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1 Introduction Between 1990 and 2000, over 700,000 people found their way to the Las Vegas metropolitan area (http://www.census.gov/prod/2001pubs/c2kbr01-2.pdf). They found homes, settled in, and turned on their taps. Miraculously, water came out. One day it might not. With thousands of newcomers per month moving into the areaâa phenomenon repeated in other states such as Arizona and Texasâ water managers are challenged as never before to do more with less. Snowpack in the western and northeastern United States appears to be decreasing (Mote et al., 2003; Hodgkins and Dudley, 2006), and groundwater overdrafting through- out the nation continues unabated in many locations. Portions of aquifers in every state along the Atlantic Coastal Plain, from New Jersey to Georgia, have had to be protected and managed to prevent continued reductions in groundwa- ter levels, land subsidence, and saltwater intrusion. The increasing pressures on water in the western United States have been highlighted in the U.S. Bureau of Reclamationâs Water 2025 initiative (Figure 1- 1). Eastern states have also moved toward planning programs to address de- mands related to scarce water resources due to periodic droughts, increasing populations, changing land use, and the links between water use and environ- mental protection (Virginia Department of Environmental Quality, 2001). Av- erage temperatures in many regions of the country are rising and are projected to continue to do so; in such areas, both supply and evaporative losses may be headed in unhelpful directions. Conservation is an important water management tool, but a 10 percent savings of waterâa significant figureâwould take care of only 18 months of population growth for a city that is growing at a rate of 7 per- cent per year, as is the case for Las Vegas. Then what? Historically, the answer has been to build a dam. Throughout the last few centuries, about 76,000 dams more than 2 m high were constructed on our rivers and streams (http://crunch.tec.army.mil/nid/webpages/nid.cfm), and many of these had seasonal or interannual water storage as their primary function. Yet with evaporation rates of 120-200 cm in states such as Arizona (see http://www.water.az.gov/dwr), the limited availability of land for construction, and the high environmental costs to stream and riparian wildlife, the building of dams and reservoirs scarcely seems to be an approach that will provide much relief in the future. All of these considerations portend increasing stresses on our water supply in the coming years and increasing burdens on our water managers. New strate- gies for water managementâwith respect to both quality and quantityâwill be required on a broad geographic scale. Options for addressing these issues 13
14 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER FIGURE 1-1 Potential water supply crises and conflicts in the western United States by the year 2025. SOURCE: U.S. Bureau of Reclamation. Available online at http://www.doi.gov/ water2025/report.pdf. Accessed September 24, 2007.
INTRODUCTION 15 include improving water use efficiency through technology and conservation, increasing supply through importation and desalination, and reuse of treated wastewater. With or without these strategies, however, there is often a need for tempo- rary detention and storage of water during times of abundance for release during times of need. Because of the shortcomings often associated with storage in aboveground reservoirsâincluding evaporative losses, land consumption, and ecological impactsâthere is increased interest in storing recoverable water un- derground as part of an overall water management plan. Storing surface water underground seems counterintuitive to many people, who consider this a "waste" because the water may move away from the recharge area and not raise the wa- ter table at all. The counterarguments to this are hydrogeological (see Chapter 3) and are not described here. Suffice it to say that while some recharged water may, indeed, never be recovered, the same is true for surface water stored in reservoirs. The circumstances under which groundwater storage may or may not be desirable relative to surface storage are among the primary themes of this report. The water to be stored may come from streams or groundwater (with or without treatment at water treatment plants), water reclamation plants, stormwa- ter, or other sources. It may be recharged through wells or infiltration basins into sands and gravels, limestones, granites, or volcanic rocks. The water may be stored for days, months, seasons, or several years. The stored water may be recovered from the aquifer by the same well that recharged it or by a downgra- dient well. After recovery, it may be used for drinking water, industrial pur- poses, golf course or lawn irrigation, agriculture, or aquatic habitat restoration. While several terms have developed over the years to describe various as- pects of this concept, with examples provided in Box 1-1, none of the existing words or expressions in the field of water management quite describes this con- cept in its entirety. For the purposes of capturing the full range of approaches considered in this study, the committee proposes the term âmanaged under- ground storage of recoverable waterâ (MUS), the rationale for which is de- scribed in Box 1-2. In this report, MUS is used to denote purposeful recharge of water into an aquifer system for intended recovery and use as an element of long-term water resource management. Managed underground storage (MUS) systems would encompass both sys- tems in which water is recharged directly using wells (including dual-purpose recharge and recovery wells) and systems that use infiltration basins. However, the term as defined would exclude riverbank filtration systems (no storage) and underground disposal of brines or recharge of water for the sole purpose of miti- gating land subsidence or aquifer depletion or to prevent saltwater intrusion (no planned recovery of the water). It is recognized, of course, that there are gray areas, such as water recharged primarily to prevent saltwater intrusion that is partially recovered on the land- ward side of the subsurface âmound.â Such are the hazards of creating new jar- gon.
16 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER BOX 1-1 Terms Used to Describe Related Water Management Approaches Involving Recharge â¢ Aquifer storage and recovery (ASR)âinjection of water into a well for storage and recovery from the same well. â¢ Aquifer storage transfer and recovery (ASTR) âinjection of water into a well for storage and recovery from a different well, generally to provide additional wa- ter treatment. â¢ Artificial recharge (AR) âintentional banking and treatment of water in aquifers. â¢ Artificial recharge and recovery (ARR) ârecharge to and recovery of water from an aquifer; that is, both artificial recharge of the aquifer and recovery of the water for subsequent use. â¢ Augmentation pondâwater body designed to supply water to river systems at defined rates during particular times. â¢ Bank filtrationâextraction of groundwater from a well or caisson near or under a river or lake to induce infiltration from the surface water body, thereby improv- ing and making more consistent the quality of water recovered. â¢ Conjunctive useâcombining the use of both surface and groundwater to mini- mize the undesirable physical, environmental, and economic effects of each solu- tion. â¢ Dry wellâsynonymous with vadose zone well. â¢ Infiltration basinâsynonymous with recharge basin. â¢ Managed (or management of) aquifer recharge (MAR)âintentional banking and treatment of water in aquifers (synonymous with AR). MUS may be consid- ered a subset of MAR. â¢ Recharge basin (or pond)âa surface facility, often a large pond, used to in- crease the infiltration of surface water into a groundwater basin; basins require the presence of permeable soils or sediments at or near the land surface and an unconfined aquifer beneath. Recharge wellâa well used to directly recharge water to either a confined or an unconfined aquifer. â¢ Soil aquifer treatment (SAT)âtreated sewage effluent, known as reclaimed wa- ter, is intermittently infiltrated through infiltration ponds to facilitate nutrient and pathogen removal in passage through the unsaturated zone for recovery by wells after residence in the aquifer. â¢ Surface spreadingârecharging water at the surface through recharge basins, ponds, pits, trenches, constructed wetlands, or other systems. â¢ Spreading basinâsynonymous with recharge basin. â¢ Underground storage and recovery (USR) âsimilar to MUS; any type of pro- ject whose purpose is the artificial recharge, underground storage, and recovery of project water. â¢ Vadose zone wellâa well constructed in the interval between the land surface and the top of the static water level and designed to optimize infiltration of water. Many additional technical terms and abbreviations may be found in the Glossary. SOURCES: Bouwer (1996); State of New Mexico, 2001, Available online at http://www.ose.state.nm.us/doing-business/ground-water-regs/ground-water-regs.html; Well Abandonment Handbook; Dillon (2005); Municipal Water District of Orange County, available online at http://www.mwdoc.com/glossary.htm; Arizona Department of Water Resources: Underground Storage and Recovery Regulations, available online at http://www.azwater.gov/dwr/Content/Find_by_Program/Wells/WellAbandonmentHandbook 5.pdf; WRIA Watershed Management Project, available online at http://www.wria1project. wsu.edu/watershedplan/WMP_Master_Glossary.pdf.
INTRODUCTION 17 BOX 1-2 Whatâs in a Name? While the concepts and practices of recharge, storage, and recovery of water have ex- isted for many years, the terms used to describe them are varied widely, and have changed over the years. In determining the terms to use as part of this study, the committee re- viewed existing terms (see Box 1-1). Some of these terms, such as infiltration ponds, de- scribe only the recharge method. Others, such as Aquifer storage transfer and recovery (ASTR), refer to single-purpose wells whereby recharge occurs in one well and recovery occurs in a downgradient well. Aquifer storage and recovery (ASR) generally refers to dual-purpose recharge and recovery wells. Other terms, such as Arizonaâs Underground Storage and Recharge (USR), were coined by legislatures or regulatory agencies in devel- oping laws and rules to describe a range of activities. In Australia and other counties, management of aquifer recharge (MAR) describes intentional banking and treatment of water in aquifers (Dillon, 2005). At the risk of adding another term to a crowded field, the concept of âPurposeful re- charge of water into an aquifer system for intended recovery and use as an element of long-term water resource managementâ requires its own phrase. For this, the committee selected managed underground storage of recoverable water (MUS). This term is slightly different from the original term developed in the creation of the study, which was sustain- able underground storage of recoverable water. The rationale for the selection of this term is as follows: Managed captures the idea that these systems are deliberately and intentionally de- veloped and operated to meet specific objectives while preventing or mitigating adverse impacts on human health and the environment. While committee members supported the concept of the development of these systems in an economically, physically, and environ- mentally sustainable manner, a consensus existed among the committee that the term âsustainableâ could not be specifically defined within the broad context of this report. The term âmanaged,â however, implies the existence of a manager, or project proponent, who is accountable for the development and operation of the system, with oversight by regulatory agencies. Underground storage refers to the deliberate placement of water into an underground location through a recharge method, which could include surface infiltration and percolation through the vadose zone to a saturated aquifer or placement directly to an underground location in a saturated aquifer. The committee has described the operation of vadose zone wells in the report, but has found few successful systems to evaluate for physical, water quality, and institutional factors. The term âstorageâ also implies that the manager of the project intends to recover the water for a particular useâas opposed to systems where the intent of the recharge is primarily to prevent land subsidence, control saltwater intrusion or movement of contaminant plumes, or generally raise groundwater levels. Recoverable water reinforces the concept that the water is being stored with the intent of recovery for a particular use. The ultimate use of the water to be stored impacts the ways in which the system is developed, operated, and regulated, particularly when re- claimed water is the source water. The committee hopes that the acronym MUS will become a useful and well- understood addition to the water management lexicon. The number of MUS projects is increasing rapidly. In 1983, there were three operating aquifer storage and recovery (ASR) systems in the United States. By 1994 there were 22 of these recharge well projects, and as of late 2005, there were about 72 systems in operation (Figure 1-2), with approximately 100 more in development (Pyne, 2005). These are located not only in the arid southwest-
18 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER 80 70 Number of ASR systems in the United States 60 50 40 30 20 10 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year FIGURE 1-2 Growth of aquifer storage and recovery systems in the United States, 1968- 2005. SOURCES: Pyne (1994, 2002); Pyne, ASR Systems, written communication, De- cember 11, 2005. Reprinted with permission from Pyne (2005). Copyright 2005 by Pyne. ern United States and in the Atlantic Coastal Plain areas, but also in the Pacific Northwest and even in the Midwest (Figure 1-3). The nationâs oldest ASR sys- tem is employed by the seaside resort community of Wildwood, New Jersey (population 5,436) and the technology is being considered for use by New York City (population 8,000,000). In the Florida Everglades, more than 300 wells have been envisioned to recharge up to 3.8 million m3 of water per day for eco- logical use, flood control, and water supply (USACE and SFWMD, 1999), while the Southern Nevada Water Authority currently has the largest ASR wellfield intended primarily for potable water supply, with more than 50 wells. At the other end of the spectrum, many small coastal towns along the Atlantic recharge water seasonally in small, one-well ASR systems to limit seawater intrusion and store water for the summer tourist season (AWWA, 2002). Suburban communi- ties in Oregon, Washington, and Colorado are developing underground storage capacity, rather than relying on agreements with larger cities that possess surface storage facilities to meet their growing water demands. Recharge through surface spreading has also grown increasingly common since early attempts in the late 1800s and is now employed in major metropoli- tan areas. For example, alluvial aquifers in Los Angeles County and the Santa Ana River watershed have been recharged through surface spreading of local river water, imported water from other watersheds, and recycled water. Today such managed recharge provides a majority of groundwater replenishment in
INTRODUCTION 19 FIGURE 1-3 Distribution of aquifer storage and recovery systems in the United States, 2005. SOURCE: D. Pyne, ASR Systems, written communication, December 11, 2005. Reprinted with permission from Pyne (2005). Copyright 2005 by Pyne. Southern California. Groundwater basins in this region support a population of more than 15 million people. In Orange County alone, managed recharge of more than 300 million m3 of water per year offsets the pumping demands on the Orange County groundwater basin, which provides well over half of the water needs for 2.3 million residents (http://www.ocwd.com). The principal wholesale water agency in the region, the Metropolitan Water District of Southern California, has developed storage agreements in several groundwater basins to provide additional supplies for drought years and emergencies. The Orange County Water District is currently constructing the largest indirect potable reuse facility in the world, which will provide 88 million m3 of highly treated recycled water per year for recharge using both wells and surface spreading. Other projects to store water under- ground are in operation or in development for many areas of the Southwest, in- cluding the rapidly growing communities of Las Vegas and Phoenix. In short, MUS has become a widely accepted tool in water managersâ portfoliosâ although, in areas of the country where this approach has not yet been applied extensively, it may still be perceived as experimental or impractical. Despite the growing utilization of MUS and its many successes, there re- main many questions about the conditions under which oneâs proposed goals can be achieved and the consequences of the use of MUS systems at large scales. Mineral transformations that occur during storage are poorly understood, as are the conditions under which inorganic or organic chemical contamination
20 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER problems may be either improved or exacerbated. The long storage times associ- ated with underground aquifers suggest that the consequences of these projectsâ either beneficial or detrimentalâwill also be long-lived. In addition to questions about the physical, chemical, and biological aspects of MUS, the widespread interest in using MUS to address water supplies raises the question of whether existing water institutions are positioned to manage the long-term and widespread consequences of such systems or to facilitate the most effective strategies. A novel technology can be a challenge for water laws and institutions that have existed for decades. Some jurisdictions have responded with specific statutory schemes that facilitate the review and implementation of MUS projects. In other areas, regulatory hurdles still greet new MUS project proposals. Interjurisdictional issues are not uncommon, since aquifer boundaries are rarely aligned with institutional boundaries. Distinct laws govern the same water before, during, and after recharge, leading to uncertainties as to how cur- rent water rights laws might apply. Ownership and responsibility when re- charged water moves in the ground, or causes perturbation of surrounding water supplies, may be unclear. Current regulation of aquifer storage systems is in the early stages of development in many parts of the country. Interagency project regulation is also often an issue, since MUS systems represent uniquely interrelated concerns of groundwater protection, water supply and water resources management and (if the system is used to store water in- tended for potable use) drinking water. Where wells are used for recharge, the federal Underground Injection Control (UIC) program applies to MUS projects. The UIC program is implemented directly by the U.S. Environmental Protection Agency (EPA) in some states and by state agencies in others. States may have their own water quality standards, over and above federal requirements, that must be followed to protect groundwater and, in some instances, drinking water supplies. Some states have developed formal procedures for review of project permit applications to involve various water quantity and quality regulatory agencies, as both state and federal agencies to streamline the regulatory and permitting process and define agency roles. Still, ensuring that management of MUS systems is performed in a balanced approach that addresses water use, groundwater protection, and drinking water regulatory concerns can be a chal- lenge. The growing interest in underground storage of water raises the need for a better understanding of MUS. There are now enough operational systems that information on long-term performance in a range of geologic and hydrogeologic environments is available. These technologies will clearly be used even more widely in the future, and an ability to evaluate the likely success of a proposed system with some accuracy is critical. Based on this, the Water Science and Technology Board organized a plan- ning meeting in Washington, D.C. in April 2003, cosponsored by the AWWA Research Foundation (AwwaRF), to assess the degree of interest in the topic, followed in time by this consensus study. A large number of institutions con-
INTRODUCTION 21 tributed financially to this report (see preface ii). The statement of task (Box 1- 3) was primarily derived from feedback received during this planning meeting. The report is intended to (1) provide an integrated assessment of physical, chemical, operational, and institutional issues; (2) identify gaps in the science and practice that limit our understanding and provide a prospective examination of how these gaps might be closed; (3) provide guidance to prevent development of systems founded on unsubstantiated assumptions or poorly conceptualized models; (4) improve the accuracy of predictions of system performance over time, especially with respect to plugging or dissolution of the aquifer; and (5) provide a scientific basis for monitoring plans to track performance of opera- tional systems and to gain knowledge for the design of future systems. The report also discusses financial and economic considerations within the context of BOX 1-3 Statement of Task Note: the original statement of task used the phrase âSustainable Underground Storageâ in lieu of âManaged Underground Storage.â The proposed study will provide an overview of some of the research and education needs and priorities concerning managed underground storage technology and implemen- tation. It will also assess geological, geochemical, biological, engineering, and institutional factors that may affect the performance of such projects, based in part on a review and evaluation of existing projects. Specifically, the study will assess and make recommendations with respect to re- search and education needs on the following questions: â¢ What research needs to be done to develop predictors of performance for under- ground storage projects based on the character of the recharge water in terms of contaminants, disinfectants, and microbes, the hydrogeology and major ion geo- chemistry of the source water and the aquifer, and the well or basin characteris- tics? â¢ What are the long-term impacts of underground storage on aquifer useâ hydraulic, geotechnical, geochemical, adsorptive capacity of contaminantsâat wellhead and regional scales, and can these impacts be ameliorated? â¢ What physical, chemical, and geological factors associated with underground storage of water may increase or decrease human and environmental health risks concerning microbes, inorganic contaminants such as nitrite, disinfectant by-products, endocrine disruptors, personal care products, pharmaceuticals, and other trace organic compounds? â¢ Are there any chemical markers or surrogates that can be used to help assure regulators and the public of the safety of water for groundwater recharge? What should we monitor and at what spatial and temporal scales? â¢ What are the challenges and potential for incorporating managed underground storage projects into current systems approaches to water management for solv- ing public and environmental water needs? â¢ How do the institutional, regulatory and legal environments at federal, state, and local levels encourage or discourage managed underground storage?
22 PROSPECTS FOR MANAGED UNDERGROUND STORAGE OF RECOVERABLE WATER challenges and opportunities. Although economic impacts are important consid- erations in MUS project planning and management, a comprehensive discussion of the topic is outside the scope of this study. To address the issues associated with MUS and meet the objectives in its statement of task, the committee met five times over a period from February 2005 to June 2006 in Washington, D.C. (twice), Irvine, California, Phoenix, Arizona, and Woods Hole, Massachusetts. The first four meetings were partly open session for information gathering and discussion; the final meeting was closed in its entirety. The committee reviewed and evaluated existing informa- tion, including that published previously in journals, consultantsâ reports, or presented orally at the meetings. Chapter 2 further defines the concept of MUS systems (summarized briefly above), provides further information on the development and history of MUS systems and how they function, and identifies the major issues associated with MUS systems to be addressed in the subsequent chapters of this report. Chapter 3 examines hydrogeological factors that determine the feasibility of aquifer re- charge, identifies knowledge gaps and research barriers in understanding hydro- geology of MUS, and outlines recommendations for further research. Chapter 4 focuses on water quality of the source, aquifer, and recovered wa- ter, particularly as related to human health and the environment. Chapter 5 ad- dresses economic, legal, and jurisdictional considerations of MUS systems. Chapter 6 has been included to address the management aspects of MUS sys- tems, providing a review of the stages of an MUS project and examining some key operational issues including clogging, monitoring and indicators, public perception, and financial considerations. Finally, Chapter 7 presents MUS in an overall water resource systems context for the nation. Within this structure, there are numerous cross-cutting themes. For exam- ple, monitoring of MUS systems is addressed as a general issue in Chapter 2, with more specific monitoring issues explored from hydrogeological, water quality, regulatory, and management perspectives in Chapters 3, 4, 5, and 6, respectively. CONCLUSION 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 cre- ates 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.
INTRODUCTION 23 REFERENCES AWWA (American Water Works Association). 2002. Survey and Analysis of Aquifer Storage and Recovery (ASR) Systems and Associated Regulatory Programs in the United States. Denver, CO: AWWA. Bouwer, H. 1996. Issues in artificial recharge. Water Science and Technology 33: 381-390. Dillon, P. 2005. Future management of aquifer recharge. Hydrogeology Journal 13:313-316. DOI 10.1007/s10040-004-0413-6. Hodgkins, G. A., and R. W. Dudley. 2006. Changes in late-winter snowpack depth, water equivalent, and density in Maine, 1926-2004. Hydrological Processes 20 (4):741-751. DOI: 10.1002/hyp.6111. Mote, P. W. 2003. Trends in snow water equivalent in the Pacific Northwest and their climatic causes. Geophysical Research Letters, 30, DOI 10.1029/2003GL0172588. Municipal Water District of Orange County. Glossary. Available online at: http://www.mwdoc.com/glossary.htm. Last accessed November 13, 2007. Pyne, R. D. G. 2005. Aquifer Storage Recovery: A Guide to Groundwater Re- charge through Wells. Second ed. Gainesville, FL: ASR Press. State of New Mexico. 2001. Arizona Department of Water Resources: Under- ground Storage and Recovery Regulations. Available online at http://www.ose.state.nm.us/doing-business/groundwater-regs/groundwater- regs.html. Accessed November 13, 2007. Well Abandonment Handbook. Available online at http://www.azwater.gov/dwr/ Content/ Find_by_Program/Wells/ WellAbandonmentHandbook5.pdf. Ac- cessed November 13, 2007. WRIA Watershed Management Project., Available online at http://www.wria1 project.wsu.edu/watersheplan/WMP_Master_Glossary.pdf. Accessed No- vember 13, 2007. USACE and SFWMD (U.S. Army Corps of Engineers and South Florida Water Management District). 1999. Central and Southern Florida Comprehensive Review Study Final Integrated Feasibility Report and Programmatic Envi- ronmental Impact Statement. Available online at http://www.everglades plan.org/pub/restudy_eis.cfm. Accessed May 2004. Virginia Department of Environmental Quality. 2001. Status of Virginiaâs Wa- ter Resources: A Report on Virginiaâs Water Supply Planning Activities. Richmond, VA: Commonwealth of Virginia.