The Rum-Saq aquifer is a part of the Arabian Nafud basin fossil aquifer system. It represents one of the last major fresh water resources for the Region, which can alleviate shortages that will become critical within the next five to ten years. A significant study has been carried out to evaluate the resource yield and reliability of supply, in advance of plans to extract upto 250 Mm3 for a minimum of 30 years, at an investment of over $630M. A substantial quantity of this water will be transmitted 350 km to the north of the proposed wellfields, to satisfy the deficits in north Jordan. Field investigations (1992-1993) included a drilling programme of 18,800 m linear metres, with some holes drilled to 1,500m depth, comprehensive geophysical logging, over 6,000 hours of pump testing at 12sites and a comprehensive synthesis of the data by means of a 3D mathematical model, extending over the 70,000 km2 of aquifer area. Additional lumped parameter modelling, hydrochemical modelling, laboratory analysis of formation cores for hydraulic parameters, was also carried out. A key factor in the reliability of the resource for beneficial use by Jordan could be the impact of production from the aquifer outside its territory, in Saudi Arabia. Resource production there (650 Mm3/a) is approximately ten fold the current production in Jordan. A risk assessment procedure was adopted to gain an insight into the critical issue, of long term reliability and how investments should be managed. The risk model included all the hydrogeological parameters, i.e. formation characteristics, inter formation relationships of leakage of poor quality water, wellfield infrastructure problems, variation of the annual (very limited) recharge, etc. In addition the risk derived from actions on the Saudi side were analysed; water resources there until recently were destined for wheat production but current trends suggest that wheat production is to drop, with a consequent supposed drop in aquifer production. However, the risk of continued high production for alternative crops (fruit or barley, etc.) or other activities (mining or other manufacturing industry) needed to be incorporated into the hydrogeological risk assessment. The presentation will highlight these issues and describe the conclusions of the risk assessment, concluding that the best option for the beneficial development of this transboundary resource might be through a joint treaty, managed and developed through an International Rum-Saq Aquifer Commission (IRSAQ). The issues in developing such an approach will be explored in the paper
