Groundwater Quality In Coastal Aquifer Research Articles

Geophysical techniques and geomatics-based mapping for groundwater exploration and sustainable development at Sidi Barrani Area, Egypt

The exploration of groundwater on the northwestern coast of Egypt holds significant importance for urbanization and sustainable development. This is due to a deficiency in water resources, particularly in the arid regions, and the increasing reliance on groundwater as an alternative water source in response to the declining rainfall in the region. Therefore, this study adopts a comprehensive approach that combines the Geographic Information System (GIS) and remote sensing techniques with a geophysical survey. The Time Domain Electromagnetic (TDEM) and Vertical Electrical Sounding (VES) methods are used in the survey to investigate and characterize the fractured limestone aquifer that dominates the study area. A pedological investigation, including both in-situ and laboratory testing, is conducted on the soil. The findings reveal multiple layers—such as the top fill layer, sandstone layer, upper limestone layer, clayey layer, middle gypsiferous limestone layer, and lower limestone layer—within the soil profile. The fill layer is typically composed of fine- to medium-grained sand. A total of 47.7 acres were lost and 28.6 acres were gained according to the results of the shoreline change over several spatial and temporal scales. Sea level rise-related shoreline changes result in saltwater intrusion, which has a substantial effect on the groundwater quality in coastal aquifers. The integration of geophysical tools indicates the presence of two geoelectrical layers in the subsurface succession. The second layer corresponds to the Marmarica limestone of the Middle Miocene, which represents a shallow water-bearing formation in the study area. This layer exhibits moderate and low resistivity, with depths ranging from 1.58 to 52.8 m and a thickness from 23.6 to 139.12 m.

Assessment and Characterization of Groundwater Quality of Malabar Coast in Kerala, India

A study was conducted to assess and characterize the groundwater quality of coastal aquifer of the Vatakara-Koyilandy stretch in the Kozhikode district of Kerala. Mann-Kendall Test was used for analysing the trend in groundwater levels. The Piper diagram was applied to determine the chemical facies of the groundwater and identify the evolution of hydrochemical parameters of groundwater sources. The source of the dissolved ions in the groundwater was described by the Gibbs diagram. The suitability of groundwater for irrigation was determined using the United States Salinity Laboratory diagram. Geostatistical tools were used to describe the spatial variability of groundwater levels and salinity and the ordinary kriging method was used to plot the spatial variability maps. It was found that Na+ was the predominant cation with maximum concentration varying from 455.6 mg/l to 1844 mg/l during pre-monsoon and post-monsoon; respectively. Concentration of Cl- in pre-monsoon and post-monsoon varied from 184 mg/l to 2417 mg/l and 99 mg/l to 714 mg/l; respectively. Other anions in the groundwater were SO42- and HCO3- with an average concentration of 239.79 mg/l and 129.59 mg/l in pre-monsoon and 110.73 mg/l and 75 mg/l in post-monsoon; respectively. The trend in groundwater in confined and semi-confined aquifers showed negative trends whereas eight wells resulted in a significantly negative trend. However, a significant decreasing trend was observed in wells near the coasts. The most dominant cations were (Na+, and K+) and the dominant anions were SO42- and Cl-. The dominant cations and anions were from the mixing of seawater with the groundwater. The Na+ ions were also found to be from the same source. In most of the area, the groundwater was highly to very high highly saline with medium sodium and not suitable for irrigation. In the unconfined aquifer, 25.2% and, in the semi-confined aquifer 24.0% area was found to be unfit for irrigation.

The Assessment of the Groundwater Quality in the Coastal Aquifers of the Essaouira Basin, Southwestern Morocco, Using Hydrogeochemistry and Isotopic Signatures

Because of anthropogenic activity and seawater intrusion, coastal aquifers worldwide frequently face a threat to their water supply due to salinization. This paper investigates the assessment of the groundwater quality in coastal aquifers of the Hauturivien aquifer in the Essaouira basin. In this study, 56 groundwater samples collected from the Hauturivian aquifer across four campaigns in 2017, 2018, 2019, and 2020 were subjected to multivariate analyses involving principal component analysis (PCA) and cluster analysis (CA) using SPSS software. Among the three main water types, the mixed Ca-Mg-Cl classification was predominant in the investigated aquifer. In addition to the natural processes (such as the water–rock interaction, ion exchange, dissolution/precipitation dynamics, and evaporation) that govern groundwater quality, current land use practices have increased salinization in this poorly drained semi-arid area. Based on assessments using Water Quality Index (WQI) and Irrigation Water Quality Index (IWQI), the water quality is suitable for human consumption, but its use for irrigation is limited to crops that can tolerate high salt levels. The stable isotopes (δ2H and δ18O) of groundwater demonstrated that local precipitation is the primary recharge source. Nonetheless, the evaporation process, influenced by various geological conditions, affects groundwater recharge, regardless of the topographical differences in the study area.

Design of groundwater monitoring network for coastal aquifers based on seawater intrusion vulnerability: A case study of Mandaue City, Philippines

Groundwater is an essential source of freshwater. However, this natural resource exhibits high vulnerability to contamination due to human activities and natural phenomena. Over extraction of groundwater and sea level rise have hastened seawater intrusion in aquifers that lie along the coasts. This has led to the accelerated deterioration of groundwater quality in coastal aquifers. Thus, there is an urgent need to develop tools to monitor groundwater resources. In this study, a framework of selecting priority areas for monitoring was applied to Mandaue City, Philippines. The monitoring areas were selected based on their vulnerability to seawater intrusion using the GALDIT-index. A collection of 77 initial public sites were investigated as potential locations of monitoring wells. The resulting network determined 45 priority areas located across the study area wherein monitoring wells should be located for the long-term observation of groundwater quality. These sites are composed of 28 from the initially investigated locations and 17 proposed sites which were determined to satisfy the required number of wells lacking in certain areas. The results of this study are intended to aid decision makers in creating groundwater management plans.

Hydrogeochemical Characterization and Identification of Factors Influencing Groundwater Quality in Coastal Aquifers, Case: La Yarada, Tacna, Peru.

The coastal aquifer La Yarada has anthropogenic and geogenic contamination that adversely affect the quality of groundwater for population and agricultural use. In this scenario, multivariate statistical methods were applied in 20 physicochemical and isotopic parameters of 53 groundwater pumping wells in October 2020, with the aim of characterizing the hydrogeochemical processes that dominate the groundwater of the coastal aquifer and the factors that cause them to optimize the effective management of water resources, delimiting areas affected by more than one salinization process. The samples were grouped into three clusters (C1, C2, and C3) with cluster analysis, the spatial distribution of C2 and C3 (reclassified in stiff diagrams), evidenced hydrogeochemical facies associated with the flow and recharge directions governed by the structural lineaments (NE-SO), favoring some areas more than others, arising different facies and hydrogeochemical processes. Factor analysis was applied from three different approaches: (1) main elements, (2) trace elements, and (3) physicochemical and isotopic parameters; exposing 6 distinguishable hydrogeochemical processes in the aquifer and factors that cause them: (i) salinization—marine intrusion, (ii) fertilizer leaching and dissolution of (Ca2+, Mg2+), (iii) wastewater mixture (NO3−), (iv) reducing conditions (Fe, Mn, Al), (v) contributions of (B, Sr), (vi) conservative mixtures and dissolution (As, F). It was validated with water quality indices (WQI) according to the national limits, delimiting 67 km2 parallel to the coast with “bad” to “very bad” quality for human consumption and unsuitable for irrigation according to the Wilcox diagram thus pre-treatment in this area is indispensable.

Seawater intrusion into coastal aquifers from semi-arid environments, Case of the alluvial aquifer of Essaouira basin (Morocco)

Marine intrusion phenomenon is the main phenomenon threatening the groundwater quality in coastal aquifers around the world. This phenomenon is generally caused by the overexploitation of aquifers, decline in the piezometric level and the rise in sea level under the climate change effect. There are several approaches to study and assess the marine intrusion phenomenon. For this study, the crossing of piezometric, hydrochemical and isotopic approaches was adopted to highlight the state of this phenomenon within the Plio-quaternary aquifer of the Essaouira basin. The couples (Na, Cl), (Ca, Mg), (Br, Cl), (δ2H, δ18O), (δ18O, Cl) were determined for 24 samples capturing the shallow aquifer of the Essaouira basin. The piezometric approach shows that negative piezometric levels are registered. The ionic ratios Br/Cl close to 1.5 and 1.7‰, Na/Cl close to 0.86, Mg/Ca and SO4/Cl weak showed that the seawater begins to invade the freshwater of the Plio-quaternary aquifer of Essaouira basin. This intrusion demonstrated by ionic ratios and corroborated by isotopic approach and the combined use of oxygen-18 contents and chlorides has a mixing rate of 15.9% at the well 11/51, 14.5% at the sample 45/51, 13.2% at the well 149/51, 13.3% at point O114 and 12.8% at the well O94. However, the results of the hydrogeochemical and isotopic approach suggest intrusion up to 2 km from the sea; this reflects a warning sign about the groundwater deterioration of the study area.

Seasonal variability of groundwater quality in coastal aquifers of Kavaratti Island, Lakshadweep Archipelago, India

Lakshadweep Archipelago is comprised of several tiny coral atolls and scattered in the Arabian Sea off the south-west of India. Ground water is the only available fresh water resource for the islanders. The groundwater quality is decreased in this island due to population growth and anthropogenic activities like sewage dumping and agricultural activities. For this study, a total of 20 groundwater samples was collected randomly from the open wells that cover the entire area of the island. The physico-chemical parameters of groundwater were analysed in pre- and post-monsoon seasons during the year 2016–2017. The concentration of a majority of the chemical constituents exceeds the standards of WHO during post-monsoon than pre-monsoon season. EC content exhibited the violation of drinking water quality standards. The highest value of EC range 1023–6874 μS/cm recorded in post-monsoon than pre-monsoon. TDS concentration range from 574.6 to 1503.4 mg/l and 665–4468 mg/l in pre and post-monsoon seasons. Geochemical evolution diagram categories the groundwater facies into Na+-K+-Cl--SO42-, Ca2+-Mg2+-HCO3-, and Ca2+-Mg2+-Cl--SO42- in both seasons. Gibbs plot revealed that the evaporation is the dominant factor controlling the mechanism of ground water hydrochemistry. The water quality index suggested that both pre-monsoon and post-monsoon around 93.95% of the samples are unsuitable for drinking purposes. The suitability of groundwater for irrigation was studied by calculating the percent of sodium, sodium adsorption ratio, magnesium hazard and Reveille's index. The Wilcox and USSL plots also indicated that most of the groundwater samples are found to be unsuitable for irrigation. HFE diagram productively delineates that groundwater of the study area has strong influence of sea water in the fresh water aquifers. The highest level of significant correlation was observed between Mg-TH (r = 0.87), EC-TDS (r = 0.86), and Cl–Na (r = 0.77) respectively. As a whole, it is observed that the groundwater is not suitable for drinking, irrigation and industrial purposes due to the exceeding of chemical parameters from their standard limits. Therefore, groundwater management measures may be worked out regionally to improve water quality by artificial recharge, rain water harvesting, periodic disinfection of the wells and saving the fresh water stocks in the island accordingly.

Hydrochemical and statistical evaluation of groundwater quality in coastal aquifers in Tamil Nadu, India

Groundwater samples were collected from 36 wells during summer and monsoon seasons in a coastal region in Tamil Nadu, India in 2011. The chemical analysis of groundwater samples indicated that groundwater in the region was fresh to saline with cationic concentrations in the order Na+ > Ca2+ > Mg2+ > K+ and anionic concentrations in the order Cl− > HCO3− > SO42− > NO3−. Most of the groundwater samples had a chemical composition dominated by sodium and chloride ions. Scatter plots suggested that the principal processes influencing groundwater quality in the area are likely to be: ion exchange; reverse ion exchange; silicate weathering and evaporation. A Gibbs plot indicated that evaporation was the dominant process influencing groundwater salinity in the summer season, whereas both water–rock interactions and evaporation influenced the chemical composition and salinity of groundwater in the monsoon season. A principal component analysis of the data shows four principal components for the monsoon and three components for the summer seasons, which account for 85% and 87% of the total variance, respectively. The assessment has indicated that there is widespread seawater intrusion in coastal aquifers, which has led to changes in hydrochemical processes in the study area.

Hydrogeochemical Evolution and Heavy Metal Contamination in Groundwater of a Reclaimed Land on Zhoushan Island

The need for valuable land has encouraged reclamation in coastal areas worldwide in the past decades. Land reclamation can alter the groundwater quality in coastal aquifers. The purpose of this study is to identify the effect of land reclamation on groundwater chemistry, especially the major ions, and heavy metals on Zhoushan Island, China. The subsurface media on the island is composed of two layers, i.e., an upper infill layer and an underlain clay layer. The upper layer is previously ocean and filled with various materials. The clay layer is the original marine sediment. The dominated Na and Cl ions in groundwater illustrate high salinity sources of groundwater in the subsurface of the reclaimed land. A mixing trend between seawater and river water of the groundwater in infill layer is also detected based on the ratios of Cl and Br. Though the heavy metal concentrations (Cd, Cr, Zn and Hg) are high in marine sediments, no significant releasing trends in the groundwater are detected in a short-term after reclamation (based on standard GB18668). Meanwhile, Fe-III concentrations in the aquifer have a strong correlation with precipitation events. Column desorption experiments and simulations indicate the Cd and Cr release from the sediment would pose a health risk when the groundwater in the infill layer being gradually flushed by fresh water. These results provide a foundation for the prediction of groundwater quality and are helpful for the future water management in a newly reclaimed land.

Degradation of groundwater quality in coastal aquifer of Sabratah area, NW Libya

Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO4 2− concentrations in groundwater near the shoreline, where localized SO4 2− anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO4 2− concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.

Hydrochemical characteristics and quality assessment of groundwater along the Manavalakurichi coast, Tamil Nadu, India

The present study was carried out to find the groundwater quality of coastal aquifer along Manavalakurichi coast. For this study, a total of 30 groundwater samples were collected randomly from open wells and borewells. The concentration of major ions and other geochemical parameters in the groundwater were analyzed in the laboratory by adopting standard procedures suggested by the American Public Health Association. The order of the dominant cations in the study area was found to be Na+ > Ca2+ > Mg2+ > K+, whereas the sequence of dominant anions was {text{Cl}}^{ - } > {text{HCO}}_{3}^{ - } > {text{SO}}_{4}^{2 - }. The hydrogeochemical facies of the groundwater samples were studied by constructing piper trilinear diagram which revealed the evidence of saltwater intrusion into the study area. The obtained geochemical parameters were compared with the standard permissible limits suggested by the World Health Organization and Indian Standard Institution to determine the drinking water quality in the study area. The analysis suggests that the groundwater from the wells W25 and W26 is unsuitable for drinking. The suitability of groundwater for irrigation was studied by calculating percent sodium, sodium absorption ratio and residual sodium carbonate values. The Wilcox and USSL plots were also prepared. It was found that the groundwater from the stations W1, W25 and W26 is unfit for irrigation. The Gibbs plots were also sketched to study the mechanisms controlling the geochemical composition of groundwater in the study area.

Multi isotopic approach to study temporal variation of groundwater quality in coastal aquifer of Saijo plain, Shikoku Island, Japan

Multi isotopic approach to study temporal variation of groundwater quality in coastal aquifer of Saijo plain, Shikoku Island, Japan

Multi isotopic approach to study temporal variation of groundwater quality in coastal aquifer of Saijo plain, Shikoku Island, Japan

In order to delineate geochemical processes and its relation with groundwater quality evolution, hydrochemical and isotopic analysis were carried out in coastal groundwater of Saijo plain, western Japan. From analytical results, even within a small distance from the coast; ionic concentration of water samples varies a lot which infers non-homogenous and patchy distribution of different aquifer system (complex geology). From stable isotopic results, it was found that most of sample points plotted near the local meteoric water line (LMWL) i.e. origin of ground water is meteoric in principle; however point away from the LMWL might favors exchange with rock minerals.

Assessment of groundwater quality in the northeastern coastal area of UAE as precursor for desalination

Extraction of brackish groundwater in coastal aquifers is believed not only to mitigate the effects of seawater intrusion but also to reduce the desalination cost of the extracted water. However, evaluation of the groundwater quality in coastal aquifers is an essential initial step before determining the locations of brackish water extraction wells and extraction rates. Therefore, this paper presents spatial and temporal assessments of the groundwater quality in the coastal aquifer of Wadi Ham located in northeastern part of UAE. This assessment is considered as precursor for evaluation of the aquifer potentiality as source for water desalination. A total of 245 water samples from 26 different observation wells were collected over the period from 1989 to 2006 to assess the origin and quality of the groundwater in this coastal aquifer. It was found that saltwater intrusion from the Gulf of Oman was not the main source of brackish water in several parts of the aquifer prior to year 2000. However, results also show that more recently seawater intrusion has become the leading factor of water salinity in the aquifer especially near the coast. It was found that seawater intrusion extended about 8 km inland from the coast of the Gulf of Oman.

Geochemical Processes Regulating Groundwater Quality in Coastal Aquifer in Odawara Region, Kanagawa Prefecture, Japan

Groundwater in the coastal aquifer in the Odawara region, the southern region of the Ashigara plain, is considerably used for industrial, agricultural and municipal water supplies. Since 1980s, many studies focused on the problems of water level decline and groundwater salinization in this region. However, for considering a better management of this groundwater resource, more precise understanding of the geochemical processes occurring in this aquifer and changes in the underground environment due to salinization is necessary. For this purpose, field surveys were carried out in winter (January and February, 2009) and in summer (July and August, 2009). More than 100 groundwater samples were collected from the unconfined and confined aquifers in the region and analyzed for their chemical and stable isotopic compositions. A series of comprehensive interpretations on water quality data using Piper diagram and Stiff diagram together with stable isotopic data have been carried out to gain insight into the spatial and temporal variations of the quality and the geochemical evolution of the groundwater. Several geochemical processes were identified as principal factors controlling the groundwater quality in this region. Silicate weathering which is the result of water rock interaction is an important process dominating unconfined and confined aquifers, over a wide area. The other geochemical processes such as ion exchange reactions and salinization are also occurring in this region. The latter process, salinization, is limited in area but an important phenomenon and seems to be caused by salt water up-coning in the confined aquifer due to the over-extraction of groundwater since 1970s. This phenomenon was detected typically at particularly deep wells in the industrial area near the coast where the pumping rate is high. These phenomena, which occurred in the study region, were summarized in a schematic conceptual model as a helpful tool for the management of the groundwater resources.