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.. ~ Green Mountain Reservoir, completed in 1943 as part of the Colorado - Big Thompson (CBT) project, has always been the focus of debate between east and west slope water users. In 1933, when plans for the CBT project were being formulated, the first conflicts surfaced. Western slope water users felt they were entitled to 1:1 compensatory storage to offset the transmountain diversions. However, on the other side of the divide, water users were only claiming liability for out-of-priority diversions. After four years of discussion, parties from both areas of the state finally reached a compromise, and in 1937, Congress adopted Senate Document 80 (50 stat. 595) prescribing the relationship between the proposed Green Mountain Reservoir, and existing western slope water rights. In order to meet all terms of the compromise, Senate Document 80 provided for construction of Green Mountain Reservoir with a total storage capacity of 154,600 a.f, (active storage, 146,900 a.f,). Of that amount, 52,000 a.f. was to be reserved for supplying replacement water for out-of-priority diversions. Storage costs for the replacement water were to be paid for by users in northeastern Colorado. The remaining 100,000 a.f. was reserved for powergene.ration; however, water woul.d: be released, free of charge, tosupp1;:Y existil'lgwae-ers users, to supply losses chargeable to delivery of replacement water, and for future domestic and/or irrigation uses. The ,most senior major water right on the Colorado River is the Grand Valley Irrigation right (1888) which historically has diverted 1000 cfs. The second most senior major right on the River is that of PSCo's Shoshone Hydropower Plant in Glenwood Canyon for 1250 cfs. Since this right is for year-round, non-consumptive use, its fulfillment results in enough water being available to satisfy Grand Valley's demand throughout the year. In light of this, Senate Document 80 proposed: "Whenever the flow of the Colorado River at the present site of ...Shoshone diversion dam" (measured by the USGS gage at Dotsero)" is less than 1250 cfs, there shall.,.be released...as part of said 52,000 a.f., the amount necessary.,.to fill the vested appropriations of water up to the amount concurrently being...withheld from such vested appropriations by...d ivers ion to the eastern slope. II In addition, Senate Document 80 also provided for future uses by stating, "Water not required for these purposes shall be available for disposal to agencies for the development of the shale oil or other industries." Although Senate Document 80 simplified the intricacies of the Colorado - Big Thompson project, the operational relationship between Green Mountain, other reservoirs, and subsequent Colorado River basin water users has remained highly complex. 721 grn/mnt