2010-11-22_REVISION - M2009023 (7)

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Investigators conclude that the major factor affecting the variability of selenium accumulation in biota at aquatic habitats was the presence of underlying Cretaceous soils. Median selenium concentrations were less than 2 micrograms per gram for plant samples, less than 7 micrograms per gram for invertebrate samples, and less than 6 micrograms per gram for whole- fish samples collected from aquatic habitats underlain by non- Cretaceous soils. Similar samples collected from aquatic habitats underlain by Cretaceous soils contained median selenium concentrations two to five times greater. Leaching of selenium from Cretaceous soils in the San Juan River area increases the accumulation of selenium concentrations in the biota and thereby increases the exposure and potential health risks associated with selenium to migratory birds, fish, and other wildlife that use these aquatic habitats extensively. Aquatic habitats presenting the greatest average exposure to excess selenium concentrations in the diets of resident wildlife are from consumption of plants, invertebrates, and fish at irrigation-drain habitats underlain by Cretaceous soils. Of the irrigation projects evaluated in the San Juan River area, the highest median selenium concentrations in algae, cattail leaves, odonate nymphs, mosquitofish, and leopard frog samples ... were collected from the east hogback irrigation drain" The specific selenium concentrations that may adversely affect razorback sucker and Colorado pikeminnow within the upper Colorado River basin are currently being debated. It is widely accepted by most scientists that selenium effect levels vary by species (Lemly 1996b, Skorupa 1998). Consequently, the selenium concentrations referenced above outline the affect level for the most sensitive endpoint tested in a test species to date. The median selenium levels in water collected between 1977 and 1981 on the San Juan River at two sample sites near the Four Corners and near Mexican Hat, Utah, reported in Butler et al. (1995) was 3 gg/L. The Four Comers site (SJ1) is upstream of the McElmo Creek confluence. In April, July, and November 1990 three selenium samples were collected at SJ I and the samples measured at 2 pg/L or less. The Mexican Hat sampling site (SJ3) is downstream of the McElmo Creek confluence and previous data for this site was collected between 1975 and 1989. In April, July, and November 1990 three selenium samples were collected at SJ3 and the samples were also measured at 2 pg/L or less (Butler et al. 1995). The razorback sucker occurs and spawns just downstream from the mouth of McElmo Creek, in what is wholly or primarily McElmo Creek water prior to mixing with San Juan River water (Dale Ryden, USFWS, pers. comm. 2001), causing contaminant levels in McElmo Creek to be of concern to the razorback sucker and possibly the Colorado pikeminnow. Analysis of selenium levels in water, sediment, and biota in the McElmo Creek drainage follows and serve as an example of potential selenium impacts from selenium-rich soils. In McElmo Creek at the Colorado-Utah State line (ME3) the median selenium level was 4 pg/L using 1977-1981 data (Butler et al. 1995). However, in March, July, and November 1990 selenium levels from three samples at ME3 were 6, 6, and 3 pg/L, respectively. In 1990 an additional sampling site on McElmo Creek (ME4) was established downstream of the confluence with Yellow Jacket Creek in Utah (Butler et al. 1995). Three samples were collected in March, July, and November 1990 at ME4 with values of 6, 9, and 3 pg/L, respectively. A sampling site 23