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<br />R. G. OTTO & ASSOCIATES <br />302 minus that at site 301) ranged from 0.1 to 1.9 ugm/1 (mean = <br />0.8, s.d. = 0.5). In the two instances when the conce~itration <br />gradient was reversed, differences were 1.9 and 0.2 ugm/1. These <br />two "exceptions" are reminders of the necessity to con+sider <br />short-term natural variability in evaluating the measurements. In <br />all cases, Uranium concentrations in Ralston Creek wer~a well below <br />the Colorado Water Quality Standard of 59 ugm/1. Nonetheless, <br />there is a suggested pattern of slightly elevated coac~antrations <br />of uranium downstream of the waste rock piles. <br />In assessing the reliability of these suggested cross-pile <br />"differences" in uranium concentrations it is instructive to make <br />~:~' <br />a comparison with the results of the Radioactive Materials License <br />(RML) Monitoring Program as discussed earlier (Table 1). The RML <br />data were collected for a similar puzpose and over a comparable <br />period of time. However, in the case of the Radioacti°~e Materials <br />License monitoring data (which are sufficient for statistical <br />evaluation), ao suggestion of a cross pile difference Baas found. <br />The mean concentrations observed above and below the w~~ste zock <br />piles in the Radioactive Materials License monitoring program are <br />substantially greater than those in the Cotter/USGS st~idy. A <br />similar situation exists F~. vne calculated vaziaaces .about the <br />means. Mean uranium concentration above the waste rocl[ piles was <br />3.4 ugm/1 (s.d. = 2.7) for the Radioactive Materials License <br />monitoring program and 2.0 ugm/1 (s.d. = 0.9) in the Cotter/USGS <br />qo <br />