Groundwater chemistry and water table variations in Bahrain

An evaluation has been carried out of the groundwater system in Bahrain. It has involved the collection of water samples from all the water bearing formations to study the quality of the groundwater. Each water sample was tested physically, chemically, and bacteriologically. Additionally, the five day biochemical oxygen demand test and hydrogen sulphide were detected. The period of the actual sampling and testing extended from mid-1990 to the beginning of 1992. The results obtained have been compared to the results of an earlier study conducted between 1978 and 1979. The investigation has also involved a statistical analysis of the variations in the sub-surface water table level in each hydrogeologic formation. The piezometric levels have been collected from monitoring boreholes/ standpipes. The levels obtained extended from the beginning of 1980 when the earliest recording started up to the end of 1991. Bahrain abstracts its fresh water from five aquifers which in descending order are the Sanad, the Alat, the Khobar, the Rus, and the Umm-Er-Radhuma Aquifers. The quality of the groundwater appears to be deteriorating. The excessive groundwater abstraction has caused the encroachment of the sea into all the sub-surface waters. As the waters become saline, they are expected to become unsuitable for human consumption and for irrigation. The deeper aquifers are believed to consist of high values of the hydrogen sulphide because the deeper geological formations contain oil rich in sulphur. land spring water is expected not to be safe bacteriologically because it is exposed to the atmosphere unlike the other boreholes in the various aquifers.The water table levels have been changing in each aquifer. The groundwater levels in the Sanad Aquifer, which is the shallowest geological formation, are expected to rise in the future in areas where the natural drainage is obstructed. This is related to the sea coast reclamation area. The rise is expected to reduce inland depending on the application of surface irrigation as well as the possible leakages from the services systems. About two kilometres south from the original shore, around Buddayya Road, the Sanad Aquifer's water table has been shown to be falling. This fall is expected to be due to overpumping from the groundwater system. Apart from the Sanad Aquifer, the piezometric levels of the underlying aquifers are expected to fall with time. Once again the fall is due to excessive groundwater abstraction. The study concludes by re-presenting the causes for the water table rise in the near-surface Sanad Aquifer and discusses the possible geotechnical consequences. It further produces some possible solutions to control the rise of the water table level.