Underground water bubble is huge help during drought

SAWS ASR facility pumped water out all year, now injecting water back in

SAN ANTONIO – Despite another drought-stricken year and very low aquifer levels, SAWS customers never faced Stage III restrictions. A reserve underground "bubble" of water, located at the Twin Oaks Aquifer Storage and Recovery Facility, or ASR as it is known, is a big reason why. As a resource, it had never been as valuable as it was in 2014.

"This year, we [pumped] almost the whole year because of the severe drought," said Roberto Macias, plant manager at the Twin Oaks facility.  "We started Jan. 2 and finally stopped this Monday. We ran over 11 months sending water into town, because they needed it."

It was the most ever needed since the inception of the facility. Millions of gallons per day traveled through a 25-mile pipeline to San Antonio; offsetting pumping restrictions.

As of Monday, water has now reversed course due to slowing demand.  It is being pumped from San Antonio and injected back into the storage facility. This process is expected to continue through early next year.

The ASR acts like a bank. Reserves are tapped into during times of need and, and now that demand is down, water is added back in. The facility came online in 2004 and built a surplus through 2010.

"We quickly found out that we could store much more water than we ever thought," said Darren Thompson, director of water resources for SAWS.

The ASR is a fascinating feat in engineering acting as underground, man-made water "bubble", suspended in sand located in the Carrizo Aquifer. Its location underground ensures no evaporation takes place.

"It's very good at holding the water where you put it," said Macias.

When it comes to how much water goes in and out, it is a delicate balancing act.

"We're doing lots of math," said Thompson. "Every week we look at drought conditions and how it's impacting the Edwards Aquifer."

Storing water is also a requirement for SAWS, through a joint agreement with the Edwards Aquifer Authority, called the Habitat Conservation Plan. By taking demand off of the Edwards Aquifer, spring flows are allowed to continue, protecting endangered species. 


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