Expert Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Growing demands for water in many parts of the nation are fueling the search for new approaches to sustainable water management, including how best to store water. Society has historically relied on dams and reservoirs, but problems such as high evaporation rates and a lack of suitable land for dam construction are driving interest in the prospect of storing water underground. The National Research Council convened a committee to assess past experiences with managed underground water storage systems and to identify research priorities for development of future underground storage projects. The resulting report concludes that managed underground storage should be considered a valuable tool in a water manager's portfolio and recommends ways to address the unique challenges posed by managed underground storage systems through research and regulatory measures.

Key Messages

  • A better understanding is needed of potential removal processes for microbes and contaminants in the different types of aquifer systems being considered for MUS.
  • A better understanding of the contaminants that might be present in each of the potential sources of recharge water is needed, especially for underutilized sources of water for MUS, such as stormwater runoff from residential areas.
  • Although failures have occurred and the potential for contaminating groundwater is a considerable risk, most MUS systems have successfully achieved their stated purposes.
  • An independent advisory panel can provide objective, third party guidance and counsel regarding design, operation, maintenance, and monitoring strategies for an MUS project. An independent panel can increase public acceptance of and confidence in the system if such trust is warranted.
  • Antidegradation is often the stated goal of water quality policies, including policies that apply to underground storage of water. For any MUS project -- including storage of potable water, stormwater, and recycled water -- it is important to understand how water quality differences between native groundwater and the stored water will be viewed by regulators, who are charged with satisfying those regulatory mandates.
  • Growing experience with MUS systems indicates that hydrogeological feasibility analysis including aquifer characterization is one of several important components in their development and implementation. The benefits of doing so include establishing the hydraulic capacity, recharge rates, residence times, and recoverable fraction of the introduced water -- all of which help identify the optimum design and viability of the MUS system.
  • MUS projects can exhibit numerous and complementary economic benefits, but they also entail costs. Some of those benefits and costs are unlikely to be incorporated in the calculations of individual water users that is, there may be spillover costs to third parties or spillover benefits that are not given market valuations.
  • New surrogates or indicators of pathogen and trace organic contaminant presence are needed for a variety of water quality parameters to increase the certainty of detecting potential water quality problems through monitoring. The categorization of chemicals and microorganisms into groups with similar fate and transport properties and similar behavior in treatment steps is one approach to streamline the list of potential contaminants to be monitored.
  • Pathogen removal or disinfection is often required prior to storing water underground. If primary disinfection is achieved via chlorination, disinfection by-products (DBPs) such as trihalomethanes and haloacetic acids are formed. These have been observed to persist in some MUS systems.
  • Regulations are, quite properly, being developed at the state level that will require a certain residence time, travel time, or travel distance for recharge water prior to withdrawal for subsequent use.
  • Relatively little research has been done to characterize the extent of vertical migration of fine-grained particles into the sediments beneath surface spreading facilities. Likewise, the science and technology of cleaning recharge basins is not well developed.
  • Some simple forms of MUS have been used for millennia, and even the most recent development -- aquifer storage and recovery -- now has about four decades of history behind it. These systems use water from a variety of sources such as surface water, groundwater, treated effluent, and occasionally stormwater.
  • Some states have created statutory schemes that are tailored to MUS projects.
  • Successful MUS involves careful and thorough chemical and microbiological monitoring to document system performance and evaluate the reliability of the process. Each MUS project needs real-time monitoring of the quality of the waters being introduced into underground storage and of waters being extracted from storage for use.
  • The development of an MUS system from project conception to a mature, well functioning system is a complex, multistage operation requiring interdisciplinary knowledge of many aspects of science, technology, and institutional issues.
  • The federal regulatory requirements for MUS are inconsistent with respect to treatment of similar projects.
  • The presence and behavior of emerging contaminants (e.g., endocrine disrupting compounds, pharmaceuticals, and personal care products) is of concern, especially with reclaimed wastewater.
  • Water resources development has been characterized by substantial federal and state subsidies. As water shortages intensify, the political pressure for investment in new technologies will increase.
  • Groundwater numerical modeling at regional and/or high resolution local scales provides a cost-effective tool for planning, design, and operation of a MUS system
  • Long-term local and regional impacts of MUS systems on both native groundwater and surface water have been recognized, including changes in groundwater recharge, flow, and discharge, and effects on aquifer matrix such as compaction of confining layers or clay interlayers during recharge and recovery cycles.
  • Surface spreading facilities sometimes require large amounts of land, particularly where large amounts of water are recharged or the geology is not ideal. Recharge well systems require less land but may have as many different factors to consider in their placement. Optimization of recharge facility placement is important but not always well understood.
  • The challenges to sustaining present and future water supplies are great and growing. The present overdrafting of aquifers and overallocation of rivers in many regions is a clear indication of these challenges, but the former also creates in many cases the underground storage potential needed to accommodate MUS systems. Thus, demand for water management tools such as MUS is likely to continue to grow.
  • The subsurface has the capacity to attenuate many chemical constituents and pathogens via physical (e.g., filtration and sorption), chemical, and biological processes. In places where the groundwater quality is saline or otherwise poor, the implementation of MUS will likely improve overall groundwater quality and provide a benefit to the aquifer.
  • To facilitate the siting and implementation of MUS systems, maps of favorable aquifers and hydrogeological characteristics can be prepared using three-dimensional (3-D) capable geographical information systems (GIS).