Groundwater pollution early warning based on QTR model for regional risk management: A case study in Luoyang city, China

Assessment and prediction of hexavalent chromium vulnerability in groundwater by Geochemical modelling, NOBLES Index and Random Forest Model

Unregulated chromite mining causes enrichment of hexavalent chromium in the groundwater. Due to unpredictable monsoonal recharge and anthropogenic dependencies on groundwater, the depth and extent of chromium pollution becomes extremely difficult to demarcate. For this specific objective, the present study was carried out in order to explore the potential of a coupled surface and sub-surface modelling approach in Sukinda valley, which accounts for 97-98 % of the total chromite reserve of India. Through ionic speciation, saturation state and clustering analysis, the most probable source and corresponding mineral stability state was investigated. In order to trace the extent, status and severity of the problem, both hydrogeologic parameters as well as the geogenic soil parameters were taken into account to develop DRASTIC, DRASTIC-L as well as NOBLES Index. While DRASTIC and DRASTIC-L model provided assessment of vulnerability due to surface leaching of contaminants, NOBLES index, speciation analysis and geochemical model provided sub-surface assessment of vulnerability due to chromium. MRSA and SPSA sensitivity analysis were applied in order to understand the most critical factor that can dominantly control the surface contamination in the groundwater. Random Forest (RF) based machine learning techniques were applied in order to integrate the sub-surface as well as surface characteristics for the purpose of prediction of chromium in the groundwater. The present study therefore presents a novel methodology of risk assessment for regions where either extensive mining activities are operational or in regions with abandoned mines with operative acid mine drainage.

Experimental investigation of light non-aqueous phase liquid mobilization in filled fractured network media

With the increasing requirement of international energy security, oil storage projects have been constructed in large numbers, but leaking petroleum-based contaminants are threatening the soil and groundwater environment. In order to assess the environmental risk of petroleum-based contaminants, an experimental apparatus was designed and developed to monitor the concentration and pressure variations of light non-aqueous phase liquid (LNAPL) in filled fractured network media. The mobilization mechanism of LNAPL was investigated by theoretical analysis and laboratory experiments; the pressure balance relationships at different interfaces were investigated. When the experimental model was unsaturated, the dynamic processes of concentration and pressure at different locations in filled fractures were explored. When the groundwater level was raised to 35 cm, the cumulative height of LNAPL (H_L) was a function of the density of LNAPL, interfacial tension, interfacial contact angle, aperture of fracture, porosity, and particle diameter of filling and H_L21 > H_L22. The final concentrations of H21, H22, H25, H26, and H27 were 0.467, 0.458, 0.026, 0.062, and 0.041 mg/mL, respectively. Subsequently, the effect of the particle diameter of filling sand on LNAPL mobilization was further discussed, the concentration of each point in the fractures increased with the increase of the particle diameter of filling sand, and its peak decreased with the increase of the burial depth. The response time of pressure at each point was advanced and the peak of pressure dynamic curve increased as the particle diameter of filling sand increased. The peak pressure heads of H12 and H13 were 22.360 cm and 25.332 cm respectively when the particle diameter of filling was 0.5-1.0 mm. The Spearman analysis results between LNAPL concentration and time showed a significant correlation (≥ 0.879, [Formula: see text]). Research results characterized the existence and mobilization of LNAPL in filled fractured network media from the perspectives of concentration and pressure, which could provide a reference for the study of the leakage and migration mechanism of LNAPL.

Multivariate and spatio-temporal groundwater pollution risk assessment: A new long-time serial groundwater environmental impact assessment system

Groundwater pollution risk assessment is an important part of environmental assessment. Although it has been developed for many years, there has not yet been a multi-dimensional method that takes into account long time series and spatial factors. We proposed a new method combines the advantages of remote sensing cloud computing, long-term groundwater modeling simulation and GIS technology to solve it efficiently. A coastal industrial park in Hainan was used as the study area. The depth of groundwater level, rainfall, topography and geomorphology, soil moisture, pollution source, pollution toxicity and other more than 10 parameters were used as the indexes. A comprehensive model with remote sensing cloud computing, DRASTIC model and Modflow + MT3DMS was established to assess the pollution risk from 2014 to 2021. The multi-year results indicated that the risk assessment of groundwater pollution was usually on the vertical coastal direction, and the risk increased from far away to near coast. With the discharge of pollutants in the industrial park, the pollution risk in the area 5 km away from the centre increased year by year until it became stable in 2019, and the risk in the centre of the park reached 1 level, covered an area of up to 145400 square metres, accounted for 0.012% of the whole study area. The assessment results in 2020 and 2021 fluctuate slightly compared with those in 2019. Therefore, in terms of groundwater resource protection and resource management, it is necessary to focus on the detection of pollution in the coastal zone and the pollution within 5 km of the centre to strictly control pollution discharge. In this study, the comprehensive assessment includes surface indicators, subsurface indicators, and pollutant indicators. Finally, we achieve a multivariate, spatial and long time series groundwater pollution risk assessment system, which is a new groundwater environmental impact assessment (GEIA) system.

Site prioritization and performance assessment of groundwater monitoring network by using information-based methodology

The arbitrary distribution of groundwater monitoring sites and the redundancy of observation data restrict the ability of monitoring network to provide reliable and effective data information. The purpose of this study is aimed at finding a quantitative method to screen ideal monitoring locations and evaluate the efficiency of the monitoring network. In terms of site selection, we use hydrogeological information, monitoring density and monitoring location to select the suitable site to monitor groundwater quality, understand the temporal trends and identify the abnormal signals of pollution sources. To evaluate the efficiency of monitoring network we used the groundwater quality data for consecutive years to evaluate the groundwater monitoring network based on information entropy and principal component analysis (PCA). The results show that the optimized groundwater monitoring network is comprised of 10 monitoring wells. The efficiency evaluation results of information entropy and PCA are basically consistent. The maximum mutual information (T) and comprehensive index of monitoring site (Laiguangying) were 1.29 and 3.25 respectively, while the minimum T and comprehensive index of monitoring site (Jinzhan) were 1.05 and -0.36 respectively, and the data efficiency was low. This study provides a good example for optimizing a groundwater pollution monitoring network.

Biogeochemistry of Iron Enrichment in Groundwater: An Indicator of Environmental Pollution and Its Management

Iron (Fe) is one of the most biochemically active and widely distributed elements and one of the most important elements for biota and human activities. Fe plays important roles in biological and chemical processes. Fe redox reactions in groundwater have been attracting increasing attention in the geochemistry and biogeochemistry fields. This study reviews recent research into Fe redox reactions and biogeochemical Fe enrichment processes, including reduction, biotic and abiotic oxidation, adsorption, and precipitation in groundwater. Fe biogeochemistry in groundwater and the water-bearing medium (aquifer) often involves transformation between Fe(II) and Fe(III) caused by the biochemical conditions of the groundwater system. Human activities and anthropogenic pollutants strongly affect these conditions. Generally speaking, acidification, anoxia and warming of groundwater environments, as well as the inputs of reducing pollutants, are beneficial to the migration of Fe into groundwater (Fe(III)→Fe(II)); conversely, it is beneficial to the migration of it into the media (Fe(II)→Fe(III)). This study describes recent progress and breakthroughs and assesses the biogeochemistry of Fe enrichment in groundwater, factors controlling Fe reactivity, and Fe biogeochemistry effects on the environment. This study also describes the implications of Fe biogeochemistry for managing Fe in groundwater, including the importance of Fe in groundwater monitoring and evaluation, and early groundwater pollution warnings.

Source analysis and health risk assessment of groundwater pollution based on multivariate statistical techniques in Kashgar Delta Area, Xinjiang, China

In this study, 63 groundwater samples were collected in the Kashgar Delta Area in Xinjiang in 2016, and then, the samples were tested and the test results were analyzed. Multivariate statistical techniques were used to determine the sources of pollution, and the USEPA (United States Environmental Protection Agency) model was used to assess the long-term health risk of groundwater to adults and children in the study area. The concentrations of groundwater chemical Na⁺, Cl^-, SO₄^2-, NH₄⁺-N, TDS, F^-, I^-, As, Fe, Mn, Pb, Hg, pH, TH, and COD_Mn, which exceed the permissible level in the study based on groundwater quality index and possibly pose a potential threat to the health of the residents in the area, which are mainly influenced by geological conditions. The source of the pollutants is the dissolution of minerals in the aquifer medium, which is greatly affected by the high-salinity groundwater environment, pH conditions, redox conditions, and evaporation and concentration effect. The values of the noncarcinogenic health risk index HQ_n follow the descending order of Cl^- > F^- > As > Fe > Mn > Pb > Hg > NH₄⁺-N; There are eight nonarcinogens and one carcinogen in groundwater of which Cl^- is the dominant noncarcinogenic factor, while As is the main carcinogenic pollutant in the study area. The health risk ratio results show that Cl^- and As are the main pollutants that pose the greatest threat to both adults' and children's health, and they should be considered as the primary indicators for health risk management and control.

A multidisciplinary approach for delineating wastewater flow paths in shallow groundwater aquifers: A case study in the southeastern part of the Nile Delta, Egypt

Groundwater pollution is a global issue in highly populated areas, the Eastern Nile Delta region is a typical example; especially around artificial wastewater drains. In the present work, a multidisciplinary approach using hydrogeochemical, geostatistical, microbiological and geophysical data was applied to determine the vulnerability conditions and to identify potential pathways through which contaminants could potentially percolate to shallow aquifers in the southern boundary of the Eastern Nile Delta. An organized groundwater sampling was conducted for hydrogeochemical investigation in rural areas along the Belbies unlined drain. This drain is known of being heavily polluted by agricultural and municipal wastewater. The hydrogeochemical analysis reveals high pollution levels by Pb, Cd, and Cr for most of the collected shallow groundwater samples nearby the drain. Additionally, NO₃^-, fecal and total coliform bacteria were observed in many samples with high concentrations. Six factors were distinguished on the basis of principal component analysis and varimax rotation, with total variance more than 78%. These factors reflected sewage contamination, lithogenic and anthropogenic effects on the shallow groundwater. Hierarchical cluster analysis revealed two main clusters of groundwater groups. Accordingly, Electrical Resistivity Tomography (ERT) was carried out in the areas of the distinguished clusters to locate potential preferential flow paths and horizons of lateral flow around the drain. The obtained resistivity models illustrate breakthrough behavior in parts of the measured profiles due to the presence of permeable paths close to the drain. The applied integrative approach is valuable for understanding the ambiguities during the interpretation process and for characterizing water quality and the aquifer vulnerability conditions. Additionally, it may guide to understand the surface water-groundwater links in order to supply the growing population with safe water.