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West Elk Mine • Fractures and faults within the stratigraphic column have provided secondary porosity, which contributes the majority of the groundwater into the mine. Most of the groundwater intercepted in the mine is collected, pumped to the surface, treated, if necessary, and released to the North Fork. Until 1996, this treated and released groundwater represented approximately 20 acre-feet of "new" water in the North Fork. This is based on the observation that most of the B-Seam dips under the North Fork in a downgradient direction from the West Elk Mine. Therefore, dischazges to the North Fork of this "developed water" constitute new water in the North Fork system. In 1996 and 1997, MCC encountered inflows up to 2,500 gpm and 8,000 gpm, respectively, which exceeded the hydraulic capacity of their treatment facilities. This necessitated the subsurface storage of water in previously mined areas or sealed sumps (see discussion in Section 2.05.6(3)(b)(iii & viii), Groundwater Quantity Effects). Isotope analysis of tritium and cazbon-14 (Mayo 1998) has been used to determine the groundwater "age" (or mean residence time) of the fault water to be at least 50 years (per H analysis) and between 5,000 and 20,000 yeazs (per 14C analysis). This fact, coupled with no known claim of reliance or water rights on these fault inflows, suggests that this water has not been appropriated. MCC has appropriated the fault water and storage rights to these inflows. Water Rights Aspects of North Fork Diversions, Fault Inflows and Sealed Panels Sumps • In light of the large fault inflows experienced by MCC in 1996 and 1997, in conjunction with MCC's utilization of sealed panels sumps, the following text has been prepared to summarize the resulting water rights implications. In addition, MCC's historic and recent pattern of diversions and return flows to the North Fork aze described. The sections entitled Mine Water System and Groundwater Quantity Effects provide helpful background information on water management at the mine, the nature of the B East Mains and 14SE Headgate fault inflows and the chazacteristics of the sumps. MCC utilizes the Mount Gunnison Pipeline water right (pumped through the Raw Water Intake Gallery) during both times of "call" and "no call" on the North Fork. Because the Mount Gunnison Pipeline is a junior water right, it is often "called out-of-priority" during the late summer and early autumn. In other words, the right cannot be used because more senior rights need the water downstream. A summary of the North Fork call records in the last five water yeazs follows: 2.05-l73 November 100 PRI !