Article Written By: Zane Liston
This spring, the Watershed Association team spent the morning at Jacobs Well with one of the great minds of hydrogeology and karst. Pat Egan, the Watershed Association’s Volunteer Coordinator and Land and Facilities Assistant, and Zane Porterfield, the Watershed Association’s Policy and Outreach Coordinator, had the rare privilege of interviewing him on the land and learning from his fifty year study of our unique hydrogeologic system.
The Watershed Association’s work over the decades has been intrinsically intertwined with supporting the best scientific minds in the state. Without visionaries like Dr. Veni, this land would remain a mystery. Our organization has been devoted to filling the knowledge gap that governments and local leaders could not, and with 30 years of citizen science, commissioned studies, and policy initiatives, we have only just begun to understand the beauty and complexity of our waters.
The Void Beneath Your Feet
Veni is a hydrogeologist who has spent five decades studying karst: the dissolving, fracturing, cave-forming landscape that underlies much of Central Texas and provides drinking water to millions of people. He runs his own consulting firm, served as president of the International Union of Speleology until 2022, and has testified before city councils, worked on every side of the regulatory table, and traced dye through aquifers on multiple continents. He is not, he will tell you, an expert on everything. But on the question of how water moves through limestone, and what it means, he is about as authoritative as it gets.
He describes his work with a line he has clearly used before, the kind of line that gets sharper with repetition.
“I’m a geologist who studies the absence of rock. I study nothing.”
The joke lands because it is also exactly true. Karst is not a substance. It is what happens when a substance is removed. Rainwater picks up carbon dioxide and becomes weak carbonic acid. Soil respiration strengthens the acid further. The water moves into fractures in solid limestone, dissolving the rock slowly, making the passage a little wider. A wider passage captures more water, which enlarges it faster. The process is self-accelerating. When a conduit becomes large enough for a person to enter, it gets called a cave — though Veni is quick to note that the word is human centric.
Texas has a specific legal definition for caves: naturally occurring, humanly enterable, underground, at least five meters in traversable length, with no dimension of the entrance exceeding the length or depth of the cavity. That last condition is what distinguishes a cave from a sinkhole. Veni helped develop this definition, and he defends the five-meter threshold on hydrogeological grounds: in Texas’s topographically modest karst, five meters is roughly where cave-adapted fauna begin to appear.
But the real threshold to Veni, the one that matters to a hydrologist rather than a wildlife biologist, is ten millimeters. “At about ten millimeters, you have what’s known as a threshold of turbulence where water begins to flow in a turbulent fashion,” Veni explained. “A hole that size, about the diameter of your pinky finger, functions hydrologically, geochemically, in terms of contaminant transport, the movement of nutrients and cave fauna, exactly the same way as any humanly enterable cave.”
This is the part that matters for management: once a fracture crosses that threshold, it stops filtering and starts conducting. Contaminants move through it the way water moves through a pipe, not the way water moves through sand. The technical framework Veni uses to describe karst is what he calls triple permeability. There is primary permeability: the microscopic movement of water through solid rock. There is secondary permeability: water moving through fractures and bedding planes. And there is conduit permeability: passages ten millimeters or larger, functioning as underground streams. Most aquifer systems have one or two of these. Karst has all three, simultaneously, in the same body of rock.
“People will ask: how old is the water in a karst aquifer? Is it tens of thousands of years old? A few minutes? A few days?” Veni said. “And the answer is yes. All of it. It depends on what part of the system you’re sampling. I’ve been in many caves where the water dripping on my head may be tens of thousands of years old, slowly worked through the rock. Meanwhile, the water rushing around my body may have just entered the aquifer a few minutes or a few days ago. That makes these systems the most complex type of aquifer body in the world.”
The Accidental Karst Scientist
Veni was a pre-med student when he first saw a cave. He had been working in the emergency room at Wilford Hall Air Force Base, eight years, active duty and reserve, and had developed a habit of using his days off to visit national parks. Big Bend first, then Guadalupe Mountains, then Carlsbad Caverns, almost by accident.
“I went in there and fell in love,” he said simply.
He came back to San Antonio and read every cave book in the UTSA library and the San Antonio Public Library. He joined the local club for cavers. When he eventually walked into the VA office at UTSA to collect GI Bill benefits, they asked for his major.
“I said, okay, fine. Geology. Because I’d been crawling through the geology for a few years as a caver. And so I had this natural curiosity.”
The rest of his career followed in the same mode. In 1981, he attended the International Congress of Speleology in Bowling Green, Kentucky, and while walking a hallway between sessions, noticed a stack of papers on top of a bookcase describing a karst program at Western Kentucky University. He applied. He was accepted, largely on the strength of his GRE scores.
He studied under Nick Crawford for his master’s degree, and under Will White at Penn State for his PhD, by his own account, two of the world’s leading karst scientists. At the time, experts believed there was ‘no karst in Texas’. George’s sole focus was to study the Edwards and Trinity systems north of his hometown of San Antonio. He returned in 1987 to set up his dissertation study area and had barely installed his field equipment when the Edwards Underground Water District called. They had a cave issue. Could he consult on it? “I said yes immediately, having no idea what it was like to be a consultant,” he said. “So I went to Barnes and Noble and bought two or three books on consulting. Read them very quickly so I could respond and write a contract.” George Veni & Associates has been operating ever since. His path to the UIS presidency followed the same arc: someone nominated him at a meeting when no one else volunteered, and he took the job. He says this without false modesty. He means it as a wisdom: that consequential things often happen sideways, and the only way to be ready for them is to know your subject cold.
What the EAA Got Right — and What the Models Get Wrong
The Edwards Aquifer Authority has some of the stronger groundwater protection powers in the nation, yet exists in a state with very little in the way of real management strategies. In the Edwards, the ‘modeled available groundwater’ is a real life ‘cap’ on use. They track the rate of recharge and do not issue new permits, so all permits have more value, and all water is limited by availability. When the Sierra Club sued to protect endangered species at Comal and San Marcos Springs, a federal court agreed that something had to change, and that an Authority model was required to manage our drinking water and maintain priceless springflow. Today, the EAA Research Park looks into cutting edge strategies to sink more water into their reserves, and the Edwards Aquifer Recharge Zone is a familiar friend to most of us.
Veni credits Gary Schindel, the EAA’s long-time chief technical officer, with doing the hard internal work of making karst expertise matter inside a bureaucracy that was not originally designed for it. But he also notes that Schindel had to import outside validation, because local expertise, however accurate, is rarely seen as sufficient. “An expert is defined as someone who lives at least 50 to 200 miles out of town. If you’re local, you’re just a local yokel. You don’t know anything. It’s a bias we all have.”
The Edwards water budget model — how much water goes in, how much comes out — is reasonably solid, Veni says. What is still being worked out is where the water comes from. We have already developed significantly in the aquifer’s recharge zone. Upland recharge through fractures, tree sinkholes, and caves is now understood to be far higher than the 2 to 6 percent estimated in earlier studies. Steve Worthington’s addition of conduit flow to the groundwater model was, in Veni’s telling, a genuine breakthrough: it acknowledged that water doesn’t just seep through limestone, it can rush through underground rivers. It is a complex system that requires highly localized study, at the same time as bird-eye view management.
In the Wimberley area, we have devoted ourselves to aquifer studies for generations, yet our larger data sets generally don’t encompass the dynamics in the field. The region has been forced to rely on an outdated model whose designated future condition (DFC) projects a 19-foot drawdown over 30 years. This means that our Desired Future Condition here in Wimberley has no flow into Cypress Creek, no flow in the Blanco, and no flow into Blue Hole. That threshold is already being exceeded at double the predicted rate in under a decade. We are actually pumping what we planned, but the water table is dropping twice as fast as we thought. We are not alone in this data disparity.
“This is a very old problem. If you look at the groundwater resources of Kinney County, Texas — I think that report dates to 1962. If you look at the water table map, Las Moras Springs is shown as a groundwater high. Now, any hydrogeologist will immediately recognize that’s ridiculous, because it’s saying water’s flowing uphill. I spoke to Ted Small, who was with the USGS and was part of that study. He said: ‘Yeah, we knew it was wrong. But we ran out of money. That was the data we had. We knew it was wrong, but we were told to publish it.'” Readers may remember our collective win at Las Moras Springs early this year, for which we sent letters of support to the local GCD to maintain the spring as ‘relevant’ to the Edwards Aquifer. This iffy science served as the basis for a potentially profound reversal of protections.
His prescription, consistent across every scale of the problem, is dye tracing — injecting fluorescent, non-toxic dye at one point and detecting it at others, measuring velocity, concentration, and dilution. It is, in the formulation of his late colleague Jim Quinlan, worth a hundred computer models or a thousand professional opinions.
“It went from there to here. End of story. You don’t believe it? We’ll do it again. Still don’t believe it? We’ll do it again. It’s empirical science. You don’t lose your dye.”
He would consider designing a tracing study for the Wimberley area — but not yet. Aquifer levels are too low. Dye dropped into a nearly static system can’t tell us much. Perhaps we can dream and plan about a study that finally answers the generational question, why we have lost Jacobs Well, and how we can repair a stressed aquifer.
The Tools of the Trade
Dye tracing is a time-tested tool, actually discovered by accident in Ancient history. Veni’s favorite example involves an absinthe distillery in France. “There was a fire. All these barrels of absinthe go pouring down the hill into a sinkhole. And for a week or two, people really enjoyed that spring water.”
He has his own version of the anecdote in Central Mexico, where he was trying to locate the upper entrance of a cave spring. Locals told him that when the system flooded, the water turned dark brown, and goats and trees washed out of the spring. “That’s a form of dye tracing,” he said. “The goats are the tracer.”
The practice has not fundamentally changed around this science, but what has advanced is the precision of detection. Early detection of dye was just holding a jar of water up to a strong flashlight and looking for a color shift. Today, spectrographic equipment measures dye concentrations at parts per billion or parts per trillion — which means a single well-designed trace can model not just whether a connection exists, but how fast contamination would move and at what concentration it would arrive, no matter how microscopic. It can give a real sense of the underground spread of the karst system.
Geophysics has undergone a similar transformation. Veni describes the early methodology with nostalgia: hammering rod electrodes into the ground by hand, sending electric signals through them, reading analog meters, writing down numbers, and then spending hours computing underground contours manually based on the changes. Now, arrays of up to 112 electrodes are deployed simultaneously, connected by cables, triggered automatically. The data downloads in minutes and feeds into GIS models that generate subsurface images of a quality that was not achievable by any method a generation ago. For conservation land acquisition more broadly, Veni describes a GIS-based model he helped develop for San Antonio’s Edwards land protection program. Its key design feature was what he calls adjacency scoring: properties that share a boundary with already-protected land receive bonus points, reflecting the compounding value of contiguous protection over scattered parcels. The model also incorporated endangered species presence as a tiebreaker when the hydrological value of two properties was roughly equivalent.
Yet still, dye tracing is the true test of impact.
The San Marcos to Barton Springs dye trace studies going back to the late 90’s are a regional landmark. Each progressive dye trace clarified mysterious connectivity across a distance that had seemed implausible, and became the template for how comprehensive tracing studies should be designed. By the 2010’s, hydrogeologists theorized that even the Blanco River watershed, in drought conditions, served as recharge for the City of Austin. What exists in the Wimberley watershed, by contrast, is a collection of piecemeal, micro-scale traces that establish connectivity on a very local level. No one has yet done for this watershed, the Trinity Recharge Zone and its head, what that study did for the Barton Springs segment of the Edwards.
So what about our role in recharge here in the Valley? The community has recently been notified of Aqua Texas’s pending permit application for nearly one million gallons per day of wastewater discharge. Existing documented discharge sites, as the Watershed Association has documented, include a largely unused golf course in Woodcreek North that applies effluent in a high-recharge area, sometimes with as little as one inch of topsoil, in a zone defined by hundreds of karst features. Other possible discharge sites include a golf course in WoodCreek that uses 50,000 gallons of groundwater monthly for irrigation, rather than the available effluent. Whether the discharge sites are hydrologically connected to drinking water sources is exactly the kind of question dye tracing was designed to answer, and could potentially help us find the best possible outcome.
“Dye tracing is the most powerful tool to prove or disprove connectivity between discharge sites and water supply features,” Veni said. “It’s objective. It’s repeatable. It’s legally defensible.”
The Limits of Aquifer Language
There is a phrase that makes George Veni visibly impatient.
The phrase is “Trinity Aquifer.”
“Trinity is a stratigraphic term. It refers to a group of rocks. It’s not a hydrologic term. Edwards Aquifer works as a term because the Edwards is a group of rocks with similar — if not identical — hydrologic characteristics. Trinity doesn’t work, because you’ve got the Upper Glen Rose, which, throughout most of the region, has a lot of clay in it and is not a good water-producing unit. Below that is the Lower Glen Rose, where we’re standing, which is a very productive aquifer. Below that is the Hensel Formation — in the Fredericksburg area, it’s a sandstone aquifer; as you come toward the Balcones Escarpment, it turns more into a shale and becomes a barrier. Below that is the Cow Creek, which is another productive limestone karst aquifer. Below that, the Hammett Shale, which doesn’t produce water.” Trinity, in our area, is an umbrella term with a wide reach.
He stopped. “So you’ve got this incredible variability. It (the Trinity Aquifer) goes from effectively zero permeability to the longest cave in Texas. As a term, it’s worthless.”
The impact of this simple shorthand can create real gaps in understanding. When regulators use a term that flattens these distinctions, they make decisions based on an average that doesn’t exist anywhere in the actual ground. An area classified under the generic “Trinity” banner may appear low-risk because someone measured the primary permeability of the Upper Glen Rose — ignoring that a shaft through the Lower Glen Rose below it could deliver a surface contaminant directly to the water table.
Veni describes exactly this scenario happening with a USGS vulnerability map — he declines to name the location out of professional courtesy, but the lesson is clear. The map rated an area as low vulnerability. The analysis had only accounted for primary permeability. The fractures and conduits underneath it were invisible to the methodology. When we generalize with karst systems, we lose clarity of impact.
“Terminology negatively affects regulation,” he said. “People will overgeneralize, miss the details. Oh, you’re just a geology geek, you don’t know what we need. No. Go to your cardiologist and tell your cardiologist that you’re not having a heart attack, that he’s just a heart geek and you know what’s really going on. You don’t do that. But we do it in groundwater management.”
Veni, a sage philosopher, also objects to the phrase “the environment” for the same underlying reason. “If I say ‘the house burned down’ — too bad for those guys. If I say ‘our house burned down’ — that’s different. You respond differently. It personalizes it. It’s not the environment, it’s not something separate and apart from us. It’s our environment. And if we keep saying that, repeating it, at some point it will sink in.” Our environment is what we are made of. This shift in consciousness is required of us as stewards, scientists, and locals to be in right relationship with this place.
Science Is Not Political
In the early 1990s, the City of San Antonio convened a committee to develop new regulations for development over the Edwards Aquifer recharge zone. A management firm was hired to mediate between developers and environmentalists. George Veni was asked to participate.
He said no.
“I told them: you’re not serious. What you’ve done is you’ve got the butcher, the baker, and the candlestick maker, and you’re trying to find a compromise between people who are not hydrogeologists. If you were serious about this, you would put a team of expert hydrogeologists together, take the best hydrogeologic data available, then run it past the attorneys in case there are legal issues. At least be working from a base of the best knowledge available.”
The committee disagreed. So did the mediation firm. They told him he was being unrealistic.
A short time later, Veni was invited to testify before San Antonio City Council. The chambers were full — standing room only, developers on one side, environmentalists on the other. He described what he was going to say before he said it, and then said it. “Very slowly, very clearly, I said: what the developers want is irrelevant. The room erupts in cheers. When they quieted down, I said: and what the environmentalists want is equally irrelevant. Stone silence. And I said: you developed this as a compromise. It needs to be based on the science.” He has worked for both sides in the decades since. He has told environmentalists their concerns were not supported by evidence. He has documented real impacts from development. He follows where the data points.
“Passion and desire are not evidence,” he said. “I understand the desire to do something good, to protect our water, keep things clean. But that’s not enough. What does the science show? Because that’s the only thing, in the long run, that’s really going to make a difference.”
Veni’s wisdom comes from a few high profile studies over the years. In 2024 and 2025, Veni was called to the Dominican Republic by locals to evaluate cave damage near a new quarry. The caves in question contain some of the highest concentrations of pre-Columbian rock art in the Caribbean. His report documented the damage. The client kept it confidential for months, then released it to the public, without exactly communicating it to George. Two weeks after Veni left on his second trip, the president of the Dominican Republic gave his state of the union address, and directly referred to Veni’s now viral research, which had polarized the nation. The president shut down the quarries and sent the military to enforce it! “I’m glad to see the interest in protecting the land,” Veni said, with the measured tone of someone who has learned not to be surprised by either failure or success. “The story stays the same, no matter who I talk to. My recommendations were that they move to a different location.”
He made a parallel point about development in San Antonio — that his advice, consistently offered and consistently ignored, has been to stay off the recharge zone. Build south, southeast, west. He pushes back on the developers’ argument that they are merely following public demand northward. “As skilled marketers, they could make the south side of San Antonio sound just as fabulous. You can actually plant a garden there. You can dig a basement. But that’s not happening.” Veni tells us sincerely that if he could go back and do it all again, he would have helped create policies to never build in the aquifer recharge zone. As we rambled through Karst Canyon on the mule, the Woodcreek North subdivision coming in and out of the treeline, we imagined the impact of those 1,300+ empty lots of karst becoming homes and driveways.
At the international level, Veni organized the International Year of Caves and Karst in 2020 and 2021 — at least 1,490 events in 53 countries, reaching approximately 320 million people. UNESCO subsequently approved an annual International Day of Caves and Karst, to be held each September 13th, chosen for the date of the UNESCO headquarters celebration.
The Hill Country, he noted, sits atop one of the most scientifically significant karst systems in the world. The caves are here. The springs are here. The endangered species are here. The overpumped aquifer, the stalled model, and the pending lawsuits are here too. We represent a challenge to the limits of human patterns, and we also have the potential to demonstrate what aware, localized policy based in science can look like. Dr. George Veni embodies the devoted steward, bringing clarity and truth to the most misunderstood parts of our environment and our own limited perspectives.