Dissolved Uranium and Arsenic in Unregulated Groundwater Sources – Western Navajo Nation

Abstract

Concentrations of dissolved uranium (U) and arsenic (As) above drinking water standards in unregulated water sources pose various human health risks. Although high natural background concentrations may occur in some environments (Runnells et al. 1992), anthropogenic contamination concerns are especially troublesome on the Navajo Nation (NN), where past U mining activity may have contaminated water supplies. This research investigated U and As groundwater contamination issues in unregulated wells in the western portion of the NN. Objectives of this research were to provide insights to human health risks by assessing the spatial extent and seasonal variability of U and As concentrations while effectively communicating the potential contamination risks to the local Navajo people. Eighty-two unregulated wells were sampled in 2018; nine of these sources exceeded the maximum contaminant level (MCL) for drinking water standards for U (30 μg/L), and 14 exceeded the MCL for drinking water standards for As (10 μg/L). U and As levels were highest in the southwest portion of the study area and seasonal variability was observed in a subset of wells, especially shallower hand dug wells and hand pumps. The results were compiled into a report that was presented to NN chapters included in the study as well as the Navajo Department of Water Resources and the NN Environmental Protection Agency. Implications for regional water quality patterns can help to direct policy recommendations for well monitoring, water use, and remediation targets.

The Navajo Nation (NN) has over 300,000 tribal members, and approximately half of the population reside on the Reservation, which spreads over parts of Arizona, New Mexico, and Utah (Figure 1) (Navajo Division of Health 2013). Additionally, the NN has some of the world’s largest uranium (U) deposits on their lands (DeLemos et al. 2007). U mining occurred on the NN from the early 1900s until 1986 (Fettus and McKinzie 2012). Navajo communities with past mining legacies have been exposed to increased levels of contaminants from mining operations (Eichstaedt 1994). There are over 500 abandoned U mine (AUM) sites and over 1,200 mine features spread throughout the NN. Mine features include pits, waste piles, and trenches. Contamination of groundwater from U mining can occur due to erosion of tailing piles and from open pit mining below the water table that produce mine waste water (US EPA 2007). Through increased exposure to water and oxygen, mining activities increase the mobilization of elements such as U and arsenic (As); therefore, the risk of contamination of natural water sources is greater in mining areas (Hoover et al. 2017; Credo et al. 2019). Arsenic is a natural occurring contaminant that is elevated in groundwater in the southwestern United States due in part to desorption reactions with metal oxides, dissolution reactions, a concentration effect due to high evaporation rates in arid zones, and mining activity (Smedley and Kinniburgh 2002). Higher As and U concentrations may occur together because both are more soluble in their oxidized form and can be co-precipitated in the same minerals. Thus, they are often found together in anomalously high concentrations associated with U mining (Smedley and Kinniburgh 2002; Mkandawire and Dudel 2005; Hoover et al. 2017). In addition, regions surrounding mines will have higher background concentrations, because rocks may occur with concentrations of U too low to be considered profitable to mine or because there are deposits that have yet to be discovered and mined. Given the dangers associated with U and As exposure, it is important to determine what communities may be at risk.

Figure 1.

Entire Navajo Nation with chapters, agencies, and abandoned uranium mines.

Areas with natural mineral deposits can have high levels of dissolved metals due to acid rock drainage (ARD). ARD, caused by the weathering and oxidation associated with all sulfide minerals, is a natural process which mobilizes metals and must be considered when creating remediation goals (Kwong et al. 2009). A subset of ARD is acid mine drainage (AMD) which occurs when mining activities increase the acidity of waters by exposing pyrite and other sulfide minerals to oxygen and water sources, thereby increasing the level of dissolved metals in the water. Also, mining operations can increase the amount of water being discharged after contact with sulfide minerals, resulting in even greater mobilization of metals (Nordstrom 2015).

The quality of water from private wells, which is not regulated by a government agency, creates concerns for public health. Twenty-three % of private wells in the United States exceeded a human-health benchmark for one or more contaminants (DeSimone et al. 2009). Unregulated wells typically have more contamination issues than regulated wells because they may not be as deep, may be located in different aquifer or geologic zones, and may be less soundly constructed than municipal wells (Johnson and Belitz 2017). Also, unregulated wells are not regularly tested for contaminants and often lack water treatment systems (Malecki et al. 2017).

However, unregulated wells provide important water sources for sparsely populated areas where regulated water sources, such as municipal water systems, are unavailable. This fact is especially evident on the NN where approximately 30% of homes lack access to municipal water supplies and rely on hauling water to meet their needs (US EPA 2018). Because many Navajo people live in low-density areas, the cost to benefit ratio of developing water infrastructure is unfeasible (US DOI 2015). Historically, livestock has played an important role in the Navajo culture and economy. Raising livestock requires relatively large amounts of land, thereby preventing some Navajo from living in areas where public water supplies are available. Instead, they live in sparsely populated areas where the closest water supply is from unregulated, shallow, windmill-powered wells originally installed for livestock use. There are approximately 900 windmill wells throughout the NN (NNDWR 2011). Data on the water quality of these unregulated sources are limited, especially for the western portion of the NN. In the middle and eastern portions of the NN extensive work has been done to collect water quality data and compile past data collected as shown by the 2017 Hoover et al. research.

The NN is within the Colorado Plateau region where the climate is largely controlled by orographic effects and elevation. Areas below 1370 m (4,500 ft) are semiarid. The average precipitation is 20 to 30 cm per year. However, some lowland areas may receive less than eight cm of precipitation per year. A majority of the NN is in a rain shadow where most of the precipitation comes from the south and is blocked by the southern rim of the Colorado Plateau. Up to 65% of the yearly precipitation occurs during the late summer months (July and August) and can result in flash flooding. All runoff goes to the Colorado River, either directly or via one of the tributaries (the San Juan and the Little Colorado Rivers) (Cooley et al. 1969).

In the western portion of the NN, rocks from the Cretaceous Dakota Formation and below are present. However, regional erosion patterns have resulted in progressively older rocks being exposed at the surface in the southwest portion of the NN (Peirce et al. 1970). Recharge of the aquifers occurs in upland areas, which divides the land into five separate hydrologic basins: Black Mesa, San Juan, Blanding, Henry, and Kaiparowits. Water that is recharged in the upland areas moves downward towards the major rivers and tributaries (Cooley et al. 1969).

The main sources of groundwater for the NN come from the Navajo (N) aquifer, the Coconino (C) aquifer, and shallow alluvium aquifers (Cooley et al. 1969). The N aquifer is an important groundwater source in areas north of the Little Colorado River and water quality is considered relatively good except in areas where past U mining and milling occurred (ADWR 2009). Formations of the N aquifer include the Jurassic Navajo Sandstone, Kayenta Formation, and Lukachukai Member of the Wingate Sandstone. These formations are hydraulically connected and act as a single aquifer (Eychaner 1983). The N aquifer receives recharge in areas near Shonto where Navajo Sandstone is exposed at the surface. In other parts of Black Mesa the N aquifer has overlying confining layers which limit recharge (Lopes and Hoffmann 1997). Groundwater that is recharged near Shonto flows radially in the southwest direction to Tuba City, as well as to the south and east (Eychaner 1983).

The C aquifer is an important groundwater source south of the Little Colorado River. North of the river the C aquifer is too deep to access and the high level of salinity (total dissolved solids) makes it undesirable to use for a drinking water source (ADWR 2009). The C aquifer includes the Pennsylvanian and Permian Upper and Middle Supai Formations, the Permian Coconino Sandstone, and the Permian Kaibab and Schnebly Hill Formations (Bills et al. 2016).

Human health risks from living close to AUM sites have been documented and include kidney diseases, hypertension, and other chronic diseases (Hund et al. 2015). However, information on the health impacts from past mining is lacking for tribal communities. The small population sizes, absent or ineffective policies, and a lack of infrastructure in tribal communities have created problems in understanding the full health impact of past mining activities (Lewis et al. 2017). While research is limited, important studies have been conducted. For example, the Navajo Birth Cohort Study is a long-term, collaborative research project that examined how U exposure affected pregnant Navajo women and their infants. Exposure risks were assessed via biomonitoring, home assessments, and surveys. This study was important to inform individuals with higher risks of the dangers they faced, as well as to develop future policies to mitigate the health risks (Hunter et al. 2015).

The Safe Drinking Water Act sets the maximum contaminant level (MCL) for U at 30 μg/L (US EPA 2000). Human health effects of chronic U exposure include kidney disease and various cancers (ATSDR 2013). The level of uptake and toxicity of different U compounds is still not well understood and requires further research (Bjørklund et al. 2017). Long-term As exposure can lead to skin problems, cardiovascular disease, and lung, bladder, liver, kidney, and skin cancers due to its toxic and carcinogenic properties (ATSDR 2007). The MCL for As in the United States is 10 μg/L (US EPA 2001). Concerns about As contamination issues have been documented world-wide in countries such as China, Pakistan, Bangladesh, India, Vietnam, Mexico, Poland, Argentina, and the United States (Smedley and Kinniburgh 2002; Ng et al. 2003; Nelson et al. 2005; Naseem et al. 2012; He and Charlet 2013; Shakoor et al. 2015; Verma et al. 2015; Chabukdhara et al. 2017). Up to 100 million people globally may face health risks caused by As contamination (Ng et al. 2003).

The NN has established water quality standards for surface water and drinking water sources. These standards are enforced at monitored wells to ensure that negative health effects do not occur. The NN Water Quality Program (NNWQP) is operated under the NN Environmental Protection Agency (NN EPA) and is responsible to ensure the water quality standards are enforced. The NNWQP states that the domestic water supply must not exceed 30 μg/L for U and 10 μg/L for As. In addition, As must not exceed 200 μg/L for livestock water. There is no listed maximum for U in livestock water (NN EPA 2007).

A pathway of exposure to contaminants can exist in drinking water from unregulated sources. As mentioned previously, the lack of access to regulated water in their homes causes about 30% of Navajo households to depend on hauling water to meet their needs (US EPA 2018). This practice of hauling water has greatly increased the cost of water for the Navajo people. The typical cost for water users in urban areas is $600 per acre-foot of water. Navajo people who depend on hauling water pay about 71 times this amount ($43,000 per acre-foot of water). For reference, one acre-foot of water is about 330,000 gallons and the per capita use of non-tribal communities near the NN is 190 gallons per day. The per capita use for the NN is 10 to 100 gallons per day and largely depends on the availability of water resources (NNDWR 2011). Considering the cost of hauling water, it is important to recognize that unregulated water sources may provide the closest and most convenient water supply. Therefore, determining the safety of using unregulated water sources for drinking water will remain an important objective for research on the NN.

Understanding the spatial variability of groundwater contamination issues is critical for future resource management. Further, improving the capacity of tribal nations to mitigate health risks and to manage their natural resources in culturally appropriate ways is critical for sustainable future resource management (Lewis et al. 2017). Objectives of this research are to provide insights on human health risks by assessing the spatial variability of U and As concentrations in unregulated groundwater on the western portion of the NN and to communicate contamination risks to the local Navajo people.

Methods

Study Area

The NN is comprised of five agencies each made up of tribal chapters, similar to states made up of counties. The study area focused on twelve chapters in the Western Agency of the NN (Figure 2). Seven of the chapters are located within the western AUM region and the remaining chapters were included in the study based on community requests to test water in those chapters. U mining occurred in the western AUM region from 1951 to 1963, and the U.S. Environmental Protection Agency (US EPA) has identified 126 AUM structures in the area correlating to that time (US EPA 2007).

Figure 2.

Western Navajo Nation, unregulated water sources, and abandoned uranium mines.

The study boundaries include the following chapters of the Western Agency in the NN: Bodaway-Gap, Cameron, Coalmine Canyon, Coppermine, Inscription House, Kaibeto, LeChee, Leupp, Navajo Mountain, Shonto, Tonalea, and Tuba City. There are 82 unregulated wells or water sources identified and tested within these chapters. Water samples from wells in this area have been collected and analyzed for U and As since 2003 by the Ingram Lab at Northern Arizona University.

The study area is sparsely populated, with Tuba City having the largest population size of the chapters. The population sizes for the chapters ranged from 542 to 9,265 as shown in Table 1 (U.S. Census Bureau 2010). The population density for the NN is much lower than the United States overall, with only 6.33 persons per square mile as compared to the U.S. average of 345 persons per square mile (Navajo Division of Health 2013).

Table 1.

Summary of populations of the chapters in the western portion of the Navajo Nation (U.S. Census Bureau 2010).

Chapter	Population
Bodaway-Gap	1,704
Cameron	1,122
Coalmine Canyon	691
Coppermine	590
Inscription House	1,252
Kaibeto	1,963
LeChee	1,660
Leupp	1,611
Navajo Mountain	542
Shonto	2,124
Tonalea	2,595
Tuba City	9,265

Chapter Resolutions for Environmental Testing

To ensure that a consensus existed for this research to be conducted, it was important to engage communities at different levels (chapter and agency). Chapter Resolutions were requested and approved to gain permission to carry out this study in the Navajo Mountain and Tuba City Chapters. Additionally, pre-existing chapter Resolutions from the Leupp and Cameron Chapters provided approval for the Ingram Lab Group’s previous water sampling. A general Resolution from the Western Agency was requested and approved at the NN Western Agency Meeting in June of 2018.

Field and Laboratory Methods

Fieldwork methods included locating unregulated wells using GPS; measuring field parameters including, pH, specific conductance, temperature, and oxidation-reduction potential (ORP); and collecting water samples. Water samples were collected in 2018 at different times of the year to evaluate seasonal variability. Water samples were filtered with 0.45 μm membrane filters (Whatman 0.45μm PVDF). Samples for cation and metal analysis were acidified in the field with ultra-pure nitric acid (VWR Aristar Ultra nitric acid) to store metals and metalloids in a soluble state. The subset of samples that had carbon and nitrogen analyses performed were filtered in the field with glass microfiber filters (Whatman Glass Microfiber Filters GF/C Diameter 47mm) into glass vials and care was taken to ensure no head space was left, since the interaction with oxygen could alter the results. Specific conductance, pH, ORP, and temperature were recorded in the field with a portable Thermo Scientific Orion 4-Star Plus meter. Calibration of the meter occurred directly before every sampling event for conductivity, pH, and ORP, and the calibration was routinely checked while in the field. For specific conductance and pH, a three-point calibration was performed with pH and conductivity standards. For the ORP, a one-point calibration was performed with Zobell’s solution, which is a potassium ferric-ferro cyanide solution with a known ORP (Eh) value. Field notes and photos were taken at every site. One field blank was collected at a random site for each sampling trip.

Water samples were analyzed for dissolved U and As using US EPA water analysis methods (6020B and 200.8) via inductively coupled plasma-mass spectrometry (ICP-MS), Thermo Fisher Scientific X-Series 2 ICP-MS. Usage of internal standardization was to correct for instrument drift and matrix effects during the data collection. For the water analysis, multi-element calibration standards were prepared containing 0, 0.1, 0.5, 1.0, 2.0, and 5.0 μg/L of the analytes, with an internal standard of 1.0 μg/L of iridium-193. The analysis was confirmed by analyzing the Standard Reference Material 1640a, which has certified concentrations of U and As. To ensure the quality of the data, other quality assurance/quality control (QA/QC) measures were followed, including analyzing blanks, analyzing calibration check standards, and the use of an internal standard (iridium-193).

Calibration standards were used to produce calibration curves for each analyte. The instrument signal for the analyte of interest and the internal standard were given in the form of counts per second (CPS). The CPS of the analyte of interest was divided by the CPS of the internal analyte. This produced a ratio that accounts for the signal of the external standard to the internal standard produced during instrument drift. The known concentration on the x-axis of the external standards was plotted on a scatter plot versus the ratio on the y-axis. After the least squares best fit line (as determined by the Excel software) was applied to the scatter plot, the resulting linear equations could be used to calculate the concentration in μg/L for each sample. The squares of the correlation coefficient values, R², were assessed with each calibration. R² values of 0.999 or better were deemed sufficient to utilize the calibration.

For each analysis, the instrument was switched from vacuum to operation mode. Once operating, the instrument was warmed-up by pumping water for 15 minutes, followed by 30 minutes in 2% nitric acid. This warm-up time allowed for the determination of contamination in the nitric acid prior to analysis. It additionally provided time for the instrument parameters to be optimized, maximizing analyte signal and increasing stability of readings at the detector. To maintain stability of reading, approximately 100 sweeps of three replicates were processed at the detector per sample.

Once the tuning was complete, the calibration standards were analyzed, first including a reagent blank, followed by the National Institute for Standards and Technology (NIST) Standard Reference Material (SRM) 1640a for trace elements in natural water, and then the diluted unknown samples. The SRM 1640a was used to check the validity of the calibration curves and the reproducibility in sample preparation prior to analysis. After every 15–20 unknown samples a check standard was analyzed to check instrument signal.

Results

The U and As data collected in 2018 were combined with past data collected by the Ingram Lab Group to examine the spatial variability. The data were entered in ArcMap Version 10.5 to create U and As concentration maps (Figures 3 and 4). These maps help to visualize the spatial variability of U and As. Additionally, the maximum, minimum, median, and mean for U and As determined for each of the 82 water samples are provided in Table 2. The highest levels of U and As were found in the southwestern portion of the Coalmine Canyon Chapter. Nine unregulated water sources exceeded the U MCL of 30 μg/L and fourteen exceeded the As MCL of 10 μg/L. Figure 5 shows the exceedances for the similar wells tested with water samples collected over dates from April to December 2018. The plot provides the MCL for U and As, along with the levels of U and As determined in the water sources. For example, the U levels between 124 and 128 μg/L at the top of the figure are the same well tested three times.

Figure 3.

Uranium concentration in parts per billion for the western portion of Navajo Nation.

Figure 4.

Arsenic concentration in parts per billion for the western portion of Navajo Nation.

Table 2.

Summary of field data collected in 2018 for groundwater in the western portion of the Navajo Nation and the overall U and As results for the 82 samples.

	Minimum	Maximum	Median	Mean
Temperature (°C)	7.1	31.3	21.2	18.9
pH	7.22	9.78	8.27	8.25
Conductivity (μS/cm)	77.6	11,980	415	540.7
Oxidation-reduction potential (volts)	0.17	0.63	0.45	0.44
U (μg/L)	BDL	560.2	2.46	2.3
As (μg/L)	BDL	234.4	2.08	2.76

BDL = Below Detection Limit (U=0.001 μg/L; As=0.030 μg/L).

Figure 5.

Arsenic and uranium levels determined from April to December 2018 compared to the maximum contaminant level (MCL) values shown as horizontal lines (As MCL = 10 μg/L; U MCL = 30 μg/L).

The highest levels of U were found in the southwestern portion of the study area (Figure 3). This area correlates with the location of a majority of the AUM sites in the study area. Mining activity may be responsible for these elevated levels; however, since pre-mining baseline levels are unknown it is impossible to determine the source. Since mining occurred in areas with high U levels these results may be due to natural sources. More spatial variability occurred for As (Figure 4) compared to U. The highest levels of As occurred in the southwestern portion of the study area, similar to U, but As levels also varied in water sources in and around the Tuba City Chapter.

The field data revealed that the water was basic and had a wide range in conductivity values (Table 2). The pH values ranged between 7.22 and 9.78. The secondary MCL (SMCL) for pH is below 6.5 and above 8.5 (US EPA 2015). Twenty-nine water sources had pH levels above 8.5. Specific conductance is a measure of how many ions are present in water and can be used to estimate the amount of total dissolved solids (TDS) (Geddes et al. 2014). The SMCL for TDS is 500 parts per million (ppm) (US EPA 2015). To estimate the amount of TDS in water the conductivity value must be multiplied by a factor between 0.55 and 0.90, which is empirically determined and beyond the scope of this study (Geddes et al. 2014). Conductivity values ranged between 78 μS/cm and 11,980 μS/cm. Using the conservative conversion factor of 0.55, any conductivity values above 910 μS/cm would exceed the SMCL of 500 ppm for TDS, which could result in deposits, staining, or salty tasting water (US EPA 2015). There were 23 water sources with conductivity values above 910 μS/cm. The highest conductivity values were found in the Leupp Chapter and the southwestern portion of the Coalmine Canyon Chapter.

The Navajo Department of Water Resources provided a well database which had aquifer information and well depth for many of the water sources in this study. The aquifer information was used to create a map (Figure 6) to visualize the trends. A majority of the wells pump water from the N aquifer. One well in the Navajo Mountain Chapter was completed in the Wingate Sandstone which is beneath the Navajo Sandstone but is hydraulically connected; therefore, it is considered part of the N aquifer (Figure 1). In the southern portion of the study area, specifically the Leupp Chapter, most wells pump water from the C aquifer. There was also a subset of wells in the southwestern portion of the study area that access water from the Chinle Formation, the Shinarump Member of the Chinle Formation, and the Moenkopi Formation which lies on top of the Coconino Sandstone layer. These layers are generally thought of as confining units and likely only produce very small amounts of water. A portion of the water sources did not have any corresponding aquifer information in the well database.

Figure 6.

Aquifer information provided by the Navajo Department of Water Resource’s Well Database for unregulated wells tested in 2018 by the Ingram Lab Group.

Some overall trends of the groundwater quality from the N and C aquifers became evident while doing this research. The N aquifer had lower conductivity levels and lower concentrations of ions compared to the C aquifer. The highest concentrations of U and As were found in wells with unknown aquifer information; however, nearby wells were located within the Moenkopi and Chinle Formations (Figure 6). While the highest levels of U and As were found in wells in the same region where past mining occurred, it is difficult to attribute these concentrations to mining activities alone. For example, one well had high levels of U and As but was not near an AUM. The closest mining operation was several miles to the north, but it was in a canyon, therefore, it is down-gradient of the well. Additionally, several wells had relatively low levels of U and As and were very close to AUMs. The complete dataset and a more in-depth analysis of all the data collected can be found in Jones 2019.

Discussion

Importance of Communicating Results

Engaging community members while designing the research plan, as well as disseminating the results back to the community members, were integral to the design and communication of this project. The community members provide information on the location and use of the wells; this information guides both the field collection and dissemination to the community. Various health risks of the contaminants were discussed, and requests from the community for testing of specific wells improved the study. The final report given back to the local people included maps of the well locations and concentrations of dissolved U and As. The report interpreted the results for each chapter in layman’s terms. A summary of the report was provided in the Navajo language as well, and dissemination was effective due to the invaluable help of chapter officials. Understanding the steps and procedures that are needed to do research on the NN was extremely important. The Resolutions that were approved helped to engender trust that this research was respectful of Navajo customs.

Unregulated water sources can cause human health issues and communicating the risks that Navajos face in drinking from these sources remains a top priority. However, language and cultural barriers may inhibit effective communication. Researchers have worked to incorporate the Navajo peoples’ perspectives to provide culturally significant communication methods (DeLemos et al. 2009). Maps can provide clear and effective ways to communicate the environmental and human health risks. Gaining feedback from Navajo community members concerning the efficacy of these maps will engender more culturally appropriate forms of communication.

A report was created with the 2018 data and copies were given to all the chapters in the study area as well as to the Navajo Department of Water Resources, the NN EPA, and the Navajo Tribal Utility Authority. Additionally, the researchers provided in-person presentations of the results to many of the chapters in the study during their monthly community meetings as well as at the Western Agency quarterly meeting. At these meetings, copies of the report were distributed to the meeting attendees, and community members had the opportunity to ask questions and talk to the researchers individually. This report was created to add to the knowledge about water quality issues for the western NN. While the report does not consider all water quality issues or possible pollutants, it can be used to direct future studies to determine where safe drinking water sources exist.

Implications for Regional Water Quality Patterns

The main source of water for the western portion of the NN comes from the N aquifer; however, increased withdrawals from the C aquifer have been proposed to supply the Navajo people with an alternative water resource (Leake et al. 2005). Seepage of contaminated mine groundwater to surface water introduces a pathway of exposure. The movement of shallow groundwater sources is influenced by precipitation and topography while deeper groundwater is more influenced by fracturing and fault zones in geologic units (Bartolo et al. 2017).

Pre-mining baseline studies to establish if natural geological sources of U and As are responsible for water contamination issues are not available for the study area. For other areas where baseline studies exist, the focus is on stream sediments and soils. The change in geochemical factors in water over time is not usually considered. However, temporal sampling is important to evaluate how geochemical factors of water can vary with seasonally. For example, biological activity and sorption rates vary due to temperature and precipitation intensities and amounts affect water flowpaths and reaction times (Levitan et al. 2014).

Determining background levels of metal concentrations is important in mining regions since remediation of these sites to levels below pre-mining levels is difficult or impossible. Natural background concentrations may be above what is considered safe for drinking water; therefore, remediation of groundwater to levels considered safe to drink may be unfeasible. When baseline studies do not exist, one method to determine background levels is to compare levels of mined areas to close by areas which were not mined (Runnells et al. 1992).

Limitations

Other wells likely exist in the study area that were not tested, since the locations of those wells were unknown. Further, it was not known which wells were commonly used by people for their drinking water; therefore, human-use surveys would be helpful for future research. Past students’ work was limited to certain wells; therefore, large gaps in the data existed. This study included a larger number of wells, but temporal change could not be studied since no long-term data exist for many wells.

Large fluxes in concentrations may be due to evaporation, precipitation, and groundwater pumping rates (concentration and dilution factors). Most of the unregulated water sources tested were windmills, which pump water into storage tanks when the wind is blowing. The storage tanks can be open on top or covered. The uncovered storage tanks allow for a greater amount of evaporation which would increase the levels of U and As found (due to concentration). Additionally, the shallow dug wells can have a large amount of evaporation occurring. The effect of evaporation and the concentration of contaminants would be greater during the hot, dry summer months. Dilution of contaminants can occur from heavy rains during the late summer months or from increased pumping of the groundwater when there is sufficient wind to power the turbine.

Water sampling methods followed how local Navajo people collected their water. Because the water was coming from holding tanks, the well could not be purged for the recommended time to ensure that the water was coming from the aquifer. The water also had time to interact with air while in the holding tank; therefore, properties of the groundwater may have changed during the time it spent on the surface. Additionally, the well construction was unknown, and there could have been leakage from an overlying aquifer, or deposition from blowing dust, which would alter concentrations. These study limitations make it hard to say if the results are truly representative of the aquifer water quality.

Conclusion

This research combined physical science with community engagement, which is critical to achieve solutions to environmental challenges. Field and chemistry work were essential to provide the data. However, social interactions, such as community presentations and discussions, were critical to make the data relevant. The relationship between researchers and community members is also important to consider. This research focused on improving relations between the two groups and creating an open dialogue that allows for solutions to problems. The results from this research can be useful to provide data for comparison to future water quality testing, for determining particularly problematic mining areas, and to determine the existence of possible natural sources of dissolved U and As. However, wells with open holding tanks provided an uncertainty in the results.

Collaboration with stakeholders was essential for this research. The Resolution process to gain permission to sample the water sources helped to make connections with stakeholders which proved to be useful for other parts of this project. Connections with community members helped to locate additional wells that the local people wanted tested. The dissemination of the results was assisted by collaborating with community officials. Therefore, it was only through collaborations with multiple stakeholders that this research was possible.

The final recommendations that were made to the Navajo people included adding signage to wells that exceeded the MCLs of U and As to warn people of the risks. It was also recommended that wells that were very low in U and As be considered for addition to the regulated water system. Closing the wells was not recommended since these water sources are also used for livestock water and were still considered safe for that purpose. Maps representing water sources with toxic U and As concentrations, along with alternative cleaner water sources, may provide effective forms of communicating risks. Water is limited for the Navajo people and the protection of water quality must remain a priority into the future. By working in collaboration with the Navajo communities and their leaders, the results from this study can be utilized by the NN to develop strategies for water utilization on their lands.

Author Bio and Contact Information

Lindsey Jones holds a MS in Environmental Sciences and Policy from Northern Arizona University. She is a recent graduate and her thesis work focused on uranium and arsenic contamination issues in unregulated water sources on the western portion of the Navajo Nation. She is currently working as an Environmental Program Specialist for Arizona’s Water Infrastructure Finance Authority. She may be contacted at lmj53@nau.edu or via mail at 700 South Osborne Dr., PO Box 5698, Flagstaff, AZ 86011.

Jonathan Credo is an MD/PhD student at the University of Arizona College of Medicine and conducts active research at Northern Arizona University. His research and clinical interests are in ecotoxicology and environmental health, examining how exposures from the environment impact the health of humans, wildlife, and the environment. His current dissertation research investigates the effect of metal exposure in minority populations. He may be contacted at jmcredo@email.arizona.edu or via mail at 700 South Osborne Dr., PO Box 5698, Flagstaff, AZ 86011.

Dr. Roderic Parnell is a Professor in the School of Earth and Sustainability at Northern Arizona University. He is a Senior Fellow of the National Council for Science and the Environment and Past-President of the Council of Environmental Deans and Directors. His research focuses on the application of earth sciences to sustainable river management in the Western U.S., and on the transformation of environmental curricula to improve sustainability education. He has also studied the effects of acid rain, volcanic emissions, and sulfide mineral deposits on terrestrial and aquatic ecosystems, publishing over 140 journal articles and papers presented at national and international meetings. He may be contacted at Roderic.Parnell@nau.edu or via mail at School of Earth and Sustainability, Box 4099, Northern Arizona University, Flagstaff, AZ 86011.

Dr. Jani C. Ingram (corresponding author) is a Professor of Chemistry and Biochemistry at Northern Arizona University (NAU). She is the Principle Investigator of the Training Core at NAU for the Partnership of Native American Cancer Prevention (NACP), and director of Bridging Native American Students to Bachelor’s Degree (BRIDGES) program. Her research is involved in the investigation of environmental contaminants with respect to their impact on health. More specifically, to address chronic uranium exposure and cancer risk to the Navajo. Further, Dr. Ingram has published 38 peer-reviewed articles. She has been and is currently funded by the National Cancer Institute, the National Institute of Health, National Science Foundation, and United States Environmental Protection Agency grant. Nationally, she serves as a counselor for the Council on Undergraduate Research. She may be contacted at Jani.Ingram@nau.edu or via mail at 700 South Osborne Dr., PO Box 5698, Flagstaff, AZ 86011.