Constructing robust and efficient experimental designs in groundwater modeling using a Galerkin method, proper orthogonal decomposition, and metaheuristic algorithms.

Estimating parameters accurately in groundwater models for aquifers is challenging because the models are non-explicit solutions of complex partial differential equations. Modern research methods, such as Monte Carlo methods and metaheuristic algorithms, for searching an efficient design to estimate model parameters require hundreds, if not thousands of model calls, making the computational cost prohibitive. One method to circumvent the problem and gain valuable insight on the behavior of groundwater is to first apply a Galerkin method and convert the system of partial differential equations governing the flow to a discrete problem and then use a Proper Orthogonal Decomposition to project the high-dimensional model space of the original groundwater model to create a reduced groundwater model with much lower dimensions. The reduced model can be solved several orders of magnitude faster than the full model and able to provide an accurate estimate of the full model. The task is still challenging because the optimization problem is non-convex, non-differentiable and there are continuous variables and integer-valued variables to optimize. Following convention, heuristic algorithms and a combination is used search to find efficient designs for the reduced groundwater model using various optimality criteria. The main goals are to introduce new design criteria and the concept of design efficiency for experimental design research in hydrology. The two criteria have good utility but interestingly, do not seem to have been implemented in hydrology. In addition, design efficiency is introduced. Design efficiency is a method to assess how robust a design is under a change of criteria. The latter is an important issue because the design criterion may be subjectively selected and it is well known that an optimal design can perform poorly under another criterion. It is thus desirable that the implemented design has relatively high efficiencies under a few criteria. As applications, two heuristic algorithms are used to find optimal designs for a small synthetic aquifer design problem and a design problem for a large-scale groundwater model and assess their robustness properties to other optimality criteria. The results show the proof of concept is workable for finding a more informed and efficient model-based design for a water resource study.

Hydrogeochemistry Assessment of Shallow Groundwater and Human Health Threats in the Northwestern Ordos Basin, China.

Groundwater is the main sources of water supply for drinking purposes in the Ordos Basin in the northwestern part of China. In order to sustain and protect the quality of groundwater resources, shallow groundwater samples were collected and analyzed to identify the hydrogeochemical characteristics, and to evaluate health risk to human. Cluster analysis showed that the 134 groundwater samples were divided into three classes (i.e., class 1, class 2, class 3). The groundwater types are mostly characterized by SO4-Cl type and SO4 type, mixed HCO3 type. The primary natural mechanisms controlling the chemical compositions are water-rock interaction and evaporation-precipitation. The extremely high concentrations of sulfate could be caused by contamination from pyrite or from infiltration of sulfate from inorganic fertilizers or from wastewater discharges. Results of the assessment of the health risks for ingestion of Cl-, NO3-, F-, Cr, and As in drinking water indicated that the total health risks are beyond the US EPA acceptable level of 10-6 per year for consumption of groundwater sourced from all three cluster classes. The highest risks were for ingestion of arsenic and chromium in groundwater. The highest total risks to adults and children were 1.51 × 10-5 and 2.45 × 10-2 (class 1), 4.12 × 10-4 and 8.98 × 10-3 (class 2), 3.06 × 10-3 and 5.49 × 10-2 (class 3), respectively. The study showed that there is a high risk of health problems among the residents of the Ordos Basin in China that are ingesting contaminated drinking water, with the health risks to children higher than the risks to adults.

Health Risk Assessment of Heavy Metals in Groundwater of Industrial Township Virudhunagar, Tamil Nadu, India.

The present investigation deals with the health risk assessment due to the heavy metals (Cd, Cr, Cu, Co, Mn, Pb, Ni, and Zn) in groundwater in the industrial township of Virudhunagar district. Twenty groundwater samples were collected, and the measured concentration of the heavy metals follows the order Pb > Ni > Zn > Co > Cr > Cd > Cu > Mn. The metal pollution indices (heavy metal evaluation index, Heavy metal pollution index, degree of contamination) were calculated using the measured heavy metal concentrations. The samples collected nearer to the industrial zone have elevated concentrations of Pb, Cd, and Ni. The carcinogenic and noncarcinogenic risks were calculated based on the measured heavy metals concentration and average daily intake of water. The calculated carcinogenic risk values (5.66 × 10-3-1.56 × 10-2) (Pb, Cd, and Ni) exceed the acceptable limit of 10-6-10-4. The noncarcinogenic risk exceeds the acceptable limit of one for the heavy metals Pb and Cr. The higher carcinogenic and noncarcinogenic risk values reveal that the study area has health risks due to Pb, Cd, Ni, and Cr metals. Furthermore, factor analysis and cluster analysis showed that the industrial impact and wastage dumpsites are the prime sources for heavy metal contamination in groundwater of the study area.

Appraisal of subsurface hydrogeochemical processes in a geologically heterogeneous semi-arid region of south India based on mass transfer and fuzzy comprehensive modeling.

The main aim of the present study was to examine the quality of the groundwater and decipher the sources of groundwater fluoride through mass balance modeling based on fluoride exposure in a geologically heterogeneous semi-arid region of southern India. This was achieved by hydrogeochemical analysis, graphical methods, and mass transfer modeling approaches. Fuzzy comprehensive technique was applied to evaluate the quality of groundwater for groundwater management. In this regard, 61 groundwater samples were obtained from open wells and bore wells and analyzed for different physicochemical parameters. The major cation and anion abundances follow the order Na+ > Ca2+ > Mg2+ > K+ and Cl- > HCO3- > SO42- > NO3- > PO43-. About 88.4% and 34.4% of the total water samples were dominated with Na+ and Cl- ions in this region, respectively. The fluoride level in groundwater ranged from 0.10 to 3.30 mg/l with a mean value of 1.04 mg/l. Nearly 25% of the groundwater samples collected from 15 villages showed fluoride concentrations exceeding the maximum permissible limit of 1.5 mg/l as per the World Health Organization recommendations for human intake. More than 85% of the samples fell under strong acid (Cl- and SO42-) type. The amount of groundwater salinization in this region was 70.5% since the Revelle index (RI) was excess in the groundwater samples (RI > 0.5 meq/l). Silicate weathering, cation exchange, and gypsum dissolution were the dominant geogenic processes in the aquifer system influencing groundwater chemistry and nullified the possibility of carbonate dissolution. Saturation indices revealed the contribution of sequestration of CaCO3 in F- enrichment. Total dissolved solids showed strong positive correlations with Na+, Ca2+, Mg2+, Cl-, SO42- and NO3- indicating the contribution of anthropogenic inputs to groundwater chemistry in addition to geogenic sources. The results of the fuzzy comprehensive method indicated that 33% of the groundwater samples fell under fair water type, 2% and 11% of the samples fell under poor and very poor quality water types, respectively. Therefore, this work will be helpful for the decision-makers to plan for the sustainable management of groundwater resources.

Phenotypic and genotypic profile of the antimicrobial resistance of bacterial isolates and evaluation of physical and chemical potability indicators in groundwater in Brazil.

The aquatic environment has received increasing attention regarding the evolution of bacterial resistance, either as a source of resistance genes or as a matrix for the dissemination of these genes. We evaluated the physicochemical, microbiological and antimicrobial resistance characteristics of 160 samples from alternative water well solutions. According to Ordinance 2914/2011 - MS, 44 (27.5%) samples were considered unsafe if at least one physicochemical parameter exceeded permissible limits. Escherichia coli were found in 30.6% of the unregistered housing estates (UHE) and 1.9% of the local sanitary surveillance system (RW). The total of 158 bacterial strains were isolated from 13 (25%) RW and 68 (63%) UHE, 132 of which (83.5%) were obtained from UHE samples. In the investigation of resistance genes, tetA, qnrS and qnrB genes were detected in three, one and eight isolates, respectively. Our results emphasize the importance of constant surveillance and control of the quality of water supplies.

Assessment of hydrogeochemical characteristics and quality of groundwater resources in relation to risk of gastric cancer: comparative analysis of high- and low-risk areas in Iran.

The chemical quality of groundwater supplies in two high-risk area (HRA) and low-risk area (LRA) for gastric cancer in Iran was assessed through hydrogeochemical analysis and water quality indices. For this aim, Piper and Schoeller diagrams and water quality index (WQI) were applied. In addition, exposure to nitrate via drinking water and its corresponding risk were also assessed using Monte Carlo simulation technique. Data on physicochemical properties of groundwater resources were obtained from Iran Water Resources Management Company. Sampling and analysis of tap water for nitrate concentration were conducted in two cities of Shiraz (as a representative of LRA) and Ardabil (as a representative of HRA). According to Piper diagrams, the dominant hydrogeochemical facies of groundwater supplies in HRA and LRA were Na-HCO3 (43.75%) and Ca-HCO3 (41.77%), respectively. The predominant cations in groundwater resources of HRA were found to be Na+ (68.06%) and Ca2+ (31.94%). For LRA, the typical cations were in decreasing trend: Ca2+ (39.64%) > Mg2+ (18.35%) > Na+ (17.26%). For two areas, HCO3-, SO42- and Cl- were, respectively, the most frequent anions. Two-sample Wilcoxon test showed that there were statistically significant difference between two areas in terms of anions and cations concentrations (p value < 0.05). The mean of total hardness (Ca2+ + Mg2+) concentration of water supplies in LRA (528.1 mg/L) was higher than HRA (263.1 mg/L), whereas the mean of Na+ concentration was found to be lower in LRA (90.6 mg/L) compared with HRA (108.1 mg/L). The sum of nitrate intake and its risk in LRA was higher than HRA. WQI results showed that drinking water quality in HRA and LRA ranged from excellent to poor and most water resources were of a good quality class. Further studies are suggested to investigate the role of drinking water in the etiology of gastric cancer in Iran.

Spatial distribution of quality of groundwater and probabilistic non-carcinogenic risk from a rural dry climatic region of South India.

Having safe drinking water is a fundamental human right, which affects directly the human health. In view of this, an effort has been made for understanding the spatial distribution of quality of groundwater in a rural dry climatic region of Andhra Pradesh, South India, and associated health risks with respect to pollutants of NO3- and F-, which cause the potential production of non-carcinogenic risk, using entropy-weighted water quality index (EWWQI) and total chronic hazard index (TCHI), where the population rely on the groundwater resource for drinking purpose. Groundwater quality observed from the present study region has an alkaline character with brackish type. The concentrations of K+, HCO3-, TDS, Na+, NO3-, F-, Mg2+ and Cl- come under the non-permissible limits in 100%, 100%, 96.67%, 90%, 73.33%, 46.67%, 13.33% and 6.67% of the groundwater samples, which deteriorate the groundwater quality, causing the health disorders. The overall groundwater quality computed, using EWWQI, ranges from 53.64 to 216.59 (122.22), which classifies the region spatially into 55%, 10% and 35% due to influences of the geogenic and anthropogenic pollutants, which are the respective medium, poor and very poor groundwater quality types prescribed for potable water. According to the TCHI evaluated with respect to pollutants of NO3- and F-, the values of TCHI for men (1.194 to 4030), women (1.411 to 4.763) and children (1.614 to 5.449) are more than its acceptable limit of one. So, the health risk of non-carcinogenic is spatially in the decreasing order of children > women > men, depending upon their sensitiveness to pollutants and also their body weights. Further, the spatial distributions of both TCH1 and EWWQI are more or less similar, following the pollution activities, which help for establishment of the fact to recognize the intensity of various vulnerable zones. Therefore, the present study suggests the suitable environmental safety measures to control the NO3-- and F--contaminated drinking water and subsequently to increase the health conditions.

Health Risk Assessment, Composition, and Distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in Drinking Water of Southern Jharkhand, East India.

The studies on polycyclic aromatic hydrocarbons (PAHs) occurrence, distribution, health risk, and composition in drinking water are limited in India and worldwide. The main objective of this study was to find the contaminant sources, composition, health risk, and distribution of USEPA's 16 priority pollutant PAHs in the drinking water samples collected between July 2019 to September 2019 from six districts of Southern Jharkhand. The Σ16PAHs mean ± standard deviation [SD] concentration values were ordered as East Singhbhum (ES) (21.5 ± 14.8 ng L-1) > West Singhbhum (WS) (16.57 ± 13.21 ng L-1) > Saraikela Kharsawan (SK) (11.48 ± 9.92 ng L-1) > Khunti (KH) (10.32 ± 9.09 ng L-1) > Simdega (SM) (9.96 ± 7.85 ng L-1) > Gumla (GU) (9.41 ± 8.63 ng L-1). The results show that ES and WS districts' groundwater samples were more contaminated by the PAHs, which may be attributed to the presence of many small-, medium-, and large-scale industries and high vehicular density in these districts. The concentrations of lower molecular weight ring (3-rings) and middle molecular weight ring (4-rings) PAHs were dominant throughout all drinking samples. The concentration of the 3-ring PAH Anthracene and 4-ring PAH Fluoranthene were dominant in all districts. The molecular ratios suggested that the potential sources of PAHs are fuel combustion and coal, grass, and wood burning. Risk assessment shows that the incremental lifetime cancer risk and risk index (RI) were ranged from 0.02 × 10-10 to 4.93 × 10-10 for children and 0.01 × 10-10 to 2.98 × 10-10 for adults. The RI values for seven carcinogenic PAHs were 8.83 × 10-10 for children and 7.38 × 10-10 for adults. Although the carcinogenic risks were within the permissible values, chronic exposure to PAHs through the ingestion of drinking water could still be a human health concern.

Assessment of groundwater safety surrounding contaminated water storage sites using multivariate statistical analysis and Heckman selection model: a case study of Kazakhstan.

Petrochemical enterprises in Kazakhstan discharge polluted wastewater into special recipients. Contaminants infiltrate through the soil into the groundwater, which potentially affects public health and environment safety. This paper presents the evaluation of a 7-year monitoring program from one of the factories and includes nineteen variables from nine wells during 2013-2019. Several multivariate statistical techniques were used to analyse the data: Pearson's correlation matrix, principal component analysis and cluster analysis. The analysis made it possible to specify the contribution of each contaminant to the overall pollution and to identify the most polluted sites. The results also show that concentrations of pollutants in groundwater exceeded both the World Health Organization and Kazakhstani standards for drinking water. For example, average exceedance for total petroleum hydrocarbons was 4 times, for total dissolved solids-5 times, for chlorides-9 times, for sodium-6 times, and total hardness was more than 6 times. It is concluded that host geology and effluents from the petrochemical industrial cluster influence the groundwater quality. Heckman two-step regression analysis was applied to assess the bias of completed analysis for each pollutant, especially to determine a contribution of toxic pollutants into total contamination. The study confirms a high loading of anthropogenic contamination to groundwater from the petrochemical industry coupled with natural geochemical processes.

[Metal content and trace elements in groundwater supply of the island of El Hierro (Canary Islands, Spain).] / Contenido de metales y elementos traza en aguas subterráneas de abastecimiento de la isla de El Hierro (islas Canarias, España).

OBJECTIVE: Volcanic eruptions are a natural source of substances potentially dangerous to human health. The island of El Hierro (Canary Islands, Spain) suffered a marine volcanic eruption in 2012, making it necessary to monitor the levels of certain elements that can alter the quality of groundwater supply. The objective of this work was to determine the content of metals and trace elements in the groundwater supply of the Isla del Hierro and to check if they met the quality parameters established in Spanish legislation. METHODS: The content of metals and trace elements (aluminum, lead, cadmium, calcium, potassium, sodium, magnesium, boron, barium, cobalt, chromium, copper, iron, lithium, manganese, molybdenum, nickel, strontium, vanadium, zinc, fluorine) in a total of 60 samples of groundwater supply and agriculture from six different sampling points on the island. The determination was carried out by inductively coupled plasma optical emission spectrophotometry (ICP-OES) and by fluoride ion selective potentiometry. The data were statistically analyzed applying the Kolmogorov-Smirnov test, Levene's statistic, Kruskal-Wallis, Mann-Whitney U, ANOVA and Tukey's test. Significant differences were those that met p<0.05. RESULTS: The highest mean concentration of lead was recorded in the Tigaday samples (0.003±0.0005 mg/L), finding statistically significant differences (p<0.05) in the lead levels between the sampling points. The elements analyzed were below the parametric values set in Royal Decree 140/2003. CONCLUSIONS: The results obtained reflect that, in all the samples analyzed, the quality parameters established in the Spanish legislation (RD 140/2003) are met, being, therefore, waters suitable for human consumption.

OBJETIVO: Las erupciones volcánicas son una fuente natural de sustancias potencialmente peligrosas para la salud humana. La isla de El Hierro (Islas Canarias, España) sufrió una erupción volcánica marina en el año 2012, siendo necesaria la monitorización de los niveles de ciertos elementos que pueden alterar la calidad de las aguas subterráneas de abastecimiento. El objetivo de este trabajo fue determinar el contenido de metales y elementos traza de las aguas subterráneas de abastecimiento de la Isla del Hierro y comprobar si cumplían los parámetros de calidad establecidos en la legislación española. METODOS: Se determinó el contenido de metales y elementos traza (aluminio, plomo, cadmio, calcio, potasio, sodio, magnesio, boro, bario, cobalto, cromo, cobre, hierro, litio, manganeso, molibdeno, níquel, estroncio, vanadio, zinc, flúor) en un total de 60 muestras de agua subterránea de abastecimiento y de agricultura procedentes de seis puntos diferentes de muestreo de la isla. La determinación fue llevada a cabo mediante espectrofotometría de emisión óptica de plasma acoplado inductivamente (ICP-OES) y mediante potenciometría de ion selectivo de fluoruro. Los datos fueron analizados estadísticamente aplicando los tests de Kolmogorov-Smirnov, estadístico de Levene, Kruskal-Wallis, U de Mann-Whitney, ANOVA y test de Tukey. Se consideraron diferencias significativas aquellas que cumplían p<0,05. RESULTADOS: La mayor concentración media de plomo se registró en las muestras de Tigaday (0,003±0,0005 mg/L), encontrándose diferencias estadísticamente significativas (p<0,05) en los niveles de plomo entre los puntos de muestreo. Los elementos analizados se encontraban por debajo de los valores paramétricos fijados en el Real Decreto 140/2003. CONCLUSIONES: Los resultados obtenidos reflejan que, en todas las muestras analizadas, los parámetros de calidad establecidos en la legislación española (RD 140/2003) se cumplen, siendo, por lo tanto, aguas aptas para el consumo humano.

Application of isotope techniques to enhance the conceptual hydrogeological model and to assess groundwater sustainability in the Pampean plain in Córdoba, Argentina.

The objective of this work is to enhance the conceptual hydrogeological model in the Río Cuarto River basin by using isotope and hydrochemical techniques. The precipitation pattern, as reflected in the average values of δ 2H and δ 18O in stations located in the plains and in the mountains, showed an isotope depletion from the East to the West, attributed to continental and altitude effects. Groundwater quality is mainly the result of two controlling factors: lithology and flow distances from recharge. The aquifers show fresh calcium/sodium bicarbonate water in the upper and medium basin (coarse fluvial sediments) which evolve to sodium sulphate and chloride waters in the low basin (mainly loess and fine alluvial sediments). The confined aquifer systems in the lower basin (C and D systems) averaged more negative stable isotope values, indicating that groundwater recharged during colder climatic conditions (Pleistocene period). Groundwater dating with 14C confirmed that groundwater ages range from modern to 45,000 years BP showing that as the water flows towards deeper layers and farther from the mountainous recharge area, groundwater age increases. The confined aquifers can potentially be exploited in order to partly cover different water needs but they should be managed in a sustainable way.

A comprehensive review of water quality monitoring and assessment in Nigeria.

Nigeria is the most populated black nation in the world with about 199 million people. About 66.3 million Nigerians do not have access to safe drinking water. In this study, research findings on water quality monitoring and assessment in Nigeria over the past two decades were systematically reviewed. There are still grave enforcement issues in Nigeria as quality guidelines are still being contravened at no cost to the infringer due to the corrupt socio-political circumstances of the country. The quality of surface water, groundwater, rainwater and commercially available water was discussed in line with their pollution sources. The quality of surface water was generally poor. Groundwater pollution has come due to landfill leachate, oil and gas exploration and production, sewage and hydrogeological interactions of the groundwater with the base rock. The hydrogeological effect has led to the observation of lead and barium in groundwater in many locations across the country. The main issue with rainwater in Nigeria is the low pH but it was observed to be fairly clean. Commercially available water (bottled or sachet) is currently the best source of drinking water for the Nigerian populace. Bottled water quality is higher than for sachet water and the latter largely influenced by microbe contamination. Future perspectives in water quality monitoring and assessment are suggested in the evaluation of emerging contaminants and micro-pollutants and the utilisation of internet-enabled technologies.

A review on the potential sources and health implications of fluoride in groundwater of Sub-Saharan Africa.

Groundwater is a major source of drinking water for millions of people around the world. Over 400 million people in Africa depend solely on it as their main source of water supply. Fluoride is a common contaminant in groundwater. In low concentration (0.5-1.0 mg/L), fluoride is needed by humans for healthy development of bones and teeth, however, a concentration >1.5 mg/L has been linked with several fluorosis and non-fluorosis diseases. Dental and skeletal fluorosis are the major fluorosis diseases commonly reported with the consumption of fluoride-rich water. Although fluoride intake through other pathways such as the drinking of tea and eating of vegetables have been reported, the drinking of fluoride-rich water remains the major pathway of fluoride into humans. Cases of high fluoride levels in groundwater have been reported in almost all the sub-Saharan Africa region but it is more prevalent in East African countries, Sudan and South Africa. Although fluoride is present in surface water mostly in the East African Rift Valley across different countries in East Africa, its significant or high levels are usually associated with groundwater. Geogenic sources such as fluorite, apatite, biotite, amphibole, micas, topaz, cryolite, muscovite and fluorspar have been identified as the major sources of fluoride in groundwater. High fluoride levels have been reported across sub Saharan Africa, with generally higher levels in East Africa resulting from the volcanic activities in the rift system. Dental fluorosis has been reported in many sub-Saharan African countries including South Africa, Tanzania, Uganda, Ethiopia, Kenya, Sudan, Niger, Nigeria, Benin, Ghana and Malawi. Geothermal temperature has been regarded as one of the driving forces for high fluoride levels recorded in groundwater from deep aquifers and geothermal springs. The most affected people with the consumption of fluoride-rich water are the poor with low socioeconomic status who live in rural areas. Some of the proposed alternative sources include rainwater and fog water harvesting and blending of water from various sources. Low-cost and sustainable deflouridation technique remains one of the best ways to treat fluoride contaminated water either at communal level or at the point-of-use.

Assessment of groundwater quality based on principal component analysis and pollution source-based examination: a case study in Ho Chi Minh City, Vietnam.

The current study aimed to assess the quality of apportion pollution sources and examine the impacts of anthropogenic activities on groundwater. The study was implemented in two sequential steps of (1) bulk examination of groundwater quality followed by principal component analysis/factor analysis (PCA/FA) to apportion pollution sources and (2) pollution source-based examination to assess the effects of anthropogenic activities. Well-water samples were taken in Ho Chi Minh City, Vietnam, in 2015 (233 samples) and 2019 (20 samples) and analyzed for 8 and 15 water quality parameters, respectively. The results showed that 99% of studied wells had pH value lower than the permissible limit, and 29, 20, 15, and 14% of studied wells had concentrations of Fe, NH4+, COD (chemical oxygen demand), and coliform, respectively, higher than the maximum permissible limit. PCA/FA revealed that three pollution sources, ranked in the order of importance: agricultural, urban, and industrial activities, could mainly contribute to enriching the pollutant concentrations of groundwater. While agricultural activities may contaminate groundwater with organic substances, the urban area may enrich bacterial-pathogen density such as E. coli and coliform, and the industrial area may contribute to contaminating groundwater with some inorganic parameters. Groundwater quality index and ANOVA showed that groundwater of the studied area was poor to very poor in quality and that in the agricultural area was the worst of the three land-use types. In brief, the groundwater quality in the studied area was degraded and agricultural activities were the most important factor causing the degradation followed by urban and industrial activities.

Hydrogeochemical processes and suitability assessment of groundwater in the Jiaodong Peninsula, China.

Groundwater is the primary source of water for domestic use and agricultural irrigation in Jiaodong Peninsula. This study collected 80 groundwater samples from Jiaodong Peninsula to characterize groundwater hydrogeochemical processes and the suitability of groundwater for domestic use and agricultural irrigation. The groundwater of Jiaodong Peninsula was categorized as slightly alkaline freshwater, with a Piper diagram classifying most samples as SO4·Cl-Ca·Mg and HCO3-Ca·Mg types. Major ions were Ca2+, Na+, SO42-, and HCO3-. The major processes driving the hydrochemistry of groundwater were identified as water-rock interactions as well as evaporation. The dissolution of silicate and cation exchange were the predominant hydrogeochemical processes responsible for groundwater chemistry. Four water samples showed seawater intrusion and some indicated pollution from anthropogenic activities such as industry, agriculture, and domestic sewage discharge. Overall, it was found that groundwater in most areas of Jiaodong Peninsula is suitable for domestic use and agricultural irrigation.

Assessment of Groundwater Quality in the Talensi District, Northern Ghana.

A comprehensive chemical quality assessment of groundwater resources in the Talensi District has been conducted using conventional graphical methods and multivariate statistical techniques. The study sought to determine the main controls of groundwater chemistry and its suitability for domestic and irrigation purposes in the district. Silicate and carbonate mineral weathering were identified as the main controls on groundwater chemistry in the district, with reverse ion exchange also playing a role. High nitrate and lead levels observed have been associated with agrochemicals and wastewater from farms and homes. Three main flow regimes have been identified with Q-mode cluster analysis, in which mixed cation water types have been revealed, where areas designated as recharge zones are dominated by Na+ + K+-Mg2+-HCO3 - fresh water types characterised by low mineralisation and pH, which evolve into Mg2+- Na+ + K+- HCO3 - fresh water type with corresponding increased mineralisation of the groundwater. Based on the water quality index (WQI) technique modified for the district and an interpolation technique using ordinary kriging developed from a well-fitted exponential semivariogram for the estimated WQIs, the groundwater quality has been spatially classified as generally 'good' to 'excellent' for domestic purposes. Generally, the quality of groundwater for domestic usage deteriorates as one moves towards the north of the district, whereas waters in the east and west present the best quality. Classifications based on the United States Salinity Laboratory (USSL), Wilcox, and Doneen diagrams suggest that groundwater from the unconfined aquifers of the district is of excellent quality for irrigation purposes.

Global Research Trends and Hotspots on Submarine Groundwater Discharge (SGD): A Bibliometric Analysis.

Submarine groundwater discharge (SGD), a major component of the hydrological cycle, has significant impacts on the sustainable development of the marine environment. This study aimed to examine the literature characteristics and research hotspots of SGD based on Web of Science's citation database from 1998-2019. With systematic bibliometric analysis, insights were made into multiple aspects including research output, subject categories, journals, countries/territories, institutions, authors, and hotspots and research trends. Results showed that the current amount of publications on SGD has increased exponentially. The characteristics of multi-subject, active international and inter-institutional collaborations were identified. There were 11 core journals publishing the research on SGD, and the number of covered journals increased linearly from 1998. USA had distinct advantages in publication outputs and took the core position in international collaborations. At present, the research hotspots of SGD mainly include the following: dynamics process and estimation of SGD with hydrogeological methods, tracer techniques, geochemical process in subterranean estuary, and dissolved material inputs to coastal waters via SGD. Citation analysis implied much development space in carbon flux transported by SGD and the implement of head as groundwater tracer. These results provided an instructive perspective of the present situation and future research direction on SGD.

Comparing Single-Objective Optimization Protocols for Calibrating the Birds Nest Aquifer Model-A Problem Having Multiple Local Optima.

To best represent reality, simulation models of environmental and health-related systems might be very nonlinear. Model calibration ideally identifies globally optimal sets of parameters to use for subsequent prediction. For a nonlinear system having multiple local optima, calibration can be tedious. For such a system, we contrast calibration results from PEST, a commonly used automated parameter estimation program versus several meta-heuristic global optimizers available as external packages for the Python computer language-the Gray Wolf Optimization (GWO) algorithm; the DYCORS optimizer framework with a Radial Basis Function surrogate simulator (DRB); and particle swarm optimization (PSO). We ran each optimizer 15 times, with nearly 10,000 MODFLOW simulations per run for the global optimizers, to calibrate a steady-state, groundwater flow simulation model of the complex Birds Nest aquifer, a three-layer system having 8 horizontal hydraulic conductivity zones and 25 head observation locations. In calibrating the eight hydraulic conductivity values, GWO averaged the best root mean squared error (RMSE) between observed and simulated heads-20 percent better (lower) than the next lowest optimizer, DRB. The best PEST run matched the best GWO RMSE, but both the average PEST RMSE and the range of PEST RMSE results were an order of magnitude larger than any of the global optimizers.

Delineation of contaminated aquifers using integrated geophysical methods in Northeast Punjab, Pakistan.

A decline in surface water sources in Pakistan is continuously causing the over-extraction of groundwater resources which is in turn costing the saltwater intrusion in many areas of the country. The saltwater intrusion is a major problem in sustainable groundwater development. The application of electrical resistivity methods is one of the best known geophysical approaches in groundwater study. Considering the accuracy in extraction of freshwater resources, the use of resistivity methods is highly successful to delineate the fresh-saline aquifer boundary. An integrated geophysical study of VES and ERI methods was carried out through the analysis and interpretation of resistivity data using Schlumberger array. The main purpose of this investigation was to delineate the fresh/saline aquifer zones for exploitation and management of fresh water resources in the Upper Bari Doab, northeast Punjab, Pakistan. The results suggest that sudden drop in resistivity values caused by the solute salts indicates the saline aquifer, whereas high resistivity values above a specific range reveal the fresh water. However, the overlapping of fresh/saline aquifers caused by the formation resistivity was delineated through confident solutions of the D-Z parameters computed from the VES data. A four-layered unified model of the subsurface geologic formation was constrained by the calibration between formation resistivity and borehole lithologs. i.e., sand and gravel-sand containing fresh water, clay-sand with brackish water, and clay having saline water. The aquifer yield contained within the fresh/saline aquifers was measured by the hydraulic parameters. The fresh-saline interface demarcated by the resistivity methods was confirmed by the geochemical method and the local hydrogeological data. The proposed geophysical approach can delineate the fresh-saline boundary with 90% confidence in any homogeneous or heterogeneous aquifer system.

Evaluating the suitability of urban groundwater resources for drinking water and irrigation purposes: an integrated approach in the Agro-Aversano area of Southern Italy.

Deterioration of groundwater quality due to the introduction of pollutants from natural and anthropic sources has become a major environmental issue. We tested three methodologies in assessing groundwater quality and intrinsic aquifer vulnerability in the Agro-Aversano area (Southern Italy). A geographic information system (GIS)-based groundwater quality index (GQI) was realized to assess groundwater quality for drinking and irrigation use and, in parallel, standard SINTACS was applied to evaluate the intrinsic vulnerability of the aquifer. Nitrate concentrations and sodium absorption ratio (SAR) in groundwater samples were used to verify the reliability of vulnerability data. GQI analysis pointed to a general poor quality of groundwater both for drinking and irrigation use, especially in sub-urban areas. The spatial pattern of water quality from GQI analysis was positively related to nitrate and fluoride concentrations for drinking use and to bicarbonate and sodium concentrations for irrigation use, whose levels exceeded the WHO and FAO recommended thresholds, respectively. Standard SINTACS was found to be inadequate for describing the aquifer state, its results showing no correlation with nitrate concentration or SAR. Because of this inconsistency, we tested a novel approach combining GQI with SINTACS analysis. Results showed positive correlation with nitrate (r = 0.63) and SAR (r = 0.64) contents, thus pointing to combined SINTACS-GQI as a more reliable approach than standard methodologies.