HomeMy WebLinkAboutResolution 2010-110 aquifer-storage change and land-surface elecation change monitoringMARANA RESOLUTION N0.2010-110
RELATING TO UTILITIES; APPROVING AND AUTHORIZING THE MAYOR TO EXECUTE
A JOINT FUNDING AGREEMENT WITH THE U.S. DEPARTMENT OF THE INTERIOR U.S.
GEOLOGICAL SURVEY TO CONTINUE FROM OCTOBER 1, 2010 THROUGHSEPTEMBER
30, 2013 THE STUDY ENTITLED AQUIFER-STORAGE CHANGE AND LAND-SURFACE
ELEVATION CHANGE MONITORING IN THE TUCSON ACTIVE MANAGEMENT AREA
WHEREAS the U.S. Geological Service, the Town of Marana, the City of Tucson, Pima
County, the Town of Oro Valley, and Metropolitan Domestic Water Improvement District have since
2003 been jointly funding a study of changes in aquifer storage and land-surface elevation in the
Tucson Active Management Area; and.
WHEREAS the land subsidence and aquifer storage project provides information needed for
the development of water resources and land planning.
NOW, THEREFORE, BE IT RESOLVED BY THE MAYOR AND COUNCIL OF THE
TOWN OF MARANA, ARIZONA, as follows:
SECTION 1. The Joint Funding Agreement between the Town of Marana and the U.S.
Department of the Interior U.S. Geological Survey attached as Exhibit A to and incorporated in this
resolution by this reference is hereby approved, and the Mayor is hereby authorized to execute it on
the Town's behalf.
SECTION 2. The various Town officers and employees are authorized and directed to
perform all acts necessary or desirable to give effect to this resolution.
PASSED AND ADOPTED BY THE MAYOR AND COUNCIL OF THE TOWN OF
MARANA, ARIZONA, this 16`'' day of November 2010.
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J celyn C~ onson, Town Clerk
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Mayor d Honea
APPROVED AS TO FORM:
Cassidy, Town Attorney
Page 1 of 2
Form 9-1366 U.S. Department of the Interior Customer#: ~~s
(oct. Zoos) U.S. Geological Survey Agreement#: 11W4AZ0osoo
Joint Funding Agreement Project#: ss719EF
TIN #: 86-3301775
Fixed Cost (~ Yes ~-~ No
Agreement
FOR
WATER RESOURCES INVESTIGATIO NS
THIS AGREEMENT is entered into as of the 13th day of October, 2010, by the U.S. GEOLOGICAL SURVEY,
UNITED STATES DEPARTMENT OF THE INTERIOR, parry of the first part, and the TOWN OF MARANA,
party of the second part.
1. The parties hereto agree that subject to availability of appropriations and in accordance with their
respective authorities there shall be maintained in cooperation an investigation of aquifer storage change
and land subsidence in the Tucson Basin and Avra Valley as described in the attached workplan, herein
called the program. The USGS legal authority is 43 USC 36C; 43 USC 50; and 43 USC 50b.
2. The following amounts shall be contributed to cover all of the cost of the necessary field and analytical
work directly related to this program. 2(b) includes In-Kind Services in the amount of $0.
by the party of the first part during the period
(a) $45,000.00 October 1, 2010 to September 30, 2013
by the party of the second part during the period
(b) $45,000.00 October 1, 2010 to September 30, 2013
(c) Additional or reduced amounts by each party during the above period or succeeding periods as
may be determined by mutual agreement and set forth in an exchange of letters between the
parties.
(d) The performance period may be changed by mutual agreement and set forth in an exchange of
letters between the parties.
3. The costs of this program may be paid by either parry in conformity with the laws and regulations
respectively governing each party.
4. The field and analytical work pertaining to this program shall be under the direction of or subject to
periodic review by an authorized representative of the party of the first part.
5. The areas to be included in the program shall be determined by mutual agreement between the parties
hereto or their authorized representatives. The methods employed in the field and office shall be those
adopted by the party of the first part to insure the required standards of accuracy subject to modification
by mutual agreement.
6. During the course of this program, all field and analytical work of either party pertaining to this program
shall be open to the inspection of the other party, and if the work is not being carried on in a mutually
satisfactory manner, either party may terminate this agreement upon 60 days written notice to the other
parry.
7. The original records resulting from this program will be deposited in the office of origin of those records.
Upon request, copies of the original records will be provided to the office of the other party.
Page2of2
Form 9-1366
continued
U.S. Department of the Interior
U.S. Geological Survey
Joint Funding Agreement
Customer #: ~~
Agreement #: 11 W4AZ00500
Project #: 96719EF
TIN #: 86-3301775
8. The maps, records, or reports resulting from this program shall be made available to the public as
promptly as possible. The maps, records, or reports normally will be published by the party of the first part.
However, the party of the second part reserves the right to publish the results of this program and, if
already published by the party of the first part shall, upon request, be furnished by the parry of the first
part, at costs, impressions suitable for purposes of reproduction similar to that for which the original copy
was prepared. The maps, records, or reports published by either party shall contain a statement of the
cooperative relations between the parties.
9. USGS will issue billings utilizing Department of the Interior Bill for Collection (form DI-1040). Billing
documents are to be rendered quarterly. Payments of bills are due within 60 days after the billing date. If
not paid by the due date, interest will be charged at the current Treasury rate for each 30 day period, or
portion thereof, that the payment is delayed beyond the due date. (31 USC 3717; Comptroller General File
B-212222, August 23, 1983).
U.S. Geological Survey
United States
Department of the Interior
USGS Point of Contact
Town of Marana
Customer Point of Contact
Name: Dorothy O'Brien, Utilities Director
Address: 5100 W. Ina Road
Marana, AZ 85743
Telephone: 520-382-2570
Email: dobrien ~ marana.com
Signatures
gy Date
Name:
Title:
gy Date
Name:
Title:
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(G By ~~ ~ ~ , .~ . ' ~~ Date l ' ~~ ~
Name: ~ % orothy O'Brien
Title: Utilities Director
gy Date ~~`~ 7 ~0
Name: E dn~~
Title: ~r
By a /I--/7~/(~
e: CJO vl C • dytSd-/I
le: ~~cu GlG~''~
Name: John P. Hoffmann
Address: 520 N. Park Ave., Suite 221
Tucson, AZ 85719
Telephone: 520-670-6671 x222
Email: jphoffma~usgs.gov
Aquifer-Storage Change and Land-Surface Elevation Change Monitoring in the Tucson
Active Management Area
FY 2011-2013
Introduction
The Tucson Active Management Area (AMA) encompasses most of the Tucson Basin and Avra Valley
within Pima County in southeastern Arizona and includes the metropolitan area of the City of
Tucson and other incorporated towns and agricultural areas. Aquifer-storage change has been
monitored by the U.S. Geological Survey (USGS) within the Tucson AMA since 1996. The USGS
began a cooperative study with Metropolitan Domestic Water Improvement District and the town of
Oro Valley in 1996 to monitor aquifer-storage change in the Lower Canada del Oro subbasin. In 1998,
the USGS began a cooperative study with the Arizona Department of Water Resources (ADWR),
Pima County, and the City of Tucson to monitor land-surface elevation change and aquifer-storage
change within a larger part of the Tucson AMA. In 2003, these two monitoring studies were
combined, and the town of Marana joined the study. This proposal outlines a scope of work for
continued and expanded monitoring of both aquifer-storage change and land-surface elevation change
in this larger area within the Tucson AMA.
The AMA regulatory goal under the Arizona Groundwater Management Act of 1980 is to create a
balanced groundwater budget by the year 2025, whereby groundwater withdrawals equal recharge-
both natural and artificial. In order to assess progress towards this goal, water managers require
information about the primary groundwater budget components of inflow, outflow, and aquifer-
storage change. Potable and non-potable water demand is being met with a combination of
groundwater, blended groundwater and Colorado River Water, and treated effluent. As the
hydrologic systems beneath the Tucson AMA respond to decreased pumping and increased artificial
recharge, water managers will benefit from the additional and independent measure of aquifer-storage
change provided by this program.
Aquifer-Storage Change
Gravity methods offer an independent means to directly measure aquifer-storage change through
measurement of local changes in the gravitational field of the Earth. Changes in the Earth's
gravitational field at a location on the surface can be caused by mass change and/or a change in
distance from the center of the Earth, such as 1) change in the amount of water stored in the
subsurface, 2) mass change in magma and geothermal reservoirs, 3) subsurface faulting, and 4) land-
surface elevation change. Fortunately, changes in groundwater storage and land-surface elevation
change are the only likely causes of gravity change in the Tucson AMA. As water is added or removed
from the aquifer, there is a change in mass and a corresponding measurable change in gravity. Since
gravity also is affected by changes in land-surface elevation, monitoring of land-surface elevation
change is essential for accurate measures of aquifer-storage change.
Regional hydrologic conditions are dominated by semiconfined and unconfined conditions. However,
a range of hydrologic conditions occurs locally including confined, unconfined, perched,
compressible, and combinations of each condition within multiple aquifer systems (Anderson and
others, 1992). An understanding of observed gravity and water-level relations will improve
understanding of the hydrologic conditions under which these relations occur, and the information
can be used to establish what water-level change represents in terms of storage change. An
understanding of gravity and water-level relations requires discussion of 1) the regional hydrogeology,
2) unsaturated zone and perched conditions that contribute to gravity change, 3) effects of well
construction on water levels, and 4) the one dimensional mass change assumptions used in the analysis
to convert gravity change at the surface to water-storage change (Pool, 2008).
Water levels in wells commonly are monitored to estimate aquifer-storage changes. However, use of
water-level variations often includes significant assumptions about the hydraulic properties of the
aquifer system. One difficulty is the heterogeneity of hydrologic properties of the aquifer; the alluvial
sediments of the aquifer vary in lithology and texture, both laterally and with depth. Thus, data from
individual wells may not represent aquifer characteristics some distance away from the well. Aquifer
characteristics can be determined at wells where water levels are monitored, but many long term and
costly tests are required and values estimated from the tests are only applicable to the small volume of
aquifer that was tested. Storage change estimated by using gravity measurements does not require
costly tests or assumptions regarding aquifer properties. As with estimates using water-level data, a
few repeat gravity measurements at limited locations also would not be sufficient for an accurate
estimation of aquifer-storage change; however, conducting repeat gravity surveys at a large network of
benchmarks offers acost-effective and direct method to estimate total storage-change over a large
portion of the AMA, including areas where data from wells are insufficient or absent.
Another consideration is monitor-well design; in the Tucson AMA, most water levels are measured in
deep wells that tap multiple aquifer layers, most of which are confined and have accordingly low
storage properties. Water levels in these deep wells are a composite of water levels from several aquifer
units. When these composite water levels are used to estimate storage changes, the hydrologic
properties used in the calculation may not reflect the range of aquifer materials over which the well is
screened. Owing to these complexities and requisite assumptions in using water-level variations as the
only indicators of storage change, understanding can be improved from the combination of repeat
gravity and water-level observations.
The combination of gravity and water level observations can be used to establish what the water-level
change represents in terms of storage change when gravity observation stations are collocated with
monitor wells. Poor correlation of water-level and measurable gravity change indicates the region
near the well is a multiple aquifer system and the water level in the well is a poor indicator of overall
storage change near the well. Positive correlation of water level and gravity change can be used to
determine if the well penetrates a confined or unconfined aquifer and estimates of specific yield can be
derived from the water-level change.
Monitoring of gravity and water levels in Tucson Basin has shown that large changes in groundwater
storage, as much as several feet of water, have occurred that were not reflected in comparable water-
level changes. Water levels following intense precipitation and infiltration, and associated gravity
increases, either tend to rise slightly or to cease or slow their declines as gravity declines. These
responses generally are manifested up to a year after the storage increase. The extents to which water
levels are influenced by storage changes are directly related to the proximity of the well to the
recharge area. Closer proximity yields an earlier and more discernable water-level response (Pool and
Anderson, 200. Water-level responses also depend on the geometry and lithology of the
sedimentary layers in the aquifer system that wells sample. Often this information is incomplete or
uncertain. With a combination of independent storage-change estimations from gravity methods and
water-level data, estimates of aquifer specific yield distribution can be improved
Land-Surface Elevation Change
Land subsidence can occur in alluvial basins when water is removed from aquifer systems (Galloway
and others, 1999). Aquifer systems in alluvial basins such as those in the Tucson AMA are supported
by the granular skeleton and the pore-fluid pressure. When groundwater is withdrawn and the pore-
fluidpressure is reduced, the granular skeleton is compressed, causing some lowering of the land
surface. Both the aquifers (sand and gravel) and aquitards (clay and silt) of aquifer systems are
deformed as a result of changes to the pore-fluid pressure and skeleton, but to different degrees. Most
permanent subsidence occurs due to the irreversible compression of aquitards during the slow (years)
process of aquitard drainage.
Permanent subsidence, seasonal elastic deformation, and uplift have been observed in Tucson Basin
and Avra Valley. Rates of land subsidence in Tucson Basin in relation towater-level decline have been
less than 0.5 foot per 100 feet of water-level decline (Carruth and others, 200. Comparison with the
Eloy and Phoenix areas (greater than 1 foot per 100 feet of decline) suggests that land subsidence
observed to date in the Tucson region has been largely elastic and recoverable. Aquifer compaction
and land subsidence can be slowed or stopped, and in areas having appropriate geologic conditions,
reversed to some extent by reducing groundwater withdrawals or through artificial recharge.
The City of Tucson has increased delivery of Central Arizona Project (CAP) water through its
recharge and recovery projects, while reducing pumping from its central well field. This has reduced
water-level declines. However, subsidence due to earlier (pre-CAP) groundwater withdrawal may
continue for some time into the future and it may take some time before the benefits of recent
reductions in groundwater pumping can be observed. Continued monitoring of areas having the
greatest potential for subsidence will provide information that municipalities and resource managers
can use in the development and implementation of subsidence prevention and mitigation strategies.
Objectives
The objectives of this project are to monitor aquifer-storage change and land surface elevation change
within the Tucson AMA.
Approach
Aquifer-Storage Change
Aquifer-storage change is monitored by measuring changes in gravity over time at a network of
benchmarks (figure 1). As stated previously, gravity is affected by mass and distance; a change in mass
or a change in elevation will cause a change in gravity. Groundwater depletion is a mass change and
land-surface elevation change is a distance change. By removing the effect of change in distance,
changes in gravity are used to determine changes in aquifer-storage.
Temporal-gravity surveys are conducted across a significant part of the Tucson AMA to detect local
changes in the gravitational field of the Earth. The method is readily applied to measurement of
aquifer-storage change in the AMA because of the occurrence of significant variations in pore-space
storage that result from groundwater withdrawal and periodic (non-continuous) focused recharge.
Two instruments are used at the network of benchmarks: the relative gravity meter and the absolute
gravity meter. The relative meter is the primary instrument by which differences in gravity are
monitored at stable monuments. Much as control benchmarks are used in conventional land
surveying, repeated relative gravity surveys for groundwater storage monitoring should include a
reference station where gravity is known to vary little, or the absolute acceleration of gravity is
monitored. The USGS owns and operates aMicro-g LaCoste A-10 field-portable absolute gravity
meter, allowing for the establishment of these reference stations as needed. This is particularly
valuable in a hydrologic context where a number of absolute stations may be located throughout a
basin, thereby serving to constrain aleast-squares adjustment of the network of gravity differences
from relative gravity surveys.
Gravity surveys are conducted annually at the entire network of benchmarks (figure 1). The network
of benchmarks may be modified and/or expanded in areas where more rapid storage change is
occurring to improve resolution and to keep the project relevant to cooperators needs. These areas
include parts of Avra Valley, Sahuarita, Marana, and the portion of Tucson over Tucson Water's
central well field. Gravity measurements will increasingly be made using the A10 portable absolute
gravimeter; this will allow for fewer relative gravity measurements, thus improving the efficiency of
data collection.
Land-Surface Elevation Change
Land-surface elevation change is monitored at the same network of benchmarks (figure 1) throughout
the Tucson AMA by measuring changes in land-surface elevation over time with the Global
Positioning System. (GPS). GPS surveys also will be conducted annually but focused in that portion
of the network that previous surveys have shown to be most active areas of land-surface elevation
change. In addition, the project will benefit from an in-kind contribution from the ADWR
Interferometric Synthetic Aperture Radar (InSAR) program in the Tucson AMA. InSAR is a
technique that utilizes interferometric processing to compare the amplitude and phase signals received
during one pass of the satellite-based SAR platform over the AMA with the amplitude and phase
signals received during a second pass of the platform over the same area but at a different time.
The InSAR data will be used by ADWR to produce aland-surface deformation product over the same
time period as the successive GPS surveys in the AMA. The GPS data will be used to compare with
and constrain the InSAR deformation information. The annual InSAR product provides a much
broader coverage of land-surface deformation information than could be feasibly obtained with GPS
alone. Thus, land-surface elevation change monitoring costs are reduced by using a combination of
GPS and InSAR technology.
Fig. 1. Proposed network for aquifer-storage and subsidence monitoring in the Tucson AMA.
4
Benefits
Aquifer-storage monitoring
Repeat gravity surveys are an efficient, noninvasive means of measuring changes in the amount of
groundwater in southwestern alluvial basins (Pool and Anderson, 2007). Monitoring changes in
groundwater storage in the Tucson AMA is a means to track progress toward the regulatory goal to
maintain a balanced groundwater budget by the year 2025. Along with water-level data, an
independent and noninvasive means of long-term aquifer-storage change monitoring will be of value as
water-supply entities in eastern Pima County strive to meet demand and fully utilize renewable water
resources. Value of the data sets will accrue as the City further implements aquifer storage and
recovery efforts by contributing to an increased understanding of the aquifer systems in the AMA and
how they will respond to future withdrawals.
Water-level data entail assumptions about aquifer and well properties; thus, monitoring gravity change
as pumping decreases in the AMA provides a direct and independent way to measure attendant
changes in the amount of water in the aquifer and determine if and when aquifer recovery is
occurring. This information in concert with other hydrogeologic data sets can be used to help
mitigate land subsidence or aquifer storage losses in potential areas of concern.
Aquifer-storage change is one of the three components of the groundwater budget. The other two are
inflow to and outflow from the aquifer system. Measurement of aquifer-storage change and measures
and estimates of outflow enable better estimation of recharge and development of a more reliable
groundwater budget for the basins. Measures of aquifer-storage change increase the reliability and
utility of groundwater flow and management models. Use of storage-change data to improve model
calibration enables additional reduction in the uncertainty of model results. The improved
understanding of the movement, distribution, volume, and availability of groundwater, to which
storage monitoring contributes, enables more effective water management in the Tucson AMA.
The results of aquifer-storage change monitoring in the Tucson AMA between 1998 and 2009 indicate
that storage change and recharge can vary considerably from year to year. Although the overall
storage change in the AMA has been negative for the period of record, the rate of storage decrease has
slowed and storage increases have been observed in Avra Valley near recharge projects and in the area
of Tucson Water's central well field. Data also indicate that the majority of recharge to aquifers in the
AMA for an entire decade or more may occur following particularly heavy rainfall events. Gravity
surveys in the Tucson AMA since 1998 have provided previously unavailable data quantifying
recharge and storage changes. These data are being used to improve the understanding of the aquifer
systems and to improve groundwater flow models that will be used in resource planning.
Land-surface elevation change monitoring
Subsidence rates increase when the stress threshold between elastic and inelastic compaction is
exceeded (Carruth and others, 2007). Because it is not always possible to reliably estimate when the
threshold might be exceeded in the Tucson AMA, infrastructure damage could occur. Some types of
infrastructure are more sensitive to changes in land slope than other types. Sewer systems are largely
gravity driven, and are designed and constructed at slopes of about 2 feet per 1,000 feet. Small slope
changes can cause operational problems under some conditions. Accurate determination of the rates,
amounts, and distribution of land subsidence, together with delineation of higher-risk areas, will
provide data upon which mitigation and protection plans can be based.
5
Differential subsidence refers to the relatively large difference in the amount of subsidence that can
occur over a relatively short distance, resulting in focused effects. For example, localized subsidence of
as little as one-half inch can damage a highway overpass. Differential subsidence has the potential to
separate pipe joints of sewer and water lines. This can lead to system disruptions and roadway
damage, similar to that which occurred beneath a section of Oracle Road several years ago.
Extensional stress can increase the susceptibility of some types of storm-water pipe to fail under
existing loads, particularly seamless, unreinforced, and cast concrete. Also vulnerable are the concrete
lining sections of engineered channels that rely on the integrity of expansion joints to prevent flood
damage. Costs to address such infrastructure failures are high. Awareness of the distribution and
magnitude of differential subsidence can help to guide the design and implementation of maintenance
and monitoring schedules, selection of monitoring methods, and the design and construction of future
infrastructure.
Groundwater withdrawal from the City's central well field has been substantially decreased as CAP
recharge and recovery projects reach full capacity. However, subsidence in response to previous
pumping is unlikely to end in the near future. Areas of subsidence will continue until aquifer systems
reach pressure equilibrium and that can take many years. Observation of the timing and magnitude of
aquifer responses will further improve the understanding of land subsidence and of how the aquifer
systems function. Monitoring data also will contribute to a better understanding of the responses of
the aquifer systems to ongoing artificial recharge and withdrawals, and will provide additional insight
for future plans for well-site selection, recharge and recovery efforts, and water-management
programs. Additionally, GPS monitoring data will continue to augment and serve as ground truth for
satellite-based InSAR information to enable broad-scale assessments of regional subsidence in the
Tucson Basin.
Products
1) Maps of annual and 5-year aquifer-storage change and subsidence made publicly available on the
web at http://az.water.usgs.gov/projects/az162.htm1.
2) Annual oral presentation of fmdings at the Southern Arizona Water Users Association, and to
cooperators, as desired.
3) Oral presentation of findings at a national or international professional society meeting (such as
AGU or GSA).
4) A USGS Scientific Investigations Report documenting land subsidence and aquifer-storage
change in the Tucson AMA from 2009-2012.
Budget/Staffing
Fixed-cost funding information for this project is provided in tables 1 and 2. Table 1 presents the
schedule of work activities over the project life. Table 2 presents the summary of funding by agency.
It is understood that all agency funds in future years are subject to appropriation.
New for 2011-2013
For the upcoming project funding cycle, some project cooperators may have to reduce their level of
funding for the project due to budget constraints. The USGS is prepared to increase the project
funding match if funds are available to preserve the objectives of the project as much as possible;
however, depending on the final level of funding available, the stated approach and workplan may
have to be adjusted to avoid a budget shortfall. If this becomes necessary during the upcoming three-
year funding cycle, discussions will be held with project cooperators to determine areas to scale back
the monitoring.
Table 1-Schedule of work activities.
Work Tasks Year 1 Year 2 Year 3
1. GPS surveys (analysis combined with ADWR InSAR data)
2. Gravity surveys
3. Data post processing, analysis, and interpretation
4. Oral Report to project cooperators
5. Oral Presentation at State/National professional meeting `., ~`
A;
6. Project coordination and technical support
7. Draft report-review, revision, and printing
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8. Final storage change and subsidence report to cooperators
Table 2-Summary of funding by agency.
Agency Funding
Match year 1 Year 2 Year 3 Total Share
Tucson Water Matched 100% 34,000 34,000 34,000 102,000
Pima County Matched 100% 15,000 15,000 15,000 45,000
Marana Matched 100% 15,000 15,000 15,000 45,000
Oro Valley Matched 100% 15,000 15,000 15,000 45,000
Metro Water Matched 100% 7,500 7,500 7,500 22,500
USGS Federal
Matching
Funds
86,500
86,500
86,500
259,500
Totals 173,000 173,000 173,000 519,000
References Cited
Anderson, T.W., G.W. Freethey, and P. Tucci, 1992, Geohydrology and water resources of alluvial
basins in south-central Arizona and adjacent states: U. S. Geological Survey, Professional Paper 1406-
D.
Carruth, R. L., D. R. Pool, and C. E. Anderson, 2007, Land subsidence and aquifer-system
compaction in the Tucson Active Management Area, south-central Arizona, 1987-2005: U. S.
Geological Survey, Scientific Investigations
Report 2007-5190.
Galloway, D.L., Jones, D.R., and Ingebritsen, S.E., 1999, Land subsidence in the United States: U.S.
Geological Survey Circular 1182, 175 p.
Pool, D. R., 2008, The Utility of Gravity and Water-Level Monitoring at Alluvial Aquifer Wells in
Southern Arizona: in GEOPHYSICS, VOL., 73, NO. 6(November-December 2008), WA49-WA59.
Pool, D. R., and Anderson, M. T., 2007, Ground Water Storage Change and land Subsidence in
Tucson Basin and Avra Valley, Southeastern Arizona, 1998-2002: U. S. Geological Survey, Water-
Resources Investigations Report 07-5275.
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