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Groundwater supplies in the United States have been on the decline since the 1950s as climate change advances and dependence on groundwater grows. One long-established method for boosting groundwater supplies is enhanced aquifer recharge (EAR), or the replenishing of groundwater reserves with water from other sources.

Besides shoring up water supplies, EAR has broader benefits that can include mitigating land subsidence and saltwater intrusion, and even restoring ecosystems. However, until recently, EAR research efforts have disproportionately focused on improving water quantity and not quality. The problem with this approach is that when water is injected into aquifers, it often disturbs geochemical chemical conditions and mobilizes toxic contaminants, such as dormant, naturally occurring substances like arsenic and uranium, or introduces new contaminants, such as pesticides. These substances can leach from sediments and soil and compromise the water. Adding to the complexity is that different regional locations have dissimilar geologies and hydrologic events (i.e., snow melts or flooding).

“Once you start artificially putting water into aquifers, you can really meddle with the geochemistry in those systems and create conditions that promote the contamination of groundwater supplies,” said Sarah Fakhreddine, an assistant professor of civil and environmental engineering. “That’s one reason why there’s been some hesitation surrounding EAR.” Yet, the need to ensure the security and supply of water underscores the push to understand the complexities associated with EAR so that we can apply it in safe, innovative ways.

Fakhreddine, who is a geochemist by training, is the lead investigator on a three-year, $1.8 million grant from the U.S. Environmental Protection Agency (EPA) that will increase our knowledge of the potential mobilization of contaminants and their risks to water quality in U.S. aquifer systems.

“Enhanced aquifer recharge is the idea that when we have excess water, like during a wet season or flood, we can capture that water and store it in aquifers for times when we really need it. Our goal is to make sure that when EAR is implemented, we fully understand the opportunities and limitations. And one of the big challenges is that the geochemical processes that control water quality really depend on where and how you implement a project,” says Fakhreddine. Factors to consider include the water source used for recharge, the area’s hydrogeology, current geochemistry of the aquifer, and how the aquifer has been historically managed.

Resilience is going to come down to having a diverse portfolio of different management practices that water managers can use.

Sarah Fakhreddine, Assistant Professor, Civil and Environmental Engineering

Fakhreddine and her team will conduct a nationwide study assessing the geochemical compatibility of aquifers with nearby water sources, which can include excess surface water and treated wastewater. The team, comprised of geochemical and hydrology experts, will leverage publicly available datasets, modeling tools, and community input to create a framework to access risks and implement safe enhanced aquifer recharge projects nationwide. They will use their findings to develop guidelines for siting, designing, and operating EAR projects so that contaminant mobilization is limited. Outputs from the project will include a guidance document, technical report, and a web-map tool to help decision-makers, including water managers and regulators.

The researchers highlight that “there is currently no water quality guidance that spans regional settings, source waters and EAR types to support safe adoption of fit-for-purpose EAR.” Fakhreddine’s project could change that, and ultimately help provide water to communities affected by extreme heat and drought.

“This study is very much focused on managed aquifer recharge, but that is just one water management practice among many,” says Fakhreddine. “It’s important to remember that there is no silver bullet solution to the water challenges we face in the future. Resilience is going to come down to having a diverse portfolio of different management practices that water managers can use.”

In addition to Carnegie Mellon University, other research institutions participating in the project include the University of California, Davis and the University of Texas at Austin, in partnership with the Ground Water Protection Council.