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Average Annual Water Depletion Estimate <br /> Evaporation from sediment ponds and haul road watering will be the primary causes of surface water <br /> depletion in the II-W South area. Seneca II-W has three (3) existing ponds and is proposing to <br /> construct three (3) additional ponds over the life of II-W South operation. The annual net lake <br /> evaporation for Hayden, Colorado is 26.46 inches. - <br /> Total maximum evaporation from the three existing ponds has been calculated at 13.2 acre-feet <br /> annually, while the proposed ponds would result in the loss of additional 6.0 acre-feet annually. This <br /> estimate assumes that all ponds are full to the level of the principal spillway at all times (i.e. worst <br /> case scenario). <br /> Based on eight (8) years of records maintained by the State Engineers Office and SCC, the annual <br /> usage of water to suppress dust on the haul roads has averaged 11.4 acre-feet per year. This results <br /> in a total annual usage of 30.6 acre-feet of surface water per year and is approximately 30 percent of . <br /> the Windy Gap trigger level of 100 acre-feet annually. <br /> Overall, this would be a minimal indirect depletion occurring over the life of the operation. See Tab <br /> 16, Attachment 16-A, "Water Rights Investigation and Plan for Augmentation" for further details. <br /> . AVERAGE ANNUAL WATER DEPLETION ESTIMATE <br /> Facility Acres Acre-Feet <br /> Pond 005 (existing) 1.4 3.1 <br /> Pond 006 (existing) 2.8 6.2 <br /> Pond 009 (existing) 1.8 4.0 <br /> Pond 015 (proposed) 0.7 1.5 <br /> Pond O16 (proposed) 1.1 2.4 <br /> Pond 017 (proposed) 0.9 2.0 <br /> Haul Road Watering 11.4 <br /> Total 6.7 30.6 <br /> Note: Surface acres of the ponds assume that water level is at principal spillway elevation. <br /> Water usage on the haul roads derived from 8-year average (1991-1998). <br /> In general, the hydrologic characteristics of reclaimed mined lands will result in lower spring run-off <br /> volumes but higher summer and fall flow base volumes. Water depletions to the Yampa River from the <br /> mining activities at II-W South will be minimal. SCC's current plan for augmentation includes the <br /> availability of 37.4 acre-feet of water from the J.C. Temple Reservoir No.1 and up to 50 acre-feet of <br /> water from the Stagecoach Reservoir to offset any potential depletions to the Yampa River. <br /> The table above represents the only sources of water depletion at the Seneca 11-W Mine. There are no <br /> water depletions due to pit water evaporation, conveyor sprays, coal processing, bath house <br /> consumption or domestic water use. <br /> 1 Revised 8/27/99 <br />