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7 Managed Underground Storage in A Water Resource Systems Context Las Vegas, Nevada, is not the only community in the United States that faces major uncertainties about its water supply. Nor are concerns about the future adequacy of water supplies confined to the arid and semiarid regions of the country. Even with increased water use efficiency and reduced per capita urban use, the prospects for continued growth of population and the economy will fuel increases in demand for municipal and industrial water. The demand for agricultural water is likely to increase as world demand for U.S. food and fiber grows with global population and as an increasing amount of irrigated acreage is put into production for the making of biofuels such as ethanol and biodiesel. Simultaneously, the continuing struggle to define and find adequate supplies of water to support environmental uses will contribute further to the growing national demand for water. At the same time, there are reasons for believing that available water sup- plies may diminish. Groundwater overdraft tends to be the rule rather than the exception nationally. Ultimately, the inevitable decline of overdraft will lead to lower aggregate levels of extractions and a diminution of available supply. Threats to water quality will continue and some of those threats will materialize, leading to contamination episodes that may render some accustomed supplies unfit for use at least on a temporary basis. Finally, current and prospective global climate change threatens to alter both the magnitude water available in some regions and the timing of water availability. The result is that our water resource systems will be characterized by growing demands and static or shrink- ing supplies. Indeed, such circumstances characterize the global water situation as well as that in the United States (Jury and Vaux, 2005). Globally, demands are increas- ing as population grows and an increasing numbers of countries no longer have sufficient water resources to provide the water services, sanitation, and food and fiber needs of their populations. The numbers of countries in these circum- stances will grow in the next two decades. Groundwater overdraft is pervasive worldwide and even more alarming than it is in the United States. Thus, for example, India and China are today feeding 400 million people with crops irrigated with unsustainable overdraft. It is not at all obvious where the water to feed these people will be found once the aquifers in question are economically exhausted (Jury and Vaux, 2005). In the United States, total withdrawals of freshwater from 66 major aquifers were es- timated at 93.3 million acre-feet (83,300 million gallons per day [Mgal/d]) for the year 2000 (Maupin and Barber, 2005). Many of these aquifers are receiving only small amounts of recharge, and considerable storage space has been created 269
270 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER through these long-term withdrawals. In particular, the greatest available storage for development of managed underground storage (MUS) systems may be in unconsolidated and semiconsolidated sand and gravel aquifers. Thus, in the appropriate circumstances, managed underground storage will offer communi- ties and regions throughout the world an opportunity to address problems of overdraft as well as another tool that can be integrated into a balanced system for managing water scarcity. The growing scarcity of water will require that water be managed more carefully and that it be used more intensively. More intensive use implies that the productivity of water in existing uses will have to be increased and also that waters that currently are not used, or are underutilized, must be the object of more intensive exploitation. Examples include flood flows (Boxes 5-4 and 5-5), urban stormwater (the stormwater-to-drinking water project in Salisbury, Aus- tralia described in Chapter 6) and reclaimed wastewater (numerous examples throughout the report).. Similarly, water will have to be managed in an inte- grated unified way that acknowledges explicitly the interrelatedness of the hy- drologic cycle and the interrelatedness of water and other natural resources. This represents a departure from the way water resources have been developed and managed in the United States. Until the late to midâtwentieth century the primary means of responding to water scarcity was to build surface water storage and conveyance projects. Sur- face water storage ultimately fell from favor because: (1) the low-cost sites were soon all developed, leaving only opportunities that were considerably more ex- pensive; (2) the costs of constructing civil works projects grew faster than other costs in the economy; (3) the competition for public funds became keener, mak- ing it more difficult to secure the financing necessary to construct large surface water facilities; and (4) the environmental damages and social impacts associ- ated with the construction and operation of surface water storage facilities be- came fully manifest at a time when public environmental awareness was grow- ing. There followed a period in which the emphasis shifted away from surface storage toward programs of conservation and more intensive management of water supplies. Improved techniques for managing water on-farm were devised and disseminated. Improved technology, including closed conduit irrigation sys- tems and water saving appliances, were developed and adopted relatively widely. The public became more aware of water and more aware of behaviors that economize on water use. Water transfers began to be accepted. Transfers included the trading of water rights and entitlements, the purchase of water in spot markets, and the development of contingent markets for water. Such trans- fers have the capacity to reallocate water away from relatively low-valued uses to relatively higher-valued use, thereby ensuring that the productivity of water is optimized. They have the added advantage of being voluntary so that no one is coerced into participating in a water transfer. There has also been a returned appreciation for the importance of some form of storage as a means of capturing and holding water that is available only
MANAGED UNDERGROUND STORAGE IN A WATER RESOURCE SYSTEMS CONTEXT 271 during wet seasons or years and of keeping that water in a location where it can be accessed readily to meet demands, whether for municipal, industrial, agricul- tural, or environmental and habitat purposes. Several methods of water storage have recently been explored and utilized that do not involve use of larger, on- stream reservoirs, including tanks and towers, former mines, and gravel pits; each of these has its own challenges and benefits. With these various water supply storage and management tools available, it has been possible to address many water scarcity issues by relying predomi- nantly on a single strategy, such as surface water storage, or a single subset of strategies like conservation measures and transfers. However, in the future no single strategy, or even a small subset of strate- gies, is likely to suffice. Even the recycling of water has its limits due to con- sumptive use on each cycle. Rather, what will be needed is an integrated strat- egy in which all measures for managing water scarcity are considered and, if appropriate, employed in a balanced, systematic fashion. In an earlier report, a committee of the National Research Council (NRC, 2004) called for water to be viewed and managed in a broad systems context The methods and techniques for managing scarcity will also have to be cast in a broad systems context so that water resources can be managed in an integrated fashion that acknowledges the interrelatedness of the hydrologic cycle and among natural resources. Managed underground storage will have to be part of this broad balanced strategy. Although much can be accomplished through programs of water conserva- tion, careful management of water, and the utilization of markets to accomplish water transfers, additional water storage will be required as the population and economy of the nation continue to grow. Managed underground storage has be- come attractive because it offers many of the benefits of surface water storage, often at less expense and without the environmental damages associated with surface water storage projects. Thus, for example, MUS can be employed to âfirm upâ water supplies that are highly variable across seasons and years. In a related way, managed underground storage can be utilized to provide drought protection and protection against the failure of surface infrastructure systems that are vulnerable to earthquakes and other natural hazards. It can also be used to improve the financial and operational efficiency of water production facilities, such as desalination and water purification plants, allowing these facilities to operate at relatively steady levels of output despite seasonal variability in water demands. In a word, storage increases the flexibility with which water can be managed. Beyond these benefits, which can be attributed to virtually any type of water storage, managed underground storage has the added benefit that it can be used to attenuate or eliminate groundwater overdraft, and such systems can also pro- vide conveyance in lieu of expensive surface water conveyance systems. Thus, there are a number of instances where managed underground storage projects have been used to meet growing demands from newly developed areas in order to avoid the costs of expensive surface conveyance systems. In addition, given the magnitude of annual groundwater overdraft in the United States, as well as,
272 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER its cumulative magnitude, there is already an enormous amount of storage ca- pacity underground and that capacity is growing daily. As a consequence, MUS has a very important potential role in addressing the intensifying water scarcity of the future. Collective experience with MUS systems is substantial. A significant num- ber of these systems are decades old, and experience indicates that many of them perform consistently and well over the longer term. However, managed under- ground storage is not a panacea. It is likely to be costly, although it is increas- ingly the least-cost alternative, and cannot by itself resolve all of our water scar- city problems. By reducing stormflow or return flows from wastewater treat- ment plants to streams, it can decrease water availability for people or ecosys- tems downstream. It can, however, play a very important role in balanced pro- grams to manage water scarcity. In anticipating, planning for, and developing MUS projects, it will be vital to bear in mind the need to view and manage water in a broad systems context. This can be greatly facilitated by the existence of regional water districts, au- thorities, and agreements of various kinds. For example, since 1972 Florida has been divided into five water management districts, which roughly correspond to surface watersheds; the South Florida Water Management District coordinates water supply, ecosystem restoration, and coastal and terrestrial water quality on a large scale. Other efforts are much newer. For example, the South Metro Wa- ter Supply Authority (Denver) was formed in 2004. It is composed of 13 water providers that have created a single master plan to foster long-term reliable wa- ter supplies through water acquisition and infrastructure. An extreme example of a regional water management approach is an agreement by which Arizona stores Colorado River water in an aquifer on behalf of Nevada. When Nevada needs to recover the water, it withdraws a quantity of Arizona's Colorado River water directly from Lake Mead, while Arizona with- draws the equivalent amount of water from the aquifer. Integrated programs of water management will differ from place to place in the balance of measures ultimately selected and in the water management schemes employed. This, of course, is a straightforward consequence of the fact that most potable water is supplied at fairly local scales and involves decisions by municipal or county politicians responsible to local constituencies. However, the complex water management challenges described throughout this report generally require a broad systems approach in conceiving, designing, building, and operating MUS projects. Six elements of such an approach are summed up in the following paragraphs. First, it is imperative that the connections between ground- and surface wa- ter be acknowledged and recognized in conceiving and designing such project. Ground- and surface waters are frequently interconnected, and alterations in the state of groundwater, for example, can have unintended consequences for inter- connected surface waters. As discussed in earlier chapters, groundwater pump- ing can lower or even eliminate baseflow in streams that support fisheries, agri- culture, or other uses. Surface water diversions to supply water for recharge
MANAGED UNDERGROUND STORAGE IN A WATER RESOURCE SYSTEMS CONTEXT 273 basins may have a similar effect. Such interconnections need to be understood and acknowledged in project planning and operations. Second, the interdependent nature of ground- and surface water quality also needs to be acknowledged. Waste sinksâland, air, and waterâcannot be man- aged in isolation from one another. In part, this is because a high qualitative standard in one sink implies a low quality standard in either or both of the other sinks. Similarly, the quantitative and qualitative status of surface water has im- plications for the quantitative and qualitative status of groundwater and vice versa. There are two mechanisms of connection: (1) degradation of surface wa- ter quality can ultimately lead to degradations in groundwater quality and vice versa; (2) regulations that call (for example) for a high standard for groundwa- ter and a low or no standard for surface water inherently ignore the interconnec- tivity and hydrological interrelatedness of water resources. The circumstances in which it makes sense to lower the quality of water in one place (e.g., surface water) in order to protect it in others (e.g., groundwater) are few. At the same time it is important to recognize the differences in waste assimilative capacity of surface and groundwaters in designing appropriate regulations. Third, with the greater use of MUS projected for surface water, including stormwater, the integration of water supply and water pollution control will be even more crucial in the future. Rather than depending primarily on technology for water treatment, controlling contamination of streams from combined sewer overflows, failing septic systems, and agricultural and urban runoff will be an important part of the solution (NRC, 2000, 2005). Since many of the regions considering MUS are located along or near coastlines, which are characterized by both intensive recreational activity and highly sensitive ecosystems, the qual- ity and quantity of water that reaches the coast is often of keen interest to water and natural resource managers (NRC, 1993). Integration of water supply and storage with stormwater runoff, pollution control, and coastal management is therefore a strategy that provides benefits across a broad sector of society. Fourth, there is a need for additional specific research efforts in order to fa- cilitate the development and implementation of MUS schemes. Some of this research is necessarily local and focused on a specific water system and its al- ternatives. However, this research should complement regional and national studies that, in turn, form part of an integrated national program of water re- sources research (NRC, 2004). The research recommended in this report does not stand in isolation from other areas of water research and is not necessarily of higher priority than all other water research needs. A reinvigorated program and its priorities need to be developed by a national partnership that includes federal, state and local interests as well as representative stakeholders (NRC, 2004). Fifth, there is a need for data and monitoring in connection with the devel- opment and operation of MUS projects. This need should be viewed from the perspective of a larger national need to reinvest in monitoring, data acquisition, and data retrieval for water resources. Specifically, the trend of disinvestment in water resources monitoring, data acquisition, and retrieval needs to be reversed soon if the nation is to address successfully, and at reasonable costs, its mount-
274 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER ing water resources problems. The need for data on generalized aquifer charac- terization and specific aquifer properties should be viewed as one element in a collaborative national program of monitoring and data collection for water re- sources. Sixth, there is a compelling need to devise appropriate institutions for the management of underground storage systems as well as the broad integrated systems that will ultimately be required to manage water scarcity. Existing laws and regulations are often inconsistent. Frequently, it is difficult to make them both effective and flexible. Management responsibilities are often fragmented among agencies, with the result that programs are uncoordinated, transactions costs are higher than they need to be, and integrated approaches to water prob- lems are difficult to develop. Agency missions and programs are sometimes too narrowly conceived as with single-purpose agencies and programs whose man- dates effectively prohibit them from viewing water problems in a broad systems context. Many existing institutional arrangements embody poorly conceived incentives that have led to unintended consequences. Also, many existing water institutions were designed in different eras for different purposes and are now ill-suited to address contemporary and future problems. Despite the compelling need for innovative institutions, support for research on institutional topicsâ research that may be the basis for institutional innovationsâhas fallen to near zero in recent decades. The need for modern institutions capable of managing underground storage, as well as water management systems in general, both efficiently and effectively is clear and urgent (NRC, 2001, 2004). Overall, albeit focused on issues surrounding managed underground stor- age, this report has highlighted the complexity of modern water management, especially in areas facing population growth, increasing competition for water for energy and the environment, earlier seasonal snowmelt, and other climate change issues. It has underlined how the interconnectedness of groundwater and surface water has opened new opportunities for conjunctive water management and identified potential risks to human and environmental health. It also has underscored some of the challenges to finding creative solutions in a legal and regulatory environment that was not created to facilitate such solutions. While managed underground storage is just a part of the answer to societyâs water management challenges, it is hoped that cities, states, and the nation will devote the necessary resources to learning how important a role MUS can play on a national scale. CONCLUSIONS AND RECOMENDATIONS Conclusion: Although failures have occurred and the potential for con- taminating groundwater is a considerable risk, most MUS systems have success- fully achieved their stated purposes. In fact, there are MUS systems that have functioned without major problems for decades. However, increasing efforts to use karst and fractured aquifers for storage will increase the potential for fail-
MANAGED UNDERGROUND STORAGE IN A WATER RESOURCE SYSTEMS CONTEXT 275 ures. Chemical reactivity of the aquifer in the former case, and uncertainty over flow paths in either case are much greater and the treatment potential is lower compared to alluvial aquifers. Learning from past positive and negative per- formance will help guide development of the many new MUS systems that are under consideration. Recommendation: Given the growing complexity of the nationâs water management challenges, and the generally successful track record of managed underground storage in a variety of forms and environments, MUS should be seriously considered as a tool in a water managerâs arsenal. Conclusion: In the future, multiple strategies are likely to be needed to manage water supplies and meet demands for water in the face of scarcity. Various water conservation and management strategies, including transfers and water recycling, can be used to stretch available water supplies. However, each of these has its limits. The use of water storage facilities remains an essential component of water management, particularly in areas where water availability varies greatly over seasons or years, such as the arid Southwest. Integrated strategies will be needed in which all measures for improving water quality and managing water scarcity are considered and, if appropriate, employed in a bal- anced, systematic fashion. Seasonal to multiyear storage of water will often be a necessary component of such strategies. Recommendation: In anticipating, planning for, and developing MUS pro- jects, water managers should consider the role and merits of MUS in conjunc- tion with other water management strategies. REFERENCES Jury W. A., and H. Vaux. 2005. The role of science in solving the worldâs emerging water problems. Proc. Nat. Acad. Sci. 102 (44):15715-15720. NRC (National Research Council). 2005. Regional Cooperation for Water Qual- ity Improvement in Southwestern Pennsylvania. Washington, DC: National Academies Press. NRC. 2004. Confronting the Nation's Water Problems: The Role of Research. Washington, DC: National Academies Press. NRC. 2001. Envisioning the Agenda for Water Resources Research. Washing- ton, DC: National Academies Press. NRC. 2000. Watershed Management for Potable Water Supply: Assessing New York City's Approach. Washington, DC: National Academies Press. NRC. 1993. Managing Wastewater in Coastal Urban Areas. Washington, DC: National Academies Press.