Groundwater Quality Protection Research Articles

Groundwater health risk assessment of North China Plain based on Monte Carlo model sensitivity analysis and morphological analysis: A case study of Shijiazhuang City.

The rapid development of the social economy and the influence of human activities can lead to aggravated groundwater pollution. Groundwater safety is the premise of residents' health. Therefore, studying the sustainable utilization and health risks of groundwater quality is important. The groundwater quality and potential health risks were evaluated in the Shijiazhuang area, which is located in the North China Plain in this paper. Based on 159 groundwater samples collected in the study area, the potential health risks of As, Cr6+, Ni, Pb, F-, and NO3 - to humans were evaluated from oral and skin contact. Results of the human health risk assessment showed that the average carcinogenic risk and non-carcinogenic risk of children are higher than those of adults. According to the spatial distribution of the total risk value, adults and children in the southwest of the study area face higher risks. Because of the uncertainty of USEPA, Monte Carlo simulation was used to calculate the probability of health risk assessment and prioritization of contaminant treatment. The results of the Monte Carlo simulation showed that the acceptable range for children is 6.82%, and the acceptable range for adults is 18.07%. According to the HRWM model, carcinogenic pollutants mainly include As, Cr6+, and Ni. The most important chemical species of As is HAsO4 2-, followed by H2AsO4 -. Similarly, CrO4 2- and Ni2+ are the main forms of Cr6+ and Ni. The results of this study can provide data support for the protection and management of groundwater quality in the North China Plain. PRACTITIONER POINTS: Children are more susceptible to carcinogenic risk than adults. After calculation, the main influencing elements are Ni and Cr. Metal morphology analysis was carried out, and the results showed that HAsO4 2-, CrO4 2-, and Ni2+ were the main types.

Contaminant Trends in Urban Groundwater: Case Study from Ljubljana (Central Slovenia)

Urban areas can significantly alter the quality status of aquifers if appropriate strategies to prevent and detect groundwater contamination are not implemented in time. The prevention of groundwater contamination should be a priority due to its potential long-term impact on the environment and the high cost of remediation. For effective and sustainable groundwater management, it is crucial to proactively monitor a wide range of compounds to prevent their spread, progression and increasing concentrations. This study is one of the few to analyse the trends of various urban groundwater contaminants (nitrate, sulphate, hexavalent chromium, pesticides, PCE and TCE) from a groundwater management perspective. Characteristic trends are assessed using linear regression and the Mann–Kendall method, while significant changes in trends are determined using the Darken and Pettitt tests. The time span of the analysed trends covers the transition period before and after the implementation of the Water Framework Directive (2000/60/EC) and the Groundwater Directive (2000/60/EC). This study confirms the effectiveness of enforcement measures to protect groundwater quality, as evidenced by several statistically significant decreasing trends. On the other hand, this study emphasises the importance of intervention-targeted sampling campaigns and the reporting of raw analytical values according to the ISO 11843 series of standards. This approach is essential to detect upward trends in emerging contaminants at an early stage and prevent them from reaching levels that could negatively impact the economy or even jeopardise the safety of drinking water supplies.

Field evaluation of carbon injection method for in-situ biological denitrification in groundwater using geochemical and metataxonomic analyses

This study focuses on the bioremediation of nitrate-contaminated groundwater, which has become a significant environmental problem due to the increasing usage of fertilizers and sewage disposal. The nitrate reduction efficiencies of biological denitrification by injection of carbon source in a pilot-scale treatment system setup were investigated at a groundwater contamination site. The field test was conducted using acetate as a carbon source for 22 days to assess the nitrate reduction efficiencies of in-situ treatment. Geochemical parameters and microbial community analysis using next-generation sequencing were performed before and after carbon source injection. After 12 h of reaction time, nitrate concentration decreased from 31.6 to 4.2 mg-N/L at PC-2, and then remained stable at 3.9 mg-N/L. The nitrate reduction rate when acetate was injected was 29.0 mg-N/L/day. Aquabacterium commune, pseudomonas brassicacearum, dechloromonas denitrificans, and Massilia FAOS were dominant species after acetate injection. Predictive metabolic pathway analysis indicated that nitrate reduction metabolisms during injection of acetate were denitrification and assimilatory nitrate reduction to ammonium. The evaluated hazard quotient of nitrate-contaminated groundwater significantly decreased after acetate injection (non-carcinogenic risk decreased from 1.176 to 0.134 for children). This research could provide fundamental information for decision-makers in nitrate-contaminated groundwater quality protection and management.

Assessment of hydrogeochemistry in groundwater using water quality index model and indices approaches

Groundwater resources around the world required periodic monitoring in order to ensure the safe and sustainable utilization for humans by keeping the good status of water quality. However, this could be a daunting task for developing countries due to the insufficient data in spatiotemporal resolution. Therefore, this research work aimed to assess groundwater quality in terms of drinking and irrigation purposes at the adjacent part of the Rooppur Nuclear Power Plant (RNPP) in Bangladesh. For the purposes of achieving the aim of this study, nine groundwater samples were collected seasonally (dry and wet season) and seventeen hydro-geochemical indicators were analyzed, including Temperature (Temp.), pH, electrical conductivity (EC), total dissolved solids (TDS), total alkalinity (TA), total hardness (TH), total organic carbon (TOC), bicarbonate (HCO3−), chloride (Cl−), phosphate (PO43−), sulfate (SO42−), nitrite (NO2−), nitrate (NO3−), sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+). The present study utilized the Canadian Council of Ministers of the Environment water quality index (CCME-WQI) model to assess water quality for drinking purposes. In addition, nine indices including EC, TDS, TH, sodium adsorption ratio (SAR), percent sodium (Na%), permeability index (PI), Kelley's ratio (KR), magnesium hazard ratio (MHR), soluble sodium percentage (SSP), and Residual sodium carbonate (RSC) were used in this research for assessing the water quality for irrigation purposes. The computed mean CCME-WQI score found higher during the dry season (ranges 48 to 74) than the wet season (ranges 40 to 65). Moreover, CCME-WQI model ranked groundwater quality between the “poor” and “marginal” categories during the wet season implying unsuitable water for human consumption. Like CCME-WQI model, majority of the irrigation index also demonstrated suitable water for crop cultivation during dry season. The findings of this research indicate that it requires additional care to improve the monitoring programme for protecting groundwater quality in the RNPP area. Insightful information from this study might be useful as baseline for national strategic planners in order to protect groundwater resources during the any emergencies associated with RNPP.

Arsenic in groundwater in the Grand Canyon region and an evaluation of potential pathways for arsenic contamination of groundwater from breccia pipe uranium mining

The Grand Canyon in northern Arizona is an international tourist destination, a home or sacred place to many Native Americans, and hosts some of the highest-grade uranium deposits in the United States. Although potential contamination of water resources by uranium from mining activities is a concern, other elements commonly associated with these uranium deposits may pose a greater risk to human populations in the area. This study presents an assessment of arsenic in groundwater in the Grand Canyon area. First, sampling results for arsenic are presented and areas with elevated arsenic concentrations are discussed. Potential pathways of groundwater contamination by arsenic from uranium mines are then discussed to elucidate situations and conditions under which elevated concentrations of arsenic might be expected to become mobilized from breccia-pipe uranium mining activities. Results for arsenic in groundwater in the study area were available for 652 samples collected from 230 sites. Arsenic concentrations in groundwater ranged from less than reporting limits in 60 samples to a maximum concentration of 875 μg/L at Pumpkin Spring. About 88% (202) of the sites sampled had a maximum arsenic concentration below the drinking water standard of 10 μg/L. Available data from near former or current breccia-pipe uranium mines in the area indicate limited evidence to-date of mining effects on elevated arsenic in groundwater, although slow groundwater flow paths in the region may result in extended times of decades or more for groundwater to reach discharge locations. Post-mining entry of groundwater into the shaft and underground mine workings, with subsequent transport of metal-enriched groundwater offsite, may be a potential pathway of groundwater arsenic contamination from mining, although concentrations would likely be attenuated by contact with sedimentary rock units and dilution with native groundwater along flow paths. Monitoring of perched groundwater at reclaimed mine sites post-reclamation could provide data on the effectiveness of clean-closure practices on protecting groundwater quality in the area.

Dye tracing of the Lusaka karstified aquifer system: implications towards urban groundwater quality protection

Management of groundwater resources requires a large amount of data, coupled with an understanding of the aquifer system behavior. In developing countries, the scarcity in groundwater data has led to aquifers being managed according to rule-of-thumb standards or even abandoned as unmanageable at times. Groundwater quality protection thus has been through prescribed separation distances often without due regard for internal and boundary characteristics that affect response rates of groundwater movement, attenuation of pollutants, and recharge. In this study, we examine the boundary characteristics of the highly vulnerable karst aquifer system in the rapidly expanding city of Lusaka using a dye tracer technique. We investigate the flow dynamics (magnitude and direction) of groundwater using dye tracer dyes (fluorescein and rhodamine) spiked in pit latrines and observed at discharge springs. The results provide irrefutable evidence that pit latrines are a source and a pathway to contamination of groundwater. Dye tracer movement in groundwater was rapid, estimated at 340 and 430m/day for fluorescein and rhodamine, respectively, through interconnected conduit density. The vadose zone (epikarst) tends to store diffuse recharge before release to the phreatic zone. These rapid groundwater movements render regulatory separation minimum distances of 30m between abstraction wells and pit latrines/septic tanks in such environments to be an ineffective means of reducing contamination. The policy focus in the protection of groundwater quality should henceforth be on robust sanitation solutions especially for low-income communities that recognize the socio-economic diversity.

Impact of Gravel Pits on Water Quality in Alluvial Aquifers

Gravel pits are considered potentially hazardous in terms of groundwater quality protection as they represent an open part of the aquifer system, increasing the aquifer’s vulnerability to contamination from the surface. The aim of this research was to determine the biogeochemical processes in gravel pits that have a positive effect on the groundwater quality in the alluvial aquifer in NW Croatia. The aquifer is situated below developed agricultural land, with high groundwater nitrate concentrations having been recorded over the last decades. The differences between two gravel pits and the surrounding groundwater were studied using in situ, hydrochemical, and isotopic parameters (δ15N-NO3 and δ18O-NO3), together with existing microbial data. The analyses of nitrogen species indicated that nitrate attenuation processes take place in gravel pits. Bacterial denitrification and nitrate uptake by algae were responsible for significant decreases in nitrate concentration. These processes were more effective in the inactive gravel pit, which has a longer water residence time and during warm periods, when microbial biomass, abundance, and activity were high. The seasonally variable microbial activity also affected trace metals, removing them from groundwater, possibly through the biosorption of metal ions. The presented research shows that the observed biogeochemical processes are associated with seasonal changes that affect the types and number of microbial communities and the chemical composition of water, resulting in gravel pits being groundwater remediation points.

Hydrogeochemical Characteristics and Groundwater Quality in a Coastal Urbanized Area, South China: Impact of Land Use

Land use transformation accompanied with various human activities affects groundwater chemistry and quality globally, especially in coastal urbanized areas because of complex human activities. This study investigated the impact of land use on groundwater chemistry and quality in a coastal alluvial aquifer (CAA) of the Pearl River Delta where urbanization continues. A fuzzy synthetic evaluation method was used to evaluate the groundwater quality. Besides, factors controlling groundwater chemistry and quality in the CAA were discussed by using a principal components analysis (PCA). Nearly 150 groundwater samples were collected. All samples were filtered on-site and stored at 4 °C until the laboratory procedures could be performed. Nineteen chemical parameters including pH, dissolved oxygen, redox potential, total dissolved solids, K+, Na+, Ca2+, Mg2+, NH4+, HCO3−, NO3−, SO42−, Cl−, I−, NO2−, Pb, Mn, Fe, and As were analyzed. Results show that groundwater chemistry in the CAA was dominated by Ca-HCO3 and Ca·Na-HCO3 facies. In addition, groundwater with NO3 facies was also present because of more intensive human activities. In the CAA, 61.8% of groundwaters were fit for drinking, and 10.7% of groundwaters were undrinkable but fit for irrigation, whereas 27.5% of groundwaters were unfit for any purpose. Poor-quality groundwaters in urban and agricultural areas were 1.1–1.2 times those in peri-urban areas, but absent in the remaining area. Groundwater chemistry and quality in the CAA was mainly controlled by five factors according to the PCA. Factor 1 is the release of salt and NH4+ from marine sediments, and the infiltration of domestic and septic sewage. Factor 2 is agricultural activities related to the irrigation of river water, and the use of chemical fertilizers. Factor 3 is the industrial pollution related to heavy metals and acid deposition. Factor 4 is the input of anthropogenic reducing sewage inducing the reductive dissolution of As-loaded Fe minerals and denitrification. Factor 5 is the I− contamination from both of geogenic and anthropogenic sources. Therefore, in order to protect groundwater quality in coastal urbanized areas, repairing old sewer systems in urban areas, building sewer systems in peri-urban areas, limiting sewage irrigation and the amount of chemical fertilizers application in agricultural areas, as well as strengthening the supervision of the industrial exhaust gas discharge in urban and peri-urban areas are recommended.

Source and evolution of sulfate in the multi-layer groundwater system in an abandoned mine—Insight from stable isotopes and Bayesian isotope mixing model

The source and evolution of sulfate (SO42−) in groundwater from abandoned mines are widely concerned environmental issues. Herein, major dissolved ions, multi-isotopes (δ34S, δ18Osulfate, δ2H and δ18Owater), machine learning (Self-organizing maps) and Bayesian isotope mixing model were used to identify the source and evolution of SO42− in an abandoned mine (Fengfeng mine, northern China) with a multi-layer groundwater system. Groundwater in the study area was mainly divided into three clusters (Cluster I, Cluster II and Cluster III), dominated by Na-SO4, Ca-SO4 and Ca-HCO3 types, respectively. According to δ2H and δ18Owater, groundwater in the study area mainly originated from atmospheric precipitation. δ34S, δ18Osulfate and SO42− suggested that bacterial sulfate reduction did not affect the SO42− isotopic composition. Dual SO42− isotopes, and MixSIAR model revealed that the main source of SO42− in the study area was pyrite oxidation/gypsum dissolution, accounting for an average of 57.4 % (gypsum), 71.24 % (pyrite oxidation) and 52.93 % (pyrite oxidation) of SO42− in the samples of Clusters I–III, respectively. Combined with the hydrochemical diagrams, the evolution of SO42− in different clusters of samples was derived. Cluster I was mainly gypsum dissolution; In contrast, Clusters II and III were mainly pyrite oxidation accompanied by carbonate dissolution, and Cluster II was also influenced by cation exchange. These findings will help in developing management strategies for protecting groundwater quality, which will provide a reference for the study of solute sources and S cycling in abandoned mines.

Achieving the One Health Goal: Highlighting Groundwater Quality and Public Health

In many regions of the world, groundwater is the main water source for multiple uses, including for drinking, irrigation, and industry. Groundwater quality, therefore, is closely related to human health, and the consumption of contaminated groundwater can induce various waterborne diseases. In the last ten years, the world has witnessed a rapid development in groundwater quality research and the assessment of associated health risks. This editorial introduced the foundation of the current Special Issue, Groundwater Quality and Public Health, briefly reviewed recent research advances in groundwater quality and public health research, summarized the main contribution of each published paper, and proposed future research directions that researchers should take into account to achieve the one health goal. It is suggested that groundwater quality protection should be further emphasized to achieve the one health goal and the UN’s SDGs. Modern technologies should be continuously developed to remediate and control groundwater pollution, which is a major constrain in the development of a sustainable society.

Mechanisms of selenate adsorption at the imogolite-water interface

Selenium (Se) can be toxic at high concentrations, mainly through exposure to contaminated groundwater and bioaccumulation in plants. Under oxidizing conditions, Se has preferential inorganic forms, Se oxyanions, which are highly soluble and weakly adsorbed on mineral surfaces. Therefore, retarding the release and migration of Se oxyanions is critical for the protection of groundwater quality. Imogolite is a tubular aluminosilicate with a high adsorptive capacity for anions, including IO3-, TcO4-, and PO43-. However, the potential adsorption of selenate on imogolite has not yet been evaluated to determine potential environmental applications including groundwater remediation. In this study, we synthesized and characterized imogolite using solid-state and electrostatic techniques. The synthesized imogolite was used to evaluate the adsorption of selenate under a range of physiochemical conditions using adsorption isotherms combined with various modeling techniques including the Freundlich model and the charge distribution at multi-site surface complexation (CD-MUSIC) model to decipher surface complexation mechanisms of selenate on imogolite. SynopsisAdsorption affinity and mechanisms of selenate on imogolite are mechanistically evaluated to understand potential environmental applications of imogolite for the protection of groundwater quality.

Investigation the Origins of Groundwater Salinity in Baghdad City by Using Environmental Isotopes and Hydrochemical Techniques

The hydrochemical and isotopic techniques have become one of the most popular and successful methods for determining the hydrogeochemical features of groundwater in recent years. A total of 15 samples were collected during wet (March, 2021) and dry (August, 2021) seasons. An approach with major elements (Cl-, Na+, Mg2+, Ca2+, and SO4 2=) and multi-isotope (2H, 18O) are used in this study to solve the geochemical variation of salinity in groundwater in Baghdad. The results of the analysis of groundwater samples in the study area showed that the major cations were Ca2+ and Na+, while the major anion was SO4, Cl, and HCO3. The Ca-SO4 and Ca-Na-Cl-SO4. hydrochemical facies are the dominant hydrochemical facies of groundwater on the Al-Karakh and Al-Russafa sides, respectively. Ca-HCO3 was found to be the dominant hydrochemical facies of the Tigris River. Human activities and geochemical processes may have caused differences in hydrochemical Facies. According to isotope analysis, the study area has multiple sources of salinity. This can be attributed to the effects of natural dissolution of the salt compounds, mixing with sewage, and industrial water sink. The results and data from this work can be used to research groundwater recharge and interaction, as well as to protect groundwater quality.

Moisture movement, soil salt migration, and nitrogen transformation under different irrigation conditions: Field experimental research

Irrigation and fertilizer application can lead to significant changes in groundwater quality. In this study, a field irrigation experiment was carried out from April 9 to 23, 2021 under irrigation and fertigation conditions to understand the mechanisms of moisture movement, soil salt migration, and nitrogen transformation in the soil profile. Continuous in-situ monitoring and sampling of soil and irrigation water, as well as stable isotopes, chemical parameters, and soluble salt analyses, were performed in this research. The results showed that the time cost by the irrigation water in the vadose zone was about 5 h. The infiltrated irrigation water was accompanied by high concentrations of soluble salts, leached from the soil layers of 20–80 cm and 100–150 cm, which is associated with the leaching of Na+, Cl−, SO42−, and Ca2+ and the dissolution of minerals such as gypsum and halite. Furthermore, the variations in nitrogen concentrations (NH4+ and NO3−) in the soil profile suggested that fertilizer application was the main source of NO3− in the soil and groundwater, while irrigation was the biggest driving force for nitrogen transport and transformation in soil. The application of urea fertilizer can increase the content of ammonium nitrogen at the soil layer of 0–80 cm. This nitrogen form can be subsequently transformed to nitrate nitrogen during the water transport to the groundwater. The current study provides a strong scientific basis for the protection and management of groundwater and soil quality in agricultural areas.

Nitrogen rate, irrigation and rainfall impacts on groundwater nitrate levels in sandy coastal golf courses

AbstractThere have been concerns over fertilizer nitrogen (N) applied to turfgrass areas affecting groundwater quality in sandy coastal areas since the 1970s . Extensive amount of small‐scale research studies has determined the major factors that contribute to excessive nitrate‐N leaching from turfgrass ecosystems. There are limited data on large‐scale groundwater monitoring of turfgrass sites, such as golf courses, which are related to management inputs. There are land‐use regulations limiting the amount of fertilized turfgrass in coastal area in the United States which assume a linear relationship between the amounts of N applied and leached. The purpose of this study is to evaluate the long‐term impact of yearly variations in N application rate, irrigation amounts, and seasonal precipitation on groundwater quality on golf courses in critical groundwater recharge areas. Two golf courses, The Bridge and Sebonack Golf Club, in this study are in eastern Long Island, NY with systematic groundwater monitoring for NO3–N. Each golf course follows best management practices (BMP) including limitations on amount, rate, source and timing of N applications as well as controlled irrigation based on on‐site evapotranspiration measurements. The results of this study clearly show that on golf courses in sandy critical groundwater recharge areas that follow BMP, the amount of N applied is not related to NO3–N levels in groundwater. Rainfall amounts more closely followed NO3–N levels in groundwater, thus abnormally high rainfall can result in higher NO3–N levels. Implementing fertilizer BMP can be very effective in protecting groundwater quality.

Effects of information on smallholder irrigation farmers’ willingness to pay for groundwater protection

AbstractIn Ghana, groundwater, accessed through wells and boreholes, is generally unregulated and may be contaminated with pollutants including excess nitrates from agricultural chemical fertilizers. Yet, studies estimating how clean groundwater is valued are not available in Ghana. In addition, some research suggests that the pre‐experiment information provided to survey respondents affects their valuation of an identical outcome. This paper estimates smallholder farmers’ preferences for groundwater protection using pre‐experiment information focused on one of two outcomes: environment or health. The double‐bounded contingent valuation (DBCV) approach is used to estimate willingness to pay (WTP) to protect groundwater quality. The estimation accounts for shift and anchoring effects, which are common issues with the DBCV method. The mean WTP from the health (environmental) information subsample is about US$19 (US$17) per acre, and the values are significantly different between the information conditions. The findings shed light on the importance of using precise information in eliciting WTP in a developing country setting.

Environmental and ecotoxicological risk assessment of pollution with light crude oil for an oil exploatation field

Global development of transportation dependent on internal combustion engines, involves major increases in the consumption of fossil fuels obtained by extracting crude oil from depths by means of wells and refining it. In this context, protection of environment and groundwater quality is an increasingly difficult objective to maintain, requiring modern methods to address possible negative effects on the environment. The current research assesses the degree of eco-toxicological and environmental risk for an oil exploitation area in case of an accidental pollution scenario with crude oil. The entire risk spectrum was analysed through a set of qualitative and quantitative risk assessment tools to highlight and quantify the most important effects caused by petroleum products on biotope and biocenoses. The primary aim of the research is to identify vulnerable environmental reservoirs for accidental oil pollution and to establish the best tools to quantify the environmental and ecotoxicological risk of groundwater contamination. The results obtained from the area showed a low to medium risk of contamination of the saturated and unsaturated area with crude oil expressed as TPH (total petroleum hydrocarbons) and a low risk of contamination with volatile organic compounds type BTEX associated contamination of biocenoses that can directly or indirectly interact with potentially polluted areas.

GROUNDWATER QUALITY EVALUATION USING STATISTICAL APPROACH AND WATER QUALITY INDEX IN AURANGABAD, BIHAR

Groundwater is the primary source of drinking water in south Bihar, and its quality can potentially affect human health. To accurately anticipate and evaluate water quality, 112 samples of groundwater were collected from Aurangabad, Bihar. Samples were taken from hand pumps and bore/tube wells. Physiochemical quality parameters, namely pH, total dissolved solids, alkalinity, hardness, magnesium, calcium, sulphate, nitrate, chloride, dissolved oxygen, and electrical conductivity were measured and compared to the Bureau of Indian Standards (BIS10500:2012). The physicochemical properties of samples were evaluated to determine their water quality index (WQI). Various water quality indicators were examined and correlated with other variables. All statistical analysis was done using RStudio4.1.1 software. On water quality data, the PCA method was employed, and four components with a total variance of 75.66% were extracted. WQI of more than 98% of the samples, either of excellent or good quality. Overall, the groundwater is drinkable. Comprehensive regulation and coordinated groundwater management are needed to protect groundwater quality and to achieve one of the Sustainable Development Goals.

Health Risk of the Shallow Groundwater and Its Suitability for Drinking Purpose in Tongchuan, China

Studying the quality and health risks of groundwater is of great significance for sustainable water resources utilization, especially in arid and semi-arid areas around the world. The current study is carried out to evaluate the quality and potential health risks of groundwater in the Tongchuan area on the Loess Plateau, northwest China. Water quality index (WQI) and hydrochemical correlation analysis were implemented to understand the status of groundwater quality. Daily average exposure dosages through the oral and dermal contact exposure pathways were taken into consideration to calculate the health risks to the human body. Additionally, graphical approaches such as Piper diagram, Durov diagram and GIS mapping were used to help better understand the results of this study. The WQI approach showed that 77.1% of the samples were of excellent quality. The most significant parameters affecting water quality were NO3−, F−, and Cr6+. The health risk assessment results showed that 27.1% and 54.2% of the samples lead to non-carcinogenic risks through oral intake for adults and children, respectively. In contrast, 12.5% of the groundwater samples would result in carcinogenic risks to the residents. This study showed that the WQI method needs to be supplemented by a health risk evaluation to obtain comprehensive results for groundwater quality protection and management in the Tongchuan area.

Source identification of methane in groundwater in shale gas development areas: A critical review of the state of the art, prospects, and future challenges

Shale gas exploration and development carry the risk of causing groundwater contamination and enhancing the greenhouse effect through methane leakage. Identifying the source of abnormal methane in groundwater of shale gas development areas is becoming a research hotspot in the fields of groundwater and climate change. This paper reviews the traditional methodology in identifying sources of methane and its deficiency in groundwater application. Then potential and advantages of using noble gases were discussed on how to overcome these limitations of the traditional method. Finally, based on noble gas, the current application status and future challenges of methane source identification in groundwater were analyzed. It can be summarized as: (1) due to chemical and/or microbial processes in the aquifer system, the traditional methodology for methane source identification, which utilizes molecular and isotopic compositions of hydrocarbon gas, has multiple interpretationsand large uncertainties; (2) the non-reactive nature and well-characterized isotopic compositions of noble gases in the atmosphere, hydrosphere, and crust, make noble gases ideal indicators of the sources of methane in groundwater. Moreover, the mechanism of formation and release of crustal noble gas prevent shale gas signatures from being interfered with by natural gas; (3) the key scientific tasks surrounding the use of noble gases for methane source identification include quantitatively separating the components of atmosphere-derived, mantle-derived, and crust-derived noble gases from the bulk noble gases in groundwater. It quantifies the solubility fractionation of noble gases induced by water-gas interaction during methane migration to the aquifer. The application of noble gases can bring a new perspective to tracing the source of methane in groundwater and is of great significance to the protection of groundwater quality in shale gas development areas and mitigation of climate change.

Detailed hydrogeological and hydrochemical reassessment of the Niger Delta Basin, South-south Nigeria

This review presents a detailed analysis of hydrogeological and hydrochemical conditions of the Niger Delta Basin. Hydrogeologically, the specific capacities recorded from different areas within this Basin vary from 6700 lit/hr/m to 13,500 lit/ hr/m. The water table is very close to the ground surface and varies from 0 to 4 meters. Unconfined groundwater aquifers occur in shallow unconfined aquifers, sands of the coastal beach ridges and river point bars, and sandy islands within the mangrove belt. There is a stable water table fluctuation which characterised the high precipitation zone. The shallow aquifers of Benin Formation are more porous than those in the Deltaic areas. In the southern areas, along the coastal zone, an artesian condition occurs. However, the aquifers are less transmissible with increased depth of the confined aquifer, owing to its more delicate texture. Therefore, more compact, and less permeable, or that there is not enough water in storage. More than half of groundwater sources in the Basin are acidic. Based on mean TDS concentration groundwater, fall in an excellent class for drinking. Groundwater classification based on conductivity showed all the reported findings indicate conductivity ranging from 250-750 μS/cm. Based on cation and anion chemistry, the Niger Delta Basin holds water of relatively acceptable drinking quality. However, the uncontrolled groundwater development, land-use changes, pollution from industrial, municipal, and agricultural effluents pose a threat to groundwater quality protection. Thus, a policy guideline is required to protect groundwater from pollution.