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<br />- l8 - <br /> <br />with Dolores River water containing concentrations of radium-226 greater than <br />3.0 ~~g/l been evaluated. Waters of the Upper Colorado River Basin of natural <br />background levels generally have radium-226 concentrations of less than 1 ~~g/l. <br />Arithmetic averages of radium-226 concentration were less than 1 :J.~g/l in the <br />Dolores River above and b~low Slick Rock and in the San Miguel River above <br />Uravan. <br /> <br />Dissolved uranium levels in stream samples were nowhere greater than 300 <br />~g/l, though the majority of values in the effluent samples ranged from lOOO to <br />7000 ~g/l. Uranium concentrations in Slick Rock plant seepage were much lower <br />than this range, on the order of lOO ~g/l, probably for reasons similar to those <br />discussed above in relation to the radium-226 level of this seepage. <br /> <br />The increase in radium-226 concentration in the Dolores River from less <br />than 1 ~~g/l below Slick Rock to greater than 3 ~~g/l just above the mouth of <br />the San Miguel River may be due to the entry of mine seepage or inflows from <br />other natural drainage. The Dolores flows through an area of many uranium <br />and vanadium mines between Slick Rock and the mouth of the San Miguel and its <br />major tributary in this reach, LaSal Creek, also drains an area of numerous <br />mines. Radium-226 levels in the San Miguel River just above the confluence <br />were lower than in the Dolores, so the noted increase was probably not due to <br />water from the San Miguel, with its higher flow, backing up into the channel <br />of the Dolores. Dissolved radium-226 levels also increased between the confluence <br />and Gateway, possibly due to the reasons noted above. <br /> <br />At Uravan mill, radium-226 levels in Plant 5 effluent were much lower <br />than those in any of the other streams coming from the mill property. This <br />stream was receiving barium treatment during the survey, designed to remove <br />radium by coprecipitation with barium sulfate. Radium-226 and uranium concen- <br />trations in the ditch drainage sampled at Station US-ll were comparable to those <br />being discharged in the process wastes, suggesting that at least part of the <br />ditch drainage is seepage from the acid leach tailings ponds located atop the <br />mesa above the mill. The ditch drainage and yellow cake tailings liquor are <br />discharged to the San Miguel River having concentrations of radium-226 greater <br />than 3 ~~g/l. However, tha arith~tic average of radium-226 concentrations in <br />the San Miguel 1.6 miles below Uravan during the low flows encountered in the <br />survey was 2.4 ~g/l. <br /> <br />Table X presents weight flow rates of dissolved radium-226 and uranium <br />past sampling points. For stations where a stream flow rate was not measured, <br />there are no results in this table. As mentioned in the section on chemical <br />results, other factors enter into consideration of weight flow rates. Waste <br />flow figures from the Uravan mill were given as annual averages and may not be <br />representative of flow conditions at the time of the survey, hence the weight <br />rates reported here may not be representative of actual conditions during the <br />survey. Rain during the second compositing cycle caused a large variation in <br />flow at Station US-6, the Dolores River just above the mouth of the San Miguel <br />River. It was impossible to insure that the portions of the composite sample <br />taken there during the second cycle were taken in proportion to flow. For <br />this reason, the sample is not truly representative of river conditions. Nor <br />is the arithmetic average flow during this period a representative one; in an <br />attempt to secure a more accurate r8presfCntacioll of riv""r conditions, the <br />