Contaminated groundwater is considered as one of the most important pathways of human exposure to the geogenic contaminants. Present study has been conducted in a part of Indus basin to investigate the presence and spatial distribution of arsenic (As) and other trace metals in groundwater. The As concentration varies from bdl-255.6 μg/L and 24.6% of the 73 collected groundwater samples have As above world health organization (WHO) guideline of 10 μg/L. High concentration of As is found along the newer alluvium of Ravi River. As is found with high bicarbonate (HCO3−) and Iron (Fe) and low nitrate (NO3−) indicating reductive dissolution of Fe bearing minerals. However, silicate weathering along with high sulphate (SO42) and positive oxidation-reduction potential (ORP) indicates mixed redox conditions. Weathering of minerals along with other major hydrogeochemical process are responsible for composition of groundwater. With 31.5% of the samples, sodium bicarbonate (Na–HCO3) is the major water facies followed by magnesium bicarbonate (Mg–HCO3) in 30% of samples. As, Fe and other trace metals including copper (Cu), cadmium (Cd), chromium (Cr), zinc (Zn) were used to calculate the health risk for children and adults in the region. Out of 73 samples, 58% has high Fe, 32.8% has high Zn, and 4.1% has high Cd which are above the prescribed limits of WHO guidelines. Health risk of the population has been assessed using chronic dose index (CDI), hazardous quotients (HQ) and hazardous index (HI) for children and adults. The mean CDI values follows the order as Fe > Zn > Cu > As > Cr > Cd, while the HQ values indicates high As hazards for both children and adults. 43.8% of the groundwater samples have high HI for adults, however, 49.3% has high HI for children indicating higher risk for children compared to adults. A large-scale testing should be prioritized to test the wells for As and other trace metals in the study region to reduce health risks.

High concentration of fluoride (up to 20.9 mg/L) in groundwater with significant variation (p = 5.9E-128) among samples was reported from Birbhum district, an acknowledged fluoride endemic region in India. The groundwater samples (N = 368) were grouped based on their hydrochemical properties and aquifer geology for hydro-geochemical characterization. Friedman’s test showed p < 0.0001 confidence level which indicates that fluoride concentration among geological groups and water groups are independent. Bland-Altman plot was used to study the inter-relationships among the groups through bias value (∂) and limit of agreement (LoA). Among the geological groups, laterites and granite-gneiss groups exhibited statistically significantly difference in fluoride geochemistry; whereas the younger and older alluvium groups displayed similar characteristics. The fluoride concentration was found to be in the order Lateritic > Granite-gneiss > Older alluvium ≥ Younger alluvium. Dissolution of minerals (such as fluorite, biotite) in laterite sheeted basalt, and granite-gneiss is the main source of groundwater fluoride in the region. Fluoride concentration is also influenced by depth of water table. Hydrochemical study indicated that fluoride concentration was higher in Na–HCO₃ than in Ca–SO₄ and Ca–HCO₃ type of groundwater. The fluoride concentration were positively correlated with Na⁺ and pH and negatively correlated with the Ca²⁺ and Mg²⁺ signifying linkage with halite dissolution and calcite, dolomite precipitation. Geostatistical mapping of WQI through empirical bayesian kriging (EBK) with respect to regional optimal guideline value (0.73 mg/L) classified that groundwater in some parts of the district are unfit for drinking purpose. Health survey (N = 1767) based on Dean’s criteria for dental fluorosis indicated presence of slight to moderate dental hazard. Besides, providing baseline data for management of groundwater quality in the study area, the study demonstrated the applicability of Bland-Altman analysis and empirical bayesian kriging (EBK) in delineation and interpolation of fluoride contaminated region.

The feasibility of reducing children’s exposure to lead (Pb) polluted soil in New Orleans is tested. Childcare centers (median = 48 children) are often located in former residences. The extent of soil Pb was determined by selecting centers in both the core and outlying areas. The initial 558 mg/kg median soil Pb (range 14–3692 mg/kg) decreased to median 4.1 mg/kg (range 2.2–26.1 mg/kg) after intervention with geotextile covered by 15 cm of river alluvium. Pb loading decreased from a median of 4887 μg/m² (454 μg/ft²) range 603–56650 μg/m² (56–5263 μg/ft²) to a median of 398 μg/m² (37 μg/ft²) range 86–980 μg/m² (8–91 μg/ft²). Multi-Response Permutation Procedures indicate similar (P-values = 0.160–0.231) soil Pb at childcare centers compared to soil Pb of nearby residential communities. At ∼$100 per child, soil Pb and surface loading were reduced within hours, advancing an upstream intervention conceptualization about Pb exposure prevention.

The phenomenon of “equifinality for different parameters” limits the link between parameters and catchment characteristics; however, solving the equifinality problem is a major challenge in the development, generalization, and application of a model. This study focused on the Yanhe River Watershed to investigate the time-varying characteristics of sensitivity and identifiability of SWAT (Soil and Water Assessment Tool) runoff and sediment parameters based on the Sobol’ and generalized likelihood uncertainty estimation methods. The results indicate that (i) the nondominated sorting genetic algorithm-II has good adaptability and reliability in parameter calibration of the SWAT model in the Yanhe River Watershed. The evaluation indicators (Nash–Sutcliffe efficiency, R², and percent bias) of monthly runoff and sediment in the Ganguyi hydrological station were all satisfactory per the SWAT model during the calibration and validation periods. (ii) The interaction between runoff and sediment parameters is a crucial reason for parameter sensitivity, which has obvious time-varying characteristics and is largely dependent on precipitation in the Yanhe River Watershed. Temporal and spatial variability of precipitation should be considered in the detailed analysis of parameter identifiability, and watershed managers should not ignore changes in the runoff process when regulating sediment. (iii) Only a relatively small number of parameters can be identified in the runoff and sediment simulation process of the Yanhe River Watershed, such as CN2 (initial soil conservation service runoff curve number for moisture condition II), CH_K2 (effective hydraulic conductivity in main channel alluvium), ALPHA_BF (baseflow alpha factor), USLE_C (cover and management factor), USLE_P (support practice factor), and USLE_K (soil erodibility factor), due to high surface runoff, reduced lag time, reduced low flows, increased peak flows, and channel erosion, respectively. More importantly, there is a strong positive correlation between parameter identifiability and parameter sensitivity. Both are effective methods of parameter diagnosis, but the identifiability of parameters is not equivalent to its sensitivity. Our results strongly suggest that a detailed parameter sensitivity and identifiability analysis is a critical step in improving hydrological model performance to reduce the risk of “equifinality for different parameters” while articulating all relevant hydrological processes.

This work was undertaken to study the influence of soil type and its physical and chemical properties on uranium sorption and bioavailability, in order to reduce the uncertainty associated with this parameter in risk assessment models and safe food production. The tests were conducted on three types of Serbian soils: alluvium, chernozem, and gajnjaca, from which 67 samples were taken. Dominant factors of uranium mobilisation: the specific content of total/available form of uranium and phosphorus, the degree of acidity (pHKCl), and humus content and their correlation, were analysed. Content of available uranium form, according to the type of soil decreases in the following order: gajnjaca > alluvium > chernozem. It was found the medium correlation between pH values and available content of uranium in chernozem and gajnjaca, statistically significant at the level of significance of 99% and the alluvium at the level of significance of 95%. Correlation coefficients in all cases were negative, indicating that the reduction in pH increases the mobility of uranium and thus its availability for the adoption of the plants. Soil pH was the only dominant factor that significantly controlled the uranium value with no further significant contribution of other soil parameters.

Small- and medium-scale mining operations in Guyana have increased significantly since the late 1980s. The majority of these gold mining operations utilize mercury (Hg) amalgamation methods in the recovery process, raising the question as to the significance of Hg inputs to the environment from mining activities. In March and April, 2001, 168 samples were collected from floodplain, sand bar, and channel bed deposits along a 350 km reach of the Mazaruni River and a 160 km reach of the Essequibo River. Distinct trends in the geochemical data suggest that much of the Hg found in the alluvial deposits is related to anthropogenic sources, including (1) Hg concentrations in floodplain, channel bed and sand bar deposits locally exceed background values defined by ferralitic soils; (2) core data reveal that Hg concentrations within floodplain deposits have increased in recent years; and (3) high Hg concentrations along the channels can be attributed to the influx of material from tributaries affected by mining operations, or to mining activities along the rivers. Recent investigations in Amazonia have argued that Hg from amalgamation mining represents a small portion of the total Hg load to riverine systems, the majority coming from the erosion of Hg enriched upland soils within deforested terrain. Geochemical data from the Essequibo and Mazaruni Rivers suggest that Hg from mining may be a more significant source in Guyana where large-scale deforestation is limited. However, it is unclear whether the increased Hg represents the direct input associated with the amalgamation process, or Hg associated with the erosion of soils and sediments that results from activities that accompany mining.

Groundwater and saline water interaction is the most common processes in the coastal aquifers that alters the quality of aquifer waters. The quaternary alluvium aquifer system is a significant water resource of southeast coastal Tamil Nadu that provides water supplies for industrial, agriculture, and domestic utilities. Hydrogeochemical investigations were attempted to analyze groundwater–saline water interactions for which a total of three hundred and sixty samples representing surface water, pore water, and groundwater samples collected from three significant locations (location A, B, and C) and analyzed for major ion concentrations. Piper plot infers surface and pore water samples representing saline water type (Na-Cl) in all the three locations due to tidal variation and sand dominant surface layer. Groundwater samples represent (Ca-HCO₃) type at location A due to fresh groundwater discharge, mixed or subterranean estuary (Ca, Mg-Cl, HCO₃) at location B due to conversion of freshwater (Ca-HCO₃) at low tide to saline water (Na-Cl) at high tide, and saline (Na-Cl) water at location C due to proximity and influence of tides. The Cl⁻/HCO₃⁻ vs. Cl⁻ plot represents two water types, such as fresh groundwater (0.5) and strongly affected by seawater intrusion (6.6). The plot (Ca²⁺+Mg²⁺)/(K⁺+Na⁺) vs. log Cl⁻ represents freshwater in location A, mixing in location B, and saline water in location C. Groundwater samples observed to be fresh in location A (20.0 km away from the coast), recirculated in location B (9.0 km away from the coast), and saline in location C (0.5 km away from the coast).

Gold mining operations in the northern Black Hills of South Dakota resulted in the discharge of arsenopyrite-bearing mine tailings into Whitewood Creek from 1876 to 1977. Those tailings were transported further downstream along the Belle Fourche River, the Cheyenne River, and the Missouri River. An estimated 110 million metric tons of tailings remain stored in alluvial deposits of the Belle Fourche and Cheyenne Rivers. Pore-water dialysis samplers were deployed in the channel and backwaters of the Belle Fourche and Cheyenne Rivers to determine temporal and seasonal changes in the geochemistry of groundwater in alluvial sediments. Alluvial sediment adjacent to the dialysis samplers were cored for geochemical analysis. In comparison to US Environmental Protection Agency drinking water standards and reference concentrations of alluvial sediment not containing mine tailings, the Belle Fourche River sites had elevated concentrations of arsenic in pore water (2570 μg/L compared to 10 μg/L) and sediment (1010 ppm compared to < 34 ppm), respectively. Pore water arsenic concentration was affected by dissolution of iron oxyhydroxides under reducing conditions. Sequential extraction of iron and arsenic from sediment cores indicates that substantial quantities of soluble metals were present. Dissolution of arsenic sorbed to alluvial sediment particles appears to be affected by changing groundwater levels that cause shifts in redox conditions. Bioreductive processes did not appear to be a substantial transport pathway but could affect speciation of arsenic, especially at the Cheyenne River sampling sites where microbial activity was determined to be greater than at Belle Fourche sampling sites.

Leachate from unlined or leaky landfills can create groundwater contaminant plumes that last decades to centuries. Understanding the dynamics of leachate movement in space and time is essential for monitoring, planning and management, and assessment of risk to groundwater and surface-water resources. Over a 23.4-year period (1986–2010), the spatial extent of the Norman Landfill leachate plume increased at a rate of 7800 m²/year and expanded by 878 %, from an area of 20,800 m²in 1986 to 203,400 m²in 2010. A linear plume velocity of 40.2 m/year was calculated that compared favorably to a groundwater-seepage velocity of 55.2 m/year. Plume-scale hydraulic conductivity values representative of actual hydrogeological conditions in the alluvium ranged from 7.0 × 10⁻⁵to 7.5 × 10⁻⁴ m/s, with a median of 2.0 × 10⁻⁴ m/s. Analyses of field-measured and calculated plume-scale hydraulic conductivity distributions indicate that the upper percentiles of field-measured values should be considered to assess rates of plume-scale migration, spreading, and biodegradation. A pattern of increasing Cl⁻concentrations during dry periods and decreasing Cl⁻concentrations during wet periods was observed in groundwater beneath the landfill. The opposite occurred in groundwater downgradient from the landfill; that is, Cl⁻concentrations in groundwater downgradient from the landfill decreased during dry periods and increased during wet periods. This pattern of changing Cl⁻concentrations in response to wet and dry periods indicates that the landfill retains or absorbs leachate during dry periods and produces lower concentrated leachate downgradient. During wet periods, the landfill receives more recharge which dilutes leachate in the landfill but increases leachate migration from the landfill and produces a more concentrated contaminant plume. This approach of quantifying plume expansion, migration, and concentration during variable hydrologic conditions provides increased understanding of plume behavior and migration potential and may be applied at less monitored landfill sites to evaluate potential risks of contamination to downgradient receptors.

Pollution by heavy metals (Co, Cu, Ni, Pb, Sb and Zn), Ra-226 and U was studied in eight profiles (1.0-1.8 m deep) in the floodplain sediments of the Ploucnice River, the Czech Republic. The element concentrations were processed by establishing local geochemical background functions from non-polluted overbank fines yet not affected by reductimorphic processes and a subsequent calculation of enrichment factors in the polluted strata. In the case of Cu and Ni, the geogenic variability of the watershed (Cretaceous marine sediments and Cenozoic volcanics and their weathering products) was successfully handled using different background functions in two parts of the studied area, which allowed us to decipher the anthropogenic and natural portions of the heavy metals and hence evaluate the history of pollution. The upper course of the river drains an extensive area of so-called chemical mining (underground acid leaching of low-grade U-bearing sediments) and hydrometallurgical processing in Straz pod Ralskem that started in the late 1960s and operated without waste-processing plants up to 1989. The river system has consequently been impacted by U and gamma-emitting Ra-226 and obviously also by divalent heavy metals (Co, Ni, Zn). In the entire study area, that pollution was preceded by increasing levels of Cu, Pb and Sb and by the Pb-206/Pb-207 ratio decreasing from 1.20 towards 1.17, which had started earlier in the twentieth century before the U mining. That pre-mining pollution can be attributed to diffuse anthropogenic activities of regional or continental importance. The most recent Pb-206/Pb-207 ratio in the Ploucnice alluvium coincides with that of peatbog profiles on the borders of the Czech Republic, showing the usefulness of floodplains as pollution archives of widespread regional to continental pollution signals.