2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT Rock exposure at the SMC and the cuesta ridge immediately to the southwest shows the Mesozoic strata on the southwest limb of the Big Gypsum Valley anticline generally dipping to the southwest. This general attitude is interrupted near the mines by numerous northwest trending faults that have vertically offset the Mesozoic rocks. Geologic cross sections prepared by CDM (2009) that show the fault relationships at each mine area in the SMC are shown in Appendix D. Note that Denison Figure 2-2 in Appendix D is equivalent to Section A-A' of Cater (1955). 5.0 SURFACE WATER HYDROLOGY The SMC study area lies within the arid high desert of the Colorado Plateau and within the Dolores River watershed. The Dolores River is located approximately 2 miles north and 3.25 miles west of the Topaz Mine site. The Dolores River flows to the north and drains an area of approximately 3,044 square miles (not including the San Miguel River) (USGS, 2020). The river head waters are in the San Juan Mountains approximately 60 miles southeast of the SMC. From the headwaters, the river flows north a distance of 252 miles to the Colorado River (Utah State, 2020). The Dolores River is the only perennial stream in the local area. All tributaries to the Dolores River in the vicinity of the SMC are ephemeral or intermittent and flow mostly as a result of runoff from high intensity precipitation events. Big Gypsum Creek in Big Gypsum Valley and Disappointment Creek in Disappointment Valley both intersect the Dolores River north and northwest the SMC, respectively. Big Gypsum Creek is approximately one-half mile east of the SMC, while Disappointment Creek is 4.5 miles south of the SMC. USGS gage station locations along the Dolores River are shown in Figure 5-1 and include : Dolores River near Slick Rock (Station 09168730), Dolores River at Bedrock (Station 09169500), and Dolores River near Bedrock (Station 0917110). A plot of the measured discharge at these stations is shown in Graph 5-1. Flows for the Dolores River near Slick Rock range from approximately 10 cubic ft per second (cfs) to 85 cfs in the winter months, and approximately 85 cfs to 3660 cfs in the summer months. An examination of gain and loss between stations Dolores River near Slick Rock (Station 09168730) and Dolores River at Bedrock (Station 09169500) generally shows that the river gains from Slick Rock to Bedrock. However, the data consistently show periods of loss also, possibly related to irrigation diversions. Western Water& Land, Inc. 12