Hydrogeochemical investigations were carried out around Fetzara Lake, Northeast Algeria, to assess the quality of groundwater for its suitability for drinking and irrigation purposes. The groundwater chemistry is mainly controlled by the water-rock interactions, but also influenced by other processes such as evapotranspiration and ion exchange. Groundwater samples collected, during two periods (1993 and 2007) from wells in the area were analyzed for pH, EC, TDS, Ca 2+ , Mg 2+ , Na + , K + , CO 3 2− , HCO 3 − , Cl − , SO 4 2− , and NO 3 −. The chemical relationships in Piper's diagram and Gibbs's diagram suggest that groundwaters mainly belong to noncarbonate alkali type and Cl − group and are controlled by evaporation dominance, respectively, due to the sluggish drainage conditions, greater water-rock interaction, and anthropogenic activities. A comparison of the groundwater quality in relation to drinking water quality standards proves that most of the water samples are not suitable for drinking. US Salinity Laboratory's and Wilcox's diagrams and %Na + used for evaluating the water quality for irrigation suggest that the majority of the groundwater samples are not good for irrigation.

This work presents results of the hydrogeological and hydrochemical studies on groundwater samples from the alluvial aquifer of Merdja in Tébessa, located in the Western part of this town. Its groundwater resources are used mainly for crop irrigation in an agriculture dominated area. Hydrochemical and water quality data obtained through a sampling period (December 2008) and analysis program indicate that nitrate pollution can be a serious problem affecting groundwater due to the use of nitrogen (N) fertilizers in agriculture. The concentration of nitrate in groundwater ranged from 19 to 281 mg/l. Considerable seasonal fluctuations in groundwater quality were observed as a consequence of agricultural practices and other factors such as annual rainfall distribution and the wadi El Kebir flow regime. The chemical composition of the water is not only influenced by agricultural practices, but also by interaction with the alluvial sediments. The dissolution of evaporites accounts for part of the Na + , K + , Cl − , SO 4 2− , Mg 2+ , and Ca 2+ , but other processes, such as calcite precipitation and dedolomitization, also contribute to groundwater chemistry.

Sinkhole collapse is one of the main limitations on the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Electrical resistivity imaging or tomography (RESTOM) is well suited to mapping sinkholes because of the ability of the technique for detecting resistive features and discriminating subtle resistivity variations. Two-dimensional electrical resistivity tomography surveys were conducted at two sinkhole sites near Cheria city where limestone is covered by about 10 m of clayey soils. A Wenner transect was conducted between the two sinkholes. The electrode spacing was 2 m. The length of transect is about 80 m. The survey results suggest that RESTOM is an ideal geophysical tool to aid in the detection and monitoring of sinkholes and other subsurface cavities.

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