Aquifer Storage and Recovery: Stored Today, Saved for Tomorrow May 2017

Aquifer storage and recovery (ASR) is a water supply and storage solution that is gaining traction in Texas and providing beneficial results for entities with active ASR systems. ASR is the use of an aquifer to store water from a different source or location during times when water is available, and the recovery of that water during times of need. The same well can be used for both putting water into an aquifer and taking it out.

As we've seen in regional and state water plans, interest in ASR projects has grown in recent years. In the 2017 State Water Plan, seven regional water planning groups (regions E, F, G, J, K, L, and O) included ASR as a recommended water management strategy. In total, ASR could create about 152,000 acre-feet of new water supply per year by 2070, constituting about 1.8 percent of all recommended water management strategies in the 2017 plan.

Before an ASR program can be implemented, though, scientific studies must be completed to determine whether ASR would be successful in a location. As the funding and science arm of the State of Texas for water supply and infrastructure projects, the Texas Water Development Board (TWDB) is able to provide grants for feasibility studies when funding is available. Our subject matter experts take an active role in overseeing the progress by reviewing quarterly progress reports, draft and final reports, and the raw data used in their development, as well as proposing changes as needed. The data from the studies is available to the public on the TWDB website. Loans through our state and federal finance programs may also be available for facility construction costs.

The scientific studies conducted for a potential ASR project can be extensive and require multiple phases. The ability to use ASR to meet water needs depends on several factors, including having (1) a source of water to store, (2) an aquifer nearby that is chemically compatible with your water and physically able to store the desired volumes, (3) capacity to treat the water before it is put into the aquifer, and (4) an affordable project.

In a typical ASR project, the feasibility study aims to help determine if ASR as a strategy looks like a possible fit for the entity. The contracted team usually reviews existing water quality, well construction, and well yield data (how much water the existing well produces). They also study the geological structure where the ASR field might be located and confirm whether there are areas within the aquifer that can physically receive the volume of water to be stored. Less permeable aquifers may not be able to receive large volumes of water or may need more wells spread over a larger area to handle the desired volume. The aquifer doesn't have to be fresh; brackish (and more saline) aquifers are also potential hosts for ASR. In general, an ASR project will lose some of the injected water to the surrounding aquifer, and the amount of water lost depends on the volume of stored water, the time of storage, and properties of the aquifer.

If the study concludes that ASR could be economically feasible, an entity may proceed to collect site-specific information. There are many ways to go about this. It typically involves drilling and sampling from the subsurface and looking at the physical and chemical composition of the rock from the zone where the water would be stored. Chemical compatibility between the stored water and the aquifer—both the aquifer's water and the host rock—is necessary. Chemically incompatible water stored in an aquifer could clog up the well and aquifer or release unwanted constituents from the aquifer such as arsenic, iron, and manganese. Source water for an ASR may need to be treated to ensure its compatibility with the aquifer. Although the process from idea to implementation of an ASR project can be lengthy, the science behind it is crucial.

Last month, we featured the San Antonio Water System (SAWS) H2Oaks Center, home to SAWS' ASR facility. Now 13 years old, the project was more than 10 years in the making when it began operating in 2004 as the Twin Oaks Aquifer Storage and Recovery facility. Much of that time was dedicated to research, feasibility studies, and prototypical tests to ensure long-term success. Source water from the Edwards Aquifer is transported to the ASR facility and stored in the Carrizo Aquifer. With 29 ASR wells, 60 million gallons per day of recovery and treatment capacity, and 120,000 acre-feet of storage, the facility is the third largest ASR system in the United States.

Another successful—although much smaller—ASR system is in Kerrville. In the mid-1980s, the City of Kerrville realized a need for additional water supplies due to estimated future population growth, water demand, and water supply. A series of studies and evaluations partially funded by the TWDB were completed between 1988 and 1992, and the first of two wells became operational in 1998. The facility diverts water from the Guadalupe River, treats the surface water to potable standards, and stores it in the Lower Trinity Aquifer. As of March 2017, the Kerrville system had approximately 2,537 acre-feet of water in storage, with potential for additional wells. The City reports that the ASR system has increased their water supply and provided a more diverse and flexible water system.

To help more communities potentially implement ASR projects, the Texas Legislature has taken an active interest in ASR and other innovative water supply strategies. In 2015, the 84th Legislature appropriated $1 million to the TWDB for demonstration projects or feasibility studies to prove up ASR or innovative storage approaches. With that funding, the TWDB was able to give three grants for ASR-related studies in Corpus Christi, New Braunfels, and Victoria. The TWDB is overseeing these studies.

The Corpus Christi ASR Conservation District, in partnership with the City of Corpus Christi, will perform exploratory drilling to evaluate the brackish portion of the Gulf Coast Aquifer as a potential storage location. This is the first drilling program to evaluate this portion of the aquifer. It will entail drilling test wells, analyzing the geochemistry of the subsurface environment, and running groundwater models to estimate the movement of stored and recovered water during ASR operations.

The Edwards Aquifer Authority, in partnership with New Braunfels Utilities, plans to drill in the brackish zone of the Edwards Aquifer to analyze it for ASR compatibility and to evaluate its hydraulic properties. The data collected from these tests will provide New Braunfels Utilities the information needed to permit an ASR well to assist in developing a full-scale ASR system. This is the first project to evaluate the brackish portion of the Edwards Aquifer as a potential storage location.

The Victoria County Groundwater Conservation District, in partnership with the City of Victoria, plans to convert an existing groundwater production well to an ASR well and store water in the Gulf Coast Aquifer. The well will be used for testing recharge, storage, and recovery of treated water from the city's distribution system. The project is the first in Texas to attempt retrofitting an existing groundwater production well to an ASR well.

ASR can be a competitive alternative water supply, despite the path to implementation being varied. Thankfully, the sharing of key learnings and insightful data is paving the way for communities across Texas to be more informed about this innovative solution and the sound scientific approaches necessary for its success.