Actinide speciation in the shallow aquifer of Mortandad Canyon

Treated waste effluent at Los Alamos has been released to the environment in Mortandad Canyon since 1963. A study has been initiated to investigate the relative mobilities of the actinides in the shallow aquifer of Mortandad Canyon. Speciation of radionuclides and their adsorption by sediment are important parameters in the evaluation of those mobilities. Plutonium concentrations and oxidation states were measured in water collected from four test wells (MCO 4, 5, 6, 7.5). A regular decrease in 239240Pu concentration was observed with increasing distance from the discharge point. The large difference between the concentrations discharged (30 to 1000 pCi/l for period 1977-1982) and those in the wells (0.02 to 5.4 pCi/l) suggests that progressive loss of plutonium from the water as it moves through the alluvium is probably more important in regulating the concentrations than the variability of concentrations in the discharged effluent. The K/sub D/s for 228Th were also determined and found to be similar to those for plutonium. The factors regulating the concentration of dissolved plutonium are probably the same as those regulating 228Th. In contrast the K/sub D/s of 241Am decrease regularly with distance from the discharge point and are about 100 times lower than those of plutonium and thorium for water in wells farthest from the discharge point