j
                       The American Recovery and Reinvestment Act (ARRA), Green Project Reserve of 2009, through the State Revolving Fund,
                       provided funding for a wide variety of qualifying projects in the categories of: green infrastructure, energy efficiency,
                       water efficiency, and other innovative projects.
                  o
                                     Green  Infrastructure  in  Arid
                                               and  Semi-Arid  Climates
   In arid and
semi-arid regions,
  many green
  infrastructure
practices may not
 be "green"at all!
                    Forward-thinking communities in water-limited regions are increasingly
                    recognizing green infrastructure as a cost-effective approach to stormwater
                    management that conserves water.
When rain falls on natural landscapes, much
of it either soaks into the ground or is returned
to the atmosphere by plants or evaporation.
Rain that is not absorbed into the soil flows
into nearby washes, arroyos, creeks, or streams.
By armoring landscapes with parking lots,
roads, and rooftops, we dramatically change
this water balance. Much less precipitation is
absorbed into the soil, and much more flows
across the land, gathering oils, pesticides,
animal waste, and trash along the way.
Gray stormwater infrastructure relies on
storm sewers to drain this water and its
pollutants to the nearest body of water—
increasing flooding, pollutant loads, and erosion,
and degrading water quality and habitat.

Green infrastructure refers to a set of practices
that mimic natural processes to retain and
use stormwater. By promoting infiltration,
evapotranspiration, and harvesting throughout
the landscape, green infrastructure preserves
and restores the natural water balance. Though
many green infrastructure practices were
first developed and applied in temperate
regions, green infrastructure is perhaps

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                           even more relevant in arid and semi-arid
                           climates. Communities, researchers, and
                           design professionals in these water-limited
                           regions are increasingly recognizing green
                           infrastructure as a cost-effective approach not
                           only to stormwater management, but to water
                           conservation as well. This guide discusses
                           the drivers, applications, and design of green
                           infrastructure in arid and semi-arid regions.
                                                   In the 1920s, approximately 5%
                                                  of precipitation in the Los Angeles
                                                   region flowed to the sea. Today,
                                               extensive impervious cover and massive
                                               stormwater conveyance systems deliver
                                                50% of the rain falling in the region to
                                                the sea, even as more than 80% of the
                                                 city's water demand is met by costly
                                                  imports from distant locations.3'4
          BENEFITS
          OF GREEN
INFRASTRUCTURE
Although this guide views green infrastructure
through the lens of stormwater management,
green infrastructure can provide many
environmental, social, and economic benefits.
Green infrastructure not only reduces runoff,
but can conserve water, recharge groundwater,
conserve energy, and improve air quality. These
environmental benefits create more sustainable
cities and towns, and translate into significant
social and economic gains. This section reviews
the multiple benefits of green infrastructure.

ENVIRONMENTAL BENEFITS
• Reduces flooding: Increasing infiltration,
 evapotranspiration, and storage where
 precipitation falls will reduce runoff and
 flooding.
• Improves water quality: Reducing runoff
 and allowing runoff to be treated by soils
 and vegetation will reduce pollutant loads
 to receiving water bodies.
• Provides habitat: Native and drought-
 adapted plants that thrive on infrequent
 precipitation can provide habitat for native
 birds and insects.
• Reduces the urban heat island effect:
 Removing pavement and planting vegetation
 can cool and shade urban neighborhoods
 in the hot summer months.
• Improves air quality: Urban vegetation
 removes pollutants from the air and can
 mitigate smog formation by reducing
 temperatures.
• Mitigates global warming: By sequestering
 carbon dioxide in soils and plant biomass,
 urban vegetation can reduce carbon dioxide
 concentrations and mitigate global warming.
• Increases groundwater recharge: In many
 cities and towns in the arid and semi-arid
 West, impervious cover and engineered
 conveyance systems reduce the amount
 of precipitation that enters the groundwater
 store. Green infrastructure practices that
 reduce impervious cover and enhance
 infiltration can increase the flow of water to
 the groundwater. The Los Angeles Basin Water
 Augmentation Study (WAS), for instance,
 estimates that the installation of green
 infrastructure practices that infiltrate the first
 %"of rainfall on each parcel could increase
 groundwater recharge in the Los Angeles
 region from 16% of annual rainfall to
 48%.5 Local conditions will shape the effect of
 green infrastructure on groundwater recharge
 in each region, but the impact of extensive
 implementation can be substantial.

SOCIAL BENEFITS
• Improves public health: Cooler summer
 temperatures and cleaner air can dramatically
 improve health, particularly for children
 and the elderly. More pedestrian-friendly
 landscapes can also promote physical activity.
• Beautifies neighborhoods: Private gardens
 and public rights-of-way irrigated with passive
 and active rainwater harvesting can create
 beautiful landscapes.

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          BENEFITS
          OF GREEN
INFRASTRUCTURE
                    CONT.
• Calms traffic: By reducing street widths and
 introducing curves, green street techniques
 can slow traffic.
• Builds communities: By beautifying
 neighborhoods and creating a unique sense
 of place, green infrastructure practices can
 increase neighborhood interaction. Neighbors
 may even work together to integrate green
 infrastructure into their neighborhood.

ECONOMIC BENEFITS
• Reduces landscape maintenance costs:
 Passive rainwater harvesting and drought
 adapted plants will require less irrigation and
 maintenance than conventional, turf-based
 landscaping.
• Increases groundwater resources:
 Groundwater provides -40% of the Nation's
 public water supply, and even more in arid
 and semi-arid regions with limited surface
 water supplies.8'9 Green infrastructure
 practices that increase groundwater
 recharge can provide significant cost savings
 by averting increased pumping costs or
 increased water imports. The Los Angeles WAS
 concluded that infiltration-based practices
 distributed across the region could increase
 groundwater recharge by 384,000 acre-feet
 per year—more than 1.5 times the volume
 captured by centralized  spreading grounds.
 Based on the cost of the current water supply,
 the study estimated the corresponding value
 at approximately $310 million per year.
• Reduces water imports: Many cities and
 towns in the West depend on costly imports
 of water from great distances to meet their
 water demand. Green infrastructure practices
 that manage stormwater through passive and
 active rainwater harvesting can reduce the
 demand for municipal water and reduce
 water imports.
• Reduces energy use: The energy required
 to import, treat, and distribute municipal
 water could be significantly reduced by using
 precipitation where it falls. The energy and
 cost savings would not be trivial. The Natural
 Resources Defense Council (NRDC) estimates
 that transportation and treatment of water
 consumes 19% of all electricity in the state
 of California.7
                                                                                 In Los Angeles, enhancing
                                                                              groundwater recharge through
                                                                            green infrastructure practices could
                                                                             supply approximately $310 million
                                                                                 worth of water per year.
                           The green roof installed by EPA Region 8 provides welcome open space in the heart of the city. Photo courtesy of Greg Davis.

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   APPLICATIONS
          OF GREEN
INFRASTRUCTURE
    Active rainwater harvesting
    in Tucson, AZ.
                      -
    Passive rainwater harvesting
    in Tucson, AZ. Photo courtesy of
    Watershed Management Croup.
    Subsurface infiltration
    basin in Rancho Mirage,
    CA. Photo courtesy of RCA
    Landscape Architects.
Green infrastructure is a versatile approach
to stormwater management that can be
applied in a range of climates and at a range of
different scales. This section discusses the many
practices that can be applied in arid and semi-
arid regions, from the scale of a single building
to the scale of a neighborhood or watershed.

RAIN GARDENS
Rain gardens (or bioretention cells) are
vegetated depressions that retain and treat
runoff from rooftops, sidewalks, and streets.
Unlike conventional gardens, rain gardens
receive most of their water from precipitation.
In the arid and semi-arid West, where landscape
irrigation accounts for about 40% of municipal
water demand, rain gardens can play an
important role in both water conservation
and stormwater management.

Rain garden design is based on three simple
components: a drainage area that collects
rainwater, a distribution system that connects
the drainage area to the receiving area, and
a receiving area that retains and infiltrates
the rainwater.

Rain gardens should be sited to treat as much
impervious area as possible, and sized to
match the volume of soil storage with the
extent of the drainage area. Excavation
may be required to increase soil storage
and accommodate plant roots, and soil
amendments may be required to increase soil
water retention and maintain  healthy plants.
In arid and semi-arid regions, rain garden
design must be conscious of the limited
water supply. The following section discusses
techniques for selecting and maintaining
vegetation in water-limited regions.

SWALES
Swales are vegetated or mulched earthen
channels that retain and treat runoff from
rooftops, sidewalks, and streets. Though
similar to rain gardens, swales are linear
features designed to convey runoff downslope.
As runoff flows through the swale, it is slowed
by the vegetation or mulch, and may be
infiltrated into the soil. Again, techniques for
selecting and maintaining vegetation in arid
and semi-arid regions are discussed in the
following section.
                                                                               For more information on passive
                                                                            rainwater harvesting with rain gardens,
                                                                           swales, and other landscape features, see
                                                                           the City of Tucson's comprehensive Water
                                                                            Harvesting Guidance Manual, available
                                                                            at http://dot.tucsonaz.gov/stormwater/
                                                                                education/waterharvest.php
POROUS PAVEMENT
Porous pavement reduces runoff volumes
and contaminant loads by allowing more
precipitation to infiltrate into the soil. Porous
pavement systems generally consist of a
permeable surface (often porous asphalt,
porous concrete, or interlocking concrete
pavers) and several layers of bedding. Water
that drains through the surface and layers of
bedding infiltrates into the soil below. Studies
have shown that porous pavement treats
the water that passes through the system
by retaining oils and heavy metals.2 Porous
pavement, therefore, provides a direct water
quality benefit by removing the contaminants
associated with streets and parking lots, as well
as an indirect water quality benefit by reducing
the volume of runoff. Porous pavement may
also reduce irrigation demand by providing
water to trees with extensive root  systems.

RAIN BARRELS OR CISTERNS
Rain barrels, cisterns, or tanks reduce
stormwater runoff and municipal water
demand by storing  rainwater from rooftops
and other impervious areas for later use. The
appropriate storage volume will depend on
the roof area, rainfall, available space, and
other site conditions, as well as the system
objectives. Whereas smaller rain barrels can
provide modest reductions in runoff volume
and irrigation demand, larger rain  cisterns or

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   APPLICATIONS
          OF GREEN
INFRASTRUCTURE
                     CONT.
    Green roof atop the EPA
    Region 8 office in Denver,
    CO. Photo courtesy
    of Greg Davis.
    Green street in Tucson, AZ.
    Photo courtesy of Watershed
    Management Group.
tanks can capture most rooftop runoff and
supply much of the irrigation demand. A
2007 study prepared for the Colorado Water
Conservation Board, for instance, found that
a 5,000-gallon cistern paired with water-
wise landscaping could provide 50% of the
irrigation demand for a 7,000-square-foot lot in
Douglas County, CO.1 The cost of these systems,
however, increases significantly with storage
volume—particularly for underground storage
construction. In sizing rainwater harvesting
systems, site owners must balance the multiple
benefits of stormwater retention and water
conservation against the costs of construction.

GREEN ROOFS
As in temperate regions, green roofs
in arid and semi-arid regions reduce and treat
stormwater runoff. The green roof installed
atop the EPA Region 8 Office in Denver,
Colorado, for instance, retains more than
80% of the rainfall it receives.

When designed appropriately, green roofs
may offer a water-efficient approach to urban
stormwater management in arid and semi-
arid regions. Though green roofs in these
regions will require irrigation throughout their
lifetimes, water efficiency can be significantly
increased by adapting green roof designs.
Irrigation requirements can be reduced by
increasing growing media depth, planting
native and drought-adapted species, and
applying drip irrigation. Municipal water
demand can be further reduced by installing
systems that irrigate green roofs with harvested
stormwater runoff and/or AC condensate.

When installed in appropriate settings, green
roofs may also  represent a cost-effective
approach to urban stormwater management.
The cost-effectiveness of a given green roof
installation depends on the benefits offered
by the green roof, as well as the value placed
upon those benefits. Green roofs not only
retain and treat stormwater, but conserve
energy, reduce heating and cooling costs,
reduce the urban heat island effect, sequester
CO2, provide habitat, and extend the lifetime
of the roof. While conventional roofs typically
require replacement every 10-20 years, green
roofs typically require replacement every
40-50 years.6 In dense, urban settings, green
roofs also provide valuable recreational space
and can reduce stormwater management
costs by reducing or eliminating the need for
stormwater vaults or ponds. EPA Region 8's
green roof, for instance, reduced the cost of the
below-ground stormwater detention vault from
about $363,800 to $150,000.

GREEN STREETS
The principles of green infrastructure are
most effective when designed as a system
and applied across a neighborhood or
watershed. Green streets are one example of
a neighborhood-scale system. Green streets
integrate rain gardens and swales into the
street design to retain and treat stormwater
while beautifying streets and slowing traffic.
Rain gardens can be installed in rights-of-way,
medians, traffic circles, and chicanes, and
rainwater can be directed into these areas by
introducing curb cuts or installing curbs flush
with the ground.

RIPARIAN BUFFERS
Riparian buffers are one example of
a watershed-scale approach to green
infrastructure. Riparian buffers restrict
development in the  land adjacent to washes,
arroyos, creeks, or streams to  reduce erosion
and preserve channel form and function. When
applied throughout a watershed, riparian
buffers can  provide multiple environmental and
social benefits. By preserving  an interconnected
network of habit, riparian buffers can increase
wildlife diversity in urban areas. Many
communities designate recreational  trails
within riparian  buffers. These trails can provide
access to nature as well  as opportunities for
physical activity.

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     SELECTING
              AND
MAINTAINING
  VEGETATION
 IN ARID AND
     SEMI-ARID
      CLIMATES
To establish green infrastructure in arid and
semi-arid climates, particular care must be
given to the selection and maintenance of
vegetation. Though some planners have
expressed skepticism about the viability of
vegetated practices in water-limited regions,
appropriately designed practices will not only
be effective and sustainable, but will
conserve water resources as well. The key
to selecting and maintaining vegetation in
water-limited regions is to follow the
principles of xeriscaping.

This section reviews these principles and
discusses their application to particular green
infrastructure practices.

1. Create a plan. The first step in designing
  landscape features that can remain healthy
  and attractive with limited irrigation is to
  create a plan balancing water supply and
  demand. By preparing  a site water budget,
  designers can choose the plant species and
  densities that best meet their aesthetic
  objectives while reducing water demand.

  The information required to prepare a site
  water budget include annual or monthly
  precipitation, mature plant size, and annual
or monthly plant water needs. Annual
water budgets will generally be appropriate
for landscapes consisting of native plants
at native densities, while monthly water
budgets will be more effective for landscapes
with exotic plants and higher plant densities.

Comprehensive lists of plant water
requirements for Arizona plants are provided
by Brad Lancaster's Rainwater Harvesting
for Drylands and Beyond, Volume 1 and the
Arizona Municipal Water Users Association's
Landscape Plan ts for the Arizona Desert. I n
other areas, landscape designers may consult
the local Cooperative Extension office, local
chapter of American Society of Landscape
Architects, local association of landscape
contractors, native plant societies,
or nurseries.
                                                                            Plant selection for rain gardens:
                                                                          Bear in mind the potential for occasional
                                                                         inundation. Though standing water should
                                                                         last no more than 72 hours, plants located
                                                                          at the lowest elevations should be able
                                                                                 to tolerate inundation.
                       Rain gardens fed by passive rainwater harvesting border the buildings and parking lots of the TAXI redevelopment project in
                       Denver, CO. The rain gardens beautify the site, reduce the urban heat island effect, and provide habitat, while reducing
                       runoff to the nearby South Platte River. Photo courtesy of Wenk Associates.

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    SELECTING
              AND
MAINTAINING
  VEGETATION
 IN  ARID AND
    SEMI-ARID
      CLIMATES
                 CONT.
2. Use low water use plants. Native and
  drought-tolerant plants can drastically
  reduce, if not eliminate, the irrigation
  requirements of green infrastructure
  practices. Note that low water use plants
  do not exclude trees. On the contrary,
  drought-adapted trees thrive on deep,
  infrequent watering, and are particularly
  suitable for green infrastructure practices.
                                Plant selection for green roofs:
                            Bear in mind the hot, windy environment,
                            the difficulty of accessing most rooftops,
                              and the importance of maintaining
                              the roof structure. Green roof plants
                              should be low growing, self shading,
                               and self-propagating, and should
                                  have shallow root systems.
                       3. Use efficient irrigation systems. Irrigation
                         systems will be most efficient when plants
                         are grouped according to their water needs,
                         and when the frequency and depth of
                         irrigation is adjusted according to plant
                         type, plant maturity, and season. Irrigation
                         schedules should be adjusted at least
                         four times per year, and in warm months,
  irrigation should take place during the night
  or early morning. Drip or low flow irrigation
  techniques will minimize evaporation, runoff,
  and weed growth.

4. Consider soil amendments. Healthy soils
  are essential to retain soil moisture, sustain
  vegetation, and treat stormwater runoff.
  Poor site soils can be amended with
  organic material.

5. Use mulch. Organic  mulch can increase
  water retention and  pollutant removal while
  building soil structure and suppressing
  weeds. Note, however, that many desert
  trees and shrubs react poorly when their
  trunks come in contact with mulch.

6. Maintenance. All landscapes require
  maintenance, and xeriscaping is no exception.

When applied to rain gardens, swales, green
roofs, and green streets, these principles will
produce sustainable green infrastructure
practices that require minimal irrigation.
Because these practices will often replace very
water intensive conventional landscaping, the
net effect will be a dramatic decline in water use.
                       This rainwater cistern installed at a residence in Tucson, Arizona supplies water for citrus trees and a small vegetable garden,
                       as well as native plants. Photo courtesy of Technicians for Sustainability.

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    NAVIGATING
WATER RIGHTS
    LAW IN THE
       ARID AND
      SEMI-ARID
             WEST
Green infrastructure approaches in the arid and
semi-arid West must recognize and adapt to the
complex legal landscape associated with water
rights law. In most western states, water law is
based on the doctrine of prior appropriation.
According to this doctrine, the diversion and
use of state waters requires a water right,  and
water rights are allocated based on the time of
appropriation ("first in time, first in right").

This doctrine does not affect most green
infrastructure practices, but the application
of this doctrine to rainwater harvesting does
raise several questions. Does the state have
jurisdiction over precipitation? Does active
rainwater harvesting require a water right?
Each state offers its own answers, and in many
states, these answers continue to evolve. While
some states have developed laws and policies
that promote rainwater harvesting, others are
extremely restrictive, and still others have no
formal policy at all.

The table below summarizes the present
stance of 11 western states toward rainwater
harvesting. The table:
• Identifies the agency responsible for the
 administration and enforcement of state water law;
• Indicates whether the state has jurisdiction
 over atmospheric rainwater;
• Indicates whether a permit would be required
 to harvest and use rainwater; and
• Identifies who may apply for rainwater
 harvesting permits if they are required.
                              State
                                         Responsible Agency
                                 Jurisdiction
                                    over
                                 Atmospheric
                                   Water?
 Permit Required?
Who May Apply for Permit
Arizona
California
Colorado
Idaho
Montana
Nevada
New Mexico
Oregon
Utah
Washington
Wyoming
Arizona Department of Water
Resources
California Environmental
Protection Agency, Division
of Water Rights
Colorado Division of Water
Resources
Idaho Department of Water
Resources
Montana Department
of Natural Resources
& Conservation, Water
Resources Division, Water
Rights Bureau
State of Nevada, Department
of Conservation & Natural
Resources, Division of Water
Resources
New Mexico Office of the
State Engineer
Water Resources Department
Utah State Engineer
Washington Department
of Ecology
Wyoming State Engineer and
Board of Control
No
No
Yes
No
Yes
Yes
No
Yes
Possibly
Possibly
Yes
No
No
Yes. Colorado law identifies
properties that may apply
for a permit
No
Yes
Technically, yes
No
No. Oregon law exempts
"the collection of
precipitation waterfrom an
artificial impervious surface"
from permit requirements
Yes
No
Technically, yes, but
residential rainwater
harvesting is regarded as
de minimus
NA
NA
1 . Residential properties that are
supplied by a well (or could qualify
for a well permit) and are not served
by a municipality or water district
2. Developers wishing to apply for
approval to be one of 10 statewide
pilot projects
NA
No formal policy
Applications not accepted
NA
NA
No formal policy
NA
No formal policy

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    NAVIGATING
WATER RIGHTS
     LAW IN THE
        ARID AND
       SEMI-ARID
                WEST
                     CONT.
Many states and municipalities recognize the
vast gains in water efficiency that rainwater
harvesting can provide, and are playing an
active role in promoting this practice. The
         State
      table below reviews innovative policies
      and incentives that western states and
      municipalities have developed to expand
      rooftop rainwater harvesting.

State/Municipal Policies and Incentives
Arizona
California
New Mexico
Oregon
Washington
A state tax credit is available for plumbing stub outs and water conservation systems
(including rainwater harvesting) through 201 1.
The city of Tucson mandates that commercial developments meet 50% of their
landscaping water requirements with harvested rainwater.
A Bernalillo County ordinance requires builders to employ certain water conservation measures.
Two of the measures builders may select are active and passive rainwater harvesting.
A draft Los Angeles ordinance would require builders to employ rainwater storage
tanks, permeable pavement, infiltration swales, or curb bumpouts to manage 100%
of the runoff from a 3/4" storm, or pay a mitigation fee.
The New Mexico State Engineer issued a Rainwater Harvesting Policy encouraging "the harvesting,
collection, and use of rain water from residential and commercial roof surface for on-site
landscape irrigation and other on-site domestic uses."
Santa Fe County's Water Harvesting Ordinance mandates the use of rain barrels, cisterns,
or catchments for small residences, and the use of buried or partially buried cisterns for large
residences and commercial buildings.
The Albuquerque Bernalillo County Water Utility Authority offers rebates for rainwater
harvesting systems based on the amount of water that can be stored.
Building Code OPSC 08-01 allows rainwater harvesting systems for residential
potable uses as a statewide alternative method.
The Washington Department of Ecology issued an Interpretive Policy Statement
clarifying that a water right is not required for rooftop harvested rainwater used on site.
Washington law states that commercial buildings that utilize active rainwater harvesting
systems must receive a 10% reduction in any municipal stormwater management fees.
Kitsap County offers a 50% reduction in stormwater management fees to new or
remodeled commercial buildings that utilize rainwater harvesting.
                            The policies above represent a few of the
                            actions that local and state governments can
                            take to remove barriers to green infrastructure
                            and provide incentives for its adoption.
                            As communities across the West struggle
                            to allocate limited water resources among
                            growing populations, green infrastructure can
                            play an important role in preserving water
                            quality while conserving water supply.
                                                     Green infrastructure offers a versatile, simple,
                                                     and cost-effective solution to several of the
                                                     arid and semi-arid West's most pressing
                                                     environmental concerns.

                                                     Additional green infrastructure resources are
                                                     available at www.epa.gov/greeninfrastructure
                                                     and www.epa.gov/smartgrowth.
                            References:

                            1 Colorado Water Conservation Board, 2007. Holistic Approach to Sustainable Water Management in Northwest Douglas County.

                            2 Dietz, M., 2007. Low Impact Development Practices: A Review of Current Research and Recommendations for Future Directions. Water, Air, and Soil Pollution,
                               186,351-363.

                            3 Green, D., 2007. Managing Water: Avoiding Crisis in California. Berkeley: University of California Press.

                            4 Los Angeles Department of Water and Power, 2009. LADWP Quick Facts and Figures, http://www.ladwp.com/ladwp/cms/ladwp000509.jsp

                            5 Los Angeles and San Gabriel Rivers Watershed Council, 2010. Los Angeles Basin Water Augmentation Study: Research, Strategy, and Implementation Report.

                            'J Michigan State University. Green Roof Research Program, http://www.hrt.msu.edu/greenroof/. Accessed 6/2010.

                            7 Natural Resources Defense Council, 2009. A Clear Blue Future: How Greening California Cities Can Address Water Resources and Climate Challenges in the 21st Century.

                             Phillips, A., ed., 2005. City of Tucson Water Harvesting Guidance Manual. City of Tucson Department of Transportation.

                            3 United States Geological Survey, 2003. Ground-Water Depletion Acrossthe Nation. USGS Fact Sheet-103-03.

                            3 United States Geological Survey, 2000. Ground-Water Resources for the Future: Desert Basins of the Southwest. USGS Fact Sheet 086-00
                                                                                                                   EPA-833-B-10-002 | MAY 2010

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