Opinion ID: 1219144
Heading Depth: 2
Heading Rank: 1

Heading: Whether the Trial Court Properly Determined the Effect of AWDI's Proposed Pumping on Surface Streams

Text: The trial court's determinations of the effects of the proposed withdrawals on the Rio Grande River, San Luis Creek, Big Spring Creek, and other surface streams are findings of fact. As such, they will not be disturbed on appeal unless wholly unsupported by the evidence. Board of County Comm'rs v. Upper Gunnison River Water Cons. Dist., 838 P.2d 840, 847 (Colo.1992); People v. City of Thornton, 775 P.2d 11, 19 (Colo.1989). The trial court was presented with extensive evidence, through expert testimony and voluminous exhibits, concerning the geologic and hydrologic characteristics of the Valley and of the Closed Basin in particular. The evidence established, and the trial court found, that underlying the lands in the Valley are two aquifers having different hydrologic properties and generally acting as separate hydrologic units. Separating them is a group of clay layers referred to as the blue clay series. The upper aquifer, called the unconfined aquifer, consists of coarse materials with relatively high hydraulic conductivities, and is situated above the blue clays, which range in depth from 35 feet on the west side of the Valley to 125 feet on the east. Most of the irrigation wells in the Valley are completed in this aquifer. [27] The lower aquifer is located below the blue clays. Although hydrologically connected at various points, the two aquifers have been separately administered by the state engineer for well permit purposes. The extent of the hydraulic connection is sufficiently slight that water in the confined aquifer is maintained under artesian pressure. The artesian condition results from a recharge of the confined aquifer by waters entering the aquifer at higher elevations at the edges of the Valley and the limited permeability of the blue clays separating the two aquifers. The evidence concerning the effects to be produced by AWDI's proposed withdrawals of water was sharply conflicting in many respects. Each side attempted to develop a comprehensive geologic and hydrologic framework for use in predicting the movement of water within the San Luis Valley as a result of such withdrawals. For this purpose AWDI and the objectors utilized complex ground water flow computer models, the objectors' model having been developed by the Colorado state engineer. By introducing into the models certain data as described to the court through expert testimony, each side attempted to demonstrate the effect of the proposed withdrawals on surface streams and the unconfined aquifer. In general, the court found the evidence presented by the objectors and utilized in operating their computer model more credible than that of AWDI. [28] In particular, the court made the critical finding that the ground water in the unconfined aquifer is in hydraulic connection with most surface streams in the San Luis Valley and their alluvium for all or portions of most years. [29] As a result, the level of the water table in the unconfined aquifer influences gain or loss to the streams. On another critical factual issue, the trial court found that the values used by AWDI for streambed conductance, which expresses the rate at which a stream will lose water to the underlying aquifer, were not credible; AWDI's data greatly underestimated loss of water through streambed leakage. The court also found that AWDI's evapotranspiration data and use of that data in its computer model materially overstated the potential for reducing loss of water by evapotranspiration by lowering the water table through pumping and thus eliminating vegetation. These are examples of some of the more important factual findings that undermined the credibility of the results predicted by the use of AWDI's computer model. The trial court also found that the State's model was originally created for administrative purposes and was far more extensive and thorough than that of AWDI. The court found that while not purporting to be able to predict with exact precision the quantity and location of stream depletions to be caused by AWDI's proposed pumping, the State's model was adequate for a determination of whether depletion to certain streams would exceed the statutory standard in the definition of nontributary water. The 7,400 acre feet per annum depletive effect on the Rio Grande River and San Luis Creek was directly predicted by the State's model and provided the basis for the trial court's finding that this effect was inconsistent with the statutory definition of nontributary water. In addition, the State's model predicted the locations where the water level in the unconfined aquifer would be drawn down by AWDI's proposed pumping. Based on expert testimony that Big Spring Creek was in hydraulic connection with the unconfined aquifer, the computer model prediction that the effect of AWDI's proposed pumping would reduce the water level in that aquifer to a particular extent, and an expert's testimony concerning the effect of such a water level reduction on Big Spring Creek, the trial court found that the creek would be depleted by approximately 3,600 acre feet per year by the proposed pumping, a reduction in itself sufficient to defeat AWDI's claim that the water it sought to withdraw was nontributary. The trial court also found that the lowering of the water level in the unconfined aquifer would adversely affect other natural streams even though such effects could not be precisely quantified because those streams were not included in the computer model. All of the trial court's findings were based on evidence in the record and will not be overturned. See, e.g., Upper Gunnison River, 838 P.2d at 847.