Groundwater overexploitation and seawater intrusion in coastal areas of arid and semi-arid regions

The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl- and SO42-, which can be attributed to seawater intrusion, where Cl is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. 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 25 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 NO3- concentration in the region

Groundwater Overexploitation and Seawater Intrusion in Coastal Areas of Arid and Semi-Arid Regions

The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl− and SO42−, which can be attributed to seawater intrusion, where Cl− is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. 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 25 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 NO3− concentration in the region

Hydrochemical characteristics and flow of the Nubian Aquifer System in Tazerbo Wellfield, SE Libya

The desert of eastern Libya forms one of the most arid regions of the Sahara. Libya suffers from a shortage in water resources due to its arid climate. On the other hand, Libya has large resources of good-quality groundwater distributed in six basin systems beneath the Sahara. In order to deal with the shortage of water in most coastal cities, the Libyan government established the Great Man-Made River Project to transport millions of cubic meters of water a day from desert wellfields to the coastal cities, where over 80% of the population lives. In this paper, a hydrogeochemical study is presented for the Nubian Sandstone Aquifer in Tazerbo Wellfield, SE Libya, based on chemical analyses and physical parameters for 108 wells. Samples were collected from 108 borewells of the Nubian Aquifer (Akakus Formation) from depth range between 280 m in the north and 500 m in the south. This study is the first hydrochemical investigation in Tazerbo and also in the whole Sahara, which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the groundwater hydrochemistry. The results of the analyses indicate soft to moderately hard, lowly mineralized, slightly alkaline groundwater, with Mg2+ as the main cation and HCO3- as the main anion. The major hydrogeochemical processes that affect the quality of water in sediments of the Nubian system at Tazerbo have been identified; the water type is mostly fresh MgHCO3, while NaHCO3 and KHCO3 are also found for some wells. These water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the aquifer by freshwater from the south

Groundwater flow and chemistry of the oases of Al Wahat, NE Libya

The quality and geochemistry of groundwater are significantly affected by the depositional environment of aquifer sediments. Miocene sediments in Al Wahat area (Jalu, Awjilah and Shakherah Oases) in the Libyan Desert at the north-east of the country have been deposited in fluvial marginal marine and marine environments. The purposes of this paper are to describe the areal distribution of the dominant water quality constituents, to identify the major hydro-geochemical processes that affect the quality of water and to evaluate the relations of sedimentary depositional environments and groundwater flow to the quality and geochemistry of water in aquifer sediments of Post-Eocene. This study is the first investigation in Al Wahat Oasis and also in the whole Sahara, which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the aquifer hydrochemistry. The area involved in this study is within the boundaries 28 degrees N-30 degrees N and 21 degrees E-23 degrees E. Eighteen wells are selected in the area, including eight piezometers, and ten samples were analysed from wells used for domestic and agricultural purposes. Results show high and significant increase in total dissolved solids, especially Na+, Cl-, SO42- and NO3- compared with the previous years. The chemical results for the groundwater samples in Al Wahat are classified according to the Stuyfzand groundwater classification system; the water type is mostly brackish and brackish-saline NaCl in the downstream direction and fresh-brackish NaHCO3 upstream. These water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the diluted saline aquifer by freshwater from the south. The different stages of cation exchange produce a chromatographic sequence of groundwater types. These cation exchange reactions during the freshening process occur mainly in the intercalated clay, resulting in a Na+ increase, and peaks of K+ and Mg2+ in the aquifer. In the north, the synsedimentary marine influence on the groundwater is stronger and the abstraction for irrigation is higher. Upconing of deep saline water and anthropogenic pollution may contribute significantly to the aquifer water quality. Calcite equilibrium and gypsum dissolution are also important hydrochemical processes in the aquifer

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 SO42- concentrations in groundwater near the shoreline, where localized SO42- anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO42- concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer

The origin of high sulfate concentrations and hydrochemistry of the Upper Miocene-Pliocene-Quaternary aquifer complex of Jifarah Plain, NW Libya

The high uncontrolled groundwater extraction in Jifarah Plain, NW Libya, causes a modification of natural flow systems, inducing seawater intrusion and causing groundwater quality deterioration. The principal aim of this study is to identify the hydrogeochemical processes in this coastal aquifer in order to verify the main sources of sulfate concentration increase that occurs in the system. In order to achieve this aim, water samples were collected from 134 sampling wells in the study area and analyzed for the major cations and anions; physical and chemical parameters were measured, such as water level, electrical conductivity, pH and temperature. The analytical results obtained in the hydrochemical study were interpreted using Piper diagram, ion correlations with Na+/Cl-, SO42-, Cl- and TDS, in conjunction with calculation of the ionic deviations of the conservative freshwater/seawater mixture and saturation indices using the PHREEQC 2.16 software. The large SO42 anomaly observed in groundwater near the coast was explained by the presence of seawater intrusion and upconing of deep saline water in these areas. This conclusion is based on high chloride concentrations, the inverse cation exchange reactions and the lower piezometric level compared to sea level. Inland, in Sabratah, the high SO42-values are related to gypsum dissolution from the Upper Miocene Formation in the lower part of the upper aquifer. These locally high SO42 concentrations in the south of the study area show overall increase in the upstream direction, which also suggests the dissolution of evaporites from the mountain aquifers in the south. High SO42-concentration is also related to the effect of the scattered sebkha deposits in some areas along the coast