2009-06-08_REVISION - M1997032 - Laserfiche WebLink

Home Browse Search

9.0 Surface Water • The Dolores River, located approximately 6.5 miles southwest from the Van 4 Mine, is the major surface water feature in the area. The river extends for 183 miles from an area northeast of Rico, Colorado, to the confluence with the Colorado River at the town of Cisco, Colorado. The Dolores River Basin is approximately 96 miles long and 34 miles wide, encompassing an area of 6,222 square miles. Most of the flow in the river originates on the western slopes of the La Plata and Rico mountains, with additional contributions from snowmelt and springs of higher mesas and mountains. The Dolores River also receives inflows from groundwater, which are estimated to be approximately 0.17 cubic ft per second per mile in the portion of the river extending from the town of Dolores to Cisco (Weir et al. 1983). Surface water bodies are not present in the direct vicinity of the Van 4 Mine. The top of Monogram Mesa slopes gently from the northeast to the southwest and surface drainage would be expected to flow from the ridge overlooking the Paradox Valley generally towards the southwest. An ephemeral drainage is present west of the mine, which flows generally towards the south into Bull Canyon. Surface water was not observed during the August 2008 site visit to the mine, but runoff within the affected areas may occur on an infrequent basis. Runoff occurring within the affected areas of the mines is contained within existing surface water detention basins. These basins are designed to retain 100 percent of runoff generated during a 100 year-24 hour storm event (CDM 2008a). The retained water is generally not discharged from the mine site, because the water evaporates rapidly in the and environment present in the area of the mine. 9.1 Design Specifications for Stormwater Management Facilities In 2008, CDM developed a report that presents a design analysis for the storm water drainage facilities at the Van 4 Mine. The scope of the report covers aspects of storm water collection, conveyance, and retention design necessary to comply with BLM and the Colorado Division of Reclamation Mining and Safety (DRMS) drainage criteria: The following procedure was used to design the drainage facilities components: 1. The peak discharge was estimated for a selected storm return interval using drainage basin characteristics. 2. A drainage channel was designed to convey water for the selected return interval based on available topographic data and aerial photos. 3. The type of channel lining was designed for the estimated flow condition. 4. Berms were designed to retain water for the selected return interval based on available topographic data and aerial photos. • 9-1 TA64986-Denison Mines\Task Order 4 - EPP Sunday Mines Group-Van4\Van4\FINAL ReporITINAL - Environmental Protection Plan Van4.doc