In this last part of the sinkhole series I will provide you with engineering methods for detecting sinkholes, temporal events that can trigger a sinkhole, and WHAT TO DO IF YOU HAVE A SINKHOLE FORM ON YOUR PROPERTY.

Engineering Methods for Detecting Sinkholes:

Soil borings or other direct testing – Borings can be reduced by “reconnaissance scannings” using the following methods:

  • Electromagnetics (EM) and DC Resistivity: detect variations in subsurface electrical properties related to anomalously thick or wet soils (electrical conductivity highs similar to our use of moisture meters in homes), or voids in the electrically conductive clay soil mantle (electrical conductivity lows)
  •  Spontaneous Potential (SP): detects naturally-occurring minute electrical currents or potentials commonly associated with concentrated vertical water infiltration (Streaming potentials)
  •  Micro-gravity: detects minute variation in gravity (subsurface voids create missing mass and lower gravity)
  •  Seismic Refraction: profiles the top-of-rock which may display conical depressions of a type associated with subsidence sinks or deep gouges or cutters which represent sinkhole-prone lineaments.
  •  Ground-penetrating radar

Temporal Sinkhole Triggers

  • Following a period of heavy or prolonged rain (washing-in supporting soils)
  • Following a period of drought (lowering the water tables, leaving cavities)
  • Following a period of housing development (adding pressure on supporting soils)
  • Over pumping existing water supply wells, or drilling of additional wells in an area (lowering the aquifer)
  • Diverting surface water from a large area and concentrating it in a single point
  • Artificially creating ponds of surface water

So now you think you might have a sinkhole or what do you do if a sinkhole develops on your property?

  • Notify your local Water Management District
  • Fence or rope the hole off
  • Keep children away!
  • Protect the area from garbage and waste
  • Contact your homeowners insurance company

Well, that concludes the three part series on sinkholes.  I hope that it has been informative, and as always, remember KNOWLEDGE IS POWER!


This is Part II of the series on sinkholes. In this blog I talk about how urbanization has affected sinkhole formation and what kind of signs to look for on your property if you suspect that a sinkhole may be forming or if you are in an area of high sinkhole formation.

Sinkhole formation is aggravated and accelerated by urbanization. Development increases water usage, alters drainage pathways, overloads the ground surface, and redistributes soil. According to the Federal Emergency Management Agency, the number of human-induced sinkholes have doubled since 1930, insurance claims for damages as a result of sinkholes has increased 1200% from 1987 to 1991, costing nearly $100 million.

To avoid the destruction of property and the contamination of groundwater, it is important to monitor potential sinkhole formation. Although a sinkhole can form without warning, specific signs can signal potential development of a sinkhole:

Site and Neighborhood Observationsordered from general-area to site-specific to property-specific

  • Indications on maps of the locations of likely sinkholes.
  • Areas known to be of thin supporting layers of sand and clay soil (look at any local excavation projects) (Sinkholes develop more frequently north of Tampa Bay where the limestone base is closest to the land surface and the supporting sand and clay layers are thin).
  • An actual sinkhole is present on or near the subject property (duh!)
  • Slumping or falling fence posts, trees, foundations on or near the property
  • Previously-buried fence posts, foundations, trees, become exposed (because of sinking ground)
  • Small rills, gullies, or bare soil areas develop (soil particles being carried away to sinkhole)
  • Cracked earth, a circular pattern of ground cracks outlining the sinking area.
  • Undercut stream banks and fallen trees along a drainage way
  • Sudden formation of small ponds (of rainfall forming where water has not collected before)
  • Wilting vegetation (small circular areas, because moisture that normally supports the vegetation is draining into a developing sinkhole – wilting is not always a sinkhole indicator)
  • circular or oval depressions in cultivated fields that may or may not pond standing water after rain events
  • Areas of cultivated fields which are not being plowed
  • Gradual, localized ground settlement (does not always indicate a sinkhole)
  • Sudden ground openings
  • Sudden ground settlement
  • Interrupted electrical or plumbing service to a building or neighborhood due to undermined, settled buried mechanical lines.

Building and Water Supply Observations

  • Discolored well water
  • Silt buildup, fresh mud deposits, muddy water (in wells? in a pond or stream?) Muddy or cloudy well water from nearby wells can indicate an early stage of sinkhole development.
  • Structural cracks in walls, floors
  • Doors or windows that don’t close properly (traced to building foundation movement)

Now you have some things that you as an individual can look for to see if you might have a sinkhole forming in your area.  In the final installment in this blog about sinkholes I will discuss Engineering methods for detecting sinkholes and temporal things that could trigger a sinkhole.  In addition, I will tell you what you should do if a sinkhole forms on your property.

Nearly every time that I have taught my course Environmental Concerns and Your Real Estate Transaction I have had someone ask me about sinkholes.  Since the topic does not really fit into the course I decided I would blog about it.  Actually it will be a three part series, since there is a lot of information.

Florida has more sinkholes than any other state in the nation. They are an obvious feature of Florida’s natural karst topography. Karst is a generic term which refers to the characteristic terrain produced by erosional processes associated with the chemical weathering and dissolution of limestone or dolomite, the two most common carbonate rocks in Florida. Dissolution of carbonate rocks begins when they are exposed to acidic water. Most rainwater is slightly acidic and usually becomes more acidic as it moves through decaying plant debris.

Limestones in Florida are porous, allowing the acidic water to percolate through their strata, dissolving some limestone and carrying it away in solution. Over eons of time, this persistent erosional process has created extensive underground voids and drainage systems in much of the carbonate rocks throughout the state. Collapse of overlying sediments into the underground cavities produces sinkholes.

Or in less technical terms, sinkholes originate beneath the surface when groundwater moves through limestone and erodes large voids, or cavities, in the bedrock. When water fills a cavity, it supports the walls and ceiling, but if the water-table drops, the limestone cavity is exposed to further erosional processes that eventually result in the collapse of the cavity, causing a surface indenture, or sinkhole.

On the surface, sinkholes may develop progressively as subtle, bowl-shaped depressions, or they may collapse suddenly into steeply sided, water-filled craters. The shape of the sinkhole, and the speed that it forms, depend on the size of the subsurface cavity and the thickness of the overburden (sediments or organic matter that rest on the limestone bedrock).

Three general types of sinkholes occur in Florida: collapse, solution, and subsidence.

Collapse sinkholes are the most common type in Florida. They happen suddenly where the overburden is thick with soils and heavy clay. Collapse sinkholes are deep, steeply-sided holes in the ground. They are frequently triggered by fluctuations in the water-table. As water levels fluctuate, the roof of the cavity is stressed and weakened. When the water-table drops too far, the cavity walls are unsupported and the ceiling becomes too weak to hold the heavy overburden. Eventually, the ceiling collapses and a sinkhole is formed. A conical debris mound left on the sinkhole floor is all that remains of the cavity ceiling.

If the water-table rises, the collapse sinkhole can fill with water, and overflow like a spring. An off-set sinkhole will have an upstream and downstream conduit as water flows into the sink and siphons underground. If the water-table drops below the sinkhole, it will remain dry and accumulate sediments and vegetation.

If the overburden is thin or absent, the surface of the limestone bedrock is broken down by erosion from wind and surface water. A bowl-shaped depression, or solution sinkhole, naturally forms slowly and continuously as chemical and physical processes erode the rock.

Subsidence sinkholes form gradually where the overburden is thin. The dissolving limestone is replaced by sand granules that fall into the depression and fill the holes. They appear as a concave depression in the ground. Subsidence sinkholes are usually only a few feet in diameter and depth because the development of the cavities in the limestone is retarded since they are filled with clay and sand. As the sediments fill the depression, they restrict the flow of water through the bottom and the hole begins to retain water. As water accumulates, a lake is formed.

What most people don’t realize is that Sinkholes provide a primary pathway for rainwater to replenish subsurface groundwater; they are an important part of the aquifer system that supplies 95% of Florida’s drinking water. The sinkhole becomes a primary site of recharge, where surface water can enter the aquifer and replenish the groundwater supply.

If left unprotected, polluted surface water can drain into sinkholes and easily contaminate the aquifers.

Unfortunately, their bad reputation for property destruction frequently overshadows the vital role sinkholes play in Florida’s natural environment.

In the next installment of information about sinkholes I will discuss the effect of urbanization on sinkhole formation and specific signs to look for that might indicate an imminent sinkhole formation.

 Gopher tortoises, Latin name Gopherus polyphemus, those cute little reptile tanks that you see feeding on grassy areas on the sides of roads are considered to be a Threatened species by the state of Florida and by several other southeastern states in which they occur.  In addition, the U. S. Fish and Wildlife Service has listed this species as Threatened in Mississippi, Louisiana and in portions of Alabama.  It is under review to be listed as a Threatened species by the Federal government in Florida, Georgia and South Carolina.

Gopher tortoises are long-lived reptiles that occupy upland habitat throughout their range including forests, pastures, and yards.  They dig deep burrows for shelter and forage on low-growing plants.  Gopher tortoises share these burrows with more than 350 other species, and are; therefore, referred to as a keystone species.  

Because development preferably occurs in upland habitats this species is in danger mostly due to the reduction of available habitat.  And if this species is affected it will also affect the 350 or so other species that rely on tortoises’ burrows for their safety and residence.  Consequently, both the tortoises and their burrows are protected. 

Prior to any land clearing or development, gopher tortoise impacts must be addressed.  There are four available options to address the presence of gopher tortoises on lands slated for development:

  1. Avoid development;
  2. Avoid destruction of tortoise burrows;
  3. Relocate tortoises on-site, usually for single-family residential construction (permit required); or
  4. Relocate them off-site (permit required).

In my state of Florida, relocation is the mitigation method preferred by the state, which has a number of approved recipient site locations for relocated tortoises.  This can be an expensive undertaking so if you are thinking of buying or selling real estate containing a resident population of gopher tortoises these are costs that should be considered when assessing the value of the property and negotiating price.  Just to give you an idea, in Florida, there are fees per tortoise that are paid to the owner of the recipient site (estimated at $800 to $1000 per tortoise).  There are also fees that are paid to the state to be used for land management and the purchase of land for conservation (minimum $200, which is applied to the first 10 burrows or 5 tortoises and $300 for each additional tortoise over the five moved to a long-term protected area and $3000 for each tortoise moved to either a short-term protected area or to an unprotected area).  In addition, there is the cost of hiring a biologist to survey the property and document the locations of gopher tortoise burrows, the cost of the biologist to apply for a permit, the fee for the permit application, and the expenses of a backhoe, operator, and biologist to carry out the relocation. 

The moral of this blog is to do your due diligence before purchasing real estate and be familiar with environmental issues that may exist on your property if you want to develop or sell it!  As with all of my blog “lessons” remember that KNOWLEDGE IS POWER!



A while ago, in fact in December of 2009 I discussed Hazardous Waste – it’s definition, who regulates issues related to it, and how having a hazardous waste problem on a property can affect the real estate value of that property.  However, I did not get into a lot of details regarding how you would determine whether a property has hazardous waste concerns.  So this blog covers that topic. 

There are basically three levels of assessment that may be taken when dealing with a property that may have hazardous waste issues associated with it.  Only one may have to be done or all three. 

Phase I Environmental Assessment:

A Phase I identifies potential environmental liabilities associated with current and past uses of property with respect to the range of contaminants within the scope of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and petroleum products.  In other words it is looking to see if any “Recognized Environmental Conditions” are present.  A Phase I Environmental Assessment is an initial environmental investigation that is limited to a historical records search to determine ownership of a site, past uses of the site, and to identify the kinds of chemical processes that were carried out at the site.   Phase I investigation tasks include (1) review of physical setting sources, historical aerial photographs and other historical record documents, and regulatory agency records; (2) site and vicinity reconnaissance for recognized environmental conditions; (3) interviews with the present property owner and others familiar with the site when possible, as well as local regulatory agency personnel; and (4) preparation of a report to document and assess any potential Recognized Environmental Conditions.  A Phase I assessment includes a site visit, but does not include any sampling. If such an assessment identifies no significant concerns, Phase II and III audits are not necessary. 

The most recent Phase I standard (ASTM – American Society for Testing and Materials E1527-2005) meets Federally-mandated “All Appropriate Inquiries” (AAI) for Phase I due diligence established in 2005 and protects potential property owners from liability for cleanup, even if they buy the property knowing that there is a likelihood of environmental contamination (this is known as the “Bona-fide Purchaser” defense).  This is a great insurance policy for Buyers, as long as the study and report are done according to the standard.

The newest buzz-word in the Phase I industry is Vapor Intrusion (VI) which, basically are any gases or vapors that have the potential to come up from the ground and impede the air quality within overlying structures.  This type of study is not currently required for most Phase Is, but it is required by HUD for proposed federally-funded multi-family housing projects.

Phase II Environmental Assessment:

A Phase II investigation includes tests performed at the site to confirm the location and identity of environmental hazards.  The investigation could include physical sampling such as soil and water collection and analyses to determine the nature and extent of contamination.  This assessment includes preparation of a report that, if indicated, includes recommendations for cleanup alternatives and a description of the recommended remediation method.

Phase III Audit:

A Phase III includes the comprehensive characterization, evaluation, and removal of contaminated materials from a site, and their legal disposal.  Sometimes the costs of cleanup are covered under a government approved program such as PLIRP (Petroleum Liability Restoration Insurance Program) or EDI (Early Detection Incentive Program).  It is important to note that in order for a “user”, usually the Buyer, to qualify for protection of AAI they have to comply with “continuing obligations” requirements, which in essence means that they must do whatever is necessary to allow assessment and cleanup operations to proceed on the property, if warranted.  If the “continuing obligations” requirements are not met, the use could risk losing liability protection from the federal government.

Hazardous Waste Studies and Real Estate:

So how does this apply to buying or selling real estate?  The single most important thing to remember for both buyers and sellers when dealing with a site that may contain hazardous waste is to make sure that you conduct sufficient research to determine if there is a problem and if yes, who the responsible party is.  Typically, the responsible party is the person who currently owns the property.  However if prior to the completion of the sale the new owner hired someone to make “All Appropriate Inquiries” using the federally-mandated ASTM Phase I Environmental Assessment guidelines, and learned of a problem before closing, they will most likely be protected from liability for cleanup even if they purchase the property knowing that there is the likelihood of environmental contamination.  This is a great insurance policy for any Buyer, as long as the studies and report are done according to the standard.  In addition, as long as all of this occurs prior to closing the current owner is still the responsible party and can be encouraged to address the issue prior to closing.  Also keep in mind, if a buyer learns of an issue during their due diligence period they can do the necessary research to ensure that the site is already covered under a cleanup program and can evaluate whether the incident will affect the desired use of the property.   Because….KNOWLEDGE IS POWER!  And knowing about the property will allow both buyers and sellers to better negotiate on the price of the property.

I know – the time between my blogs is way too long and inexcusable.  I can expect to build up a consistent following when I don’t post very often!  My only excuse is that my blog is informational and educational not a commentary on what is happening in my life.  So I apologize to the following that I have that it has been so long again!

This blog is a continuation of the topic of mitigation.  In my last blog I discussed options for mitigating for wetland impacts.  For this one I will outline the types of compensation commonly used to offset impacts to threatened and endangered wildlife species.  My November 2009 blog discussed threatened and endangered species and outlined the types of activities that typically constitute impacts. 

Threatened and Endangered Species and Mitigation

The trick with protected species is to avoid “taking” them.

The determination of whether an impact has occurred to protected species is relatively more straightforward than that for wetlands – if you take down a tree containing a bald eagle nest you have impacted that eagle or if you bulldoze over the top of a gopher tortoise burrow you have impacted that tortoise.  If a site development proposes activities that may “incidentally” impact threatened and endangered species as a result of otherwise lawful activities permits allowing those impacts may be issued by regulatory agencies.  If permits are issued they typically come with the provision that compensation must be completed to offset those impacts.

Compensation Alternatives

In general there are three techniques that can be used to mitigate for impacts to protected species.   They are:  On-site preservation/buffers, Off-site purchase of land, and relocation.

On-site preservation/buffers:  On-site Preservation is mostly used for species that are sedentary and that need large tracts of very specific types of plant communities such as Florida Scrub Jays.  If there are scrub jays on a property, it might be necessary to set aside the entire portion of the property that is inhabited by scrub jays that is then maintained in its natural state and periodically managed to make sure that the conditions stay suitable for that species.

An on-site buffer might be used if you have a species that can be particularly sensitive to human disturbance such as bald eagles.  For example if there is a bald eagle nest on the property, buffers restricting development of up to 1500 feet from the nest could be required. 

Often on-site preservation is a component of buffers (as with the land in the 1500 foot buffer around a bald eagle nest) but buffers can be required beyond the boundaries of actual inhabited boundaries, such as with a gopher tortoise.

Off-site purchase of land:  This method would include the purchase of land away from the development site that either already provides habitat and resident protected species similar to that on the development site or that could be enhanced or restored through management to create suitable habitat for species that are proposed for impact.

Relocation: This is the removal of a species from the development tract and transporting it to an appropriate recipient site away from the development.  This can include a portion of the property that is not slated for development or land off-site that has been set aside as a conservation area.  Most people are familiar with the concept of relocating gopher tortoises off a property being developed.  This currently is the mitigation method being pushed by the state.  A number of approved relocation tracts have been established and the tortoises are excavated from their burrows and transported to one of these recipient sites.  An example of the cost for that could be $800 to $1000/tortoise to the owner of the recipient site and another $300 to the state to be used for land management in addition to the cost of the permit itself.

Real Estate and Threatened and Endangered Species

As with wetlands, there is no size limit on a property that can be occupied by protected species and; therefore, be subject to permitting and possibly the need to complete mitigation.  

How much actual land is buildable (not inhabited by protected species), whether you can obtain a permit to impact occupied habitat to open up more land for development, and the cost of mitigation may all contribute to the value that can be put on the land if you are a Seller.   Just like with wetlands, the Seller has the choice of addressing some or all of these issues prior to the sale of the property or of leaving it up to the buyer to deal with.  If the Seller does some of the work sometimes they can recoup at least a portion of the money laid out for those activities within the sales price.

Remember “Buyer Beware”?  That applies here again.  Buyers need to be sure to build plenty of due diligence time into the contract for purchase so that they can determine if the site is occupied by any threatened or endangered species and to coordinate with regulatory agencies to determine if developing the property is even feasible and; consequently, what mitigation might be required. 

Knowing that additional monies will have to be laid out for complex permitting and mitigation may allow a buyer to negotiate a better price for the property, leaving them with the funds to complete the development even with the protected species permitting challenges and costs that they may face.  So let’s say you are thinking of buying a piece of property that is occupied by gopher tortoises, you will need to know how much the property is listed for but also how much money might have to be budgeted for environmental studies, permitting, and mitigation such as relocation – all before any other construction costs are considered.  The price offer to the seller might deduct some or all of these projected costs from the asking price of the property.

So as with my other blogs, my advice is hire an environmental consultant to make sure you are aware of environmental issues that you will be dealing with regardless if you are the Seller or the Buyer.  Remember KNOWLEDGE IS POWER!

In several of my previous blogs (and I apologize for the length of time between my last blog and this one) I mentioned the term “mitigation”.  This term was used in relation to compensation that might be required for impacts to wetlands or protection species that resulted from development.  For this blog I am going to concentrate on Wetland Mitigation.  If you don’t remember the types of activities that constitute impacts to wetlands refer back to my September 2009 blog.  (Please note that most of the following information is specific to Florida rules and regulations since that is where I am located; however, most of these concepts and methodologies are also recognized by the U.S. Army Corps of Engineers and are likely to apply in other states, as well.)

There is an awful lot of information and specialized knowledge that goes along with the determination of what actions will be considered to be impacts, the calculation of the loss of wetland function (impact) if those wetlands are affected by development, and the determination of the type and amount of compensation that will be required to offset those impacts.  It’s way too much to get into in a blog.  So the purpose of this blog, hopefully, is to give you a little more familiarity with the concepts of impact and mitigation and to provide you with a brief outline of mitigation alternatives available if it is determined that proposed land improvements will cause wetland impacts. 

Wetlands and Mitigation

Wetlands are important components of water resources because they often serve as spawning, nursery and feeding habitat for many species of fish and wildlife, and because they often provide important flood storage, nutrient cycling, detrital production, recreational and water quality functions.  Other surface waters such as lakes, ponds, reservoirs, other impoundments, streams, rivers and estuaries also often provide such functions, and in addition may provide flood conveyance, navigation and water supply functions to the public.  Not all wetlands or other surface waters provide all of these functions, nor do they provide them to the same extent. A wide array of biological, physical and chemical factors affect the functioning of any wetland or other surface water community.

The regulatory agencies have decreed that development can not cause a net adverse impact on wetland function such as those described above that is not offset by mitigation.  In other words, there can be “no net loss of wetland function”.  In Florida, the state agencies use a complicated numerical evaluation system called the Uniform Mitigation Assessment Methodology (UMAM) to determine how much wetland function may be lost as a result of development and; therefore, how much mitigation will be required to compensate. 

Wetland mitigation is defined as an action or series of actions taken to offset adverse impacts that would otherwise cause a regulated activity to fail to meet the “no net loss of wetland function” requirement.  The UMAM method used to determine net wetland function lost is used to evaluate the property or activities proposed as mitigation to ensure that what is proposed is sufficient to offset those impacts.

You should know that prior to allowing compensation for wetland impacts; as part of the permitting process, the developer must first prove to the regulatory agencies that they have eliminated/avoided wetland impacts to the maximum extent.  Following that, if impacts will still occur they have to prove that they have reduced/minimized impacts to wetlands.  Only after that step is completed will any remaining impacts be considered for mitigation.  There are multiple ways to mitigate for lost wetland function.

Compensation Alternatives

In general, there are five mitigation methods: Creation, Restoration, Enhancement, Preservation, or Purchase of Credits from a Mitigation Bank.  Mitigation can and most likely will be a combination of one or more of these.

  • Creation: The conversion of other land forms into wetlands or surface waters.
  • Restoration: The converting back to historic conditions of a wetland, surface water, or upland, which currently exists as a land form different from its historic condition.
  • Enhancement: The improvement of the ecological value of wetlands, surface waters, or uplands that have been degraded in comparison to their historic conditions.
  • Preservation: Protection of wetlands, surface waters, or uplands from adverse impacts by placing a conservation easement or other land use restriction over a property or by donation of fee simple interest in the property.
  • Purchase of Credits from a Mitigation Bank: Mitigation banking means the restoration, creation, enhancement and, in exceptional circumstances, preservation of wetlands and/or other aquatic resources within large tracts of land for the express purpose of providing compensatory mitigation in advance of authorized impacts to similar resources.  Once permitted, mitigation banks have a set number of credits they have been allocated (based on improvements they have made on or will make to the land) that developers, for a fee, can have withdrawn as a means of offsetting adverse wetland impacts.

Real Estate and Wetland Mitigation

There is no limit on the size of the property that can have wetlands and; therefore, be subject to permitting and potentially the need for mitigation if wetlands end up being impacted.  Permitting wetland impacts and providing compensation for those impacts can be costly and time consuming and should be considered by the Seller when placing a value on property.  The Seller has the choice of addressing these issues prior to the sale of the property, in which case they may be able to recoup some of the money laid out for those activities or of leaving it up to the buyer to tackle them.

As indicated in earlier blogs,  it is very important for a Buyer of vacant land to remember that it will be their responsibility to know what they are buying.  The Buyer needs to build plenty of due diligence time into the contract for purchase so that they can determine what issues might be present and to coordinate with regulatory agencies to determine if developing the property is even feasible if there will be wetland impacts and; consequently, mitigation.  Knowing that additional monies will have to be laid out for complex permitting and mitigation may allow a buyer to negotiate a better price for the property, leaving them with the funds to complete the development even with the environmental permitting challenges and costs that they may face.

So hire an environmental consultant to make sure you are aware of environmental issues that you will be dealing with regardless if you are the Seller or the Buyer.  Remember KNOWLEDGE IS POWER!