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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
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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
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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
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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~.
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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-
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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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Representative terms from entire chapter:
drinking water
72
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13
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 these—regional 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 manage—basins 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
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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.
