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Fruitland Formations and overlying surface water features such as streams and springs. <br /> However, the State Engineer finds this concern to be unsupported based on rebuttal <br /> testimony. <br /> Second, the State Engineer finds there is clear and convincing evidence that the NSJB <br /> Model more than adequately integrates the conceptual model and data underlying that <br /> model into a numerical model utilizing MODFLOW. MODFLOW is a well-established <br /> tool for modeling ground water flow. All of the parties to this proceeding conceded that <br /> an appropriately-developed MODFLOW model is a useful tool for the State Engineer's <br /> administration and permitting of wells pursuant to C.R.S. § 37-90-137(7). <br /> Here there was substantial evidence that the NSJB Model was properly developed. The <br /> testimony of Adam Bedard,P.E. provided a thorough description of how the NSJB <br /> conceptual model was translated into a numerical model. The numerical model <br /> appropriately reflects the geologic and hydrogeologic data developed for the NSJB <br /> conceptual model. The staff of the State Engineer questioned whether the NSJB Model <br /> should have relied upon a general head or drain boundary to define the boundary of the <br /> model. The State Engineer finds the testimony of Mr. Bedard to provide a convincing <br /> justification for the use of a drain boundary. The staff of the State Engineer also raised <br /> other questions regarding implementation of the NSJB Model, including how the river <br /> length was calculated, and how the model sums and lumps the net coal and carbonaceous <br /> shale intervals into individual model layers. The testimony of Mr. Bedard adequately <br /> responded to these concerns. The staff of the State Engineer testified that their concerns <br /> with respect to these issues had been adequately addressed. Certain parties also <br /> questioned the appropriateness of the vertical conductivity values used in the NSJB <br /> Model. There was no evidence, however, that this concern of anisotropy bias caused any <br /> inaccuracy in calibrating the model. Also, the model conservatively assumed continuous <br /> layers with a constant horizontal permeabilities, which is an idealized representation of <br /> the lenticular and discontinuous nature of this stratigraphy. Indeed, the evidence <br /> indicated that the model likely over estimated the horizontal permeability of the coal <br /> layers (the predominant flow path), thus conservatively reducing the area found <br /> nontributary by the model despite the anisotropy ratios used in the NSJB Model. <br /> Third, the State Engineer finds the calibration results for the NSJB Model provide <br /> additional clear and convincing evidence that the NSJB Model accurately delineates areas <br /> within the Fruitland Formation in the Northern San Juan Basin as nontributary. Mr. <br /> Bedard noted that calibration of the NSJB Model was able to rely upon a large dataset, <br /> including transient heads. The availability of these data resulted in a model with very <br /> good calibration results. Dr. McCord agreed that one of the strengths of the NSJB Model <br /> was the robust calibration approach employed to refine model parameters to improve the <br /> fit to observational data. Dr. McCord found it especially notable that this calibration <br /> approach included a transient calibration. <br /> Certain parties objected to the manner in which calibration of the NSJB Model addressed <br /> certain issues. Specifically, certain parties noted that the recharge value for the model <br /> was decreased from 160 acre-feet per year to approximately 130 acre-feet per year as part <br /> Produced Nontributary Ground Water Rules 2 CCR 402-17, Statement of Basis and Purpose <br /> -14- <br />