2010-11-22_REVISION - M2009023 (7)

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marine sediments. Percolation of irrigation water through these soils and sediments leaches selenium into receiving waters. Collecting irrigation return water in a reservoir could concentrate selenium and have adverse affects to fish and wildlife. However, the soils of Red Mesa are not selenium rich soils and they have been irrigated for more than 80 years. Therefore, an increase in selenium levels in critical habitat from storing Red Mesa return flows is not expected. The proposed project will not bring additional lands under irrigation; therefore, impacts to water quality from leaching of contaminants from irrigation are not expected to increase significantly. However, the project's depletion, even though it is relatively small, would cause a proportionate decrease in dilution, which in turn would cause a proportionate increase in heavy metal, selenium, salts, PAHs, pesticides, and other contaminant concentrations in the Colorado River. An increase in contaminant concentrations in the river would likely result in an increase in the bioaccumulation of these contaminants in the food chain which could adversely affect the endangered fishes, particularly the predatory Colorado pikeminnow. Selenium is of particular concern due to its effects on fish reproduction and its tendency to concentrate in low velocity /areas that are important habitats for Colorado pikeminnow and razorback sucker. Physical Habitat The flow targets outlined in the San Juan River flow recommendations are designed to provide sufficient spring flows to create and maintain important habitats including: cobble bar construction; scouring of fine sediment from the interstitial spaces from the cobble so it is suitable for spawning; flushing sediments from backwaters; maintaining channel complexity; overbank flows to provide nursery habitat for razorback sucker; and appropriate water temperatures for spawning. Water depletions during spring runoff affect physical habitat in several ways. High spring flows are very important for creating and maintaining complex channel geomorphology and suitable spawning substrates, and in creating and providing access to off-channel habitats. The proposed Long Hollow Reservoir will typically store water from December 1 " - February 15a', flows on the La Plata and San Juan rivers generally peak in late May. Therefore, impacts to peak flows within critical habitat are expected to be minimal. The criteria for peak flows on the San Juan River will be met with Long Hollow Reservoir in place. Biological Environment The modification of flow regimes, water temperatures, sediment levels, and other habitat conditions caused by water depletions has contributed to the establishment of nonnative fishes. To the extent that it would reduce flows and contribute to further habitat alteration, the Project would contribute to an increase in nonnative fish populations. Endangered fishes would experience increased competition and predation as a result. However, the proportionate amount of depletion caused by this project would be small (1,535 acre-feet out of 852,810 acre-feet) compared to the overall depletions occurring in the San Juan River. Therefore, the overall proportionate increase in nonnative fishes would be small. The proposed project includes the following conservation measure: fish screens will be installed on the outlet of Long Hollow Reservoir. With the conservation measure in place, contribution of nonnative fish from Long Hollow Reservoir to the San Juan River is expected to be minimal. 26