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-36- Description of Hydrologic En vironmer;t - Precipitation and Runoff (Cont'd) Figure 1. The average monthly flows are illustrated on Table 2, along with the inflows to the North Fork of the Gunnison River frorn Minnesota Creek. These figures were utilized to determine the amount of outflow via the North Fork of the Gunnison River from the basin. Obviously, such predictions are not entirely correct. For example, less than 3 years of data existed for Minnesota Creek and 1 year (1977) included drought conditions. However, for purposes of this assess- ment, such figures provide a rough approximation of flows through the general area. PROBABLE HYDROLOGIC CONSEQUENCES OF TIfE BLUE RIBBON MINE Cround Water The potential aquifers which may be affected by the Blue Ribbon Mine are the alluvium of Hubbard Creek, the Rollins sandstone and the Lenticular sandstones located stratigraphically above and below the mine. The alluvium of Hubbard Creek is the only aquifer which is in use within the permit and adjacent areas. This aquifer supplies the water which is consumed at the Blue Ribbon P1ine. The mine utilizes the only well located in the Hubbard Creek alluvium as a water supply. This aquifer is an isolated body of alluvium. Up and downstream of the mine, the Hubbard Creek stream valley narrows and the stream flows over resistant sandstone bedrock. Removal of water from the Hubbard Creek aquifer causes a depletion in base flow in Hubbard Creek at the downstream extent of the alluvium. The impacts of this depletion are discussed in the following section on the probable hydrologic consequences of mining on surface waters. The Rollins sandstone is the most significant regional bedrock aquifer in the North Fork Drainage Basin. This aquifer outcrops in a narrow steep reach along Hubbard Creek about a mile downstream of the mining operation. Recharge to this aquifer is limited within the Hubbard Creek Drainage. No wells are completed in the Rollins sandstone beloto the mine in the Hubbard Creek Drainage and the potential use is limited by the steep valley slopes below the mine and the aquifers limited recharge area. The only potential impacts to this aquifer would be a slight decrease in the quantity and a slight degradation in the quality of waters recharging the aquifer. No ground water from the Rollins sandstone will appear as mine inflows within the Blue Ribbon Mine since the mine workings are all topographically above the Rollins sandstone. The Blue Ribbon Afine may affect the quantity of ground water in strata which overlies the mine workings. Only minor discontinuous lenticular and interbedded sandstones have been identified through drilling above the permit and adjacent areas. Most of these sandstones are dry. Others support localized perched aquifers. These strata may be dewatered into the mine 1) through faults and fractures and/or 2) through conduits created by subsidence.