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I I I I I I I I I I I I I I I I I I I ',:on .~ 115 from California's use to off stream storage in Arizona on behalf of Nevada entities would have been approximately 30,000 af However, this action would have had no impact on California users because 1997 was a surplus water supply year and all Lower Basin demands were met. The diversion and use of a quantity ofICUA by the consuming State entity will be made possible through the Secretary's release of an equal amount oflCUA. The storing State entity may develop ICUA by arranging for a willing entity to forbear from its ordinary use of Colorado River water. However, in Arizona, the storing State entity would, for example, pump the groundwater previously stored to satisfy its needs and create ICUA by reducing its Colorado River water order by an offsetting amount. After all of the stored groundwater is removed, the aquifer would be at the same level as it would have been in the absence of the interstate program for off stream storage, In Arizona, because ofthe requirement to leave 5% of the stored water in the ground, the water level in the aquifer should be slightly higher than it would have been without the program, The obligation to deliver 1,5 maf of Colorado River water to Mexico is set forth in the "Treaty Between the United States and Mexico," signed February 3, 1944 and effective November 8, 1945 (1944 Mexican Water Treaty) and Minute No, 242 of the International Boundary and Water Commission, Implementation of the Preferred Alternative will not impact the 1.5 maf obligation under the 1944 Mexican Water Treaty, Mexico is also entitled to an additional 200,000 af of Colorado River water during any year in which Colorado River water is available in excess ofthe quantity necessary to satisfy the requirements in the United States and the guaranteed 1. 5 maf annual quantity to Mexico, The Preferred Alternative, which would allow unused basic and/or surplus apportionment to be stored off stream, could result in a minor reduction in the quantity of surplus water available for delivery to Mexico in the long term, Reclamation estimated the potential impact of off stream storage on delivery of surplus to Mexico by using Reclamation's Colorado River System Simulation Model (CRSSez), which is a computerized model of the Colorado River system's reservoirs and river reaches, In the most likely scenario, 1,2 maf of Colorado River water would be stored off stream in Arizona for the benefit of an authorized entity in Nevada, Water would be stored in 12 annual increments between 1999-2015, at a rate of 100 kafper year. During the 12 years water is being placed into off stream storage between 1999-2015, the annual water deliveries to Mexico are projected to average 2,487 mafwithout the rule and 2.464 mafwith the Rule, These projected water deliveries are based on a conservative 70R strategy that presumes water is stored only in surplus years, Hydrological conditions in the next few years are favorable for a surplus detennination, This quantity of water will provide Mexico with the 200 kaf of surplus Mexico is entitled to in any year in which Colorado River water exists in excess of that necessary to satisfy the requirements in the United States and the guaranteed quantity of 1.5 maf of annual deliveries to Mexico. This off stream storage of 1.2 maf is not considered to have a significant effect on flows to Mexico because deliveries to Mexico are projected to average about I maf in excess of the 1.5 maf annual and surplus deliveries to Mexico during the storage period due to flood control releases, The off stream storage of this 1,2 maf of water is therefore projected to reduce the average quantity of 15