Geochemistry and hydrology of perched groundwater springs: assessing elevated uranium concentrations at Pigeon Spring relative to nearby Pigeon Mine, Arizona (USA)
The processes that affect water chemistry as the water flows from recharge areas through breccia-pipe uranium deposits in the Grand Canyon region of the southwestern United States are not well understood. Pigeon Spring had elevated uranium in 1982 (44 μg/L), compared to other perched springs (2.7–18 μg/L), prior to mining operations at the nearby Pigeon Mine. Perched groundwater springs in an area around the Pigeon Mine were sampled between 2009 and 2015 and compared with material from the Pigeon Mine to better understand the geochemistry and hydrology of the area. Two general groups of perched groundwater springs were identified from this study; one group is characterized by calcium sulfate type water, low uranium activity ratio 234U/238U (UAR) values, and a mixture of water with some component of modern water, and the other group by calcium-magnesium sulfate type water, higher UAR values, and radiocarbon ages indicating recharge on the order of several thousand years ago. Multivariate statistical principal components analysis of Pigeon Mine and spring samples indicate Cu, Pb, As, Mn, and Cd concentrations distinguished mining-related leachates from perched groundwater springs. The groundwater potentiometric surface indicates that perched groundwater at Pigeon Mine would likely flow toward the northwest away from Pigeon Spring. The geochemical analysis of the water, sediment and rock samples collected from the Snake Gulch area indicate that the elevated uranium at Pigeon Spring is likely related to a natural source of uranium upgradient from the spring and not likely related to the Pigeon Mine.
KeywordsMining Hydrochemistry USA Groundwater age Radioactive isotopes
Géochimie et hydrologie des émergences de nappes perchées : interprétation des fortes concentrations en uranium de la Source du Pigeon au regard de la proche Mine du Pigeon, Arizona (Etats-Unis d’Amérique)
Les processus qui affectent l’hydrochimie lorsque l’eau s’écoule depuis les zones de recharge à travers les dépôts uranifères des cheminées brèchiques de la région du Grand Canyon dans le Sud-Ouest des Etats Unis ne sont pas bien compris. La Source du Pigeon avait en 1982 une concentration en uranium élevée (44 μg/L) en comparaison des autres émergences perchées (2.7–18 μg/L), dès avant les opérations minières à la Mine du Pigeon voisine. Les émergences des nappes perchées de la zone entourant la Mine du Pigeon ont été échantillonnées entre 2009 et 2015 et comparées aux matériaux de la Mine du Pigeon afin de mieux comprendre la géochimie et l’hydrologie de la zone. Deux groupes principaux d’émergences de nappes perchées ont été identifiés à partir de cette étude ; un groupe est caractérisé par une eau de type sulfaté calcique, des valeurs basses du rapport 234U/238U de l’activité uranium (RAU), et un mélange d’eau avec une composante actuelle, et l’autre groupe par une eau de type sulfaté calcique et magnésien, des valeurs plus hautes du RAU, et des âges au radiocarbone indiquant une recharge de l’ordre de plusieurs milliers d’années. Les analyses statistiques multivariées en composantes principales sur des échantillons de la Mine du Pigeon et des sources indiquent des concentrations en Cu, Pb, As, Mn, et Cd qui distinguent les infiltrations liées à la mine des émergences des nappes perchées. La surface piézométrique indique qu’à la Mine du Pigeon la nappe perchée s’écoulerait probablement vers le Nord-Ouest, loin de la Source du Pigeon. Les analyses géochimiques des échantillons d’eau, de sédiments et de roches prélevés dans la zone du Ravin du Serpent indiquent que la teneur élevée en uranium de la Source du Pigeon est due probablement à une cause naturelle de l’augmentation de l’uranium en amont de la source et probablement non à la Mine du Pigeon.
Hidrología y geoquímica de manantiales de agua subterránea colgada: análisis de las concentraciones elevadas de uranio en el Manantial Pigeon relacionado con las inmediaciones de la Mina Pigeon, Arizona (EEUU)
Los procesos que afectan a la química del agua como los flujos de agua desde las zonas de recarga a través de los depósitos de uranio de brecha tipo cilíndrica en la región del Gran Cañón del suroeste de los Estados Unidos no son bien conocidos. El Manantial Pigeon tuvo un contenido elevado de uranio en 1982 (44 μg/L), en comparación con otros manantiales colgados (2.7–18 μg/L), antes de las operaciones mineras en las cercanía de la Mina Pigeon. Entre 2009 y 2015 se muestrearon los manantiales de agua subterránea colgada en un área cercana a la mina Pigeon y se compararon con el material de la Mina Pigeon para entender mejor la hidrología y la geoquímica de la zona. En este estudio se identificaron dos grupos generales de manantiales de agua subterránea; un grupo se caracteriza por el agua tipo sulfatada cálcica, con valores bajos de la relación de actividad 234U/238U (UAR), y una mezcla de agua con algún componente de agua moderna, y el otro grupo por agua tipo sulfatada cálcica magnésica, con valores más altos de UAR, y con edades de radiocarbono que indican una recarga del orden de varios miles de años. Un análisis estadístico multivariado de componentes principales de la Mina Pigeon y las muestras de los manantiales indican concentraciones Cu, Pb, As, Mn, y Cd relacionadas con los lixiviados de la mina en los manantiales de agua subterránea colgada. La superficie potenciométrica del agua subterránea indica que el agua subterránea colgada en la Mina Pigeon probablemente fluya hacia el noroeste lejos del Manantial Pigeon. El análisis geoquímico de las muestras de agua, sedimentos y rocas recogidas de la zona de Snake Gulch indican que el uranio elevado del Manantial Pigeon probablemente esté relacionado con una fuente natural de uranio aguas arriba a partir de manantiales y no es probable relacionarlo con la Mina Pigeon.
上层滞水泉的地球化学和水文状况:评价 (美国) 亚利桑那州Pigeon 矿附近Pigeon泉水中升高的铀含量摘要
水从补给区流经美国西南部大峡谷地区角砾岩管道铀矿时,其影响水化学的过程并未人们所深入了解。在附近的Pigeon矿开采之前,与其它上层滞水泉 (2.7–18 μg/L) 相比,1982年Pigeon泉的铀含量 (44 μg/L) 升高。2009年到2015年对Pigeon矿周边区域的上层滞水泉进行了采样,并与Pigeon矿的物质进行了对比,以便更好地了解该区域的地球化学和水文状况。通过本研究,确定了两组上层滞水泉。一组为硫酸钙类型水,铀活动比率234U/238U值低,混合着现代水的成分,另一组为硫酸钙镁类型水,铀活动比率234U/238U值较高,放射碳年龄表明为几千年前的补给水。Pigeon矿和泉水样的多元统计主要成分分析表明,通过Cu、 Pb、 As、 Mn 及 Cd的含量,能区分采矿有关的滤淋液和上层滞水泉。地下水压力面表明,Pigeon矿上层滞水很可能流向远离Pigeon泉的西北。对从Snake Gulch地区收集的水样、沉积物样和岩石样进行的地球化学分析表明,Pigeon泉水中的铀含量升高很可能与泉处自然铀源的反梯度有关,而与Pigeon矿无关。
Geoquímica e hidrologia de nascentes de aquíferos suspensos: avaliando concentrações elevadas de urânio na Nascente de Pigeon relativa à Mina de Pigeon nas proximidades, Arizona (EUA)
Os processos que afetam as características químicas da água quando essa flui das áreas de recarga, e atravessa os depósitos de urânio em zonas de brecha na região do Grand Canyon no sudoeste dos Estados Unidos não são muito bem compreendidos. A Nascente de Pigeon apresentou elevados teores de urânio em 1982 (44 μg/L), comparada a outras nascentes de aquíferos suspensos (2.7–18 μg/L), antes do início das atividades de mineração na Mina de Pigeon, nas proximidades. Nascentes de aquíferos suspensos numa área ao redor da Mina de Pigeon foram amostradas entre 2009 e 2015 e comparadas com material proveniente da mina, para que se pudesse entender melhor a geoquímica e hidrologia da área. Dois grupos mais abrangentes de águas subterrâneas de aquíferos suspensos foram identificados por este estudo, um grupo é caracterizado por águas do tipo cálcio-sulfatadas, com baixos valores da razão de atividade de urânio (RAU) 234U/238U, e uma mistura de água com algum componente de recargas recentes, e o outro grupo é composto por águas do tipo sulfatadas ricas em cálcio-magnésio, com valores RAU mais altos, e idades de radiocarbono indicando recarga na ordem de muitos milhares de anos atrás. Análise estatística multivariada dos principais componentes da Mina de Pigeon e amostras da nascente indicam concentrações distintas de Cu, Pb, As, Mn, e Cd dos lixiviados relacionadas à mina, em relação as concentrações das águas subterrâneas dos aquíferos suspensos. A superfície potenciométrica da água subterrânea indica que as águas subterrâneas dos aquíferos suspensos na Mina de Pigeon muito provavelmente fluam em direção noroeste, longe da nascente de Pigeon. A análise geoquímica de amostras de água, sedimento e rocha, coletadas na área de Snake Gulch indicam que e o teor elevado de urânio na Nascente de Pigeon é provavelmente relacionado à uma fonte natural de urânio à montante da nascente, e provavelmente não relacionada à Mina de Pigeon.
Changes in chemistry that occur as water flows from source areas through breccia-pipe uranium deposits in the Grand Canyon region (USA) are not well understood. Snake Gulch and Jumpup Canyon are tributaries to Kanab Creek located about 30 km north of Grand Canyon National Park (GRCA) where Kanab Creek ultimately flows into the Colorado River. Snake Gulch and Jumpup Canyon were chosen for a focused geochemical study because there is a reclaimed breccia pipe uranium mine (Pigeon Mine), collapse features and unmined breccia pipes, and several perched groundwater springs in the drainages.
Solution-collapse features known as breccia pipes are found throughout this region of Arizona, including within the Snake Gulch study area (Fig. 2). Breccia pipes are thought to form by dissolution and karst development in the underlying Mississippian Redwall Limestone rock unit, with progressive collapse moving upwards through time into overlying rock units, forming a rubble (breccia) filled column that can be as much as 1,000 m or more in height (Alpine and Brown 2010; Fig. 3). Breccia pipes are roughly circular in plan view, about 100 m in diameter, and are often characterized by inward dipping beds along the margins (Otton and Van Gosen 2010). Other collapse features found in the Snake Gulch area and throughout the Grand Canyon Region include sinkholes in the Kaibab and Toroweap formations and local and shallow collapse caused by dissolution of gypsum in the Kaibab and Toroweap formations (Billingsley et al. 2008). In absence of breccia at the surface, the most effective way to determine if a breccia pipe underlies a collapse is by drilling.
Some breccia pipes contain concentrated deposits of uranium, copper, silver, lead, zinc, cobalt, and nickel minerals (Wenrich 1985; Wenrich et al. 1989; Finch et al. 1992). Uranium mineralization in breccia pipes likely occurred after previous episodes of mineralizing fluids moving through the pipe which created reducing conditions within areas of the pipe that allowed for uraninite deposition (Wenrich 1985; Huntoon 1996). Mining of breccia pipes for copper, lead, zinc, and silver in the Grand Canyon region began in the 1860s, with uranium mining beginning in the 1950s. The Pigeon breccia pipe (Pigeon Pipe) was discovered in 1980 and the Pigeon Mine began extraction of uranium in 1984 (Otton et al. 2010). Mining was complete by late 1989 and the site was then reclaimed. About 2.6 million kg of uraninite (U3O8) were extracted from Pigeon Mine from ore located in the breccia pipe in a similar stratigraphic horizon as Hermit Formation and Supai Group (Fig. 3).
The climate in the study area is semiarid to arid with temperature decreasing and precipitation increasing with increasing elevation. Average annual temperature at Page, AZ was 15.4 °C for January 1997 through December 2008 (Western Regional Climate Center 2016). Freezing winter temperatures are common on the Kaibab Plateau and summer temperatures may exceed 38 °C in the inner canyons of the area. Average annual precipitation ranges from 500 to 800 mm on the Kaibab Plateau to less than 300 mm in the Kanab Creek canyon (PRISM Climate Group 2015). The ratio of annual evaporation to precipitation is about 2:1 in the higher altitudes on the Kaibab Plateau and as much as 5:1 at lower elevations near Snake Gulch (Alpine and Brown 2010; PRISM Climate Group 2015; Farnsworth et al. 1982). Groundwater in the area occurs in locally perched aquifers of limited extent and in the deeper regional Redwall-Muav aquifer, which is several hundred meters below the perched groundwater (Fig. 3). The perched water-bearing zone in the Snake Gulch area is probably recharged by a combination of local precipitation and precipitation falling on the elevated portion of the Kaibab plateau to the east of the study area, which has the highest recharge potential in the area (Flint and Flint 2007). Groundwater in the perched system discharges at several springs in the Snake Gulch area or may migrate deeper into the subsurface (Bills et al. 2010). The direction of groundwater flow in the perched and regional groundwater systems was not previously well defined in the study area, owing to limited potentiometric surface data.
Materials and methods
Water samples were collected from nine spring sites between August 2009 and August 2015. Five sites (Pigeon, Rock, Slide, Upper Jumpup, and Willow springs) were sampled more than one time during the sampling period. Water samples were collected following standard US Geological Survey protocols—US Geological Survey (variously dated). Field parameters including pH, water temperature, specific conductance, dissolved oxygen, and barometric pressure were measured at the spring site just before the water sample was collected. Spring discharge was measured by using volumetric techniques. Water samples were filtered (0.45 μm) for major cations, trace and rare earth elements, alkalinity, carbon-14, uranium, radium and strontium isotopes, and all, except for the alkalinity and carbon-14 samples, were preserved to pH <2 by using ultrapure nitric acid. Unfiltered samples were collected for major anions, tritium, and stable isotopes. Alkalinity titrations using the incremental equivalence method were performed within 5 h of sample collection—US Geological Survey (variously dated).
Water samples were analyzed for major, trace, and rare-earth elements by the USGS National Research Program Laboratory in Boulder, Colorado. Inductively coupled plasma-mass spectrometry (ICP-MS) is used for the following elements; Al, As, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Ga, Gd, Ho, La, Li, Lu, Mn, Mo, Nd, Ni, P, Pb, Pr, Rb, Re, Sb, Se, Sm, Sn, Sr, Tb, Te, Th, Ti, Tl, Tm, U, V, W, Y, Yb, Zn, and Zr (Garbarino and Taylor 1996; Taylor 2001). Inductively coupled plasma optical emission spectrophotometer (ICP-OES) is used for the following elements; Ca, Cr, Fe, K, Mg, P, S, SiO2, and Ti (Garbarino and Taylor 1979). Anions Cl, F, NO3 and SO4 were analyzed by ion chromatography. Samples were analyzed in triplicate and the average is used for the final value. The precision for all methods analyzed by the USGS National Research Program Laboratory in Boulder, Colorado was 4% or better depending on the element.
Stable isotope ratios (δ18O and δ2H) were measured at the USGS Reston Stable Isotope Laboratory (following methods by Révész and Coplen 2008a, b), the 2-sigma uncertainties are 0.2‰ for oxygen and 2‰ for hydrogen isotopic ratios reported relative to Vienna Standard Mean Ocean Water. Strontium isotope ratios (87Sr/86Sr) were measured by the USGS National Research Program Laboratory in Menlo Park, California by using methods described in Bullen et al. 1996 and are precise to 0.00002 or better at the 95% confidence level. Tritium was measured at the USGS Menlo Park Tritium Lab using the electrolytic enrichment liquid scintillation counting method with a detection limit of 0.3 pCi/L (0.09 TU, tritium units).
Multiple laboratories were used to analyze the 234U/238U activity ratio (UAR). The USGS National Research Program Laboratory in Reston, Virginia analyzed UAR by methods described in Kraemer et al. 2002 for samples of Wildband, Pigeon, Rock, Slide, Willow, and Upper Jumpup springs collected between 2009 and 2012. Uranium isotopes (234U, 235U, and 238U) were measured using method ASTM D 3972 by Eberline Services in Richmond, California for samples from Rock and Slide springs in 2011 and Wildband, Pigeon, and Willow springs in 2012; by Test America in Richland, Washington for Pigeon Spring in 2014; and by ALS Environmental in Fort Collins, Colorado for Slide, Upper Jumpup, Horse, Table Rock, and Warm springs in 2015. The values from the two labs for all seven paired samples were similar (differences of 0.002–0.198 UAR values corresponding to 0.1–3.6% difference). If two UAR values were available, the value from the USGS National Research Program Laboratory was used.
Carbon-14 and carbon-13/12 were analyzed by the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) at Woods Hole Oceanographic Institution. Carbon-14 values reported by the NOSAMS as pM were denormalized using Eq. 5 of Plummer et al. 2012 to pmC. NetpathXL was used to compute corrected groundwater ages using model (11) “Revised F&G solid ex” (Parkhurst and Charlton 2008). Values used in the computation of groundwater age were carbon-14 values of 0 pmc for carbonate rock and 100 pmc for soil CO2, and assuming δ13C values of 0 and −1.2‰ for carbonate rock and −22‰ for soil CO2 (Hart et al. 2010).
Sediment and associated leachate samples presented in this report were collected and analyzed according to methods described in Otton et al. 2010. A brief summary of the methods used by Otton et al. 2010 is included next for reference. Solid samples were digested using a mixture of hydrochloric, nitric, perchloric, and hydrofluoric acids, heated to 110 °C to dryness and redissolved in nitric acid then aspirated into ICP-AES and ICP-MS. Some of the sediment samples were leached using two different solutions: deionized water (DI) equilibrated with the atmosphere to produce a simulated rainwater solution and water containing 300 mg/L of hydrogen carbonate. Solid samples were sieved to less than 2 mm then split into 50-g subsamples and processed according to the Hageman and Briggs Field Leach Test (Hageman and Briggs 2000). The final supernatant liquid following the leach test was filtered and acidified then analyzed for chemical analysis including trace element analysis using ICP-MS (Lamothe et al. 2002). Additional solid and leachate sample data not published in Otton et al. 2010, but analyzed by the same methods, for site PS-08 and ore from the Pigeon Mine are presented in this report.
Principal components analysis (PCA) was used to reduce the complex data structure (many samples and many elements) to a fewer number of principal component vectors. The PCA was used to visualize the trace metal concentrations for sediment and water samples for the following elements As, Ba, Cd, Ce, Cu, La, Li, Mn, Mo, Pb, Rb, Sb, Se (water only), Sr, U, V, Y, and Zn. Data were logarithmically transformed to make the data more normally distributed, and then data were normalized or scaled (subtracting the mean and dividing by the variance) prior to computing a Euclidean distance matrix, which is the implicit matrix underlying a PCA analysis (Clarke and Warwick 2001). PCA generates linear combinations of variables that are represented with principal component vectors. The first principal component (PC1) accounts for the greatest proportion of variance in the data and each successive orthogonal component accounts for next greatest proportion of the variance. Contributions from the variables are expressed as loadings where the highest loadings are interpreted as the most significant. Directionality of the loadings (±) is also interpretable, indicating increasing or decreasing variable values. For elements with values less than the reporting limit, a value of half of the reporting limit was used for the PCA (Antweiler and Taylor 2008).
A cluster analysis was also used to identify similar groups in the spring samples by evaluating minimum differences within groups and maximum differences among groups. The cluster analysis used a simple agglomerative, hierarchical clustering technique with a group average linkage option. A similarity profile (SIMPROF) test was used to statistically evaluate whether or not a specified set of samples, which are not a priori assigned into groups, do not differ from each other in multivariate structure (Clarke and Warwick 2001). SIMPROF is a permutation test that statistically tests different groups (p ≤ 0.05) by computing the likelihood that individual groups were not generated purely by chance alone.
PHREEQCI version 3.3.3 (Charlton and Parkhurst 2002; Parkhurst and Appelo 2013) was used to determine geochemical properties of the sampled waters including saturation indices. The WATEQ4F database was used with the default pe value of 4 since none of the water samples indicate reducing conditions.
Potentiometric contours were created in ArcMap 10.3.1 using groundwater elevations from USGS (2015) contoured using natural neighbor interpolation. The lines were then modified so that contour lines were discontinuous across Snake Gulch where the elevation of the bottom of the canyon is deeper than the projected contour line and adjusted on the east side of the map north of Warm Springs to mimic the Muav Fault trace, which likely affects groundwater flow paths. Contour lines are dashed where approximate.
Results and discussion
This section is organized in three sections: the first presents and discusses water chemistry results, the second considers the groundwater flowpath and residence time of groundwater in a geologic context, and the last discusses potential sources of elevated uranium at Pigeon Spring based on the information presented in the first two sections.
Site characteristics and water-quality parameter values for springs in the Snake Gulch study area. NM not measured
Elevation (m asl)
Specific conductance (μS/cm)
Dissolved oxygen (mg/L)
Upper Jumpup (2)
Water type for the majority of the springs in Snake Gulch is calcium sulfate—Fig. S1 of the electronic supplementary material (ESM). Slide, Horse, and Upper Jumpup springs were calcium-magnesium sulfate type waters. These three springs discharge at the southeastern end of the study area. Warm Spring was a calcium-magnesium hydrogen carbonate-sulfate water and was the only spring included in this study which discharges upgradient of Snake Gulch and of the Big Springs Fault.
Saturation indices for spring samples were calculated using PHREEQC where negative values indicate undersaturation with respect to that mineral phase and positive values indicate oversaturation; values near zero may indicate minerals that react to equilibrium. The Kaibab Formation is composed of gypsiferous siltstones, sandstone, gypsum, limestone, sandy and cherty limestone; the Toroweap Formation is composed of gypsiferous siltstone, silty sandstone, gypsum, limestone and sandy limestone; the Coconino Sandstone is a fine-grained quartz sandstone and the Hermit Formation is composed of calcareous sandstone and siltstone (Billingsley et al. 2008). Gypsum dissolution is likely contributing to the calcium and sulfate ion composition of most of the springs. The saturation index for gypsum was negative (−0.1 to −0.94) for nearly all spring samples, indicating that the water could still dissolve more gypsum, with the exception of Wildband Spring (+0.04) which indicates sufficient reaction to attain gypsum equilibrium. Wildband Spring also had the highest specific conductance. Most spring waters were near equilibrium or oversaturated with respect to calcite (+0.04 to +1.21), indicating that the potential to precipitate calcite. Two samples had negative saturation indices for calcite: Warm Spring (−0.67) and one sample from Upper Jumpup Spring in 2015 (−0.81). Saturation indices were negative for all uranium minerals included in the PHREEQC simulations (Table S2 of the ESM).
Uranium (U) concentrations from springs in the study area, values in micrograms per liter
U, 1982 sample (Hopkins et al. 1984)
U, 1st recent sample
U, 2nd recent sample
U, 3rd recent sample
Evidence for uranium mobility can be determined from geochemical conditions and uranium isotopes. Conditions that favor uranium mobility in groundwater are presence of detectible dissolved oxygen and dissolved inorganic carbon. Waters from this study all had measurable dissolved oxygen and dissolved inorganic carbon primarily present as hydrogen carbonate. The isotopic composition of uranium in groundwater can be used to evaluate the proximity of the uranium source. Natural uranium consists of three isotopes 238U, 235U, and 234U with relative abundances of approximately 99.27, 0.72, and 0.0057%, respectively. The 235U/238U ratio exhibits an extremely small range of variation in nature (0.05–0.11 from springs in this study), but 234U/238U can vary widely and values can be greater than 1 due to alpha recoil where during alpha decay of 238U the recoiling 234Th nuclei can be ejected from the solid to aqueous phase and then decay to 234U with typical values in natural waters between 1 and 3, and values greater than 10 have been reported (Kronfeld 1974; Osmond and Cowart 1976; Szabo 1982). Uranium in undisturbed rocks and minerals older than approximately 1 million years, reaches a state of radioactive equilibrium (or secular equilibrium) where the rate of decay of 234U is limited by the rate of decay of 238U, and the UAR approaches 1; uranium mineralization in the breccia pipes of the area likely occurred between 141 and 200 million years ago (Wenrich 1985). Bulk dissolution of the solid phase uranium in breccia pipes in a chemically aggressive environment (e.g., fresh mill tailings or fresh exposures of ore) results in the release of uranium that has an isotopic composition similar to that of the rock (i.e., a UAR value close to 1.0). Water in contact with high-grade uranium ore that has a recent history of oxidation and leaching are a mix of material with UARs both greater than and less than 1.0 (Cowart and Osmond 1977).
Groundwater flowpaths and residence times
The groundwater potentiometric surface generated for the study area indicates that groundwater is generally moving toward the west–northwest in the area south of Snake Gulch and to the northwest in the area north of Snake Gulch (Fig. 7). The Harrisburg Member of the Kaibab Formation is dipping between 2 and 5° to the northwest to the west of the Muav fault (Billingsley et al. 2008). The potentiometric surface shows groundwater flow to be moving in a similar direction to the dip of the surface rocks of the Kaibab Formation. Pigeon Spring discharges from a south facing canyon wall in Pigeon Canyon before it merges with Snake Gulch. Gettings and Bultman (2005) show magnetic and gravity geophysical evidence of a fracture network along Pigeon Canyon trending towards the northeast that may provide a preferential pathway for perched water to flow towards Pigeon Spring as well as a potential conduit for precipitation to enter the groundwater system. The Muav Fault has offsets of 24–110 m before merging with the Big Springs Fault (146 m offset south of Big Springs) after which the Muav fault has 366 m of offset then 61 and 37 m of offset as the fault continues to the north (Billingsley et al. 2008). The Muav and Big springs Fault cut into the Hermit Formation at land surface just north of Mangum Springs (Fig. 7; Billingsley et al. 2008). The springs in Snake Gulch emerge from units including the Hermit Formation and younger units, and movement of water in these units across the Muav and Big Springs faults would be offset from the area of greatest recharge on the Kaibab Plateau. Slide Spring is the largest discharging spring in this study and according to the flowpath determined from the potentiometric contours groundwater moving towards this spring would cross the Muav and Big Springs faults in an area where the Hermit Formation was not exposed at the surface and may also be controlled by fracture networks presented in Gettings and Bultman 2005 (Fig. 7).
Pigeon, Wildband, Willow, and Rock springs were sampled for tritium, and ranged from 0.25 to 0.59 TU. Upper Jumpup, Slide and Horse springs had low tritium values (0–0.11 TU). Values of tritium peaked during the period of nuclear bomb testing in the 1950s and 1960s and then decreased over the next decades. In recent precipitation (after 1992), tritium values have stopped decreasing, and average values of tritium in precipitation range from 5.1 TU in Camp Verde to 8.9 TU in Flagstaff (Eastoe et al. 2012). The tritium data indicate that the groundwater present at the spring sites was either primarily recharged in the decades prior to 1952 (submodern) or is a mixture of post bomb pulse and tritium dead water. Using the laboratory detection limit of 0.09 TU and an initial tritium value of 8.9 TU from Flagstaff, AZ, water with detectable tritium could have been recharged 82 years prior to sample collection. Therefore, the presence of detectable tritium indicates that there is some component of water recharged after 1932 for samples collected in 2014.
Samples from Pigeon, Upper Jumpup, Horse, and Slide springs plot in the region indicating that they may be old waters that could have undergone 14C decay (Fig. 8; Han et al. 2012). Upper Jumpup Spring plots near the threshold for waters that could have undergone dedolomitization characterized by the dissolution of dolomite and gypsum enriched in δ13C or could be explained by calcite (CaCO3) precipitation on plots including hydrogen carbonate (Fig 8b, c; Han et al. 2012).
Values used in the computation of groundwater age of Pigeon, Upper Jumpup, Horse, and Slide Spring using NetpathXL (Parkhurst and Charlton 2008) were carbon-14 values of 0 pmc for carbonate rock and 100 pmc for soil CO2, and assuming δ13C values of 0‰ for carbonate rock and −22‰ for soil CO2 (Hart et al. 2010). δ13C for the rock units Kaibab, Toroweap and Hermit formations are −1.0, −1.4 and −1.3‰ respectively from rocks near the south rim of the Grand Canyon and well cuttings near Williams AZ (Bills et al. 2007). The average of the three δ13C rock unit values is −1.2 and was also used for the δ13C value of carbonate rock in NetpathXL to understand the difference in groundwater age interpretation if the groundwater was interacting with carbonate rock with this carbon isotope signature.
Groundwater age in years results from NetpathXL
Uncorrected age (years BP)
Ingerson and Pearson (corrected age years BP)
Revised Fontes and Garnier (solid exchange) (corrected age years BP)
The calculated corrected groundwater ages are sensitive to the value of δ13C in the soil gas CO2 and carbonate rock, with the oldest ages using 0‰. Using a value of −1.2‰ decreases the corrected age for the springs and also results in negative ages for some of the Pigeon Spring samples indicating that the correction methods are not appropriate for calculating the groundwater age or that the sample plots near the zero age line if the carbonate rock is −1.2‰ δ13C. There was some variation in the δ13C data from Bills et al. (2007) where the range of δ13C in the Kaibab was −2 to −0.2; Toroweap was −1.8 to −1, and the Hermit was −2.3 to −0.3, so analysis of δ13C in rock units from this study area would help with the interpretation of the age dating of the groundwater for Pigeon, Slide, Horse, and Upper Jumpup springs. A soil gas CO2 value of −22‰ for δ13C was used based on the values from Hart et al. 2010 for C3 plant dominated areas in Utah. The biome for the majority of the study area is Great Basin Conifer (Arizona Game and Fish 2015) which is dominated by C3 plants and the Great Basin Desert Scrub biome is present in lower elevations on the western side of the study area. The plant communities have been similar for the last 14,040 years BP in the area to the north of the Grand Canyon, which includes the range of corrected groundwater ages (Anderson et al. 2000). Appelo and Postma (2005) report −27‰ for δ13C of C3 plants and some arid zone C4 plants have a heavier δ13C value of −13‰ (Farquhar et al. 1989; Vogel 1993). The −22‰ value may represent a mixture of C3 and C4 plants and provides a good estimation for the age of the groundwater in this study. Soil gas δ13C value for the study area would help better constrain the age of the perched groundwater at the sampled springs.
Potential sources of elevated uranium at Pigeon Spring
The Pigeon Mine was prepared and developed from 1982 to 1984, mining began in 1984 and ended in 1989, and the site has since been reclaimed (Otton et al. 2010). During mine development, perched water was encountered in the mineshaft on the order of 27 L/min and was noted to decrease during the beginning of mining production to about 15 L/min in 1985 then decreased further to 7 L/min in 1986 and to 0 L/min in May 1987 (Arizona Department of Environmental Quality 2010). Before June 1986, perched water encountered in the mining operations was directed to a wastewater evaporation pond (Arizona Department of Environmental Quality 2010). After June 1986, perched water was used for mining operations (Arizona Department of Environmental Quality 2010).
The tritium measured at Pigeon Spring ranges from 0.25 to 0.40 TU, which indicates that the water was recharged prior to 1952 (Eastoe et al. 2012) or that the water is a mixture of modern and old water. The tritium data do not preclude the possibility of older groundwater present in the mineshaft from contributing to Pigeon Spring; however, the regional groundwater system indicates that groundwater from the mining area would not move toward Pigeon Spring unless there is an unknown fracture connecting the mine and spring.
Geochemical and isotopic data indicate that the elevated uranium concentration at Pigeon Spring is likely related to groundwater interaction with a mineralized breccia pipe hydrologically upgradient from the spring and not related to Pigeon Mine. Before mine development at Pigeon Mine the Pigeon Spring had strongly anomalous uranium concentration of 44 μg/L in Billingsley et al. 1983 and they state that a possibility exists that the water which emerges in Pigeon Spring has dissolved uranium from another mineralized collapse structure similar to the one at Pigeon Pipe. Wenrich et al. 1994 noted that Pigeon Spring is topographically higher than the ore body at Pigeon Mine and that mineralized pipes tend to occur in clusters, so there is a good possibility that Pigeon Spring contains water that has flowed through one or more mineralized pipes. In addition to Pigeon Spring (elevation 1,512 m) discharging groundwater above the ore body at Pigeon Mine (1,169–1,329 m), the elevation of the contacts between rock layers exposed in Snake Gulch decrease in elevation to the west between Pigeon Spring and Pigeon Mine (Billingsley et al. 2008). Two implied bedding measurements in the Kaibab Formation between Pigeon Spring and Pigeon Mine also indicate beds dipping to the northwest (Billingsley et al. 2008).
Geochemical anomalies and iron mineralization are commonly found in the breccia pipes in stratigraphic units above the uranium ore in breccia pipes (Kaibab and Toroweap formations and Coconino Sandstone; Wenrich et al. 1988, 1997; Wenrich 1985; Van Gosen and Wenrich 1989). At the Hermit Mine an ore zone was found in the Toroweap Formation (Energy Fuels Nuclear Inc. 1990). Otton et al. (2010) noted elevated uranium, iron and limonite on the surface of the Kaibab Formation to the east and south of the Pigeon Mine. They suggest these zones may have formed by fluids circulating near the Pigeon Pipe during ore formation. Water discharging at Pigeon Spring most likely moved through the Kaibab and Toroweap formations, according to the strontium isotopes and potentiometric surface contours, so contact with geochemically anomalous deposits in those formations above the main uranium ore bodies are possible.
A multivariate principal component analysis (PCA) was conducted on the solid samples from Otton et al. 2010 to understand if there is a signature of elements associated with the Pigeon Mine material that may be distinct from soil surrounding the mine derived from the Kaibab Formation (Fig. S2 of the ESM). The first principal component (PC1) and second principal component (PC2) of the PCA of the sediment, soil, rock, and ore samples explained 75.9% of the variation in the data (Fig. S2 of the ESM). Soil, ore, mud, and waste rock samples associated with mining activities have a positive association with PC1 which has positive loadings of the elements U, Cd, Pb, Sb, As, Cu, Mo, and Zn. The waste rock followed by ore samples are most correlated with the PC1 axis, but separate along the PC2 axis because of greater correlation of ore samples to the negative loading elements V, Ce, La, Rb, Sr, Y, Li, and Ba. Kaibab rock is most influential in defining the positive extent of PC2, which is also more associated with soils and stream sediments in areas not or less affected by mining activities. The samples related to reclaimed and mining surface soils, and mine-affected stream sediments are more correlated with the negative axis of PC2, but less than the ore samples. PC2 appears to explain some of the material form and the ways in which it was processed—for example, the Kaibab Formation sample material outside the mine and stream sediment upgradient of the mine are more highly correlated to the positive axis of PC2, while the processed and disturbed materials in and around the mine are more correlated with elements such as V, Ce, La, Rb, Sr, Y, Li, and Ba. The soil near the limonite outcrop PS-08 is more similar to the reclaimed mining sediments and stream sediment downstream of the mining activities, rather than sediments derived from the Kaibab Formation or the ore and waste rock (Fig. S2 of the ESM).
The leachate samples from Otton et al. 2010 were compared with the spring samples collected between 2009 and 2015 during this study to determine the similarity between water derived from leaching through mining materials and the springs of the study. The spring samples were more similar to each other than to the leachate samples, of which the leachate of soil near the limonite PS-08 was most similar to the spring samples. The first two PCs explained 68.6% of the variation in the PCA of the springs and leachate data, but the water showed a similar pattern as the solid materials in that mining-activity related leachate samples separated from the spring samples along PC1 (Fig. S3a of the ESM). Leachates from mining related soils, ore, mud, and waste rock are more correlated to the elements Cu, Pb, As, Mn, and Cd. Waste rock samples are most highly correlated with the positive axis of PC1 and PC2 (high loadings for Y, Ce, and La), resulting in greater separation from other samples in the PCA plot. Leaching processes also show a potential pattern with multivariate dispersion (spread of samples) being less for waste mud and mine operations soil samples as compared to waste rock, ore, and limonite, which appear to more reactive to rainwater leaching. The short-term (1 h) rain leachate of the waste rock defined the most positive coordinate along PC1 and PC2, whereas the 24 h river water ore leachate sample defined the most negative value along PC2. The negative axis of PC2 had higher loadings of the elements Mo, Sb, and V. The soil near the limonite PS-08 was most similar to the spring samples and the short-term rain leachate plotted closest to the springs.
A PCA on only the spring samples resulted in PC1 and PC2 explaining 54.2% of the variation in the spring sample data set. PC1 is the primary gradient for which samples are separating in the PCA plot. The elements U, Sr, Li, and Mo have high negative loadings on PC1 and Pigeon, Willow, Rock, and Wildband Spring samples are correlated with the negative axis of PC1 (Fig. S3b of the ESM). Zinc is the primary element positively loading on PC1 that distinguishes Upper Jumpup, Slide, Warm, Horse, and Table Rock springs from the other springs. The elements Rb, Se, and As have greater positive loadings on PC2, whereas Ba, Cu, Pb, and Y have greater negative loadings. The sample from Wildband Spring has the greatest correlation with the negative axis of PC2, while samples from Willow, Horse, Table Rock, and Warm springs are less correlated. The subset and reanalysis of PCA for the springs indicated that Pigeon Spring was significantly similar (cluster analysis grouping) to Rock and Willow springs and that U, Sr, Li, and Mo were loading highly along this axis (Fig. S3b of the ESM). These spring samples were separated from Upper Jumpup and Slide springs, which are significantly similar and can be explained by the high loading of Zn on this axis along with Horse, Table Rock and Warm springs (Fig. S3b of the ESM).
While U concentrations are highest at Pigeon Spring, the PCA suggests that composition of the other elements makes Pigeon Spring more similar to Rock, and Willow springs compared with mining material leachate. Mining leachates separated from the spring samples primarily due to differences in Cu, Pb, As, Mn, and Cd concentrations and these concentrations are not anomalously elevated at Pigeon Spring compared to the other samples in the study area (Fig. S3a of the ESM).
Two general groups of perched groundwater springs from Snake Gulch and Jumpup Canyon were identified from this study. The first is characterized by calcium-sulfate-type water, low UAR values, and low tritium values indicating some component of modern recharge (Pigeon, Rock, Willow, Wildband and Table Rock springs). The second is characterized by calcium-magnesium sulfate type water, higher UAR values, radiocarbon ages indicating recharge on the order of thousands of years ago and very low tritium (Slide, Upper Jumpup and Horse springs). Warm Spring represents a calcium-magnesium hydrogen carbonate-sulfate type water, with the greatest UAR, low tritium and represents modern water which likely recharged at a higher elevation compared with the Snake Gulch Springs and Upper Jumpup Spring.
Sediments derived from mining related material are distinct from sediments derived from the Kaibab Formation primarily related to U, Cd, Pb, Sb, As, Cu, Mo, and Zn. Water leached from the mining sediments at Pigeon Mine are distinct compared with the perched groundwater springs from this study for Cu, Pb, As, Mn, and Cd, and these elements may provide a good indication of connection of waters with mining related materials.
Pigeon Spring has elevated uranium compared to the other springs in the area, but the concentration is more similar to leachate from soil derived from an iron-enriched outcrop located stratigraphically above the main uranium ore body of a mineralized breccia pipe than it is to the ore or processed mining material. Iron mineralization and an enriched trace element suite similar to the uranium ore is known to occur in the Kaibab and Toroweap formations and Coconino Sandstones above the uranium ore in some mineralized breccia pipes. Pigeon Spring discharges from the Toroweap Formation near the Coconino Sandstone contact and strontium isotopes indicate the water at Pigeon Spring may have moved through the Kaibab and Toroweap formations. The perched groundwater flow in the area is moving towards the northwest and does not support groundwater movement from the Pigeon Mine towards Pigeon Spring. Further investigation into the groundwater elevation between Pigeon Mine and Pigeon Spring and upgradient of Pigeon Spring is needed to constrain the source of elevated uranium at Pigeon Spring. Wastewater from Pigeon Mine may be also be moving through the subsurface and further investigation downgradient of the mine is also important.
The geochemical and hydrologic investigation presented in this paper was supported by the USGS Toxic Substances Hydrology Program and the Bureau of Land Management. USGS employees Jessica Anderson, Jamie Macy, Kurt Schonauer, Joel Unema, Corey Sannes, and Geoff Debenedetto from the Arizona Water Science Center were critical in helping collect the spring samples from often remote locations. David Parkhurst (USGS) provided technical direction and support. We also thank two anonymous reviewers for their contribution.
- Alpine AE, Brown KM (2010) Introduction. In: Alpine A (ed) Hydrological, geological, and biological sites characterization of breccia pipe uranium deposits in northern Arizona. US Geol Surv Sci Invest Rep 2010-5025Google Scholar
- Arizona Department of Environmental Quality (2010) Pigeon Mine water discharge graph. ADEQ, Phoenix, AZGoogle Scholar
- Arizona Game and Fish (2015) Arizona’s ecoregions and vegetative communities. Arizona Game and Fish Department, Phoenix, AZGoogle Scholar
- Billingsley GH, Antweiler JC, Ellis CE (1983) Mineral resource potential of the Kanab Creek roadless area, Coconino and Mohave counties, Arizona. US Geol Surv Misc Field Study MF-1627-AGoogle Scholar
- Billingsley GH, Priest SS, Felger TJ (2008) Geologic map of the Fredonia 30′ × 60′ quadrangle, Mohave and Coconino counties, Northern Arizona. US Geol Surv Sci Invest Map 3035Google Scholar
- Bills DJ, Flynn ME, Monroe SA (2007) Hydrogeology of the Coconino Plateau and adjacent areas, Coconino and Yavapai counties, Arizona. US Geol Surv Sci Invest Rep 2005-5222Google Scholar
- Bills DJ, Tillman FD, Anning DW, Antweiler RC, Kraemer TF (2010) Historical and 2009 water chemistry of wells, perennial and intermittent streams, and springs in northern Arizona. In: Alpine A (ed) Hydrological, geological, and biological sites characterization of breccia pipe uranium deposits in northern Arizona. US Geol Surv Sci Invest Rep 2010-5025Google Scholar
- Charlton SR, Parkhurst DL (2002) PHREEQCI-A graphical user interface to the geochemical model. US Geol Surv Fact Sheet PHREEQC FS-031-02Google Scholar
- Clarke KR, Warwick RM (2001) Change in marine communities: an approach to statistical analysis and interpretation, chap 4. In: Clarke KR, Gorley RN (eds) PRIMER-E, 2nd edn. PRIMER-E, Plymouth, UK, 8 ppGoogle Scholar
- Energy Fuels Nuclear (1990) Review of shaft and raise closure plan at the Hermit Mine of Energy Fuels Nuclear, Inc. Behre Dolbear, Greenwood Village, COGoogle Scholar
- Farnsworth RK, Thompson ES, Peck EL (1982) Evaporation atlas for the contiguous 48 United States. Nat Ocean Atmos Admin Tech Rep NWS33, NOAA, Silver Spring, MDGoogle Scholar
- Finch WI, Pierson CT, Sutphin HB (1992) Grade and tonnage model of solution collapse breccia pipe uranium deposits: In: Bliss JD (ed) Developments in mineral deposit modeling. US Geol Surv Bull 2004, pp 36–38Google Scholar
- Flint LE, Flint AL (2007) Regional analysis of ground-water recharge: In: Stonestrom DA, Constantz J, Ferre TPA, Leake SA (eds) Ground-water recharge in the arid and semi-arid southwestern United States. US Geol Surv Prof Pap 1703Google Scholar
- Garbarino JR, Taylor HE (1996) Inductively-coupled plasma-mass spectrometric method for the determination of dissolved trace elements in natural water. US Geol Surv Open-File Rep 94-358, 49 ppGoogle Scholar
- Gettings ME, Bultman MW (2005) Candidate-penetrative-fracture mapping of the Grand Canyon Area, Arizona, from spatial correlation of deep geophysical features and surficial lineaments. US Geol Surv Digital Ser 121Google Scholar
- Hageman PL, Briggs PH (2000) A simple field leach for rapid screening and qualitative characterization of mine waste material on abandoned mine lands, in ICARD 2000. Proceedings from the 5th International Conference on Acid Rock Drainage, Denver, CO, May 21–24, 2000, Society for Mining, Metallurgy, and Exploration, Englewood, CO, pp 1463–1475Google Scholar
- Hopkins RT, Fox JP, Campbell WL, Antweiler JC (1984) Analytical results and sample locality map of stream-sediment, panned-concentrate, soil, and rock samples from the Kanab Creek (B3060) Roadless Area, Coconino Mohave counties, Arizona. US Geol Surv Open-File Rep 84-291Google Scholar
- Huntoon PW (1996) Large-basin ground water circulation and paleo-reconstruction of circulation leading to uranium mineralization in Grand Canyon Breccia Pipes, Arizona. Mt Geol 33(3):71–84Google Scholar
- Ingerson E, Pearson FJ Jr (1964) Estimation of age and rate of motion of ground water by the 14C method. In: Recent researches in the fields of hydrosphere, atmosphere and nuclear geochemistry. Editorial Committee for Sugawara Volume, Maruzen, Tokyo, pp 263–283Google Scholar
- Lamothe PJ, Meier AL, Wilson SA (2002) The determination of forty-four elements in aqueous samples by inductively coupled plasma-mass spectrometry, chap H. In: Taggart JE (ed) Analytical methods for chemical analysis of geologic and other materials. US Geol Surv Open-File Rep 2002-223-H, 11 pp. http://pubs.usgs.gov/of/2002/ofr-02-0223/. Accessed 18 Nov 2009
- Monroe SA, Antweiler RC, Hart RJ, Taylor HE, Truini Margot Rihs JR, Felger TJ (2005) Chemical characteristics of ground-water discharge along the south rim of Grand Canyon in Grand Canyon National Park, Arizona, 2000–2001. US Geol Surv Sci Invest Rep 2004-5146, 59 ppGoogle Scholar
- Osmond JK, Cowart JB (1976) The theory and uses of natural uranium isotopic variations in hydrology. Atomic Energy Rev 14:620–679Google Scholar
- Otton JK, Van Gosen BS (2010) Uranium resource availability in breccia pipes in northern Arizona: In: Alpine A (ed) Hydrological, geological, and biological sites characterization of breccia pipe uranium deposits in northern Arizona. US Geol Surv Sci Invest Rep 2010-5025Google Scholar
- Otton JK, Gallegos TJ, Van Gosen BS, Zielinski RA, Johnson RH, Hall SM, Arnold LR, Yager DB (2010) Effects of 1980s uranium mining in the Kanab Creek area of northern Arizona. In: Alpine A (ed) Hydrological, geological, and biological sites characterization of breccia pipe uranium deposits in northern Arizona. US Geol Surv Sci Invest Rep 2010-5025Google Scholar
- Parkhurst DL, Appelo CAJ (2013) Description of input and examples for PHREEQC version 3: a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. US Geol Surv Tech and Methods, book 6, chap A43, USGS, Reston, VA, 497 ppGoogle Scholar
- Parkhurst DL, Charlton SR (2008) NetpathXL: an Excel® interface to the program. NETPATH: US Geol Surv Tech and Methods 6-A26, USGS, Reston, VA, 11 ppGoogle Scholar
- Pendall EG (1997) Precipitation seasonality recorded in D/H ratios of Pinyon Pine cellulose in the Southwestern United States. PhD Thesis, Univ of Arizona, Tuscon, AZ, USAGoogle Scholar
- Plummer LN, Bexfield LM, Anderholm SK, Sanford WE, Busenberg E (2012) Geochemical characterization of ground-water flow in the Santa Fe Group aquifer system, Middle Rio Grande Basin, New Mexico (ver. 1.2, November 20, 2012). US Geol Surv Water Resour Invest Rep 03-04131, 395 ppGoogle Scholar
- PRISM Climate Group (2015) United States average annual precipitation, 1931–2010. Oregon State University, PRISM Climate Group, Corvallis, OR. http://www.prism.oregonstate.edu/normals/. Accessed 22 Dec 2015
- Révész K, Coplen TB (2008a) Determination of the δ(2H/1H) of water: RSIL lab code 1574, chap C1. In: Révész K, Coplen TB (eds) Methods of the Reston stable isotope laboratory. US Geol Surv Tech and Methods, book 10, chap C1, USGS, Reston, VA, 27 ppGoogle Scholar
- Révész K, Coplen TB (2008b) Determination of the δ(18O/16O) of water: RSIL lab code 489, chap C2. In: Révész K, Coplen TB (eds) Methods of the Reston stable isotope laboratory. US Geol Surv Tech and Methods, book 10, chap C2, USGS, Reston, VA, 28 ppGoogle Scholar
- Tamers MA (1967) Radiocarbon ages of groundwater in an arid zone unconfined aquifer. In: Isotope techniques in the hydrological cycle, AGU Monograph 11, AGU, Washington, DC, pp 143–152, doi:10.1029/GM011p0143
- Tamers MA, Scharpenseel HW (1970) Sequential sampling of radiocarbon in groundwater. In: Isotope Hydrology 1970. International Atomic Energy Agency, Vienna, pp 241–256Google Scholar
- Taylor HE (2001) Inductively coupled plasma-mass spectrometry: practices and techniques. Academic, New York, 294 ppGoogle Scholar
- US Department of the Interior (2012) Record of Decision: Northern Arizona withdrawal: Mohave and Coconino counties, Arizona.http://www.blm.gov/pgdata/etc./medialib/blm/az/pdfs/withdraw/feis.Par.88586.File.dat/NorthernArizona-ROD- v20-1%2011%202012_wsignederrata.pdf. Accessed 26 May 2016
- US Geological Survey (2015) National Water Information System: US Geological Survey database. http://waterdata.usgs.gov/nwis. Accessed 18 Nov 2015
- US Geological Survey (variously dated) National field manual for the collection of water-quality data: US Geol Surv Tech of Water-Resour Invest, book 9, chaps A1–A10. http://pubs.water.usgs.gov/twri9A. Accessed November 2016
- UNESCO (2016) World Heritage List: Grand Canyon. http://whc.unesco.org/en/list/75. Accessed 26 May 2016
- Van Gosen BS, Wenrich KJ (1989) Ground magnetometer surveys over known and suspected breccia pipes on the Coconino Plateau, northwestern Arizona. US Geol Surv Bull 1683-C, 31 ppGoogle Scholar
- Wenrich KJ, Van Gosen BS, Balcer RA, Scott JH, Mascarenas JF, Bedinger GM, Burmaster Betsi (1988) A mineralized breccia pipe in Mohawk Canyon: lithologic and geophysical logs. US Geol Surv Bull 1683-A, 66 ppGoogle Scholar
- Wenrich KJ, Chenoweth WL, Finch WI, Scarborough RB (1989) Uranium in Arizona: In: Jenney JP, Reynolds SJ (eds) Geologic evolution of Arizona. Arizona Geol Soc Dig 17:759–794Google Scholar
- Wenrich KJ, Boundy SQ, Aumente-Modreski R, Schwarz SP, Sutphin HB, Been JM (1994) A hydrogeochemical survey for mineralized breccia pipes: data from springs, wells, and streams on the Hualapai Indian Reservation, northwestern Arizona. US Geol Surv Open-File Rep 93-619Google Scholar
- Wenrich KJ, Billingsley GH, Huntoon PW (1997) Breccia-pipe and geologic map of the northeastern part of the Hualapai Indian Reservation and Vicinity, Arizona. US Geol Surv Misc Invest Series Map I-2440Google Scholar
- Western Regional Climate Center (2016) Western Regional Climate Center, Page Arizona station KPGA January 1997–December 2008. http://www.wrcc.dri.edu/. Accessed 8 June 2016
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.