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Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Casey J.R. Jones, D.K. Adams, A.C. Comrie, M.J. Anderson, R.N. Gorley, K.R. Clarke · U.S. Geological Survey

USGS Publications · Papers · License: Public Domain

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Prepared in cooperation with the Hopi Tribe

Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Scientific Investigations Report 2025–5038 U.S. Department of the Interior U.S. Geological Survey

Cover. Chevelon Canyon, about 7 miles upstream from the confluence of Chevelon Creek and the Little Colorado River, Arizona. Coconino sandstone is exposed. Photograph by Jon Mason, U.S. Geological Survey, June 27, 2020.

Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona By Casey J.R. Jones

Prepared in cooperation with the Hopi Tribe

Scientific Investigations Report 2025–5038

U.S. Department of the Interior U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2025

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–392–8545. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/ or contact the store at 1–888–275–8747. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Jones, C.J.R., 2025, Assessment of water chemistry of the Coconino aquifer in northeastern Arizona: U.S. Geological Survey Scientific Investigations Report 2025–5038, 30 p., https://doi.org/10.3133/sir20255038. ISSN 2328-0328 (online)

iii

Acknowledgments The author would like to acknowledge Celeste Journey, U.S. Geological Survey hydrologist Emeritus, for her statistical expertise. Jon Mason, U.S. Geological Survey hydrologist Emeritus, proposed the initial study. The author also would like to acknowledge the many women and men who have sampled and analyzed groundwater in the area since 1933.

Contents Acknowledgments��iii Abstract��1 Introduction��1 Purpose and Scope��3 Previous Investigations��3 Description of Study Area��3 Geology��3 Evaporites��5 Groundwater Movement��7 Approach and Methods��7 Data Compilation��7 Quality Assurance��11 Graphical and Statistical Analysis��11 Results��12 Discussion��16 Potential for Use as Potable Water��17 Conclusions��17 References Cited��28

Figures 1.

2. 3.

4. 5.

6. 7. 8. 9.

Map of the approximate extent of the Coconino aquifer, boundaries of the Hopi Reservation and Navajo Nation, and the locations of the Coconino aquifer groundwater sites included in this study, northeastern Arizona��2 Generalized stratigraphic section of rock units in the study area and surrounding areas, northeastern Arizona��4 Map of the approximate extent of halite, the Holbrook Anticline, and three surface solution-collapse features—McCauley Sinks, Richard Lake, and an area referred to as “The Sinks,” in northeastern Arizona��6 Aerial photograph of McCauley Sinks as seen looking north��6 Graph showing distribution of the concentration of total dissolved solids in Coconino aquifer groundwater samples from 117 sites in the northeastern Arizona study area��12 Interpolated total dissolved solids and major ion chemistry distribution in the Coconino aquifer in the northeastern Arizona study area��13 Trilinear diagram and water-type classification of groundwater samples in the Coconino aquifer in the study area��14 Groundwater types of sites in the Coconino aquifer in the study area, based on the ratios of major ions present��15 Principal component analysis of major ions in the groundwater sites in the Coconino aquifer in the study area��16

Tables 1.

Well and spring locations and selected construction data for Coconino aquifer groundwater sites included in this study, northeastern Arizona��8 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona��18 3. Ranges of constituents in the study area and corresponding Environmental Protection Agency maximum contaminant levels, treatment techniques, and (or) secondary maximum contaminant levels, Coconino aquifer, northeastern Arizona��16

Conversion Factors U.S. customary units to International System of Units

Multiply

To obtain

Length inch (in.)

2.54

centimeter (cm)

inch (in.)

25.4

millimeter (mm)

foot (ft)

0.3048

meter (m)

mile (mi)

1.609

kilometer (km)

Area square mile (mi2) square mile (mi2)

259.0 2.590

hectare (ha) square kilometer (km2)

Volume cubic foot (ft3)

28.32

cubic decimeter (dm3)

cubic foot (ft3)

0.02832

cubic meter (m3)

Flow rate foot per year (ft/yr)

0.3048

meter per year (m/yr)

cubic foot per second (ft3/s)

0.02832

cubic meter per second (m3/s)

inch per year (in/yr)

25.4

millimeter per year (mm/yr)

vii

International System of Units to U.S. customary units

Multiply

To obtain

Length centimeter (cm)

0.3937

inch (in.)

millimeter (mm)

0.03937

inch (in.)

meter (m)

3.281

foot (ft)

kilometer (km)

0.6214

mile (mi)

Area hectare (ha)

0.003861

square mile (mi2)

square kilometer (km2)

0.3861

square mile (mi2)

Volume cubic decimeter (dm3)

0.03531

cubic foot (ft3)

cubic meter (m3)

35.31

cubic foot (ft3)

Flow rate meter per year (m/yr)

3.281

foot per year ft/yr)

cubic meter per second (m3/s)

35.31

cubic foot per second (ft3/s)

millimeter per year (mm/yr)

0.03937

inch per year (in/yr)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F – 32) / 1.8. Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 × °C) + 32.

Datums Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Supplemental Information Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C). Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (µg/L).

Abbreviations EPA

U.S. Environmental Protection Agency

MCL

maximum contaminant level

NWIS

U.S. Geological Survey National Water Information System

PCA

principal component analysis

SMCL

secondary maximum contaminant level

TDS

total dissolved solids

USGS

U.S. Geological Survey

Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona By Casey J.R. Jones

Abstract The Coconino aquifer was investigated as a potential groundwater resource for the Hopi Tribe and Navajo Nation in northeastern Arizona. Basic groundwater chemistry, including major ions, total dissolved solids, and selected trace metal concentrations, are presented and analyzed to characterize the Coconino aquifer. The geochemical compositions of groundwater are associated with changes in geology and groundwater movement and are compared to drinking-water standards to determine suitable areas for potential groundwater resource development. Dissolved-solids concentrations in much of the Coconino aquifer water were higher than the U.S. Environmental Protection Agency’s secondary drinking-water standard of 500 milligrams per liter (mg/L) due to a buried halite body in the southeastern part of the study area. However, trace metal concentrations were generally low. Groundwater may need to be treated for high dissolved-solids concentrations before it is suitable for use as a resource for the Hopi Tribe and Navajo Nation.

Introduction The Coconino aquifer is a multiple-aquifer system that extends throughout northeastern Arizona, northwestern New Mexico, southwestern Colorado, and southeastern Utah (fig. 1). In northern Arizona, the Coconino aquifer underlies most of the Navajo Nation and the entirety of the Hopi Reservation. Despite its substantial area, wells drilled into the Coconino aquifer are most common in the southern and eastern extent of the aquifer. The Coconino aquifer is deeply buried elsewhere, likely buried to depths greater than 3,000 feet (ft) in some areas to the north. Total dissolved solids (TDS) concentrations are likely high in the Coconino aquifer water [greater than 2,000 milligrams per liter (mg/L)] in much of these areas (Bills and others, 2007). Shallower, more accessible aquifers overlie the Coconino aquifer in this region, including the Navajo aquifer, the primary water source for the Hopi Tribe and the southwestern Navajo Nation (Mason,

2021). Sustainable water resources for the Hopi Tribe and Navajo Nation are limited due to their location in an arid to semi-arid desert environment with minimal precipitation and groundwater recharge. However, as groundwater demand increases to keep up with population growth, the Coconino aquifer has the potential to serve as a source of water for a larger portion of the Hopi Tribe and Navajo Nation. Increased water production from the regional Coconino aquifer has the potential to provide greater water security to both Tribes. This report focuses on groundwater chemistry of the Coconino aquifer between Flagstaff, Arizona, and the area just east of Holbrook, Arizona, and from south of the Little Colorado River to the southern end of the Hopi Reservation (fig. 1). Coconino aquifer water users in the study area include the southwestern part of the Navajo Nation and the cities of Flagstaff, Winslow, and Holbrook (including their surrounding communities; Hart and others, 2002). Although previous studies and production from existing wells have shown that the Coconino aquifer can produce large quantities of water (for example, Mann, 1976), less has been done to examine the suitability of the water quality for development throughout the region. Water chemistry is extremely variable in this area, partially due to high dissolved solids from evaporite deposits near the base of the Coconino aquifer in the southeastern part of the study area (Cooley and others, 1969; Mann, 1976). The U.S. Environmental Protection Agency (EPA) has established non-mandatory secondary drinking-water standards of 500 mg/L for TDS. Above this level, water may taste bad and (or) cause staining and corrosion. However, potable drinking water generally has TDS concentrations of less than 3,000 mg/L (U.S. Environmental Protection Agency, 1987; Stanton and others, 2017). The EPA formally defined potential underground sources of drinking water as having a TDS concentration less than 10,000 mg/L (U.S. Environmental Protection Agency, 1987). Although TDS concentrations in some groundwater in the study area far exceed the EPA secondary maximum contaminant level (SMCL) of 500 mg/L, other areas show substantially lower dissolved-solids concentrations (Hoffmann and others, 2006; Bills and others, 2007).

2 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona 111°30'

111°

110°30'

110°

HOPI RESERVATION 35°30' 87 89

San Fran cis co

t t le

Wa s h

NAVAJO NATION RESERVATION

Color ado

ver Ri

Flagstaff

35°

Winslow 40

re ek

C lon ve e Ch

COCONINO COUNTY NAVAJO COUNTY

YAVAPAI COUNTY

C lea

34°30' Base from U.S. Geological Survey digital data, various scales and dates; Web Mercator projection; World Geodetic System of 1984

lo r

o tle C Lit

Holbrook

377

o Riv er

0 0

180

20 20

40 MILES 40 KILOMETERS

EXPLANATION

UTAH

Navajo Nation Reservation COLORADO

Hopi Reservation Coconino aquifer Wells and springs Coconino Sandstone well Coconino Sandstone spring

Map area

ARIZONA

Kaibab Formation well NEW MEXICO

Kaibab Formation spring Supai Formation well

Figure 1. Approximate extent of the Coconino aquifer, boundaries of the Hopi Reservation and Navajo Nation, and the locations of the Coconino aquifer groundwater sites included in this study, northeastern Arizona. Figure is modified from Robson and Banta (1995).

Description of Study Area 3 Besides TDS, other constituents, such as major cations and anions (calcium, magnesium, sodium, potassium, sulfate, chloride, and bicarbonate) and trace metals (arsenic, uranium, barium, lead, copper, and fluoride, among others), influence the suitability of groundwater for development. The U.S. Geological Survey (USGS), in cooperation with the Hopi Tribe, led this study to describe the basic groundwater chemistry of the Coconino aquifer. This effort provides information to identify potential areas for groundwater resource development.

Purpose and Scope The purpose of this report is to describe the basic groundwater chemistry of the Coconino aquifer along the Interstate-40 corridor between Flagstaff, Ariz., and the area just east of Holbrook, Arizona. Specifically, major ion, trace metal, and TDS concentrations are presented and analyzed to identify differing groundwater chemistry in association with changes in geology and groundwater movement, and to compare groundwater chemistry to drinking-water standards to determine suitable areas for potential groundwater-resource development.

Previous Investigations The hydrogeology and chemistry of the Coconino aquifer in the study area have been described in several previous studies. Darton (1910) compiled some of the first geologic data from the area between Kingman, Arizona, and Albuquerque, New Mexico, to explore groundwater prospects for the Atchison, Topeka, and Santa Fe Railway. Gregory (1916) described the geography, climate, surface water, and groundwater of the Navajo Nation and Hopi Reservations; the hydrogeology in this area was later expanded on by Cooley and others (1969). Harrell and Eckel (1939) presented a comprehensive groundwater study of the Holbrook area, including chemical analyses from 118 wells and springs. Bills and Flynn (2002) and Bills and others (2007) summarized the hydrogeology of the Coconino Plateau. Hart and others (2002) compiled existing Coconino aquifer data from the Little Colorado River Basin to produce a generalized groundwater budget. Hoffmann and others (2006) presented geological, hydrological, and chemical data from the Coconino aquifer near Leupp, Arizona, and Jones and Robinson (2021) presented groundwater levels and basic chemistry of the Coconino aquifer in northeastern Arizona. Evaporites in the study area also have been explored. Bahr (1962) described evaporite karst features on the Holbrook Anticline. Mann (1976) characterized Coconino aquifer water in southern Navajo County and produced an early delineation of the extent of salt beds. Neal and others (1998, 2013) and Rauzi (2000) described evaporite karst in the Holbrook sedimentary basin. Neal and Colpitts (1997)

and Neal and Johnson (2002) described specific Holbrook Basin karst expressions (Richard Lake and McCauley Sinks, respectively).

Description of Study Area The study area is within the Little Colorado River Basin in the southern part of the Colorado Plateau, specifically between Flagstaff, Arizona, and the area just east of Holbrook, Arizona, and from south of the Little Colorado River to the southern end of the Hopi Reservation (Fenneman and Johnson, 1946; fig. 1). Most of the topography is developed on nearly horizontal sedimentary rocks around 5,000 ft in elevation (Hart and others, 2002). The primary surface feature is the Little Colorado River, which parallels Interstate-40 and discharges into the Colorado River northwest of the study area. The Little Colorado River, along with its tributaries, flows through incised canyons in the Coconino Sandstone. Other local topographic relief is provided by folds and solution-collapse features. More detail will be provided on the solution-collapse features in the “Geology” section of this report. The climate in the study area is classified as arid to semi-arid (Bills and others, 2007). Average annual precipitation near Winslow was less than 8 inches (in.) from 1991 to 2020 (PRISM Climate Group, 2022). The months with the highest amount of rainfall, July–September, coincide with the North American monsoon (Adams and Comrie, 1997). Mean monthly temperature values from 1991 to 2020 near Winslow were highest in July and August at more than 75 degrees Fahrenheit, with the lowest temperatures in December and January at around 35 degrees Fahrenheit (PRISM Climate Group, 2022).

Geology The Coconino aquifer is named after the primary water-bearing rock unit within the aquifer, the Coconino Sandstone, but the saturated and hydraulically connected parts of the Kaibab Formation, the Toroweap Formation, the Schnebly Hill Formation, and the upper and middle part of the Supai Formation also constitute part of the Coconino aquifer in the study area (fig. 2; Bills and others, 2000; Bills and Flynn, 2002; Hart and others, 2002; Bills and others, 2007). The Supai Formation ranges in age from Pennsylvanian to Permian and consists of red siltstone and sandstone (Irwin and others, 1971; Blakey, 1990). Divided into three parts, only the upper and middle parts of the Supai Formation are hydraulically connected to the Coconino aquifer; the lower part of the Supai Formation acts as a confining layer for underlying groundwater in the Redwall-Muav aquifer (Bills and others, 2000).

4 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

0–150

The Moenkopi Formation forms a confining layer where present

MOENKOPI FORMATION

Solution channels and caves

10–650

KAIBAB FORMATION

0–150

TOROWEAP FORMATION

300–960

COCONINO SANDSTONE

Coconino aquifer

Relative thickness, in feet

0–1,700

SCHNEBLY HILL FORMATION

UPPER PART OF SUPAI FORMATION

600–2,000

MIDDLE PART OF SUPAI FORMATION

LOWER PART OF SUPAI FORMATION

50–300

0–400 0–200

Supai Formation

Confining layer

Redwall-Muav aquifer

REDWALL LIMESTONE

TEMPLE BUTTE AND MARTIN FORMATIONS, UNDIVIDED MUAV LIMESTONE BRIGHT ANGEL SHALE TAPEATS SANDSTONE

GRANITOID AND METAMORPHIC ROCKS

Figure 2. Generalized stratigraphic section of rock units in the study area and surrounding areas, northeastern Arizona. Modified from Bills and others (2007, fig. 11). Muav Limestone and Bright Angel Shale refer to the Muav Limestone and Bright Angel Shale of the Tonto Group. Thickness ranges for the Tapeats Sandstone and Bright Angel Shale are not noted due to lack of data in the study area.

Description of Study Area 5 The Hermit Formation overlies the Supai Formation in some areas of northern Arizona. Consisting of red-brown siltstone and sandstone, the Hermit Formation is lithologically similar to the Supai Formation. In much of the study area, the boundary becomes unclear and the Hermit and Supai Formations are indistinguishable. For this reason, the Hermit Formation is usually omitted from stratigraphic columns in this area (Irwin and others, 1971; Blakey, 1990; Bills and others, 2000). The Permian Schnebly Hill Formation is an important Coconino-aquifer component in the Holbrook Basin, with a thickness as much as 1,700 ft (fig. 2; Blakey, 1990; Bills and others, 2000). The Schnebly Hill Formation is reddish brown to reddish orange and comprises sandstone, mudstone, limestone, and evaporites (Blakey, 1990). East of Holbrook, the Corduroy Member of the Schnebly Hill Formation contains halite and other evaporites of early Permian age as much as 650 ft thick (Blakey, 1990; Conway and Cook, 2013). When present, the Schnebly Hill Formation intertongues with the overlying Coconino Sandstone (Bills and others, 2000; Hoffmann and others, 2006). The Permian Coconino Sandstone is typically the main water-bearing unit of the aquifer (Hart and others, 2002). The Coconino Sandstone is a tan to white, crossbedded, quartz sandstone of eolian origin (Darton, 1910; Blakey, 1990). In Leupp, geologic logs indicate thicknesses from 300 to 960 ft (Hoffmann and others, 2006). Near Winslow, Coconino Sandstone thickness is about 800 ft (Mann, 1976). The Permian Toroweap Formation is only known to be present in the western part of the study area. Bills and others (2000; p. 26) describe the formation as beds of “carbonate sandstone, red beds, silty sandstone, siltstone, limestone, and thin layers of gypsum.” The formation is often indistinguishable from Coconino Sandstone, but according to Sorauf and Billingsley (1991), a distinction between the Toroweap Formation and the white, quartz sandstone of the Coconino Sandstone can be observed near Flagstaff to the west of the study area; where indistinct, the Toroweap Formation is often considered to be part of the Coconino Sandstone (Bills and others, 2000). The Permian Kaibab Formation is often expressed as a light-gray limestone from 10 to 650 ft thick. Sinkholes and depressions formed by dissolution are present on the surface, as well as fractures formed by jointing and faulting in the subsurface (Irwin and others, 1971; Bills and others, 2000). In parts of the study area where the Coconino aquifer is not exposed, the red to reddish-brown Triassic Moenkopi Formation overlies the aquifer (Mann, 1976). Consisting largely of mudstone and siltstone, the Moenkopi Formation acts as a confining layer when not heavily fractured. In some areas, the Moenkopi Formation can supply small amounts of water to wells (Cooley and others, 1969; Bills and others, 2000). North of the study area, the shallower Navajo, Dakota, and Toreva aquifers are present and often used for water supply (Mason, 2021).

Evaporites Beds of halite underlie about 3,500 mi2 in the southeastern part of the study area, with a maximum thickness near the center of an aggregate of 655 ft of salt in 1,500 ft of Schnebly Hill Formation strata (fig. 3). Close to the depositional center of the halite, a zone of potash covers about 600 mi2. The potash, consisting of sylvite, carnallite, and polyhalite, is nearly 40 ft thick and overlies the halite (Rauzi, 2000). To the south and southeast, halite transitions into gypsum and anhydrite and extends farther than the halite (Rauzi, 2000, pl. 2). Dissolution of evaporite beds by the movement of Coconino aquifer groundwater has led to numerous solution-collapse features in the study area. Solution-collapse features in evaporite rocks are developed similarly to those in limestone, but the time scale is shorter. Evaporites such as halite and gypsum can form karst features in a matter of days to years due to their high solubility. Evaporite karst features form near the outer edges of a salt deposit (Johnson, 1997). In the study area, the dissolution front is currently migrating to the northeast, and karst features are forming in real time (Bahr, 1962; Johnson, 1997; Neal and others, 1998). The Holbrook Anticline is present near the southwestern extent of halite, and the axis can be mapped at the surface for more than 60 miles (mi; fig. 3). The northern flank follows a regional dip of about 2 degrees. On the southern side, the regional dip is interrupted and the average dip is about 15 degrees, although some dips can be steeper. Numerous karst sinks are present on the southern flank (Bahr, 1962). More than 500 sinkholes, joints, compression ridges, and other solution-collapse features have been identified along the Holbrook Anticline and the parallel Dry Lake Syncline to the immediate southwest (Mann, 1976; Conway and Cook, 2013). The Holbrook Anticline is not expressed below the salt layer, which may suggest that dissolution is a factor of its formation (Neal and others, 1998). Just west of the Holbrook Anticline, near the western limits of evaporites of the Schnebly Hill Formation, McCauley Sinks provide a conspicuous karst surface expression (fig. 4). McCauley Sinks include about 50 sinkholes up to 50 meters (m) deep and 100 m in diameter. They appear in three semi-circular “rings” within a 3-kilometer (km) wide depression (Neal and Johnson, 2002). Along with several other, smaller depressions west of the Holbrook Anticline, these structures are related to the dissolution front of the halite and appear similar to breccia pipes on the Colorado Plateau (Neal and Johnson, 2002). However, where these other breccia pipes originate in the Mississippian Redwall Limestone and (or) the Cambrian Muav Limestone of the Tonto Group, the McCauley Sinks and Richard Lake likely originate due to collapse following salt dissolution in the Schnebly Hill Formation. Similar to other karst features in the area, pressure ridges following the general trend of the Holbrook Anticline are present near both structures (Neal and Johnson, 2002). To the southeast of the study location is an area known as “The Sinks,” which includes more than 250 sinkholes, joint fissures, and other collapse features also related to halite dissolution (Neal and others, 1998).

6 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona 111°30'

111°

110°30'

110°

109°30'

109°

EXPLANATION

35°30'

Coconino-aquifer boundary

Flagstaff

ARIZONA NEW MEXICO

Study area

Winslow

35°'

Approximate extent of halite Anticline

Holbrook

Richard Lake 34°30'

McCauley Sinks HO

The Sinks

Map area

TIC

ARIZONA

Saint Johns

Snowflake

NEW MEXICO

LIN

Payson

E Show Low

Base from U.S. Geological Survey digital data, various scales and dates; Web Mercator projection; World Geodetic System of 1984

0 0

25 25

50 MILES 50 KILOMETERS

Figure 3. Approximate extent of halite, the Holbrook Anticline, and three surface solution-collapse features—McCauley Sinks, Richard Lake, and an area referred to as “The Sinks,” in northeastern Arizona. Halite extent is from the U.S. Geological Survey (USGS) National Map (https://www.usgs.gov/programs/national-geospatial-program/national-map).

Chevelon Canyon

McCauley Sinks

Pressure ridges

Figure 4. McCauley Sinks as seen looking north. Chevelon Canyon is in the background of the photograph. Pressure ridges are present in the foreground of the photograph. Photograph by Jon Mason, U.S. Geological Survey, June 27, 2020.

Approach and Methods 7

Groundwater Movement Groundwater in the Coconino aquifer generally moves northward, parallel to the regional dip of the strata (Mann, 1976; Hart and others, 2002). Most recharge occurs as snowmelt near the Mogollon Rim to the south; rain events are often flashy and contribute to runoff (Mann, 1976). The Coconino aquifer is unconfined in most of the study area. To the north, the Moenkopi Formation creates confined conditions. The age of groundwater in the Coconino aquifer around Flagstaff in the eastern part of the study area has been estimated as modern to about 7,000 years (Bills and others, 2000). Well yields from Coconino aquifer wells inventoried by previous studies varied substantially in the study area, from a few gallons per minute to about 2,800 gallons per minute (Mann, 1976; Bills and others, 2000; Hoffmann and others, 2006). Although several factors affect well yields, including pump design and formation lithology, Bills and others (2000) suggested that the greatest effect on Coconino aquifer well efficiency probably is due to proximity to faults and fractures. Jones and Robinson (2021) discussed wells monitored as part of the USGS C-Aquifer Monitoring Program between Flagstaff and Holbrook, Arizona. They found that measured groundwater levels fluctuate seasonally, and suggested that infiltration from surface water from summer monsoon events and spring snowmelt have the potential to influence wells, as does higher rates of pumping in the summer months. Although some monitored wells have shown little change in groundwater levels (for example, USGS site number 351023111062002, near Leupp), others have shown decreasing water-level trends (for example, USGS site number 345023110111401, south of Holbrook, has decreased about 11 ft from 1969 to 2018; Jones and Robinson, 2021; U.S. Geological Survey, 2023).

Approach and Methods This report assesses the distribution of major ions, trace metals, and total dissolved solids in the Coconino aquifer. Data used in this report were limited to water-chemistry results from well and spring samples available in the USGS National Water Information System (NWIS) database (U.S. Geological Survey, 2023). No new samples were collected as part of this study. Results within this report provide a representation of the

groundwater resource in the Coconino aquifer area in relation to potential potable water based on major-ion chemistry, TDS, and selected trace elements.

Data Compilation The USGS NWIS database was queried to find existing groundwater sites (wells and springs) that had water-chemistry data associated with them. Those groundwater sites with wells screened-in or springs discharging from the Coconino aquifer and having major ion and (or) TDS data were selected for inclusion in this study. A total of 130 sites with samples dating from 1933 to 2008 were identified (fig. 1; table 1; U.S. Geological Survey, 2023). These sites were generally in proximity to the Little Colorado River and Interstate-40. Few wells are drilled into the Coconino aquifer in Hopi Tribal Lands or Navajo Nation north of Interstate-40. Some wells may be screened in multiple formations, and it is not always clear which unit(s) the well is producing from. The aquifer coded in NWIS is considered to be the producing unit for this study. Most wells used (118) were screened in the Coconino Sandstone (fig. 1). Additionally, four of the spring sites discharge from the Coconino Sandstone where it is exposed in canyon walls along Clear and Chevelon Creeks. Three wells and one spring are sourced by the Kaibab Formation in the western part of the study area. Four wells are screened in the Supai Formation. No wells or springs sourced from the Hermit, Toroweap, or Schnebly Hill Formations were present in NWIS in the study area. Numerous study sites have been sampled multiple times. When computing the median values from all sites for the parameters of pH, specific conductance, and total dissolved solids, the most recent values from each site were used. In three cases, the date when the most recent sample was collected had two samples collected; in those cases, the average value of the two samples was used in the statistical analysis. Additionally, there were 23 samples with estimated results for TDS that were used in the statistical analysis. When computing the water type for sites with multiple samples the most recent sample collected containing all the constituents necessary to compute water type was used.

8 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona Table 1. Well and spring locations and selected construction data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023). [ft, feet; bls, below land surface; N/A, not applicable; --, information not available]

USGS site number

USGS station name

Site type

Geologic formation well is completed in (or spring discharges from)

Well depth (ft bls)

342526110155501

A-18-20 30CCD

Well

Coconino Sandstone

145

343149110002701

A-13-22 10CCA

Well

Coconino Sandstone

260

343225110545001

A-13-13 01DDB2

Well

Coconino Sandstone

997

343239110340001

A-13-17 05CAA

Well

Coconino Sandstone

843

343314111183801

A-14-10 32DBD

Well

Coconino Sandstone

600

343423111194001

A-14-10 30ACA

Well

Coconino Sandstone

1,050

343438110155001

A-14-20 30CAA

Well

Coconino Sandstone

400

343640110353001

A-14-17 18BBB

Well

Coconino Sandstone

800

343756111154001

A-14-10 02ACB

Well

Kaibab Formation

420

343914110082601

A-15-21 32ACB

Well

Coconino Sandstone

430

343918110121301

A-15-21 36BCB

Well

Coconino Sandstone

340

343950110061201

A-15-21 27DBD

Well

Coconino Sandstone

816

344058111033101

A-15-12 15DDC

Well

Coconino Sandstone

780

344104110375201

A-15-16 15DDC

Well

Coconino Sandstone

900

344221110081801

A-15-21 08DDC

Well

Coconino Sandstone

400

344239109595701

A-15-22 10DBA

Well

Coconino Sandstone

300

344303111124301

A-15-11 05BDC

Well

Coconino Sandstone

800

344349110064201

A-15-21 03BAC1

Well

Coconino Sandstone

715

344407110171801

A-16-19 36CCB1

Well

Coconino Sandstone

800

344457110065001

A-16-21 27CCD

Well

Coconino Sandstone

635

344502110261601

A-16-18 28DCB

Well

Coconino Sandstone

750

344516110320301

A-16-17 27BCA

Well

Coconino Sandstone

815

344644110023301

A-16-22 17CDC

Well

Coconino Sandstone

160

344644110024201

A-16-22 17CCD

Well

Coconino Sandstone

450

344720109585001

A-16-22 14ADB

Well

Coconino Sandstone

309

344720110135201

A-16-20 16BAC

Well

Coconino Sandstone

450

344749111051901

A-16-12 09BBB

Well

Coconino Sandstone

1,000

344757110261201

A-16-18 09ACD1

Well

Supai Formation

620

344908110202901

A-16-19 04BBC

Well

Coconino Sandstone

328

345011110201101

A-17-19 28CCB

Well

Coconino Sandstone

280

345212110012901

A-17-22 17DDB

Well

Coconino Sandstone

240

345223110522301

A-17-14 17ADD

Well

Coconino Sandstone

600

345308110125301

A-17-20 10CAA3

Well

Coconino Sandstone

110

345316110170910

A-17-19 12CBD

Well

Coconino Sandstone

475

345320110144710

A-17-20 08BDB

Well

Coconino Sandstone

200

345340110193001

A-17-19 04DDC

Well

Coconino Sandstone

550

345344110165101

A-17-19 01CDA

Well

Coconino Sandstone

470

345345110175201

A-17-19 02DBC

Well

Supai Formation

495

345350111015501

A-18-12H35DAD

Well

Coconino Sandstone

680

345410110153201

A-17-20 06DBA

Well

Coconino Sandstone

325

345415110200801

A-17-19 04BDB

Well

Coconino Sandstone

430

Approach and Methods 9 Table 1. Well and spring locations and selected construction data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued [ft, feet; bls, below land surface; N/A, not applicable; --, information not available]

USGS site number

USGS station name

Site type

Geologic formation well is completed in (or spring discharges from)

Well depth (ft bls)

345425110562101

A-17-13 02BBA

Well

Coconino Sandstone

600

345444110192501

A-18-19 33DAD2

Well

Coconino Sandstone

410

345500110210301

A-18-19 32BDD

Well

Coconino Sandstone

500

345519110314201

A-18-17 34ABB

Spring

Coconino Sandstone

N/A

345548110480201

A-18-15 30BCC

Well

Coconino Sandstone

560

345653110394001

A-18-16 20AAD

Spring

Coconino Sandstone

N/A

345707110552001

A-18-13 13CCD

Well

Coconino Sandstone

475

345730110483001

A-18-14 13ACC

Well

Coconino Sandstone

1,000

345730110485001

A-18-14 13BDC

Well

Coconino Sandstone

900

345746110483701

A-18-14 13BAD

Well

Coconino Sandstone

1,100

345750110482501

A-18-14 13ABD2

Well

Coconino Sandstone

620

345750110482701

A-18-14 13ABD1

Well

Coconino Sandstone

315

345750110482801

A-18-14 13ABD3

Well

Coconino Sandstone

293

345757110484301

A-18-14 13BAA

Well

Coconino Sandstone

700

345800111184701

A-18-10 02CCB

Spring

Kaibab Formation

N/A

345821110295101

A-18-17 12CBA

Well

Coconino Sandstone

330

345840110513001

A-18-14 09AAC

Well

Coconino Sandstone

450

345859110381801

A-18-16 10CBC2

Spring

Coconino Sandstone

N/A

345906110383301

A-18-16 10CAC

Spring

Coconino Sandstone

N/A

345910110352001

A-18-17 06CBB2

Well

Coconino Sandstone

106

345942110462401

A-18-15 05ABB

Well

Coconino Sandstone

350

350002110355501

A-19-16 36DDB [Winslow I-40 Well]

Well

Coconino Sandstone

610

350030110420901

A-19-15 36ABA

Well

Coconino Sandstone

400

350040110384401

A-19-16 28DDD

Well

Coconino Sandstone

150

350042110425601

A-19-15 26DDA

Well

Coconino Sandstone

227

350050110424801

A-19-15 25CBC

Well

Coconino Sandstone

303

350051110430001

A-19-15 26DAC

Well

Coconino Sandstone

120

350124110450901

A-19-15 28AAC

Well

Coconino Sandstone

400

350125110450801

A-19-15 28AAB

Well

Coconino Sandstone

220

350150111040001

A-19-12H15CBB

Well

Coconino Sandstone

760

350158110403601

A-19-16 20BCD

Well

Coconino Sandstone

198

350205110513301

A-19-14 21ACA

Well

Coconino Sandstone

220

350210110560001

A-19-13 23ABB

Well

Coconino Sandstone

450

350210111011001

A-19-12H13BAD

Well

Coconino Sandstone

690

350400111004001

A-19-13 07BBB

Well

Coconino Sandstone

570

350407110332101

A-19-17 05DDD

Well

Coconino Sandstone

680

350414110412201

A-19-16 06CAD

Well

Coconino Sandstone

282

350417110413301

A-19-16 06CDB

Well

Coconino Sandstone

195

350420110590001

A-19-13 05DAB

Well

Coconino Sandstone

570

350427110512501

A-19-14 04DAB

Well

Coconino Sandstone

410

10 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona Table 1. Well and spring locations and selected construction data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued [ft, feet; bls, below land surface; N/A, not applicable; --, information not available]

USGS site number

USGS station name

Site type

Geologic formation well is completed in (or spring discharges from)

Well depth (ft bls)

350428110484901

A-19-14 01CAB

Well

Coconino Sandstone

270

350440110411801

A-19-16 06ACC

Well

Coconino Sandstone

185

350446110502501

A-19-14 03AAC2

Well

Coconino Sandstone

650

350447110502301

A-19-14 03AAC1

Well

Coconino Sandstone

800

350450110522001

A-19-14 04BBB

Well

Coconino Sandstone

600

350451110494901

A-19-14 02BAC

Well

Coconino Sandstone

727

350518110554801

A-20-13 35DDA

Well

Coconino Sandstone

400

350538110560401

A-20-13 35BDA

Well

Coconino Sandstone

400

350600111015001

A-20-12H24CBB

Well

Coconino Sandstone

640

350618111015601

A-20-12H23ADD

Well

Coconino Sandstone

650

350637110485401

A-20-14 25B

Well

Coconino Sandstone

320

350653110573801

A-20-13 22CCB

Well

Coconino Sandstone

350

350700111054001

A-20-12 14CAC

Well

Coconino Sandstone

650

350706111014701

A-20-12H13CBB [Sunshine Well]

Well

Coconino Sandstone

1,155

350756111154001

A-20-11 07ADD

Well

Coconino Sandstone

950

350810111105001

A-20-11 12BAA

Well

Coconino Sandstone

3,628

350816110531001

A-20-14 17B

Well

Coconino Sandstone

250

350839111005301

A-20-12H01DDA

Well

Coconino Sandstone

650

350845110540101

A-20-14 07C

Well

Coconino Sandstone

200

350909111165401

A-20-10S01AAA

Well

Coconino Sandstone

935

350957110562601

05 144-10.76X05.75 [PW-3]

Well

Coconino Sandstone

1,096

350958110562201

05 144-10.67X05.72(1)

Well

Coconino Sandstone

1,180

351001110562601

05 144-10.79X05.73

Well

Coconino Sandstone

426

351022111061801

05 145-05.92x05.31 [OW-1]

Well

Coconino Sandstone

351023111062002

05 145-05.96X05.28 (2) [PW-1A]

Well

Coconino Sandstone

351052110491701

05 144-04.07X04.75

Well

Coconino Sandstone

440

351053110332501

05 143-03.22X04.73

Well

Coconino Sandstone

907

351122111101301

05 145-09.63X04.20

Well

Coconino Sandstone

717

351142110563401

05 144-10.91X03.80

Well

Coconino Sandstone

253

351144111161201

A-21-11 19BCB

Well

Coconino Sandstone

935

351214111022101

05 145-02.25X03.18 [OW-2B]

Well

Coconino Sandstone

1,069

351215111021701

05 145-02.17X03.15

Well

Coconino Sandstone

388

351238111084101

05 145-08.18X02.71

Well

Coconino Sandstone

717

351442110581601

05 144-12.50X00.37

Well

Coconino Sandstone

425

351448111012701

05 145-01.37X00.22

Well

Coconino Sandstone

570

351519111120701

05 132-11.42X16.88

Well

Supai Formation

351525111035801

05 132-03.74X16.74

Well

Coconino Sandstone

635

351739111001501

05 132-00.32X14.24

Well

Kaibab Formation

425

351748110592301

05 131-13.51X13.98

Well

Kaibab Formation

200

351749111003401

05 132-00.52X14.00

Well

Coconino Sandstone

400

351758111000901

05 132-00.14X13.82

Well

Coconino Sandstone

405

UNSURV

UNSURV UNSURV

1,161

Approach and Methods 11 Table 1. Well and spring locations and selected construction data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued [ft, feet; bls, below land surface; N/A, not applicable; --, information not available]

USGS site number

USGS station name

Site type

Geologic formation well is completed in (or spring discharges from)

Well depth (ft bls)

351804111060301

05 132-05.70X13.70

Well

Coconino Sandstone

391

351815110505001

05 131-05.50X13.50

Well

Coconino Sandstone

510

351818110054901

05 132-05.47X13.45

Well

Coconino Sandstone

687

351831111054501

05 132-05.41X13.21

Well

Coconino Sandstone

351930111184801

A-22-10 03ACD

Well

Supai Formation

582 2,400

352117111132901

05 132-12.70X10.02

Well

Coconino Sandstone

806

352119111132901

05 132-12.70X09.98

Well

Coconino Sandstone

716

352226111081401

05 132-07.77X08.69

Well

Coconino Sandstone

422

Quality Assurance

Graphical and Statistical Analysis

Water-chemistry samples were analyzed using methods described in Fishman and Friedman (1989), Fishman (1993), and Fishman and others (1994). Major ion data included dissolved calcium, magnesium, sodium, potassium, chloride, sulfate, and bicarbonate (computed from alkalinity or acid-neutralizing capacity). When potassium was not measured, sodium was used by itself in the ion balance and analyses; potassium concentrations are considered minor. In order to validate the dissolved-ion data, the ion balance of samples was checked by converting the concentrations of cations and anions in the sample from milligrams per liter to milliequivalents per liter for comparison. Theoretically, if all ions have been correctly determined, the total milliequivalents per liter of cations should equal the total milliequivalents per liter of anions in a sample (Hem, 1985). Most samples had differences of less than 5 percent between cation and anion concentrations expressed as milliequivalents per liter. Four samples had ion balances with differences from 6 to 12 percent; these samples are included in this study because the percent differences are low, and other unmeasured ions and trace metals may potentially contribute to the ion balances (Hem, 1985). Potassium was not measured in all water samples which undoubtably affected the ion balance of samples where it was missing. However, because potassium is usually a minor constituent of natural waters the omission was considered acceptable. The TDS of groundwater was analyzed using the sum of constituents method (Fishman and Friedman, 1989). Specific conductance, or the ability of a solution to conduct an electric current, is a function of the concentration and charge of the ions (Hem, 1985; Fishman and Friedman, 1989). Specific conductance and TDS from samples used in this study showed a strong relationship as should be expected with an R2 value of 0.98.

The geochemical compositions of water-chemistry samples were graphically depicted with stiff and trilinear diagrams (similar to Piper [1944]). Analyses were performed using R statistical software (v.4.2.2; R Core Team, 2022). Water-chemistry data were downloaded from NWIS using the dataRetrieval package (De Cicco and others, 2022), and stiff diagrams and piper diagrams were created using the smwrGraphs package (Lorenz and Diekoff, 2017). Prior to plotting, concentration data, in milligrams per liter, were transformed to milliequivalents per liter. TDS were plotted in ArcMap (v. 10.8.1, Esri, Redlands, California) and interpolated using the “spline with barriers” method. In addition to the graphical methods described above, principal component analysis (PCA) on the major ion data was performed in Primer 7 (Clarke and others, 2014; v7.0.17, PRIMER-E Ltd., Plymouth, United Kingdom) to investigate associations in the data. PCA was conducted on transformed and normalized major ion data to better understand how the selected factors explained the observed variation among sites (Clarke and others, 2014). Briefly, PCA captures as much of the variability in the original multi-dimensional space as possible within the two axes of the plane. Output from the PCA includes eigenvalues (variances of each principal component axis), eigenvectors (coefficients for the linear combination of input factors that defines the plane), and principal component scores (coordinates of the samples on the PC axes computed using eigenvector coefficients). A percent variance explained (from eigenvalues) is computed to quantify the extent to which the two principal component axes of the plane provide an accurate representation of the true association between the factors in the original multi-dimensional space.

12 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Results Water chemistry of the Coconino aquifer varied throughout the study area. The pH values for 112 sites ranged from 6.7 to 11.1, with a median of 7.6 (table 2, found at the end of this report). Three sites had samples that exceeded the SMCL range for pH for drinking water (6.5–8.5; U.S. Environmental Protection Agency, 2015). SMCLs are not enforced or considered to cause health effects, but may affect the taste, color, or corrosiveness of water. USGS site number 345757110484301 exceeded the SMCL with 1 pH value of 8.6, although 16 other samples from the site ranged from 7.4 to 8.1. USGS site number 351758111000901 exceeded the SMCL with a pH value of 9.2, and USGS site number 350407110332101 had the highest pH value of the sites with a pH of 11.1. Specific conductance values from 126 sites ranged from 110 to 15,200 microsiemens per centimeter (µS/cm), with a median of 1,220 µS/cm. Total dissolved solids ranged from 199 to 10,400 milligram per liter (mg/L) from 117 sites, with a median of 755 mg/L (table 2, found at the end of this report). Maximum TDS exceeded the SMCL in about 73 percent of sites with data (85 of 117; fig. 5). TDS was highest (10,400 mg/L) at USGS site number 344407110171801. This 800-ft well is completed in the Coconino Sandstone and is located south of Holbrook in the southeastern

part of the study area. Other sites with high TDS (USGS site number 350407110332101, 6,580 mg/L; USGS site number 351815110505001, 5,800 mg/L; USGS site number 351053110332501, 5,470 mg/L; and USGS site number 351052110491701, 5,030 mg/L; figs. 5 and 6) are located north of Winslow (table 2, found at the end of this report; fig. 5). A map of interpolated TDS concentrations was created for the study area (fig. 6). Areas of high TDS include the area northwest of The Sinks and Snowflake in the southeastern part of the study area and a broad area north of Winslow. This broad area is unconstrained by TDS sample data; however, a well drilled in the mid-2000s by the Hopi Tribe at the Village of Moenkopi north of the study area required reverse osmosis treatment for municipal use demonstrating that salinity concentrations are elevated in that area (Jon Mason, oral commun., 2023). Spatial distributions of TDS are consistent with a similar map of the southeastern part of the study area from Mann (1976). Figure 6 also displays water-chemistry stiff diagrams at sites with available data. These stiff diagrams are used to spatially compare ionic composition of water samples (Stiff, 1951). Water-chemistry data were adequate to create stiff diagrams for 111 sites; when sites were too close together to distinguish, a representative diagram from one site is displayed in figure 6.

100

Percentage of sites below a certain concentration

351052110491701

350407110332101 351815110505001 351053110332501

344407110171801

Environmental Protection Agency (EPA) secondary maximum contaminant level (SMCL) of 500 milligrams per liter for total dissolved solids

2,000

4,000

6,000

8,000

10,000

12,000

Maximum measured total dissolved solids concentration in groundwater at a site, in milligrams per liter

Figure 5. Distribution of the concentration of total dissolved solids (TDS) in Coconino aquifer groundwater samples from 117 sites in the northeastern Arizona study area. Five sites with the highest TDS are labeled with the corresponding U.S. Geological Survey site number.

20 0 20

Chloride Bicarbonate Sulfate

C lea

ee Cr

Winslow

351052110491701

Base from U.S. Geological Survey digital data, various scales and dates; Web Mercator projection; World Geodetic System of 1984

350407110332101

351053110332501

RESERVATION

NAVAJO NATION

Richard Lake

Cr lon e McCauley ev Sinks Ch

377

0 10

344407110171801

10 20 KILOMETERS

Snowflake

The Sinks

Holbrook

20 MILES

v er

180

110°

Figure 6. Interpolated total dissolved solids (TDS) and major ion chemistry distribution (U.S. Geological Survey, 2023) in the Coconino aquifer in the northeastern Arizona study area. Not all sites with TDS have major ion data to display. When sites with major ion data were too close together to distinguish, one representative diagram is displayed.

34°30'

o Wa

ad olor

ARIZONA

35°

San F ran cis c

ive

351815110505001

110°30'

C tle Lit

Map area

Milliequivalents per liter

Sodium+potassium Calcium Magnesium

Stiff diagram of total dissolved solids measurements

Total dissolved solids measurement location

0 to 500 501 to 1,243 1,244 to 2,041 2,042 to 2,971 2,972 to 3,946 3,947 to 5,009 5,010 to 6,028 6,029 to 7,180 7,181 to 8,598 8,599 to 10,415

Li ttl

Total dissolved solids, in milligrams per liter

NAVAJO COUNTY

111°

COCONINO COUNTY

o k

ad lor o eC ee

EXPLANATION

Results 13

14 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona The chemical composition of groundwater was further characterized based on the ratios of major ions present in the water (Hem, 1985). This classification is typically called the water type. Water type is determined by comparing the relative concentrations in milliequivalents of the cations and anions in water separately. To be classified as a specific water type, there must be a dominant cation and anion each making up more than 50 percent of the total. For example, if calcium makes up more than 50 percent of the cations and bicarbonate makes up more than 50 percent of the anions in the water, it is classified as a calcium-bicarbonate water type (or just calcium-bicarbonate water). If no cations and anions make up more than 50 percent of the total, the water is classified as a mixed water type (Hem, 1985). The water types correspond to areas of a trilinear diagram (fig. 7).

Using this method of classification, 42 percent of the sites (47 of 111) have a sodium-chloride water type. These sites correlate with high TDS in the study area, located to the southeast and north of the Little Colorado River (figs. 6, 7, and 8; table 2, found at the end of this report). Another 14 percent (15 of 111) of the sites are a calcium-sulfate water type. About 15 percent (17 of 111) of the sites are considered calcium-bicarbonate water. The calcium-dominated water is mostly located to the west of the study area (fig. 8; table 2, found at the end of this report). The remaining 29 percent (32 of 111) are a mixed water type. They are referred to as calcium-magnesium-chloride sulfate type because combinations of these cations and anions make the majority of the ions (fig. 7; table 2, found at the end of this report).

100

EXPLANATION Water type

80 60

Sodium-bicarbonate type

lfat

gne

chl

Calcium-sulfate type

siu

Calcium-sodium-bicarbonate type

lciu

Calcium-magnesium-chloride sulfate type

Sodium-chloride type

II III

ori

III 20

Total dissolved solids, in milligrams per liter 199 0

Calcium-bicarbonate type

10,400 20

Bic

60 80

100

Calcium

100

Chloride

Percent

Figure 7. Trilinear diagram and water-type classification of groundwater samples in the Coconino aquifer in the study area. The relative size of the circles represents total dissolved-solids concentrations.

100

arb ona t

lfat

siu

100

ssi

gne

100

ota

IV di So

100

Results 15 111°30'

111°

110°30'

110°

HOPI RESERVATION 35°30'

Map area 87

ARIZONA 89

San Fran cis co

t t le

Wa s h

Color ado

NAVAJO NATION RESERVATION

ver Ri

Flagstaff

35°

Winslow

re ek

C lea

C lon ve e Ch

lo r

EXPLANATION

o tle C Lit

Holbrook

Sodium-chloride type Calcium-magnesiumchloride sulfate type 34°30'

Calcium-sulfate type Base from U.S. Geological Survey digital data, various scales and dates; Web Mercator projection; World Geodetic System of 1984

COCONINO COUNTY NAVAJO COUNTY

YAVAPAI COUNTY

Water type Calcium-bicarbonate type

377

o Riv er

0 0

180

20 20

40 MILES 40 KILOMETERS

Figure 8. Groundwater types of sites in the Coconino aquifer in the study area, based on the ratios of major ions present.

The loading plot depicts computed PCA of the normalized major ion data and explains 66 percent of the cumulative variability among the data (fig. 9). The principal component along axis 1 (PC1) accounted for 46.1 percent of variation. The principal component along axis 2 (PC2) accounted for an additional 19.9 percent of variation. Vectors plotted on the PC1 represented a positive loading for bicarbonate and negative loading for all other variables. Vectors plotted on the PC2 represented a positive loading in calcium, magnesium, and sulfate, and a negative loading in sodium (+potassium), chloride, and bicarbonate ions. Additionally, non-sodium-chloride water types plotted along a line defined by the bicarbonate vector on one end to magnesium, calcium, and sulfate on the other end, whereas sodium-chloride water types changed along a different line that included the sodium and chloride vectors. Of these major ions, chloride and sulfate have Environmental Protection Agency (EPA) SMCLs that affect drinking water (table 3; U.S. Environmental Protection Agency, 2015). The SMCL for both ions is 250 mg/L;

exceedances can cause the water to taste salty. Chloride exceeded the SMCL in 122 samples from 50 sites (about 45 percent of the sites) in the study area. Sulfate exceeded the SMCL in 68 samples from 46 sites (about 41 percent of the sites). Either chloride, sulfate, or both ions exceeded the SMCL in 154 samples from 69 sites (about 62 percent of the sites) Selected trace metals also were analyzed. Although most sites did not have any data (with the exception of fluoride, which was measured at 126 sites), available data are presented along with EPA regulations (table 3). Only one sample exceeded the EPA maximum contaminant limit (MCL) for any of the trace metals measured. Unlike SMCLs, MCLs are legal limits of constituents in drinking water that are designed to protect human health (U.S. Environmental Protection Agency, 2009). USGS site number 344407110171801, an 800-foot well in the Coconino Sandstone, exceeded the MCL and SMCL for fluoride (MCL is 4 mg/L; SMCL is 2 mg/L; and sample concentration was 5.4 mg/L). Fluoride concentrations for 126 sites ranged from 0 to 5.4 mg/L.

16 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona 10

EXPLANATION

Principal component analysis axis 2 (19.9 percent of variation)

Water type Calcium-bicarbonate type 5

Sodium-chloride type

Magnesium

Calcium-magnesium-chloride sulfate type

Sulfate Calcium

Calcium-chloride type Total dissolved solids, in milligrams per liter

1,000

Sodium (+ Potassium)

−5

Chloride

4,000 Bicarbonate

8,000 14,000

−10 −10

−5 0 5 Principal component analysis axis 1 (46.1 percent of variation)

20,000

Figure 9. Principal component analysis (PCA) of major ions in the groundwater sites in the Coconino aquifer in the study area. Table 3. Ranges of constituents in the study area and corresponding Environmental Protection Agency (EPA) maximum contaminant levels (MCLs), treatment techniques (TT), and (or) secondary maximum contaminant levels (SMCLs; U.S. Environmental Protection Agency, 2015), Coconino aquifer, northeastern Arizona. [Abbreviations: µg/L, micrograms per liter; mg/L, milligrams per liter; --, not applicable; TT*, treatment techniques; <, less than]

Chemical symbol

No. of sites with measurement

Range

EPA MCL (or TT*)

EPA SMCL

112

6.8–11.1

6.5–8.5

Total dissolved solids

117

199–10,400 mg/L

500 mg/L

Chloride

Cl-

0.01–3,980 mg/L

250 mg/L

Sulfate

SO42-

1.3–2,620 mg/L

250 mg/L

Arsenic

<1–7 µg/L

10 µg/L

Constituent pH

Barium

11.8–262 µg/L

2,000 µg/L

Copper

0.32–30 µg/L

1,300 µg/L*

1,000 µg/L

Lead

<0.08–30 µg/L

15 µg/L*

Fluoride

F-

126

0–5.4 mg/L

4 mg/L

2 mg/L

Arsenic, barium, copper, and lead were measured at 22 sites for a total of 38 samples. Arsenic concentrations ranged from less than 1 to 7 µg/L (MCL is 10 µg/L). Barium concentrations ranged from 11.8 to 262 µg/L (MCL is 2,000 µg/L). Copper and lead do not have an MCL, but instead are regulated in water systems by treatment techniques (TT). Treatment techniques do not apply to single elements, but no more than 10 percent of tap water samples can exceed the TT action level, or corrective measures must be used (U.S. Environmental Protection Agency, 2009). Copper concentrations ranged from 0.32 to 30 µg/L (TT action level is 1,300 µg/L). Lead concentrations ranged from less than 0.08 to 30 µg/L (TT action level is 15 µg/L). Uranium

concentrations were only measured at two sites near Leupp, Arizona, in 2005, and were 2.45 and 4.60 µg/L (MCL is 30 µg/L).

Discussion Subsurface deposits of halite in the southeastern part of the study area influence the groundwater chemistry. High TDS, which can occur naturally in groundwater due to the dissolution of rocks, likely results from the solution of halite along the regional groundwater flow path. Sodium-chloride

Conclusions 17 is highly soluble in water but is concentrated in many of the groundwater sites in the study area, suggesting a persistent source. Despite the salt-dissolution features at McCauley Sinks and Richard Lake, TDS is interpreted to be in a low range for the study area near these features (Neal and Johnson, 2002; fig. 6). This supports Neal and Johnson’s (2002) conclusion that dissolution here may indeed be less active than in the past, as the dissolution front migrates to the northeast. Another hypothesis presented by Neal and Johnson (2002) is that wells are too shallow to penetrate deep groundwater with high TDS. The top of the saltwater zone is variable, and well logs are not always available. Mann (1976) attributes this irregularity to fractures in the siltstone of the Supai Formation beneath the Coconino aquifer. Other evaporites that are often present along with naturally forming halite can supply additional ions to groundwater (Richter and Kreitler, 1991). Calcium and sulfate in groundwater likely result from dissolution of gypsum (CaSO4 2H20) and anhydrite (CaSO4), which extend beyond the halite bed. Mann (1976) suggested that sodium, sulfate, and chloride in the Coconino aquifer also may be contaminated from the Moenkopi Formation when wells are open in both stratigraphic layers. However, due to the mudstone and siltstone present, the Moenkopi Formation acts as a confining unit unless heavily fractured. The calcium, magnesium, and bicarbonate present in the west and southwest may be from water moving downward through the carbonate Kaibab Formation (Mann, 1976). Bills and others (2007) recorded low strontium-isotope (87Sr/86Sr) measurements from wells and springs near Flagstaff that indicate inflow interacting with the Kaibab Formation and volcanic rocks.

Potential for Use as Potable Water High concentrations of TDS in much of the study area affect the quality of Coconino aquifer water for potential potable use. In the southeastern part of the study area, and north of the Little Colorado River, about 73 percent of Coconino aquifer samples contain TDS greater than the SMCL of 500 milligrams per liter (mg/L) up to concentrations greater than 10,000 mg/L. Although this falls into the TDS range that can be potentially remediated, desalination of groundwater for potable use can be costly and energy intensive (Stanton and others, 2017). Trace metals have not been widely measured, but most concentrations are less than the MCLs for drinking water. Fluoride exceeded the MCL in one sample (table 3). Although both arsenic and uranium samples were less than the MCLs (10 µg/L As and 30 µg/L U), these elements have been a concern for the Navajo Nation and Hopi Tribe. Jones and others (2020) found that both arsenic and uranium exceeded the EPA MCL in western Navajo Nation in unregulated water sources, including around Leupp, Arizona.

Water containing elevated TDS can be used for livestock watering and (or) irrigation in some cases. Irrigation water with specific conductance values ranging from 750 to 1,500 µS/cm may have detrimental effects on sensitive crops, whereas higher specific conductance values may affect many crops (Zaman and others, 2018). Sodium hazard, which describes how sodium affects the soil, and ion toxicity are other potential hurdles. Less is known about Coconino aquifer water north of the study area on the Hopi Reservation and Navajo Nation. Wells in these areas penetrate the shallower Navajo, Dakota, and Toreva aquifers (Mason, 2021). The Hopi Tribe did drill a single municipal well into the Coconino aquifer at the Village of Moenkopi north of the study area. Water from that well required reverse osmosis treatment demonstrating that salinity concentrations are elevated in that area (Jon Mason, oral commun., 2023). However, to the northeast of the study area, near Arizona’s border with New Mexico, Coconino aquifer water contains less dissolved solids (less than 500 mg/L; U.S. Geological Survey, 2023).

Conclusions As population and development increase in the arid Hopi Reservation and Navajo Nation of northeastern Arizona, the Coconino aquifer has been considered for development as a supplemental groundwater resource. In cooperation with the Hopi Tribe and analyzing existing groundwater samples collected since 1933, the water chemistry of the Coconino aquifer was characterized to determine its potential suitability as a source of drinking water for the Hopi Tribe and Navajo Nation. Buried halite bodies in the southeastern part of the study area influence the dissolved-solids concentrations in the area. As groundwater moves along the regional dip to the north, sodium, chloride, and other ions are dissolved and transported through the system. The resulting plume of sodium-chloride groundwater differs from the groundwater to the south and west. Total dissolved solids (TDS), sulfate, and chloride exceed the U.S. Environmental Protection Agency (EPA) secondary maximum contaminant level for taste and odor in many samples. Measured trace metals are less than the EPA maximum contaminant level (MCL), except for one sample of fluoride. Water chemistry data from this study indicate that in much of this area, while the aquifer is potentially productive, it will likely need treatment before it is suitable for human consumption. Few Coconino aquifer wells exist north of the study area in the Hopi Reservation and (or) Navajo Nation. Characterizing the groundwater chemistry of the aquifer resource in this area could reveal its suitability for development as a water supply.

[Sample date: MM/DD/YYYY, month/day/year. Water type: Water type refers to major ion distribution and is only listed if used in the analysis (most recent complete sample). Abbreviations: SC, specific conductance; µS/cm, microsiemens per centimeter; Ca2+ , calcium; Mg+, magnesium; mg/L, milligrams per liter, Na+ + K+, sodium+potassium; SO42-, sulfate; Cl, chloride; HCO-, bicarbonate; TDS, total dissolved solids; --, no data available; E, estimate; <, less than]

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

Water type

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

342526110155501

6/14/1946

2,220

112

290

281

470

206

1,330

sodium-chloride

0.5

343149110002701

9/5/1972

1,060

7.1

150

17.2

350

289

729

calcium-sulfate

0.7

343225110545001

5/15/1952

540

346

0.4

343225110545001

5/11/1966

7.8

6.7

110

226

0.1

343225110545001

8/3/1992

519

7.5

4.8

1.3

352

285

calcium-bicarbonate

<0.1

343239110340001

6/20/1972

499

7.6

3.3

4.1

310

275

calcium-bicarbonate

343314111183801

8/5/1994

540

7.4

2.3

1.7

1.9

285

0.1

343423111194001

8/26/1975

476

265

0.1

343438110155001

9/21/1972

1,870

7.7

292.1

430

219

1,020

0.3

0.3 0.11

343438110155001

8/5/1992

1,840

7.8

272

430

221

990

343640110353001

7/5/1969

454

232

sodium-chloride --

343640110353001

8/17/2000

450

7.9

54.7

4.89

12.1

5.51

E 268

262

3.7

343756111154001

7/13/1978

640

7.4

4.9

7.2

350

331

calcium-bicarbonate

0.1

343914110082601

6/11/1958

2,260

296

130

930

150

1,780

calcium-sulfate type

calcium-magnesium-chloride sulfate

0.2

-0

343918110121301

9/12/1972

638

7.7

76.9

180

371

343950110061201

1/1/1974

1,080

702

344058111033101

6/17/1966

532

7.5

2.8

330

308

calcium-bicarbonate

344104110375201

1/1/1966

449

7.8

252

344104110375201

9/12/2000

410

7.3

49.9

27.5

4.95

13.4

5.04

E 246

216

E 0.6

0.17

0.4

0.3

344221110081801

2/14/1934

120*

120

160

252

344221110081801

6/11/1946

110

120*

110

160

260

344239109595701

9/5/1972

1,150

8.2

66.5

350

204

733

calcium-sulfate

0.6

344303111124301

6/22/1966

475

7.5

4.8

6.5

294

274

calcium-bicarbonate

0 --

calcium-magnesium-chloride sulfate

344349110064201

4/1/1974

670

436

344407110171801

5/8/1968

15,200

6.8

670

190

2,800

2,620

3,980

276

10,400

344457110065001

4/1/1974

600

390

344502110261601

7/24/1969

5,500

7.9

944.4

1,500

217

2,700

sodium-chloride

344516110320301

7/24/1969

4,930

7.9

913.8

330

1,400

152

2,860

sodium-chloride

344644110023301

8/5/1986

1,270

7.2

100

100.1

270

140

765

344644110024201

5/17/1968

7.2

180

236

344644110024201

8/19/1992

1,090

7.8

661

344720109585001

9/12/1972

4,230

7.3

210

794

1,600

350

364

3,200

344720110135201

6/15/1965

1,110

7.7

110

120

138

303

-sodium-chloride --

-calcium-magnesium-chloride sulfate -sodium-chloride --

5.4

0.4

0.2

<10

0.3

0.6

0.2

18 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued [Sample date: MM/DD/YYYY, month/day/year. Water type: Water type refers to major ion distribution and is only listed if used in the analysis (most recent complete sample). Abbreviations: SC, specific conductance; µS/cm, microsiemens per centimeter; Ca2+ , calcium; Mg+, magnesium; mg/L, milligrams per liter, Na+ + K+, sodium+potassium; SO42-, sulfate; Cl, chloride; HCO-, bicarbonate; TDS, total dissolved solids; --, no data available; E, estimate; <, less than]

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

344720110135201

8/5/1986

1,120

7.2

112.1

130

140

639

344720110135201

8/20/1992

1,650

7.8

111.9

120

140

301

639

344749111051901

11/10/1933

315

7.5

205

344757110261201

9/6/1972

5,470

1,003.4

370

1,500

179

3,120

344757110261201

9/14/1995

5,200

8.1

953.4

340

1,500

3,020

Water type -calcium-magnesium-chloride sulfate -sodium-chloride ---

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

<10

0.3

0.2

344908110202901

6/18/1946

413

770

273

1,110

225

344908110202901

4/23/1968

4,190

7.1

760

240

1,100

236

2,350

sodium-chloride

0.9

345011110201101

4/24/1968

2,800

6.7

540

166

700

129

1,500

sodium-chloride

0.8

345011110201101

8/4/1986

3,500

7.4

563.2

320

820

1,940

<30

0.6

345212110012901

8/18/1992

6,500

7.8

140

1,107.2

250

1,600

204

3,250

0.2

-sodium-chloride

345223110522301

5/3/1966

7.5

8.7

123

0.1

259

calcium-bicarbonate

345308110125301

8/5/1986

840

7.4

59.5

150

487

<10

0.4

345316110170910

8/17/1972

1,320

7.4

142.5

230

180

232

794

calcium-magnesium-chloride sulfate

0.5

345320110144710

9/12/1972

885

7.7

102.1

130

201

491

calcium-magnesium-chloride sulfate

0.5

345340110193001

6/5/2007

1,220

7.6

60.3

35.6

134.42

128

168

E 673

0.23

24.8

<0.12

E 0.32

0.4

345340110193001

6/19/2008

1,300

7.3

61.2

37.1

138.52

131

178

E 687

0.66

24.1

0.118

0.37 0.3

345344110165101

8/13/1992

1,160

132.2

170

160

219

680

calcium-magnesium-chloride sulfate

345345110175201

1/12/1968

1,140

7.3

140

114

169

256

651

calcium-magnesium-chloride sulfate

0.6

345350111015501

5/12/1966

637

7.4

154

240

425

0.3

345350111015501

10/5/1978

650

7.4

13.2

150

220

403

calcium-bicarbonate

0.2

345350111015501

8/17/1995

635

7.6

140

5.4

390

0.2

0.4

345410110153201

7/24/1968

839

7.4

113

198

445

345415110200801

6/5/2007

1,900

7.5

38.6

240.67

204

347

E 1060

calcium-magnesium-chloride sulfate --

0.27

20.2

<0.12

345425110562101

5/11/1966

626

7.7

128

252

398

0.51

0.4

0.1 0.2

10/19/1978

650

7.5

12.4

150

240

430

calcium-bicarbonate

8/16/1995

620

7.6

10.6

130

7.9

390

0.2

345444110192501

5/25/1994

1,430

7.5

182.4

130

260

790

0.4

345444110192501

5/4/1995

1,500

7.6

192.6

130

280

826

0.4

345444110192501

5/7/1996

1,520

7.8

202.5

190

270

909

0.4

345444110192501

4/17/1997

1,480

7.5

56.6

32.8

194.49

134

279

822

0.45

345444110192501

4/9/1998

1,500

7.8

56.5

34.4

203.45

133

289

836

0.38

345444110192501

6/2/1999

1,550

7.8

56.2

32.1

187.4

127

282

810

0.35

345444110192501

7/26/2001

1,540

7.6

202.4

130

290

830

0.34

Conclusions 19

345425110562101 345425110562101

USGS site number 345500110210301

Sample

date

(µS/cm)

8/17/1992

1,290

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

7.9

152.2

150

190

262

730

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

calcium-magnesium-chloride sulfate type

0.2

1.2

23.1

<0.16

0.31

1.6

25.4

<0.16

<0.8

0.31

Water type

345519110314201

7/6/2005

4,800

6.9

86.8

58.5

796.63

255

1,280

245

E 2610

345519110314201

6/23/2006

4,660

7.1

78.7

49.9

769.83

251

1,270

248

2,550

345519110314201

12/1/2010

4,680

7.9

345519110314201

12/1/2010

4,680

7.9

sodium-chloride

345519110314201

9/18/2012

4,730

7.7

345519110314201

9/19/2017

4,720

7.4

345519110314201

9/25/2018

4,520

7.6

345519110314201

9/25/2018

4,520

7.6

345519110314201

6/18/2019

4,730

7.3

345548110480201

5/3/1966

345548110480201

10/19/1978

7.6

480

168

745

236

1,630

2,900

7.4

462.5

170

740

230

1,620

-sodium-chloride

0.2

0.2 --

345653110394001

2/28/2006

2,280

7.5

345653110394001

6/28/2006

2,300

7.6

25.4

372.98

41.2

601

E 1230

0.28

85.4

<0.08

0.4

0.15

345653110394001

12/2/2010

2,370

7.8

345653110394001

9/20/2017

2,320

7.7

345653110394001

6/19/2019

2,140

7.5

345653110394001

6/19/2019

2,320

7.5

345653110394001

6/10/2022

2,320

7.7

0 0

345707110552001

11/20/1933

2,270

7.6

136

232

345730110483001

4/27/1955

7.8

13*

110

246

361

sodium-chloride --

345730110483001

7/13/1955

7.7

30*

145

249

421

345730110483001

11/14/1955

20*

120

251

387

0.1

345730110483001

1/2/1957

7.4

254

338

0.1 0.1

345730110483001

6/5/1957

7.7

252

308

345730110483001

12/6/1957

7.6

229

331

0.1

345730110483001

5/2/1958

7.6

229

311

0.1

345730110483001

1/4/1959

8.1

271

318

0.1

345730110483001

11/17/1959

7.3

100

261

374

0.1 0.2

345730110483001

6/16/1960

7.7

249

351

345730110483001

2/17/1961

7.6

26*

120

256

422

0.4

345730110483001

6/3/1963

7.7

33*

115

256

412

345730110483001

10/16/1964

7.6

108

37*

112

295

433

calcium-bicarbonate

0.3

20 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

Water type

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

345730110483001

10/25/1965

7.6

133*

215

288

609

0.2

345730110483001

9/17/1901

0.1

345730110485001

10/20/1953

7.4

35*

110

268

397

345730110485001

1/8/1955

7.9

14*

251

348

345730110485001

4/27/1955

8.1

22*

120

251

380

345730110485001

7/13/1955

7.7

31*

150

242

425

345730110485001

11/14/1955

8.2

39*

130

249

412

345730110485001

1/2/1957

7.7

251

333

0.1

345730110485001

6/5/1957

7.5

244

303

0.1

345730110485001

12/6/1957

7.5

229

333

0.1

345730110485001

5/2/1958

7.7

229

318

0.1

345730110485001

1/4/1959

8.1

254

291

0.1

345730110485001

11/17/1959

7.3

271

359

0.1

345730110485001

6/16/1960

7.6

246

345730110485001

2/17/1961

7.6

33*

120

276

425

0.3

345730110485001

6/3/1963

7.7

42*

135

261

433

0 0.3

345730110485001

10/16/1964

7.7

118

23*

278

388

345730110485001

10/25/1965

7.5

76*

110

281

437

0.3

345730110485001

3/3/1966

587

7.6

7.1*

257

348

0.2

345730110485001

1/4/1979

570

7.5

8.9*

110

250

370

calcium-bicarbonate

0.1

345746110483701

1/10/1963

7.6

64*

106

537

0.3 0.4

345746110483701

1/10/1963

7.6

113

64*

111

106

249

539

345746110483701

10/16/1964

7.6

116

152*

100

214

300

748

0.3

345746110483701

10/25/1965

7.6

288*

250

254

300

1,030

0.2 0.2

3/1/1966

1,720

8.1

230

134

360

263

975

3/1/1966

1,610

8.2

200

128

315

260

888

0.1

345746110483701

3/2/1966

1,490

180

124

290

263

851

0.3

345750110482501

8/22/1953

7.5

87*

120

124

256

572

sodium-chloride

345750110482501

8/25/1953

7.5

79*

110

264

524

345750110482501

1/8/1955

7.7

166*

110

252

237

751

345750110482501

4/27/1955

7.9

167*

135

258

249

803

345750110482501

8/12/1955

7.9

169*

120

290

240

822

345750110482501

11/14/1955

228*

140

296

242

902

Conclusions 21

345746110483701 345746110483701

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

Water type

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

345750110482501

1/2/1957

7.6

297*

120

468

246

1,130

0.1

345750110482501

6/5/1957

7.6

163*

346

242

765

0.1

345750110482501

12/6/1957

7.6

171*

140

262

232

808

0.1

345750110482501

5/2/1958

7.9

207*

372

229

892

0.1

345750110482501

1/4/1959

8.1

267*

150

402

232

1,050

0.1 0.4

345750110482501

11/17/1959

7.2

254*

110

432

256

1,060

345750110482501

6/16/1960

7.6

243*

150

394

239

1,050

345750110482501

2/17/1961

7.6

164*

150

260

256

839

0.3

345750110482501

6/3/1963

7.8

136

331*

155

486

288

1,270

345750110482501

10/16/1964

7.7

135

382*

220

500

273

1,380

0.3

345750110482501

10/25/1965

345750110482501

3/2/1966

7.5

389*

325

390

251

1,340

0.4

2,100

8.1

310

140

500

183

1,150

0.2

345750110482501

3/3/1966

1,850

7.5

250

130

410

258

1,040

0.2

345750110482501

6/13/1989

2,500

7.7

350*

140

520

1,270

<100

0.2

345750110482501

5/1/1990

2,400

7.7

310*

130

560

1,250

0.3

345750110482501

7/9/1991

2,300

7.7

340*

140

500

260

1,230

0.2 0.1

345750110482501

5/21/1992

2,270

7.7

350*

140

490

255

1,240

345750110482501

5/5/1993

2,450

360*

140

570

1,330

sodium-chloride --

0.3

345750110482501

5/26/1994

2,440

7.6

360*

130

570

1,320

0.2

345750110482501

5/4/1995

2,400

7.5

340*

130

510

1,240

0.2

345750110482501

5/7/1996

2,340

7.5

340*

130

510

1,230

0.2 0.17

345750110482501

4/17/1997

2,410

7.7

81.7

36.9

373*

139

615

1,390

345750110482501

6/1/1999

2,300

7.7

73.3

35.9

322*

131

528

1,230

0.18

345750110482501

6/13/2000

2,290

7.7

36.7

324*

135

517

E 1230

0.17 0.2

345750110482501

9/5/2001

2,350

7.5

330*

130

490

1,210

345750110482501

5/23/2007

1,110

7.8

80.2

36.4

323*

135

526

E 1240

0.68

29.2

0.13

1.5

0.2

345750110482501

6/18/2008

2,400

7.6

36.2

326*

137

506

E 1220

0.79

0.352

11.4

0.22

345750110482701

11/21/1933

3.5

105

246

calcium-bicarbonate

345750110482801

3/2/1966

2,100

8.1

310

140

500

183

345750110482801

5/4/1966

1,870

7.6

250

132

395

262

-sodium-chloride

0.2

0.1

345757110484301

11/15/1953

7.4

161*

140

212

276

762

345757110484301

1/8/1955

7.7

93*

100

246

276

689

345757110484301

4/27/1955

8.1

140*

125

208

264

714

22 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

Water type

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

345757110484301

7/13/1955

7.9

117*

120

202

254

688

345757110484301

11/14/1955

7.9

143*

120

226

264

736

0.2

345757110484301

1/2/1957

7.6

140*

140

200

256

720

0.1

345757110484301

6/5/1957

7.5

169*

284

266

798

0.1

345757110484301

12/6/1957

7.5

147*

140

216

244

742

0.1

345757110484301

5/2/1958

7.6

115*

206

242

631

0.1

345757110484301

1/4/1959

7.9

193*

160

258

290

872

0.1

345757110484301

11/17/1959

7.3

133*

226

276

708

0.5

345757110484301

6/16/1960

7.6

144*

135

224

271

769

0.1

345757110484301

2/17/1961

7.7

158*

140

224

276

793

0.4

345757110484301

6/3/1963

7.7

101

215*

135

312

276

931

345757110484301

10/16/1964

7.7

125

202*

120

294

293

903

0.3

345757110484301

11/17/1964

1,370

8.6

180

123

280

150

0.2

345757110484301

10/25/1965

7.5

294*

230

308

288

807

0.3

0.4

0.7

sodium-chloride

345800111184701

8/4/1995

530

7.8

18.4

307

345821110295101

3/3/1970

6,670

320

1,100*

830

1,760

164

345840110513001

8/22/1995

570

7.7

342

0.2

345859110381801

6/30/2005

6,250

7.2

92.9

65.3

1,148.58

301

1,750

284

E 3500

<0.6

23.3

0.25

1.4

0.32

<1.2

0.32

345859110381801

6/28/2006

6,390

7.4

90.6

58.9

1,108.08

296

1,750

248

E 3430

345859110381801

9/20/2017

6,110

7.2

345859110381801

6/19/2019

6,040

7.1

345906110383301

6/30/2005

6,300

7.3

98.3

68.1

1,188.86

299

1,710

280

E 3510

345906110383301

6/28/2006

6,180

7.6

89.8

57.2

1,087.97

288

1,680

280

E 3340

345910110352001

3/8/1967

4,500

7.2

280

730

680

1,060

274

2,930

345910110352001

8/12/1992

4,650

7.9

816

220

1,200

282

2,510

345942110462401

11/20/1933

218

340

632

510

198

-sodium-chloride

sodium-chloride

0.75

23.4

1.4

0.33

0.18

<0.6

0.75

28.2

<0.08

E 0.36

0.32

0.6

0.2

0 0.3

sodium-chloride sodium-chloride

0.14

345942110462401

3/2/1966

2,080

7.5

300

140

470

246

sodium-chloride

350002110355501

6/16/1972

5,870

7.5

150

1007.5

1,500

267

3,380

sodium-chloride

0.2

350030110420901

4/16/1971

2,380

386*

690

0.33

350040110384401

6/13/1966

105

920*

300

1,360

283

sodium-chloride

0.3

350042110425601

2/8/1979

4,400

773.9

100

1,200

200

2,290

sodium-chloride

0.2

350050110424801

1/21/1954

7.6

630

120

920

260

2,040

sodium-chloride

0.2

Conclusions 23

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

Water type

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

350050110424801

8/12/1992

3,500

8.1

572.4

920

1,820

0.1

350051110430001

1/9/1979

4,500

7.9

854.5

110

1,300

230

2,490

0.2

350051110430001

8/12/1992

4,550

802.9

130

1,200

227

2,360

sodium-chloride

0.1

350124110450901

11/2/1978

2,750

412.3

170

670

230

1,500

sodium-chloride

0.2

350125110450801

11/28/1967

2,760

7.5

430

155

665

244

1,500

0.4

350125110450801

1/21/1972

2,500

7.8

373*

110

750

192

sodium-chloride

350150111040001

6/22/1966

652

7.2

154

230

417

calcium-bicarbonate

0.1

350158110403601

2/27/1979

6,650

7.7

1212

300

1,800

190

3,550

sodium-chloride

0.2

350205110513301

11/11/1933

240

135

392

264

350205110513301

5/11/1966

1,890

7.3

260

135

413

265

0.1

350205110513301

10/5/1978

1,880

7.3

241.9

150

390

250

1,030

calcium-bicarbonate

0.2

350210110560001

6/18/1966

512

309

0.2

350210110560001

11/28/1967

814

7.4

27*

123

248

465

calcium-bicarbonate

0.4

350210111011001

11/1/1966

992

7.7

103

358

194

706

0.3

0.2

<0.1 0

350210111011001

6/22/1978

950

7.4

110

38.8

320

190

660

350210111011001

8/10/1992

1,000

7.8

110

39.6

340

181

674

350400111004001

11/20/1933

226

224

512

350400111004001

6/10/1966

778

7.5

205

230

502

350400111004001

8/2/1995

720

7.9

23.3

200

435

350407110332101

5/2/1966

12,100

11.1

6,580

350414110412201

4/30/1965

3,390

7.4

620

200

840

254

2,200

calcium-sulfate --

0.2

0.1

0.5

0.7 0.6

calcium-magnesium-chloride sulfate

sodium-chloride

350417110413301

4/30/1965

3,370

7.6

620

190

840

246

2,190

sodium-chloride

350420110590001

6/18/1966

805

7.5

101

212

236

537

calcium-magnesium-chloride sulfate

0.3

350427110512501

3/8/1954

1,420

160

132

250

258

798

sodium-chloride

0.6 0.1

350428110484901

10/11/1965

3,400

7.9

100

584.9

224

898

231

1,970

350428110484901

9/21/1966

3,800

7.2

158

574*

328

930

238

2,170

350428110484901

8/16/1995

3,300

7.6

551.8

160

840

1,800

350440110411801

4/30/1965

2,560

7.6

430

160

595

272

-sodium-chloride -sodium-chloride

0.2

0.6

350446110502501

8/22/2006

2,870

8.1

75.5

35.6

429.99

145

698

239

1,510

sodium-chloride

1.2

28.8

1.28

2.3

0.19

350447110502301

10/25/1978

2,850

7.5

462.6

160

760

240

1,640

sodium-chloride

0.2

350450110522001

8/19/1966

1,340

7.5

160

153

227

264

801

350450110522001

10/30/1978

1,300

161.8

140

240

250

783

350451110494901

8/21/1954

2,800

7.8

74.4

41.8

550

175

830

244

-sodium-chloride --

0.2

0.1

24 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

350451110494901

11/3/1958

2,810

7.3

460

152

705

241

1,560

350451110494901

11/13/1958

2,810

7.6

460

146

705

243

1,560

Water type -sodium-chloride

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

0.4

0.3

350518110554801

11/20/1933

750

157

232

488

350518110554801

3/12/1953

808

143

233

0.2

350518110554801

5/12/1966

799

7.6

147

236

490

calcium-magnesium-chloride sulfate

0.1

calcium-magnesium-chloride sulfate

350538110560401

12/5/1978

750

7.5

38.7

170

210

508

350600111015001

7/8/1946

891

105

280

225

600

0.2

350600111015001

5/1/1966

890

7.5

106

281

224

608

calcium-sulfate

0.2

350618111015601

8/10/1992

880

7.8

110

22.5

270

206

584

calcium-sulfate

< 0.1

350637110485401

2/26/1934

3,510

720

176

1,120

262

2,280

350637110485401

12/5/1978

3,600

7.8

643.9

170

1,000

1,890

350653110573801

5/11/1966

975

7.6

193

100

223

-sodium-chloride

0.2

calcium-magnesium-chloride sulfate

0.1

350700111054001

9/18/1967

407

7.6

2.3

2.5

264

231

calcium-bicarbonate

0.1

350700111054001

8/2/1995

410

7.7

4.8

1.4

225

0.1

350706111014701

11/20/1933

108

295

226

350706111014701

3/3/1953

859

269

207

0.3

350706111014701

10/12/1978

850

7.6

26.7

240

200

529

0.2

350706111014701

2/28/2005

860

7.5

107

45.5

27.84

265

21.7

217

587

0.5

12.6

0.101

1.1

0.23

0.22

0.2

350706111014701

2/28/2005

856

7.5

106

44.9

27.78

265

21.6

207

E 582

350756111154001

9/18/1967

607

7.4

126

178

354

calcium-sulfate --

0.5

12.4

E 0.075 --

350756111154001

7/12/1978

600

7.8

120

170

352

calcium-magnesium-chloride sulfate

0.2

350810111105001

9/18/1967

1,080

7.2

101

345

164

692

calcium-sulfate

0.2

350816110531001

1/3/1979

1,220

7.8

112.5

190

180

240

755

calcium-magnesium-chloride sulfate

0.1

350839111005301

5/12/1966

832

7.5

253

198

565

calcium-sulfate

0.1

350845110540101

5/11/1966

1,360

7.5

110

225

189

236

800

350845110540101

12/5/1978

1,300

7.5

122.5

250

220

170

806

0.1

350909111165401

9/18/1967

454

7.5

3.9

236

251

0.2

-calcium-magnesium-chloride sulfate

7/12/1978

450

7.4

9.7

7.6

210

254

calcium-bicarbonate

0.2

2/9/2005

1,230

8.3

88.6

43.5

120.15

267

125

217

767

1.3

25.3

0.082

2.5

0.32

350957110562601

2/24/2005

1,160

7.9

102

52.8

77.53

250

123

232

E 734

0.4

16.9

1.3

0.25

350957110562601

2/24/2005

1,160

7.8

104

53.5

79.87

251

123

220

734

0.5

19.1

1.1

0.26

calcium-magnesium-chloride sulfate

E 0.04 <0.08

Conclusions 25

350909111165401 350957110562601

date

(µS/cm)

350957110562601

3/23/2005

1,180

350958110562201

2/9/2005

USGS site number

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

7.3

106

55.1

75.08

247

121

E 742

1,200

7.7

107

50.7

82.6

253

129

216

742

351001110562601

5/11/1954

1,170

100

260

130

220

736

351001110562601

6/6/1973

1,180

7.9

100

82.4

280

130

200

760

Water type -calcium-magnesium-chloride sulfate -calcium-magnesium-chloride sulfate

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

2.45

16.5

0.08

E 0.052

0.25

2.4

0.23

0.2

0.35

351022111061801

2/21/2005

1,180

8.1

122

56.7

58.82

385

64.9

194

797

0.2

14.3

0.108

1.6

0.21

351022111061801

2/25/2005

1,180

7.6

125

59.2

61.6

386

65.4

186

803

0.5

15.7

0.346

1.5

0.22

351022111061801

2/25/2005

1,190

7.6

127

59.5

61.51

386

65.4

188

808

0.6

14.8

0.66

1.8

0.23

3.1

0.2

1.4

0.24

0.22

calcium-sulfate

351023111062002

2/13/2005

1,170

110

51.6

57.03

385

65.2

193

E 779

0.2

19.4

351023111062002

2/19/2005

1,160

7.6

124

57.8

60.67

384

66.1

172

E 793

0.3

14.9

351023111062002

2/19/2005

1,170

7.6

124

58.1

60.06

383

62.7

176

E 789

0.4

15.8

351023111062002

3/15/2005

1,150

7.3

127

59.2

351052110491701

10/12/1955

8,340

7.2

130

1,700

59.61

calcium-sulfate

E 0.071 E 0.054 E 0.064

379

64.6

E 791

4.6

11.8

0.177

0.21

450

2,510

300

5,010

0.6

351052110491701

6/6/1973

8,620

100

1,706.30

380

2,600

220

5,030

sodium-chloride

0.53

351053110332501

4/7/1964

8,330

7.8

190

1,800

1,470

1,960

5,470

sodium-chloride

1.3

351122111101301

9/7/1950

1,160

753

0.2

351142110563401

9/7/1950

1,470

140

246

218

235

881

0.2 0.15

351142110563401

9/8/1965

1,530

8.1

98.2

49.9

144.32

232

220

192

944

351144111161201

9/18/1967

633

7.4

135

166

368

351144111161201

3/7/1979

610

7.7

26.5

180

150

422

351214111022101

4/22/2005

841

7.4

98.3

42.6

29.41

255

21.6

200

E 561

calcium-magnesium-chloride sulfate -calcium-magnesium-chloride sulfate --

0.3

E 0.2

16.2

0.25

E 0.061

351214111022101

4/22/2005

842

7.4

100

43.5

29.32

255

21.7

201

E 563

calcium-sulfate

0.2

14.8

0.13

1.1

0.26

351215111021701

9/7/1950

840

264

202

calcium-sulfate

0.2

calcium-magnesium-chloride sulfate

0.4

0.2

0.25

351238111084101

4/22/1955

1,020

7.3

100

312

190

351442110581601

9/8/1965

1,190

102

77.6

222

107

198

744

351442110581601

4/19/1973

1,120

7.9

104

41.3

68.7

203

112

196

752

351448111012701

9/8/1965

1,020

98.2

57.9

249

177

676

0.2

351448111012701

10/11/1978

990

7.7

250

210

629

calcium-magnesium-chloride sulfate

0.2

351519111120701

11/20/1953

346

4.1

4.5

211

199

calcium-bicarbonate

0.4

351525111035801

11/2/1953

846

235

217

555

0.6

-calcium-magnesium-chloride sulfate --

26 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

Table 2. Selected field parameters and water-chemistry data for Coconino aquifer groundwater sites included in this study, northeastern Arizona (U.S. Geological Survey, 2023).—Continued

USGS site number

Sample

date

(µS/cm)

Ca2+

Mg+

Na+ + K+

SO42-

Cl-

HCO-

TDS

(mg/L)

351525111035801

9/8/1965

880

8.2

90.2

40.1

36.34

253

29.4

167

590

351739111001501

9/7/1965

1,430

98.2

49.9

132.64

226

194

205

906

351739111001501

3/17/1966

96.2

47.4

129.98

239

198

197

880

351748110592301

9/8/1965

1,740

7.6

110

183.8

245

280

240

1,080

351748110592301

3/17/1966

1,680

182

260

290

220

1,040

Water type calcium-sulfate -calcium-magnesium-chloride sulfate -calcium-magnesium-chloride sulfate

Arsenic

Uranium

Barium

Lead

Copper

Fluoride

(µg/L)

(mg/L)

0.25

0.15

0.3

351749111003401

4/5/1959

1,400

7.4

100

120

240

200

230

847

0.4

351749111003401

9/7/1965

1,470

7.8

133.3

240

200

210

908

0.2

351749111003401

6/25/1969

1,390

7.8

142

190

200

230

860

0.1

351758111000901

3/5/1958

8.5

351758111000901

7/11/1960

9.2

351758111000901

3/17/1966

1,380

132

240

200

890

351804111060301

8/19/1951

1,840

102

210

258

340

209

1,080

calcium-magnesium-chloride sulfate

0.2

351804111060301

9/8/1965

1,900

8.1

92.2

46.2

218.93

251

339

141

1,130

0.2

351804111060301

3/3/1967

1,840

77.2

44.4

227.74

288

345

188

1,160

0.2

351804111060301

11/2/1972

1,750

8.1

72.1

47.4

211.35

237

345

118

1,090

351815110505001

5/30/1959

8,350

7.6

430

130

1,500

910

2,600

276

5,800

sodium-chloride

0.18

0.2 0.2

351815110505001

5/31/1959

8,500

7.7

450

110

1,500

900

2,600

246

5,800

351818110054901

4/14/1953

1,030

230

100

208

646

351818110054901

9/7/1965

1,380

102

46.2

111.05

236

185

204

870

calcium-magnesium-chloride sulfate

0.2

calcium-sulfate

0.3 0.2

351831111054501

9/7/1965

1,100

90.2

42.6

71.58

216

107

206

702

351930111184801

7/18/1965

756

7.5

221

182

sodium-chloride

351930111184801

7/31/1995

740

34.9

210

455

352117111132901

7/6/1972

2,710

8.5

106

48.6

371.65

301

597

161

1,710

sodium-chloride

0.3

352119111132901

6/10/1951

2,610

104

360

275

598

201

1,510

sodium-chloride

0.2

352226111081401

4/7/1955

2,020

7.8

260

262

395

235

1,190

sodium-chloride

0.2

*Sodium only is reported.

Conclusions 27

28 Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

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Manuscript approved for publication April 23, 2025 Tacoma and Moffett Field Publishing Service Centers Edited by Jeff Suwak and Vanessa Ball Illustration support by JoJo Mangano Layout and design by Luis Menoyo

Jones—Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona—SIR 2025–5038

ISSN 2328-0328 (online) https://doi.org/10.3133/sir20255038

Assessment of Water Chemistry of the Coconino Aquifer in Northeastern Arizona

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