Model reconstruction of nitrate pollution of riverbank filtration using 15N and 18O data,Karany, Czech Republic

Stable isotopes of O (δ¹⁸O) in water and N (δ¹⁵N) in ${\text{NO}}_3^{-}$ have been used as natural indigenous groundwater tracers for sources of water and of ${\text{NO}}_3^{-}$ at two riverbank filtration (RBF) water supply systems. Both RBF systems (Skorkov and Sojovice) have wells in unconsolidated Quaternary sediments close to the Jizera River (Czech Republic) that have been affected by increasing ${\text{NO}}_3^{-}$ concentrations. The area is underlain by Turonian sandstones and marls that form a deeper bedrock aquifer. Sources of ${\text{NO}}_3^{-}$ are local sewerage systems and landfills (point sources) and seasonal application of manure and inorganic fertilizers (diffuse sources).At RBF Skorkov recharge to wells can be modelled using a two-component model with 60% river water contribution and 40% of very shallow groundwater with an average residence time of one month. During periods of abundant precipitation, groundwater originates entirely from the unsaturated zone of the Quaternary aquifer; extensive pumping for over 40 a has created new, bypassing flow paths that preferentially drain the contaminated unsaturated zone. During dry periods, wells are recharged by longer residence time groundwater from the Quaternary aquifer.At RBF Sojovice there is an additional recharge component of groundwater from the Turonian aquifer, which is sandier at this locality; this contains denitrified ${\text{NO}}_3^{-}$ with highly positive δ¹⁵N values.     

Geochemistry of surface and ground water in Guiyang,China: Water/rock interaction and pollution in a karst hydrological system

The chemical compositions of the surface/ground water of Guiyang, the capital city of Guizhou Province, China are dominated by Ca²⁺, Mg²⁺, ${\text{HCO}}_3^{-}\text{and}{\text{SO}}_4^{2-}$, which have been derived largely from chemical weathering of carbonate rocks (limestone and dolomite). The production of ${\text{SO}}_4^{2-}$ has multiple origins, mainly from dissolution of sulfate evaporites, oxidation of sulfide minerals and organic S in the strata, and anthropogenic sources. Most ground water is exposed to soil CO₂ and, therefore, the H₂CO₃ which attacks minerals contains much soil C. In addition, the H₂SO₄ produced as a result of the oxidation of sulfides in S-rich coal seams and/or organic S, is believed to be associated with the chemical weathering of rocks. The major anthropogenic components in the surface and ground water include K⁺, Na⁺, Cl⁻, ${\text{SO}}_4^{2-}\text{and}{\text{NO}}_3^{-}$, with Cl⁻ and ${\text{NO}}_3^{-}$ being the main contributors to ground water pollution in Guiyang and its adjacent areas. The seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities. The higher content of ${\text{NO}}_3^{-}$ in ground water compared to surface water during the summer and winter seasons, indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates.     

Isotopic tracing of perchlorate sources in groundwater from Pomona,California

The groundwater of Pomona, California, is contaminated with perchlorate (${\text{ClO}}_4^{-}$). This water is treated to reduce the ${\text{ClO}}_4^{-}$ concentration to less than 6 μg L⁻¹ for compliance with California Department of Public Health drinking water regulations. A study of the isotopic composition of oxygen and chlorine in ${\text{ClO}}_4^{-}$ has been conducted to determine the source of the contamination. Isotopic compositions were measured for ${\text{ClO}}_4^{-}$ samples extracted from 14 wells, yielding ranges of δ¹⁸O values from −10.8‰ to −8.0‰, Δ¹⁷O values from +4.6‰ to +7.5‰, and δ³⁷Cl values from −12.8‰ to −8.9‰. Evaluation of mixing proportions using published isotopic data for three ${\text{ClO}}_4^{-}$ end-members (synthetic, Atacama, and indigenous natural ${\text{ClO}}_4^{-}$) indicates that contamination is dominantly (85–89%) Atacama ${\text{ClO}}_4^{-}$ derived from past use of imported Chilean nitrate fertilizer in citrus cultivation. This interpretation is consistent with (1) aerial photography archives showing extensive citrus fields surrounding Pomona in the early- to mid-20th century, (2) mass-balance estimates for ${\text{ClO}}_4^{-}$, and (3) numerical hydrologic models yielding travel-times for ${\text{ClO}}_4^{-}$ from fields to wells that are in the range of 15 to >100 years. The hydrologic models predict that ${\text{ClO}}_4^{-}$ contamination of Pomona groundwater will persist for decades into the future.     

Fluoride and arsenic hydrogeochemistry of groundwater at Yuncheng basin,Northern China

High fluoride and arsenic concentrations in groundwater have led to serious health problems to local inhabitants at Yuncheng basin, Northern China. In this study, groundwater with high fluoride and arsenic concentration at Yuncheng basin was investigated. A majority of the samples (over 60%) belong to HCO₃ type water. The predominant water type for the shallow groundwater collected from southern and eastern mountain areas was Ca/Mg-Ca-HCO₃ types. For the shallow groundwater from flow through and discharge area it is Na-HCO₃/SO₄-Cl/SO₄/Cl type. The predominant water type for the intermediate and deep groundwater is of Na/Ca/Mg-Ca-HCO₃ type. According to our field investigation, fluoride concentration in groundwater ranges between 0.31 and 14.2 mg/L, and arsenic concentration ranges between 0.243 and 153.7 μg/L. Out of seventy collected groundwater samples, there are 31 samples that exceed the World Health Organization (WHO) standard of 1.5 mg/L for fluoride, and 15 samples exceeds the WHO standard of 10 μg/L for arsenic. Over 40% of high fluoride and arsenic groundwater are related to the Na-HCO₃ type water, and the other fifty percent associated with Na-SO₄-Cl/HCO₃-SO₄-Cl type water; little relation was found in calcium bicarbonate type water. A moderate positive correlation between fluoride and arsenic with pH were found in this study. It is due to the pH-dependent adsorption characteristics of F and As onto the oxide surfaces in the sediments. The observed negative correlation between fluoride and calcium could stem from the dissolution equilibrium of fluorite. The high concentration of bicarbonate in groundwater can serve as a powerful competitor and lead to the enrichment of fluoride and arsenic in groundwater. Most of the groundwater with high fluoride or arsenic content has nitrate content about or over 10 mg/L which, together with the observed positive correlations between nitrate and fluoride/arsenic, are indicative of common source of manmade pollution and of prevailing condition of leaching in the study area.