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The Sangre de Cristo range provides a backdrop for center pivot irrigation of a potato field near Alamosa deep aquifer system in the San Luis Valley. The rules are premised on the state engineer's conclusion that the Rio Grande Basin is over appropriated and new groundwater withdrawals will be detrimental to senior water rights and Rio Grande Compact deliveries. Under the proposed rules, any new groundwater withdrawals should not cause fluctuations in the artesian pressure greater than the ranges which occurred between 1978 -2000, a relatively stable period for the aquifer. Well pumping will only be permitted if an existing surface or groundwater water right equal to the amount requested is permanently retired or diverted. In other words, someone wanting to drill a new well under these rules would have to take an existing well out of production. Rio Grande Water Conservation District Manager Steve Vandiver, RGWCD engineer Allen Davey, and hydro- geolo- gy expert James Slattery testified during the confined aquifer rules trial that the valley's water supply is overappropriat- ed and the current level of groundwater use unsustainable. Davey testified his studies reveal a long -term decline in the San Luis Valley's confined aquifer. Hydrologist Charles Brendecke testified that the aqui- fer declined at an average rate of 58,387 acre -feet per year from 1970 to 2002. Peter Ampe, the attorney general's lead counsel, told Judge Kuenhold that Senate Bill 222 was enacted because the San Luis Valley aquifer systems are unique. Like a great bowl, over geologic time, the San Luis Valley accumulated thou- sands of feet of what are called basin -fill deposits. The deposits form the valley's aquifer system. In the northern portion of the basin, all streams flow into a closed basin, an internal drainage encompassing approxi- mately two- thirds of the valley. In this area, streams such as the La Garita, Carnero, Saguache and 'San Luis flow into the closed basin and do not have a natural outlet to the Rio Grande. Five main geological layers exist beneath the valley's surface, explained William Schre6der, the state's computer modeler. The unconfined or shallow aqui- fer lies in the first layer. Beneath a blue clay layer, which may be hundreds of feet thick in some places, are the deeper lay- ers that make up the confined aquifer. Attorneys protesting the rules argued that the San Luis Valley is not geologi- cally or hydrologically unique; and the rules interfere with individuals' con- stitutional rights to appropriate water. They said that the rules are unnecessary because an ample supply of water is available. They argued the Rio Grande Basin inflow of 1.15 million acre -feet from precipitation and irrigation seep- age greatly exceeds total pumping of 640,000 acre feet, and therefore the aquifer is not in danger. Steven Bushong, one of the objec- tors' attorneys, told the judge the San Luis Valley's confined aquifer contains an estimated 1 billion acre -feet of water. If that is the case, he argued, the 1.5 mil- lion acre foot loss in the aquifer recorded by Davey in the last 30 years would still leave 99.8 percent of the water. The objectors' computer modeling witness Bill Hahn said the effect of new withdrawals of 10,000 acre -feet per year over 100 years would be minimal. 1 2 C O L O R A D O FOUNDATION F❑ R WATER E D U C A T I O N U