A Project Manager's Guide to Karst & Cave Surveys in Central Texas

If you are acquiring property or planning construction in Central Texas, your site may sit on karst: caves, sinkholes, and underground drainage that can harbor federally protected species. This guide walks you through karst-related ESA compliance so you can make informed decisions and keep your project on schedule. Zara Environmental holds a USFWS Section 10(a)(1)(A) permit and performs these surveys in-house.

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When a Karst Feature Survey Is Required

A Karst Feature Survey is a protocol-driven survey conducted under US Fish and Wildlife Service (USFWS) guidance. It applies to projects in Bell, Bexar, Comal, Medina, Travis, and Williamson Counties when any portion of the site falls within Karst Zone 1, 2, 3a, or 3b, or within a 500-foot buffer of those zones. The buffer exists because the zone maps carry a mapping margin of error of more than 400 feet. Projects located entirely within Zone 4a or 4b and outside the 500-foot buffer do not require a Karst Feature Survey.

The survey identifies karst features (caves, sinkholes, solution cavities, and similar openings) and assesses each one to determine whether it provides suitable habitat for listed species. If suitable habitat is confirmed, the next step is a Presence/Absence Survey to determine whether listed species actually occupy the feature.

A note on salamanders: Several Central Texas Eurycea salamanders are federally listed. Flowing or standing water in a karst feature may trigger a Salamander Presence/Absence Survey as well.

Common Regulatory Agencies Involved

  • US Fish and Wildlife Service (USFWS)
  • Texas Parks and Wildlife Department (TPWD)
  • US Army Corps of Engineers (USACE)
  • Texas Commission on Environmental Quality (TCEQ)

Timing & Seasonality

Karst Feature Surveys and karst invertebrate Presence/Absence Surveys can be conducted year-round, but weather matters. Features are not entered during heavy rain or flooding, and temperature extremes or low humidity can make a survey invalid. Salamander surveys are tied to water: at least 8 of the 15 required surveys must occur between February 1 and September 1 of the same year, and a dry site cannot be surveyed to infer absence.

When to engage a karst consultant: ideally once your project footprint is confirmed, so the survey covers exactly what will be affected. Engaging earlier, during feasibility and routing, lets you identify features to avoid before the layout is locked in.

Estimated Project Timeline and Cost

Estimated Timeline

(with reporting)

4-6weeks for a Karst
Feature Survey
plus roughly 10 weeks if Presence/Absence Surveys are needed

Estimated Cost

(survey through Presence/Absence)

$18,000 - $65,000+
About $18,000 for a 50-acre Karst Feature Survey. Presence/Absence Surveys run roughly $28,000-$35,000 for 1-2 features and $50,000-$65,000 for 10 features.

iNote: Timelines and costs vary widely depending on project specifics. Zara provides detailed estimates with every proposal.

What to Expect from a Karst Feature Survey

Karst work is sequential. Each phase determines whether the next is needed, so many projects finish after the Karst Feature Survey and never move on to Presence/Absence Surveys. Habitat assessments, excavations, and Presence/Absence Surveys must be performed by, or under the direct supervision of, USFWS Section 10(a)(1)(A) permit holders. Zara holds this permit and performs all of this work in-house.

How long are results good for? USFWS recommends repeating a Karst Feature Survey if none has been conducted on the property within the last 10 years. A salamander absence finding expires three years after surveys are completed.

No two karst projects are identical, but most follow this general sequence.

Phase
Duration
What Happens
1
Karst Zone Determination
Duration: During Scoping
Confirm whether any part of the project falls within Karst Zone 1, 2, 3a, or 3b, or within 500 feet of those zones.
2
Karst Feature Survey (Surface Walking)
Duration: 2-4 Weeks Fieldwork
A karst geologist and/or biologist walks the assessment area on foot to locate and document karst features. This can be done concurrently with fieldwork for a TCEQ Geologic Assessment, if one applies.
3
Habitat Assessment
Duration: Concurrent with Fieldwork
A USFWS Section 10(a)(1)(A) permit holder, or a qualified geologist with written USFWS approval, evaluates each feature against physical and biological criteria to decide whether it could support listed species.
4
Excavation (if necessary)
Duration: Included as Needed
Some features must be opened by hand to see whether they lead to habitat. Digging stops when a cave is reached, when solid bedrock or packed clay without airflow is hit, or when safety becomes a concern.
5
Reporting
Duration: 4 Weeks
The Karst Feature Survey report documents every feature and its habitat determination. If no suitable habitat is found, the project can proceed on the karst side.
6
Presence/Absence Survey (if needed)
Duration: 6 Weeks Fieldwork, 4 Weeks Reporting
If suitable habitat is confirmed, Zara's Section 10(a)(1)(A) permitted biologists conduct a series of 14 surveys spaced no more than 72 hours apart to determine whether listed species occupy the feature. A negative result does not absolutely confirm absence.

Why Are There So Many Presence/Absence Surveys?

USFWS requires a high level of confidence that a species is absent before a site can advance with development or construction. Current protocols call for 14 Presence/Absence Surveys per karst feature and 15 for salamanders. A single visit can confirm presence, but establishing probable absence is harder. Repeated surveys across different conditions, including day and night visits and, ideally, both spring and fall, reduce the risk of missing a species that is present but undetected.

A cave pseudoscorpion on a rock
Cave pseudoscorpion

On-Call Construction Monitoring

A karst feature can be as small as a fist-sized hole and may go undetected until grading peels back the surface. For this reason, many project managers keep a Section 10(a)(1)(A) permitted construction monitor, like Zara's, on call during ground-disturbing work. If a void is encountered, work within a set distance (typically 50 feet) stops, and the monitor responds promptly to assess whether suitable karst invertebrate habitat is present.

If no suitable habitat is present, construction continues. If suitable habitat is present, the work stoppage stays in place, best management practices (BMPs) are installed, and Presence/Absence Surveys follow USFWS protocol. Voids too small to enter can instead be baited and checked for a minimum of 14 days. On-call monitoring keeps timelines on track and gives you a fast, defensible response when a feature turns up unexpectedly.

A Zara scientist in a safety vest surveying a cave
Surveying a cave discovered during road construction.

Key Considerations

What factors impact the scope, timing, and cost of Karst Feature Surveys?

  • Size of the assessment area: Cost is anchored to acreage. Larger sites take longer to walk and may require bigger field teams.
  • Location: The county and karst zone determine which species may be present, which requirements apply, and whether a regional habitat conservation plan (for example, in Bexar or Williamson County) offers a streamlined path.
  • What is found: Finding no suitable habitat keeps cost and schedule at a minimum. Confirmed suitable habitat moves you into Presence/Absence Surveys (roughly 10 additional weeks), and that cost scales with the number of features surveyed.
  • Water on site: Springs or water within a karst feature can trigger salamander surveys, which are tied to flow conditions and the February through early September window.
  • Agency timelines: Anything that requires USFWS review or consultation adds time that is outside everyone's control.

Choose Zara Environmental for Karst Management Services

  • Hundreds of karst habitat surveys completed for public and private clients, including TxDOT, military installations, and regional habitat conservation plans.
  • USFWS Section 10(a)(1)(A) permit holders for karst invertebrates and Eurycea salamanders, backed by karst geologists who map, excavate, and evaluate features.
  • Technical experts in Karst Feature Surveys, proficient in safely accessing and navigating cave systems, including vertical and confined-space work.
  • End-to-end project support, from karst zone determination through Presence/Absence Surveys, construction monitoring, and agency coordination.
Looking up from inside a cave at a scientist at the entrance
Mapping a cave found during construction, Bexar County.

Founded by leading karst scientists, Zara Environmental has been performing complex karst management services under demanding conditions since 2003. Our team collaborates closely with regulatory agencies to advance best practices and brings industry-leading expertise to every feature we evaluate. Through a proactive approach and comprehensive capabilities, we help clients manage risk effectively and keep project schedules intact.