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I I Shumway Arroyo just above its confluence with the San Juan River. the San Juan River above the SJGS weir, and the San Juan River below the Shumway Arroyo (Figure 6). I I The analytical procedures used were EPA methods with much lower detection limits than the standard EPA analytical methods. Analyses of the second set of water samples did not detect any PAHs, arsenic, ur mercury. Seienium was estimated at I.U microgram per liter (l.lg/L) in the sample from the San Juan River above the weir, which is at the low end of the concentration range of I to 3 l1g1L currently identified as a concern for aquatic life by USFWS (Waddell 1995), and well below the standard for drinking water of 50 l1g/L. Selenium was not detected in the sample from the San Juan River collected downstream. I I I Analyses of this second set of sediment samples identified PAHs in samples from all locations, all at concentrations below the detection limit of the original analysis. All PAH analytes were identified in the sediment sample from Westwater Arroyo. Benzo(b)fluoranthene was detected in sediment samples from all other locations. The presence of benzo(g,h,i)perylene was estimated for the sediment samples from the San Juan River below Shumway Arroyo and from Shumway Arroyo. Benzo(a)anthracene, benzo(a)pyrene. and benzo(b)fluoranthene were detected in sediment samples from both San Juan River samples. In addition, benzo(g,h,i)perylene was detected in the sample from the San Juan River below Shumway Arroyo. Sediment quality criteria have not been developed for these constituents to provide a basis of comparison. I I I The presence of selenium was identified in sediment samples from all locations, with concentrations estimated at less than 0.5 milligram per kilogram (mglkg) for all samples, which is less than the USFWS identified concentrations of concern of2 mg/kg in sediment (Waddell 1995). Arsenic was also detected in sediment samples from all locations. with a maximum concentration of 3.1 mglkg in the sample taken from Shumway Arroyo. Mercury was not detected in any of the sediment samples. I 6.2,2.2 Westwater Arroyo I The Westwater Arroyo typically only flows in response to off-site storm water runoff, which occurs principally during the months of July and August. 6.2,2.3 San Juan River I The San Juan River carries approximately 1.5 million AF of water per year past the SJGS weir. The major impact on flow is the Navajo Dam, which has the capacity of releasing up to 5.000 cubic feet per second cfs through its main outlet works. Imponant contributors to flow are storm water runoff and snowmelt into the river itself, flow from the Animas and La Plata rivers, a variety of irrigation return flows, and groundwater seepage along the length of the river. r The SJGS does not pump water from the San Juan River to its storage reservoir on a regular schedule. Rather, pumping schedule and rates are managed on the basis of demand for water and river water quality. Consequently, pumping rates are typically lowest during the spring when water consumption by SJGS is relatively low, and when river water turbidity is high. Alternately, pumping is at its highest during the summer months when plant water consumption peaks and river water turbidity is relatively low. 19 "n1t..~" ~ <, . .. . . l-'.