Opinion ID: 2584073
Heading Depth: 1
Heading Rank: 7

Heading: Denver Basin Ground Water

Text: The Denver Basin is a large kidney-shaped region measuring approximately 6,700 square miles in area with approximate boundaries stretching from Greeley on the north, Colorado Springs on the south, the front-range hogback on the west, and Limon on the east. Topper et al., Ground Water Atlas of Colorado, at 85-86. The basin is composed of four sedimentary rock and mostly confined aquifers, which lie underneath each other, separated by layers of impermeable materials. All four deep aquifers lie below the alluvial aquifer, which covers the entire surface area of the Denver Basin and may reach in places to a depth of one hundred and twenty-five feet. These deep aquifers descend in the following order by depth: Dawson, Denver, Arapahoe, and Laramie-Fox Hills aquifers, and vary in size and shape, with the deeper aquifers occupying larger areas. Id. Collectively, all four are referred to as the Denver Basin Aquifers by the General Assembly. [18] In Water Rights of Park County Sportsmen's Ranch LLP v. Bargas, 986 P.2d 262, 265 (Colo.1999), we held that although some of these aquifers may extend into other parts of the state, the legislature intended to provide for specific rules governing withdrawal of the deep waters from these four aquifers as they exist in the Denver Basin only. [19] 986 P.2d at 275. Our understanding of the allocation, administration, and management of the Denver Basin is complicated by the Basin's geography and by the statutory rules the General Assembly has adopted to classify Denver Basin ground water. First, a substantial portion of the eastern half of the basin lies within the boundaries of four designated ground water basins. [20] As a consequence, the deep Denver Basin aquifers are administered and managed by different state entities depending upon whether the waters are located within or outside of a designated ground water basin. Second, the General Assembly has enacted a relaxed formulation for determining whether Denver Basin ground water is tributary or nontributary. See § 37-90-103(10.5). For Denver Basin ground water, whether located inside or outside the boundaries of a designated basin, the legislature has statutorily mandated that the water contained in each aquifer is less hydraulically connected to the surface waters than it may be in fact. See Park County Sportsmen's Ranch, 986 P.2d at 266. [21] This relaxed standard for determining Denver Basin nontributary ground water is offset by the statutory requirement that the users of this water may consume only ninety-eight per cent of the water withdrawn to avoid material injury to vested surface rights. A user must relinquish to the stream system the right to consume two percent of the water withdrawn. Id. at 267; § 37-90-137(9)(b); 2 C.C.R. § 402-6, Rule 8 (1985). For nondesignated ground water located within the Denver Basin, the legislature adopted an additional modification of the rule distinguishing tributary from nontributary ground water. [22] Subsection 37-90-103(10.7) classifies withdrawals from these four aquifers that will deplete the flow of a natural stream within one hundred years at an annual rate of greater than one-tenth of one percent of the annual rate of withdrawal as not nontributary water. Hence, Denver Basin ground water, located outside of a designated basin, that is partially tributary because it does not satisfy the definition of Denver Basin nontributary ground water shall nevertheless be administered on the basis of land ownership as if it were nontributary, provided its use is augmented. [23] Whether portions of the Denver Basin aquifers lie underneath designated ground water basin areas, subject to Commission jurisdiction, or nondesignated areas, subject to either the jurisdiction of the state engineer or the water court, the allocation of Denver Basin ground water is subject to the same standard: withdrawals are based upon an aquifer life expectancy of one hundred years and the quantity of water available for withdrawal shall be that quantity of water underlying the land owned by the applicant or someone acting with her consent. § 37-90-137(4)(b)(I) & (II); § 37-90-111(5). [24]