Will the Carrizo-Wilcox go dry? No (but…)

I’ve gotten a couple calls about a recent Wall Street Journal article (paywalled) where I am “quoted” as saying the following about the Carrizo-Wilcox Aquifer:

“Robert Mace, executive director at the Meadows Center for Water and the Environment at Texas State University, said the aquifer could run dry much sooner, likely within 10 to 20 years.”

The first thing I’ll note is that is not a quote (no quotation marks)–it’s an interpretation of what I said, which was far more complicated and, as such, not ideal for a pithy newspaper article. What I said was that with everyone and their third uncle seeking permits and sinking wells into the Carrizo-Wilcox Aquifer (cities, fabs, data centers, and developments, among others), those wells would start interfering with each other enough to affect production, probably in 10 to 20 years.

Let me be clear: the Carrizo-Wilcox Aquifer will not go dry. However, the economics of producing big water from the aquifer might.

There’s a poo-ton of water stored in the Carrizo-Wilcox, on the order of millions of acre-feet. Folks (including some that should know better) take that volume, divide by current or projected use, and proclaim hundreds if not thousands of years of supply. Our water problems are solved! However, the Carrrizo-Wilcox is not a bathtub full of water simply pining for the pump. It’s much more complicated than that.

I hold that the value of confined aquifers such as the Carrizo-Wilcox is in their artesian heads, and artesian heads are easy to deplete. An artesian head is where an aquifer is under pressure such that water levels (hydraulic heads) are pushed above the top of an aquifer hydraulically capped with tighter rocks such as shale. Sometimes that pressure brings the water level above the land surface and a well can freely flow without the need of a pump. These wells are known colloquially as artesian wells. But note that an artesian well does not need to flow at land surface; it just needs a water-level above the top of the aquifer.

Artesian heads can be substantial. For example, artesian heads under Dallas used to be more than 1,000 feet above the top of the aquifer. The productivity of a well is not only a function of how easily water moves through an aquifer but also of the background head in the aquifer compared to the pumping level in the well. The larger the difference between the two, the greater your ability to produce water from the well and the aquifer. This is, in part, why the Vista Ridge project placed their well field in the deepest part of their water holdings, to take advantage of those artesian heads.

When those background heads decline, your ability to produce decreases. At some point, that decreased ability leads to decreased well production. In extreme cases, the reduction of artesian head causes groundwater production, at least for large users, to become economically nonviable. This happened in the Trinity Aquifer underneath Dallas and Fort Worth where pumpers depleted almost all the artesian head, thus decreasing well yields and forcing large water users to seek alternative water supplies. Note that in this case, less than 1% of the water stored in the aquifer had been removed before large pumpers abandoned the aquifer. In other words, the water stored in the aquifer was irrelevant.

And that’s my point.

Will the experience with the Carrizo-Wilcox Aquifer be different than the Trinity under Dallas and Fort Worth? Possibly. However, we’re already seeing large declines in artesian heads in the Carrizo-Wilcox. Long-term production in the Bryan-College Station area (Aggies!) has caused several hundred feet of water-level declines and affected water levels over an area 100 miles wide. The Vista Ridge Project turned on their pumps in 2020 resulting in hundreds of feet of water-level declines in just a few years. With substantially more pumping expected to come online, the pumping projects will start to interfere with each other, probably lowering yields.

But note my hedging (may, possibly, blahblahblah). Just because this happened in the Trinity Aquifer doesn’t mean it will happen in the Carrizo-Wilcox. The Carrizo-Wilcox transmits water more readily than the Trinity, so perhaps that offsets, in whole or in part, my concerns. In addition, the desperate need for water may offset any economic challenges to come. My “prediction” is a hypothesis subject to testing, and the testing will happen in real time.

The article’s author, Matt Wirz, has my deepest respect. He had a enormous job in distilling a lot of complicated issues down to their essence for a readable article. And you can see, based on what I wrote above, why a reporter (and his editors) would be disinclined to give me the podium. While I wince at the wording in the article (I’m an academic–wincing is required), the sentiments are accurate. The water that folks think is there may not be.

At the very least, the article is prompting discussions about the supply, and that is good news. And if you are a water user talking to your water supplier and they assure you by dividing the water in the bathtub by your use, I suggest you talk to someone else.