Abstract:To be able to overcome water shortages, Abu Dhabi Emirate started an Aquifer Storage and Recovery (ASR) project with desalinated seawater (DSW) as source water near Liwa. It is the largest DSW-ASR project in the world (stored volume~10 Mm 3 /year), and should recover potable water for direct use. DSW is infiltrated into a desert dune sand aquifer using "sand-covered gravel-bed" recharge basins. In this study, we evaluate the hydrogeological and hydrogeochemical stratification of the (sub)oxic target aquifer, and water quality changes of DSW during trial infiltration runs. We predict water quality changes of DSW after 824 d of infiltration, during 90 d of intensive recovery (67% recovered) without storage (scenario A), as well as after 10 years of storage (scenario B, with significant bubble drift). Monitoring of preceding trials revealed a lack of redox reactions; little carbonate dissolution and Ca/Na exchange; much SiO 2 dissolution; a strong mobilization of natural AsO 4 3− , B, Ba, F, CrO 4 2− , Mo, Sr and V from the (sub)oxic aquifer; and immobilization of PO 4 , Al, Cu, Fe and Ni from DSW. The Easy-Leacher model was applied in forward and reverse mode including lateral bubble drift, to predict water quality of the recovered water. We show that hydrogeochemical modeling of a complex ASR-system can be relatively easy and straightforward, if aquifer reactivity is low and redox reactions can be ignored. The pilot observations and modeling results demonstrate that in scenario A recovered water quality still complies with Abu Dhabi's drinking water standards (even up to 85% recovery). For scenario B, however, the recovery efficiency declines to 60% after which various drinking water standards are exceeded, especially the one for chromium.

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Abstract. Observations acquired by Gravity Recovery And Climate Experiment (GRACE) mission indicate a mass loss of 146 ± 6 mm equivalent water height (EWH) in northern Iraq between 2007 and 2009. These data are used as an independent validation of lake mass variations and a rainfall-runoff model, which is based on local geology and climate conditions. Model inputs are precipitation from Tropical Rainfall Measurement Mission (TRMM) observations, and climatic parameters from Global Land Data Assimilation Systems (GLDAS) model parameters. The model is calibrated with observed river discharge and includes a representation of the karstified aquifers in the region to improve model realism. Lake mass variations were derived from Moderate Resolution Imaging Spectroradiometer (MODIS) in combination with satellite altimetry and some in situ data. Our rainfall–runoff model confirms that northern Iraq suffered a drought between 2007 and 2009 and captures the annual cycle and longer trend of the observed GRACE data. The total mass depletion seen by GRACE between 2007 and 2009 is mainly explained by a lake mass depletion of 75 ± 3 mm EWH and a natural groundwater depletion of 39 ± 8 mm EWH. Our findings indicate that anthropogenic groundwater extraction has a minor influence in this region, while a decline in lake mass and natural depletion of groundwater play a key role.

In arid to semi-arid countries water scarcity on a national level is seemingly contradicted by the local occurrence of sometimes large amounts of domestic wastewater. Consequently, in many countries this wastewater is considered as an additional source of water, particularly for irrigation purposes. The government of Egypt is planning to use wastewater in land reclamation in many areas on the Eastern and Western fringes of the Nile Valley and Delta. A preliminary survey on the effects of wastewater irrigation was carried out by the Research Institute for Groundwater (RIGW) in the Gabal el Asfar area (Greater Cairo) in 1990-1991. A general framework of reuse of sewage effluent for irrigation in Egypt was discussed. The hydrogeological setting of the Gabal el Asfar area, the groundwater flow system and the thickness of the unsaturated zone were described. The impact on groundwater quality from sewage effluent irrigation has been assessed and the migration of pollution was evaluated. The main objective of the present study is to analyze and explain changes in groundwater quality between 1991 and 1994. The study is executed within the framework of the Environmental Management Groundwater Resources project.