Constituents In Groundwater Research Articles

CHEMICAL CONSTITUENTS OF SOME WELLS WATER IN SINAI (EGYPT) AND THEIR SUITABILITY OF QUALITY TO DIFFERENT USE ACTIVITIES

The study site of Wadi Sidri locates at west central Sinai, on the easternside of the Suez Gulf. Wadi Sidri is considered one of the most importanthydrographic basins in Sinai Peninsula because it receives, seasonally aconsiderable amounts of rainfall, most of it flows in the form of floodstowards the Suez Gulf. Other amounts of these rainfalls are surface run off andcatchment or stored as groundwater in a lot of wells amongst the area ofstudy.The present investigation aims at studing the chemical constituents ofgroundwater of the wells in Wadi Sidri, and to evaluate their suitability forirrigation or for other uses in different agriculture proposes; sharing in thedevelopment of the area. Chemical analysis for 21 ground water samples werecollected from 21 selected wells from Sidri valley.Data can be summarized as follow: Relatively use of groundwater in different human activities depend upon thegeneral moderate values of pH, TDS, SAR, pHc and adj SAR and adj RNa. Hydro-chemical parameters intended that the determination of the ion ratiosis important to distinguish between groundwater having pale salinitycharacteristics and those mineralized resulting by evaporation processes. Themost important parameters are: (Na + K) / Cl, (SO4 / Cl), (Ca / Mg) and (Na /K). The hypothetical salts assemblages in groundwater result from thecombination between cations and anions. Groundwater of the studied wellsreflect the existence of two assemblages salts of; NaCl, MgCl2, MgSO4,CaSO4 and Ca (HCO3)2 beside to NaCl, Na2SO4, CaSO4, MgSO4 and Ca(HCO3)2.Many heavy and trace elements (Fe, Mn, Zn, Cu, Pb and Cd) are present ingroundwater with low concentration (less than 0.lppm), but sometimes muchhigher, particularly if the water has been in contact with mineralized rock orore bodies.

An Empirical Evaluation of the Influence of Ethanol on Natural Attenuation of Gasoline Constituents

AbstractSince the 1990s, questions have arisen as to whether the release of ethanol‐blended fuel will inhibit natural attenuation of other gasoline constituents in groundwater. This study evaluated the hypothesis that ethanol affects hydrocarbon attenuation and whether the use of ethanol‐blended fuel alters the applicability of monitored natural attenuation (MNA) as an approach for managing risks at fuel‐release sites. Groundwater data from California's GeoTracker database were used to compare attenuation of benzene, toluene, methyl tert‐butyl ether (MTBE), and tert‐butyl alcohol (TBA) at sites with and without detections of ethanol. Excel‐based tools were developed to conduct attenuation evaluations on thousands of wells simultaneously. Ethanol was detected at least once in 4.5% of the wells and 0.6% of the samples of which it was analyzed. The distribution of Mann‐Kendall concentration trend analysis results and first‐order attenuation rates were essentially the same at sites with or without ethanol detections. Median plume lengths were shorter at sites where ethanol had not been detected compared to sites where ethanol was detected (36 vs. 43 m for benzene; 36 vs. 42 m for toluene; 43 vs. 52 m for MTBE; and 44 vs. 59 m for TBA). However, the distribution of plume lengths was similar irrespective of ethanol concentrations, suggesting other factors may influence plume elongation. Finally, while anaerobic ethanol degradation can result in methane generation, the distributions of methane concentrations were the same at sites with and without ethanol detections. These results suggest that the use of ethanol‐blended fuel should not limit the application of MNA at most biodegrading fuel‐release sites.

Exploration of physico-chemical parameters and ionic constituents from groundwater used in irrigation of Tangail district, Bangladesh

The study was conducted for exploration of physico-chemical parameters and ionic constituents of groundwater used in irrigation of four upazilas namely Tangail Sadar, Kalihati, Delduar and Nagarpur upazila of Tangail district during the months of March, April and May of 2015. The physico-chemical parameters (pH, EC and TDS), ionic constituents (Ca2+, Mg2+, Na+, K+, Cl-, CO32-, HCO3-, PO43- and SO42-) and trace metal (Fe and Mn) were analyzed to assess the quality of irrigation in relation to soil properties and crop growth. The pH of groundwater indicates slightly alkaline in nature. As regards to EC the groundwater was in ‘good’ class and medium salinity hazards in quality for irrigation and the concentration of TDS indicates water as fresh water. The concentration of Ca2+, Mg2+, Na+, K+, Cl-, CO32-, HCO3-, PO43- and SO42- of groundwater were recorded within the permissible limit for irrigation and these ions might not create hazardous impact on soil ecosystem for growing crops. The trace amount of Fe and Mn was detected in irrigation water. In the study area, the groundwater was within the recommended limit and would not create problem for irrigation and that have not long term effects on irrigating agricultural crops which could be safely used for irrigation purposes.Res. Agric., Livest. Fish.3(1): 115-119, April 2016

Use of single-well push–pull tracer tests to simulate a dynamic saltwater–freshwater interface

Two single-well injection–extraction (“push–pull”) tracer tests were performed in a groundwater monitoring well located in the Horonobe coastal sedimentary basin, Japan. The aim of the experiment was to investigate the in situ behavior of groundwater constituents when different mineralized fluids intrude into the aquifer (e.g., through a dynamic saltwater–freshwater interface). Artificially produced brackish water was used as the test fluid in the first experiment and deionized water in the second. Results from mixing models strongly suggest rapid mobilization and demobilization of ions within the aquifer as a reaction to the intruding fluids. Hydraulic modeling of the conservative chloride ions yielded effective porosities of about 1 %. These results show that the transport of ions is dependent on the composition and mineralization of the fluid. The refreshening of an aquifer leads to increased mobilization of ions and, in addition, to an increase of dispersivity due to clay swelling. This has consequences not only for dynamic saltwater–freshwater systems (aquifers in coastal areas and aquifer storage and recovery systems), but also for all systems in which chemically altered fluids come into contact within an aquifer (as, for example, can occur during geothermal heat/energy generation, or during CO2 storage).

Elucidating hydraulic fracturing impacts on groundwater quality using a regional geospatial statistical modeling approach

Hydraulic fracturing operations have been viewed as the cause of certain environmental issues including groundwater contamination. The potential for hydraulic fracturing to induce contaminant pathways in groundwater is not well understood since gas wells are completed while isolating the water table and the gas-bearing reservoirs lay thousands of feet below the water table. Recent studies have attributed ground water contamination to poor well construction and leaks in the wellbore annulus due to ruptured wellbore casings. In this paper, a geospatial model of the Barnett Shale region was created using ArcGIS. The model was used for spatial analysis of groundwater quality data in order to determine if regional variations in groundwater quality, as indicated by various groundwater constituent concentrations, may be associated with the presence of hydraulically fractured gas wells in the region. The Barnett Shale reservoir pressure, completions data, and fracture treatment data were evaluated as predictors of groundwater quality change. Results indicated that elevated concentrations of certain groundwater constituents are likely related to natural gas production in the study area and that beryllium, in this formation, could be used as an indicator variable for evaluating fracturing impacts on regional groundwater quality. Results also indicated that gas well density and formation pressures correlate to change in regional water quality whereas proximity to gas wells, by itself, does not. The results also provided indirect evidence supporting the possibility that micro annular fissures serve as a pathway transporting fluids and chemicals from the fractured wellbore to the overlying groundwater aquifers.

Hydrochemical considerations for identifying water from basaltic aquifers: The Israeli experience

Abstract Study region Yizre’el-Harod-Bet She’an valley, Lower Galilee and Golan Heights, Israel. Study focus Identification of pure groundwater that infiltrated the widespread alkali olivine basalts in the replenishment areas of the study region. New hydrological insights for the region The groundwater is characterized by equivalent ratios such as Na/Cl > 1; Na/HCO3− 1; 1000Br/Cl in the range of 1–2.5; δ34Ssulfate 1 and HCO3−/(Ca + Mg + Na + K) > 0.7. Application of these parameters to analyses showing only the main constituents of groundwater reveals that in the study area the contribution of unmixed groundwater from basaltic catchments is largely restricted to the Golan Heights. Mixing of groundwater by interaquifer flow is a common phenomenon all over the area.

Zinc Isotope Fractionation as an Indicator of Geochemical Attenuation Processes

Isotope ratio measurements have been used to trace environmental processes, especially in subsurface environments. In this study, we evaluated the potential to use zinc (Zn) stable isotope ratios as indicators of attenuation processes, including sorption and precipitation. Zn isotope fractionation was observed during distinctly different precipitation processes. Isotope measurements confirmed an increasing trend in aqueous δ66Zn in solution during sphalerite (ZnS) formation, but a decreasing trend in δ66Zn during the precipitation of hydrozincite [Zn5(CO3)2(OH)6] and hopeite [Zn3(PO4)2·4H2O]. In contrast, time-dependent sorption of Zn onto ferrihydrite at a fixed pH did not cause isotopic fractionation in the solution over the duration of the experiments. These findings suggest potential applications of stable isotope measurements in aqueous environments for determining reaction pathways (e.g., precipitation with common groundwater constituents) leading to Zn attenuation.

An evaluation of health risk to the public as a consequence of in situ uranium mining in Wyoming, USA

In the United States there is considerable public concern regarding the health effects of in situ recovery uranium mining. These concerns focus principally on exposure to contaminants mobilized in groundwater by the mining process. However, the risk arising as a result of mining must be viewed in light of the presence of naturally occurring uranium ore and other constituents which comprise a latent hazard. The United States Environmental Protection Agency recently proposed new guidelines for successful restoration of an in situ uranium mine by limiting concentrations of thirteen groundwater constituents: arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, nitrate (as nitrogen), molybdenum, radium, total uranium, and gross α activity. We investigated the changes occurring to these constituents at an ISR uranium mine in Wyoming, USA by comparing groundwater quality at baseline measurement to that at stability (post-restoration) testing. Of the groundwater constituents considered, only uranium and radium-226 showed significant (p < 0.05) deviation from site-wide baseline conditions in matched-wells. Uranium concentrations increased by a factor of 5.6 (95% CI 3.6–8.9 times greater) while radium-226 decreased by a factor of about one half (95% CI 0.42–0.75 times less). Change in risk was calculated using the RESRAD (onsite) code for an individual exposed as a resident-farmer; total radiation dose to a resident farmer decreased from pre-to post-mining by about 5.2 mSv y−1. Higher concentrations of uranium correspond to increased biomarkers of nephrotoxicity, however the clinical significance of this increase is unclear.

The role of anthropogenic and natural factors in shaping the geochemical evolution of groundwater in the Subei Lake basin, Ordos energy base, Northwestern China

Groundwater resources are increasingly exploited for industrial and agricultural purposes in many arid regions globally, it is urgent to gain the impact of the enhanced anthropogenic pressure on the groundwater chemistry. The aim of this study was to acquire a comprehensive understanding of the evolution of groundwater chemistry and to identify the impact of natural and anthropogenic factors on the groundwater chemistry in the Subei Lake basin, Northwestern China. A total of 153 groundwater samples were collected and major ions were measured during the three campaigns (August and December 2013, May 2014). At present, the major hydrochemical facies in unconfined groundwater are Ca–Mg–HCO3, Ca–Na–HCO3, Na–Ca–HCO3, Na–HCO3, Ca–Mg–SO4 and Na–SO4–Cl types, while the main hydrochemical facies in confined groundwater are Ca–Mg–HCO3, Ca–Na–HCO3, Na–Ca–HCO3, Ca–HCO3 and Na–HCO3 types. Relatively greater seasonal variation can be observed in the chemical constituents of confined groundwater than that of unconfined groundwater. Rock weathering predominates the evolution of groundwater chemistry in conjunction with the cation exchange, and the dissolution/precipitation of gypsum, halite, feldspar, calcite and dolomite are responsible for the chemical constituents of groundwater. Anthropogenic activities can be classified as: (1) groundwater overexploitation; (2) excessive application of fertilizers in agricultural areas. Due to intensive groundwater pumping, the accelerated groundwater mineralization resulted in the local changes in hydrochemical facies of unconfined groundwater, while the strong mixture, especially a large influx of downward leakage from the unconfined aquifer into the confined aquifer, played a vital role in the fundamental variation of hydrochemical facies in confined aquifer. The nitrate contamination is mainly controlled by the local hydrogeological settings coupled with the traditional flood irrigation. The deeper insight into geochemical evolution of groundwater obtained from this study can be beneficial to improving groundwater management for sustainable development in the rapidly industrialized areas.

Use of lithium tracers to quantify drilling fluid contamination for groundwater monitoring in Southeast Asia

Drilling is widely used in groundwater monitoring and many other applications but has the inherent problem of introducing some degree of external contamination into the natural systems being monitored. Contamination from drilling fluid is particularly problematic for (i) wells with relatively low water flow rates which are difficult to flush; and for (ii) hydrogeochemical research studies of groundwaters hosted by incompletely consolidated shallow sediments, which are widely utilized as sources of drinking water and irrigation water across many parts of Asia. Here, we develop and evaluate a method that can be simply used to quantify the extent of drilling fluid contribution to a water sample either to optimize sample collection for reduced contamination, or to allow a correction for contamination to be made. We report the utility of lithium chloride tracers using both field and laboratory analytical techniques to quantitatively evaluate and correct for drilling fluid contamination of casing waters through an investigation of 15 sites in Kandal Province, Cambodia. High analytical errors limit the practicality and resolution of field-based lithium ion selective electrode measurements for purposes other than broad estimates of gross contamination. However, when laboratory analysis is integrated with the method (e.g. via inductively coupled plasma atomic emission spectrometry analysis), lithium tracers can provide a robust and accurate method for evaluating drilling-related contamination if appropriate samples are collected. Casing water is susceptible to contamination from drilling fluid which was shown to be significantly reduced within two to three well volumes of flushing but can still persist above background for greater than seven well volumes of flushing. A waiting period after drilling and prior to water sampling was shown to further decrease contamination due to dilution from the surrounding aquifer, particularly in more permeable wells. Contamination values were generally <3% for 34 monitoring wells across 15 sites after flushing a mean of 4.6 ± 3.8 well volumes, even when lithium-spiked water was directly injected during flushing to remove settled mud/debris. Operational issues can be encountered which can (i) lead to contamination being much higher than the mean if wells are highly unproductive and clay-dominated or (ii) lead to higher flushing volumes than the mean particularly in sandy areas where fine sand may enter the well screening. General correction factors have been provided for typical monitoring wells in poorly consolidated shallow aquifers in Southeast Asia, and examples provided for how to correct other groundwater data for contamination. For most analytes such as sodium or dissolved organic carbon (DOC), specific corrections may not be necessary for the typical magnitude of contamination encountered, particularly when the differences in concentrations between the drilling fluid and groundwater are relatively small. In the particular circumstance where drilling fluid may have much higher DOC than groundwaters, or vice versa with drilling fluid having much lower DOC than groundwaters in organic-rich alluvial sediments, corrections may still be necessary and significant. Similarly, for highly sensitive parameters such as 14C model age or other age-related parameters (such as tritium, chlorofluorocarbons (CFCs) or sulfur hexafluoride (SF6)), corrections can be significant in typical field scenarios particularly when contamination values are high and/or there is a large difference in age between groundwater and drilling fluid. The lithium method was verified with comparison to changes in concentration of a suite of representative and naturally occurring groundwater constituents as a function of well flushing from relatively low and high permeability groundwater monitoring wells to further illustrate the technique.

Facile synthesis of alumina-decorated multi-walled carbon nanotubes for simultaneous adsorption of cadmium ion and trichloroethylene

An adsorbent was prepared by decorating alumina onto the surface of multi-wall carbon nanotubes (MWCNTs) for simultaneous removal of cadmium ion (Cd(II) ion) and trichloroethylene (TCE) from groundwater. Structural characterization demonstrated that the nanocomposites was successfully synthesized and exhibited large surface area and restrained aggregation property. Batch experiments were conducted under various conditions (i.e., different pH, the presence of other groundwater constituents) to investigate the removal of Cd(II) ion or/and TCE by the alumina-decorated multi-walled carbon nanotubes (Al2O3/MWCNTs) and the underlying mechanisms. The adsorption kinetics of Cd(II) ion and TCE followed the pseudo-second-order kinetic model and exhibited 3-stage intraparticle diffusion mode. Equilibrium data of Cd(II) ion and TCE were best fitted by Langmuir and Freundlich model, respectively. The adsorption mechanisms of Al2O3/MWCNTs toward Cd(II) ion and TCE mainly involved in the electrostatic interactions, the hydrogen bond interactions and the protonation or hydroxylation of Al2O3. The maximum adsorption capacities of Al2O3/MWCNTs for TCE and Cd(II) ion were 19.84mg/g and 27.21mg/g, respectively, which were higher than that of Al2O3, MWCNTs and the functionalized MWCNTs. The results suggested that the Al2O3/MWCNTs could be considered as an effective and promising adsorbent for simultaneous removal of Cd(II) ion and TCE from groundwater.

Efficient removal of uranium from aqueous solution by zero-valent iron nanoparticle and its graphene composite

Zero-valent iron nanoparticle (ZVI-np) and its graphene composites were prepared and applied in the removal of uranium under anoxic conditions. It was found that solutions containing 24ppm U(VI) could be completely cleaned up by ZVI-nps, regardless of the presence of NaHCO3, humic acid, mimic groundwater constituents or the change of solution pH from 5 to 9, manifesting the promising potential of this reactive material in permeable reactive barrier (PRB) to remediate uranium-contaminated groundwater. In the measurement of maximum sorption capacity, removal efficiency of uranium kept at 100% until C0(U)=643ppm, and the saturation sorption of 8173mgU/g ZVI-nps was achieved at C0(U)=714ppm. In addition, reaction mechanisms were clarified based on the results of SEM, XRD, XANES, and chemical leaching in (NH4)2CO3 solution. Partially reductive precipitation of U(VI) as U3O7 was prevalent when sufficient iron was available; nevertheless, hydrolysis precipitation of U(VI) on surface would be predominant as iron got insufficient, characterized by releases of Fe2+ ions. The dissolution of Fe0 cores was assigned to be the driving force of continuous formation of U(VI) (hydr)oxide. The incorporation of graphene supporting matrix was found to facilitate faster removal rate and higher U(VI) reduction ratio, thus benefitting the long-term immobilization of uranium in geochemical environment.

Modelling the hypothetical methane-leakage in a shale-gas project and the impact on groundwater quality

The hypothetical leakage of methane gas caused by fracking a 1,000-m deep Cretaceous claystone horizon at Damme, Germany, is simulated in a TOUGHREACT reactive-transport model with 5,728 elements. A hypothetical leakage zone connects the Cretaceous horizon with a Quaternary potable-water aquifer (q1). Methane gas rises up to the q1 horizon in less than 2 days in all calculated scenarios. The simulations include the major constituents of groundwater as well as the seven most hazardous trace components that are natural constituents of groundwater (As, Cd, Cr, Ni, Pb, Se and U). The general trend is characterised by depletion of the natural hazardous components with decreasing acidity and oxygen fugacity in the relevant pH range (7–9). Nevertheless, the concentrations of elements whose dominant aqueous species are negatively charged in this pH range (Cr and Se) rise against the general trend due to desorption reactions. Slight enhancement effects are produced by the dissolution of contaminant-bearing oxides such as Cr-bearing goethite. In summary, the geological risks of a fracking operation are minor. The technical risks are more important. This is especially the case when rising methane gas gets into contact with fracking fluid that accidentally escapes through faulty well seals.

Perchloroethylene (PCE) oxidation by percarbonate in Fe2+-catalyzed aqueous solution: PCE performance and its removal mechanism

The performance of Fe2+-catalyzed sodium percarbonate (SPC) stimulating the oxidation of perchloroethylene (PCE) in groundwater remediation was investigated. The experimental results showed that PCE could be completely oxidized in 5min at 20°C with a Fe2+/SPC/PCE molar ratio of 8/8/1, indicating the effectiveness of Fe2+-catalyzed SPC oxidation for PCE degradation. Fe2+-catalyzed SPC oxidation was suitable for the nearly neutral pH condition, which was superior to the conventional Fenton oxidation in acidic condition. In addition, the investigations by using hydroxyl radical scavengers and free radical probe compounds elucidated that PCE was degraded mainly by hydroxyl radical (HO) oxidation in Fe2+/SPC system. In conclusion, Fe2+-catalyzed SPC oxidation is a highly promising technique for PCE-contaminated groundwater remediation, but more complex constituents in groundwater should be carefully considered for its practical application.

Bimetallic nickel–iron nanoparticles for groundwater decontamination: Effect of groundwater constituents on surface deactivation

The incorporation of catalytic metals on iron nanoparticles to form bimetallic nanoparticles (BNPs) generates a class of highly reactive materials for degrading chlorinated hydrocarbons (e.g., trichloroethylene, TCE) in groundwater. Successful implementation of BNPs to groundwater decontamination relies critically on the stability of surface reactive sites of BNPs in groundwater matrices. This study investigated the effect of common groundwater solutes on TCE reduction with Ni–Fe (with Ni at 2 wt.%) bimetallic nanoparticles (herein denoted as Ni–Fe BNPs). Batch experiments involving pre-exposing the nanoparticles to various groundwater solutions for 24 h followed by reactions with TCE solutions were conducted. The results suggest that the deactivation behavior of Ni–Fe BNPs differs significantly from that of the well-studied Pd–Fe BNPs. Specifically, Ni–Fe BNPs were chemically stable in pure water. Mild reduction in TCE reaction rates were observed for Ni–Fe BNPs pre-exposed to chloride (Cl−), bicarbonate (HCO3−), sulfite (SO32−) and humic acid solutions. Nitrate (NO3−), sulfate (SO42−) and phosphate (HPO42−) may cause moderate to severe deactivation at elevated concentrations (>1 mM). Product analysis and surface chemistry investigations using high-resolution X-ray photoelectron spectroscopy (HR-XPS) reveal that NO3− decreased particle reactivity mainly due to progressive formation of passivating oxides, whereas SO42− and phosphate elicited rapid deactivation as a result of specific poisoning of the surface nickel sites. At similar levels, phosphate is the most potent deactivation agent among the solutes examined in this study. While our findings point out the desirable quality of Ni–Fe nanoparticles, particularly their greater electrochemical stability compared to Pd–Fe BNPs, its susceptibility to chemical poisoning at high levels of complexing ligands is also noted. Groundwater chemistry is therefore an important factor to consider when choosing appropriate material(s) for decontaminating the complex environmental media.

Microbially Mediated In Situ Desorption Accelerates Remediation of Large Gasoline Product Plume

Remediation of a large separate‐phase hydrocarbon product and associated dissolved‐phase gasoline plume was accelerated by coupling multiphase extraction with in situ microbial stimulation. At the beginning of remediation activities, the separate‐phase hydrocarbon plume extended an estimated seven acres with product thickness measuring up to 2.1 feet thick. Within 18 months after beginning extraction, reduction of gasoline constituents in groundwater became asymptotic and measureable product disappeared from the upgradient source area. At that time, the remediation team initiated a program of limited in situ anaerobic bioremediation with the goal of stimulating production of natural surfactants from native microbes to release petroleum from the soil matrix. Groundwater concentrations of gasoline constituents increased gradually over the next three years, improving recovery without biofouling the pump‐and‐treat infrastructure. Using this approach, the groundwater component of the remedy was completed in less than five years, substantially less than the 10 years to 15 years predicted by modeling. This strategy demonstrated a more sustainable approach to remediation, reducing electrical usage by an estimated 800 megawatt hours, reducing infrastructure requirements, and preserving an estimated 150 million gallons of groundwater for this arid agricultural area. © 2014 Wiley Periodicals, Inc.

Use of Chemical and Isotopic Signatures to Distinguish Between Uranium Mill‐Related and Naturally Occurring Groundwater Constituents

AbstractChemical and isotopic signatures were determined in groundwater samples to aid in distinguishing the source of contamination in three desert arroyos and a buried channel (the swale) near Shiprock, New Mexico. The contamination in the swale and one of the arroyos, Many Devils Wash, was previously attributed to a former uranium mill site because of the similar suite of contaminants (nitrate, selenium, sulfate, and uranium) and the close (0.8 km) proximity. The other two arroyos are far removed from the mill site and could not have received contamination from it. Principal component and cluster analysis indicated similarities in groundwater chemistry among the swale and the three arroyos that contrasted with groundwater chemistry at the disposal cell. Disposal cell groundwater is characterized by high uranium and bicarbonate concentrations, whereas that in remaining study areas is characterized by high sodium and sulfate, but lower uranium concentrations. Mancos Shale forms the bedrock in the region and contains elevated concentrations of the same chemical constituents that appear in the swale and arroyo groundwater. Dissolved sulfate in arroyo groundwater was depleted in sulfur‐34, in contrast to mill‐derived sulfate with more enriched sulfur‐34. Uranium‐234 to uranium‐238 activity ratios (ARs) were near the secular equilibrium value of 1 in mill site groundwater, whereas ARs in all arroyo groundwater samples exceeded 2. Elevated tritium activities present in mill site groundwater (49 to 142 pCi/L) are attributed to the mill being operated during atomic bomb testing in the 1950s and 1960s. The combined chemical and isotopic results indicate that groundwater in Many Devils Wash and the swale was likely derived from the Mancos Shale and not from the milling operation.

Multivariate Geostatistical Model for Groundwater Constituents in Texas

Although many studies have explored the quality of Texas groundwater, very few have investigated the concurrent distributions of more than one pollutant, which provides insight on the temporal and spatial behavior of constituents within and between aquifers. The purpose of this research is to study the multivariate spatial patterns of seven health-related Texas groundwater constituents, which are calcium (Ca), chloride (Cl), nitrate (NO3), sodium (Na), magnesium (Mg), sulfate (SO4), and potassium (K). Data is extracted from Texas Water Development Board’s database including nine years: 2000 through 2008. A multivariate geostatistical model was developed to examine the interactions between the constituents. The model had seven dependent variables—one for each of the constituents, and five independent variables: altitude, latitude, longitude, major aquifer and water level. Exploratory analyses show that the data has no temporal patterns, but hold spatial patterns as well as intrinsic correlation. The intrinsic correlation allowed for the use of a Kronecker form for the covariance matrix. The model was validated with a split-sample. Estimates of iteratively re-weighted generalized least squares converged after four iterations. Matern covariance function estimates are zero nugget, practical range is 44 miles, 0.8340 variance and kappa was fixed at 2. To show that our assumptions are reasonable and the choice of the model is appropriate, we perform residual validation and universal kriging. Moreover, prediction maps for the seven constituents are estimated from new locations data. The results point to an alarmingly increasing levels of these constituents’ concentrations, which calls for more intensive monitoring and groundwater management.

Mapping the potential human health implications of groundwater pollution in southern Sri Lanka

Abstract In southern Sri Lanka, irrigation influences the concentrations of faecal bacteria and inorganic toxic contaminants in groundwater. We develop a groundwater vulnerability map describing the potential human health implications of harmful constituents in the Uda Walawe Basin, by overlaying geological and land use data with information describing the irrigation system, the oxygen isotope composition of water bodies, and the concentrations of selected contaminants. Given the limited data available, we examine the spatial distribution of harmful constituents and the potential human health risks. Fluoride poisoning from groundwater is the greatest health threat in our study area, where fluoride concentrations ranging from 0.1 to 9.2 mg/L are associated with a geologic origin. Arsenic occurs in high concentrations, up to 0.4 mg/L, in areas with low recharge, although the source of arsenic is not clear. Nitrate concentrations are low, ranging from 0.4 to 23 mg/L, despite high fertilizer inputs, except in areas with low recharge and non-favourable reducing conditions, where concentrations up to 136 mg/L are found. Faecal bacteria decrease from surface water via shallow groundwater to deep groundwater. Irrigation water appears to play a major role in increasing microbial contamination and diluting inorganic constituents in groundwater. Hence, the most important determinants for mapping groundwater vulnerability are local geology and infiltration of irrigation water. The method we present provides a qualitative, yet practical, alternative to commonly used vulnerability mapping techniques for countries where high human health risk via consumption of groundwater is inevitable, and thus acts as a tool for selecting preventive and curative measures.

Hydrogeophysical investigations on the Pleistocene aquifer, Kom Hamada area, West Nile Delta, Egypt

Hydrogeophysical investigations of the Pleistocene aquifer at the Kom Hamada area, Egypt, have been conducted to determine the characteristics of groundwater. The main water-bearing formations in the study area are composed of Quaternary deposits. Water samples were taken and chemically analyzed at 29 sites. The constructed iso-salinity contour map of the study area showed an increase in salinity from 451.75 mg/l at eastern parts to 1,091.85 mg/l at western parts. The groundwater of the study area showed a hydrochemical evolution from Ca–HCO3 at the eastern side to Na–Cl at the western side. Some of groundwater constituents have high concentration values exceeding the safe limit for drinking. Eighteen vertical electrical soundings (VES) were conducted in the study area. These soundings were conducted near existing wells to obtain layer parameters of the various penetrated layers and to calculate the petrophysical characteristics of the aquifers. The resistivity of the first water-bearing layer ranges between 34 and 47 Ω m. The thickness of this layer ranges between 26 and 79 m. This layer represents the first aquifer, where it is followed by another water-bearing layer with resistivity ranges between 29 and 62 Ω m and extends downward. The two aquifers are hydraulically connected. Variation of the resistivities of these two water-bearing layers is mainly due to the lithological variation. The resistivity values along with the TDS values of the two water-bearing layers indicate fresh to brackish water types.