Estimates indicate that Texas loses between five to six million acre-feet of water per year to evaporation from surface water supply reservoirs. These evaporative losses are huge — equivalent to 25 percent of the statewide water demand in 2010. Near Austin, Lake Travis lost 206,000 acre-feet in 2011, significantly more than the 166,000 acre-feet the city used that year. In a hot and dry climate, and with Texas facing a growing gap between water supply and demand, water storage reservoirs plagued by evaporation contribute to loss of a valuable resource. Aquifer storage and recovery (ASR), whereby water supplies are stored underground, may provide a useful strategy for managing and protecting water supplies. However, in order for ASR to be effective, Texas will need to enact policies that ensure the protection of groundwater resources and property rights and, ideally, ease the regulatory disconnect between surface water and groundwater.
ASR works by pumping excess water (for example, surface water or treated municipal or industrial wastewater) into aquifers for short- or long-term storage. (A successful ASR project requires that water remain in the aquifer and not travel to the surface via a spring, for example.) When needed, that water is pumped and put to beneficial use. ASR offers a number of benefits over conventional surface reservoirs. Storage aquifers may be located — provided the hydrogeology supports it — where the water is needed most, such as underneath a metropolitan or agricultural area. ASR may also reduce the need to build surface reservoirs, which are controversial, expensive, prone to silt build-up, limited by topography and harmful to the environment. Additionally, ASR may stabilize or reverse water levels in an aquifer that has declined due to heavy pumping. But perhaps most importantly, ASR permits the storage of large amounts of water in a way that protects the water from evaporative losses.
In the United States, there are 133 active ASR projects, including projects in Arizona, Nevada, Colorado, California, Florida and Washington. ASR — also known as underground water storage and recovery — has played a key role in Arizona’s water management plan since 1986. The state uses both infiltration basins over highly porous soil and injection wells to refill its aquifers. The Arizona Department of Water Resources issues all permits for the projects, and only renewable sources of water that cannot be used directly may be stored long-term. The department tracks all volumes of stored and recovered water. Arizona’s water plan is an example of conjunctive use, the coordinated management of surface and groundwater. This type of regulatory system facilitates implementation of complex ASR projects and allows for storage of excess surface flows underground, safe from an arid climate that would cause severe evaporation losses.
The Texas Legislature authorized ASR in 1995, and currently, three ASR projects (El Paso Water Utilities, City of Kerrville, and San Antonio Water System) are operating in Texas. The system in El Paso injects treated municipal wastewater into the Hueco Bolson aquifir. Kerrville treats excess flows from the Guadalupe River to drinking water standards prior to storage in the Lower Trinity aquifer. In San Antonio, ASR allows the San Antonio Water System to draw its full allotment from the Edwards Aquifer. This water is treated to drinking water standards and stored in the Carrizo-Wilcox aquifer, where 60 million gallons per day may be pumped in times of need. As parts of the state head into a fifth year of drought, expansion of ASR projects is being discussed in the 2015 legislative session (HB 655). Although the practice is currently allowed under Texas law, a number of hurdles exist for widespread implementation of ASR.
First, would-be ASR developers in Texas are constrained by burdensome permitting requirements. In order to gain a permit, an ASR developer must first obtain a temporary permit and execute a pilot project, which is then evaluated by the Texas Commission on Environmental Quality before a longer-term permit may be issued. To implement an ASR project, developers must meet the requirements both for a permit (or permit amendment) to appropriate state water and for a Class V injection well permit. Class V wells inject nonhazardous liquids into or near underground sources of drinking water. Additionally, if the project is to be located in an aquifer under the jurisdiction of a groundwater conservation district or multiple districts, the developer must also comply with district rules. Likewise, entities that would collect flood flows — water otherwise entering the Gulf of Mexico — for an ASR project must acquire a surface right for these flows, an expensive and time-consuming proposition.
As lawmakers in Austin seek to facilitate the use of ASR in Texas, it is important that they take into account a number of considerations, namely the question of conjunctive use, protection of groundwater resources, and property rights — of those who store the water and those who own any surrounding native groundwater. Texas law regulates surface water and groundwater separately; these disparate regimes make the implementation of a robust ASR program that takes advantage of greater surface flows during unseasonably wet years difficult. A regulatory framework that considers the connectivity between surface and groundwater would greatly aid water planning and management. Lawmakers should also mandate sufficient safeguards to ensure that groundwater resources are protected. This may be accomplished by testing or treating water prior to infiltration or injection. And finally, any successful ASR scheme must utilize sufficient hydrogeological modeling and adequate groundwater pumping monitoring to insure the injected water will be available in the future for beneficial use. Properly managed ASR projects can provide evaporation-proof water reservoirs, protect groundwater resources and increase water security.
Additional sources:
http://www.twdb.state.tx.us/innovativewater/asr/
http://www.edwardsaquifer.net/pdf/TWDB_2011_ASR_assessment.pdf
http://twri.tamu.edu/publications/txh2o/summer-2014/is-it-time-for-texas-to-welcome-asr/
http://www.twdb.texas.gov/innovativewater/asr/projects/pirnie/doc/2011_03_asr_final_rpt.pdf
__________________________________________________________________________________________________
Regina M. Buono is the Baker Botts Fellow in Energy and Environmental Regulatory Affairs at the Baker Institute Center for Energy Studies.
Katherine R. Zodrow is a postdoctoral research associate at the Baker Institute Center for Energy Studies and the Department of Civil and Environmental Engineering at Rice University.