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<br />, <br /> <br />Water Quality. Soil erosion and streambank disturbances are <br /> <br /> <br />factors leading to significant short-term impacts on water quality <br /> <br /> <br />because of ~urbidity and sediment increases during construction. <br /> <br />Temporarily degraded water quality would occur in each tributary <br /> <br /> <br />affected by a road/pipeline crossing or diversion structure placement-. <br /> <br />The Blue River would be similarly affected by siphon construction. <br /> <br />Because more than 85 percent of phosphorus and 70 percent of <br />nitrogen in surface water runoff are associated with sediment parti- <br />cles, disturbed soils eroded from construction sites would increase the <br />loading of phosphorus and nitrogen in any waterway the soils enter. <br />The greater the amount of soil loss, the greater the amount of loading. <br />Affected waters would include the Blue River, Dillon Reservoir, Green <br />Mountain Reservoir, and numerous streams affected by construction <br />activities. Transporting dissolved phosphorus and nitrogen along with <br />diverted waters into Dillon Reservoir during operation of the project <br />would accelerate the existing eutrophication processes in the reser- <br />voir. Degradation of wster quality in Dillon Reservoir due to nutr{ent <br />increases would be a significant long-term impact. Turbidity and <br />sedimentation effects can be mitigated by employing soil-erosion- <br />control measures wherever soil disturbances occur. Nutrient impacts on <br />Dillon Reservoir could be mitigated by routing diverted Esst Gore <br />tributary flows around Dillon Reservoir directly to the Roberts Tunnel <br />portal through a pipeline. The capital cost of this opt ion would be <br />$20 to $25 million with an increase in annual operating costs of <br />between $300,000 and $500,000. <br /> <br />Aquatic Life. Significant short-term impacts to fish populations <br />and spawning habitat in tributary stream reaches below construction <br />areas would occur because of excessive soil erosion and sediment <br />deposition on channel bottoms. Spawning habitat degradation would only <br />last s few years with average or above-average spring runoff condi- <br /> <br />15 <br />