2010-11-22_REVISION - M2009023 (7)

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However, PAHs do not appear to be a limiting factor to native fishes in the San Juan at this time (Holden 2000). Selenium (a trace element) occurs naturally in many soil types, and is abundant in the drier soils of the West. Selenium enters surface waters through erosion, leaching and runoff. Sources of selenium, both anthropogenic and natural, in the San Juan River, have been reported by O'Brien (1987), Blanchard et al. (1993), and Thomas et al. (1998). Selenium, although required in the diet of fish at very low concentrations (less than 0.5 micrograms per gram on a dry weight basis (gg/g), is toxic at higher levels (> 3 pg/g), and may be adversely affecting endangered fish in the upper Colorado River Basin (Hamilton et al. 2004). Excess dietary selenium causes elevated concentrations of selenium to be deposited into developing eggs, particularly the yolk. If concentrations in the egg are sufficiently high, developing proteins and enzymes become dysfunctional and lead to deformed embryos.that may be at higher risk for mortality. Selenium concentrations in the San Juan River Basin are of particular concern because of its documented effects on fish and wildlife reproduction and survival and high levels detected in some locations within the Basin (Blanchard et al. 1993, Wilson et al. 1995, Thomas et al. 1998). Selenium concentrations can be elevated in areas where irrigation occurs on soils which are derived from or which overlie Upper Cretaceous marine sediments. In fact, Thomas et al. (1998) found that: "Water samples from sites with Cretaceous soils had significantly greater selenium concentrations than water samples from sites with non-Cretaceous soils. Water samples from Department of the Interior project irrigation-drainage sites developed on Cretaceous soils contained a mean selenium concentration about 10 times greater than those in samples from Department of the Interior project sites developed on non-Cretaceous soils." Percolation of irrigation water through these soils and sediments leaches selenium into receiving waters. Other sources of selenium include power plant fly ash and oil refineries. Water depletions, by reducing dilution effects, can increase the concentrations of selenium and other contaminants in water, sediments, and biota (Osmundson et al. 2000). Tributaries to the San Juan carry higher concentrations of selenium than found in the mainstem river immediately upstream from their confluence with the San Juan. Increased selenium concentrations may also result from the introduction of ground water to the mainstem of the river along its course. Although these levels are diluted by the flow of the San Juan, the net effect is a gradual accumulation of the element in the river's flow as it travels downstream. For example, concentrations of selenium in water samples collected from the mainstem of the San Juan River exhibited a general increase in concentration levels with distance downstream from Archuleta, New Mexico, to Bluff, Utah, (<1 µg/1 to 4 µg11) (Wilson et al. 1995). The safe levels of selenium concentrations for protection of fish and wildlife in water are considered to be <2 µg/l and toxic levels are considered to be >2.7 µg/1(Lemly 1993, Maier and Knight 1994, Wilson et al. 1995). In 1995, Colorado's Water Quality Control Commission reduced the chronic selenium standard from 17 µg/L to 5 µg/L. The Service recommended the level be lowered to 2 µg/L (Service 1998). 21