Hydrochemical and geoelectrical investigation of the coastal shallow aquifers in El-Omayed area, Egypt

Monitoring and assessment of the coastal aquifers are becoming a worldwide concern for the need of additional and sustainable water resources to satisfy demographic growth and economic development. A hydrochemical and geoelectrical investigation was conducted in the El-Omayed area in the northwestern coast of Egypt. The aim of the study was to delineate different water-bearing formations, provide a general evaluation of groundwater quality, and identify the recharge sources in aquifers. Thirty-seven water samples were collected and chemically analyzed from the sand dune accumulations and oolitic limestone aquifers. Fifteen profiles of vertical electrical soundings (VESs) were obtained in the oolitic limestone aquifer to examine the variations of subsurface geology and associated groundwater chemistry. The groundwater reserves in the El-Omayed area are mainly contained in sand dune accumulations and oolitic limestone aquifers. The aquifer of sand dune accumulations contains freshwater of low salinity (average total dissolved solids (TDS)?=?974 mg/l). Groundwater of oolitic limestone aquifer is slightly brackish (average TDS?=?1,486 mg/l). Groundwater of these aquifers can be used for irrigation under special management for salinity control, and regular leaching as indicated by electrical conductivity and sodium adsorption ratio. Results of VES interpretation classified the subsurface sequence of oolitic limestone aquifer into four geoelectric zones, with increasing depth, calcareous loam, gypsum, oolitic limestone, and sandy limestone. Oolitic limestone constitutes the main aquifer and has a thickness of 12–32 m.     

Delineating shallow saline groundwater zones from Southern India using geophysical indicators

A geophysical survey was conducted over an industrial belt encompassing 80 functional leather factories in Southern India. These factories discharge untreated effluents which pollute shallow groundwater where electrical conductivity (EC) value had a wide range between 545 and 26,600 μS/cm (mean, 3, 901 μS/cm). The ranges of Na⁺ and Cl^? ions were from 46 to 4,850 mg/L (mean, 348 mg/L) and 25 to 10,390 mg/L (mean, 1,079 mg/L), respectively. Geoelectrical layer parameters of 37 vertical electrical soundings were analyzed to demarcate fresh and saline water zones. However, the analysis not did lead to a unique resolution of saline and fresh waters. It was difficult to assign a definitive value to the aquifer resistivity of any area. Thus, geophysical indicators, namely longitudinal unit conductance (S), transverse unit resistance (T), and average longitudinal resistivity (R _s), were calculated for identifying fresh and saline waters. Spatial distributions of S, T, and R _s reflected widely varying ranges for the saline and fresh water zones. Further, the empirical relation of formation factor (F) was established from pore-water resistivity and aquifer resistivity for fresh and saline aquifers, which may be used to estimate local EC values from the aquifer resistivity, where well water is not available.     

Assessment of seawater impact using major hydrochemical ions: a case study from Sadras, Tamilnadu, India

The impact of seawater intrusion was investigated using major hydrogeochemical ions to evaluate the origin of salinity in Sadras watershed located between Buckingham Canal and Bay of Bengal in the southeastern coast of India. From empirical data collected twice during pre- and post-monsoon seasons, it was found that groundwater was slightly acidic to mildly alkaline, and more than 44% of groundwater samples had EC > 3,000 ??S/cm in both the seasons. Results of principle component analysis (PCA) showed that Na^?+?, Cl^???, Mg^2?+?, and SO $_{4}^{\,\, 2-}$ concentrations had the highest loading factor and the samples affected by saline/seawater were separated from the cluster. Hydrochemical processes that accompany the saline/seawater were identified using ionic changes. It was observed during sampling periods that the mixing due to saline/seawater intrusion varied from 4.82?C7.86%. Negative values of ionic change (e _change) for Na^?+? and K^?+? decreased with the increasing fraction of seawater. Furthermore, salinity, sodium adsorption ratio, percentage of sodium Na (%), and exchangeable sodium percentage in well samples showed that groundwater was unsuitable for irrigation purposes.     

Groundwater Quality Monitoring in Shallow and Deep Aquifers in Saidabad Tahsil Area, Mathura District, India

Water availability in arid regions is both sporadic and highly variable in quantity. If the water quality shows large variations of salinity and concentration of other chemical constituents with depth and time span, it has considerable effect on the entire hydrological set up of the area. In the Saidabad tahsil area, the deep aquifers that supply water to borewells in the alluvial plain of the Mathura region, Uttar Pradesh, have higher salinity than those of the dugwells from the shallow aquifers. The excessive drilling of tubewells and high yield tubewells are resulting in deterioration of water quality of the shallow aquifers. On the contrary, the chemical constituents such as, Na⁺, K ⁺, Cl ^-, andHCO ₃ ^- show higher concentration in shallow aquifers than deep aquifers. A study carried out to monitor water quality in this region reveals that the groundwater quality varies with depth and time span in shallow and deep aquifers. Factors controlling variations in salinity and concentration of chemical constituents of the water in the two types of aquifers are discussed. The relative merits of the shallow water for potability are pointed out with respect to salinity concentrations and public health.     

Salinity variations in the water resources fed by the Etnean volcanic aquifers (Sicily, Italy): natural vs. anthropogenic causes

In this paper, in an attempt to reveal possible changes connected to natural or anthropogenic causes, the main results of hydrogeochemical monitoring carried out at Mount Etna are evaluated. We report on the salinity contents of the groundwaters that flow in fractured volcanics, which make up the flanks of the volcano. These waters, analyzed for major ion chemistry, were sampled regularly from 1994 to 2004. Basing on nonparametric Sen??s slope estimator, time series of groundwater composition reveal that the salinity of most of the Etnean aquifers increased by 0.5% to 3.5% each year during this period. This change in the water chemistry is clearly referable to the overexploitation of the aquifers. This increasing trend needs to be inverted urgently; otherwise, it will cause a shortage of water in the near future, because the maximum admissible concentration of salinity for drinking water will be exceeded.     

The role of land use change on the sustainability of groundwater resources in the eastern plains of Kurdistan,Iran

In this study, land use change and its effects on level and volume of groundwater were investigated. Using satellite images and field measurements, change in land uses was determined from 1998 to 2007. By analyzing the observation wells data and preparing the zoning maps in GIS, groundwater level fluctuations were assessed. Considering the area corresponding to these fluctuations, changes in aquifers volume were calculated. The rain gauge and synoptic stations data were used to calculate meteorological parameters and evapotranspiration. The water requirement of the main crops was determined by CROPWAT software. Results showed an increase in average rainfall and crops water requirement. The classification of satellite images showed that 11,800 ha was increased in lands under irrigated crops cultivation, while 27,655 ha of rangeland was declined in the region. Groundwater levels dropped an average of 7 m, equal to 63.4 MCM reductions in volume of water in the aquifer.     

Deterioration of coastal groundwater quality in Island and mainland regions of Ramanathapuram District, Southern India

A study was carried out in the Island and mainland regions of Ramanathapuram District to characterize the physico-chemical characteristics of 87 groundwater samples in Island and 112 groundwater samples in mainland which include pH, EC, TDS, salinity, total alkalinity, calcium hardness, magnesium hardness, total hardness, chloride and fluoride. Heavy inorganic load in majority of the groundwater samples has been estimated due to the salinity, TDS, TH and chloride beyond the threshold level which substantiates the percolation of sea water into the freshwater confined zones. Although the groundwater sources are available in plenty, the scarcity of potable water is most prevalent in this coastal area. The Water Quality Index (WQI) and Langeleir Saturation Index (LSI) have also been calculated to know the potable and corrosive/incrusting nature of the water samples. The statistical tools such as principal component analysis, box plots and correlation matrix have also been used to explain the influence of different physico-chemical parameters with respect to one another among the groundwater samples. The percentage of groundwater samples in mainland was more than that in Island with respect to the acceptable limit of WHO drinking standard, especially in TDS, CH, TH and chloride but the converse is observed in the case of fluoride. About 8 % of the mainland aquifers and 42 % of Island aquifers were identified to have fluoride greater than 1.5 mg/l. The signature of salt-water intrusion is observed from the ratio of Cl/CO ₃ ^2? ?+?HCO₃ and TA/TH. A proper management plan to cater potable water to the immediate needs of the people is to be envisaged.     

Earth-tide-induced fluctuations in the salinity of an inland river,New South Wales,Australia: a short-term study

Wybong Creek discharges salts into the agriculturally and industrially important Hunter River in New South Wales, Australia. Abrupt increases in salinity occur periodically in the mid-Wybong Creek catchment. In order to understand the processes which cause these abrupt increases, changes in surface and groundwater were investigated. It is shown that salinity increases can be attributed to highly discrete groundwater discharge directly into the river from below. Hourly electrical conductivity data measured in the river showed regular, diurnal electrical conductivity fluctuations of up to 350 μS cm^?1. These fluctuations could not be attributed to barometric pressure, temperature, or evapotranspiration. Instead, a similar periodicity in surface water electrical conductivity and groundwater height in nearby groundwater wells was found. Fluctuations were of similar periodicity to the orthotides which cause fluctuations in surface water height and are induced by Earth tides. The geology in the mid-catchment area indicates conditions are optimal for Earth tides to impact groundwater. The reporting of orthotidal changes in water chemistry in this article is believed to be the first of its kind in the scientific literature, with the large fluctuations noted having important implications for water monitoring and management in the catchment. Further research investigating Earth-tide-induced phases of groundwater heights will better constrain the relationships between surface water chemistry and groundwater height.     

Modeling interactions between saturated and un-saturated zones by Hydrus-1D in semi-arid regions (plain of Kairouan,Central Tunisia)

In semi-arid areas like the Kairouan region, salinization has become an increasing concern because of the constant irrigation with saline water and over use of groundwater resources, soils, and aquifers. In this study, a methodology has been developed to evaluate groundwater contamination risk based on the unsaturated zone hydraulic properties. Two soil profiles with different ranges of salinity, one located in the north of the plain and another one in the south of plain (each 30 m deep) and both characterized by direct recharge of the aquifer, were chosen. Simulations were conducted with Hydrus-1D code using measured precipitation data for the period 1998–2003 and calculated evapotranspiration for both chosen profiles. Four combinations of initial conditions of water content and salt concentration were used for the simulation process in order to find the best match between simulated and measured values. The success of the calibration of Hydrus-1D allowed the investigation of some scenarios in order to assess the contamination risk under different natural conditions. The aquifer risk contamination is related to the natural conditions where it increased while facing climate change and temperature increase and decreased in the presence of a clay layer. Hydrus-1D was a useful tool to predict the groundwater level and quality in the case of a direct recharge and in the absence of any information related to the soil layers except for the texture.     

Integrated approach for demarcating subsurface pollution and saline water intrusion zones in SIPCOT area: a case study from Cuddalore in Southern India

This paper deals with a systematic hydrogeological, geophysical, and hydrochemical investigations carried out in SIPCOT area in Southern India to demarcate groundwater pollution and saline intrusion through Uppanar River, which flows parallel to sea coast with high salinity (average TDS 28, 870 mg/l) due to back waters as well as discharge of industrial and domestic effluents. Hydrogeological and geophysical investigations comprising topographic survey, self-potential, multi-electrode resistivity imaging, and water quality monitoring were found the extent of saline water intrusion in the south and pockets of subsurface pollution in the north of the study area. Since the area is beset with highly permeable unconfined quaternary alluvium forming potential aquifer at shallow depth, long-term excessive pumping and influence of the River have led to lowering of the water table and degradation of water quality through increased salinity there by generating reversal of hydraulic gradient in the south. The improper management of industrial wastes and left over chemicals by closed industries has led surface and subsurface pollution in the north of the study area.     

北京城市副中心海绵城市建设对地下水环境影响评价

以城市副中心北运河西岸湿地（甘棠大桥段）作为典型面状海绵体,利用2018年5月—9月采集的300组地表水和地下水监测数据,分析典型海绵体地下水水化学特征及形成机制,探讨不同含水层之间水力联系,并以Cl-为指示因子,结合其他水化学指标研究分析典型面状海绵体建设背景下地下水与地表水之间的交互作用及影响程度。结果显示,在垂向上,10 m、20 m含水层地下水之间联系密切,且受大气降水影响明显;在平面上,地表水对10 m、20 m含水层组地下水的影响距离为90 m～120 m,地表水对30 m含水层组地下水的影响距离为80 m～90 m。     

Assessment of phenol infiltration resilience in soil media by HYDRUS-1D transport model for a waste discharge site

The movement of contaminants through soil imparts a variety of geo-environmental problem inclusive of lithospheric pollution. Near-surface aquifers are often vulnerable to contamination from surface source if overlying soil possesses poor resilience or contaminant attenuation capacity. The prediction of contaminant transport through soil is urged to protect groundwater from sources of pollutants. Using field simulation through column experiments and mathematical modeling like HYDRUS-1D, assessment of soil resilience and movement of contaminants through the subsurface to reach aquifers can be predicted. An outfall site of effluents of a coke oven plant comprising of alarming concentration of phenol (4–12.2 mg/L) have been considered for studying groundwater condition and quality, in situ soil characterization, and effluent characterization. Hydrogeological feature suggests the presence of near-surface aquifers at the effluent discharge site. Analysis of groundwater of nearby locality reveals the phenol concentration (0.11–0.75 mg/L) exceeded the prescribed limit of WHO specification (0.002 mg/L). The in situ soil, used in column experiment, possess higher saturated hydraulic conductivity (K _S ?=?5.25?×?10^?4 cm/s). The soil containing 47 % silt, 11 % clay, and 1.54 % organic carbon content was found to be a poor absorber of phenol (24 mg/kg). The linear phenol adsorption isotherm model showed the best fit (R ²?=?0.977, RMSE?=?1.057) to the test results. Column experiments revealed that the phenol removal percent and the length of the mass transfer zone increased with increasing bed heights. The overall phenol adsorption efficiency was found to be 42–49 %. Breakthrough curves (BTCs) predicted by HYDRUS-1D model appears to be close fitting with the BTCs derived from the column experiments. The phenol BTC predicted by the HYDRUS-1D model for 1.2 m depth subsurface soil, i.e., up to the depth of groundwater in the study area, showed that the exhaustion point was reached within 12 days of elapsed time. This clearly demonstrated poor attenuation capacity of the soil to retard migration of phenol to the groundwater from the surface outfall site. Suitable liner, based on these data, may be designed to inhibit subsurface transport of phenol and thereby to protect precious groundwater from contamination.     

Pesticide occurrence in groundwater and the physical characteristics in association with these detections in Ireland

This study explores the associations of pesticide occurrence in groundwater to geological characteristics of the monitoring points (MPs) contributing area. Pesticide analyses were undertaken during a 2-year groundwater monitoring campaign which generated 845 samples. MCPA and mecoprop were the most frequently detected pesticides in groundwater. Each MP (n?=?158) had a specifically delineated zone of contribution (ZOC) and the dominant physical characteristics present from nine national datasets were recorded for each ZOC. Associations between detections in groundwater and the dominant physical characteristic in each MPs ZOC tested were then statistically analyzed using Fisher’s exact test, logistic regression, and multiple logistic regression. The original physical characteristic datasets used that were associated with detections in groundwater were the type of MP, aquifer type, and Quaternary deposit type. Logistic regression revealed that springs, regionally important aquifer types, aquifers with a karstic flow regime, and alkaline Quaternary deposits in existence above karst aquifers in a MP’s ZOC were more likely to have a pesticide detection in groundwater. Multiple regression from this exploratory work showed some mutual dependency between soil association, aquifer type, and the Geological Survey of Ireland groundwater vulnerability map. The combination of national monitoring data and physical attribute datasets can be used to explore key areas where groundwater is more vulnerable to pesticide contamination.     

Study on the hydrogeochemical characteristics in groundwater, post- and pre-tsunami scenario, from Portnova to Pumpuhar, southeast coast of India

Natural hazards cause great damage to humankind and the surrounding ecosystem. They can cast certain indelible changes on the natural system. One such tsunami event occurred on 26 December 2004 and caused serious damage to the environment, including deterioration of groundwater quality. This study addresses the groundwater quality variation before and after the tsunami from Pumpuhar to Portnova in Tamil Nadu coast using geochemical methods. As a part of a separate Ph.D. study on the salinity of groundwater from Pondicherry to Velankanni, water quality of this region was studied with the collection of samples during November 2004, which indicated that shallow aquifers were not contaminated by sea water in certain locations. These locations were targeted for post-tsunami sample collection during the months of January, March and August 2005 from shallow aquifers. Significant physical mixing (confirmed with mixing models) within the aquifer occurred during January 2005, followed by precipitation of salts in March and complete leaching and dissolution of these salts in the post-monsoon season of August. As a result, maximum impact of tsunami water was observed in August after the onset of monsoon. Tsunami water inundated inland water bodies and topographic lows where it remained stagnant, especially in the near-shore regions. Maximum tsunami inundation occurred along the fluvial distributary channels, and it was accelerated by topography to a certain extent where the southern part of the study area has a gentler bathymetry than the north.     

Hydrochemical and water quality assessment of groundwater in Doon Valley of Outer Himalaya, Uttarakhand, India

The present study discusses ion sources and assesses the chemical quality of groundwater of Doon Valley in Outer Himalayan region for drinking and irrigational purposes. Valley is almost filled with Doon gravels that are main aquifers supplying water to its habitants. Recharged only by meteoric water, groundwater quality in these aquifers is controlled essentially by chemical processes occurring between water and lithology and locally altered by human activities. Seventy-six water samples were collected from dug wells, hand pumps and tube wells and were analysed for their major ion concentrations. The pH is varying from 5.6 to 7.4 and electrical conductivity from 71 to 951 μmho/cm. Groundwater of Doon valley is dominated by bicarbonate contributing 83% in anionic abundance while calcium and magnesium dominate in cationic concentrations with 88%. The seasonal and spatial variation in ionic concentration, in general, is related to discharge and lithology. The high ratio of (Ca + Mg)/(Na + K), i.e. 10, low ratio of (Na + K)/TZ+, i.e.0.2 and also the presence of carbonate lithology in the northern part of valley, is indicative of carbonate dissolution as the main controlling solute acquisition process in the valley. The low abundance of silica content and high HCO?/H?SiO? ratio also supports carbonate dissolution and less significant role of silicate weathering as the major source for dissolved ions in Doon Valley. The analytical results computed for various indices show that water is of fairly good quality, although, hard but have moderate dissolved solid content. It is free from sodium hazard lying in C?-S? and C?-S? class of USSL diagram and in general suitable for drinking and irrigation except few locations having slightly high salinity hazard.     

Groundwater stress and vulnerability in rural coastal aquifers under competing demands: a case study from Sri Lanka

Rural coastal aquifers are undergoing rapid changes due to increasing population, high water demand with expanding agricultural and domestic uses, and seawater intrusion due to unmanaged water pumping. The combined impact of these activities is the deterioration of groundwater quality, public health concerns, and unsustainable water demands. The Kalpitiya peninsula located northwest of Sri Lanka is one area undergoing such changes. This land area is limited and surrounded almost completely by sea and lagoon. This study consists of groundwater sampling and analysis, and vulnerability assessment using the DRASTIC method. The results reveal that the peninsula is experiencing multiple threats due to population growth, seawater intrusion, land use exploitation for intensive agriculture, groundwater vulnerability from agricultural and domestic uses, and potential public health impacts. Results show that nitrate is a prevalent and serious contaminant occurring in large concentrations (up to 128 mg/l NO₃?CN), while salinity from seawater intrusion produces high chloride content (up to 471 mg/l), affecting freshwater sources. High nitrate levels may have already affected public health based on limited sampling for methemoglobin. The two main sources of nitrogen loadings in the area are fertilizer and human excreta. The major source of nitrogen results from the use of fertilizers and poor management of intense agricultural systems where a maximum application rate of up to 11.21 metric tons N/km² per season is typical. These findings suggest that management of coastal aquifers requires an integrated approach to address both the prevalence of agriculture as an economic livelihood, and increasing population growth.     

Integrated techniques to identify groundwater vulnerability to pollution in a highly industrialized terrain, Tamilnadu, India

Investigation has been made to identify groundwater vulnerability to pollution by using geoelectric and hydrochemical investigations in an important industrial town Mettur located in Tamilnadu state of India. Schlumberger vertical electric soundings were carried out in 23 locations and groundwater samples collected from bore wells in the same locations. The resistivity value with <20 Ωm up to a depth of 36 m indicate contamination of groundwater in areas influenced by sewages from industries, domestic and agricultural practices in the central and southern part of the study area. The calculated specific conductance was noted higher than EC in central and southern part of the study area with low resistivity indicating the contaminated nature of groundwater. Concentrations of Ca, Na, Mg and K along with Cl, HCO(3), SO(4) and NO(3) were higher in certain locations when compared with WHO and ISI standards. The facies concept demarcated four groups based on the nature of groundwater contamination. The trace elements Fe and Pb were higher in locations confined to industrial zones and Zn and Cu were within the prescribed limit in all the samples.     

Delineation of soil and groundwater contamination using geophysical methods at a waste disposal site in Çanakkale, Turkey

Direct current (DC) resistivity, self potential (SP) and very low frequency electromagnetic (VLF-EM) measurements are carried out to detect the spread of groundwater contamination and to locate possible pathways of leachate plumes, that resulted from an open waste disposal site of Canakkale municipality. There is no proper management of the waste disposal site in which industrial and domestic wastes were improperly dumped. Furthermore, because of the dumpsite is being located at the catchment area borders of a small creek and is being topographically at a high elevation relative to the urban area, the groundwater is expected to be hazardously contaminated. Interpretations of DC resistivity geoelectrical data showed a low resistivity zone (<5 ohm-m), which appears to be a zone, that is fully saturated with leachate from an open dumpsite. The VLF-EM and SP method, support the results of geoelectrical method relating a contaminated zone in the survey area. There is a good correlation between the geophysical investigations and the results of previously collected geochemical and hydrochemical measurements.     

Regional assessment of groundwater quality for drinking purpose

Owing to limited surface water during a long-term drought, this work attempted to locate clean and safe groundwater in the Choushui River alluvial fan of Taiwan based on drinking-water quality standards. Because aquifers contained several pollutants, multivariate indicator kriging (MVIK) was adopted to integrate the multiple pollutants in groundwater based on drinking- and raw-water quality standards and to explore spatial uncertainty. According to probabilities estimated by MVIK, safe zones were determined under four treatment conditions—no treatment; ammonium–N and iron removal; manganese and arsenic removal; and ammonium–N, iron, manganese, and arsenic removal. The analyzed results reveal that groundwater in the study area is not appropriate for drinking use without any treatments because of high ammonium–N, iron, manganese, and/or arsenic concentrations. After ammonium–N, iron, manganese, and arsenic removed, about 81.9–94.9% of total areas can extract safe groundwater for drinking. The proximal-fan, central mid-fan, southern mid-fan, and northern regions are the excellent locations to pump safe groundwater for drinking after treatment. Deep aquifers of exceeding 200 m depth have wider regions to obtain excellent groundwater than shallow aquifers do.     

Estimation of spatial distrubition of groundwater level and risky areas of seawater intrusion on the coastal region in Çarşamba Plain,Turkey, using different interpolation methods

Groundwater level plays a significant role in coastal plains. Heavy pumping and excessive use of near-coast groundwater can increase the intrusion of seawater into the aquifers. In the present study, groundwater levels were measured at 59 groundwater wells at different times during pre- and post-irrigation seasons (April and September of the year 2012) in Çar?amba Plain, Turkey. To select the best method, two deterministic interpolation methods (inverse distance weighing (IDW) with the weights of 1, 2, and 3 and radial basis function (RBF) with spline with tension (SPT) and completely regularized spline (CRS)) and two stochastic methods (ordinary kriging (OK) with spherical, exponential, and Gaussian variograms) and cokriging (COK)) were compared and then the best interpolation method was used to evaluate the spatial distribution of groundwater levels in different seasons and seasonal changes. A total of nine different techniques were tested. Also, risky areas of seawater intrusion in coastal area were determined using the best methods for two periods. The performance of these interpolation methods is evaluated by using a validation test method. Statistical indices of correlation (R ²), mean absolute error (MAE), and root-mean-square error (RMSE) were used to select and validate the best methods. Comparisons between predicted and observed values indicated RBF as the optimal method for groundwater level estimation in April and September. When the best method RBF and the worst method IDW were compared, significant differences were observed in the spatial distribution of groundwater. Results of the study also revealed that excessive groundwater withdrawals during the post-irrigation season dropped the groundwater levels up to 2.0 m in some sections. With regard to seawater intrusion, 9,103 ha of land area was determined to be highly risky and risky.