Ambient groundwater quality of the McMullen Valley Basin: a 2008-2009 baseline study

              II
III
Ambient Groundwater Quality of the
McMullen Valley Basin: A 2008-2009 Baseline Study
By Douglas C. Towne
Maps by Jean Ann Rodine
Arizona Department of Environmental Quality
Open File Report 2011-02
ADEQ Water Quality Division
Surface Water Section
Monitoring Unit
1110 West Washington St.
Phoenix, Arizona 85007-2935
Thanks:
Field Assistance: Jason Jones, Brent Mitchell, David Pinol and Dennis Turner.
Special recognition is extended to the many well owners who were kind enough
to give permission to collect groundwater data on their property.
Photo Credits: Douglas Towne
Report Cover: Well #23 pumps a prodigious amount of groundwater for use on the nearby
irrigated fields of cantaloupe near the town of Aguila. Like many wells in the
Eastern Regional aquifer, samples from the well exceeded aesthetics-based
standards for fluoride.
IV
Other Publications of the ADEQ Ambient Groundwater Monitoring Program
ADEQ Ambient Groundwater Quality Open-File Reports (OFR):
Gila Valley Sub-basin OFR 09-12, November 2009, 99 p.
Agua Fria Basin OFR 08-02, July 2008, 60 p.
Pinal Active Management Area OFR 08-01, June 2007, 97 p.
Hualapai Valley Basin OFR 07-05, March 2007, 53 p.
Big Sandy Basin OFR 06-09, October 2006, 66 p.
Lake Mohave Basin OFR 05-08, October 2005, 66 p.
Meadview Basin OFR 05-01, January 2005, 29 p.
San Simon Sub-Basin OFR 04-02, October 2004, 78 p.
Detrital Valley Basin OFR 03-03, November 2003, 65 p.
San Rafael Basin OFR 03-01, February 2003, 42 p.
Lower San Pedro Basin OFR 02-01, July 2002, 74 p.
Willcox Basin OFR 01-09, November 2001, 55 p.
Sacramento Valley Basin OFR 01-04, June 2001, 77 p.
Upper Santa Cruz Basin OFR 00-06, Sept. 2000, 55 p. (With the U.S. Geological Survey)
Prescott Active Management Area OFR 00-01, May 2000, 77 p.
Upper San Pedro Basin OFR 99-12, July 1999, 50 p. (With the U.S. Geological Survey)
Douglas Basin OFR 99-11, June 1999, 155 p.
Virgin River Basin OFR 99-04, March 1999, 98 p.
Yuma Basin OFR 98-07, September, 1997, 121 p.
ADEQ Ambient Groundwater Quality Fact sheets (FS):
McMullen Valley Basin FS 11-03, 2010, 6 p.
Gila Valley Sub-basin FS 09-28, November 2009, 7 p.
Agua Fria Basin FS 08-15, July 2008, 4 p.
Pinal Active Management Area FS 07-27, June 2007, 7 p.
Hualapai Valley Basin FS 07-10, March 2007, 4 p.
Big Sandy Basin FS 06-24, October, 2006, 4 p.
Lake Mohave Basin FS 05-21, October 2005, 4 p.
Meadview Basin FS 05-01, January 2005, 4 p.
San Simon Sub-basin FS 04-06, October 2004, 4 p.
Detrital Valley Basin FS 03-07, November 2003, 4 p.
San Rafael Basin FS 03-03, February 2003, 4 p.
Lower San Pedro Basin FS 02-09, August 2002, 4 p.
Willcox Basin FS 01-13, October 2001, 4 p.
Sacramento Valley Basin FS 01-10, June 2001, 4 p.
Yuma Basin FS 01-03, April 2001, 4 p.
Virgin River Basin FS 01-02, March 2001 4 p.
Prescott Active Management Area FS 00-13, December 2000, 4 p.
Douglas Basin FS 00-08, September 2000, 4 p.
Upper San Pedro Basin FS 97-08, August 1997, 2 p. (With the U.S. Geological Survey)
These publications are available on-line.
Visit the ADEQ Ambient Groundwater Monitoring Program at:
www.azdeq.gov/environ/water/assessment/ambient.html
V
VI
Table of Contents
Abstract ................................................................................................................................................................... 1
Introduction ............................................................................................................................................................ 2
Purpose and Scope ..................................................................................................................................... 2
Physical and Cultural Characteristics.......................................................................................................... 2
Hydrology................................................................................................................................................................ 4
Lithology.................................................................................................................................................... 4
Groundwater............................................................................................................................................... 5
Wells.......................................................................................................................................................... 9
Investigation Methods ............................................................................................................................................ 9
Sampling Strategy ...................................................................................................................................... 9
Sampling Collection................................................................................................................................. 12
Laboratory Methods ................................................................................................................................. 12
Data Evaluation .................................................................................................................................................... 14
Quality Assurance .................................................................................................................................... 14
Data Validation ........................................................................................................................................ 18
Statistical Considerations .......................................................................................................................... 20
Groundwater Sampling Results ........................................................................................................................... 23
Water Quality Standards / Guidelines ....................................................................................................... 23
Suitability for Irrigation............................................................................................................................ 33
Analytical Results .................................................................................................................................... 33
Groundwater Composition .................................................................................................................................. 36
General Summary..................................................................................................................................... 36
Constituent Co-Variation .......................................................................................................................... 41
Isotope Comparison.................................................................................................................................. 43
Groundwater Quality Variation................................................................................................................. 45
Summary and Conclusions .................................................................................................................................. 52
Recommendations................................................................................................................................................. 56
References ............................................................................................................................................................. 57
Appendices
Appendix A – Data on Sample Sites, McMullen Valley basin, 2008-2009 .............................................. 59
Appendix B – Groundwater Quality Data, McMullen Valley basin, 2008-2009 ...................................... 65
VII
Maps
ADEQ Ambient Monitoring Program Studies......................................................................................................... IV
Map 1. McMullen Valley Basin .............................................................................................................................. 3
Map 2. Sample Sites ............................................................................................................................................. 13
Map 3. Water Quality Status................................................................................................................................. 24
Map 4. Arsenic...................................................................................................................................................... 26
Map 5. Fluoride..................................................................................................................................................... 27
Map 6. Nitrate ....................................................................................................................................................... 28
Map 7. TDS........................................................................................................................................................... 30
Map 8. Gross alpha ............................................................................................................................................... 31
Map 9. Radon........................................................................................................................................................ 32
Map 10. Water chemistry...................................................................................................................................... 38
Map 11. Hardness ................................................................................................................................................. 40
Diagrams
Diagram 1. Hydrologic cross-section parallel to McMullen Valley........................................................................ 7
Diagram 2. Hydrologic cross-section parallel to Harrisburg Valley ....................................................................... 7
Diagram 3. Hydrologic cross-section perpendicular to McMullen Valley .............................................................. 8
Diagram 4. Specific paths of hydrologic cross-sections.......................................................................................... 8
Diagram 5. Salinity hazard of McMullen Valley wells ......................................................................................... 33
Diagram 6. Sodium hazard of McMullen Valley wells ......................................................................................... 33
Diagram 7. Water chemistry pie chart................................................................................................................... 36
Diagram 8. Piper tri-linear water chemistry diagram ............................................................................................ 37
Diagram 9. Hardness classification pie chart......................................................................................................... 39
Diagram 10. TDS – sodium relationship ............................................................................................................... 41
Diagram 11. Oxygen – deuterium relationship...................................................................................................... 44
Diagram 12. Oxygen – deuterium relationship...................................................................................................... 44
Diagram 13. Seven aquifer TDS box plot ............................................................................................................. 45
Diagram 14. Seven aquifer nitrate box plot........................................................................................................... 45
Diagram 15. Seven aquifer hardness box plot ....................................................................................................... 46
Diagram 16. Seven aquifer potassium box plot..................................................................................................... 46
Diagram 17. Five aquifer pH-field box plot .......................................................................................................... 49
Diagram 18. Five aquifer TDS box plot ................................................................................................................ 49
Diagram 19. Five aquifer bicarbonate box plot ..................................................................................................... 50
Diagram 20. Five aquifer deuterium box plot........................................................................................................ 50
Diagram 21. Groundwater divide locations........................................................................................................... 53
VIII
Figures
Figure 1. The Salome Frog ................................................................................................................................. 10
Figure 2. Centennial Wash flooding Wenden, January 2010............................................................................... 10
Figure 3. Domestic well in the Forepaugh aquifer............................................................................................... 11
Figure 4. Irrigation well near Aguila in the Eastern Regional aquifer ................................................................. 11
Figure 5. Meter on irrigation well near Aguila in the Eastern Regional aquifer.................................................. 11
Figure 6. Domestic well north of Salome in the Perched aquifer ........................................................................ 11
Figure 7. Domestic well north of Salome in the Western Regional aquifer......................................................... 21
Figure 8. Irrigation well south of Salome in the Southern Regional aquifer ....................................................... 21
Figure 9. Domestic well south of Salome in the Southern Regional aquifer ....................................................... 21
Figure 10. Irrigation well north of Salome in the Western Regional aquifer......................................................... 21
Figure 11. Irrigation well northeast of Salome in the Mixed aquifer..................................................................... 22
Figure 12. Cascading well northeast of Salome in the Western Regional aquifer ................................................. 22
Figure 13. Stock well northeast of Wenden in the Western Regional aquifer ....................................................... 22
Figure 14. Domestic well near Harcuvar in the Harcuvar aquifer ......................................................................... 22
Tables
Table 1. ADHS/Test America laboratory water methods and minimum reporting levels used in the study......... 15
Table 2. Summary results of McMullen Valley basin duplicate samples from the ADHS laboratory ................. 17
Table 3. Summary results of McMullen Valley basin split samples from the ADHS / Test America labs........... 19
Table 4. McMullen Valley basin sites exceeding health-based (Primary MCL) water quality standards ............ 25
Table 5. McMullen Valley basin sites exceeding aesthetics-based (Secondary MCL) water quality guidelines.. 29
Table 6. Summary statistics for McMullen Valley basin groundwater quality data ............................................. 34
Table 7. Correlation among McMullen Valley basin groundwater quality constituent concentrations using Pearson
correlation probabilities......................................................................................................................... 42
Table 8. Variation in groundwater quality constituent concentrations among five aquifers using Kruskal-Wallis
test with the Tukey Test .......................................................................................................................... 47
Table 9. Summary statistics (95% Confidence Intervals) for groundwater quality constituent concentrations with
Significant concentration differences among five aquifers ..................................................................... 48
Table 10. Variation in groundwater quality constituent concentrations among three aquifers using Kruskal-Wallis
test with the Tukey Test .......................................................................................................................... 51
IX
Abbreviations
amsl above mean sea level
ac-ft acre-feet
AGF/yr acre-feet per year
ADEQ Arizona Department of Environmental Quality
ADHS Arizona Department of Health Services
ADWR Arizona Department of Water Resources
ARRA Arizona Radiation Regulatory Agency
AZGS Arizona Geological Survey
As arsenic
bls below land surface
BLM U.S. Department of the Interior Bureau of Land Management
oC degrees Celsius
CI0.95 95 percent Confidence Interval
Cl chloride
EPA U.S. Environmental Protection Agency
F fluoride
Fe iron
gpm gallons per minute
hard-cal hardness concentration calculated from calcium and magnesium concentrations
HUC Hydrologic Unit Code
LLD Lower Limit of Detection
MMU McMullen Valley Groundwater Basin
Mn manganese
MCL Maximum Contaminant Level
ml milliliter
msl mean sea level
ug/L micrograms per liter
um micron
uS/cm microsiemens per centimeter at 25° Celsius
mg/L milligrams per liter
MRL Minimum Reporting Level
MTBE Methyl tertiary-Butyl Ether
ns not significant
ntu nephelometric turbidity unit
pCi/L picocuries per liter
QA Quality Assurance
QAPP Quality Assurance Project Plan
QC Quality Control
SAR Sodium Adsorption Ratio
SDW Safe Drinking Water
SC Specific Conductivity
su standard pH units
SO4 sulfate
TDS Total Dissolved Solids
TKN Total Kjeldahl Nitrogen
USGS U.S. Geological Survey
VOC Volatile Organic Compound
* significant at p ≤ 0.05 or 95% confidence level
** significant at p ≤ 0.01 or 99% confidence level
X
Ambient Groundwater Quality of the McMullen Valley Basin: A 2008-2009 Baseline Study
Abstract - In 2008-2009, the Arizona Department of Environmental Quality (ADEQ) conducted a baseline
groundwater quality study of the McMullen Valley basin located in west-central Arizona. The basin consists of the
drainage of the ephemeral Centennial Wash within McMullen Valley and the surrounding mountains.6 Groundwater
is predominantly used for irrigation near the communities of Aguila, Wenden and Salome.7 The City of Phoenix has
purchased farms near Salome to obtain the water rights for potential transfer to Maricopa County for municipal use.7
The main source of groundwater in the basin is the Regional aquifer. 24 Heavy pumping near Aguila and Salome has
produced a groundwater divide near the La Paz-Maricopa County line creating Eastern and Western Regional
aquifers.25 In terms of spatial extent and groundwater storage these are the largest aquifers in the basin. 25 Low hills
east of Aguila that minimize groundwater movement divide the Eastern Regional aquifer from the Forepaugh
aquifer.43 A subsurface extension of the Harquahala Mountains that limits groundwater movement separates the
Western Regional aquifer from the Southern Regional aquifer located in Harrisburg Valley.25 Another subsurface
geologic feature separates the Harcuvar aquifer from the Southern and Western Regional aquifers lying to the east. 24
Groundwater movement between the Western Regional aquifer and the overlaying Perched aquifer is restricted by
the Lake-bed Unit, a layer of fine-grained sediments. 24 These deposits, however, are absent in an area one mile
northeast of Salome where groundwater flowing from the Perched aquifer into the Western Regional aquifer is
termed the Mixed aquifer. 24
To characterize regional groundwater quality, samples were collected from 124 wells. The wells supply water for
irrigation, domestic, municipal and stock uses throughout the basin. Inorganic constituents and oxygen and
deuterium isotopes were collected from all wells. At selected wells, radon (79 sites), radiochemistry (50 sites) and
pesticide (2 sites) samples were also collected. In addition to the 124 wells, 12 additional wells were sampled for
field parameters and nitrate.
Primary maximum contaminant levels (MCLs) for inorganic constituents were exceeded at 54 of the 124 sites (44
percent). These enforceable standards define the maximum concentrations of constituents allowed in water supplied
for drinking water purposes by a public water system and are based on a lifetime daily consumption of two liters. 38
Constituents exceeding Primary MCLs include arsenic (24 sites), fluoride (27 sites), nitrate (25 sites), and selenium
(2 sites). Primary MCLs for radionuclides were exceeded at 9 of the 50 sites (18 percent) including gross alpha (9
sites) and uranium (4 sites). Elevated concentrations of arsenic and fluoride likely occur naturally. Elevated nitrate
concentrations appear to be caused by nitrogen-laden recharge resulting from irrigation applications and wastewater
from septic systems. Gross alpha and uranium exceedances are likely naturally occurring though may be impacted
by anthropomorphic activities.42 Secondary MCLs were exceeded at 87 of 124 sites (70 percent). These are
unenforceable aesthetics guidelines that define the maximum constituent concentration that can be present in
drinking water without an unpleasant taste, color, or odor.38 Constituents above Secondary MCLs include chloride
(13 sites), fluoride (69 sites), manganese (2 sites), pH (19 sites), sulfate (8 sites), and TDS (31 sites).
The basin’s most important groundwater quality issue is the absence of the Lake-bed Unit northeast of Salome. 24
Nearby wells commonly exceed water quality standards and guidelines; nitrate concentrations were elevated up to
seven times the 10 mg/L health-based water quality standard. This is the result of percolating irrigation water
containing salts and nitrate recharging the Perched aquifer. With a higher static water level than the Regional
aquifer, groundwater drains downward from the Perched aquifer into the Western Regional aquifer. This impacted
area is referred to in this report as the Mixed aquifer. 24 TDS, sodium, chloride, sulfate, and nitrate were significantly
higher in the Perched and Mixed aquifers than in all the other aquifers (Kruskal-Wallis with Tukey test, p ≤ 0.05).
Both the Eastern and Western Regional aquifers had water quality issues. In the Eastern Regional aquifer, southeast
of Aguila, some sample sites exceeded standards for fluoride and, to a lesser degree, arsenic. Similarly, in the
Western Regional aquifer near Wenden, sample sites also exceeded standards for fluoride and, to a lesser degree,
arsenic. The Eastern Regional aquifer exhibited significantly lower concentrations of TDS, sodium, and boron than
in the Western Regional aquifer; the opposite pattern occurs with well depth and groundwater depth. (Kruskal-
Wallis with Tukey test, p ≤ 0.05) These differences may result from poor quality irrigation recharge minimally
impacting the Eastern Regional aquifer because of the great depths needed to percolate to groundwater. Almost all
the sites sampled in the Forepaugh aquifer exceeded water quality standards for fluoride and arsenic. Fluoride
concentrations commonly were up to three times the health-based standard. Few water quality standards were
exceeded in the Southern Regional and Harcuvar aquifers; both appear to consist of more recent recharge.
2
INTRODUCTION
Purpose and Scope
The McMullen Valley groundwater basin
encompasses approximately 591 square miles in
west-central Arizona.5 The western portion of the
basin is located in La Paz County, the southeastern
portion is in Maricopa County and a small portion in
the northeast is in Yavapai County (Map 1). The
economy of McMullen Valley is predominantly
based on agriculture as well as serving the needs of
the area’s retired population. Groundwater is the
primary source for agricultural, municipal, stock and
domestic water supply within the basin. 6
The McMullen Valley basin is one of the few
groundwater basins in Arizona designated for out-of-basin
transport of groundwater. The City of Phoenix
has purchased 14,000 acres of agricultural land to
obtain the water rights for potential future transport
of groundwater to the Phoenix Active Management
Area for municipal uses. 7
The Arizona Department of Environmental Quality
(ADEQ) Ambient Groundwater Monitoring program
was originally charged with characterizing nitrate
concentrations in the town of Salome to explore the
possibility of creating a Nitrogen Management Area.3
The study was subsequently expanded to characterize
the groundwater quality of the entire McMullen
Valley basin.
Sampling by the ADEQ Ambient Groundwater
Monitoring program is authorized by legislative
mandate in the Arizona Revised Statutes §49-225,
specifically: “...ongoing monitoring of waters of the
state, including...aquifers to detect the presence of
new and existing pollutants, determine compliance
with applicable water quality standards, determine
the effectiveness of best management practices,
evaluate the effects of pollutants on public health or
the environment, and determine water quality
trends.” 3
Benefits of ADEQ Study – This study, which
utilizes accepted sampling techniques and
quantitative analyses, is designed to provide the
following benefits:
 A general characterization of regional
groundwater quality conditions in the
McMullen Valley basin identifying areas
with water quality concerns.
 A characterization of nitrate concentrations
in groundwater in areas of housing
developments using septic systems for
wastewater disposal in areas south of the
town of Salome
 A process for evaluating potential
groundwater quality impacts arising from a
variety of sources including mineralization,
mining, agriculture, livestock, septic tanks,
and poor well construction.
 A guide for identifying future locations of
public supply wells.
 A guide for determining areas where further
groundwater quality research is needed.
Physical Characteristics
Geography – The McMullen Valley basin is located
within the Basin and Range physiographic province
which is characterized by broad alluvial valleys
separated by mountain ranges. The kidney-shaped
basin is oriented northeast-to-southwest and is about
15 miles wide and 48 miles long.
The basin is bounded on all sides, except the
northeast, by mountains. The Harcuvar Mountains
are to the north, the Harquahala and Vulture
Mountains are to the south, and the Little Harquahala
and Granite Wash Mountains are to the west. A ridge
near the railroad siding of Divide marks the eastern
boundary that separates it from the Upper
Hassayampa basin. At the southwest end of the basin
is Harrisburg Valley, oriented perpendicular to the
axis of McMullen Valley.
The basin is drained by Centennial Wash, an
ephemeral tributary of the Gila River that heads
about 20 miles east of Aguila and discharges from the
basin through “the Narrows” into the Harquahala
basin.25 Elevations in the McMullen Valley basin
range from 5,720 feet above sea level atop
Harquahala Peak to approximately 1,700 feet above
mean sea level at “the Narrows”. Elevation of the
McMullen Valley floor typically ranges from 1,900
to 2,200 feet. 7
Within McMullen Valley are the communities of
Aguila, Wenden, and Salome. The latter two
communities had a combined population of 2,246
permanent residents in 2000.1 Agriculture is the main
industry although the area is increasingly a
destination for retirees either as permanent residents
or, more often, seasonal visitors.
3
4
Approximately 14,600 acres were farmed in 2007 of
which 79 percent were flood irrigated and 21 percent
drip irrigated. 7 Crops grown in 2007 included melons
(60 percent), cotton (19 percent), sorghum (8 percent)
and minor amounts of chilies, oats, alfalfa, corn,
guayule, and pistachio. Irrigated agriculture has
spatially decreased in the basin with 34,200 acres
farmed as recently as 1980.25
There are two irrigation districts: the Aguila
Irrigation District and the McMullen Valley Water
Conservation District. All wells and ditches are
privately owned in both districts as neither has a
consolidated distribution system. Both districts were
formed in order to potentially contract water and
power from the Colorado River; groundwater is
currently the only water supply. 7
The City of Phoenix purchased and/or leased
approximately 16,000 acres of farmland in the
Salome/Wenden area in 1986 with plans to
eventually pump and transport groundwater from this
area to Phoenix to use as for municipal purposes. 24
Until this groundwater transfer occurs, Phoenix is
managing these farm properties by leasing them to
farm operators.24 About 93 percent of private lands in
the McMullen Valley Water Conservation District
are owned by the City of Phoenix. 24
Climate – The arid climate of the McMullen Valley
basin is characterized by hot summers and mild
winters. Precipitation occurs predominantly as rain
in either late summer, localized monsoon
thunderstorms or in winter as widespread, low
intensity rain that sometimes includes snow
especially at higher elevations. Annual precipitation
averages about 7 inches. 25
Geology - The McMullen Valley basin is
characterized by two principal physiographic
features:
 mountainous regions, and
 an intermontane, sediment-filled basin.
The mountains consist of relatively impermeable,
granites, gneisses and variably metamorphosed-to-unmetamorphosed
sedimentary and volcanic rocks. 24
The basin-fill is comprised largely of unconsolidated
to consolidated sedimentary rocks that have been
eroded from the surrounding mountains and
deposited within the basin. 24
Early basin sedimentation was characterized by
deposition of alluvial fans by streams emanating from
the bordering mountains into a subsiding basin. Over
time, these alluvial fans coalesced to form a broad
bajada projecting from the mountains toward the
center of the basin, with sediments becoming finer
towards the center of the basin. 24
Although through-flowing drainage occurred at this
time, basin stratigraphy suggests it was eventually
replaced by internal drainage characteristic of a
closed basin. With no external drainage, bajada
deposition was joined by a lake-depositional
environment, accumulating evaporite, and fine-grained
sand, silt, and clay deposits as thick as 1,100
feet. Subsequently, external drainage was re-established
and alluvial deposition once again
became the dominant form of basin sedimentation. 24
HYDROLOGY
Lithology
McMullen Valley’s long sedimentation history has
resulted in depositional sediments over 5,000 feet
thick in its western portion increasing to over 6,000
feet in the eastern portion. 6 The basin-fill has been
classified into three main stratigraphic units based on
lithologic characteristics and depositional
environments. These units are, in order of deposition:
 the Alluvial Fan/Fanglomerate Unit,
 the Lake-bed Unit, and
 the Upper Alluvial Fill Unit. 24
Alluvial Fan/Fanglomerate Unit –These deposits
are the main water bearing unit in the basin, directly
overlie bedrock, and are found throughout the basin.
Comprised of sediments that created the bajada
during the early formation of the basin, the lithology
of the unit ranges from relatively coarse,
heterogeneous detritus on the flanks of the mountains
to somewhat finer, better sorted material toward the
center of the basin. 24
This unit is composed primarily of poorly sorted
gravel and coarse sand but may locally contain clay,
silt and fine sand. Cementation, which significantly
affects its hydraulic characteristics, varies greatly
within this unit but appears to be more prevalent in
the eastern portion of the basin. The maximum
thickness of this unit is unknown but gravity data
suggest it’s greater than 5,000 feet thick. 24 Two
cones of depression near Aguila and in the
Salome/Wenden area that have been in existence
since at least 1958, limit the flow of groundwater. 9, 25
The cones of depression create a groundwater divide
between Aguila and Wenden that trends northwest to
5
southeast in the vicinity of the county line. The
boundary between the coalescing cones of depression
is not exactly known because of the scarcity of water
level data in the middle of the basin; its location will
also vary slightly with time due to pumping rates in
the two subareas. 24
Lake-Bed Unit – These deposits were created when
events perhaps related to the Basin and Range
structural formation closed the basin causing it to
drain internally. This created a playa-lake
environment which resulted in a deposition of fine-grained
sediments including clay, silt, and very fine
sand; with local evaporate deposits, near the center of
the subsiding basin. 24 Lake-bed deposits have a
relatively low permeability and form a confining
layer above the Regional aquifer. This unit, however,
may contain local saturated sand lenses which are
sufficiently permeable to act as perched aquifers. A
few wells have produced limited amounts of poor-quality
water from these sand lenses. 24
The lake-bed unit covers about 140 square miles of
the western portion of the basin. It is not found to the
east of the La Paz-Maricopa County line. The unit
has a maximum recorded thickness of 1,100 feet
approximately four miles northwest of the town of
Wenden. A hydrologic cross-section extending from
three miles northeast of Wenden through Salome to
Harcuvar is shown in Diagram 1. 24
Notably, this unit is absent at one location within the
main body of the deposit approximately a mile
northwest of the town of Salome. The lack of any
lake-bed deposits at this location may be due to either
the presence of a topographic high at this location at
the time of sedimentation or due to post-depositional
erosion and removal of the unit. 24
Upper Alluvial Fill Unit – This unit consists largely
of unconsolidated gravel, sand, silt and clay
deposited by Centennial Wash and its tributaries after
the re-establishment of external drainage. Where the
Upper Alluvial Fill unit overlies the Lake-Bed unit,
the contact is generally evident. However, in the
absence of lake-bed sediments, the contact between it
and the underlying Alluvial Fan/Fanglomerate Unit is
less pronounced. 24
Found throughout the basin, this unit’s thickness
varies from near zero near the mountain fronts to at
least 560 feet near the town of Aguila and is typically
100-200 feet thick in western McMullen Valley,
decreasing to less than 50 feet thick in southeastern
Harrisburg Valley.24 In the Aguila area, the Upper
Alluvial Fill unit has, for the most part, been
dewatered from heavy pumping for irrigation use. 25
Groundwater
In the McMullen Valley basin, the land surface
gradient is greater than the slope of the water table;
thus the depth to water increases northeastward along
the valley floor and laterally from the axis of the
valley.6 Recharge occurs only by rainfall and
agricultural return flows; consequently groundwater
withdrawals by agriculture greatly exceed recharge
and cause depletion of the aquifer. 6
Aquifers – Seven unique aquifers were identified in
the McMullen Valley basin based on water quality
data collected for this report in conjunction with
previously published hydrologic studies.
 The main aquifer system is the Regional
aquifer which can be subdivided into
Eastern, Western and Southern aquifers
based on water quality data, groundwater
flow patterns and geologic structures.
 Two aquifers of more limited productivity
were also identified: the Forepaugh aquifer
located in the extreme eastern portion of the
basin and the Harcuvar aquifer located in the
extreme western portion of the basin.
 A Perched aquifer is located above the
Western Regional aquifer separated by an
aquitard composed of fine-grained lake
deposits. There is a half-mile gap in the
aquitard about a mile northeast of the town
of Salome where the Perched and Western
Regional aquifers merge to form the Mixed
aquifer of limited spatial extent.
Regional Aquifer – Found throughout McMullen
Valley, the aquifer consists of the Alluvial
Fan/Fangolmerate Unit found underlying the Lake-bed
Unit in the western portion of the basin and
underlying the Upper Alluvial Fill Unit in the eastern
portion of the basin.
Stratigraphic data suggest that the Regional aquifer is
mainly composed of coalescing heterogeneous
deposits of poorly sorted, coarse gravel and sand.
Although thought to be hydrologically connected, the
sediments heterogeneous nature results in highly
variable hydraulic properties throughout the aquifer.
Intergranular cementation also impacts the aquifer’s
hydraulic properties. In general, cementation
increases in the basin from west to east, around the
6
basin’s margins, and in proximity to bedrock. 24
Available water quality data indicate, for the most
part, that it contains good quality water suitable for
drinking and irrigation uses. 24 For the purposes of
this study, the Regional Aquifer is divided into three
areas:
 Eastern Regional Aquifer: consisting of
basin areas roughly lying east of the La Paz-
Maricopa County line, a cone of depression
caused by irrigation pumping near Aguila
has essentially divided the basin near where
the Lake-bed Unit peters out. 24, 25
 Western Regional Aquifer: consisting of
basin areas roughly lying west of the La
Paz-Maricopa County line, a cone of
depression caused by irrigation pumping
near Aguila has essentially divided the basin
near where the Lake-bed Unit begins. 24, 25
 Southern Regional Aquifer: is present in
basin areas lying south of the western
subsurface extension of the Harquahala
Mountains that partially retards the
movement of groundwater from the
Harrisburg Valley area to the zone of heavy
pumping around Salome and Wenden
(Diagram 2).24 This subsurface structural
extension becomes indistinct further west
near the community of Harcuvar.
Forepaugh Aquifer – For the purposes of this report,
this aquifer is considered separate from the Eastern
Regional aquifer. The steep hydraulic gradient
between the Forepaugh and Eastern Regional
aquifers is evidence of their poor connection. 43 The
aquifer is found near the community of Forepaugh in
the easternmost area of the McMullen Valley basin.
The aquifer is separated from the Eastern Regional
aquifer by some low hills (in Townships 7 and 8
North, Range 8 West) and an unnamed ridge that
extends southeastward from the northeast end of the
Harcuvar Mountains. 43
Harcuvar Aquifer – For the purposes of this report,
this aquifer is considered separate from the Southern
and Western Regional aquifers. The aquifer is found
near the community of Harcuvar located three miles
west of Salome along U.S. Highway 60.
Groundwater flow is limited in the Alluvial
Fan/Fanglomerate Unit from Harcuvar to areas to the
east (see Diagram 1) by the thickness of the Lake-bed
Unit which extends almost down to bedrock.
Perched Aquifer – Present only in the western
portion of the basin, this shallow aquifer includes
isolated, water-bearing sand lenses within the Lake-bed
Unit and water-bearing zones within the
overlying Upper Alluvial Fill Unit. The Perched
aquifer system is not a significant water source and
little information is known about the occurrence and
movement of water within it. 24 However, since it is
composed of discontinuous sand and gravel lenses,
the Perched aquifer may actually be a system
composed of several aquifers that may not all be
hydrologically connected. 24
Natural recharge to the perched aquifer is the result
of percolation from the ephemeral Centennial Wash
and its tributaries. However, most recharge comes
from deep percolation of excess irrigation water as
well as minor amounts of wastewater discharged
from septic systems. As such, the water quality in the
Perched aquifer is generally poor. 24
Mixed Aquifer – In general, the Regional and
Perched aquifers appear to act independently of one
another relative to applied hydraulic stresses. This
suggests that the intervening Lake-bed Unit is an
effective barrier to the downward percolation of
ground water, effectively isolating the two aquifers.
However, short circuiting between the two aquifers
takes place within some wells that penetrate both
aquifers. This occurs through perforations or breaks
in the well casing within the Perched aquifer system
which allows water to enter the casing and cascade
down the well to the Regional aquifer. The total
annual volume of this leakage between aquifers is not
known but has been estimated to be as much as 40
acre-feet per leaking well. 24
Stratigraphic data suggest that the Regional aquifer
also receives natural recharge from the Perched
aquifer in certain locations. These areas include along
the perimeter of the Lake-bed Unit as water from the
Perched aquifer spills over the edge into the Regional
aquifer. 24 For the purposes of this study, the effects
of water from the Perched aquifer entering the
Regional aquifer through cascading wells and along
the perimeter of the Lake-bed Unit was not
considered separately. However another area where
water from the two aquifers merges was analyzed in
the study.
7
Diagram 1. Hydrologic cross section of western McMullen Valley stretching from Harcuvar (on the left) through
Salome to four miles northeast of Wenden. 24
Diagram 2. Hydrologic cross section of Harrisburg Valley from two miles north of Salome (on the left) to three
miles southeast of the town. 24
8
Diagram 3. Hydrologic cross section of western McMullen Valley stretching from four miles north of Salome (on
the left) southeast to a point one mile southeast of Wenden. 24
Diagram 4. Map showing the paths of
three hydrologic cross sections in
western McMullen Valley. 24
9
The Perched and Regional aquifers appear to be in
direct contact in a one-half mile gap where lake-bed
sediments are absent about one mile northeast of
Salome.24 Since the Perched aquifer has a higher
static water level, groundwater tends to drain
downward from the Perched aquifer to the Western
Regional aquifer in this area. Although the phrase,
“Persistent Degraded Water Quality Zone” has been
used to describe the area by previous studies, the area
will be called the Mixed aquifer in this report. 24
Wells
Groundwater development in the McMullen Valley
basin began with mining, stock and domestic wells in
the early 1900s. Substantial increases in groundwater
pumping did not occur until the mid-1950s with the
development of irrigated agriculture. Wells for
irrigation increased in numbers through the 1970s
until tapering off in the 1980s. 24 The majority of
wells are located near the axis of McMullen Valley
where agricultural activities and the communities of
Aguila, Salome and Wenden are located. There are
also many domestic wells throughout Harrisburg
Valley. On the flanks of the basin, only a few wells
for stock or domestic use, are found.
The oldest wells in the western part of the basin were
shallow wells that obtained water predominantly
from the Perched aquifer system. As deeper wells
began to be drilled, many were perforated in both the
Perched and Regional aquifers. More recently drilled
wells are perforated only in the Regional aquifer.
Cross-contamination between aquifers occurs via
cascading water in wells perforated in both aquifers.
Other cross-contamination causes include breaks in
the well casing, voids behind the casing, and by
leakage through filter packs surrounding the casing in
rotary-drilled wells. 24 The City of Phoenix estimates
that at least 15 of its 42 wells blend water from both
the Perched and Regional aquifers based on well
construction data and video surveys. 24
Irrigation wells tapping the Regional aquifer produce
150 to 3,500 gallons per minute (gpm); the wide
range in production is attributed to encountering
more permeable beds of sand and gravel within the
aquifer and to individual well characteristics. 25
Although groundwater withdrawals have occurred
since the early 1900s, withdrawals increased greatly
beginning in the 1950s. The most significant
withdrawals occurred between 1971 and 1981 with
an annual average of 123,000 acre-feet. Production
peaked at 144,000 acre-feet in 1981.24 Groundwater
pumping in the basin averaged 89,100 acre-feet
annually from 2001 to 2005. 7
INVESTIGATION METHODS
ADEQ collected samples from 124 groundwater sites
to characterize regional groundwater quality in the
McMullen Valley basin (Map 2). Specifically, the
following types of samples were collected:
 oxygen and deuterium isotopes at 124 sites
 inorganic suites at 124 sites
 radon at 79 sites
 radionuclide at 50 sites
 perchlorate at 24 sites
 pesticides at 2 sites
Twelve (12) additional sites were also sampled only
for physical parameters and nitrate.
No bacteria sampling was conducted because
microbiological contamination problems in
groundwater are often transient and subject to a
variety of changing environmental conditions
including soil moisture content and temperature. 18
Sampling Strategy
The study focused on regional groundwater quality
conditions that are large in scale and persistent in
time. It was originally designed as a targeted
investigation to determine nitrate concentrations in
groundwater in Salome where residences use septic
systems for domestic wastewater disposal. The data
collected would assist in determining if existing
conditions or trends in nitrogen loading to the aquifer
will cause or contribute to an exceedance of the
Aquifer Water Quality Standard for nitrate. This
would potentially warrant the establishment of a
Nitrogen Management Area to control nitrogen
loading to groundwater as described in the Arizona
Administrative Code R18-9-A317(c). 3 After the
nitrate data in Salome was collected, the study was
expanded into an ambient baseline study of the entire
McMullen Valley basin.
Wells pumping groundwater for irrigation, stock,
municipal and domestic purposes were sampled for
this study, provided each well met ADEQ
requirements. A well was considered suitable for
sampling if the owner gave permission to sample, if a
sampling point existed near the wellhead, and if the
well casing and surface seal appeared to be intact and
undamaged.2, 8 Other factors such as construction
information were preferred but not essential. Some
10
Figure 2 – McMullen Valley occasionally has prolific surface water flows such as when Centennial Wash in the
foreground flooded the nearby community of Wenden during heavy precipitation in mid-January, 2010. Flows in
Centennial Wash peaked at 9,938 cubic feet per second. Farm fields and the Harcuvar Mountains lie to the north
of the inundated community.
Figure 1. The largest community in McMullen
Valley, Salome was founded by Dick Wick Hall in
1904. Publisher of the Salome Sun, his humorous
columns about life in the desert were so popular they
were syndicated in 28 newspapers around the
country from 1925-26. The Salome Frog is one of his
most famous characters, an amphibian seven years
old who cannot swim because of a lack of water.
Despite McMullen Valley appearing to be a dry,
desolate place, the basin has tremendous water
resources. ADWR estimates that 15,100,000 acre-feet
is stored in aquifers.6 This factor led to the City of
Phoenix purchasing and/or leasing almost 16,000
acres of farmland in the Salome-Wenden area in
1986.24 Eventually, Phoenix plans to pump
groundwater from the area and convey it in the
Central Arizona Project to use for municipal
purposes.7
11
Figure 3 – ADEQ’s Jason Jones samples a domestic
well in the Forepaugh aquifer located east of
Aguila. Many sites in the Forepaugh aquifer had
health-based exceedances of fluoride and arsenic.
Figure 4 – The Harcuvar Mountains are the
backdrop to an irrigation well located east of the
town of Wenden in the Western Regional aquifer.
Groundwater from the well is used to grow alfalfa.
Samples from the 850-foot deep well revealed very
soft water that exceeded health-based water
quality standards for arsenic and fluoride.
Figure 5 – Like many deep wells pumping from
the Eastern Regional aquifer, Well #23 located
along U.S. Highway 60 east of the community of
Aguila is a productive irrigation well pumping at
over 1,500 gallons per minute.
Figure 6 – A 180-feet-deep well provides water for
domestic uses near irrigated farmland north of
Salome. The shallow well draws water from the
Perched aquifer which is separated from the
underlying Western Regional aquifer by a layer of
fine sediments that restrict groundwater flow.24
Samples from the well exceeded health-based
water quality standards for arsenic nitrate and
selenium; concentrations of chloride, fluoride, sulfate
and TDS exceeded aesthetics-based water quality
guidelines. The Harcuvar Mountains are in the
background.
12
requests to sample wells were denied because of fears
of how the data would be used; other wells were not
sampled because they lacked proper sampling ports.
For this study, ADEQ personnel sampled 124 wells
with the following types of pumps: submersible
pumps (82 wells), turbine pumps (40 wells) and hand
bailers (2 monitoring wells). In addition, of the 12
wells sampled only for physical parameters and
nitrate, 9 wells had submersible pumps and 3 wells
had turbine pumps.
Submersible pumps produce water for municipal,
domestic and/or stock use, turbine pumps produce
water for irrigation use and bailers were used with
monitoring wells that were installed to delineate
contamination plumes from underground storage
tanks. Additional information on groundwater sample
sites is compiled from the Arizona Department of
Water Resources (ADWR) well registry in Appendix A. 7
Sample Collection
The sample collection methods for this study
conformed to the Quality Assurance Project Plan
(QAPP) 2 and the Field Manual For Water Quality
Sampling. 8 While these sources should be consulted
as references to specific sampling questions, a brief
synopsis of the procedures involved in collecting a
groundwater sample is provided.
After obtaining permission from the owner to sample
the well, the volume of water needed to purge the
well of three bore-hole volumes was calculated from
well log and on-site information. Physical
parameters—temperature, pH, and specific
conductivity—were monitored at least every five
minutes using an YSI multi-parameter instrument.
To assure obtaining fresh water from the aquifer,
after three bore volumes had been pumped and
physical parameter measurements had stabilized
within 10 percent, a sample representative of the
aquifer was collected from a point as close to the
wellhead as possible. In certain instances, it was not
possible to purge three bore volumes. In these cases,
at least one bore volume was evacuated and the
physical parameters had stabilized within 10 percent.
Sample bottles were filled in the following order:
1. Pesticides
2. Perchlorate
3. Radon
4. Inorganic
5. Radionuclide
6. Isotope
Pesticide samples were collected in unpreserved, 1
gallon amber glass containers.
Perchlorate and isotope samples were collected in
unpreserved, 500 ml polyethylene bottles.
Radon samples were collected in two unpreserved,
40-ml clear glass vials. Radon samples were
carefully filled to minimize volatilization and
subsequently sealed so that no headspace remained. 16
The inorganic constituents were collected in three, 1-
liter polyethylene bottles: samples to be analyzed for
dissolved metals were delivered to the laboratory
unfiltered and unpreserved where they were
subsequently filtered into bottles using a positive
pressure filtering apparatus with a 0.45 micron (μm)
pore size groundwater capsule filter and preserved
with 5 ml nitric acid (70 percent). Samples to be
analyzed for nutrients were preserved with 2 ml
sulfuric acid (95.5 percent). Samples to be analyzed
for other parameters were unpreserved. 27
Radionuclide samples were collected in two
collapsible 4-liter plastic containers and preserved
with 5 ml nitric acid to reduce the pH below 2.5 su. 4
All samples were kept at 4oC with ice in an insulated
cooler, with the exception of the isotope and
radiochemistry samples. Chain of custody
procedures were followed in sample handling.
Samples for this study were collected during 16 field
trips between April 2008 and June 2009.
Laboratory Methods
The pesticide and inorganic analyses for this study
were conducted by the Arizona Department of Health
Services (ADHS) Laboratory in Phoenix, Arizona.
Inorganic sample splits analyses were conducted by
Test America Laboratory in Phoenix, Arizona. A
complete listing of inorganic parameters, including
laboratory method, EPA water method and Minimum
Reporting Level (MRL) for each laboratory is
provided in Table 1.
Perchlorate samples were analyzed by the Texas
Tech University Environmental Services Laboratory
in Lubbock, Texas.
Radon samples were analyzed by Radiation Safety
Engineering, Inc. Laboratory in Chandler, Arizona.
13
14
Radionuclide samples were analyzed by the Arizona
Radiation Agency Laboratory in Phoenix and
radiochemistry splits by the Radiation Safety
Engineering, Inc. Laboratory. The following EPA
SDW protocols were used: Gross alpha was
analyzed, and if levels exceeded 5 picocuries per liter
(pCi/L), then radium-226 was measured. If radium-
226 exceeded 3 pCi/L, radium-228 was measured. If
gross alpha levels exceeded 15 pCi/L initially, then
radium-226/228 and total uranium were measured. 4
Isotope samples were analyzed by the Department of
Geosciences, Laboratory of Isotope Geochemistry
located at the University of Arizona in Tucson,
Arizona.
DATA EVALUATION
Quality Assurance
Quality-assurance (QA) procedures were followed
and quality-control (QC) samples were collected to
quantify data bias and variability for the McMullen
Valley basin study. The design of the QA/QC plan
was based on recommendations included in the
Quality Assurance Project Plan (QAPP) and the
Field Manual For Water Quality Sampling. 2, 8 Types
and numbers of QC samples collected for this study
are as follows:
 Inorganic: (15 duplicates, 9 splits, and 10
blanks).
 Nitrate only: (2 duplicates and 1 split)
 Radionuclide: (no QA/QC samples)
 Radon: (1 duplicate)
 Isotope: (1 duplicate)
 Perchlorate (2 duplicates)
Based on the QA/QC results, sampling procedures
and laboratory equipment did not significantly affect
the groundwater quality samples.
Blanks - Equipment blanks for inorganic analyses
were collected to ensure adequate decontamination of
sampling equipment, and that the de-ionized water
was not impacting the groundwater quality
sampling.8 Equipment blank samples for major ion
and trace element analyses were collected by filling
unpreserved bottles with de-ionized water.
Equipment blank samples for nutrient analyses were
collected with de-ionized water and preserved with
sulfuric acid.
Systematic contamination was judged to occur if
more than 50 percent of the equipment blank samples
contained measurable quantities of a particular
groundwater quality constituent. The equipment
blanks contained specific conductivity (SC)-lab and
turbidity contamination at levels expected due to
impurities in the source water used for the samples.
The blank results indicated systematic contamination
with SC (detected in 8 equipment blanks) and
turbidity (detected in 8 equipment blanks). Single
detections of nitrate (0.055 mg/L) and phosphorus
(0.021 mg/L) also occurred.
For SC, the eight equipment blanks had a mean (3.4
uS/cm) which was less than 1 percent of the SC mean
concentration for the study. The SC detections may
be explained in two ways: water passed through a de-ionizing
exchange unit will normally have an SC
value of at least 1 uS/cm, and carbon dioxide from
the air can dissolve in de-ionized water with the
resulting bicarbonate and hydrogen ions imparting
the observed conductivity.27
For turbidity, equipment blanks had a mean level
(0.0476 ntu) less than 1 percent of the turbidity
median level for the study. Testing indicates turbidity
is present at 0.01 ntu in the de-ionized water supplied
by the ADHS laboratory, and levels increase with
time due to storage in ADEQ carboys.27
Duplicate Samples - Duplicate samples are identical
sets of samples collected from the same source at the
same time and submitted to the same laboratory. Data
from duplicate samples provide a measure of
variability from the combined effects of field and
laboratory procedures.8 Duplicate samples were
collected from sampling sites that were believed to
have elevated constituent concentrations as judged by
field SC values. Fifteen duplicate inorganic samples
and two nitrate duplicate samples were collected in
this study.
Analytical results indicate that of the 36 constituents
examined, 25 had concentrations above the MRL.
The maximum variation between duplicates was less
than 10 percent (Table 2). The only exceptions were
turbidity (60 percent), TKN (52 percent), and barium
(17 percent). The median variation between
duplicates was less than 2 percent except with
carbonate (23 percent), chromium (11 percent),
turbidity and TKN (9 percent), and total phosphorus
(5 percent).
The lone isotope and radon duplicate samples showed
less than a 1 percent maximum variation between
duplicates as did one of the two perchlorate duplicate
samples. However, the other perchlorate sample had
results of 0.336 ug/L and < 0.05 ug/L.
15
Table 1. Laboratory Water Methods and Minimum Reporting Levels Used in the Study
Constituent Instrumentation ADHS / Test America
Water Method
ADHS / Test America
Minimum Reporting Level
Physical Parameters and General Mineral Characteristics
Alkalinity Electrometric Titration SM2320B / M2320 B 2 / 6
SC (uS/cm) Electrometric EPA 120.1/ M2510 B -- / 2
Hardness Titrimetric, EDTA SM 2340 C / SM2340B 10 / 1
Hardness Calculation SM 2340 B --
pH (su) Electrometric SM 4500 H-B 0.1
TDS Gravimetric SM2540C 10 / 10
Turbidity (NTU) Nephelometric EPA 180.1 0.01 / 0.2
Major Ions
Calcium ICP-AES EPA 200.7 1 / 2
Magnesium ICP-AES EPA 200.7 1 / 0.25
Sodium ICP-AES EPA 200.7 1 / 2
Potassium Flame AA EPA 200.7 0.5 / 2
Bicarbonate Calculation Calculation / / M2320 B 2
Carbonate Calculation Calculation / / M2320 B 2
Chloride Potentiometric Titration SM 4500 CL D / E300 5 / 2
Sulfate Colorimetric EPA 375.4 / E300 1 / 2
Nutrients
Nitrate as N Colorimetric EPA 353.2 0.02 / 0.1
Nitrite as N Colorimetric EPA 353.2 0.02 / 0.1
Ammonia Colorimetric EPA 350.1/ EPA 350.3 0.02 / 0.5
TKN Colorimetric EPA 351.2 / M4500-
NH3 0.05 / 1.3
Total Phosphorus Colorimetric EPA 365.4 / M4500-PB 0.02 / 0.1
All units are mg/L except as noted
Source 16, 27
16
Table 1. Laboratory Water Methods and Minimum Reporting Levels Used in the Study--Continued
Constituent Instrumentation ADHS / Test America
Water Method
ADHS / Test America
Minimum Reporting Level
Trace Elements
Aluminum ICP-AES EPA 200.7 0.5
Antimony Graphite Furnace AA EPA 200.8 0.005 / 0.003
Arsenic Graphite Furnace AA EPA 200.9 / EPA 200.8 0.005 / 0.001
Barium ICP-AES EPA 200.8 / EPA 200.7 0.005 to 0.1 / 0.01
Beryllium Graphite Furnace AA EPA 200.9 / EPA 200.8 0.0005 / 0.001
Boron ICP-AES EPA 200.7 0.1 / 0.2
Cadmium Graphite Furnace AA EPA 200.8 0.0005 / 0.001
Chromium Graphite Furnace AA EPA 200.8 / EPA 200.7 0.01 / 0.01
Copper Graphite Furnace AA EPA 200.8 / EPA 200.7 0.01 / 0.01
Fluoride Ion Selective Electrode SM 4500 F-C 0.1 / 0.4
Iron ICP-AES EPA 200.7 0.1 / 0.05
Lead Graphite Furnace AA EPA 200.8 0.005 / 0.001
Manganese ICP-AES EPA 200.7 0.05 / 0.01
Mercury Cold Vapor AA SM 3112 B / EPA 245.1 0.0002 / 0.0002
Nickel ICP-AES EPA 200.7 0.1 / 0.01
Selenium Graphite Furnace AA EPA 200.9 / EPA 200.8 0.005 / 0.002
Silver Graphite Furnace AA EPA 200.9 / EPA 200.7 0.001 / 0.01
Thallium Graphite Furnace AA EPA 200.9 / EPA 200.8 0.002 / 0.001
Zinc ICP-AES EPA 200.7 0.05
Radionuclides
Gross alpha beta Gas flow proportional
counter EPA 900.0 varies
Co-Precipitation Gas flow proportional
counter EPA 00.02 varies
Radium 226 Gas flow proportional
counter EPA 903.0 varies
Radium 228 Gas flow proportional
counter EPA 904.0 varies
Uranium Kinnetic phosporimeter EPA Laser
Phosphorimetry varies
All units are mg/L
Source 14, 16, 27
17
Table 2. Summary Results of McMullen Valley Basin Duplicate Samples from the ADHS Laboratory
Difference in Percent Difference in Concentrations
Parameter Number
Minimum Maximum Median Minimum Maximum Median
Physical Parameters and General Mineral Characteristics
Alk., Total 15 0 % 3 % 0 % 0 10 0
SC (uS/cm) 15 0 % 1 % 0 % 0 100 0
Hardness 15 0 % 8 % 1 % 0 20 1
pH (su) 15 0 % 1 % 0 % 0 0.1 0
TDS 15 0 % 7 % 0 % 0 100 0
Turb. (ntu) * 13 0 % 60 % 9 % 0 8 0.5
Major Ions
Bicarbonate 15 0 % 3 % 0 % 0 20 0
Carbonate 3 0 % 23 % 7 % 0 13 0.1
Calcium 15 0 % 8 % 0 % 0 2 0
Magnesium 11 0 % 7 % 1 % 0 3 0.1
Sodium 15 0 % 5 % 0 % 0 20 0
Potassium * 14 0 % 3 % 1 % 0 0.1 0.01
Chloride 15 0 % 5 % 0 % 0 40 0
Sulfate 15 0 % 4 % 0 % 0 100 0
Nutrients
Nitrate (as N) 15 0 % 9 % 0 % 0 4 0.1
Phosphorus * 3 5 % 9 % 5 % 0.003 0.01 0.0008
TKN * 4 3 % 52 % 9 % 0.02 0.34 0.03
Trace Elements
Arsenic 9 0 % 4 % 1 % 0 0.001 0.0002
Barium * 12 0 % 17 % 2 % 0 0.011 0.001
Boron 14 0 % 3 % 0 % 0 0.01 0
Chromium 11 0 % 11 % 1 % 0 0.009 0.001
Fluoride 15 0 % 6 % 0 % 0 2.0 0
Selenium 5 0 % 5 % 1 % 0 0.002 0.001
All concentration units are mg/L except as noted with certain physical parameters.
* Potassium, turbidity, copper, total phosphorus, TKN, and barium each were detected near the MRL in one duplicate sample and not detected in the
other duplicate sample.
18
Split Samples - Split samples are identical sets of
samples collected from the same source at the same
time that are submitted to two different laboratories
to check for laboratory differences.8 Nine inorganic
split samples were collected and analytical results
were evaluated by examining the variability in
constituent concentrations in terms of absolute levels
and as the percent difference. One additional split
sample was collected and analyzed for only nitrate.
Analytical results indicate that of the 36 constituents
examined only 25 had concentrations above MRLs
for both ADHS and Test America laboratories. The
split results of the 25 constituents having
concentrations above MRLs are provided in Table 3.
The maximum variation between splits was less than
15 percent. The only exceptions were turbidity (69
percent), selenium (52 percent), potassium (42
percent), chloride (26 percent), nitrate (25 percent),
carbonate (21 percent) and chromium (20 percent).
Split samples were also evaluated using the non-parametric
Sign test to determine if there were any
significant (p ≤ 0.05) differences between ADHS
laboratory and Test America laboratory analytical
results.20 Both chloride and potassium concentrations
reported by the Test America laboratory were
significant higher than those reported by the ADHS
laboratory; sodium followed a similar trend but just
missed being significantly higher (Sign test, p ≤
0.05).
Resample Sites – During the course of the study,
five sites originally sampled for nitrate were
resampled at a later date for the full suite of inorganic
constituents. Nitrate concentrations were evaluated
using the Wilcoxon test to determine if there were
any significant (p ≤ 0.05) differences between sample
periods. No significant differences were found in
nitrate concentrations between the sample periods
(Wilcoxon test, p ≤ 0.05).
Based on the results of blanks, duplicates and the
split sample collected for this study, no significant
QA/QC problems were apparent with the
groundwater quality collected for this study.
Data Validation
The analytical work for this study was subjected to
the following five QA/QC correlations. 21 The
analytical work conducted for this study was
considered valid based on the quality control samples
and the QA/QC correlations.
Cation/Anion Balances - In theory, water samples
exhibit electrical neutrality. Therefore, the sum of
milliquivalents per liter (meq/L) of cations should
equal the sum of meq/L of anions. However, this
neutrality rarely occurs due to unavoidable variation
inherent in all water quality analyses. Still, if the
cation/anion balance is found to be within acceptable
limits, it can be assumed there are no gross errors in
concentrations reported for major ions.21
Overall, cation/anion meq/L balances of McMullen
Valley basin samples were significantly correlated
(regression analysis, p ≤ 0.01). Of the 124 samples
collected, 64 (or 52 percent) were within +/-2
percent.
Because of low cation/high anion sums, 45 samples
(or 36 percent) had > 2 percent differences with 17
samples having 5 to 10 percent differences and 2
samples having a greater than 10 percent difference
with 12 percent being the highest difference. The
samples with low cation sums were generally
collected on field trips conducted between April -
May 2009. The ADHS laboratory was alerted but
found no reason for the differences. 27
Because of high cation/low anion sums, 15 samples
(or 12 percent) had > 2 percent differences with 3
samples having 5 to 10 percent differences and 3
samples having a greater than 10 percent difference
with 30 percent being the highest difference. The
samples with high cation sums were generally
collected on field trips conducted between July 2008
and January 2009. The ADHS laboratory indicated
some chloride concentrations may have been reported
as non-detect by the PC-Titration system when the
concentration was likely greater than 10 mg/L.27
SC/TDS - The SC and TDS concentrations measured
by contract laboratories were significantly correlated
as were field-SC and TDS concentrations (regression
analysis, r = 0.99, p ≤ 0.01). The TDS concentration
in mg/L should be from 0.55 to 0.75 times the SC in
μS/cm for groundwater up to several thousand TDS
mg/L.21 Groundwater high in bicarbonate and
chloride will have a multiplication factor near the
lower end of this range; groundwater high in sulfate
may reach or even exceed the higher factor. The
relationship of TDS to SC becomes undefined for
groundwater with very high or low concentrations of
dissolved solids.21
Hardness - Concentrations of laboratory-measured
and calculated values of hardness were significantly
correlated (regression analysis, r = 0.99, p ≤ 0.01).
Hardness concentrations were calculated using the
following formula: [(Calcium x 2.497) +
(Magnesium x 4.118)]. 21
19
Table 3. Summary Results of McMullen Valley Basin Split Samples From ADHS/Test America Labs
Difference in Percent Difference in Levels
Constituents Number
Minimum Maximum Minimum Maximum
Significance
Physical Parameters and General Mineral Characteristics
Alkalinity, total 9 0 % 5 % 0 20 ns
SC (uS/cm) 9 0 % 4 % 0 150 ns
Hardness 7 0 % 13 % 0 10 ns
pH (su) 9 0 % 13 % 0.05 1.77 ns
TDS 9 0 % 7 % 0 400 ns
Turbidity (ntu) 5 7 % 69 % 0.06 44 ns
Major Ions
Calcium 9 0 % 9 % 0 10 ns
Magnesium 8 0 % 4 % 0 2 ns
Sodium 9 0 % 5 % 0 10 ns
Potassium 8 2 % 42 % 0.1 2.2 **
Carbonate 2 11 % 21 % 10 26 ns
Chloride 9 0 % 26 % 0 80 **
Sulfate 9 0 % 7 % 0 90 ns
Nutrients
Nitrate as N 10 0 % 25 % 0.01 36 ns
Trace Elements
Arsenic 5 1 % 5 % 0.0001 0.001 ns
Barium 7 2 % 11 % 0.001 0.03 ns
Boron 5 3 % 13 % 0.05 0.4 ns
Chromium 7 0 % 20 % 0 0.008 ns
Fluoride 9 0 % 8 % 0 0.8 ns
Selenium 3 16 % 52% 0.0062 .0011 ns
Zinc 1 5 % 5 % 0.007 0.007 ns
ns = No significant difference
** = Significant difference at p ≤ 0.01 or 99 % confidence level
* = Significant difference at p ≤ 0.05 or 95 % confidence level
All units are mg/L except as noted
20
SC - The SC measured in the field at the time of
sampling was significantly correlated with the SC
measured by contract laboratories (regression
analysis, r = 0.99, p ≤ 0.01).
pH - The pH value is closely related to the
environment of the water and is likely to be altered
by sampling and storage.21 Still, the pH values
measured in the field using a YSI meter at the time of
sampling were significantly correlated with
laboratory pH values (regression analysis, r = 0.91, p
≤ 0.01).
Temperature / GW Depth /Well Depth –
Groundwater temperature measured in the field was
compared to well depth and groundwater depth.
Groundwater temperature should increase with depth,
approximately 3 degrees Celsius with every 100
meters or 328 feet. 9 Well depth was significantly
correlated with temperature (regression analysis, r =
0.69, p ≤ 0.01); so was groundwater depth (regression
analysis, r = 0.54, p ≤ 0.01).
Statistical Considerations
Various methods were used to complete the statistical
analyses for the groundwater quality data of the
study. All statistical tests were conducted on a
personal computer using SYSTAT software.40
Data Normality: Data associated with 29
constituents were tested for non-transformed
normality using the Kolmogorov-Smirnov one-sample
test with the Lilliefors option.11 Results of
this test revealed that none of the 29 constituents
examined were normally distributed.
Spatial Relationships: The non-parametric Kruskal-
Wallis test using untransformed data was applied to
investigate the hypothesis that constituent
concentrations from groundwater sites having
different aquifers were the same. The Kruskal-Wallis
test uses the differences, but also incorporates
information about the magnitude of each difference.40
The null hypothesis of identical mean values for all
data sets within each test was rejected if the
probability of obtaining identical means by chance
was less than or equal to 0.05.
If the null hypothesis was rejected for any of the tests
conducted, the Tukey method of multiple
comparisons on the ranks of data was applied. The
Tukey test identified significant differences between
constituent concentrations when compared to each
possibility with each of the tests. 21 Both the Kruskal-
Wallis and Tukey tests are not valid for data sets with
greater than 50 percent of the constituent
concentrations below the MRL.20
Correlation Between Constituents: In order to
assess the strength of association between
constituents, their concentrations were compared to
each other using the Pearson Correlation Coefficient
test.
The Pearson correlation coefficient varies between -1
and +1; with a value of +1 indicating that a variable
can be predicted perfectly by a positive linear
function of the other, and vice versa. A value of -1
indicates a perfect inverse or negative relationship.
The results of the Pearson Correlation Coefficient test
were then subjected to a probability test to determine
which of the individual pair wise correlations were
significant. 40
Like Kruskal-Wallis and Tukey tests, the Pearson test
is not valid for data sets with greater than 50 percent
of the constituent concentrations below the MRL.20
21
Figure 7 – This 970-foot, domestic well tapping the
Western Regional aquifer met all water quality
standards; only water quality guidelines for pH-field
and fluoride were exceeded.
Figure 8 – ADEQ’s Dennis Turner samples a 512-
foot deep irrigation well located in Harrisburg
Valley south of Salome. Samples from the well
exceeded water quality guidelines for TDS and
fluoride. The radon concentration (6,894 pCi/L)
exceeded the proposed health-based standards for
radon (300 and 4,000 pCi/L). This was one of
highest radon concentrations ever sampled in
Arizona; two nearby wells had still higher levels. The
nearby granite geology may influence the high
radon concentrations.
Figure 9 – ADEQ’s Dennis Turner samples a 470-
foot deep well in Harrisburg Valley. Although most
samples collected from wells in the Southern
Regional aquifer met health-based water quality
standards, samples from this well exceeded the 10
mg/L standard for nitrate. Water quality guidelines
for chloride, fluoride, sulfate and TDS were also
exceeded. A radon sample had concentrations of
10,241 piC/L the highest level ever recorded by the
ADEQ ambient monitoring program.
Figure 10 – ADEQ’s Dennis Turner samples
irrigation Well #23 located north of Salome. Like
many deep wells pumping from the northwest
portion of the Western Regional aquifer, samples
from this well met all water quality standards and
guidelines.
22
Figure 11 – This 500-foot well provides water to
irrigate the grounds of a trailer park just northeast
of Salome. Unfortunately, due to the absence at this
location of the Lake-bed Unit, the Regional aquifer
merges with the poor quality water in the Perched
aquifer to form the Mixed aquifer. As a result,
health-based water quality standards were
exceeded for arsenic and nitrate in samples from
this well. In addition, water quality guidelines for
chloride, sulfate and TDS were exceeded.
Figure 12 – ADEQ’s Aleks Argals, Travis Barnum,
and Brent Mitchell assist in sampling this 700-foot
well between Salome and Wenden. Although the
well’s location appears to be outside the Mixed
aquifer, arsenic, nitrate and fluoride exceeded
water quality standards; pH-field, chloride, sulfate
and TDS exceeded water quality guidelines. Water
cascading from the Perched aquifer down the well
may be impacting the sample’s water quality.
Figure 13 – This stock well located several miles
east of Wenden just south of U.S Highway 60 had
the highest fluoride concentrations found in the
basin at 22 mg/L. Other wells in the Wenden area,
especially those east of town exceeded the health-based
water quality standard for fluoride (4.0
mg/L) with those closest to Harquahala Mountains
having the most elevated concentrations. Samples
from these wells were depleted in calcium allowing
large concentrations of fluoride to occur if a source
for fluoride ions is available for dissolution. 28
Figure 14 – The Harcuvar aquifer is created by the
Lake-bed Unit which extends almost down to
bedrock and effectively limits groundwater flow in
the Alluvial Fan/Fanglomerate Unit to areas to the
east the vicinity of the community.24 Groundwater
in the aquifer has significantly different isotope
values than other sample sites in the basin. Six
samples collected from wells in this area each had
this unique isotope value range. Aside from oxygen
and deuterium isotope values, constituent
concentrations in the Harcuvar aquifer were not
significantly different from those in the three
Regional and Forepaugh aquifers (Kruskal-Wallis
with Tukey test, p ≤ 0.05).
23
GROUNDWATER SAMPLING RESULTS
Water Quality Standards/Guidelines
The ADEQ ambient groundwater program
characterizes regional groundwater quality. An
important determination ADEQ makes concerning
the collected samples is how the analytical results
compare to various drinking water quality standards.
ADEQ used three sets of drinking water standards
that reflect the best current scientific and technical
judgment available to evaluate the suitability of
groundwater in the basin for drinking water use:
 Federal Safe Drinking Water (SDW)
Primary Maximum Contaminant Levels
(MCLs). These enforceable health-based
standards establish the maximum
concentration of a constituent allowed in
water supplied by public systems.38
 State of Arizona Aquifer Water Quality
Standards. These apply to aquifers that are
classified for drinking water protected use.
All aquifers within Arizona are currently
classified and protected for drinking water
use. These enforceable State standards are
identical to the federal Primary MCLs. 3
 Federal SDW Secondary MCLs. These non-enforceable
aesthetics-based guidelines
define the maximum concentration of a
constituent that can be present without
imparting unpleasant taste, color, odor, or
other aesthetic effects on the water.38
Health-based drinking water quality standards (such
as Primary MCLs) are based on the lifetime
consumption (70 years) of two liters of water per day
and, as such, are chronic not acute standards.38
Exceedances of specific constituents for each
groundwater site is found in Appendix B.
Inorganic Constituent Results - Of the 124 sites
sampled for the full suite of inorganic constituents in
the McMullen Valley study, 33 (27 percent) met all
SDW Primary and Secondary MCLs.
Health-based Primary MCL water quality standards
and State aquifer water quality standards for
inorganic constituents were exceeded at 54 of the 124
sites (44 percent; Map 3; Table 4).
Constituents exceeding Primary MCLs include
arsenic (24 sites) (Map 4), fluoride (27 sites) (Map
5), nitrate (25 sites) (Map 6), and selenium (2).
Potential health effects of these chronic Primary
MCL exceedances are provided in Table 4. 3, 38
Aesthetics-based Secondary MCL water quality
guidelines were exceeded at 87 of 124 sites (70
percent; Map 3; Table 5).
Constituents above Secondary MCLs include
chloride (13 sites), fluoride (69 sites), manganese (2
sites), field-pH (19 sites), sulfate (8 sites), and TDS
(31 sites) (Map 7). Potential impacts of these
Secondary MCL exceedances are provided in Table
5.38
In addition, of the 12 sites sampled for only nitrate,
11 (92 percent) met nitrate Primary MCL standards
and 10 (83 percent) met pH Secondary MCL
standards.
Radiochemical Constituent Results - Health based
Primary MCL water quality standards and State
aquifer water quality standards were exceeded at 9 of
the 50 sites (18 percent; Map 8; Table 4) at which a
radionuclide sample was collected.
Of the 50 sites sampled for radionuclides, 9 sites (18
percent) exceeded gross alpha Primary MCL
standards and 4 (8 percent) exceeded uranium
Primary MCL standards.
Radon is a naturally occurring, intermediate
breakdown product from the radioactive decay of
uranium-238 to lead-206.38
Of the 79 sites sampled for radon, 3 exceeded the
proposed 4,000 picocuries per liter (pCi/L) standard
that would apply if Arizona establishes an enhanced
multimedia program to address the health risks from
radon in indoor air.
Sixty-eight (68) sites exceeded the proposed 300
pCi/L standard for states that would apply if Arizona
doesn’t develop a multimedia program (Map 9). 38
Organic Constituent Results There were no positive
detections of any of the 20 organochlorine
compounds analyzed in the 2 pesticides samples
collected from shallow wells near irrigated fields.
24
25
Table 4. McMullen Valley Basin Sites Exceeding Health-Based (Primary MCL) Water Quality
Standards
Constituent Primary
MCL
Number of Sites
Exceeding
Primary MCL
Highest
Concentration
Potential Health Effects of
MCL Exceedances *
Nutrients
Nitrite (NO2-N) 1.0 0 - -
Nitrate (NO3-N) 10.0 25 122 Methemoglobinemia
Trace Elements
Antimony (Sb) 0.006 0 - -
Arsenic (As) 0.01 24 0.110 Dermal and nervous system
toxicity
Barium (Ba) 2.0 0 - -
Beryllium (Be) 0.004 0 - -
Cadmium (Cd) 0.005 0 - -
Chromium (Cr) 0.1 0 - -
Copper (Cu) 1.3 0 - -
Fluoride (F) 4.0 27 22 Skeletal damage
Lead (Pb) 0.015 0 - -
Mercury (Hg) 0.002 0 - -
Nickel (Ni) 0.1 0 - -
Selenium (Se) 0.05 2 0.0755 Circulatory problems
Thallium (Tl) 0.002 0 - -
Radiochemistry Constituents
Gross Alpha 15 9 130 Cancer
Ra-226+Ra-228 5 0 - -
Radon ** 300 68 10,241 Cancer
Radon ** 4,000 3 10,241 Cancer
Uranium 30 4 120 Cancer and kidney toxicity
All units are mg/L except gross alpha, radium-226+228 and radon (pCi/L), and uranium (ug/L).
* Health-based drinking water quality standards are based on a lifetime consumption of two liters of water
per day over a 70-year life span.39
** Proposed EPA Safe Drinking Water Act standards for radon in drinking water.
26
27
28
29
Table 5. McMullen Valley Basin Sites Exceeding Aesthetics-Based (Secondary MCL) Water
Quality Standards
Constituents Secondary
MCL
Number of Sites
Exceeding
Secondary MCLs
Concentration
Range
of Exceedances
Aesthetic Effects of MCL
Exceedances
Physical Parameters
pH - field <6.5 ;
>8.5 19 9.68 slippery feel; soda taste;
deposits
General Mineral Characteristics
TDS 500 31 4,400 hardness; deposits; colored
water; staining; salty taste
Major Ions
Chloride (Cl) 250 13 930 Salty taste
Sulfate (SO4) 250 8 1,350
Rotten-egg odor,
unpleasant taste and
laxative effect
Trace Elements
Fluoride (F) 2.0 69 22 Mottling of teeth enamel
Iron (Fe) 0.3 0 - -
Manganese (Mn) 0.05 2 0.089
black to brown color;
black staining;
bitter metallic taste
Silver (Ag) 0.1 0 - -
Zinc (Zn) 5.0 0 - -
All units mg/L except pH is in standard units (su). Source: 38
30
31
32
33
Suitability for Irrigation
The groundwater at each sample site was assessed as
to its suitability for irrigation use based on salinity
and sodium hazards. Excessive levels of sodium are
known to cause physical deterioration of the soil and
vegetation. 39 Irrigation water may be classified using
specific conductivity (Diagram 5) and the Sodium
Adsorption Ratio (Diagram 6) in conjunction with
one another. 39
Groundwater sites in the McMullen Valley basin
display a wide range of irrigation water
classifications. The 124 sample sites are divided into
the following salinity hazards: low or C1 (0), medium
or C2 (85), high or C3 (31), and very high or C4 (8).
The 124 sample sites are divided into the following
sodium or alkali hazards: low or S1 (79), medium or
S2 (23), high or S3 (11), and very high or S4 (11).
Diagram 5. Salinity Hazard of McMullen Valley Wells
0%
69%
25%
6%
Low
Medium
High
Very High
Diagram 6. Sodium Hazard of McMullen Valley Wells
63%
19%
9%
9%
Low
Medium
High
Very High
Analytical Results
Analytical inorganic and radiochemistry results of the
McMullen Valley basin sample sites are summarized
(Table 6) using the following indices: minimum
reporting levels (MRLs), number of sample sites over
the MRL, upper and lower 95 percent confidence
intervals (CI95%), median, and mean. Confidence
intervals are a statistical tool which indicates that 95
percent of a constituent’s population lies within the
stated confidence interval.40 Specific constituent
information for each groundwater site is found in
Appendix B.
34
Table 6. Summary Statistics for McMullen Valley Basin Groundwater Quality Data
Constituent
Minimum
Reporting
Limit (MRL)
# of Samples /
Samples
Over MRL
Median
Lower 95%
Confidence
Interval
Mean
Upper 95%
Confidence
Interval
Physical Parameters
Temperature (C) 0.1 134 / 134 28.6 28.3 28.9 29.5
pH-field (su) 0.01 136 / 136 7.94 7.93 8.05 8.10
pH-lab (su) 0.01 124 / 124 8.20 8.22 8.20 8.33
Turbidity (ntu) 0.01 124 / 121 0.11 0.44 1.24 2.04
General Mineral Characteristics
T. Alkalinity 2.0 124 / 124 145 153 164 176
Phenol. Alk. 2.0 124 / 27 > 50% of data below MRL
SC-field (uS/cm) N/A 124 / 124 662 800 945 1090
SC-lab (uS/cm) N/A 124 / 124 638 776 931 1086
Hardness-lab 10.0 124 / 114 82 98 131 164
TDS 10.0 124 / 124 390 481 588 695
Major Ions
Calcium 5.0 124 / 124 19 26 35 45
Magnesium 1.0 124 / 106 7.5 8.6 11.4 14.2
Sodium 5.0 124 / 124 102 116 145 175
Potassium 0.5 124 / 121 2.5 2.5 2.9 3.2
Bicarbonate 2.0 124 / 124 170 178 190 201
Carbonate 2.0 124 / 27 > 50% of data below MRL
Chloride 1.0 124 / 123 48 77 103 130
Sulfate 10.0 124 / 124 48 68 98 128
Nutrients
Nitrate (as N) 0.02 136 / 136 3.7 7.1 10.1 13.0
Nitrite (as N) 0.02 124 / 5 > 50% of data below MRL
TKN 0.05 124 / 33 > 50% of data below MRL
T. Phosphorus 0.02 124 / 23 > 50% of data below MRL
35
Table 6. Summary Statistics for McMullen Valley Basin Groundwater Quality Data—Continued
Constituent
Minimum
Reporting
Limit (MRL)
Number of
Samples
Over MRL
Median
Lower 95%
Confidence
Interval
Mean
Upper 95%
Confidence
Interval
Trace Elements
Antimony 0.005 124 / 0 > 50% of data below MRL
Arsenic 0.01 124 / 72 0.006 0.006 0.007 0.009
Barium 0.1 124 / 89 0.037 0.049 0.059 0.070
Beryllium 0.0005 124 / 0 > 50% of data below MRL
Boron 0.1 124 / 116 0.22 0.28 0.37 0.45
Cadmium 0.001 124 / 0 > 50% of data below MRL
Chromium 0.01 124 / 82 0.018 0.019 0.023 0.026
Copper 0.01 124 / 16 > 50% of data below MRL
Fluoride 0.20 124 / 124 2.4 2.5 3.2 3.9
Iron 0.1 124 / 0 > 50% of data below MRL
Lead 0.005 124 / 0 > 50% of data below MRL
Manganese 0.05 124 / 2 > 50% of data below MRL
Mercury 0.0005 124 / 0 > 50% of data below MRL
Nickel 0.1 124 / 0 > 50% of data below MRL
Selenium 0.005 124 / 20 >50% of data below MRL
Silver 0.001 124 / 0 > 50% of data below MRL
Thallium 0.002 124 / 0 > 50% of data below MRL
Zinc 0.05 124 / 15 > 50% of data below MRL
Radiochemical Constituents
Radon* Varies 79 / 79 602 651 1,031 1,411
Gross Alpha* Varies 50 / 50 6.9 7.0 12.9 18.8
Gross Beta* Varies 50 / 50 5.7 5.1 9.9 14.6
Ra-226+228* Varies 50 / 3 > 50% of data below MRL
Uranium** Varies 50 / 9 > 50% of data below MRL
Isotopes
Oxygen-18 Varies 124 / 124 - 10.1 - 10.0 - 9.8 - 9.7
Deuterium Varies 124 / 124 - 74.0 - 71.9 - 70.5 - 69.2
All units mg/L except where noted or * = pCi/L, ** = ug/L, and *** = 0/00
36
GROUNDWATER COMPOSITION
General Summary
Groundwater in the McMullen Valley basin was
predominantly of sodium-chloride or sodium-mixed
chemistry (Map 10) (Diagram 7 and 8). The water
chemistry at the 124 sample sites, in decreasing
frequency, includes sodium-mixed (58 sites), sodium-bicarbonate
(43 sites), mixed-bicarbonate (11 sites),
mixed-mixed (5 sites), sodium-chloride (3 sites),
mixed-chloride (2 sites) and calcium-chloride and
calcium-bicarbonate (1 site apiece) (Diagram 8 –
middle diagram).
Of the 124 sample sites in the McMullen Valley
basin, the dominant cation was sodium at 104 sites
and calcium at 2 sites; at 18 sites, the composition
was mixed as there was no dominant cation (Diagram
8 – left diagram).
The dominant anion was bicarbonate at 55 sites and
chloride at 6 sites; at 63 sites the composition was
mixed as there was no dominant anion (Diagram 8 –
right diagram).
Diagram 7. Water Chemistry of McMullen Valley Wells
46%
2%
9%
4%
2%
1%
1%
35%
Sodium-bicarbonate
Sodium-mixed
Sodium-chloride
Mixed-bicarbonate
Mixed-mixed
Mixed-chloride
Calcium-bicarbonate
Calcium-chloride
Diagram 7 – Of the 124 inorganic sample sites in the McMullen Valley basin, the majority
consist of either sodium-mixed or sodium-bicarbonate water chemistry types. Cations, or those
major ions that are positively charged, are predominantly (83 percent) sodium. The others are
of a mixed composition except for 2 percent of samples that are predominantly calcium.
Anions, of those major ions that are negatively charged, are almost equally divided among
mixed (50 percent) and bicarbonate (45 percent); the remainder consist of chloride (5
percent).
37
Diagram 8 – The Piper trilinear diagram shows that all the sodium-bicarbonate
samples consist of sites situated in the Harcuvar, Forepaugh, the Eastern, Southern or
Western Regional aquifers. The other samples from these aquifers are also chemically
similar to the sodium-bicarbonate water chemistry. In contrast, the samples collected
from sites in the Mixed or Perched aquifers tend to be distinct because chloride and
sulfate ions make up a high percentage of their anion sums.
38
39
At 136 wells (124 sampled wells plus 12 wells at
which only field parameters and nitrate samples were
collected) levels of pH-field were slightly alkaline
(above 7 su) at 135 sites and slightly acidic (below 7
su) at 1 site.19 Of the 135 sites above 7 su, 63 sites
had pH-field levels over 8 su and 6 sites had pH-field
levels over 9 su.
TDS concentrations were considered fresh (below
1,000 mg/L) at 108 sites, slightly saline (1,000 to
3,000 mg/L) at 14 sites and moderately saline (3,000
to 10,000 mg/L) at 2 sites (Map 7).19
Hardness concentrations were soft (below 75 mg/L)
at 57 sites, moderately hard (75 – 150 mg/L) at 38
sites, hard (150 – 300 mg/L) at 19 sites, and very
hard (above 300 mg/L) at 10 sites (Diagram 9 and
Map 11).15
Nitrate (as nitrogen) concentrations at most sites may
have been influenced by human activities (Map 6).
Nitrate concentrations were divided into natural
background (0 sites at <0.2 mg/L), may or may not
indicate human influence (53 sites at 0.2 – 3.0 mg/L),
may result from human activities (56 sites at 3.0 – 10
mg/L), and probably result from human activities (17
sites >10mg/L).23
Most trace elements such as antimony, beryllium,
cadmium, copper, iron, lead, manganese, mercury,
nickel, selenium, silver, thallium and zinc were
rarely–if ever—detected. Only arsenic, barium,
boron, chromium and fluoride were detected at more
than 20 percent of the sites.
Hardness Concentrations of
McMullen Valley Basin Samples
46%
31%
15%
8%
Soft
Moderately Hard
Hard
Very Hard
Diagram 9 – This pie chart illustrates that almost half of the sample sites in the McMullen Valley basin
were characterized by having soft water. Soft water was especially prevalent in samples collected from the
Eastern and Western Regional aquifers; 10 such samples had no detection of hardness at the 10 mg/L
minimum reporting level. The highest hardness concentrations tended to be at sites located in the Perched
or Mixed aquifers or in the Southern Regional aquifer at the southern most sites in the Harrisburg Valley.
40
41
Constituent Co-Variation
The co-variation of constituent concentrations was
determined to examine the strength of the
association. The results of each combination of
constituents were examined for statistically-significant
positive or negative correlations. A
positive correlation occurs when, as the level of a
constituent increases or decreases, the concentration
of another constituent also correspondingly increases
or decreases. A negative correlation occurs when, as
the concentration of a constituent increases, the
concentration of another constituent decreases, and
vice-versa. A positive correlation indicates a direct
relationship between constituent concentrations; a
negative correlation indicates an inverse
relationship.40
Several significant correlations occurred among the
124 sample sites (Table 7, Pearson Correlation
Coefficient test, p ≤ 0.05). Several important
correlations were identified:
 Positive correlations occurred among
arsenic, boron and fluoride.
 Positive correlations occurred among nitrate,
TDS and all major ions except for
bicarbonate.
TDS concentrations are best predicted among major
ions by sodium concentrations (standard coefficient =
0.66), among cations by sodium concentrations
(standard coefficient = 0.81) (Diagram 10) and
among anions, chloride (standard coefficient = 0.58)
(multiple regression analysis, p≤ 0.01).
0 500 1000 1500
Sodium (mg/L)
0
1000
2000
3000
4000
5000
Total Dissolved Solids (mg/L)
Diagram 10 – The graph illustrates a strong positive correlation between two constituents; as TDS
concentrations increase so do sodium concentrations. The regression equation for this relationship is y =
3.3x +114, n = 124, r = 0.91 (regression, p ≤ 0.01). TDS concentrations are best predicted among cations by
sodium concentrations with a standard coefficient of 0.81 (multiple regression analysis, p ≤ 0.01).
42
Table 7. Correlation among McMullen Valley Basin Groundwater Quality Constituent Concentrations Using Pearson Correlation Probabilities
Constituent Temp pH-f TDS Hard Ca Mg Na K Bic Cl SO4 NO3 As B Cr F O D
Physical Parameters
Temperature ++ - - - - - - - - - - - - - - - - -
pH-field - - - - - - - - - - - - - - - - - + ++ ++ - -
General Mineral Characteristics
TDS ++ ++ ++ ++ ++ ++ ++ ++ + -
Hardness ++ ++ ++ ++ ++ ++ ++ + - -
Major Ions
Calcium ++ + ++ ++ ++ ++ ++ - -
Magnesium ++ ++ ++ ++ - + +
Sodium ++ ++ ++ ++ ++
Potassium + ++ ++ ++ - - - - ++ +
Bicarbonate - + ++
Chloride ++ ++
Sulfate ++ ++
Nutrients
Nitrate
Trace Elements
Arsenic ++ ++
Boron ++
Chromium - - - -
Fluoride - -
Isotopes
Oxygen ++
Deuterium
Blank cell = not a significant relationship between constituent concentrations
+ = Significant positive relationship at p ≤ 0.05
++ = Significant positive relationship at p ≤ 0.01
- = Significant negative relationship at p ≤ 0.05
- - = Significant negative relationship at p ≤ 0.01
43
Isotope Comparison
Groundwater characterizations using oxygen and
hydrogen isotope data may be made with respect to
the climate and/or elevation where the water
originated, residence within the aquifer, and whether
or not the water was exposed to extensive
evaporation prior to collection.14 This is
accomplished by comparing oxygen-18 isotopes
(δ18O) and deuterium (δD), an isotope of hydrogen,
data to the Global Meteoric Water Line (GMWL).
The GMWL is described by the linear equation:
δD = 8δ18O + 10
where δD is deuterium in parts per thousand (per mil,
0/00), 8 is the slope of the line, δ18O is oxygen-18 0/00,
and 10 is the y-intercept.12
The GMWL is the standard by which water samples
are compared and represents the best fit isotopic
analysis of numerous worldwide water samples.
Isotopic data from a region may be plotted to create a
Local Meteoric Water Line (LMWL) which is
affected by varying climatic and geographic factors.
When the LMWL is compared to the GMWL,
inferences may be made about the origin or history of
the local water.14
The LMWL created by δ18O and δD values for
samples collected at sites in the McMullen Valley
basin were compared to the GMWL. The δD and
δ18O data lie to the right of the GMWL. Meteoric
waters exposed to evaporation characteristically plot
increasingly below and to the right of the GMWL.
Evaporation tends to preferentially contain a higher
percentage of lighter isotopes in the vapor phase and
causes the water that remains behind to be
isotopically heavier.14
Groundwater from arid environments is typically
subject to evaporation, which enriches δD and δ18O,
resulting in a lower slope value (usually between 3
and 6) as compared to the slope of 8 associated with
the GMWL.14
The data for the McMullen Valley sub-basin doesn’t
quite conform, having a slope of 7.4, with the LMWL
described by the linear equation:
δD = 7.418O + 2.2
The LMWL for the McMullen Valley sub-basin (7.4)
is lower than the Lake Mohave basin (7.8) but higher
than most other basins in Arizona such as Detrital
Valley (5.15), Agua Fria (5.3), Sacramento Valley
(5.5), Big Sandy (6.1), Pinal Active Management
Area (6.4), Gila Valley (6.4) and San Simon (6.5).30,
31, 32, 33, 34, 35, 36, 37
The isotopic data were plotted on two graphs.
Samples from the Eastern, Southern and Western
Regional aquifers and the Harcuvar aquifer are
plotted in Diagram 11 while samples collected from
sites in the Forepaugh, Mixed, Perched and the
Harcuvar aquifers are plotted in Diagram 12.
Along the Local Meteoric Water Line (LMWL) the
plots highest on the precipitation trajectory were the
distinct cluster of six samples collected from wells in
Harcuvar aquifer. The six samples are the most
enriched or isotopically the heaviest sites and appear
to have undergone considerable evaporation before
being recharged and are likely produced from
summer monsoon precipitation.
Below the Harcuvar aquifer samples, many Southern
Regional aquifer samples plot high on the
precipitation trajectory while Western and Eastern
Regional aquifer samples are usually the most
depleted and tend to plot lowest on the precipitation
trajectory. The light signatures of these depleted
samples suggest that the water was not provided by
recharge from Centennial Wash or its tributaries but
consists of water that was likely recharged during
cooler climatic conditions roughly 8,000-12,000
years ago. The majority of samples from the
Forepaugh, Mixed and the Perched also are depleted
and don’t appear to be the result of recent recharge.
44
-12 -11 -10 -9 -8 -7
Delta Oxygen (0/00)
-90
-80
-70
-60
-50
-40
Delta Deuterium(0/00)
^
H H
^
+
+
+
++
+
+
+
+
H
^^
^
+
+
+
+
+
+
+
^
^^
^ ^
^^ ^
^
+
*** **
* **
*
++
+
^
^
^ ^
^
^^
*
*
^
+
+
*
*
^
*
*
*
^
^
^
^
*
*
*
*
*
H HH
+
+
+
H
^^*
^
+
++
*
-12 -11 -10 -9 -8 -7
Delta Oxygen (0/00)
-90
-80
-70
-60
-50
-40
Delta Deuterium (0/00)
$
$
H H
H
$
$
^
$
$
$
$ $
*
*
^^
$
H HH
*
H
*
^ ^^
^
^
^
$ *
Diagram 11. The groundwater sites
collected for the McMullen Valley basin
study that were drawing water from the
Eastern, Southern, and Western Regional
aquifers and the Harcuvar aquifer were
plotted according to their oxygen-18 and
deuterium isotope values. Along the
Local Meteoric Water Line (LMWL)
starting from highest on the precipitation
trajectory (upper right of graph), the
following types of samples predominantly
plot: Harcuvar aquifer (H), Southern
Regional aquifer (+), Eastern Regional
aquifer (*), and Western Regional aquifer
(^). Generally the Harcuvar aquifer
samples are the most enriched followed
by a cluster of samples predominantly
from the Southern Regional aquifer.
Samples from the Eastern and Western
Regional aquifer samples form a cluster
at the bottom of the graph and are the
most depleted in the basin.
Diagram 12. The groundwater sites
collected for the McMullen Valley basin
study that were drawing water from the
Harcuvar aquifer (H), Mixed aquifer ($),
Perched aquifer (*), and Forepaugh
aquifer (^) were plotted according to
their oxygen-18 and deuterium isotope
values. Along the Local Meteoric Water
Line (LMWL) starting from highest on the
precipitation trajectory (upper right of
graph), the following types of samples
predominantly plot: Harcuvar aquifer (H)
and then a cluster of samples from the
other aquifers. There are two outliers
from the lower cluster of samples. The
lone enriched sample from the Forepaugh
aquifer was collected on the southern
edge of the basin and consists of recent
precipitation. The lone enriched sample
from the Perched aquifer is a shallow
monitoring well located in an area of
irrigated farming and also appears to be
recharged by recent precipitation.
45
Groundwater Quality Variation
Among Seven Aquifers - Twenty-eight (28)
groundwater quality constituent concentrations were
compared between seven aquifers: Eastern Regional
(29 sites), Western Regional (34 sites), Southern
Regional (29 sites), Perched (6 sites), Mixed (11
sites), Forepaugh (9 sites) and Harcuvar (6 sites).
Because not all sites had the same constituents
collected, site totals vary for well characteristics,
field parameters, nitrate, radon and radionuclide
constituents.
Significant concentration differences were found with
26 constituents (Kruskal-Wallis with Tukey test, p ≤
0.05).
SC-field, SC-lab, TDS (Diagram 13), magnesium,
sodium, chloride, sulfate, and nitrate (Diagram 14)
were significantly higher in Perched and Mixed
aquifers than in the three Regional, Forepaugh and
Harcuvar aquifers. Hardness (Diagram 15), calcium,
potassium, barium and gross beta were significantly
higher in the Mixed aquifer than in the three
Regional, Forepaugh and Harcuvar aquifers.
Complete results are found in Table 8. Summary
statistics in the form of 95% confidence intervals are
provided for those constituents with significant
concentration differences between aquifers in Table
9.
E. Regional
Forepaugh
Harcuvar
Mixed
Perched
S. Regional
W. Regional
Aquifers
0
1000
2000
3000
4000
5000
TDS (mg/L)
E. Regional
Forepaugh
Harcuvar
Mixed
Perched
S. Regional
W. Regional
Aquifers
0
50
100
150
Nitrate as N (mg/L)
Diagram 14. Sample sites collected
from the Perched and Mixed aquifers
have significantly higher nitrate
concentrations than sample sites collected
from the Regional, Forepaugh and
Harcuvar aquifers; nitrate concentrations
in the Perched aquifer are also
significantly higher than in the Mixed
aquifer (Kruskal-Wallis with Tukey test, p
≤ 0.01). The Perched and Mixed aquifers
are likely impacted by nitrogen-laden
recharge from irrigated fields and, to a
minor degree, septic systems. 24 Nitrate
concentrations from wells in the Perched
and Mixed aquifers often exceed the 10
mg/L Primary MCL with concentrations
sometimes exceeding 50 mg/L.
Diagram 13. Sample sites collected from
the Perched and Mixed aquifers have
significantly higher TDS concentrations than
sample sites collected from all the other
aquifers in the McMullen Valley basin; TDS
concentrations in the Perched aquifer are
also significantly higher than in the Mixed
aquifer (Kruskal-Wallis with Tukey test, p ≤
0.01). The Perched and Mixed aquifers are
likely impacted by highly saline recharge
from irrigated fields and, to a lesser degree,
poor quality recharge from septic systems. 13
Numerous sumps that catch irrigation tail
water for reuse also allow large volumes of
poor quality irrigation return flow water to
percolate to the aquifer. 24
46
E. Regional
Forepaugh
Harcuvar
Mixed
Perched
S. Regional
W. Regional
Aquifers
0
500
1000
1500
2000
Hardness (mg/L)
E. Regional
Forepaugh
Harcuvar
Mixed
Perched
S. Regional
W. Regional
Aquifers
0
5
10
15
20
25
Fluoride (mg/L)
Diagram 15. Samples collected
from sites in the Mixed aquifer had
significantly higher hardness
concentrations than samples collected
from sites in the Eastern, Western and
Southern Regional aquifers, the
Forepaugh aquifer and Harcuvar
aquifer (Kruskal-Wallis with Tukey
test, p ≤ 0.05). Calcium and
magnesium followed a similar
pattern to hardness.
Diagram 16. Samples collected from
wells in the Forepaugh aquifer have
significantly higher fluoride
concentrations than samples collected
from all other aquifers except the
Perched aquifer. The Perched aquifer
has significantly higher fluoride
concentrations than the Southern
Regional, Mixed, and Harcuvar aquifers
(Kruskal-Wallis with Tukey test, p ≤
0.05). The median fluoride
concentration for both the Forepaugh
and Perched aquifers exceeded the 4.0
mg/L health based water quality
standard. Previous studies have noted
that for unknown reasons the lowest
fluoride concentrations tend to be north
and west of the town of Salome, a
conclusion that was verified by this
ADEQ study. 25
47
Table 8. Variation in Groundwater Quality Constituent Concentrations Among Seven Aquifers
Using Kruskal-Wallis Test with the Tukey Test
Constituent Significance Significant Differences Among Aquifers
Well Depth ** E. Regional > All other aquifers Forepaugh > Perched & S. Reg.
W. Regional > Harcuvar, Perched and S. Regional Mixed > Perched
Groundwater Depth ** E. Regional > All aquifers except Forepaugh Forepaugh > Mixed, Perched & S. Reg.
Harcuvar, Mixed & W. Regional > Perched & S. Reg.
Temperature - field ** Forepaugh, Mixed & W. Regional> Perched & S. Regional
E. Regional > Harcuvar, Perched & S. Regional Harcuvar > Perched
pH – field ** E. Regional, Forepaugh & W. Regional> Mixed & S. Regional
pH – lab ** E. Regional & W. Regional. > Mixed & S. Regional.
Forepaugh > Mixed
SC - field ** Perched > All other aquifers
Mixed > Forepaugh, Harcuvar, E. Regional, S. Regional & W. Regional
SC - lab ** Perched > All other aquifers
Mixed > Forepaugh, Harcuvar, E. Regional, S. Regional & W. Regional
TDS ** Perched > All other aquifers
Mixed > Forepaugh, Harcuvar, E. Regional, S. Regional & W. Regional
Turbidity * Perched > All other aquifers
Hardness ** Mixed > E. Regional, Forepaugh, Harcuvar, S. Regional & W. Regional
Calcium ** Mixed > All other aquifers
Magnesium ** Mixed> E. Regional, Forepaugh, Harcuvar, S. Regional & W. Regional
Perched > E. Regional, Forepaugh & W. Regional
Sodium ** Perched > All other aquifers
Mixed > E. Regional, S. Regional, W. Regional & Forepaugh
Potassium ** Mixed > All other aquifers
S. Regional > E. Regional & Forepaugh
Bicarbonate ** S. Regional > E. Regional, Forepaugh & W. Regional
Harcuvar > E. Regional & Forepaugh
Chloride ** Perched & Mixed > All other aquifers
Sulfate ** Perched > All others aquifers
Mixed > Forepaugh, E. Regional, S. Regional & W. Regional
Nitrate (as N) ** Perched > All other aquifers
Mixed > Forepaugh, Harcuvar, E. Regional, S. Regional & W. Regional
Arsenic ** -
Barium * Mixed > E. Regional, Forepaugh, W. Regional & Harcuvar
Boron ** Perched > All other aquifers
Chromium ** E. Regional > Mixed, S. Regional & Harcuvar
W. Regional > S. Regional & Harcuvar
Fluoride ** Forepaugh > All other aquifers except Perched
Perched > Mixed, S. Regional & Harcuvar
Oxygen ** Harcuvar > All other aquifers
S. Regional > E. Regional & W. Regional Perched > W. Regional
Deuterium ** Harcuvar > All other aquifers
S. Regional > E. Regional, Forepaugh, Mixed & W. Regional
Gross Alpha ns -
Gross Beta ** Mixed > All other aquifers
Radon ns -
ns = not significant * = significant at p ≤ 0.05 or 95% confidence level ** = significant at p ≤ 0.01 or 99% confidence level
48
Table 9. Summary Statistics (95% Confidence Intervals) for Groundwater Quality Constituents With
Significant Concentration Differences Among Seven Aquifers
Constituent Forepaugh Harcuvar Perched Mixed West
Regional
East
Regional
South
Regional
Well Depth 630 to 767 496 to 534 50 to 209 512 to 724 781 to 944 993 to 1343 301 to 432
Groundwater
Depth 461 to 527 334 to 371 -46 to 220 289 to 418 375 to 435 467 to 577 150 to 219
Temperature
- field 25.3 to 33.4 25.0 to 26.9 22.6 to 26.8 27.0 to 32.1 30.1 to 32.1 29.4 to 31.3 25.5 to 26.4
pH – field 7.91 to 8.67 - - 7.32 to 7.81 8.14 to 8.44 8.00 to 8.40 7.55 to 7.75
pH – lab 8.15 to 8.62 - - 7.64 to 8.20 8.33 to 8.54 8.21 to 8.48 8.08 to 8.17
SC - field 423 to 577 540 to 1016 1336 to 5529 1507 to 2653 637 to 865 500 to 575 714 to 1017
SC - lab 393 to 549 538 to 838 1359 to 5357 1479 to 2589 605 to 868 460 to 540 696 to 1027
TDS 235 to 331 329 to 525 789 to 3683 921 to 1791 369 to 546 277 to 321 424 to 631
Turbidity -0.14 to 1.9 0.02 to 0.09 -2.6 to 28.6 -0.6 to 2.5 -0.1 to 1.6 0.2 to 0.6 -0.4 to 1.9
Hardness -1 to 129 62 to 132 - 148 to 737 35 to 86 56 to 97 119 to 201
Calcium -3 to 38 16 to 35 4 to 83 47 to 213 11 to 26 13 to 24 31 to 54
Magnesium 2 to 10 5 to 12 1 to 58 7 to 55 2 to 7 6 to 10 10 to 18
Sodium 58 to 89 94 to 131 251 to 1092 146 to 341 95 to 167 62 to 78 100 to 143
Potassium 1.0 to 1.9 2.8 to 4.0 0.6 to 3.5 3.4 to 7.9 2.1 to 3.0 1.7 to 2.3 3.1 to 3.9
Bicarbonate 114 to 186 218 to 262 - 118 to 233 159 to 196 144 to 178 213 to 252
Chloride 19 to 31 6 to 32 92 to 810 238 to 455 51 to 83 33 to 50 53 to 117
Sulfate 27 to 44 47 to 92 0 to 1012 73 to 393 45 to 91 28 to 37 60 to 115
Nitrate
(as N) 0 – 7.2 -1 to 19 18 to 97 24 to 51 2.7 to 8.4 2.7 to 4.2 3.7 to 8.0
Arsenic - - - - - - -
Barium 0.02 to 0.05 0.02 to 0.04 - 0.06 to 0.17 0.04 to 0.07 0.04 - 0.07 -
Boron 0.14 to 0.28 0.3 to 0.5 0.6 to 2.4 0.16 to 0.82 0.22 to 0.67 0.14 to 0.18 0.20 to 0.30
Chromium - 0.005 to 0.005 - 0.004 to 0.024 0.020 to 0.036 0.030 to 0.043 0.009 to 0.015
Fluoride 4.4 to 12.2 0.7 to 1.4 0.5 to 13.8 0.4 to 1.8 1.8 to 5.0 2.2 to 3.6 1.7 to 2.6
Oxygen -10.5 to -9.5 -7.4 to -7.0 -10.2 to -8.6 -10.2 to -9.6 -10.7 to -10.2 -10.5 to -10.0 -9.6 to -9.0
Deuterium -77.5 to 68.5 -51.8 to -49.6 -75.1 to -64.4 -74.2 to -70.5 -76.3 to -72.7 -75.6 to -71.5 -68.3 to -63.2
Gross Alpha - - - - - - -
Gross Beta 2.3 to 7.2 -6.7 to 19.9 3.6 to 17.6 -18 to 120 3.0 to 10.5 2.4 to 4.8 5.1 to 9.6
Radon - - - - - - -
All units in milligrams per liter (mg/L) unless otherwise noted
49
Among Five Aquifers - Twenty-eight (28)
groundwater quality constituent concentrations were
compared between Eastern Regional (29 sites),
Western Regional (34 sites), Southern Regional (29
sites), Forepaugh (9 sites) and Harcuvar (6 sites)
aquifers; sites in the Perched and Mixed aquifers
were not included because their extreme values often
masked more subtle differences between the other
aquifers. Because not all sites had the same
constituents collected, site totals vary for well
characteristics, field parameters, nitrate, radon and
radionuclide constituents.
Significant concentration differences were found with
24 constituents (Kruskal-Wallis with Tukey test, p ≤
0.05).
There were three general patterns. Well depth,
groundwater depth, temperature, pH-field (Diagram
17), pH-lab and chromium were significantly higher
in the Eastern and Western Regional aquifers than the
Southern Regional aquifer. SC-field, SC-lab, and
TDS (Diagram 18) were significantly higher in
Southern and Western Regional aquifers than the
Eastern Regional aquifer. Hardness, calcium,
magnesium, bicarbonate (Diagram 19), oxygen and
deuterium (Diagram 20) were significantly higher in
the Southern Regional aquifer than in the Eastern and
Western Regional aquifers. Complete results are
found in Table 10.
E. Regional
Forepaugh
Harcuvar
S. Regional
W. Regional
Aquifers
6
7
8
9
10
pH - field (su)
E. Regional
Forepaugh
Harcuvar
S. Regional
W. Regional
Aquifers
0
500
1000
1500
2000
TDS (mg/L)
Diagram 18. Samples collected from sites
in the Southern Regional aquifer had
significantly higher TDS concentrations than
samples collected from sites in the Eastern
Regional and Forepaugh aquifers; sites in
the Western Regional aquifer had
significantly higher TDS concentrations than
sites in the Eastern Regional aquifer
(Kruskal-Wallis and Tukey test, p ≤ 0.05).
The significantly greater depth to
groundwater in the Eastern Regional
aquifer delays the mixing of water laden
with salts from excess irrigation applications
percolating to the aquifer.13
Diagram 17. Samples collected from
sites in the Eastern Regional, Western
Regional and Forepaugh aquifers had
significantly higher pH values than
samples collected from sites in the
Southern Regional aquifer (Kruskal-Wallis
with Tukey test, p ≤ 0.05). Based on
isotope values, the Southern Regional and
Harcuvar aquifers appear to receive
more recent recharge and groundwater
in such areas is usually near neutral (6.9 –
7.4 su) whereas in downgradient areas,
pH values in groundwater can through
hydrolysis reactions increase up to 9.5 su.28
50
E. Regional
Forepaugh
Harcuvar
S. Regional
W. Regional
Aquifers
0
100
200
300
400
500
Bicarbonate (mg/L)
E. Regional
Forepaugh
Harcuvar
S. Regional
W. Regional
Aquifers
-90
-80
-70
-60
-50
-40
Deuterium(0/00)
Diagram 19. Samples collected from
sites in the Southern Regional and
Harcuvar aquifers had significantly
higher concentrations of bicarbonate
than samples collected from sites in the
Eastern Regional, Forepaugh and
Western Regional aquifers (Kruskal-
Wallis and Tukey test, p ≤ 0.05).
Elevated bicarbonate concentrations
are often associated with recharge
areas. 28 Since calcium, magnesium and
bicarbonate are significantly greater in
the Southern Regional aquifer, this is
another indication that groundwater in
that aquifer is of more recent origin
than the Eastern and Western Regional
aquifers.
Diagram 20. Samples collected from
sites in the Harcuvar aquifer had
significantly higher deuterium values than
samples collected from sites in the Eastern
Regional, Forepaugh, Western Regional,
and Southern Regional aquifers (Kruskal-
Wallis with Tukey test, p ≤ 0.01). Similarly,
samples collected from sites in the
Southern Regional aquifer were
significant higher than those collected
from the Eastern Regional, Forepaugh,
Western Regional aquifers.
Samples from the Harcuvar and Southern
Regional aquifers generally plotted higher
on the precipitation trajectory and were
isotopically heavier or more enriched than
samples collected from the Eastern
Regional, Forepaugh or Western Regional
aquifers. This pattern is yet another
indication that groundwater in that
aquifer is of more recent origin than the
Eastern and Western Regional aquifers.
51
Table 10. Variation in Groundwater Quality Constituent Concentrations Between Five Regional Aquifers
Using Kruskal-Wallis with the Tukey Test
Constituent Significance Significant Differences Among Recharge Sources
Well Depth ** E. Regional > All aquifers
W. Regional > Harcuvar & S. Regional Forepaugh > S. Regional
Groundwater Depth ** All aquifers > S. Regional
E. Regional > W. Regional, Harcuvar & S. Regional
Temperature - field ** E. Regional & W. Regional > Harcuvar & S. Regional
Forepaugh> S. Regional
pH – field ** E. Regional, Forepaugh & W. Regional > S. Regional
pH – lab ** E. Regional & W. Regional > S. Regional
SC - field ** S. Regional > E. Regional & Forepaugh
W. Regional > E. Regional
SC - lab ** S. Regional > E. Regional & Forepaugh
W. Regional > E. Regional
TDS ** S. Regional > E. Regional & Forepaugh
W. Regional > E. Regional
Turbidity ns -
Hardness ** S. Regional > W. Regional, E. Regional & Forepaugh
Calcium ** S. Regional > W. Regional, E. Regional & Forepaugh
Magnesium ** S. Regional > W. Regional, E. Regional & Forepaugh
Sodium ** W. Regional > E. Regional & Forepaugh
Potassium ** S. Regional & Harcuvar > Forepaugh & E. Regional
W. Regional > Forepaugh S. Regional > W. Regional
Bicarbonate ** S. Regional & Harcuvar > Forepaugh, W. Regional & E. Regional
Chloride ** S. Regional > E. Regional, Forepaugh & Harcuvar
Sulfate ** S. Regional> E. Regional
Nitrate (as N) ** -
Arsenic ** -
Barium ns -
Boron ** W. Regional > E. Regional
Chromium ** E. Regional & W. Regional > Harcuvar & S. Regional
Fluoride ** Forepaugh > all aquifers
Oxygen ** Harcuvar > all aquifers
S. Regional > E. Regional & W. Regional
Deuterium ** Harcuvar > all aquifers
S. Regional > E. Regional, Forepaugh & W. Regional
Gross Alpha ns -
Gross Beta * -
Radon ns -
ns = not significant * = significant at p ≤ 0.05 or 95% confidence level ** = significant at p ≤ 0.01 or 99% confidence level
All units mg/L except temperature (degrees Celsius) and SC (uS/cm)
52
SUMMARY AND CONCLUSIONS
The groundwater quality of the McMullen Valley
basin will be described in the following order: the
Forepaugh aquifer, Eastern Regional aquifer,
Western Regional aquifer, the Mixed aquifer, the
Perched aquifer, Southern Regional aquifer, and the
Harcuvar aquifer.
Forepaugh Aquifer – Located in the easternmost
section of the McMullen Valley basin, groundwater
in this aquifer is partially separated from the Eastern
Regional aquifer by low hills and an unnamed ridge
east of Aguila.43 The steep hydraulic gradient
between the two aquifers indicates they are poorly
connected.43
All nine of the groundwater samples collected in the
Forepaugh aquifer exceeded health-based water
quality standards. At eight sites, water quality
standards for fluoride were exceeded with
concentrations as high as 15 mg/L, almost four times
the health based water quality standard. Fluoride
concentrations above 5 mg/L are controlled by
calcium through precipitation or dissolution of the
mineral fluorite. 28 In a chemically closed hydrologic
system such as the McMullen Valley basin, calcium
is removed from solution by precipitation of calcium
carbonate and the formation of smectite clays. High
concentrations of dissolved fluoride may occur in
groundwater depleted in calcium if a source of
fluoride ions is available for dissolution. 28
Six groundwater samples collected from the
Forepaugh aquifer also exceeded health-based water
quality standards for arsenic; concentrations were as
high as 0.022 mg/L, over twice the 0.01 mg/L
standard. Arsenic concentrations may be influenced
by similar reactions as fluoride, including exchange
on clays or with hydroxyl ions. Other factors such as
aquifer residence time, an oxidizing environment,
and lithology likely effect arsenic concentrations. 28, 29
A well located on an isolated ranch on the southern
periphery of the basin, near bedrock, exceeded nitrate
and gross alpha water quality standards. The nitrate
exceedances may have been the result of nearby
corrals that sometimes hold livestock, a source which
has been thought to the cause of elevated nitrate
concentrations in other isolated stock wells around
Arizona. 31, 32 Fractured rock aquifers do not filter
wastewater as efficiently as porous aquifers which
can result in groundwater contamination.41 The
elevated gross alpha concentrations may result from
the nearby granite geology, which often is correlated
with high concentrations of radionuclide
constituents.23
Eastern Regional Aquifer – In the McMullen
Valley basin, groundwater formerly moved from east
to west in the Regional aquifer. However, two large
cones of depression caused by heavy pumping for
irrigation uses near Aguila and also in the
Salome/Wenden area have limited this flow creating
the Eastern Regional aquifer (Diagram 21). 25 The
aquifer consists of basin areas generally from the La
Paz-Maricopa County line east to the Forepaugh
aquifer and lacks the confining Lake-bed Unit above
it. The Eastern Regional aquifer is directly connected
to the Upper Alluvial Fill unit, which has largely
been dewatered in the area. 25
Although 28 percent of the 29 groundwater samples
collected in the Eastern Regional aquifer exceeded
health-based water quality standards, most of these
sites were located south and southeast of Aguila.
Fluoride and arsenic were the most common
constituents exceeding health-based water quality
standards. One well located on isolated ranch on the
southern periphery of the basin, near bedrock, also
exceeded nitrate and gross alpha water quality
standards.
Most sample sites in the Eastern Regional aquifer
west of Aguila met water quality standards and/or
guidelines. The only exception was that many sample
sites exceeded the Secondary MCL for fluoride.
Overall, 69 percent of sites in the Eastern Regional
aquifer exceeded the aesthetics-based, 2 mg/L
guideline for fluoride. Exchange of sorption-desorption
reactions are an important control for
lower (< 5 mg/L) fluoride concentrations. 28 The
weathering of rocks releases fluoride ions into
solution. As pH levels increase down gradient, more
hydroxyl ions may exchange for fluoride ions,
thereby increasing the fluoride in solution. 28
Well depth and groundwater depth in the Eastern
Regional aquifer were significantly greater than for
those in the Western or Southern Regional aquifers
(Kruskal-Wallis with Tukey test, p ≤ 0.05). This is
likely an important factor in why the Eastern
Regional aquifer exhibits significantly lower TDS,
sodium and boron than the Western Regional aquifer.
Excess water laden with salts from irrigation
applications has further to percolate to recharge the
water table that is also concurrently, moving deeper
because of heavy pumping for irrigation. 13 Soil
testing has indicated it would take approximately 7 to
10 years for recharge water to percolate 70 feet. 13
This allows the Eastern Regional aquifer to be, at this
53
time, minimally impacted by poor quality irrigation
recharge.
Western Regional Aquifer – The Western Regional
aquifer no longer receives significant groundwater
flow from areas east of the La Paz-Maricopa County
line (Diagram 21) because of cones of depression
caused by heavy pumping for irrigation uses near
Aguila and also in the Salome/Wenden. 25
The Western Regional aquifer also roughly correlates
to the spatial expanse of the Lake-bed Unit, a layer of
fine grained sediments that acts as a confining layer
between the upper Perched aquifer and the lower
Western Regional aquifer. 24 However, some
irrigation wells in the Western Regional aquifer
produce water that is a product of both the Regional
and Perched aquifers. The cascading wells are caused
by leaking water from the Perched aquifer that occur
due to breaks that have developed in the casing, voids
behind the casing, and through filter packs
surrounding the casing in rotary-drilled wells.24
Through well logs and video examination of well
casings, some irrigation wells have been identified as
contributing to the cross-contamination between the
Western Regional aquifer and the Perched aquifer.24
However, not all of these connecting wells exhibited
elevated constituent concentrations which could be a
result of seasonal fluctuations in water quality
reported by earlier studies. 24 Sampling in September
during the latter stages of the growing season
indicates that the improved water quality is because
the plumes of poor-quality groundwater near the well
had largely been removed by heavy pumping for
irrigation purposes. 22
Diagram 21. Map showing depth to groundwater shows the groundwater divide in the northeast portion of
the diagram that divides the Eastern and Western Regional aquifers. The divide was created by cones of
depression caused by heavy pumping for irrigation use in the Eastern Regional aquifer near the town of
Aguila and in the Western Regional aquifer near the towns of Wenden and Salome. The groundwater divide
between the Western Regional aquifer and the Southern Regional aquifer is also shown in the southwestern
portion of the diagram. 24
54
Because of the difficulty in ascertaining which wells
were actually producing water that was a mixture of
the two sources, no additional characterization was
done for the purposes of the ADEQ report. All the
wells in question were designated as producing water
from the Western Regional aquifer. Of the total
recharge to the Western Regional aquifer, an
estimated 15 percent is a result of cross-connection
flow through wells. 24 Overall, cross contamination
through cascading wells is thought to have a fairly
small impact on the water quality of the Western
Regional aquifer. 24
The groundwater quality of the Western Regional
aquifer follows a similar pattern to that found in the
Eastern Regional aquifer. Although 41 percent of the
34 groundwater samples collected in the Western
Regional aquifer exceeded health-based water quality
standards, most of these sites were located around or
east of Wenden, In contrast, most sample sites in the
Western Regional aquifer west and north of Salome
met water quality standards and/or guidelines.
Sample sites in the Wenden area, where elevated pH
levels frequently occurred, most commonly exceeded
health based water quality standards for fluoride (32
percent). Fluoride concentrations were as high as 22
mg/L, more than five times the health based water
quality standard. Arsenic was exceeded at 27 percent
of sample sites while nitrate was exceeded at 5
percent of sites. Fluoride and arsenic exceedances
appear to be naturally occurring influenced by the
same chemical processes detailed in the Eastern
Regional aquifer summary. 28, 29
The most important water quality aspect of the
Western Regional aquifer—and the McMullen Valley
basin—is the gap in the Lake-bed Unit northeast of
Salome. The absence of the aquitard here allows
poor quality groundwater in the Perched aquifer to
drain downward. 24 So important is this process that,
for the purposes of this report, this area is denoted as
a separate aquifer and referred to as the Mixed
aquifer.
Mixed Aquifer - In general, the intervening Lake-bed
Unit is an effective barrier to the downward
percolation of ground water, isolating the Perched
and Western Regional aquifer from one another. 24
However, in a one-half mile gap where lake-bed
sediments are absent one mile northeast of Salome
there is no separation between the Perched and
Western Regional aquifer. 24 Because the static water
level of the Perched aquifer is higher than the
regional water table, poor quality groundwater tends
to drain downward from the Perched aquifer to the
Western Regional aquifer in this area at the perimeter
of the Lake-bed Unit. 24
Wells pumping water in the vicinity of the Lake-bed
Unit gap also exhibit such different water quality
than that of other wells situated in the Western
Regional aquifer that this area is considered a
separate aquifer, the Mixed aquifer, for the purposes
of this study.
Of the 11 samples collected from wells in this area,
all sites exceeded water quality standards and/or
guidelines for nitrate and TDS; exceedances also
occurred frequently with fluoride, chloride, sulfate,
arsenic, gross alpha, uranium, selenium, and
manganese. In particular, nitrate concentrations were
elevated up to seven times the 10 mg/L health-based
water quality standard. The elevated radionuclide
concentrations such as uranium may be linked to the
downward movement of high alkalinity water
combined with alluvial material eroded from nearby
granite bedrock.26 Other studies have shown that
high alkalinity recharge liberates naturally occurring
uranium that is absorbed to aquifer sediments. 42
Although the lake bed sediment gap is not shown as
extending further northeast along U.S. Highway 60,
here there is another area of elevated constituent
concentrations.24 Several wells in between these two
areas that don’t show any impacts of recharge from
the Perched aquifer. Although an earlier report shows
this as a zone of permanently degraded water quality,
it may be just a product of cascading wells at the
northeast end.
TDS, hardness, calcium, magnesium, sodium,
potassium, chloride, sulfate, nitrate, barium, boron
and gross beta concentrations in the Mixed aquifer
were generally significantly higher than for those
found in the Western, Southern or Eastern Regional
aquifers or the Forepaugh or Harcuvar aquifers
(Kruskal-Wallis with Tukey test, p ≤ 0.05).
Based on this data, the water quality of the Mixed
aquifer does not appear to be able to support
domestic or municipal uses without treatment.
Perched Aquifer – Present only in the western
portion of the basin, this shallow aquifer composed of
discontinuous sand and gravel lenses is probably a
system composed of several aquifers that may not all
be hydrologically connected. 24 Little information is
55
known about the occurrence and movement of water
within it. The aquifer is not a significant water
source, estimated to contain around 500,000 acre-feet
which is estimated to be 8 percent of the total
groundwater in storage in the Western Regional
aquifer above a depth of 1,200 feet. 24 However, the
Perched aquifer system is important because of its
impact on the water quality of other associated
aquifers. 24
Although natural recharge occurs from ephemeral
flows in Centennial Wash and its tributaries, most
recharge comes from deep percolation of irrigation
water as well as minor amounts of wastewater
discharged from septic systems. 24 As such, previous
studies postulated that the water quality in the
Perched