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.

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.

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^- > SO₄^2- > NO₃^- > PO₄^3-. 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 SO₄^2-) 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^-, SO₄^2- and NO^3- 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.

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.

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.

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 Σ_16PAHs 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.

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.

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.

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.

[Metal content and trace elements in groundwater supply of the island of El Hierro (Canary Islands, Spain).]

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.

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 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 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^-, SO₄^2- 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.

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⁺, SO₄^2-, 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.

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.

Multi-indicator analysis of the influence of old municipal landfill sites on the aquatic environment: case study

The study aim was to analyse the influence of a municipal solid waste landfill site in operation for over 10 years on the aquatic environment using multiple indicators. The water around the landfill area must be controlled due to the possibility of leachate interaction with harmful substances in the environment. The tests were carried out on the basis of 24 indicators, of which four were the most significant: depth of groundwater retention, ammoniacal nitrogen (NH4-N), dissolved oxygen (DO), and polycyclic aromatic hydrocarbons (PAHs). The assessment of the quality of the surface water and groundwater and the analysis of the leachate pollution indices enabled the interpretation of the influence of a specific municipal waste landfill on the nearby water environment condition, despite not exceeding the permissible content at the highest average concentration of NH4-N at 1.34 mg L-1. The differences were significant at the level of p < 0.05 in the content of DO in the water below the landfill. The concentration of NH4-N in the groundwater below the landfill was statistically significantly correlated with the depth of the groundwater deposits (r = 0.609). Similarly, the surface water below the landfill site showed a statistically significant relation in the piezometer, which was also below the landfill, to ammoniacal nitrogen (r = 0.749). This result confirmed the statistically significant differences in the aquatic environment and the correlations with NH4-N and that, below the landfill, the penetration water seepage is moderate with a low waste accumulation not exceeding 10 Mg per day.

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.

Adsorption of nitrate, phosphate, nickel and lead on soils: Risk of groundwater contamination

Agricultural activities pose a significant risk of groundwater pollution. Indeed, fertilizers and treated wastewater used for irrigation are, in part, responsible for the deterioration of groundwater and surface water quality. In some cases, soil may provide a protective barrier against this pollution, but this depends on the nature of the soil and the contaminant. This work presents the effect of the soil clay content on the retention of four different pollutants in order to evaluate the risk they represent for the groundwater. These contaminants are generated by two main agricultural activities: 1/soil fertilization with phosphate and nitrate fertilizers and 2/irrigation with treated wastewater in which heavy metals such as nickel and lead are persistent. Firstly, the characterization of the sand and clay used in this work was performed and showed a cation exchange capacity of 1.24 and 25 meq/100 g, a specific surface area of 0.12 and 67.98 m²/g and a percentage of organic matter of 0.15 and 2% for sand and clay, respectively. The retention isotherms on all pollutants and the Langmuir, Freundlich, Freundlich-Langmuir, Hill and Koble-Corrigan models were applied. All experimental isotherms have been successfully adjusted using the Koble-Corrigan expression. The amounts of nitrates, phosphates, nickel and lead retained by the sandy soil, for an initial pollutant concentration equal to 1 meq/L, were evaluated at 0.29, 3.89, 5.97 and 8.56 μeq/g respectively. In contact with a soil containing 30% clay, the adsorbed amounts were estimated at 3.55, 15.00, 6.97 and 8.79 μeq/g for nitrates, phosphates, nickel and lead, respectively. These results mean that the pollutants that pose the greatest risk of groundwater contamination when carried by water through sandy soil are classified as follows lead < nickel < phosphate < nitrate while for a clayey soil, the classification becomes as follows: phosphates < lead < nickel < nitrate.

Spatial patterns, geochemical evolution and quality of groundwater in Delta State, Niger Delta, Nigeria: implication for groundwater management

Delta State of the Niger Delta, Nigeria, is an oil exploration and production region that is characterized by huge revenue generation but with its attendant waste generation and oil spillage that impact the environment. The variability in the hydrochemical characteristics, hydrochemical controlling processes and quality in space has been investigated. The pH of the groundwater samples ranged from slightly acidic to slightly alkaline nature. Biological oxygen demand and chemical oxygen demand of the coastal area are higher than those of the inland area indicating more domestic and industrial contamination. Total dissolved solid values across the region indicated fresh and brackish water for the coastal area and fresh water only for the inland area. The orders of abundance of the cations and anions for the coastal and inland areas are Ca>Mg>Na>K/Cl>HCO₃>SO₄>NO₃ and Na>Ca>K>Mg/HCO₃>Cl>NO₃>SO₄ respectively. A Piper diagram identified four hydrochemical facies, namely CaHCO₃, NaHCO₃, NaCl and CaMgClSO₄. Ionic cross plots and correlation matrix revealed that the groundwater chemistry of the inland area is predominantly influenced by silicate weathering and ion exchange processes while those of the coastal area are influenced by silicate weathering, ion exchange processes and seawater tidal flushing. The groundwater from the coastal area is more polluted by heavy metals than those from the inland area. The observed variability may be attributed to effects of industrial wastes and exploration activities. In terms of water quality for domestic and irrigation, the groundwater of the coastal and the inland areas are not generally potable and suitable as drinking and irrigation water sources.

Application of Dempster-Shafer theory and fuzzy analytic hierarchy process for evaluating the effects of geological formation units on groundwater quality

This study investigates the impacts of different geological units on groundwater quality of an aquifer in southern Iran. The Kriging interpolation technique with a Gaussian semivariogram model was employed to prepare groundwater maps for different water quality constituents. In the next stage, two different models based on fuzzy analytic hierarchy process (AHP) and Dempster-Shafer theory (DST) were used to evaluate the overall water quality index based on the World Health Organization's drinking water standard in different parts of the aquifer. The DST model was able to generate water quality maps with 99.5%, 99%, and 95% confidence levels. The water quality maps were subsequently compared with the geology map of the area to determine the effects of different soil types on the water quality of the aquifer. Both methods showed poor water quality indices in the areas with an Asmari formation containing elevated levels of chloride and sodium ions. Comparison of water quality maps generated by the fuzzy-AHP and DST model revealed that the DST could more reliably handle the uncertainty in the water quality data, and thus was able to generate more accurate water quality maps. Increasing the confidence level in the DST model yielded water quality maps with a decreased overall water quality index. Results of this study could assist water management practices to generate water quality maps for their groundwater resources with confidence levels commensurate socio-economic importance of the region.

On the problem of the spatial distribution delineation of the groundwater quality indicators via multivariate statistical and geostatistical approaches

This paper highlights the advantages of multivariate statistical and geostatistical methods to compile the hydro-geochemical properties of groundwater. A total of 123 samples were collected from wells located in Saveh aquifer, in 2015. Seven parameters including total dissolved solids (TDS), sodium adsorption ratio( SAR), electrical conductivity (EC), sodium (Na⁺), total hardness (TH), chloride (Cl^-), and sulfate (SO₄^2-) were analyzed, compiled, and interpreted statistically and geostatistically. At first, factor analysis gave rise to produce a factor representing 94% of the variability. Also, variography was calculated and compiled to define spatial regression and experimental variograms were plotted by GS⁺ software, then, the best theoretical models were fitted on the variograms and an estimation map was prepared based on geostatistical relationship presented in the paper. Smoothing effect is one of the main drawbacks of forward geostatistical methods, on the contrary, inversed methods are subjected to no smoothing effect. Results showed that geostatistical inversed methods could reveal more reliable results than forward methods. Eventually, the map of the estimated factor, as well as error maps, was compiled. According to the evaluation of fractal dimensions, the estimated factor explained the variability of all hydrogeochemical parameters and groundwater quality was categorized as the safe, normal, and anomalous class, ranged from - 1.10 to 1.10, 1.11 to 3.1, and more than 3.1, respectively.

Groundwater quality assessment in an industrial hotspot through interdisciplinary techniques

Dependency on groundwater has increased due to unprecedented growth of industries as well as settlements. Therefore, assessment of groundwater quality to determine its impact on human and environment has become essential. The major objective of this study was to frame a methodology for complete assessment of groundwater quality in a highly industrialized area comprising of iron, steel, fertilizer, cement, chemical, heavy machinery manufacturing, thermal power, coal mining, and allied industries. Physico-chemical parameters of water samples were analyzed from strategic locations during pre- and post-monsoon seasons. The primary analysis through the water quality index showed 50% of the sampling locations in pre-monsoon and 65% in post-monsoon seasons have very poor quality. Hence, the health risk calculated through hazard index indicates that the water is unsafe for drinking. Chemical indices such as sodium percentage, sodium adsorption ratio, residual sodium carbonate, permeability index, and magnesium hazard suggest that the water can be used for irrigation. High corrosivity ratio at 90% sampling locations specifies its unsuitability for use in industrial production. Factor analysis and other statistical methods justified that the pollution of groundwater was attributed to geogenic, as well as anthropogenic, activities. This research demonstrates the usefulness of interdisciplinary techniques for complete assessment of groundwater quality and representation of complex data set into a presentable and understandable form for proper communication with public, regulatory authorities, as well as policy makers, responsible for water management.

New light in the dark - a proposed multidisciplinary framework for studying functional ecology of groundwater fauna

Groundwaters provide the vast majority of unfrozen freshwater resources on the planet, but our knowledge of subsurface ecosystems is surprisingly limited. Stygofauna, or stygobionts -subterranean obligate aquatic animals - provide ecosystem services such as grazing biofilms and maintaining water quality, but we know little about how their ecosystems function. The cryptic nature of groundwaters, together with the high degree of local endemism and stygofaunal site-specific adaptations, represent major obstacles for the field. To overcome these challenges, and integrate biodiversity and ecosystem function, requires a holistic design drawing on classical ecology, taxonomy, molecular ecology and geochemistry. This study presents an approach based on the integration of existing concepts in groundwater ecology with three more novel scientific techniques: compound specific stable isotope analysis (CSIA) of amino acids, radiocarbon analysis (¹⁴C) and DNA analyses of environmental samples, stygofauna and gut contents. The combination of these techniques allows elucidation of aspects of ecosystem function that are often obscured in small invertebrates and cryptic systems. Carbon (δ¹³C) and nitrogen (δ¹⁵N) CSIA provides a linkage between biogeochemical patterns and ecological dynamics. It allows the identification of stygofaunal food web structures and energy flows based on the metabolic pathway of specific amino groups. Concurrently, ¹⁴C provides complementary data on the carbon recycling and incorporation within the stygobiotic trophic webs. Changes in groundwater environmental conditions (e.g. aquifer recharge), and subsequent community adaptations, can be pinpointed via the measurementof the radiocarbon fingerprint of water, sediment and specimens. DNA analyses are a rapidly expanding approach in ecology. eDNA is mainly employed as a biomonitoring tool, while metabarcoding of individuals and/or gut contents provides insight into diet regimes. In all cases, the application of the approaches in combination provides more powerful data than any one alone. By combining quantitative (CSIA and ¹⁴C) and qualitative (eDNA and DNA metabarcoding) approaches via Bayesian Mixing Models (BMM), linkages can be made between community composition, energy and nutrient sources in the system, and trophic function. This suggested multidisciplinary design will contribute to a more thorough comprehension of the biogeochemical and ecological patterns within these undervalued but essential ecosystems.

Bayesian Hierarchical Models as Tools to Evaluate the Association Between Groundwater Quality and the Occurrence of Type 2 Diabetes in Rural Saskatchewan, Canada

There is growing interest in the role of environmental exposures in the development of diabetes. Previous studies in rural Saskatchewan have raised concerns over drinking water contaminants, including arsenic, which has been identified as a possible risk factor for diabetes. Using administrative health and water-quality surveillance data from rural Saskatchewan, an ecological study design was used to investigate associations between concentrations of arsenic, water health standards and aesthetic objectives, and the incidence and prevalence of diabetes. Mixtures of contaminants measured as health standards or as aesthetic objectives were summarized using principal component (PC) analysis. Associations were modeled using Bayesian hierarchical models incorporating both spatial and unstructured random effects, standardized for age and sex, and adjusted for socioeconomic factors and a surrogate measure for smoking rates. Arsenic was not associated with an increased risk of diabetes. For private wells, having groundwater arsenic concentrations in the highest quintile was associated with decreased cumulative diabetes incidence for 2010-2012 (risk ratio [RR] = 0.854, 95% credible interval [CrI] 0.761-0.958) compared with the lowest quintile, a result inconsistent with other studies. For public water supplies, having a first PC score for health standards (primarily summarized selenium, nitrate, and lead) in the third quintile (RR = 1.101, 95% CrI 1.019-1.188), fourth quintile (RR = 1.088, 95% CrI 1.003-1.180), or fifth quintile (RR = 1.115, 95% CrI 1.026-1.213) was associated with an increase in 2010 diabetes prevalence compared with the first quintile. An increase in the PC scores for the third aesthetic objective in private wells (characterized primarily by iron and manganese) was associated with decreased diabetes incidence, although a meaningful dose-response relationship was not evident. No other associations between PC scores for health standards or aesthetic objectives from public or private water supplies and diabetes were identified.

Guideline levels for PFOA and PFOS in drinking water: the role of scientific uncertainty, risk assessment decisions, and social factors

Communities across the U.S. are discovering drinking water contaminated by perfluoroalkyl and polyfluoroalkyl substances (PFAS) and determining appropriate actions. There are currently no federal PFAS drinking water standards despite widespread drinking water contamination, ubiquitous population-level exposure, and toxicological and epidemiological evidence of adverse health effects. Absent federal PFAS standards, multiple U.S. states have developed their own health-based water guideline levels to guide decisions about contaminated site cleanup and drinking water surveillance and treatment. We examined perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) water guideline levels developed by the U.S. Environmental Protection Agency (EPA) and state agencies to protect people drinking the water, and summarized how and why these levels differ. We referenced documents and tables released in June 2018 by the Interstate Technology and Regulatory Council (ITRC) to identify states that have drinking water and groundwater guideline levels for PFOA and/or PFOS that differ from EPA's health advisories (HAs). We also gathered assessment documents from state websites and contacted state environmental and health agencies to identify and confirm current guidelines. Seven states have developed their own water guideline levels for PFOA and/or PFOS ranging from 13 to 1000 ng/L, compared to EPA's HA of 70 ng/L for both compounds individually or combined. We find that the development of PFAS guideline levels via exposure and hazard assessment decisions is influenced by multiple scientific, technical, and social factors, including managing scientific uncertainty, technical decisions and capacity, and social, political, and economic influences from involved stakeholders. Assessments by multiple states and academic scientists suggest that EPA's HA is not sufficiently protective. The ability of states to develop their own guideline levels and standards provides diverse risk assessment approaches as models for other state and federal regulators, while a sufficiently protective, scientifically sound, and enforceable federal standard would provide more consistent protection.

Applying multivariate statistics for identification of groundwater resources and qualities in NW Turkey

This study, performed in Çanakkale-Ezine in NW of Turkey, analyzes the physicochemical properties of 37 groundwater wells. These 37 wells were chosen to represent each geological unit in the study area. The main purpose of the study and its contribution to the literature is to produce information about the resources and availability of groundwater by using multivariate statistical methods and lithology. For determination hydrochemical facies of groundwater, Piper trilinear diagram was used. Gibbs diagram was applied for determining the mechanism of groundwater chemistry and diagram showed that the interaction of rock-water is more dominant in the study area. Multivariate statistics were applied to physicochemical properties for identification origins of waters. According to the Piper diagram, 16 of the wells were identified as Ca-HCO₃ type, 13 of them as Ca-Cl type, 5 of them as mixed Ca-Mg-Cl type, 2 of them as Na-Cl type, and 1 as Ca-Na-HCO₃ type. In the study with the purpose of determining the resources of groundwater, the physicochemical properties of the wells are analyzed with hierarchical cluster (HCA) and non-hierarchical cluster (K-means) methods, and the resources are associated with the lithology based on these methods. A total of 37 wells are divided into five different clusters through the HCA method. Further, for the interpretation of the resources of the groundwater, the facies of the waters on the Piper diagram are evaluated based on the five clusters generated through the HCA method and on the lithology. In the study, the results obtained from the K-means method are not significant and in line with the lithology for the interpretation of the resources of the groundwater. In conclusion, this study with limited dataset reveals that using HCA method is very effective to identify the origins of groundwater and present the association with lithology.

A health-based regulatory chain framework to evaluate international pesticide groundwater regulations integrating soil and drinking water standards

Pesticide residues in groundwater, mainly transported from contaminated soil, may threaten drinking water sources and cause adverse health effects. Therefore, pesticide groundwater standards were implemented by international environmental agencies to ensure the quality of groundwater, which serves as the direct drinking water source in many countries. However, regulatory inconsistencies are always found among groundwater, soil, drinking water, and even health standards due to the lack of communication among the regulatory processes. This study first developed a health-based regulatory chain framework to analyze pesticide groundwater regulations integrating soil, drinking water, and health regulations. Six regulatory indexes associated with probabilistic risk assessments and pesticide transport modeling were constructed to evaluate the performance of pesticide groundwater regulations identified from 56 countries. Worldwide pesticide groundwater regulations were analyzed by quantifying the impact on the downstream (exposure pathways in general) pesticide drinking water standards and human health and the influence from upstream (environmental pathways in general) soil regulations. The results indicated that in general, worldwide pesticide soil regulations do not encompass a sufficient number of pesticides or provide appropriate standard values to be compatible with groundwater regulations. The computed indexes between pesticide groundwater and drinking water regulations indicated more positive results than soil regulations because most European nations have groundwater regulations that are compatible with those of drinking water. However, most pesticide groundwater regulations could not protect human health according to the health-based indexes. Hopefully, the regulatory framework developed in this study will help environmental agencies comprehensively evaluate and establish pesticide groundwater regulations.

Monitoring and assessment of groundwater quality in a khondalitic terrain, Andhra Pradesh, India

The groundwater quality assessment for the drinking and irrigation purpose is carried out in the Kandivalasa River Sub Basin covered with khondalitic suite (Garneti ferrous, Sillimanite, Gneiss) of rocks, near Cheepurupalli town of Vizianagaram district, Andhra Pradesh, India. The analysis for the groundwater quality for drinking has shown the slightly alkaline nature and high values of alkalinity in the study area. A very high concentration of total dissolved solids value is observed at one pocket where there has been contamination by many fertilizer industries located nearby the study area. The groundwater is highly affected by the nitrate. Higher fluoride values are obtained at few pockets. Most of the samples in the study area are categorized as very hard category. According to the Piper trilinear diagram, it can be observed that the carbonate hardness and secondary salinity have occupied at major part of study area. From the analysis of sodium adsorption ratio, salinity hazard, sodium percentage, residual sodium carbonate, and Kelly's ratio, all the groundwater samples except at few locations fell under the category of good to excellent for irrigation. The prepared integrated groundwater quality maps for the drinking purpose and agricultural purposes are indicating that, by and large, the low-lying areas are having poor groundwater quality than the uplands for drinking as well as agricultural needs which means that the groundwater quality of the basin is following the topography.

Temporal Variability of Faecal Contamination from On-Site Sanitation Systems in the Groundwater of Northern Thailand

We investigated the impacts of on-site sanitation systems to local groundwater. In this year-long study, we monitored the response of faecal contamination levels to hydroclimatological factors including rainfall and groundwater table. Concentration of faecal indicators-E. coli (ESC), Enterococcus (ENT), nitrate-in thirteen pairs of shallow and deep wells were determined every 7-14 days. All samples from shallow wells were tested positive for faecal contamination (ESC and ENT > 1 MPN/100 mL) but concentration varies. A maximum of 24,000 MPN/100 mL were recorded in some shallow wells. Water from deep wells showed lower susceptibility to contamination with only 4 and 23% of samples tested positive for ESC and ENT, respectively. Concentrations of ESC and ENT were lower too, with a maximum of 5 MPN/100 mL and 28 MPN/100 mL, respectively. Fluctuation in contamination among the wells was described by four archetypal responses to hydroclimatological forcing: (i) flushing during the onset of wet season, (ii) dilution over the course of the wet season, (iii) concentration during the dry season, and (iv) synoptic response to storms. Previous studies attempting to link the prevalence of faecal/waterborne diseases and temporal factors (e.g., dry vs wet season) have produced differing outcomes. Our study may help explain the relevant hydrological mechanisms leading to these varying observations. Presently, most communities in Thailand have access to 'improved' sanitation systems. However, due to the unsustainable implementation of these systems, the otherwise viable drinking-water resources in the form of the abundant local groundwater has become a genuine health hazard.

Optimal groundwater security management policies by control of inexact health risks under dual uncertainty in slope factors

Groundwater remediation is a complicated system with time-consuming and costly challenges, which should be carefully controlled by appropriate groundwater management. This study develops an integrated optimization method for groundwater remediation management regarding cost, contamination distribution and health risk under multiple uncertainties. The integration of health risk into groundwater remediation optimization management is capable of not only adequately considering the influence of health risk on optimal remediation strategies, but also simultaneously completing remediation optimization design and risk assessment. A fuzzy chance-constrained programming approach is presented to handle multiple uncertain properties in the process of health risk assessment. The capabilities and effectiveness of the developed method are illustrated through an application of a naphthalene contaminated case in Anhui, China. Results indicate that (a) the pump-and-treat remediation system leads to a low naphthalene contamination but high remediation cost for a short-time remediation, and natural attenuation significantly affects naphthalene removal from groundwater for a long-time remediation; (b) the weighting coefficients have significant influences on the remediation cost and the performances both for naphthalene concentrations and health risks; (c) an increased level of slope factor (sf) for naphthalene corresponds to more optimal strategies characterized by higher environmental benefits and lower economic sacrifice. The developed method could be simultaneously beneficial for public health and environmental protection. Decision makers could obtain the most appropriate remediation strategies according to their specific requirements with high flexibility of economic, environmental, and risk concerns.

Remediating Contaminant Plumes in Groundwater with Shallow Excavations Containing Coarse Reactive Media

A groundwater flow and mass transport model tested the capability of shallow excavations filled with coarse, reactive media to remediate a hypothetical unconfined aquifer with a maximum saturated thickness of 5 m. Modeled as contaminant sinks, the rectangular excavations were 10 m downgradient of an initial contaminant plume originating from a source at the top of the aquifer. The initial plume was approximately 259 m long, 23 m wide, and 5 m thick, with a downgradient tip located approximately 100 m upgradient of the site boundary. The smallest trench capable of preventing offsite migration was 11 m long (measured perpendicular to groundwater flow), 4 m wide (measured parallel to groundwater flow), and 3 m deep. Results of this study suggest that shallow trenches filled with coarse filter media that partially penetrate unconfined aquifers may be a viable alternative for remediating contaminated groundwater at some sites.

Indexing method for assessment of pollution potential of leachate from non-engineered landfill sites and its effect on ground water quality

Dumping of solid waste in a non-engineered landfill site often leads to contamination of ground water due to leachate percolation into ground water. The present paper assesses the pollution potential of leachate generated from three non-engineered landfill sites located in the Tricity region (one each in cities of Chandigarh, Mohali and Panchkula) of Northern India and its possible effects of contamination of groundwater. Analysis of physico-chemical properties of leachate from all the three landfill sites and the surrounding groundwater samples from five different downwind distances from each of the landfill sites were collected and tested to determine the leachate pollution index (LPI) and the water quality index (WQI). The Leachate Pollution Index values of 26.1, 27 and 27.8 respectively for landfill sites of Chandigarh (CHD), Mohali (MOH) and Panchkula (PKL) cities showed that the leachate generated are contaminated. The average pH values of the leachate samples over the sampling period (9.2 for CHD, 8.97 for MOH and 8.9 for PKL) show an alkaline nature indicating that all the three landfill sites could be classified as mature to old stage. The WQI calculated over the different downwind distances from the contamination sites showed that the quality of the groundwater improved with an increase in the downwind distance. Principal component analysis (PCA) carried out established major components mainly from natural and anthropogenic sources with cumulative variance of 88% for Chandigarh, 87.1% for Mohali and 87.8% for Panchkula. Hierarchical cluster analysis (HCA) identifies three distinct cluster types for the groundwater samples. These clusters corresponds to a relatively low pollution, moderate pollution and high pollution regions. It is suggested that all the three non-engineered landfill sites be converted to engineered landfill sites to prevent groundwater contamination and also new sites be considered for construction of these engineered landfill sites as the present dumpsites are nearing the end of their lifespan capacity.

Natural and anthropogenic factors affecting the shallow groundwater quality in a typical irrigation area with reclaimed water, North China Plain

In this study, the hydrochemical characteristics of shallow groundwater were analyzed to get insight into the factors affecting groundwater quality in a typical agricultural dominated area of the North China Plain. Forty-four shallow groundwater samples were collected for chemical analysis. The water type changes from Ca·Na-HCO₃ type in grass land to Ca·Na-Cl (+NO₃) type and Na (Ca)-Cl (+NO₃+SO₄) type in construction and facility agricultural land, indicating the influence of human activities. The factor analysis and geostatistical analysis revealed that the two major factors contributing to the groundwater hydrochemical compositions were the water-rock interaction and contamination from sewage discharge and agricultural fertilizers. The major ions (F, HCO₃) and trace element (As) in the shallow groundwater represented the natural origin, while the nitrate and sulfate concentrations were related to the application of fertilizer and sewage discharge in the facility agricultural area, which was mainly affected by the human activities. The values of pH, total dissolved solids, electric conductivity, and conventional component (K, Ca, Na, Mg, Cl) in shallow groundwater increased from grass land and cultivated land, to construction land and to facility agriculture which were originated from the combination sources of natural processes (e.g., water-rock interaction) and human activities (e.g., domestic effluents). The study indicated that both natural processes and human activities had influences on the groundwater hydrochemical compositions in shallow groundwater, while anthropogenic processes had more contribution, especially in the reclaimed water irrigation area.

Quality of tube well water intended for irrigation and human consumption with special emphasis on arsenic contamination at the area of Punjab, Pakistan

In the present study, the tube well water quality and the associated health risks, emphasizing on arsenic contamination, were investigated in rural and urban samples from Tehsil Mailsi located in Punjab, Pakistan. Arsenic concentrations (μg/L) were ranged from 12 to 448.5 and which exceeded the WHO recommended limit (10 μg/L) in all cases. The calculated average daily dose (3.3 × 10^-0.4 to 1.2 × 10^-0.2 mg/kg day) and hazard quotient (1.1-40) reflected the potential health risk to local population due to tube well water consumption as drinking purpose. Sodium percent (Na%), sodium absorption ratio, residual sodium carbonate, Kelly's index and magnesium absorption ratio were also determined to assess the suitability of tube well water for irrigation purpose. The resulting piper plot revealed the Na-Ca-HCO₃ type water chemistry of the area and generally alkaline environment. The spatial distribution of arsenic in the tube well waters pinpoints the significant contribution of anthropogenic activities to arsenic pollution. Nevertheless, different statistical tools, including principal component analysis, hierarchical cluster analysis and correlation matrices, revealed the contribution of both natural and anthropogenic activities and alkaline type of aquifers toward the high level of arsenic contamination.

Groundwater quality in Ghaziabad district, Uttar Pradesh, India: Multivariate and health risk assessment

This study aimed to assess the quality of groundwater and potential health risk due to ingestion of heavy metals in the peri-urban and urban-industrial clusters of Ghaziabad district, Uttar Pradesh, India. Furthermore, the study aimed to evaluate heavy metals sources and their pollution level using multivariate analysis and fuzzy comprehensive assessment (FCA), respectively. Multivariate analysis using principle component analysis (PCA) showed mixed origin for Pb, Cd, Zn, Fe, and Ni, natural source for Cu and Mn and anthropogenic source for Cr. Among all the metals, Pb, Cd, Fe and Ni were above the safe limits of Bureau of Indian Standards (BIS) and World Health Organization (WHO) except Ni. Health risk in terms of hazard quotient (HQ) showed that the HQ values for children were higher than the safe level (HQ = 1) for Pb (2.4) and Cd (2.1) in pre-monsoon while in post-monsoon the value exceeded only for Pb (HQ = 1.23). The health risks of heavy metals for the adults were well within safe limits. The finding of this study indicates potential health risks to the children due to chronic exposure to contaminated groundwater in the region. Based on FCA, groundwater pollution could be categorized as quite high in the peri-urban region, and absolutely high in the urban region of Ghaziabad district. This study showed that different approaches are required for the integrated assessment of the groundwater pollution, and provides a scientific basis for the strategic future planning and comprehensive management.

Model-based classification of CPT data and automated lithostratigraphic mapping for high-resolution characterization of a heterogeneous sedimentary aquifer

Cone penetration testing (CPT) is one of the most efficient and versatile methods currently available for geotechnical, lithostratigraphic and hydrogeological site characterization. Currently available methods for soil behaviour type classification (SBT) of CPT data however have severe limitations, often restricting their application to a local scale. For parameterization of regional groundwater flow or geotechnical models, and delineation of regional hydro- or lithostratigraphy, regional SBT classification would be very useful. This paper investigates the use of model-based clustering for SBT classification, and the influence of different clustering approaches on the properties and spatial distribution of the obtained soil classes. We additionally propose a methodology for automated lithostratigraphic mapping of regionally occurring sedimentary units using SBT classification. The methodology is applied to a large CPT dataset, covering a groundwater basin of ~60 km² with predominantly unconsolidated sandy sediments in northern Belgium. Results show that the model-based approach is superior in detecting the true lithological classes when compared to more frequently applied unsupervised classification approaches or literature classification diagrams. We demonstrate that automated mapping of lithostratigraphic units using advanced SBT classification techniques can provide a large gain in efficiency, compared to more time-consuming manual approaches and yields at least equally accurate results.

Setback distances between small biological wastewater treatment systems and drinking water wells against virus contamination in alluvial aquifers

Contamination of groundwater by pathogenic viruses from small biological wastewater treatment system discharges in remote areas is a major concern. To protect drinking water wells against virus contamination, safe setback distances are required between wastewater disposal fields and water supply wells. In this study, setback distances are calculated for alluvial sand and gravel aquifers for different vadose zone and aquifer thicknesses and horizontal groundwater gradients. This study applies to individual households and small settlements (1-20 persons) in decentralized locations without access to receiving surface waters but with the legal obligation of biological wastewater treatment. The calculations are based on Monte Carlo simulations using an analytical model that couples vertical unsaturated and horizontal saturated flow with virus transport. Hydraulic conductivities and water retention curves were selected from reported distribution functions depending on the type of subsurface media. The enteric virus concentration in effluent discharge was calculated based on reported ranges of enteric virus concentration in faeces, virus infectivity, suspension factor, and virus reduction by mechanical-biological wastewater treatment. To meet the risk target of <10^-4infections/person/year, a 12 log₁₀ reduction was required, using a linear dose-response relationship for the total amount of enteric viruses, at very low exposure concentrations. The results of this study suggest that the horizontal setback distances vary widely ranging 39 to 144m in sand aquifers, 66-289m in gravel aquifers and 1-2.5km in coarse gravel aquifers. It also varies for the same aquifers, depending on the thickness of the vadose zones and the groundwater gradient. For vulnerable fast-flow alluvial aquifers like coarse gravels, the calculated setback distances were too large to achieve practically. Therefore, for this category of aquifer, a high level of treatment is recommended before the effluent is discharged to the ground surface.

Identification of the hydrogeochemical processes and assessment of groundwater quality using classic integrated geochemical methods in the Southeastern part of Ordos basin, China

Insufficient understanding of the hydrogeochemistry of aquifers makes it necessary to conduct a preliminary water quality assessment in the southern region of Ordos Basin, an arid area in the world. In this paper, the major ions of groundwater have been studied aiming at evaluating the hydrogeochemical processes that probably affect the groundwater quality using 150 samples collected in 2015. The two prevalent hydrochemical facies, HCO₃Mg·Na·Ca and HCO₃Mg·Ca·Na type water, have been identified based on the hydrochemical analysis from Piper trilinear diagram. Compositional relations have been used to assess the origin of solutes and confirm the predominant hydrogeochemical processes responsible for the various ions in the groundwater. The results show that the ions are derived from leaching effect, evaporation and condensation, cation exchange, mixing effect and human activities. Finally groundwater quality was assessed with single factor and set pair methods, the results indicate that groundwater quality in the study region is generally poor in terms of standard of national groundwater quality. The results obtained in this study will be useful to understand the groundwater quality status for effective management and utilization of the groundwater resource.

A national-scale assessment of micro-organic contaminants in groundwater of England and Wales

A large variety of micro-organic (MO) compounds is used in huge quantities for a range of purposes (e.g. manufacturing, food production, healthcare) and is now being frequently detected in the aquatic environment. Interest in the occurrence of MO contaminants in the terrestrial and aquatic environments continues to grow, as well as in their environmental fate and potential toxicity. However, the contamination of groundwater resources by MOs has a limited evidence base compared to other freshwater resources. Of particular concern are newly 'emerging contaminants' such as pharmaceuticals and lifestyle compounds, particularly those with potential endocrine disrupting properties. While groundwater often has a high degree of protection from pollution due to physical, chemical and biological attenuation processes in the subsurface compared to surface aquatic environments, trace concentrations of a large range of compounds are still detected in groundwater and in some cases may persist for decades due to the long residence times of groundwater systems. This study provides the first national-scale assessment of micro-organic compounds in groundwater in England and Wales. A large set of monitoring data was analysed to determine the relative occurrence and detected concentrations of different groups of compounds and to determine relationships with land-use, aquifer type and groundwater vulnerability. MOs detected including emerging compounds such as caffeine, DEET, bisphenol A, anti-microbial agents and pharmaceuticals as well as a range of legacy contaminants including chlorinated solvents and THMs, petroleum hydrocarbons, pesticides and other industrial compounds. There are clear differences in MOs between land-use types, particularly for urban-industrial and natural land-use. Temporal trends of MO occurrence are assessed but establishing long-term trends is not yet possible.

Hydrogeochemical investigations in a drained lake area: the case of Xynias basin (Central Greece)

In Xynias drained Lake Basin's area, central Greece, a hydrogeochemical research took place including groundwater sampling from 30 sampling sites, chemical analysis, and statistical analysis. Groundwaters present Ca-Mg-HCO3 as the dominant hydrochemical type, while their majority is mixed waters with non-dominant ion. They are classified as moderately hard to hard and are characterized by oxidizing conditions. They are undersaturated with respect to gypsum, anhydrite, fluorite, siderite, and magnesite and oversaturated in respect to calcite, aragonite, and dolomite. Nitrate concentration ranges from 4.4 to 107.4 mg/L, meanwhile 13.3 % of the samples exceed the European Community (E.C.) drinking water permissible limit. The trace elements Fe, Ni, Cr, and Cd present values of 30, 80, 57, and 50 %, respectively, above the maximum permissible limit set by E.C. Accordingly, the majority of the groundwaters are considered unsuitable for drinking water needs. Sodium adsorption ratio values (0.04-3.98) and the electrical conductivity (227-1200 μS/cm) classify groundwaters as suitable for irrigation uses, presenting low risk and medium soil alkalization risk. Factor analysis shows that geogenic processes associated with the former lacustrine environment and anthropogenic influences with the use of fertilizers are the major factors that characterized the chemical composition of the groundwaters.

Groundwater quality analysis using multivariate statistical techniques (case study: Fars province, Iran)

This research investigated the quality of groundwater of 298 wells during 10 years, in Fars province, southern Iran, to survey spatial variation of groundwater quality and also major sources of hydro-chemical components for drinking and agricultural uses. To classify the sampling stations in each year, hierarchical cluster analysis, using the Euclidean distances and "Ward" method, was used. According to the results of cluster analysis, there were three quality groups in groundwater of the research area: first group of 170 wells with type of Ca-HCO3, second group of 98 wells with type of Ca-HCO3, and third group of 30 wells with type of Na-Cl. Hydro-chemical parameters were increased from the first to the third group, and on the basis of Schoeller and USSL diagrams, the water of wells of the third group was considered unsuitable for irrigation and drinking. Principal component (PC) analysis and factor analysis reduced the complex and voluminous data matrix into three main components, accounting for more than 80 % of the total variance. The first PC contained TDS, EC, TH, Na(+), Cl(-), Mg(2+), SO4 (2-), Ca(2+), and SAR parameters. Therefore, the first dominant factor was salinity. In PC2, HCO3 and pH were the dominant parameters, which may indicate weathering of silicate minerals. The PC3 contained high loadings for NO2 (2-) and NO3 (-). This factor indicates anthropogenic contaminants that may be caused by improper disposal of domestic wastes or the use of chemical fertilizers in agriculture and leaching of them.

Impact of Preservation of Subsoil Water Act on Groundwater Depletion: The Case of Punjab, India

Indian states like Punjab and Haryana, epicenters of the Green Revolution, are facing severe groundwater shortages and falling water tables. Recognizing it as a serious concern, the Government of Punjab enacted the Punjab Preservation of Subsoil Water Act in 2009 (or the 2009 act) to slow groundwater depletion. The objective of this study is to assess the impact of this policy on groundwater depletion, using panel data from 1985 to 2011. Results from this study find a robust effect of the 2009 act on reducing groundwater depletion. Our models for pre-monsoon, post-monsoon, and overall periods of analysis find that since implementation of the 2009 act, groundwater tables have improved significantly. Second, our study reveals that higher shares of tube wells per total cropped area and increased population density have led to a significant decline in the groundwater tables. On the other hand, rainfall and the share of area irrigated by surface water have had an augmenting effect on groundwater resources. In the two models, pre-monsoon and post-monsoon, this study shows that seasonality plays a key role in determining the groundwater table in Punjab. Specifically, monsoon rainfall has a very prominent impact on groundwater.

Zonal management of multi-purposes groundwater utilization based on water quality and impact on the aquifer

Groundwater is widely used for drinking, irrigation, and aquaculture in the Pingtung Plain, Southwestern Taiwan. The overexploitation and poor quality of groundwater in some areas of the Pingtung Plain pose great challenges for the safe use and sustainable management of groundwater resources. Thus, establishing an effective management plan for multi-purpose groundwater utilization in the Pingtung Plain is imperative. Considerations of the quality of the groundwater and potential impact on the aquifer of groundwater exploitation are paramount to multi-purpose groundwater utilization management. This study proposes a zonal management plan for the multi-purpose use of groundwater in the Pingtung Plain. The zonal management plan is developed by considering the spatial variability of the groundwater quality and the impact on the aquifer, which is defined as the ratio of the actual groundwater extraction rate to transmissivity. A geostatistical Kriging approach is used to spatially delineate the safe zones based on the water quality standards applied in the three groundwater utilization sectors. Suitable zones for the impact on the aquifer are then spatially determined. The evaluation results showing the safe water quality zones for the three types of utilization demands and suitable zones for the impact on aquifer are integrated to create a zonal management map for multi-purpose groundwater utilization which can help government administrators to establish a water resource management strategy for safe and sustainable use of groundwater to meet multi-purpose groundwater utilization requirements in the Pingtung Plain.

[Medical hydrogeology is an independent interdisciplinary branch of the science about groundwater]

The use of groundwater in population water supply systems gains more and more importance because of increasing degradation of the quality of surface water sources. At the same time there are changed concepts on ubiquitous high quality of groundwater. The executed analysis offoreign and domestic literature allowed authors to determine the character and causes of negative changes in the composition of groundwater. In the large body of investigations there were established cause-and-effect relationships between a number of noninfectious (including cardiovascular and cancer) and infectious diseases and anthropogenic pollution and the natural composition of groundwater. In the article there is substantiated the formation of a new interdisciplinary scientific direction - medical hydrogeology. On the basis of current data on the medical and ecological significance of the quality, quantity and regime of the groundwater, geological conditions of the shaping of their composition, there was shown the need of the consideration of the hydrological situation in making water supply management solutions safe for the health of the population. In this regard, there were considered the interrelationship and interdependence of allied disciplines - hygiene, ecological toxicology and epidemiology, hydrogeochemistry, hydrogeology. There was pointed the importance of the acquisition of based on hydrogeology medical specialists of the water supply profile for sharing with hygienists of the effective solution of tasks of the management of groundwater sources.

Indoor Air Contamination from Hazardous Waste Sites: Improving the Evidence Base for Decision-Making

At hazardous waste sites, volatile chemicals can migrate through groundwater and soil into buildings, a process known as vapor intrusion. Due to increasing recognition of vapor intrusion as a potential indoor air pollution source, in 2015 the U.S. Environmental Protection Agency (EPA) released a new vapor intrusion guidance document. The guidance specifies two conditions for demonstrating that remediation is needed: (1) proof of a vapor intrusion pathway; and (2) evidence that human health risks exceed established thresholds (for example, one excess cancer among 10,000 exposed people). However, the guidance lacks details on methods for demonstrating these conditions. We review current evidence suggesting that monitoring and modeling approaches commonly employed at vapor intrusion sites do not adequately characterize long-term exposure and in many cases may underestimate risks. On the basis of this evidence, we recommend specific approaches to monitoring and modeling to account for these uncertainties. We propose a value of information approach to integrate the lines of evidence at a site and determine if more information is needed before deciding whether the two conditions specified in the vapor intrusion guidance are satisfied. To facilitate data collection and decision-making, we recommend a multi-directional community engagement strategy and consideration of environment justice concerns.

Metrics for Assessing the Quality of Groundwater Used for Public Supply, CA, USA: Equivalent-Population and Area

Data from 11,000 public supply wells in 87 study areas were used to assess the quality of nearly all of the groundwater used for public supply in California. Two metrics were developed for quantifying groundwater quality: area with high concentrations (km(2) or proportion) and equivalent-population relying upon groundwater with high concentrations (number of people or proportion). Concentrations are considered high if they are above a human-health benchmark. When expressed as proportions, the metrics are area-weighted and population-weighted detection frequencies. On a statewide-scale, about 20% of the groundwater used for public supply has high concentrations for one or more constituents (23% by area and 18% by equivalent-population). On the basis of both area and equivalent-population, trace elements are more prevalent at high concentrations than either nitrate or organic compounds at the statewide-scale, in eight of nine hydrogeologic provinces, and in about three-quarters of the study areas. At a statewide-scale, nitrate is more prevalent than organic compounds based on area, but not on the basis of equivalent-population. The approach developed for this paper, unlike many studies, recognizes the importance of appropriately weighting information when changing scales, and is broadly applicable to other areas.