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<br />02 4 @anium downstream from John Martin Reservoir also <br />exceeded the proposed drinking-water standard. <br />A Spearman's rho correlation analysis of <br />uranium with total dissolved solids, specific conduc- <br />tance, major dissolved ions, and selected dissolved <br />trace elements shows strong correlation except for <br />manganese (table 25). The strong positive correlation <br />between uranium and specific conductance (r=0.91) <br />indicates that uranium is soluble and is conserved in <br />solution (Zielinski and others, 1995). Major dissolved <br />constituents show strong positive correlation (r>O.87) <br />probably because processes that result in elevated <br />dissolved-solids concentrations also result in elevated <br />dissolved uranium concentrations. Uranium also <br />shows strong positive correlation with selenium <br />(r=0.82). Selenium can be elevated in the shales and <br />limestones commonly present in tbe lower Arkansas <br />River Basin (Turekian and Wedepohl, 1961; Hatten, <br />1969; Schultz and others, 1980) and can concentrate <br />in oxic saline waters of the Western United States <br />(Zielinski and others, 1995). <br />The gross alpha and gross beta analyses are <br />regarded as a rapid, quantitative measure of gross <br />sample activity (Thatcber and others, 1977). Gross <br />alpha activity serves as a gross indicator for high <br />levels of natural radionuclides and is used in particular <br />to screen for radium (U.S. Environmental Protection <br />Agency, 1986b). The principal sources for naturally <br />occurring radioactivity in water are the weathering of <br /> <br />Table 25. Spearman's coefficients of correlation for <br />dissolved uranium and selected water-quality constituents in <br />the Arkansas River, April 199o-March 1993 <br /> <br />[no number of paired values; <. less than] <br /> <br />Constituent or <br />characteristic <br />Specific conductance <br />Total dissolved solids, <br />residue at <br />180 degrees Celsius <br />Calcium, dissolved <br />Magnesium, dissolved <br />Sodium. dissolved <br />Chloride, dissolved <br />Sulfate, dissolved <br />Iron, dissolved <br />Manganese, dissolved <br />Selenium. dissolved <br /> <br />Correlation <br />coefficient <br />0.91 <br />.96 <br /> <br />Probability <br />value <br /><0.001 <br /><.001 <br /> <br />n <br /> <br />47 <br />39 <br /> <br />40 <br />40 <br />40 <br />40 <br />40 <br />40 <br />40 <br />31 <br /> <br />.97 <br />.96 <br />.96 <br />.87 <br />.91 <br />-.68 <br />.IS <br />.82 <br /> <br /><.001 <br /><.001 <br /><.001 <br /><.001 <br /><.001 <br /><.001 <br />.348 <br /><.001 <br /> <br />rocks containing radioactive minerals and fallout of <br />cosmic-ray-produced nuclides (Thatcher and others, <br />1977). Gross beta activity is used to screen for man- <br />made radionuclides that are introduced through activi- <br />ties including nuclear weapons testing, discharge from <br />nuclear power plants or medical facilities, leaching <br />from a radionuclide waste depository, or other nuclear <br />accidents (U.S. Environmental Protection Agency, <br />1986b). The proposed U.S. Environmental Protection <br />Agency maximum contaminant level (MCL) for <br />adjusted gross alpha radiation concentrations is <br />15 pCilL. Gross alpha concentrations were reported in <br />micrograms per liter as natural uranium but can be <br />converted to picocuries per liter by multiplying by <br />0.68 (Thatcher and others, 1977). Adjusted gross <br />alpha represents total gross alpha measurements minus <br />radium-226 and uranium measurements (U.S. Envi- <br />ronmental Protection Agency, 1991). The proposed <br />rule suggests that radium-226 and/or uranium concen- <br />trations should be obtained if unadjusted gross alpha <br />concentration exceeds 15 pCiIL. Radium-226 and <br />uranium then can be subtracted from the unadjusted <br />gross alpha concentration for comparison to the MCL. <br />Dissolved-gross alpha concentrations exceeded <br />15 pCiIL for three separate analyses, twice at Las <br />Animas and once at the Below John Martin Reservoir <br />site. Total suspended gross alpha concentrations <br />exceeded the MCL for 12 separate analyses at Avon- <br />dale, Catlin Dam, and Las Animas. However, median <br />gross alpha concentrations only exceeded the MCL at <br />Catlin and Las Animas for total suspended concentra- <br />tions. Total suspended gross alpha concentrations may <br />sometimes reflect higher gross alpha concentrations <br />than in filtered (dissolved) samples because of large <br />amounts of suspended sediment in the samples. One <br />component of gross alpha radiation is natural uranium. <br />Natural uranium concentrations in the soil and ground <br />water are relatively high downstream from Avondale <br />and may contribute to the higher gross alpha concen- <br />trations at the downstream sites (Zielinski and others, <br />1995). <br />The proposed drinking-water standard for beta <br />particle and photon activity is 4 mremlyr (U.S. Envi- <br />ronmental Protection Agency, 1993). If the gross beta <br />particle activity is greater than 50 pCiIL, the water <br />samples should be analyzed to determine which radio- <br />nuclides are present (U.S. Environmental Protection <br />Agency, 1991). Four separate analyses for suspended <br />total gross beta exceeded 50 pCilL with two each <br />occurring at Catlin Dam and Las Animas. All of the <br /> <br />WATER QUALITY 59 <br />