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<br />2 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Direct observations of stream impacts associated with effiuent and accidental spills of uranium <br />mill wastes from the Uravan mill site on the lower San Miguel River were made by Sigler et a1. <br />(1966), and included fISh kills, fish avoidance movements, and drastic pH swings (7.6 to 4.3). <br /> <br />A 1989 court order under the EPA Superfund Program to remove tailings from the Uravan site <br />may significantly improve water quality in the Dolores River. Clean up operations were in progress <br />at the Uravan site in 1990 and 1991. Removal of mill tailings and stabilization of riverside ponds <br />were scheduled to be completed in phases by mid-I992. Informal site visits were made during each <br />field trip by BIO/WEST in 1990, to observe progress of clean up operations at the Uravan site. <br />Based on the magnitude of changes that occurred in 1990, it appeared that clean up was proceeding <br />at a significant rate. <br /> <br />Construction and closure of McPhee Dam on the upper Dolores River in 1984 significantly <br />affected the hydrology of the system. Capture and storage of runoff in McPhee Reservoir reduced <br />the magnitude and altered timing of spring peaks below the dam. This effect was attenuated below <br />the confluence of the San Miguel River, which was free flowing and still exhibited a relatively normal <br />hydrograph. Late summer and early fall base flows in the Dolores River have been augmented by <br />more constant base releases from the dam during these periods. Prior to closure of McPhee Dam, <br />in March of 1984, the Dolores River above the confluence of the San Miguel was often dewatered <br />from irrigation diversions. Although the potential impacts of McPhee Dam operations associated with <br />altered timing and magnitude of peak runoff need to be further addressed, augmented late summer <br />flows may represent a beneficial change for native fishes utilizing the Dolores River drainage, <br /> <br />Augmentation of late summer and early fall flows from McPhee Dam may also improve water <br />quality in certain reaches of the Dolores River during base flow periods, particularly in the 10-mile <br />reach between the confluence of the San Miguel River and Paradox Valley. Saline ground water <br />inputs at Paradox Valley are diluted within base flows were augmented by dam releases. Benefits of <br />this dilution are less profound below the confluence of the San Miguel River, where that river <br />generally doubles the flow of the Dolores River. The beneficial effect of dilution occurs only when <br />releases from McPhee Dam exceed normal pre-dam flows. <br /> <br />2.0 STUDY AREA <br /> <br />This investigation was conducted in the Dolores River from Bradfield Bridge (RM 177) to the <br />confluence with the and Colorado River (RM 0.0) (Figure 1). Reconnaissance prior to sampling <br />showed that the Dolores River from Disappointment Creek (RM 124,7) to Bradfield Bridge (RM <br />177,0) was characteristic of a clear, cool fishery and would be less likely to provide habitat for <br />Colorado squawfish, Consequently this reach was sampled less intensively than the downstream <br />reaches where warmer and more turbid conditions existed. Fishes in the upper reach were sampled <br />by (CDOW) in 1987-89 as part of a river otter reintroduction program. These data were provided <br />to BIO/WEST and incorporated into this Final Report. <br /> <br />The 177-mile study area was divided into six reaches. The four lowest reaches are similar to those <br />established by the Service in 1981 (Valdez et a1. 1982). This study extended approximately 125 miles <br />further upstream than the study by the Service, consequently two additional reaches were added, The <br />six reaches used in this study were defined as follows: <br />