flooding and subsequent increase in water
pumping. Cracks in the apartment buildings coincided with the water pumping, an
estimated 17,000 m3 of water was removed and the settlement area measured between 30
to 60 cm (approximately 1 – 2 feet in depth) which severely damaged two buildings and
37
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required them to be demolished (Pando et al., 2012). Spain’s government took on the
task and costs to resettle the occupants of 362 apartments, demolition, and rebuilding the
structures; the occupants returned to their rebuilt homes in 2002 (Pando et al., 2012).
III. METHODOLOGY
Introduction
The purpose of this study is to examine the theory that sinkholes are becoming an
increasing problem within the US and that communities are not well prepared to deal
with the rising incidences of costly urban sinkholes that result in substantial property
damages, disrupt communities, and lives taken. The overall goal of this research is to
show that communities must be knowledgeable about the hazards of sinkholes so they
can make informed decisions about how best to protect their residents from the
potentially devastating results of sinkholes. A mixed methods approach with a pragmatic
worldview was used to evaluate data. According to Creswell, “there is more insight to be
gained from the combination of both qualitative and quantitative research than either
form by itself” (2009, p. 203). The aggregation of data was comprised of journal articles,
case studies, government reports and documents, documentaries, materials from subject
matter experts, and newspaper articles. Data was reviewed and analyzed to elicit
conclusions that support, validate, or deny the theory. To date, to the best of the author’s
knowledge, this study was the first of its kind to comprehensively examine this problem.
URBAN SINKHOLES
38
Data Collection
Primarily qualitative data was concurrently collected chiefly from open sources
via the Internet. A focus on materials gathered was placed on peer-reviewed and
government articles. Primary sources of literature examined included government
reports, after action reports, statistical data, legislature, audio and visual, materials such
as photographs and video coverage. Secondary sources included journal articles, case
studies, documentaries, and newspaper articles. In an attempt to minimize bias and
provide a well-rounded analysis, different viewpoints, possibly conflicting, were
incorporated.
Search engines including EBSCO, LexisNexis, ProQuest, and Google were
utilized to search for current literature on notable sinkhole events in the US and abroad in
order to validate the theory that incidences of costly and dangerous sinkholes are
increasing. Literature was examined to compare the different types and causes of
sinkholes, areas prone to sinkhole activity, and prevalence of sinkholes. Relevant
sinkhole topics researched to further complement this study included insurance coverage,
disclosure laws, and reparation for property sellers, developers, and builders. Other
subjects for review included remediation and mitigation for sinkholes, and costs
associated with sinkholes. Information compiled for analysis was mostly qualitative in
nature but certain quantitative information like statistical records on claims reports,
URBAN SINKHOLES
39
fatalities, and financial costs, was examined. Data with matching traits and
characteristics was grouped and categorized by emerging patterns.
The research started with a scientific definition of the different types of sinkholes,
what areas in the US are prone to development of sinkholes and why. The USGS
provided the most concise and easily understood definitions on solution, suffosion, coversubsidence, and cover-collapse sinkholes, karst topography and causes. This first step in
the research process helped to identify and understand the relationships between the
independent variables of evaporative rocks and karst terrain, and dependent variables of
rainfall, aquifers, weather conditions, and human activity. Likewise, other relevant terms
were researched and defined as they emerged such as water table, karstification, and
dewatering. The Bayou Corne sinkhole in Louisiana demonstrated how a human-induced
sinkhole could threaten a local community, cause a state of emergency, and it served to
underline the critical relationship between human activities and the “long-term
sustainability of tampering with karstic environments” (Jovanelly 2014, p. 1).
A comprehensive review of case studies on recent sinkholes in Louisiana, Texas,
Kentucky, and Florida served to validate the plethora of hazards sinkholes pose to
communities. Specifically, the sinkholes in Bayou Corne, Daisetta, Bowling Green, and
Seffner were chosen because they vary in size, are in different states, and each affected
their local community; these sinkhole events were examined to deduce similarities and
dissimilarities and their impact on communities. Emergency response activities were
URBAN SINKHOLES
40
researched for each sinkhole. Louisiana, Texas, Kentucky, Florida, and Pennsylvania
state hazard mitigation plans were reviewed for inclusion of sinkholes as rated hazards.
Additionally, outcomes and methods for remediation on the different sinkholes were
researched. When available, costs incurred or estimated were collected.
Data on the availability of sinkhole insurance coverage was most easily acquired
on the state of Florida, primarily from governmental press releases and reports including
the Florida Senate, FLOIR, and the Florida Department of Financial Services. Similar
data was not as abundant for the other states listed as prone to sinkholes. The obtained
statistical data supports this paper’s assertion that sinkholes place a financial burden on
communities.
Data on remediation measures came from company websites that offer
remediation, case studies, and scholarly articles. Containment measures on the Daisetta
sinkhole chiefly came from scientific and scholarly articles. The data on the array of
methods currently available for detecting and mapping sinkholes essentially came out of
scientific, governmental, and scholarly articles. It is not within the scope of this paper to
outline all of the various detecting and mapping methods, thus only the most widely used
methods were included in the research.
How well property owners are protected was deduced from the examination of
insurance coverage, regulations, and laws pertinent to sinkholes. Interestingly, only
Florida has mandatory sinkhole insurance coverage, and Tennessee law mandates that
URBAN SINKHOLES
41
insurance companies that offer homeowner property insurance must make sinkhole
coverage available (Thomas, 2006, 2010). States like Missouri and some others prone to
sinkhole activity offer sinkhole coverage as a separate rider or standalone plan (DIFP,
2015). Insurance data on the different sinkhole coverage came mostly from state
departments of insurance.
The Federal Emergency Management Agency (FEMA) website was queried for
historical data on sinkholes. While the website and toolkit for local damage assessment
included the term sinkhole, the newly published 2015 hazard mitigation assistance
guidance did not. Surprisingly, little data was available, although, FEMA’s website did
list several denied appeals for sinkhole assistance (FEMA, 2012, 2015).
Scope and Limitations
This study was limited to urban sinkholes that affect people, destroy property,
disrupt communities, and require remediation. The overall lack of a nationally
maintained historical database on sinkhole events with damage assessments was
unanticipated. The states with case studies did not list all sinkholes or track them in the
same way. As anticipated, Florida had the most amount of statistical data on the
incidences and insurance costs of sinkholes. A comparison analysis between Louisiana,
Texas, Kentucky, and Florida was not a viable option due to the lack of valid and
publicly available statistics. CoreLogic, a privately owned company that provides natural
risk assessments to its global customers, analyzes and tracks reported sinkhole activity in
42
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Florida. In other states prone to sinkhole events, similar data was discovered in hazard
mitigation plans, however, only some mentioned notable sinkholes and costs. Thus, the
collected statistics on reported sinkholes was uncertain. As expected, there was a wealth
of news article on notable sinkhole events. In contrast, the limited amount of
professional and formal research on community hazard management of sinkholes made it
challenging to evaluate some of the data procured from publicly available sources.
IV. FINDINGS
Introduction
The prevalence and type of karst topography vary significantly from state to state
and in other parts of the world, thus resulting in variable formations of sinkholes. A
wealth of scientific literature clearly demonstrates understanding of the natural, and
human factors that trigger or induce the development of sinkholes. The same is true for
sinkhole risks and hazards, remediation and mitigation. However, a noticeable bias was
evident in the abundance of literature that discussed carbonate karst versus the
corresponding lack of literature on evaporative karst. A simple Google search for states
prone to sinkholes produced numerous sinkhole maps, but few illustrated karst and what
type of karst existed in addition to sinkholes. Unfortunately, most publically available
maps only show the location of sinkholes and fail to provide any additional information
indicating the type or severity of the sinkholes, or karst terrain.
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Prevalence
Karst regions make up about 25 percent of the world’s land topography (North et
al., 2014; Veni et al., 2001). On a global scale, while there are specific areas vulnerable
to the formation of sinkholes, they are primarily found in areas comprised of karst terrain
with either carbonate (limestone, dolomite, and marble) or evaporite (halite, gypsum, and
anhydrite) bedrock. Karst regions provide valuable natural resources including water,
fossil fuels, natural gasses, and minerals; 25 percent of the world’s drinking water derives
from karst geology (North et al., 2014). Geologists consider caves as subsurface
manifestations of karst landscapes and karst regions provide homes to rare, endangered
species, and their “caves preserve fragile prehistoric material for millennia” (Vena et al.,
2001, p. 5). Over 20,000 caves exist in the US and countries such as Italy, Belize, and
China are home to iconic karst landscapes (North et al., 2014). Vital water sources,
springs, caves, and other structures that are aesthetically appealing typically populate
Karst regions making them popular sites for urban development. Louisville (Kentucky),
St. Louis (Missouri), Nashville (Tennessee), and Austin (Texas) are just a few of the
major cities in the US built in karst regions (Veni et al., 2001).
In the US, the percentage of the terrain with carbonate and evaporative rock is
between 35-40 percent with 20 percent designated as karst regions, as shown in Figure 1
(USGS, 2014). Some states and countries have vast karst regions whereas others have
very little to none, making the prevalence of sinkholes problematic more on state and
URBAN SINKHOLES
44
local levels than on a national or international level. For instance, not all states in the US
are prone to sinkholes as only 20 states have major karst regions (Veni et al., 2001).
Greater than 6,500 sinkholes have been reported in the US since the 1950s, many of
which occurred in Pennsylvania, Kentucky, and Florida (Kemmerly, 1993; North et al.,
2014). In Pennsylvania, 3,610 sinkholes were reported in 2013, an increase of 26 percent
from 2010 (Pennsylvania State, 2013, pp. 345-346). Damages from cover-collapse
sinkholes are so common in some states, like in Kentucky, that local authorities deal with
them as a routine issue and rarely report incidences to any governing agency (Kentucky
State, 2010). A Kentucky Geological Survey on sinkholes from 2000 to 2003, using GIS
data, field reconnaissance, and the standard 1:24,000 scale for topographic maps,
revealed 101,176 sinkholes and that 55 percent of the land surface is comprised of
karstified bedrock (Florea, 2005, p. 120). According to CoreLogic, their sinkhole
database lists over 23,000 sinkholes for Florida (Botts, Du, & Jeffery, 2013).
Nowhere else in the world are so many people touched by sinkholes as in
Florida. Weekly, at least one sinkhole forms somewhere in the state and does
some type of property damage. Although we hear the most about the larger
sinkholes, hundreds of sinkholes from in Florida each year that we never hear
about and that never make the news. (Brinkmann, 2013, p. 16)
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State Sinkhole Maps
Figure 9. Texas Sinkhole Map (Harbert, A., 2014).
Unfortunately, despite the prevalence of karst topography and sinkholes in the
US, few state government agencies track all sinkhole occurrences; sinkholes can be
underreported or unreported when they do not impact people, infrastructure, or are
considered too small to be of consequence. For example, Kentucky’s database and map
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are state-sponsored products that account for all sinkholes whereas Florida’s database is
an artifact that primarily records sinkholes reported due to property damages (Kentucky
Geological Survey, 2014). The results of a Google search for state sinkhole maps
produced positive results for many states including Alabama, Florida, Kentucky,
Missouri, Pennsylvania, Tennessee, and Texas.
The publicly accessible sinkhole maps were typically the works of state agencies,
such as departments of natural resources and state geological survey. In some cases,
private companies, universities, and researchers provide documented sinkhole maps
freely available to the public. In Texas, geologist Artemis Harbert (2014) developed a
sinkhole map (see Figure 9) as a Geographic Information Systems (GIS) web project and
posted it on the Internet providing free GIS data and database on sinkholes in Texas; his
map was the only sinkhole map for Texas found via Google search. In Florida and
Kentucky, people can readily download County sinkhole maps that show the location of
reported sinkholes. Pennsylvania provides the public with an interactive map that
indicates the presence of sinkholes and depressions since 1985 within one-half mile of
any point chosen on the map (Pennsylvania Department of Conservation and Natural
Resources, n.d.).
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Figure 10. Missouri Sinkhole Map (Missouri Department of Natural Resources, n.d.)
Publically available sinkhole maps only reveal the location of sinkholes on a
fairly large-scale (without street names or address numbers, or Global Positioning System
[GPS] coordinates) and do not include demographics such as type, diameter, depth, or
whether or not the sinkhole caused damage thus they are of limited utility (see Figure 10).
In Florida, people can pay private companies like “Sinkhole Assistant” or “CoreLogic” to
find out if their home or property is located near previously reported sinkholes and
sinkhole indicators; reports include a more detailed topography map including property
addresses and street names that clearly illustrate the location of sinkholes and/or
indicators (Sinkhole Assistance, 2015; CoreLogic, 2015).
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Unlike national flood maps, there are no national sinkhole maps. Because there is
no national standardization of data elements, different criteria is used by states that track
and map sinkholes thereby complicating the ability to gain a full understanding of the
prevalence, hazards, risks, and costs of sinkholes that affect communities across the US.
The majority of maps do not combine karst terrain with sinkhole occurrences; Texas and
Florida Maps had most descriptive maps that included those elements.
Natural and Human Factors
Natural and human factors influence the development of sinkholes (see Table 2).
Sinkholes are a naturally occurring geological phenomenon and under natural conditions
take years to form, longer than a human lifespan, even thousands of years. In comparison,
induced sinkholes caused by human activities are relatively abundant, and reduce the
natural timeframe to just hours or days (Newton, 1987). Human factors have directly
induced the majority of the thousands of sinkholes reported in the eastern US.
Table 2. Natural and Human Factors
Land Topography
Karst
Karstification
Overburden
Carbonate Rock
Evaporite Rock
Salt Domes
Natural Factors
Weather conditions
Drought
Heavy Rains
Oscillation in water table
Human Factors
Urbanization
Land & Water Use
Agriculture
Construction
Mining
Water Pumping
Natural Factors. Land topography plays the biggest factor in the prevalence and
type of sinkhole formations. This includes karst bedrock (carbonate or evaporative),
URBAN SINKHOLES
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bedrock karstification (existing breakdowns in bedrock with cavities, fissures, or caves),
type, and thickness of overburden (sand or clay and thin or thick), and existence of water
(i.e., aquifers, heavy rainfall). Gypsum is a highly soluble rock with “a dissolution rate
that can be up to 100 times greater than that of carbonate rocks,” and topography with
gypsum that coexists with underground water “rapidly leads to the formation of cavities
and sinkholes that may present different typologies” (Pando et al., 2012, p. 507). The
prevailing risk from this type of topography comes from cavities that collapse and ground
settlement. Rock salt, found and mined in salt domes, is about 1,000 times more soluble
than limestone, thus mining in and around salt domes poses serious risks for the
formation of sinkholes (Ford & Williams, p. 256). Thin, sandy overburden is more
susceptible to developing sinkholes than thick, clayey overburden. Moreover, thin, sandy
overburden is prone to developing solution or subsidence sinkholes whereas thick, clayey
overburden is cohesive enough to hold overburden together while cavities form
underneath and correlates with cover-collapse sinkholes (USGS, 2014).
Karst terrain supported by water, like aquifers, are extremely sensitive to
oscillations in the water table; removal of water simultaneously removes ceiling and wall
support for overburden and the removal of too much water can lead to the ceiling
collapsing over existing voids (USGS, 2014). Droughts cause the water table to lower
revealing voids no longer supported by buoyant water, resulting in sinkholes.
Conversely, storms accompanied by heavy rainfall (e.g., tropical storms) also cause
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sinkholes because rainwater becomes acidic as it leaches into the ground and in areas
with poor drainage capacity the water pools and dissolves the bedrock, thereby creating
voids that turn into sinkholes (Newton, 1987). Additionally, heavy rainfall saturates
overburden above cavities thereby increasing ceiling loads making it too heavy for cavity
ceilings to support, resulting in a collapse of overburden into the voids. Rises in the
water table in areas where the water table is near the surface, such as in Florida, can
transform sinkholes into springs (Brinkmann, 2013; Veni et al., 2001).
Human Factors. Almost all of the human factors are associated with
urbanization. As populations continue to grow, more people utilize karst land for
development, mining of natural resources, agriculture, and as water resources, all of
which involve activities that affect fragile and sensitive karst environments and cause
increased sinkhole development. Human land and water use-induced triggers can be
divided into two main categories to provide an easy to understand overview of how
humans induce sinkholes, those that affect water tables or hydrologic environment, and
those that affect the land via construction.
Land Use. Construction, grading, deforestation, or other earth-moving projects in
karst areas can trigger the collapse of pre-existing voids by altering the land surface,
changing overburden load, by shocks or vibration (e.g., from blasting, drilling), or by
thinning the overburden (Kohl, 2001). Building impermeable structures such as parking
lots and buildings alters the way water naturally soaks into the ground. Instead of a
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51
wide dispersal of runoff, water is diverted, concentrated and permeates soil in single
points. Construction practices include altering the hydrologic environment by creating
dams, ponds, and wells that divert or impound water (Newton, 1987).
Water Use. Water pumping for human or agricultural use is a leading cause of
human-induced sinkholes because they drastically drop the water table, causing an effect
similar to turning off the water and then flushing the toilet. The process of construction
often diverts or impounds surface drainage changing the load of overburden by the
addition or subtraction of water (Newton, 1987). Clayey soils expand and increase in
weight when saturated with water, up to 50 percent larger in volume than when dry, and
shrink during dry spells; thus, cycles of wet and dry stress karst landscapes and result in
the development of sinkholes (Kohl, 2001). Construction and mining operations often
withdraw large amounts of water as part of a dewatering process causing the roofs over
existing cavities to collapse. Agricultural and mining practices often include excessive
groundwater withdrawals. Water pumpage greatly accelerates fluctuations in water
tables than what would otherwise occur under natural conditions causing a larger
amount of erosion, downward migration of deposits, wall weakening, and cavity
enlargement in existing voids (Newton, 1987). As an example, while drilling for a new
irrigation well in Florida in 1998 that included water pumping to flush the well, hundreds
of various sized sinkholes, some greater than 150-feet in diameter, abruptly developed
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and affected around 20 acres of forested land within a 6-hour period (Tihansky, 1999, p.
138).
Hazard Risks
Costly Damages and Fatalities. Sinkholes pose numerous hazards ranging from
flooding, minor to major property damages, and losses when sinkholes cause surface
sagging or depressions, resulting in sinking, cracks, and collapse of buildings and
engulfment of property such as cars, buildings, and lives. Sinkholes can remain
undetected for many years, and then dramatically and suddenly open up, rapidly growing
incredibly large while swallowing everything in its path. In 1981, a sinkhole opened up
in Winter Park Florida and over the course of a single day grew to almost 350 feet in
diameter and 100 feet deep, engulfing a swimming pool, car dealership, and several
buildings; the sinkhole caused about $4 million dollars in damages (Brinkmann, 2013,
p.108; Jurie, 1991, p. 403).
Costly property and structural damages are the most obvious and tangible
associated risks with development of sinkholes in karst environments. According to
Kaufmann (2013), “direct losses due to these hazards average in the tens of millions of
dollars per year” and indirect losses derived from pre-construction geotechnical
examinations, illnesses from contaminated water, and remediation, are several times that.
The literature review substantiated that residents, business owners, and local and state
governments can incur substantial financial burdens when dealing with sinkholes.
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Louisiana assumed $16 million in related costs in response to the Bayou Corne sinkhole,
and TBC settled a class action lawsuit for $48.1 million for affected residents, in addition
to over $3.5 million billed by the state and Parish (“Louisiana Governor,” 2013; Miller,
2014; Mitchell, 2015). Texas spent almost $10,000 to determine to cause of the Daisetta
sinkhole, owners of the NCM anticipated spending over $3 million in repairs, and
Hillsborough County estimated spending greater than $90,000 to acquire and repurpose
empty lots due to sinkhole related damages (Edelstein, 2014; Hobson, 2014; Railroad
Commission of Texas, n.d.). Although rare, sinkholes can result in fatalities, as was the
case when a sinkhole in Florida swallowed a man asleep in his bed. In 1962, South
Africa, a sinkhole over 180 feet across engulfed a building, and 29 lives were lost (Veni
et al., 2001).
Water Contamination. Contamination of water resources is a major
environmental hazard in karst. Sources of drinking water are of critical importance to
community’s sustainability. Globally, up to 25 percent of people rely on water sources
from karst terrain, more in some areas than others; “in South China alone well in excess
of 100 million people live on karst” (Ford & Williams, 2007, p. 441). In the US, around
40 percent of the supply of drinking water comes from karst aquifers which lie
underneath 40 percent of the land east of the Mississippi River (Ford & Williams, 2007,
p. 441; USGS, n.d.). Sinkholes directly convey pollutants, contaminants, and trash,
including pathogens such as bacteria and parasites, into aquifers and other groundwater
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sources via numerous fissures and openings in the karst terrain, these typically bypass
natural filtration processes that soil provides, resulting in contaminated water sources.
Thus, pollution of sources of drinking water poses a serious threat as the flow of water
from rain, and runoff follows the path of least resistance through conduits in karst terrain
and enters aquifers and wells (Peterson & Vondracke, 2006). In 2000, Escherichia Coli
(e-coli) contaminated the municipal water supply in Walkerton, Ontario with a population
around 5,000. E-Coli infection accounted for 2,300 people becoming sick and seven
fatalities. The bacterium was thought to have originated from storm water drainage from
a recently manured field that infiltrated the karstic aquifer (Ford & Williams, 2007, p.
449).
Intangible Hazards. To fully address hazards associated with sinkholes,
intangible hazards that affect people’s emotional and spiritual well-being must also be
mentioned. Psychological hazards from sinkholes are the same as those for other
disasters that result in the loss of loved ones, disrupted communities, loss of sense of
security, damaged or demolished family homes, loss of property values, and adverse
effects from dealing with other stressful activities such as insurance claims, remediation,
evacuation, and relocation. Likewise, the emotional toil of living with constant anxiety
and fear in a house that moans, creaks, pops, has cracks in the walls and foundation, and
with doors and windows that fail to properly close, is impossible to quantify. The
literature review on case studies outlines some of the hazards as mentioned earlier. For
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instance, the fatality of Jeffrey Bush in Florida, the Bayou Corne incident that disrupted
the Assumption Parish community with evacuation, displacement, and health concerns
from bubbling gas, and the Daisetta sinkhole concerns about the possible contamination
of public water supplies, demonstrate some of the intangible hazards not typically
addressed with sinkholes.
When communities or individuals experience extraordinarily distressing events,
situations, or threats, the result can include negative mental health outcomes. At least 90
percent of people exposed to disasters fully recover and do not develop major mental
health disorders. A few may develop disorders that include “acute stress disorder,
posttraumatic stress disorder [PSTD], major depression, generalized anxiety disorder,
substance abuse, somatization disorders, adjustment disorder, complications of
bereavement, family violence and child or spouse abuse” (Raphael, & Newman, 2000, p.
25). An affected community’s normal daily functioning activities can be altered
temporarily or permanently as social cohesiveness is disrupted and roles and use of
resources change, particularly when response and recovery include multiple levels of
response agencies that inundate the community. Relief efforts aimed at helping can also
create stress as people attempt to maneuver impersonal and complicated bureaucracies.
Although intangible hazards are not the focus of this research, they are an important
factor that must be considered and are briefly mentioned here in an effort to provide a
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better picture of hazards that are not typically addressed as potential consequences of
living in karstic environments.
V. DISCUSSION
Introduction
Around 6,500 sinkholes were reported in the US between 1950 and 1987, and a
more recent geological survey from 2000 to 2003 revealed over 100,000 sinkholes in
Kentucky while CoreLogic lists over 23,000 sinkholes in their Florida database (Botts et
al., 2013; Florea, 2005). While city planners, emergency managers, and authorities pay
significant attention to hazard risks such as terrorism, hurricanes, and earthquakes,
continuing expansion of populations, human activities, and subsequent development in
karst areas puts more people and property at risk from sinkhole occurrences. Living in
karst terrain, sinkholes, and complications arising from sinkholes can pose numerous
hazard risks of which communities and property owners are often unaware. Direct
hazards are seemingly easy to comprehend including engulfment, destruction, or damages
to property and structures, and condemnation of houses. It is doubtful that the owners of
the NCM in Kentucky would have built their facility over an existing sinkhole if they had
previously been aware of the hazard. Assumption Parish and Diasetta residents may have
chosen a different place to live if they had been aware of the potential hazards of living
on or near a salt dome. Likewise, if the Bush family had been aware of the sinkhole
beneath their house, Jeffrey Bush may not have lost his life.
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57
Indirect hazards are often not fully understood or appreciated, including financial
burdens derived from remediation and mitigation, water contamination, and emotional
distress from evacuation, community disruption, displacement, and loss of property, and
lives. Vacationers at the Summer Bay Resort most certainly did not wish to include the
experience of fearing for their lives during their vacation. Over 100 guests had to quickly
evacuate the resort at night as windows blew out, the ground shook, and walls and
ceilings collapsed (see Figure 11); many of the guests only had 30 minutes or less to
evacuate the building with their families and possessions (Hightower, 2013). Response
to sinkholes like the one that destroyed the Summer Bay Resort, Bayou Corne, and
Diasetta can be more complex than for other types of hazards and often involve a bevy of
local, state, and sometimes, federal involvement.
Figure 11. Summer Bay Resort (Hightower, 2013)
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Emergency Response
Sinkholes that affect communities can be very complex, and responses to them
depend on their size, impact, and location. When sinkholes develop in urban areas with
dense populations or in critical infrastructures, they can be disastrous and result in a state
of emergency for local communities and states. Sinkholes such as the one in Kentucky’s
NCM resulted in several different agencies responding even though it was not an
emergency as it did not impact or threaten lives, critical infrastructure, utilities or
otherwise negatively affect the local community. In fact, that sinkhole actually had a
positive impact on the community as it served to raise awareness and education of
sinkholes, and increased attendance at the museum; the increased interest in seeing the
sinkhole prompted the museum authorities to delay fixing it for several months.
Response to the Kentucky sinkhole mostly included local agencies such as the local fire
department, geologists, and structural engineers from a nearby university, construction
workers and heavy machine operators, insurance adjusters, and the media (National
Corvette Museum, 2014; Everson, 2014). Other agencies that may have responded to the
sinkhole event included local, regional, or state EPA, OEM, police, Geological Survey,
and the mayor or governor, as was the case with the Louisiana sinkhole.
In contrast, response to the Bayou Corne sinkhole prompted the local authorities
and state governor to issue a state of emergency as the sinkhole posed a threat to the local
community of Assumption Parish (APPJ, 2012a). Response to the sinkhole required
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response activities from a widely diverse array of local, state, regional, and federal
responders that included all of the aforementioned and many others such as mining
authorities, medical and laboratory services, the ARC, DOT, GOHSEP, DNR, DEQ, and
the state National Guard; response to the Diasetta sinkhole was similar to the Bayou
Corne response. Response to the Seffner, Florida sinkhole included many of the agencies
as mentioned earlier and search and rescue, utilities and public works, housing, and social
services (Merrill, 2013). Many at-risk states mention sinkholes in their CEMPs and/or
State Hazard Mitigation Plans (SHMPs) but thus far, “no coherent [national or regional]
policy response has been formulated regarding mitigation or remediation of existing
sinkhole hazards in the United States” (Jurie, 1991, p. 1).
FEMA guidance for federal response includes Emergency Support Functions
(ESFs), designed to provide emergency support for specific issues such as transportation,
communications, firefighting, public safety, or search and rescue. Each ESF consists of
an organizational listing that groups governmental and private capabilities by function
and delineates roles, responsibilities, and scope. Incident commanders can activate one
or more ESFs; it only take a single call to activate all departments or agencies belonging
to the ESF, thus ESFs alleviate delays in response, help protect property and people, and
help communities quickly return to normal following events. For example, incident
commanders can activate ESF #9 – Search and Rescue to coordinate, or serve as a
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primary or support agency, for search and rescue operations. Unfortunately, a specific
ESF for sinkholes does not currently exist (FEMA, 2008).
Detection and Identification
Detecting and identifying karst terrain and the frequency and size of previous and
existing sinkholes are essential steps in predicting when and where new sinkholes are
likely to develop. It takes a lot of work from a variety of sources to investigate, research,
compile, and analyze data to detect and identify karst with any accuracy. Geologists use
a plethora of mapping tools to detect and identify sinkholes. Mapping tools can include:
topographic maps, photogrammetry, GPR, InSAR, Laser Imaging Detection and Ranging
(LIDAR), high resolution Digital Elevation Models (DEMs), images gathered from aerial
photographs, satellites, historical documentary data of previous, and filled sinkholes,
relationships with triggers (human/natural factors), and field surveys (Ford & Williams,
2007; Gutiérrez, Cooper, & Johnson, 2008). Mapping and more intrusive tools provide a
wealth of information ranging from type and thickness of overburden, voids, bedrock
composition, type of karst, and karstification.
Mapping alone will not reveal the presence of all existing or previous sinkholes,
particularly in populated areas. Thus mapping must be combined with other data to gain
a more complete accounting of sinkhole activity. A collection of historical data is
important as filled or otherwise mitigated sinkholes and triggers can be impossible to
detect via mapping tools. Field surveys allow inspection and detection of signs of
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instability not revealed via other means. Intrusive and more expensive methods and
techniques such as drilling boreholes, probing, and trenching provide more specific
details on stratigraphy and structure of deposits (Gutiérrez et al., 2008). Another crucial
step in sinkhole hazard analysis is investigation of local hydrology; it is imperative to
understand the velocity and flow path of groundwater in karst terrain as fluctuations in
the water table is a primary trigger for development of sinkholes. Sinkhole databases of
maps currently exist, but they can be difficult to interpret and even more challenging to
determine the exact location of existing sinkholes. Furthermore, most current publicly
available databases do not possess specific information on reported sinkholes; they do not
indicate frequency, influencing factors, diameter, depth, associated damages or losses,
and remediation efforts.
Predictability
While no single method will yield 100 percent accuracy in identification of
existing sinkholes, they can indicate which areas are more prone to forming sinkholes and
based upon composition, they can also determine the most likely type of sinkholes that
could develop in studied areas (Jurie, 1991). As populations increase, human activities in
karstic environments also increase promulgating the evolution of sinkholes and ultimately
placing more people and properties at risk. Methodologies and accuracy of predicting
future sinkholes are very similar to predicting flood events. Analysis of human and
natural factors, previous chronological history, detection, and identification of karst,
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62
make it possible to predict the likelihood of future occurrences and type of sinkholes but
it is impossible to predict exactly where, when or what size such an individual occurrence
will entail. The ability to predict the frequency of sinkhole development can be difficult
or even impossible to calculate because previous sinkhole events are not identifiable in
many instances, records of previous sinkholes do not exist or are incomplete, and bias in
historical data to only record major events (Gutiérrez et al., 2008).
A thorough analysis of triggers in identified risk areas is a key factor in predicting
future occurrences. As previously stated, up the three-quarters of new sinkholes are
direct results of human activities. For instance, dewatering that lowers the water table in
karst landscapes is a known and primary trigger for sinkholes. Construction can
influence sinkhole development by diverting natural water pathways, vibrating the
ground, and increasing overburden. Likewise, natural triggers like seasonal weather and
storms cause sinkholes, such as during Florida’s sinkhole season between March and
May when water levels are typically low (Jurie, 1991). Tropical Storm Debby inundated
Florida in 2012 at a time when the local aquifers were extremely low due to extended
drought conditions. The low water level combined with a sudden additional weight of
the overburden from the deluge surpassed the weight-bearing capacities in previously
unknown cavities, resulting in the formation of hundreds of sinkholes (Kromhout, n.d.).
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Remediation and Mitigation
Remediation. Remediation of sinkholes and the damages they cause is limited to
two options, ignore the sinkholes and damages, or fix them. Property owners can pay
thousands of dollars in repairing damages, and those with insurance often rely upon their
insurers for damage losses. Large, open sinkholes pose many safety hazards to people
and the environment; fixing them abates potential water contamination to water sources
and alleviates safety hazards at sinkhole openings. Fixing large sinkholes involves filling
in the hole with either impermeable grout mixtures or graded filtration systems as shown
in Figure 12 (Missouri Department of Natural Resources, n.d.).
Grout mixtures have been a cost effective and popular method used to repair
many Florida sinkholes that threaten homes and other structures. For example, in 2000
grout was used to fill and stabilize several sinkholes in a detention basin in North Florida
and in Plant City where two large sinkholes had damaged a road causing the city to close
100 feet of the road and spend about $60,000 in repairs (Jammal, Casper, & Sallam,
2010; Parker, 2000). Unfortunately, grouting or cement plugs can block or otherwise
alter the natural paths of water flow, bypass or provide poor water filtration, and result in
creating additional sinkholes (Gutiérrez et al., 2008; Jammal et al., 2010). Moreover,
grouting can add significant weight to overburden in the immediate and nearby areas
thereby triggering settlement of buildings, causing damage not only to property being
remediated but also to nearby structures (Zisman & Clarey, 2013). Rather than filling
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sinkholes with grout fixtures and altering the natural path of water, West Virginia and
Missouri are two states that use graded filtration as fillers that allow water to freely flow
through them (West Virginia Department of Environment Protection, 2005).
Planting vegetative buffers around sinkholes helps to reduce runoff from moving
contaminants into sinkholes and contaminating local surface waters and aquifers. Buffers
are also effective in reducing flashy stream discharge or flood intensity in streams. The
Army Corps of Engineers modeling studies demonstrated that flood peaks could by
reduced up to 50 percent in just a few years by reducing watershed runoff by 10 percent
(Petersen & Vondracek, 2006, p. 387). According to Petersen and Vondracek (2006),
planting vegetative buffers around sinkholes in agricultural areas can reduce runoff
contaminants like salts, fecal matter, pathogens, fertilizers, and pesticides thereby
improving water quality.
In Petersen and Vondracek’s (2006) study on water quality affected by sinkholes
in Minnesota, they found that while 98-feet wide vegetative buffers may reduce
sedimentation and pollution up to 80 percent, they would be quite expensive. In
southeastern Minnesota, cropland planted with row crops, account for approximately 60
percent of the land. Costs to place 49-feet wide buffers around all of the approximately
8,340 mapped sinkholes in Minnesota would reduce available cropland by over a
thousand acres and result in $260,000 annually in lost revenue (Petersen & Vondracek,
2006, p. 380). However, it is not feasible to place 98-feet wide vegetative buffers in
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densely populated areas, and even 49-feet wide buffers would prove challenging. It is
more plausible in high-risk areas such as Florida when occurrences result in the
condemnation of several adjacent properties such as what happened in Seffner where
Jeffrey Bush lost his life.
Figure 12. Graded Filter System (Missouri Department of Natural Resources, n.d.)
Mitigation. The safest mitigation strategy is to avoid human activities in karst
terrain, especially in areas most susceptible to developing sinkholes. Unfortunately, this
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is not always a feasible strategy, particularly in built environments. Preventive measures
include comprehensive land and water use management that limit human activities such
as development, water pumping, and mining in high-risk areas via planning, building
codes, zoning, policies, and regulations. CEMPs and SHMPs that address risks and
hazards associated with sinkholes and insurance coverage are mitigation measures that
can help protect communities, property owners, and reduce expenses.
Legal Frameworks. Although all states have some basic laws regarding water,
only a few like Alabama and Florida, have more comprehensive laws that regulate and
record water withdrawal from ground and surface resources (Hendrick, 2013). Local and
county ordinances are more specific than state laws and address storm-water management
(runoff) and land use (development). However, few directly address karst environment
or sinkholes (Ziegler & Williams, 2014). Greene County, Missouri, is one of the notable
few that specifically and comprehensively reference karst and sinkholes in its zoning
ordinances.
As an example per Greene County Article IV, Section 28 “Sinkhole Use
Standards” of its zoning regulations, a sinkhole evaluation report that includes a site plan,
area map, evaluation of flooding, and evaluation of water quality must be submitted to
the country for approval for any land development projects (Section 107 – Sinkholes and
Karst Features [Section 107], 1999). Developers of land with sinkholes must abide by
certain regulations and standards including submitting a map that plots lot lines and
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sinkhole limits, sinkhole flooding area (may require a registered geologist evaluation),
and setbacks. Setbacks are standardized at 25-feet back from sinkhole rims or flooding
area, for all buildings and 100-feet back for on-site waste-water systems, and use of
pesticides and fertilizers within 25-feet of sinkhole rims or flooding area is likewise
prohibited (Section 107, 1999). Moreover, construction on sinkholes is not allowed
except under special circumstances; grading that involves sinkholes and some Special
Flood Hazard Areas that include sinkholes on the Flood Insurance Rate Maps (FIRMs)
require individual permits, thus requiring an additional floodplain development permit
(Section 107, 1999).
Caves are karstic features that provide habitat for a multitude of animals and
fauna and many caves hydrologically connect with local environments. More than 25
states have passed cave protection acts. Protection of caves is important as they provide
habitats for endangered species and because they can be a source of local water
contamination as they can readily convey trash and pollutants into local aquifers and
other water sources. Federal laws such as the Federal Cave Resources Protection Act of
1988 protects significant caves on most federal lands and the National Park Service Act
of 1916 provide protection for show caves that are national parks including the Mammoth
Cave (Kentucky, Carlsbad Caverns (New Mexico), and Oregon Caves (Huppert, 2000, p
221). However, other caves have little or no legal protection. According to Huppert
(2000), at least six states, including Minnesota, need cave protection laws. Minnesota
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and its municipalities, has not adopted cave protection acts despite having karst and
karstic features such as sinkholes, springs, and caves in the southeastern section of the
state; “the city of Austin, Texas, in contrast, developed watershed regulations with
incorporated language that protects groundwater, caves, and associated biota” (Minnesota
Pollution Control Agency, 2015; Ziegler & Williams, 2014, p. 10).
State Hazard Mitigation Plans. CEMPs and, or SHMPs that address karst areas
that are prone to sinkholes, can prove greatly beneficial to emergency managers,
government authorities, decision-makers, and other stakeholders. SHMPS increase
awareness of sinkhole hazards and help planners make better decisions by identifying and
quantifying sinkhole hazards and risks, potential damages and losses, mitigation
strategies, and align risk reduction activities with state, local, and community objectives.
Pennsylvania’s 2013 SHMP comprehensively dedicates a chapter on sinkholes
approximately 12 pages long covering karst geology, process of sinkhole formation, past
occurrences, associated costs, identifies, ranks, and assesses sinkholes risks, including
loss estimates at state and jurisdictional levels, and includes karst and sinkhole maps
(Pennsylvania State, 2013). Pennsylvania’s SHMP states “subsidence and sinkholes have
the potential to affect 811,610 structures in the Commonwealth with over $195 billion in
exposed buildings and contents” (Pennsylvania State, 2013, p. 352).
Missouri’s SHMP chapter on sinkholes is around six pages long, it includes many
of the same topics, but in far less detail (accounts only notable sinkhole events), and
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assesses the development of sinkholes as a high probability with low severity (State of
Missouri, 2013). In surprising contrast, Texas SHMP assesses expansive soils as a
natural hazard, but it does not mention karst or sinkholes (State of Texas, 2013a).
Interestingly, the Texas SHMP 2013 update mentions sinkholes as a category of
subsidence on two pages, lists three sinkhole events including Daisetta, and assesses the
risk of frequency of occurrence as unlikely (State of Texas, 2013b).
Insurance. Insurance coverage for sinkhole damages and losses is not available
to all homeowners prone to sinkhole activity “Florida and Tennessee are the only states to
require insurance companies to offer sinkhole coverage” (Thomas, n.d.). Insurers in
some states offer separate, optional coverage for sinkhole damages as rider policies.
Tennessee laws require insurers of homeowners property insurance to make optional
sinkhole coverage available only upon request at the initial purchase of insurance and,
unlike Florida, the law does not mandate inclusion of sinkhole coverage in homeowners
policies. Tennessee insurers can cancel, decline or not renew sinkhole insurance if
repairs to sinkhole claims are not in compliance with insurers approved remediation plan
or if there is a risk of future sinkhole damages (Anderson, 2014).
State laws require Florida insurers to provide standard homeowners coverage for
“catastrophic ground collapse” (Chamberlain, 2013). Essentially, the property must meet
a list of criteria to qualify. Namely, geological activity must have caused visible damages
to a structure that resulted in an “abrupt collapse of ground cover,” and government
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authorities must condemn the property and issue orders to vacate the structure, such as
what happened in Seffner Florida with the Bush residence (Chamberlain, 2013;
Kromhout, n.d., p. 2). Florida laws exclude coverage for appurtenant structures (e.g.,
driveways or patios) and insurance companies can withhold sinkhole coverage until the
property passes an inspection; insurers can exclude sinkhole coverage if inspections
reveal evidence of sinkhole activity (Chamberlain, 2013). Passing an “insurance
inspection” can relay a false sense of security in sinkhole prone areas as demonstrated by
the development of the sinkhole in the Bush residence that had previously passed an
insurance inspection prior to issuance of coverage (Brinkmann, 2013).
People owning properties with existing or previous sinkhole activity can face
difficult decisions when they are unable to obtain insurance. Should they live with
constant worry about damages or potential damages and hope that their homes remain
intact and do not succumb to a catastrophic collapse and perhaps risk injuries or death, or
take their losses and move to a safer location? Many homeowners in Florida are retired
geriatrics that used their life savings to purchase their homes and do not have financial
resources to relinquish their homes for a substantial loss. Even those with insurance have
little recourse other than to pay out of pocket for sustained damages not deemed
catastrophic. One 64 year-old Floridian homeowner whose house was built in 2003 then
developed visible cracks in walls and floors stated, “we pay our insurance but ‘Citizens’
doesn’t want to pay to fix the house, and I can’t sell my house because ‘it’ has no value”
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(Harrington & DeWitt, 2014). An engineering firm detected a sinkhole on the property
and recommended remediation via grouting but also informed the homeowner that
insurance would not pay for it (Harrington & DeWitt, 2014).
Many people in Florida cannot afford the staggering prices of insurance premiums
just for sinkholes that can range from $2,000 to 6,000 dollars, in addition to regular and
flood insurance. When coupled with geological testing fees of around $2,500 dollars, and
10 percent deductible on remediation costs up to $100,000 dollars; homeowners with
sinkholes can expect to pay a tab of around $30,000 dollars for a house valued at
$300,000 dollars, completely out-of-pocket (Harrington & DeWitt, 2014). Consequently,
Florida residents will be less likely to report sinkholes, sinkhole statistics will not be
accurate as those that are reported will most likely only include catastrophic collapses,
and more people are put in jeopardy living in houses atop suspected and known
sinkholes.
FEMA. Homeowners are not the only ones faced with substantial financial
burdens due to sinkhole damages, local, and state government must also find a way to
fund costly repairs due to sinkholes. When disasters strike, and a presidential declaration
of disaster is declared, FEMA often assists citizens, local, and state governments to
respond and recover. Per the 1988 Stafford Act, the federal government does not have a
role to play until disasters overwhelm local and state capabilities as is often the case with
hurricanes, severe flooding, and other weather related phenomena. FEMA provided
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primarily debris cleanup and infrastructure assistance in response and rebuilding efforts
for Hurricane Katrina (2005) and Sandy (2012); flooding and hurricanes are the
predominate and most costly natural disasters that impact communities in the US
(Edwards, 2014). FEMA offers a wide variety of programs designed to assist local and
state authorities with planning, responding to, and recovering from hazards. More
importantly, FEMA has programs designed to assist with mitigation including the
following:
(1) Pre-Disaster Mitigation program (PDM), providing funding for hazard
mitigation planning and implementation;
(2) Hazard Mitigation Grant Program (HMGP), providing funding for long-term
mitigation after issuance of a major disaster declaration, and;
(3) Flood Mitigation Assistance (FMA) program, providing funds to implement
measure to reduce or eliminate the risk of flood damage to structures insured under the
National Flood Insurance Program (FEMA, 2015).
However, thus far, FEMA has not considered that damages from sinkholes met
qualifications and determined at least one Floridian request for assistance as ineligible.
For example, FEMA denied a request for sinkhole repairs on a road and retention pond
post Hurricane Frances as sinkholes in that region “are associated with natural
topographical conditions that were in existence prior to Hurricane Frances” and that “the
appearance of sinkholes was inevitable because of this topography and not a direct result
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of the disaster” (FEMA, 2012). This year, New York Senator Schumer and Pennsylvania
Senator Casey requested FEMA update their hazard mitigation policies and programs to
make sinkhole repairs and cleanup, eligible for assistance (Casey, 2015).
Senator Schumer specifically sought funding to repair sinkhole damages to a road
in Kingston, New York with an estimated cost of over $7 million dollars. Since
Hurricane Irene in 2011, the damaged road has remained closed. The sinkhole has
affected the community of Kingston by diverting traffic away from local businesses,
temporarily disrupting local utilities, and has caused problems with the local wastewater
treatment facility due to conveyance of sediments (Schumer, 2015). FEMA’s current
FY15 Hazard Mitigation Guidance published February 27, 2015, does not include
sinkholes and FEMA has not publically announced any addendums or changes that
address sinkhole inclusion in the wake of the senator’s request; it may be too early to tell
whether or not FEMA will adopt new guidance on sinkhole mitigation.
VI. SUMMARY
Summary and Recommendations
Globally, sinkholes are prevalent in many different countries, including the US.
Tangible and intangible damages and losses incurred from sinkholes cost property
owners, communities, local, and state governments tens of millions of dollars every year.
Louisiana accumulated $16 million dollars in Bayou Corne sinkhole-related costs, Texas
spent around $10,000 dollars just to investigate the cause of the Daisetta sinkhole, and
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74
Hillsborough County emptied its coffers by about $90,000 to acquire and repurpose
sinkhole damaged empty lots. In 2009 and 2010, Florida insurance claims costs were
$406 and $396 million respectively, and estimated $486 million for 2011. Communities
do not typically plan for or anticipate the exorbitant costs related to sinkholes because
they do not fully comprehend or are unaware of the complex hazards sinkholes pose.
This research will enhance the knowledge of communities, general populace, authorities,
decision makers, stakeholders, and emergency managers on the complex issues sinkholes
pose which, in turn, can lead to better regulation via implementation of legislative action
to reduce of human activities that trigger sinkholes, better protect communities and
prepare them for future occurrences.
Up to three-quarters of the increasing occurrences of sinkholes that impact
communities are directly attributable to human activities. With a burgeoning population
worldwide, development in karst terrain susceptible to the development of sinkholes will
likewise continue to increase resulting in a greater need for intervention. Understanding
the karst landscape and being aware of natural and human factors that influence sinkhole
development, are the first steps in determining associated hazard risks, response,
mitigation and remediation policies that help alleviate or reduce the occurrence of future
sinkholes, and reduce damages and losses associated with sinkholes.
Comprehensive planning for land and water use, and development practices that
include consideration of sinkhole prone areas, including site selection of new
URBAN SINKHOLES
75
construction, mines, and quarries, would help build long-term sustainability. Zoning in
urban karst landscapes should have standard setbacks, and where possible, restrict highrisk areas to natural landscapes such as forests or pasture that are less prone to associated
hazards. The adoption of sinkhole-resistant building codes that address foundations,
storm-water, and runoff management, and mandate site evaluations (e.g., topographic
maps, geologic maps, aerial photographs, field inspections, and historical research)
should be mandatory in those areas identified at risk. Property owners and homeowners
would not need to purchase expensive insurance or suffer property damages if developers
ensured building and development sites were safe; if developers and builders were at risk
for litigation for selecting unsafe sites, they would more likely adopt methods for
appropriate and safe site selection.
As the development of a sinkhole in an urban environment can require an
extensive, multifaceted, integrated, and coordinated response from a host of various
agencies, it only makes sense to plan for these occurrences accordingly. City planners,
government officials, local experts (e.g., geologists, hydrologists, and structural
engineers) emergency response and environmental agencies, and other stakeholders like
insurance companies, all have a stake in preparing for, preventing, responding to,
mitigating and recovering from sinkhole occurrences that affect communities. To that
end, states and communities at risk for sinkholes should engage in emergency planning
and develop Emergency Operations Plans (EOPs) that include sinkholes and an ESF
URBAN SINKHOLES
76
specifically for response to sinkholes. As depicted in Figure 8, the scene at sinkhole sites
can involve multiple agencies with numerous emergency response personnel, equipment,
vehicles (ambulance, fire, and police vehicles), and mobile command vehicles. The
creation of an ESF for sinkhole response could assist in future sinkhole occurrences that
impact communities by providing a structure that incorporates scope, roles and
responsibilities of trained responders thus potentially saving time, costs, further property
damages, and possibly injuries or lives.
Currently, while sinkhole maps exist for many of the at-risk states, most only
indicate reported sinkhole locations on a large-scale map, making it difficult to precisely
determine their actual location. Some states, like Florida, make county maps available to
the public, but, they do not contain street names, addresses, or GPS coordinates, and none
of them indicate the type, severity, size of reported sinkholes, or whether the sinkholes
caused damages. Very few maps available to the public combine karst and type of karst
or bedrock, with sinkholes; the Texas map was one of very few that included both in
addition to salt domes. Although detecting and mapping karst and sinkholes is a complex
and costly endeavor, such maps should be developed and dispersed to the public so they
can assess hazard risks and make better and informed preparedness, response and
recovery plans in addition to future development decisions.
The public should not have to pay private companies such as sinkhole.assistant
and CoreLogic to find out whether or not damaging sinkholes have affected their
URBAN SINKHOLES
77
community. A standardized, government-sponsored state and national database, listing
all sinkholes past and present, size, type, and any associated damages, should be readily
available. Such a database would prove greatly beneficial to emergency and city
managers in predicting, anticipating and preparing for future sinkholes, would aid
developers in proper site selection, help buyers make informed decisions, and allow for
appropriate zoning and comparable insurance premiums.
Conclusion
In the US, up to 40 percent of the terrain is comprised of carbonate and
evaporative rock with 20 percent designated as karst regions that are susceptible to
sinkholes. Karst aquifers provide 40 percent of US drinking water. Despite the vast
amount of karst terrain in the US and prevalence of sinkholes, this study concludes that
most communities are not well prepared for the development of urban sinkholes that
adversely affect communities. Sinkholes cause millions of dollars in damages annually
by engulfing or damaging homes and buildings, disrupting or even destroying
communities, and taking lives. States most at risk for costly sinkhole damages include
Alabama, Florida, Kentucky, Missouri, Pennsylvania, Tennessee, and Texas. Moreover,
several major cities including Louisville, St. Louis, Nashville, and Austin are located in
karst terrain. Sinkholes can rapidly convey pollutants and trash from surface runoff into
local aquifers thereby contaminating drinking water resources. Damages in communities
affected by sinkholes, such as the Bayou Corne or Diasetta sinkholes, are incalculable in
URBAN SINKHOLES
78
both dollar and emotional figures. The continuing increase in population simultaneously
increases consumption of water resources, alteration of water paths, and development on
karst terrain, thereby increasing occurrences of sinkholes.
Natural and human factors can increase and induce or trigger the frequency of
sinkholes. Weather is a leading natural factor as droughts lower the water table, thereby
removing the buoyant support in existing voids rendering them unable to support the
overburden thus resulting in sinkholes. Tropical storms and hurricanes accompanied with
heavy downpours dump tons of water onto the soil increasing the weight of the overburden
that cavity ceilings are unable to support, resulting in multiple collapses; this is particularly
true when a storm follows drought conditions as the voids have less support than normal.
Human activities, mainly dewatering activities, account for the formation of many
sinkholes as the sudden drop in water tables exposes cavities without the wall and ceiling
support water normally provides, resulting in ceiling collapses.
Unfortunately, there is not a single method that can detect a sinkhole with 100
percent accuracy. Geologists employ a variety of mapping tools and methods including
GPR, bore testing, field observations, and many others to detect and identify sinkholes;
homeowners can expect to pay around $2,500 to have their property inspected for
sinkhole activity. Homeowners with sinkholes face the financial burden of paying outof-pocket for repairs that can cost thousands of dollars unless they have sinkhole
insurance to help defray the costs. FEMA has mitigation programs to help with costs in
URBAN SINKHOLES
79
the wake of presidentially declared disasters, but thus far, their programs do not offer
assistance for sinkhole damage associated costs.
Options for remediating sinkholes include filling the cavities with grout or graded
filter systems and installation of structural supports. For example, the NCM in Kentucky
filled its sinkhole with a filter system and structural supports; grouting is a more popular
and less costly method often used in Florida. However, most sinkholes are preventable
through judicious management of land and water use including appropriate ordinances,
planning codes, policies, regulations, and zoning. One effective mitigation measure for
existing sinkholes is to plant expansive vegetative buffers around the rim of sinkholes;
the buffers can dramatically help prevent water contamination and decrease flood
intensity.
As current laws in most of the at-risk states are not designed to protect property
owners, often it is up to the homeowners to do their research before purchasing property
in at-risk locations and they are most often solely responsible for any damages caused by
sinkholes. Optional sinkhole insurance can assist with damages and losses, but insurance
companies do not always have to offer or provide insurance coverage; in fact, only two
states have laws mandating insurance companies to offer or provide sinkhole coverage.
In Florida, by law, insurance companies must cover catastrophic losses. Florida
Insurance companies are not responsible for covering any costs associated with
stabilizing structures such as houses or business buildings, nor for filling sinkholes
URBAN SINKHOLES
80
beforehand; almost like refusing to fix a dental cavity until decay damages the tooth so
severely that it either needs a root canal or extraction.
This study examined why the incidences of sinkholes that result in substantial
property damages, disrupt communities, and take lives, is increasing so that communities
can better plan for, respond to, mitigate, and recover from future sinkhole events.
Sinkholes are natural phenomenons that under normal circumstances take many, even
hundreds of years to development; unfortunately, human activities often accelerate that
timeframe to just hours or days. We have the technology to predict, detect, and identify
karst, karstification, and sinkholes, and the capability to remediate and mitigate
sinkholes. It is within our grasp to control human activities that trigger the development
of sinkholes and ultimately build long-term sustainable communities, but this will require
action by governmental authorities and others to develop policies and procedures to
ensure this happens.
81
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Appendix
Acronym
Description
AACOG
Alamo Area Council of Governments
APPJ
Assumption Parish
ARC
American Red Cross
BRC
Blue Ribbon Commission
CEMPs
Comprehensive Emergency Management Plans
CPT
Cone Penetrometer Test
DEM
Digital Elevation Model
DEQ
Department of Environmental Quality
DIFP
Department of Insurance Financial Institutions & Professional
Registration
DNR
Department of Natural Resources
DOT
Department of Transportation
EOP
Emergency Operations Plan
EPA
Environmental Protection Agencies
ESF
Emergency Support Function
FEMA
Federal Emergency Management Agency
FIRM
Flood Insurance Rate Map
FLOIR
Florida Office of Insurance Regulation
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GIS
Geographic Information Systems
GOHSEP
Governor’s Office of Homeland Security and Emergency Preparedness
GPS
Global Positioning System
GPR
Ground Penetrating Radar
InSAR
Interferometric Synthetic Aperture Radar
LIDAR
Laser Imaging Detection and Ranging
NCM
National Corvette Museum
NG
OEM
Office of Emergency Management
SHMP
State Hazard Mitigation Plan
TDS
Total Dissolved Solids
TBC
Texas Brine Company
USGS
US Geological Survey
US
National Guard
United States
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