Underground Reservoir Technology Advances

Texas summers are so hot that in many West Texas reservoirs, more water evaporates than gets used by people. In 2011, more water evaporated out of Lakes Travis and Buchanan in Central Texas than was used by their largest city customer, Austin.

So what about storing water underground — in manmade reservoirs?

More Texas communities are exploring the idea, which has found traction in states like Florida and California, and Texas lawmakers have introduced legislation to help it along. The basic concept of the technology — which is awkwardly named aquifer storage and recovery, or ASR — is to inject water into an aquifer for storage, hundreds of feet down, and pump it back up when it is needed. Proponents say that the technology reduces evaporation, is cheaper and faster to build than surface reservoirs, and avoids some of the issues associated with flooding land.

“You don’t flood a bunch of bottomland hardwoods, or take thousands and thousands of acres of cropland out of service,” said James Dwyer, an Austin-based engineer with CH2M Hill, an engineering company.

There are three such reservoirs in Texas — one in El Paso, one in Kerrville and a third in San Antonio. The $250 million San Antonio project, completed years ago, held about 91,000 acre-feet of water as of last October, which equates to about 8 percent of the total volume of Lake Travis near Austin. In the San Antonio project, Edwards Aquifer water that is already cleaned and chlorinated is injected 400 to 600 feet underground into the Carrizo Aquifer. When it comes back up, additional chloride and some fluoride are added before it is distributed to customers.

“I think this will be the future of water storage — it has to be,” said state Rep. Lyle Larson, R-San Antonio, who said he had recently visited the nation’s largest ASR project in Las Vegas, which opened in 1987 and has stored more than 320,000 acre-feet of water. “We can’t just continue to lose 50 percent of our product to evaporation, and our climate’s not getting any better.”

Larson has filed House Bill 3013, which makes clear that ASR projects are eligible for water-plan funding, such as the Legislature is separately considering. The bill has been referred to the House Natural Resources Committee but has not yet been heard in the committee.

HB 3013 also instructs the Texas Water Development Board to create guidelines for groundwater districts that would oversee ASR projects in their area. Larson said the “right of capture” enshrined in Texas law means that landowners own the water that comes up from under their land. A better regulatory framework is necessary, Larson said, to “make sure that the water [the ASR project has] stored is not taken by someone else. That’s the biggest apprehension, to be candid with you.”

Dwyer, the CH2M engineer, said that aquifer storage projects can cost just 10 percent as much as reservoirs, and the permitting process is far faster. One potential issue, he said, is minerals like arsenic getting into the underground water. This has been an issue in places like Florida, he said, but not in any of the three existing Texas ASR projects.

Jim Lester, president of the Houston Advanced Research Center, a nonprofit that focuses on sustainable technologies, said that Texas would want to avoid putting ASR projects in uranium-mining areas, but the technology can avoid the concerns about eminent domain that can cripple surface-reservoir projects. Also, “you don’t have to worry about dam safety,” he said.

Texas water experts say that other communities interested in the technology include Corpus Christi, New Braunfels and the Lavaca-Navidad River Authority. To move forward, ASR projects need a permit from the Texas Commission on Environmental Quality.

Senate Bill 1429, by state Sen. Juan "Chuy" Hinojosa, D-McAllen, would reduce study costs for a Corpus Christi groundwater district if it decides to go forward with an underground reservoir storage project. The bill is being discussed in the Natural Resources Committee.

Sanjeev Kalaswad, a program specialist with the Innovative Water Technologies program, an arm of the Texas Water Development Board that focuses on "nontraditional" water supplies, said that sandy aquifers and limestone can sometimes be good places to store water. (The Carrizo near San Antonio, where the San Antonio Water System stores water underground, is an example of a sandy aquifer.) “Clay is not good, that’s for sure, because it does not hold water,” he said.

Dwyer, the engineer, said that as Texas turns to reusing more nonpotable water, some of that could be stored in reservoirs. El Paso already does this, pumping cleaned-up sewage water into an aquifer for further, natural cleansing before it is pumped back up. Water utilities in Texas and elsewhere have not turned more to the technology, he said, because the utilities are by nature “risk-averse” and prone to looking warily at little-used technologies. 

Florida has had dozen of projects, and “it’s been a learning process,” said Bob Verrastro, lead geologist with the South Florida Water Management District. Water utilities there like the technology because it rains hardest in the summer, when the snowbirds have left the state and demand for water is low. Some projects injected water into aquifers that were too saline, and others had trouble pumping out as much as they put in, he said.

So in South Florida, roughly half the utilities discontinued the projects. But for “utilities where ASR has been successful — they love them,” Verrastro said.