SEPTEMBER 2013

Arizona Department
of Environmental Quality

FACT SHEET

Janice K. Brewer, Governor • Henry R. Darwin, Director

Publication Number: FS 13-11

Ambient Groundwater Quality of the Upper Hassayampa Basin:
A 2003-2009 Baseline Study – June 2013
Introduction
A baseline groundwater quality study of the Upper
Hassayampa basin was conducted from 2003 to
2009 by the Arizona Department of Environmental
Quality (ADEQ) Ambient Groundwater Monitoring
Program. ADEQ carried out this task pursuant to
Arizona Revised Statutes §49-225 that mandates
ongoing monitoring of waters of the state including
its aquifers. This fact sheet is a synopsis of the ADEQ
Open File Report 13-03.1
The Upper Hassayampa groundwater basin covers
approximately 787 square miles within Maricopa
and Yavapai counties and is located about 60 miles
northwest of Phoenix (Map 1). The basin is characterized by mid-elevation mountains and had an
estimated population of 10,479 in 2000.2 The largest
population center is the Town of Wickenburg. Other
communities include Congress and Groom Creek.
Low-intensity livestock grazing is the predominant
land use and most ranches have limited acreages

Map 1 – Sample sites in the Upper
Hassayampa basin are colorcoded according to their water
quality status: No Water Quality
Exceedences, Secondary MCLs
Exceedences, Primary MCL Exceedances, and Primary and Secondary
MCL Exceedances.
(Map by Jean Ann Rodine)

of irrigated pasture to raise additional animal feed.
There are no surface water diversions or impoundments besides small stock ponds within the basin.2
Groundwater is the only source for public water
supply, domestic, irrigation and industrial purposes.
Public water supply uses the most groundwater in
the basin.2

Figure 1 – The storage tank of the “ML Windmill” also serves as
a sign post along the rugged Wagoner Road that connects the
communities of Kirkland Junction located west of the basin
and Crown King located east of the basin.

The basin is bounded on the north by the Weaver
Mountains, on the northwest by the Date Creek
Mountains, on the south by the Vulture Mountains,
and on the east by the Bradshaw Mountains. Elevations range from approximately 7,000 feet above
mean sea level (amsl) in the Bradshaw Mountains
to 1,900 feet amsl along the Hassayampa River
about five miles south of Wickenburg. The basin
is comprised of federal land managed by the U.S.
Forest Service (25 percent) and Bureau of Land
Management (BLM) (21 percent), State Trust lands
(38 percent) and private land (16 percent).2

Hydrology
The basin is drained by the Hassayampa River which
flows from north to south. The river is intermittent
over much of its course but has perennial flow in
its upper reaches in the Bradshaw Mountains and
where bedrock brings groundwater to the surface
a few miles south of Wickenburg. Some of its
tributaries, – including Antelope Creek, Ash Creek,
Minnehaha Creek, and Weaver Creek – have limited
stretches of perennial flow.2
Groundwater is found primarily in the basin-fill sediments found in the southeast portion of the basin.
The aquifer consists of gravel, sand, silt and clay and
is capable of yielding several hundred gallons per
minute. Smaller alluvial deposits are found along
the Hassayampa River in the northern part of the
basin. Groundwater is also found in limited amounts
in the consolidated crystalline and sedimentary
rocks that constitute most of the basin.2

OUR VISION
To lead Arizona and the
nation in protecting
the environment and
improving the
quality of life for
the people of our
state.

Groundwater movement mirrors surface flow,
going from north to south. Depth to groundwater
varies across the basin, ranging from just a few
feet below land surface along some stretches of
the Hassayampa River to more than 1,000 feet
below land surface in the center of the basin.
Natural recharge for the basin is estimated to be
8,000 acre-feet per year while groundwater use is
estimated to be 3,900 acre-feet per year.2
Methods of Investigation
To characterize regional groundwater quality,
samples were collected from 34 sites (27 wells and
seven springs). Of the 27 wells, 20 had submersible pumps, six were windmills, and one was a
monitoring well.
Samples for inorganic constituents and isotopes
(oxygen and deuterium) were collected from each
site while radon (17 sites) and radionuclide (12
sites) samples were collected at selected sites.
Sampling protocol followed the ADEQ Quality Assurance Project Plan (see www.azdeq.gov/function/
programs/lab/). The effects of sampling equipment
and procedures were not significant based on
quality assurance/quality control evaluations.

Arizona Department
of Environmental Quality

Water Quality Sampling Results
Groundwater sample results were compared with
the Safe Drinking Water Act (SDWA) health and
aesthetics-based water quality standards.
Public drinking water systems must meet healthbased, water quality standards, called Primary
Maximum Contaminant Levels (MCLs), when supplying water to their customers. These enforceable
standards are based on a daily lifetime (70 years)
consumption of two liters.3 Primary MCLs were
exceeded at nine of the 34 sites (27 percent). Constituents exceeding Primary MCLs include arsenic
(one site), gross alpha (five sites), and nitrate (four
sites).
Public drinking water systems are encouraged
by the SDWA to meet unenforceable, aestheticsbased water quality guidelines, called Secondary
MCLs, when supplying water to their customers. Water exceeding Secondary MCLs may be
unpleasant to drink and/or create unwanted
cosmetic or laundry effects but is not considered a
health concern.3 Secondary MCLs were exceeded
at 13 of the 34 sites (38 percent). Constituents
exceeding Secondary MCLs include chloride
(one site), fluoride (four sites), iron (two sites),
manganese (four sites), sulfate (one site), and TDS
(eight sites).

FACT SHEET

Publication Number: FS 13-11

Radon is a naturally occurring, intermediate
breakdown product from the radioactive decay of
uranium-238 to lead-206. Of the 17 sites sampled
PRINCIPLES AND VALUES
for radon, none exceeded the proposed 4,000
We advocate for Arizona’s environment.
per standards
liter (pCi/L)
standard that would apWe picocuries
adhere to the highest
of
technical professionalism.
ply if Arizona establishes a multimedia program to
We commit to the highest standards
of ethical behavior.
address the health risks from radon in indoor air.3
We are committed to openness, honesty
andEight
transparency.
sites (47 percent) exceeded the proposed
We foster relationships built on respect,
300 pCi/L standard that would apply if Arizona
courtesy and service.
3
not develop
Wedoes
value creativity,
innovation a multimedia program.
and performance.

We turn challenges into opportunities.
We value our employees
and work as a team.

Groundwater Composition
Groundwater composition varied throughout the
basin in the following ways:
• Groundwater chemistry in the basin is most
commonly calcium-bicarbonate or mixedbicarbonate.
• Levels of pH measured in the field were slightly
alkaline (above seven standard units) except for
five sample sites that were slightly acidic (below
seven standard units).
• Total dissolved solids (TDS) concentrations
were considered fresh (below 999 mg/L) at 32
sites and slightly saline (1,000 – 3,000 mg/L) at
two sites.
• Hardness concentrations were moderately hard
(75 - 150 mg/L) at two sites, hard (151 - 300
mg/L) at 22 sites, very hard (301 – 600 mg/L)
at eight sites, and extremely hard (above 600
mg/L) at two sites.
• Nitrate (as nitrogen) concentrations at most
sites may have been influenced by human
activities and were divided into natural background (eight sites at <0.2 mg/L) may or may
not indicate human influence (20 sites at 0.2
– 3.0 mg/L) ), may result from human activities
(two sites at 3.0 – 10 mg/L), and probably result
from human activities (four sites > 10 mg/L).4
• Most trace elements such as aluminum,
antimony, arsenic, beryllium, boron, cadmium,
chromium, iron, lead, manganese, mercury,
nickel, selenium, silver, and thallium were rarely
detected. Only barium, fluoride, and zinc were
detected at more than one-third of the sites.

Figure 2 – Intermittent flow in the Hassayampa River at the
Wagoner Road Bridge. The stream is perennial at higher and
lower elevations in the basin.

Figure 3 – An unused aqueduct, the Leppe Wash flume, is
located on the historic TK Bar Ranch along the Hassayampa
River near Kirkland, Arizona.

Oxygen and deuterium isotope values at most
sites appear to be a product of the elevation at
which the sample sites were located. The five
samples that experienced little evaporation were
characterized as depleted and were collected from
sites located high in the Bradshaw Mountains. The
remaining 29 samples were more enriched, suggesting the water from these lower elevation sites
was subject to much greater evaporation.5

OUR VISION
To lead Arizona and the
nation in protecting
the environment and
improving the
quality of life for
the people of our
state.

Arizona Department
of Environmental Quality

Groundwater Patterns

Discussion

Groundwater constituent concentrations were
influenced by recharge group and geology.
Constituents such as temperature, pH-lab, sodium,
potassium, chloride, fluoride, oxygen-18 and
deuterium had significantly higher constituent
concentrations at sites with enriched samples
than at sites with depleted samples (Kruskal-Wallis
test, p ≤ 0.05). Constituents such as temperature,
sodium, sulfate, nitrate, fluoride, and deuterium
had significantly greater concentrations in sites
located in unconsolidated sediments than in consolidated rock; turbidity had the opposite pattern
(Kruskal-Wallis test, p ≤ 0.05).

Groundwater in the basin is generally suitable for
drinking water use based on the results of this
ADEQ ambient study. Samples from 20 of the 34
sites met all water quality standards.3 Moreover,
samples from four other sites had only minor
exceedances of aesthetics-based standards for
TDS, iron, and/or manganese, making 24 of the 34
sample sites (71 percent) acceptable as a drinking
water source. Of the remaining 10 sample sites,
the constituents that most commonly impacted
the acceptability of water for drinking purposes
were gross alpha and nitrate.

Recharge Group

Figure 4 – Sites consisting of enriched samples have significantly higher sodium concentrations than sites consisting of
depleted samples (Kruskal-Wallis, p ≤ 0.05). Recharge areas
typically have low sodium concentrations though sodium
often becomes the dominant cation in downgradient areas. 8

Geology

Figure 5 – Sample sites located in unconsolidated sediments
have significantly higher nitrate concentrations than sample
sites located in consolidated rock (Kruskal-Wallis, p ≤ 0.05).
This pattern may be due to increased residential and commercial development that has occurred in basin-fill areas.

Gross alpha exceeded health-based, water quality
standards in radionuclide samples collected from
five sites. Radionuclide samples were collected
however, at only 12 of the 34 sites, so gross alpha
had a 42 percent water quality standard exceedance rate. This finding is not unexpected as large
portions of the basin consist of granitic geology
and a few sites were in the vicinity of historic
mining activity, both of which are associated with
elevated radionuclide concentrations in groundwater.6 Based on these results, future basin studies
should better characterize gross alpha concentrations by collecting additional radionuclide
samples.
Nitrate exceeded health-based, water quality standards in samples collected from four wells. Three
exceedances were barely over the 10 mg/L nitrate
(as nitrogen) standard while the fourth was almost
double the standard at 19 mg/L. Potential nitrogen sources included effluent from septic systems
and wastewater from agricultural operations.
Arsenic was the other health-based exceedance in
a sample which also had the study’s highest fluoride concentrations and pH levels. Chemically, the
sample was similar to groundwater in the nearby
McMullen Valley basin.7 Hydroxyl ion exchange
is the likely reason for the elevated fluoride and
arsenic concentrations. The high pH value
(8.41 standard units) of the sample allows an
exchange of hydroxyl for fluoride ions thereby
increasing fluoride in solution.8 Arsenic is also
affected by reactions with hydroxyl ions though
elevated concentrations are also influenced by
aquifer residence time, an oxidizing environment,
and lithology. 8
Another sample with unusual water chemistry
was collected east of Wickenburg. The sample
exceeded water quality standards for gross alpha,
TDS, sulfate, fluoride, and manganese and had
the study’s highest concentrations of TDS (2,300
mg/L) and sulfate (1,100 mg/L). The sulfate result
was almost nine times the next highest concentration found in the basin. Based on these results,
the sample is strongly influenced by nearby
inactive mines.8 Furthermore, the presence of

FACT SHEET

Publication Number: FS 13-11

high concentrations of iron, manganese, and TKN
combined with a non-detection of nitrate suggest
unusual reducing conditions in the groundwater.8
PRINCIPLES AND VALUES
Thus, the sample from this remote stock well apWe advocate for Arizona’s environment.
sitestandards
specific
We pears
adhere toto
thebe
highest
of and probably is not reflectechnical professionalism.
tive
of
regional
groundwater
conditions.
We commit to the highest standards
of ethical behavior.

In the basin, there is some tendency for constituent concentrations to be significantly higher in
groundwater sites collected in unconsolidated
We value creativity, innovation
andsediment
performance. and/or which consist of enriched reWecharge.
turn challenges
into opportunities.
These
trends however, do not impact the
We value our employees
acceptability
of these sites for use as a drinking
and
work as a team.
water source.

We are committed to openness, honesty
and transparency.
We foster relationships built on respect,
courtesy and service.

References Cited
1

Towne, D.C., 2013, Ambient groundwater quality
of the Upper Hassayampa basin: A 2003 - 2009
baseline study: Arizona Department of Environmental Quality Open File Report 13-03, 52 p.

2

Arizona Department of Water Resources website,
www.azwater.gov/azdwr/default.aspx, accessed
06/4/13.

3

U.S. Environmental Protection Agency website,
www.epa.gov/waterscience/criteria/
humanhealth/, accessed 05/24/12.

4

Madison, R.J., and Brunett, J.O., 1984, Overview
of the occurrence of nitrate in ground water of
the United States, in National Water Summary
1984-Water Quality Issues: U.S. Geological Survey
Water Supply Paper 2275, pp. 93-105

5

Earman, Sam, et al, 2003, An investigation of the
properties of the San Bernardino groundwater
basin, Arizona and Sonora, Mexico: Hydrology
program, New Mexico Institute of Mining and
Technology, 283 p.

6

Lowry, J.D. and Lowry, S.B., 1988, “Radionuclides
in Drinking Waters,” in American Water Works Association Journal, 80 (July), pp. 50-64.

7

Towne, D.C., 2011, Ambient groundwater quality
of the McMullen Valley basin: A 2008 - 2009 baseline study: Arizona Department of Environmental
Quality Open File Report 11-02, 94 p.

8

Robertson, F.N., 1991, Geochemistry of ground
water in alluvial basins of Arizona and adjacent
parts of Nevada, New Mexico, and California: U.S.
Geological Survey Professional Paper 1406-C, 94 p.

For More Information Contact:
Douglas C. Towne
Hydrologist, ADEQ Monitoring Unit
1110 W. Washington St. #5330D
Phoenix, AZ 85007
email: dct@azdeq.gov
www.azdeq.gov/environ/water/assessment/
ambient.html#studies