SAWS: Twin Oaks - Aquifer Storage & Recovery
Aquifer Beaker

Edwards Aquifer

Aquifer Level 645.3'
8/20/18 - Official

The Edwards aquifer and its catchment area in the San Antonio region is about 8,000 square miles and includes all or part of 13 counties in south-central Texas.

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Stage 2:
Water On Your Day

Watering with an irrigation system or sprinkler is allowed only once a week from 7-11 a.m. and 7-11 p.m. on your designated watering day as determined by your address.

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Aquifer Level 645.3 | Stage 2: Water On Your Day

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Twin Oaks - Aquifer Storage & Recovery

Aquifer Storage & Recovery

Achieving water supply diversity through efficiency and innovation.

Among the rolling ranchlands of southern Bexar County, San Antonio Water System operates one of the largest reservoirs of its kind anywhere in the U.S. — filled with enough water to supply the entire city for four months. Never seen it? That's because it's all underground! Let Sarah take you on the 90 second tour.

The Aquifer Storage & Recover program is a key component of the SAWS 2017 Water Management Plan. The first major project funded by SAWS customers through the Water Supply Fee, SAWS opened the Twin Oaks ASR (location is now known as H2Oaks Center) in June 2004.

ASR technology is relatively new. SAWS stores excess Edwards Aquifer drinking water during rainy times in a large-scale underground water storage facility in south Bexar County for use during our dry South Texas summers or prolonged droughts. SAWS recovered more than 50,000 acre-feet*An acre-foot of water is equivalent to 325,851 gallons. of stored Edwards Aquifer water during the record-breaking drought between 2011 and 2014.

What are the Benefits of ASR Technology?

  • Environmentally friendly method of storing Edwards Aquifer drinking water in the Carrizo Aquifer.
  • Water stored during the year can be used during dry, hot periods.
  • Maximizes use of pumpage allocations from the Edwards throughout the year.
  • Underground storage means no evaporation.
  • Less vulnerable to contamination than surface storage.
  • Most land directly above the underground reservoir can continue its prior use.

ASR Model

ASR technology is a proven method of storing water underground. SAWS enlisted the help of some of the world's leading ASR experts on this project. The concept is simple. Water is pumped from the Edwards Aquifer throughout the year and stored in the Carrizo Aquifer in southern Bexar County. Later, during the hot, dry periods, the drinking water is pumped back into the existing distribution system to help meet demand. If water is not required to be recovered during the current year, it can remain in storage until required in a future year.

As of February 2018, more than 157,000 acre-feet of water was stored underground.

Why use an ASR technology in San Antonio?

  • Allocations from Edwards Aquifer are limited by legislation and Edwards Aquifer Authority rules.
  • During wet periods, there was no method to store allocations that were not used.
  • There is no carry over or credit for pumping rights not used in a given year. This means "use it or lose it."
  • Stored water recovery can lessen the effect of drought on the Edwards Aquifer.
  ASR Demand Curve
 

We strive to be environmentally sensitive leaving our job sites – like this one near the ASR project – preserved in their natural splendor.

Saving for a Sunny Day

About 200,000 acre-feet*An acre-foot of water is equivalent to 325,851 gallons. or more of excess Edwards Aquifer water can be diverted to storage in the Carrizo Aquifer (injection mode). The water is withdrawn during dry periods (recovery mode) to help maintain spring flows in New Braunfels and San Marcos, ensuring the protection of endangered species. This also lessens the effect of drought on the Edwards Aquifer.

More Facts About Aquifer Storage and Recovery

  • H2Oaks Center is the third largest groudwater ASR facility in the nation.
  • While not required by state law, a mitigation program has been implemented to assist area well owners that may be impacted by draw down during the recovery phase.
  • 29 ASR wells constructed.
  • Approximately 60 million gallons per day (mgd) well field capacity.
  • 30 mgd water treatment capacity.
  • 45 miles of 45-inch steel pipe and 10 miles of 42-inch steel pipe integrating water at Artesia, Seale and Randolph pump stations.
  • Environmentally friendly method of storing Edwards Aquifer drinking water in the Carrizo Aquifer.
  • Water stored during the year can be used during dry, hot months.
  • Maximizes use of pumpage allocations from the Edwards throughout the year.
  • Underground storage means less evaporation.
  • Less vulnerable to contamination than surface storage.
  • Most land directly above the underground reservoir can continue its prior use.

Rev. 4/2018