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<br />- 30 - <br /> <br />9. Concentrations of dissolved radium-226 were below 1 ~~g/l in stream <br />samples taken from the Dolores River above and immediately below Slick Rock, <br />and from the San Miguel River above Uravan. Corresponding levels of dissolved <br />radium-226 were found in the s~epage from Slick Rock upgrading plant and in <br />stripped ion exchange liquor from Uravan mill. This latter stream was being <br />barium treated for radium removal during the survey. <br /> <br />10. Concentrations of dissolved uranium in stream samples were consi- <br />derably less than recommended limits of 20,000 ~g/l. The highest uranium <br />concentrations in effluent streams were about 1/3 this level. <br /> <br />lL <br />cipitated <br />the milL <br />conclusion <br /> <br />Much of the radium-226 in Uravan mill discharges is apparently pre- <br />in the San Miguel River within a very short distance downstream from <br />This may occur through interaction with the precipitation noted in <br />4 above, <br /> <br />l2. <br />creased in <br />seepage or <br /> <br />The weight of dissolved radium-226 in the river system generally in- <br />a downstream direction, possibly due to natural inflows and mine <br />drainage in addition to the contributions made in mill discharges. <br /> <br />13. Background levels of radium-226 in sediment samples were about twice <br />as high in the Dolores River above Slick Rock as in the San Miguel River above <br />Naturita. Levels of radium-226 were higher in sediment samples taken'immediately <br />below uranium mills than in samples taken immediately above mills. <br /> <br />l4. Levels of radium-226 in sediments taken at the mouth of the Dolores <br />River may show an accumulation of radium-226 in sediment to be occurring <br />between Gateway and the mouth of the Dolores River. <br /> <br />15. Bottom organisms were most prevalent on the San Miguel River above <br />Uravan. This stream supports a limited population below Uravan mill. Dolores <br />River quality is not favorable for the support of a good bottom fauna popula- <br />tion in the immediate Slick Rock and Gateway areas. <br /> <br />16. Within the limitations of the bioassay toxicity test, and in view <br />of the limited number of fish tested, the following conclusions may be drawn <br />concerning the probable toxicity of the various effluents to fish in the <br />Dolores-San Miguel River system: <br /> <br />a. Burro Mine drainage should not be toxic to rainbow trout. <br />Slick Rock plant effluent is more toxic, having killed half the <br />test fish in 72 hours in concentrations of about 2 percent. <br /> <br />b. Plant 5 waste should be the most toxic to fish of the wastes <br />tested from Uravan; yellow cake press filtrate and red cake tails were <br />less toxic to the test trout respectively. Ditch drainage from <br />Uravan was essentially nontoxic to the test trout in 72 hours. <br /> <br />c. A minimum flow of 252 cfs in the San Miguel River is required <br />(neglecting antagonism or synergism) for adequate dilution of wastes <br />from Uravan mill so that the combination of wastes and river water <br />not be toxic to young trout. Over the period of record, flow of the <br />San Miguel River at Uravan has been less than 250 cfs 70 percent of <br />the time. <br />