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1 Groundwater and Society Groundwater, water stored in and transmitted through geologic ma- terials uncler saturated conditions, is a critical national resource and is often the limiting resource for growth ant] development. The U.S. Geo- Togical Survey (USGS) Water Resources Division (WRD) historically has taken the lead among federal agencies in gathering and distributing groundwater information. The WRD has established a Ground-Water Resources Program (GWRP) to "examine and report on critical issues affecting the sustainability of the nation's ground-water resources." Four activities have been given top priority (USGS, 1998~: · Scientific assessments of critical groundwater issues: Key issues identified by the USGS include groundwater depletion, groundwater- surface water interactions, freshwater/saltwater relations, and ground- water processes in complex geologic environments. · Regional and national overviews: Ongoing status reports on the nation's water resources. · Improved access to ~roundwater data: Easy-to-use Internet inter- faces and a national groundwater database. · Research and methods development: New tools for groundwater investigations. As noted in the Preface, the committee endeavored in this study to provide general guidance to the USGS on the development of such a program relevant to regional and national assessment of groundwater re- 6
Introduction 7 sources and to render a consensus opinion on whether the four proposed activities are consistent with national priorities and the mission of the WRD. A different National Research Council ~C) committee (Research Opportunities and Priorities for the EPA, or "ROPE" committee) was given a similar but broader charge in 1995; it was asked to identify and prioritize issues to be addressed in research by the U.S. Environmental Protection Agency (EPA). That committee not only reported on a list of issues, but also made more general recommendations (NRC, 1997a). Of note, the committee recommended that problem-driven research at the EPA be balanced with core research, which emphasizes gaining im- proved understanding of physical, chemical, and biological processes that underlie environmental systems. This advice seems relevant to the USGS National Groundwater Program. The USGS shares an interest with other agencies, including the EPA, in advancing understanding of such processes. The wording of the USGS priority of "scientific as- sessments of critical groundwater issues" allows latitude in balancing problem-driven research with core research. However, the committee believes that core research should not be done ad hoc but should be ap- proached explicitly and systematically, as a vital component of a na- tional groundwater program. The USGS has a long tradition of systematically building the base of understanding of geologic and hydrologic properties on a state-by-state basis, through its district offices. Studies of processes have also been undertaken, but less systematically. The present challenge is to begin working in a multiple-district, regional context, achieving a national synthesis. To some extent this was done in the Regional Aquifer-System Analysis (RASA) Program (Sun and Johnson, 1994) in which the hy- drostratigraphy of adjacent states was reconciled and interpreted to cre- ate regional maps and conceptual process models. It is now necessary to broaden that perspective by integrating processes as well as properties across regions, and extrapolating the understanding of processes at key sites to larger areas. The need for national synthesis is driven by the needs of federal policy and decision-makers. This need is likely to in- crease as environmental decisions achieve a more integrated global scope. The committee concurs with earlier NRC reports (e.g., NRC, 1997a) that the task of environmental monitoring and investigation of gIobal- scale issues is too great for any one agency. Interagency cooperation is
8 Investigating Groundwater Systems necessary, as is rapid dissemination of research and data. "Providing accessible groundwater data" and "regional and national overviews" are appropriate priorities and are fundamental to information dissemination to cooperators, decision-makers, and other scientists. Finally, in addition to providing data and regional and national over- views, the USGS should devote resources to the development of research tools and methods. Highly efficient state-of-the-art tools are needed for measuring environmental variables (e.g., groundwater quality, ground- water levels, subsidence, permeability, and fluxes), for modeling systems and their interactions (e.g., surface water-groundwater interactions), and for interpreting or communicating information for wide use, especially in decision-making. Because the USGS's task in environmental moni- toring and basic data gathering is enormous, a strong incentive for effi- ciency exists. We concur, therefore, that "research and methods devel- opment" is a high-priority activity. Having broadly endorsed the stated priorities, the committee dis- cussed and researched the implications of these priorities for the WRD's activities. The Statement of Task (see the Preface) inspired the eight following questions, which guided the committee's discussions: 1. What are the major groundwater problems and core research needs of the nation? (Chapters 1 and 4) 2. How is the term "region" defined? What constitutes a "regional" assessment? (Chapter2) 3. How should regional issues be identified and prioritized by the WRD? (Chapter3) 4. How can issue-driven studies be generalized and synthesized at regional and national scales? (Chapter 4) 5. Can cooperation among the various WRD programs, and among the four USGS divisions, help the WRD to undertake its priority activi- ties? (Chapter 3) 6. What kinds of collaborative arrangements with other local, state, federal, and private institutions would assist the WRD in carrying out regional assessments? (Chapter 3) 7. What tools and methods for streamlining core research and prob- lem-centered research hold the most promise for development and use by the WRD? (Chapter4) S. What groundwater information do the clients ant] cooperators of WRD require, and in what format? How can that information be
Introduction made as widely and rapidly available as possible? (Chapter 5) 9 Advocating future directions for the USGS WRD first requires an argument for devoting resources to the study of groundwater at a re- gional scale, and then it requires an argument that the proposed direc- tions are appropriate for the USGS. The remainder of this chapter ad- dresses the first argument; Chapter 2 addresses the historic and future USGS role in groundwater investigations. A CRITICAL RESOURCE Drinking and Irrigation Water Water for drinking and irrigation is perhaps society's most limiting natural resource. Groundwater constitutes only 22 percent of all fresh- water used in the United States, but it provides 62 percent of the potable water supply. Roughly 50 percent of the U.S. population and 97 percent of the rural population rely on groundwater as their primary source of drinking water (Figure 1.1~. About 40 percent of the nation's public water supply comes from groundwater (Alley et al., 1999; Solley et al. 1998~. In Florida, for example, the Biscayne aquifer is the only source of drinking water for more than 3 million people, about one-quarter of the state's population. In the San Antonio, Texas, area, the Edwards aquifer is the sole source of drinking water for over ~ million people. Similarly, in the Middle Rio Grande basin, the Santa Fe Group aquifer system is the sole source of municipal supply for the city of Albuquerque and many of the surrounding communities, serving about 40 percent of New Mexico's population. The need for drinking water supplies is not expected to lessen. Based on trends from the past 45 years, water use is expected to grow as population increases, despite per capita declines in use attributed to en- ergy cost, efficiency, conservation and reuse, and regulation (Solley et al., 1998~. Especially in the water-poor western states, the persistent search for potable water to fuel urban growth has resulted in pressures on water supplies that may not be sustainable. A variety of water-supply problems have been documented and discussed in NRC reports on small- to large-scare systems ~C, 1997b,c; NRC, 1998~.
10 Investigating Groundwater Systems f :: I: ~~ i: .. ~~ -~sIt39 ~~- ~~r ~= .~n t~ FIGURE 1.1 Percentage of population using groundwater as drinking water in each ofthe 50 states, as of 1995. SOURCE: USGS, 1998. Groundwater is also the mainstay of agriculture- about 64 percent of all groundwater is used for irrigation. Groundwater provides about 37 percent of irrigation and livestock water supplies nationwide, but in states such as Iowa, Illinois, Mississippi, Missouri, and Wisconsin, this figure is over 90 percent (Solley et al., ~ 998~. As discussed above, agri- cultural and urban areas are increasingly in competition for the same water resource base. Streamflow and Ecosystems In the past few decades, the coupling of surface and groundwater systems has become increasingly apparent. Groundwater-surface water interaction is now recognized as the primary control for such processes as wetland function and riparian habitat maintenance and the geochemi- cal and hydrologic fluxes across the recharge and discharge boundaries of shallow aquifer systems. Groundwater-surface water interactions involve both matter (in-
Introduction 11 eluding organisms) and energy, and they occur at all spatial and temporal scales (Winter et al., 1998~. Interactions can occur between groundwater and streams (Harvey and Bencala, 1993), lakes (Winter, 1981), wetlands (Siegel, 1988), and estuaries, bays, and coastal areas (Correll et al., 1992; Valiela et al., 1992~. Figure 1.2 depicts some of the interrelation- ships between a stream and its adjacent groundwater reservoir. Changes in groundwater levels may have major impacts on surface water systems. Rivers literally have been rerouted (Reisner, 1993) or completely dried up (Figure 1.3) by pumping. Conversely, large vol- umes of stream water may infiltrate into riverbanks at high stage. Bank storage is an important flood-wave attenuation mechanism that is used extensively in engineering hydrology and flood-routing calculations; it also sustains riparian vegetation and may improve surface water quality (Whiting and Pomeranets, 1997~. However, detailed field and modeling studies have also revealed the complexity and variability of shallow groundwater flow paths and their interconnection with streams, lakes, and wetlands. The direction and magnitude of flows between the two systems can vary rapidly in response to even small changes in boundary conditions (Squillace, 1996; Wondzell and Swanson, 1996; Morrice et al., ~ 997~. These changes, in turn, may have a major impact on critical habitats in these environments. Similarly, riparian buffers are increasingly recog- nized as playing a crucial role in mitigating the flux of nutrients and flood water for large systems such as the Missouri and Mississippi River ba- sins and Chesapeake Bay. The biological and riparian processes con- trolling nutrient loads and critical habitats for migratory waterfowl and endangered species in these unique environments are dependent on groundwater-surface water interactions over the range of riparian flow regimes. Water quality changes in one of the reservoirs may also manifest themselves in the other. Water from a contaminated stream may be drawn into an aquifer by groundwater pumpage (Duncan et al., 1991~. This contaminated groundwater may eventually discharge back into sur- face water (SquiTIace et al., 1993~. A THREATENED RESOURCE A limited understanding of the nature of groundwater flow and re-
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14 Investigating Ground water Systems has resulted in a legacy of groundwater contamination associated with accidental, improper, or unintended waste disposal. Historically, waste disposal practices relied on landfi~ling, with little regard for the possible connection between groundwater and the surrounding environment. In some cases, direct injection of liquid waste into aquifers has been util- ized as a waste disposal "technology" in residuals management. By the 1950s, the contamination of the nation's waters by mining, agricultural and industrial chemicals, and sewage had so compromised water supplies that a broad array of federal and state environmental laws and statutes were enacted (NRC, 1993, 1998~. These laws have pro- vided substantial protection against further contamination, but many water supplies have been, and continue to be, damaged or threatened by sIow-moving contaminant plumes. Also, as noted earlier, groundwater contamination has the potential to reach surface water bodies and the organisms that live in them. The public recognizes groundwater contamination as a health threat because of highly visible litigation, notably Love Canal, New York (Ma- zur, 1998), and Woburn, Massachusetts the site described in the book and movie A Civil Action (Herr, 1995~. Other books have highlighted the nation's groundwater supply and contamination problems in a man- ner accessible to nontechnical readers (e.g., Chapelle, 1997; Reisner, 1993~. Public concerns over water supply and contamination have led to increased federal and state funding to address fundamental and applied water-related problems. The NRC has prepared a broad array of synthe- sis and evaluation reports highlighting the nation's evolving understand- ing of groundwater and surface water contaminant causes, transport, and remediation strategies (e.g., NRC, 198S, 1990, 1993~. Remediation of contaminated industrial sites, often known as "brownfields," is currently a nationwide concern. As our understanding of recharge, contaminant transport, and mixed aqueous phase flow in groundwater grows, the potential scope and impacts of historical waste disposal practices and accidental spills continue to broaden far beyond what was previously thought. For example, stag from the steel industry is ubiquitous in industrial regions and has even been used to reclaim land (Box 1 . 11. However, water passing through this material may have a pH as high as 12 and may transport trace metals, volatile organic compounds (VOCs), pesticides, and polychiorinated biphenyls (PCBs). Likewise, nonpoint source pollution, especially from agricultural and urban sources, has become pervasive. For example, groundwater in
introduction 15
16 Investigating Groundwater Systems an agricultural region covering most of southeastern Washington state has a median nitrate concentration of 9.3 mg/L as nitrogen (the EPA drinking-water standard is 10 mg/L) (Nolan et al., 1998~. In the urban- ized Coastal Santa Ana basin, volatile organic compounds and pesticides were detected in all monthly and storm samples from surface water- monitoring sites, and in about half of the 20 deep (150-to 300-m) pro- ductions wells, some of them in confined settings (Belitz, ~ 999~.
Introduction 17 AN OVERDEVELOPED RESOURCE Large-scale development of groundwater resources has resulted in many undesirable consequences. Three of theseregional subsidence, saTt-water intrusion, and resource depletion are discussed here. Regional Subsidence Large-scale development and groundwater extraction can result in irreversible aquifer consolidation and regional subsidence. One of the most infamous examples occurred in the San Joaquin Valley of Califor- nia, where Poland et al. (1975) estimated that by 1970 subsidence in ex- cess of one foot had affected over 5,200 square miles of irrigable land. Other areas of notable subsidence from groundwater pumping are Houston-Galveston, Texas; Baton Rouge, Louisiana; Santa Clara Val- ley, California; and the Phoenix area in Arizona (USGS, 1999a). Sink- holes, a particular form of subsidence, are common in the southeastern United States, where pumping from carbonate aquifers has induced col- lapse. The cumulative impacts of subsidence can have widespread and un- anticipated consequences, including substantial damage to regional in- frastructure. Sanitary sewers, for example, are generally designed to flow by gravity to minimize pumping costs. Modest regional subsidence can alter hydraulic grade lines and result in costly damage to water and sewer lines and underground pipelines (NRC, 1995a). Flow in canals can become sluggish or can be reversed entirely. Foundations and road- ways can be damaged. Well casings can be crushed by the drag exerted by the subsiding earth. Relatively small cumulative changes in elevation resulting from subsidence alter regional drainage patterns and may sig- nificantly change flood risks and drainage in coastal areas and may de- crease the flood protection provided by levees and flood-control struc- tures. As an example, Kreitier (1977) estimated that because of subsi- dence, had Hurricane Carla struck the Houston~alveston region in 1976 rather than 1961, it would have inundated an additional 25 square miles of land adjacent to Galveston Bay.
18 Investigating Grounatwater Systems Salt-Water Intrusion Salt-water intrusion in coastal areas is a serious problem, especially along the Atlantic coast (Figure 1.4) where it affects areas from Cape Cod to Miami. In this region, heavy pumping from freshwater aquifers has resulted in the intrusion of salt water, threatening freshwater sup- plies. Indeed, the aquifers of Brooklyn, New York, were destroyed in the 1930s because of salt-water intrusion induced by excessive pumping, which Towered the water table to 30-50 feet below sea level (Fetter, 1994, p. 367~. Incidences of salt-water intrusion into coastal aquifers have been documented in almost all coastal states (USGS, 1998~. Controlling salt-water intrusion is costly and/or management- intensive. For example, water authorities in Tampa, Florida, are planning to build a $95 million desalination plant to replace a por- tion of their groundwater pumpage and thereby protect their re- source from intrusion (Daniels, 2000~. In southern California, water managers must continuously maintain a system of hydraulic barriers to- intrusion using artificial recharge of storm runoff and reclaimed water combined with pumping wells that continuously remove salt water from the aquifer (http://ca.water.usgs.gov/gwatias/coastal/la.htmI). Over 3,000 recharge basins, serving to control drainage and manage ground- water resources, blanket Nassau and Suffolk Counties, Long Island (Ku and Aaronson, 1992~. Clearly, salt-water intrusion will continue to be one of the most challenging problems for water managers in coastal re- gions. Resource Depletion The concept of a "safe" or "sustainable" yield of a basin has under- gone a long history from the first use of the term "safe yield" by Lee (1915~. Although the operational definition may vary from basin to ba- sin (see Chapter 2), sustainable groundwater resource development may generally be viewed as the quantity of groundwater that can be legally extracted from a hydrologic basin over the Tong term without causing severe economic, social, ecological, and hydrologic consequences. Meaningful investigations of groundwater resource sustainability cannot be limited to county or state boundaries. Accurate quantification of the dynamics of pumping, recharge, consumptive use, and return flows on
Introduction 19 A..._ ~ .... ~ ....... Id FIGURE I.4 Areas of salt-water intrusion into freshwater aquifers along the Atlantic coast. SOURCE: USGS, 1998. regional scales is necessary to evaluate sustainable levels of aquifer de- velopment. Characteristic response times and feedbacks between these interrelated processes constrain and characterize both the physical sys- tem (e.g., streamflow, depth to water table) and the institutional struc- tures affecting the distribution of benefits and impacts of groundwater use. Large-scaTe groundwater depletion has substantial economic costs associated with increases in pumping costs and reduced well yields. However, the economic value of groundwater extraction varies with en- ergy costs and market prices for irrigated agricultural crops. In fact, these economic forces can cause groundwater to be profitably extracted
20 Investigating Grour~d~water Systems these economic forces can cause groundwater to be profitably extracted beyond the point of sustainability. The cumulative effects of large-scale groundwater development influence, and are influenced by, socioeco- nomic factors that can effectively transform regional groundwater sup- plies into a nonrenewable resource. The High Plains aquifer (Figure 1.5), an important source of water in parts of Colorado, Nebraska, Texas, New Mexico, Kansas, Oklahoma, South Dakota, and Wyoming, is the classic example of this. About 20 percent of irrigated land in the United States is found in this important agricultural region, and about 30 percent of all groundwater used nationwide for irrigation comes from the High Plains aquifer. Between 1940 and 1980, the average water-level decline was about 10 feet, and it exceeded 100 feet in parts of Texas, Oklahoma, and southwestern Kan- sas (Dugan and Cox, 1994~. Pumping lifts and pumping costs have in- creased in many areas, especially in Texas, making irrigated agriculture less profitable. Since 1980, further declines of over 20 feet over multi- county areas have been common (Gutentag et al., 1984; Zwingle and Richardson, 1993; http://www.ne.cr.usgs.gov/highplains/-hp96_web_- report/hp96_factsheet.htrn#-WLS096 ), although local recoveries have also been noted (Dugan and Sharpe, 1994~. Other aquifers that are being exploited unsustainably ("mined") in- clude aquifer systems of the ciry Southwest (e.g., the Albuquerque basin of New Mexico), the Sparta aquifer of Arkansas, Louisiana, and Missis- sippi, and the Chicago-Milwaukee area aquifer system. THE NECESSITY FOR CONJUNCTIVE MANAGEMENT Groundwater depletion, subsidence, salt-water intrusion, and con- tamination caused by growing demands for municipal, agricultural, in- dustrial, and environmental water may render groundwater a limiting resource for future growth and development. Focusing on these specif- ics, however, obscures the need to understand and managebasins in an integrated manner. The following examples illustrate the integrated approach. The USGS Middle Rio Grande Basin Study (see Bartolino, 1997b; http://rmmcweb.cr.usgs.gov/public/mrgb/) and Southwestern Ground- Water Resources Project (http://az.water.usgs.gov/swgwrp/Pages/Over- view.htmI) are examples of projects involving fully appropriated surface
Introduction ~ _~...... x i! .] :0 :: · ~0 :~ ~~ ~ ~ Yc~I - ,~ ~}~ ~ ~ ~ :~{C`3= ~~ .~XcP~ ~ . Cat ~V' ° ~'~'~1 ~ ~ .,, ~~~c.% ~ ~ r ~= ~~ $ TIC - C 'C ~ ~~ ,20CC~ : rim ~ Aft. ~ : ~ ~ t r ~$ r: ~ ~ ~ ARC i,: Y<43.~O r ~ ~ ~ 0 . . ~ ' i- >. ~ ~ ~= ~ ~~ ~~ (C. I: ~ ~ ~~$C'~O~C'0~ >. ' ~'~ : ~ sO~:~:0 ~ : ~~$~ : : i. ~ .: ~ 21 FIGURE 1.5 Water-level declines in the High Plains aquifer, 1980- 1995. SOURCE: USGS, 1998. water systems for which new regional water resources must be devel- oped through conjunctive use of surface water and groundwater. In fact, throughout much of the southwestern United States, surface water is virtually fully appropriated or, in some cases, overappropriated. Signifi- cant regional municipal and irrigation demands may directly conflict with riparian environmental requirements, critical to these fragile eco- systems. USGS research has documented the dramatic decline in ripar- ian vegetation associated with groundwater withdrawals (Winter et al., 1998~. The variability and robustness of this sensitive rip arian environ- ment is also linked to stresses from the hydroclimatic system, for which
22 Investigating Groundwater Systems persistent forcings, such as the regional signature of the El Nino-South- em Oscillation, are recognized as significant sources of interannual variation. The effects of this variability on groundwater recharge and the frequency of extreme events must be taken into account in managing these systems sustainably. Large-scale water resource development has similarly produced a range of impacts in complex systems like the Florida Everglades. Among other factors, intensive exploitation of groundwater resources to support both agricultural and municipal water demands has resulted in wholesale changes in the regional water balance and has adversely af- fected the ecology of this unique system. Surface water engineering for flood protection and irrigation demands has imposed anthropogenic variability on the regional hydraulic forcings of the groundwater system. Intricate networks of actively operated canals disrupt the shallow aquifer flow. The delicate coupling of surface and subsurface flow in this low- gradient region critically constrains the restoration opportunities for this system. As a final example, the Atlantic coastal plain aquifers pose their own distinct challenges for water management. Groundwater-surface water interactions are especially complex in the heterogeneous, unlithified materials that characterize this region, and fluxes into and out of the sub- surface are particularly sensitive to changes in land use and surface drainage associated with urbanization. The spatial distribution of re- charge and discharge, aIreacly highly irregular in these heterogeneous sediments, is made further complex in urban areas by impermeable sur- faces, leaky pipes, interbasin transfers, and variable land use. The chem- istry of groundwater discharge may also be affected by industrial activity or by intense agricultural uses such as poultry farming. Changes in dis- charge rates and quality can have major impacts on the health and pro- ductivity of rip arian, estuarine, and coastal wetlands that provide critical spawning grounds and essential habitat for migratory waterfowl. Fi- nally, Tong-term pumping around the major cities has led to complex patterns of salt-water intrusion of both deep and shallow aquifers. Because they are interconnected, groundwater and surface water of- ten behave as one reservoir and should be treated and managed as a sin- gle resource (Winter et al., 1998~. With regard to water use and alloca- tion, this concept has been recognized for some time and is frequently referred to as "conjunctive use" (Young and Bredehoeft, 1972), and in- tegrated management of the resource is referred to as "conjunctive man-
Introduction 23 agement." Managers in water-stressed environments recognize the op- portunities to enhance the capacity and reliability of regional water sup- plies through the integrated management of surface water and ground- water. The institutional establishment of recharge districts illustrates the importance of, and opportunity for, integrated management. The variability, dynamic response, and integrating behavior of groundwater flow systems motivate the need for risk-based planning and evaluation of groundwater resources. This variability has not tradition- ally been considered in conventional resource evaluation. Resource as- sessment, recognizing the inherent variability of recharge, flow, and transport processes, is inherently incompatible with the institutional structures that manage water through property rights. Appropriative water law, which treats the rights to water as a static deterministic prop- erty right and adheres to the premises of "first in time, first in right" and "if you don't use it, you lose it," raises institutional obstacles to inte- grated conjunctive management of surface and subsurface water supplies in that it does not adequately account for the inherent spatial and tempo- ral variabilities in groundwater and surface water stocks and flows and for groundwater-surface water interconnections. Improved understanding of groundwater-surface water interactions enhances the opportunities for joint management and transfers between surface and subsurface supplies through artificial recharge, now com- monly synonymous with aquifer storage and recovery (ASR). However, in some Western states, uncertainty in the ability to maintain the right to surface water that is artificially recharged and subsequently extracted as groundwater represents a major institutional obstacle to successful im- plementation of conjunctive management among competing, and poten- tially cooperating, water users. For example, until the New Mexico leg- islature recently amended state water law, anyone artificially recharging surface water would immediately lose the right to that water once it en- tered the saturated zone and became groundwater. The change was prompted by the city of Albuquerque's desire to implement an ASR pro- gram, in which it would recharge excess surface water to replenish groundwater supplies. Prior to the law change, the city would have lost the right to any surface water it recharged to the aquifer.
24 Investigating Groundwater Systems CONCLUSIONS Groundwater is critical to the present and future needs of the United States; 130 million people now rely on it for drinking water (USGS, 1998) and have a stake in its sustainability and protection from contami- nation. But groundwater's role as a component of the hydrologic cycle is equally important. Groundwater has a critical function in maintaining ecosystems, and its connection to surface water dictates that groundwa- ter and surface water must be treated and managed as a single resource (Winter et al., 1998~. As society approaches an era that will likely be characterized by great natural and human-induced hydrologic stresses, the USGS is well positioned to maintain its leadership role in monitor- ing, protecting, and assessing a resource that is essential to the well- being of the nation. The next chapter discusses these roles.
