Kevin H. Johannesson

Treatment of nondetects in multivariate analysis of groundwater geochemistry data

Abstract Principal components analysis (PCA) is used to evaluate similarities in the trace element chemistry of groundwaters. Many of the trace elements, however, occur at concentrations below the detection limits (DL), which presents problems for statistical analyses. Since the optimal methods for dealing with the ‘ In this study, a new approach was developed to determine the best substitution methods when dealing with the ‘DL’ values for a given data set. Monte Carlo simulation experiments, using a mixture multivariate model, were performed to test the effects of substitution of the ‘ When ‘

Origin of middle rare earth element enrichments in acid waters of a Canadian High Arctic lake

–Middle rare earth element (MREE) enriched rock-normalized rare earth element (REE) patterns of a dilute acidic lake (Colour Lake) in the Canadian High Arctic, were investigated by quantifying whole-rock REE concentrations of rock samples collected from the catchment basin, as well as determining the acid leachable REE fraction of these rocks. An aliquot of each rock sample was leached with 1 N HNO3 to examine the readily leachable REE fraction of each rock, and an additional aliquot was leached with a 0.04 M NH2OH · HCl in 25% (v/v) CH3COOH solution, designed specifically to reduce Fe-Mn oxides/oxyhydroxides. Rare earth elements associated with the leachates that reacted with clastic sedimentary rock samples containing petrographically identifiable Fe-Mn oxide/oxyhydroxide cements and/or minerals/amorphous phases, exhibited whole-rock-normalized REE patterns similar to the lake waters, whereas whole-rock-normalized leachates from mafic igneous rocks and other clastic sedimentary rocks from the catchment basin differed substantially from the lake waters. The whole-rock, leachates, and lake water REE data support acid leaching or dissolution of MREE enriched Fe-Mn oxides/oxyhydroxides contained and identified within some of the catchment basin sedimentary rocks as the likely source of the unique lake water REE patterns. Solution complexation modelling of the REEs in the inflow streams and lake waters indicate that free metal ions (e.g., Ln3+, where Ln = any REE) and sulfate complexes (LnSO4+) are the dominant forms of dissolved REEs. Consequently, solution complexation reactions involving the REEs during weathering, transport to the lake, or within the lake, cannot be invoked to explain the MREE enrichments observed in the lake waters.

Rare earth element fractionation and concentration variations along a groundwater flow path within a shallow, basin-fill aquifer, southern Nevada, USA

Abstract Rare earth element (REE) concentrations were measured in 5 well water samples and 3 springs located along a groundwater flow path in a shallow, tuffaceous alluvial aquifer from southern Nevada, USA. The REE concentrations in these groundwaters decrease in the direction of groundwater flow. A previous investigation demonstrated that REE solid-liquid phase partitioning coefficients (i.e., Kd’s) for groundwaters from tuffaceous alluvial aquifers in southern Nevada are relatively high (mean Kd = 102.6). Our groundwater REE data, in conjunction with these Kd’s, support strong sorption of aqueous REEs to aquifer surface sites as the primary removal mechanism of REEs from these groundwaters. In addition, relatively high aqueous REE concentrations occur at distinct locations along the groundwater flow path. The elevated REE concentrations are explained by addition of deeper groundwaters, influx of geothermal waters from a hot spring system, differences in solution complexation, and/or mixtures of regional and local recharge sources. Solution complexation modelling of REEs in the groundwaters indicate that carbonate complexes account for more than 99% of each REEs in solution. Moreover, groundwater Yb/Nd ratios (a measure of REE fractionation) are associated with alkalinity (HCO3− + CO32−; r = 0.71). The data and speciation model results indicate that REE fractionation (i.e., the observed heavy REE, HREE, enrichments compared to rock-sources) is controlled by formation of progressively stronger carbonate complexes in solution with increasing atomic number, which inhibits HREE sorption compared to light REEs (LREE); and a greater affinity for the LREEs to sorb to surface sites in the local tuffaceous alluvial aquifers compared to the HREEs.

Origin of rare earth element signatures in groundwaters of circumneutral pH from southern Nevada and eastern California, USA

Concentrations of the rare earth elements (REE) were measured in circumneutral pH groundwaters from southern Nevada and Death Valley, CA. Groundwaters from the regional lower Paleozoic carbonate-rock aquifer (Cambrian–Devonian) have flat shale-normalized patterns that closely resemble the shale-normalized patterns of the aquifer rock samples (principally Cambrian). Groundwaters associated with younger carbonate rocks (chiefly Permian) in the study region exhibit heavy REE (HREE) enriched, shale-normalized REE patterns with substantial negative Ce anomalies that also mimic these carbonate rocks. In addition, groundwaters from the felsic volcanic rock aquifers have the same flat to light REE (LREE) enriched shale-normalized patterns with large negative Eu anomalies as the felsic volcanic rocks. The similar REE patterns of all the groundwaters and associated aquifer rocks studied suggest that the groundwaters inherited REE signatures from the host rocks through which they flow. Because negative Ce anomalies are not an uncommon feature of carbonate rocks of marine origin, the negative Ce anomalies reported here for these groundwaters may reflect a Permian marine Ce signature. Previously, we demonstrated that carbonate complexes dominate REE speciation in southern Nevada and Death Valley groundwaters. Moreover, solid–liquid partitioning coefficients (Kd) indicate that the affinity of LREEs to sorb to aquifer surface sites is substantially greater than for the HREEs in the southern Nevada carbonate- and felsic volcanic-rock alluvial aquifers. Consequently, the HREEs enrichments reported here for groundwaters associated with younger Paleozoic carbonate rocks compared to these source rocks is consistent with REE carbonate complexation and preferential removal of LREEs to aquifer surface sites.

Deciphering groundwater flow systems in Oasis Valley, Nevada, using trace element chemistry, multivariate statistics, and geographical information system

The origin of groundwater discharging via evapotranspiration and from springs within Oasis Valley, Nevada, is of concern owing to the close proximity of the Nevada Test Site (NTS) and the possible contamination of groundwater as a result of underground nuclear testing. Principal components analysis, cluster analysis, and population partitioning, along with a Geographical Information System, were used to decipher groundwater flow patterns in Oasis Valley, Nevada. These multivariate statistical techniques were applied to the trace element chemistry of groundwater samples collected from 26 springs and wells within Oasis Valley, the NTS, and the Nellis Air Force Range. The results of all statistical analyses showed similar geographical trends in the trace element chemistry of the groundwaters included in this study. Differences are observed between the groundwaters from the NTS and those of Oasis Valley based on the concentrations of the elements Li, Ge, Mo, Rb, Ba, U, and Ru. A concentration gradient is observed from lower concentrations in the NTS to increasing concentrations toward Oasis Valley suggesting groundwater flow in an overall southwestward direction from the NTS. Also, a different trace element signature is observed for the waters collected in the northern and western region of Oasis Valley, suggesting another source of groundwater to this area.

Rare earth element geochemistry of groundwaters from a thick till and clay-rich aquitard sequence, Saskatchewan, Canada

Rare earth elements (REE) were determined in groundwater samples collected from a thick till and clay-rich aquitard sequence located in southern Saskatchewan, Canada. The groundwaters are Na-Mg-SO4-type waters that range from highly concentrated brines (e.g., I up to 2 moles/kg) near the ground surface to relatively dilute waters (I ≈ 0.04 moles/kg) at depth. The majority of these groundwaters have pH values between 7 and 8, although the deepest samples are more alkaline (9 ≤ pH ≤ 9.6). Groundwater REE concentrations are relatively constant in the overlying till but increase by up to a factor of 50 in the underlying clay bedrock. Shallow groundwaters have heavy REE (HREE)—enriched shale-normalized patterns, whereas the REE patterns of the deep groundwaters are relatively flat. Solution complexation modelling indicates that variations in REE patterns reflect differences in solution complexation across the REE suite. In the shallow groundwaters, strongly adsorbed, positively charged carbonate complexes (LnCO3+), sulfate complexes (LnSO4+), and free metal ion species (Ln3+) dominate the speciation of light REEs (LREE), whereas HREEs occur chiefly as more stable, negatively charged dicarbonato complexes [i.e., Ln(CO3)2−)]. For the deepest groundwaters, however, all of the REEs are predicted to occur in solution as dicarbonato complexes. The large HREE enrichments of the shallow groundwaters reflect the greater affinity of the positively charged LREE solution species to adsorb to clay minerals or coatings on clay minerals in the aquitard sequence compared to the more stable, negatively charged HREE dicarbonato complexes. On the other hand, the flat REE patterns of the deep groundwaters reflect the dominance of the negatively charged dicarbonato complex for all REEs. The solution complexation model along with the strong positive correlation between REEs and [CO32−]F(0.79 ≤ r ≤ 0.95), and to a lesser extent pH (0.57 ≤ r ≤ 0.72), indicates that carbonate ion concentrations, and thus pH, exert important controls on aqueous REE concentrations in these groundwaters.

Using multivariate statistical analysis of groundwater major cation and trace element concentrations to evaluate groundwater flow in a regional aquifer

Groundwater samples were collected from 11 springs in Ash Meadows National Wildlife Refuge in southern Nevada and seven springs from Death Valley National Park in eastern California. Concentrations of the major cations (Ca, Mg, Na and K) and 45 trace elements were determined in these groundwater samples. The resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis (PCA), to investigate the chemical relationships between the Ash Meadows and Death Valley spring waters, to evaluate whether the results of the PCA support those of previous hydrogeological and isotopic studies and to determine if PCA can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters. The results of the PCA indicated that groundwaters from the regional Paleozoic carbonate aquifers (all of the Ash Meadows springs and four springs from the Furnace Creek region of Death Valley) exhibited strong statistical associations, whereas other Death Valley groundwaters were chemically different. The results of the PCA support earlier studies, where potentiometric head levels, δ18O and δD, geological relationships and rare earth element data were used to evaluate groundwater flow, which suggest groundwater flows from Ash Meadows to the Furnace Creek springs in Death Valley. The PCA suggests that Furnace Creek groundwaters are moderately concentrated Ash Meadows groundwater, reflecting longer aquifer residence times for the Furnace Creek groundwaters. Moreover, PCA indicates that groundwater may flow from springs in the region surrounding Scottys Castle in Death Valley National Park, to a spring discharging on the valley floor. The study indicates that PCA may provide rapid and relatively cost-effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated. Copyright

Oxyanion Concentrations in Eastern Sierra Nevada Rivers – 3. Boron, Molybdenum, Vanadium, and Tungsten

Water samples were collected from 10 locations along the Truckee River system, 14 locations along the Walker River system, and 12 locations along the Carson River, and analyzed for B, Mo, V, W, Na, Cl, and pH. Boron concentrations ranged from approximately 2 μmol/kg in the upper reaches of the Truckee River to almost 1,200 μmol/kg in Pyramid Lake. Molybdenum, V, and W had concentrations in the nanomolal range; Mo varied from a low of about 12 nmol/kg to a high of 3,200 nmol/kg (Walker Lake); V ranged from 9 nmol/kg to approximately 470 nmol/kg; and W varied from a low value around 0.8 nmol/kg (West Walker River) to 1,030 nmol/kg. The high concentrations of these oxyanion-forming trace elements in the rivers reflects (1) the relative stability of these oxyanions (e.g., MoO42-, HVO42-, WO42-, B(OH)3, and/or B(OH)4-) in the alkaline, well oxygenated river and lake waters, (2) contributions of hydrothermal waters (especially for B), and (3) weathering of rocks/regolith with high concentrations of these elements. In the case of Mo, V, and W, each exhibited relatively conservative behavior in the upper, oxygenated reaches of all three rivers. During the study period the region experienced a prolonged drought such that the lower reaches of each river were typified by no flow or stagnant waters and probably low oxygen and/or anoxic conditions (although not measured). Reductive processes occurring in the low flow to stagnant reaches of each river could have led to removal of Mo, V, and W from solution as coprecipitates with Fe monosulfides, or via sorption to Fe oxides/oxyhydroxides and/or organic matter. Boron, however, exhibited essentially no or minor removal from these rivers, and instead was added to each river via B-rich hydrothermal waters (e.g., Steamboat Creek from Steamboat Hot Springs), or by B-rich groundwaters via base-flow during the extensive drought.

Major ion geochemistry of groundwaters from southern Nevada and eastern California, USA

The dissolved ionic constituents of groundwaters are, in part, a record of the minerals and rocks in aquifers through which the water has flowed. The chemical composition and association of these major ions in groundwaters have been used to trace groundwater flow paths and sources. In general, the chemical composition of water in carbonate-rock aquifers is dominated by calcium, magnesium, and bicarbonate, whereas sodium, chloride, and sulfate can be dominant ions in the water that comes from volcanic aquifers or clay minerals. Since the 1990’s, we have dealt with the geochemistry of groundwaters from more than 100 springs and wells in southern Nevada and eastern California, USA for major solutes and trace elements. This paper compiles the hydrochemical data of major ions of these groundwaters. Based on major ion geochemistry, groundwaters from southern Nevada and eastern California can be classified as carbonate aquifer water, volcanic aquifer water, and mixing water (either mixing of carbonate and volcanic aquifer waters or mixing with local recharges). Piper and Stiff diagrams of major ions have graphically shown the general chemical characteristics, classifications, and mixing relationships of groundwaters from southern Nevada and eastern California.

Determination Of The Optimal Mixture Distribution

The proportions of groundwater contributing to Ash Meadows National Wildlife Refuge from the Spring Mountains, Pahranagat Valley, and the Nevada Test Site are determined using the concentrations of the rare earth elements in samples collected from wells and springs within each of these areas. In a previous study, the mixing potions were deterined using a trial and error method where different proportions of water from each of the three sites were tested to find the best match to the Ash Meadows waters. This method results in a solution that may not be optimal. In this study, the determination of the optimal mixing proportion is formulated as a restricted minimization problem, which is then solved by the method ofLagrange multipliers. Introduction Understanding the flow of groundwater is of crucial importance when evaluating the health risks associated with underground contamination. Information on the origin of groundwater as well as the direction of flow is provided through the use of conservative groundwater tracers. In the case of multiple sources of groundwater, these tracers can also be used to determine the proportions that each acquifer system contributes to a given area. Johannesson et al. (1979) investigated the use of rare earth elements (REE) as tracers of groundwater flow into the Ash Meadows National Wildlife Refuge (see Fig. 1). The rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were shown to behave relatively conservatively (travel along with the groundwater) in this environment. Earlier studies using deuterium (Winograd and Friedman, 1972) and uranium isotopes (Cowart, 1979; Osmond and Cowart, 1982) Transactions on Modelling and Simulation vol 22,