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Discussion of Specific Concerns Regarding Basin-Specific Rules <br /> As part of this rulemaking proceeding, several parties proposed alternate rules that <br /> identify portions of formations within specific basins of the State as nontributary for <br /> purposes of the State Engineer's administration of wells pursuant to C.R.S. § 37-90- <br /> 137(7). The State Engineer is adopting the following basin-specific rules. The bases for <br /> the State Engineer's adoption of these rules, and responses to some of these issues and <br /> concerns raised by various parties regarding the rules, are set forth below. <br /> Rule for Piceance Basin—Mesaverde Formation (see Rule 17.7.D.1). The State Engineer <br /> finds there is clear and convincing evidence supporting his adoption of a rule identifying <br /> water withdrawn from the Cameo and South Canyon Coal Groups of the Mesaverde <br /> Formation by wells located within a delineated area of the geologic formation known as <br /> the Piceance Basin, in the Muddy Creek Drainage north of Paoma Reservoir in Delta and <br /> Gunnison Counties, Colorado to be nontributary for purposes of his administration and <br /> permitting of wells pursuant to C.R.S. § 37-90-137(7). <br /> The State Engineer's finding is based primarily upon testimony and evidence provided <br /> regarding an analysis performed by Gary Witt, P.G. using the Glover-Balmer method for <br /> purposes of determining the timing of depletions to stream flow resulting from <br /> withdrawal of ground water from the Cameo and South Canyon Coal Groups. The State <br /> Engineer finds there is clear and convincing evidence that this analysis identifies <br /> nontributary areas in manner that is consistent with C.R.S. § 37-90-103(10.5) and, <br /> therefore,provides a useful tool for the State Engineer's administration and permitting of <br /> ground water wells pursuant to C.R.S. § 37-90-137(7)within this delineated area. <br /> First, the State Engineer finds that the Glover method is an appropriate method for <br /> determining the timing of depletions to stream flow for purposes of C.R.S. §§ 37-90- <br /> 103(10.5) and 37-90-137(7). Although less sophisticated than numerical flow models <br /> such as the U.S.G.S. MODFLOW modeling code ("MODFLOW"), the Glover method is <br /> nonetheless a well-established method for analyzing ground water flow, with an <br /> extensive history of use in Colorado for determining impacts of ground water pumping <br /> upon stream flow. This history has demonstrated the Glover method to be generally a <br /> "conservative"method for determining whether water removed in the course of ground <br /> water pumping is nontributary, in that the method is generally regarded as overestimating <br /> the impact of such pumping on such surface streams. Dave McElhaney, P.G., Chief of <br /> the Hydrogeological Services Branch for the Office of the State Engineer, testified that in <br /> his experience he had never observed water determined to be nontributary through the <br /> Glover method to later be found tributary through use of a MODFLOW model. <br /> Second, the State Engineer finds the inputs to the Glover-Balmer method to be <br /> appropriate in the case of Mr. Witt's analysis of the Cameo and South Canyon Coal <br /> Groups. The basic values needed to operate the Glover-Balmer method are <br /> transmissivity, storativity, and a distance from the pumping well to the nearest potential <br /> point at which depletions could occur. The State Engineer finds the storativity values <br /> relied upon by Mr. Witt are reasonable. The transmissivity values relied upon by Mr. <br /> Produced Nontributary Ground Water Rules 2 CCR 402-17, Statement of Basis and Purpose <br /> -11- <br />