Spotting Subsurface Risk Before Excavation

As a licensed land surveyor, you’re often the first credentialed professional to set foot on a project site. That timing is an asset, and in areas prone to subsurface instability, it comes with a real responsibility to document what you observe before the earthmovers show up.

Think of it as being a disciplined observer and communicator in the critical window between site award and ground disturbance, without overstepping your professional role.

Here’s how surveyors can play a meaningful role in early subsurface risk management without overreaching. In many cases, that includes helping identify potential sinkhole risk, as well as other signs of subsurface instability, before construction begins.

Why Surveyors Are Positioned to Catch Early Warning Signs

Geotechnical engineers are often brought in after an initial site evaluation has begun, and, in some cases, surface conditions have already been disturbed. Surveyors, by contrast, walk the ground early in the parcel acquisition process, performing topographic surveys, boundary surveys, and ALTA/NSPS work, when the natural surface is still intact and readable.

That gives you a window to observe and document conditions that could signal subsurface voids, dissolution features, or unstable soils. In karst terrain* especially (think Florida, Tennessee, Kentucky, Missouri, Pennsylvania, and parts of Texas), what you see on the surface can be a direct indicator of what’s happening below it.

The key word here is observe. You’re not diagnosing geotechnical conditions; you’re evaluating. You’re creating a documented record of surface anomalies that should trigger further investigation by qualified subsurface professionals.

* Karst is a landscape created when water dissolves rocks. In Wisconsin, dolomite and some limestone are typical soluble rocks. The rocks are dissolved mostly along fractures and create caves and other conduits that act as underground streams.¹ To assist with this evaluation, refer to the U.S. Geological Survey map indicating where these soils may be found.²

Surface Indicators Worth Documenting

You don’t need ground-penetrating radar to spot the signs and in certain soil conditions GPR performs poorly. Several conditions observed during routine fieldwork can provide clues to suggest subsurface instability:

Depression Features

Circular or elongated depressions in otherwise flat terrain, especially those that appear to have no natural drainage explanation (holes or depressions do not exist naturally unless there is an underlying cause)
Subtle bowl-shaped areas that don’t show up clearly on existing topo but are apparent when you’re walking the site
Depressions that are consistently wet or hold water longer than surrounding areas

Vegetation and Soil Anomalies

Patches of stressed, dead, or unusually dense vegetation in patterns inconsistent with terrain
Areas of excessive vegetation growth, especially in dry seasons, can indicate a subterranean water source which can cause subsurface erosion
Soil that appears recently disturbed or settled with no clear human cause
Surface cracking, particularly linear or polygonal patterns in open areas, which can indicate tension cracking above a forming void

Structural and Infrastructure Clues

Sinkholes or small holes (even animal-sized) in the yard or pasture, which can be surface expressions of deeper dissolution
Tilted or cracked utility poles, fence posts, or old foundations on or adjacent to the site
Pavement or old hardscape with subsidence patterns, sagging, or cracking inconsistent with typical settlement
Transformers, or other heavy infrastructure, which has settled unevenly

Drainage Oddities

Areas where surface water visibly disappears without a clear outlet, a classic indicator of karst drainage
Alternately areas where water appears without an identifiable source
Streams that “lose” flow between two points or suddenly go underground
Unusual ponding patterns in dry weather

Treat these observations as potential warning signs and document them accordingly.

How to Document It: Observation vs. Interpretation

This distinction is critical, both professionally and legally. Your job is to record what you observed, not to render a geotechnical opinion.

In your field notes and reports, use language like:

“Surveyor observed a circular depression approximately 8 feet in diameter and 2 feet deep at approximately [coordinates]. No drainage outlet visible. Flagged for further evaluation.”
“Small void openings noted along the northeastern portion of the parcel, consistent in appearance with surface expressions of subsurface dissolution. Owner and project team notified.”
“Surface cracking noted in a linear pattern running approximately N35°E for 40 feet in the southeast corner of the site. Pattern and location documented in field notes and photographed.”
“Field crew documented a small stream entering the property near the northeast corner of the property and running in a southwesterly direction. After approximately two hundred feet, the stream disappeared into a rocky area with no visible continuation of the flow.”

What to avoid:

Declaring that a sinkhole exists beneath the surface
Quantifying subsurface void depth or extent
Recommending specific engineering solutions
Certifying that conditions are or are not safe for construction
Making any declaration, affirmation or statement beyond your area of expertise

What to capture:

GPS/survey coordinates of anomalies
Photographs with metadata – Most data collectors have built-in cameras which make this exercise simple and quick.
Dimensions (depth, diameter, length) where measurable from the surface
Notation of any visible changes in soil characteristics (simply note there is a change, not a specific soil identification, unless you are trained to do so)
Date and time of observation
Weather and recent rainfall context (relevant to void visibility and surface condition)
A notation that the feature was communicated to the client/project team
If a surveyor’s report is prepared for the project, a notation of your observations should also be included.

If your deliverable is an ALTA/NSPS survey or topographic survey, consider whether an additional observation note or table is appropriate. Item #21 of Table A is left blank for just such a notation or observation.

Some practitioners include a “Site Observations” section outside the standard certification to document conditions that fall outside scope but warrant attention.

Review your state’s licensing standards and your firm’s legal guidance before adding such notation.

Coordinating With Geotech and Owners

Documenting what you found is step one. Step two is making sure the information reaches people who can act on it.

With the property owner or developer:

Be clear and direct without causing unnecessary alarm or speculating beyond what you observed.

“During fieldwork, we noted several surface features that may warrant further subsurface investigation before finalizing site design” is an accurate, professional way to communicate the finding. Put it in writing.

With the geotechnical engineer:

If a Geotech is already engaged, share your field notes and photos as early as possible. Your observations may influence where they target their borings, which saves money and improves the investigation’s value. If a Geotech hasn’t been engaged yet, your documentation may be exactly what prompts the owner to bring one on.

With the design team:

Architects and civil engineers making foundation decisions need to know about surface anomalies before they complete their designs. A note passed along early, even an informal one, is far better than a surprise during excavation.

A structural engineer designing a foundation without a current soils analysis from the Geotech is rolling dice in a very expensive game. Your notations might prevent such imperative research from being overlooked.

The role here is straightforward: observe, document, and communicate. Leave the geotechnical determinations, site safety calls, and liability for subsurface conditions to the professionals whose scope covers them.

Special Considerations by Region

If you practice in karst-prone areas, you’re already familiar with the elevated stakes. But subsurface void risk isn’t limited to limestone terrain:

Old mining regions (Appalachia, parts of the Midwest): Abandoned mine voids can lie at surprisingly shallow depths. Look for subsidence patterns, old shaft collars, and anomalous depressions consistent with pillar collapse.
Coastal and Gulf Coast areas: Dissolution of carbonate rock is common in Florida and parts of Texas. Shallow sinkholes can develop rapidly, sometimes within hours after heavy rainfall.
Areas of heavy surface water usage: Farming or industrial uses can draw heavily on surface and subsurface water supplies in their immediate vicinity, leading to subsidence.
Former industrial sites: Underground storage tanks, old utility vaults, and basement remnants can create voids that behave similarly to natural cavities from a risk standpoint.
Fill areas: Sites graded over depressions, stream channels, or demolished structures may have poorly compacted or void-ridden fill that won’t show up on existing topo.

Your awareness of local geology is professional knowledge that sharpens how carefully you walk a site and what you look for—even if it stops short of geotechnical expertise.

The Bigger Picture: Surveyors as Risk Communicators

The surveying profession is evolving in ways that place greater value on the surveyor’s role as an early-stage project resource—not just a data-gatherer, but a knowledgeable field professional who can flag conditions that affect project viability and safety.

As a function of our duties when surveying, we may see areas of a project site that will remain unobserved by others until the site has been cleared and the evidence we might encounter is lost.

Subsurface risk documentation is one of the clearer examples of this expanded value. When a sinkhole opens mid-construction, the financial and liability costs can be significant. When a surveyor documents concerning surface features early and the right professionals respond, those costs can often be avoided entirely.

That’s a concrete contribution to better project outcomes.

Remember, assumption is the mother of all mistakes, so don’t take it for granted that someone else will see the evidence of possible subsurface issues and report it. It is better if information is repeatedly reported instead of lost in translation.

Keep Your Practice Sharp with Continuing Education

Staying current on best practices in site observation, documentation protocols, and professional scope management is part of what separates a good surveyor from a great one.

McKissock Learning offers continuing education courses designed specifically for licensed land surveyors, covering topics that help you navigate complex field situations, stay compliant with evolving standards, and deliver greater value to your clients.

Explore McKissock’s Land Surveyor continuing education courses today. Find the credits you need to maintain your license while building the expertise to handle whatever the field throws at you.

The observations and documentation practices described in this post are general guidance for informational purposes. Always consult applicable state licensing standards, professional liability considerations, and legal counsel when determining appropriate scope of services in your jurisdiction.