626 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



from controlled low-level releases or by accident. The few that exist in this country are 

 located at Rocky Flats, Colo. (Johnson, Svalberg, and Paine, 1974); Oak Ridge, Term. 

 (Dahlman, Bondietti, and Eastwood, 1975); the Savannah River plant near Aiken, S. C. 

 (D. Paine, 1977, Battelle, Pacific Northwest Laboratories, private communication); Idaho 

 Falls, Idaho (D. Markham, 1976, Rockwell Hanford Operations, Richland, Wash., private 

 communication), and Hanford near Richland, Wash. (Emery, Klopfer, and Weimer, 

 1976). These ponds are managed in association with fuel separation, reprocessing, and 

 reactor testing operations. The three unmanaged freshwater systems reported to have 

 received small amounts of plutonium include the Miami River near Miamisburg, Ohio 

 (Bartelt, Wayman, and Edgington, 1975), Sawmill Creek at Argonne, 111. (Singh and 

 Marshall, 1977), and streams leading to the Rio Grande River near Los Alamos, N. Mex. 

 (Hakonson, Nyhan, and Purtymun, 1976). Although amounts of plutonium released to 

 these aquatic systems are usually quite small, concentrations accumulated in waste ponds 

 are often significantly above background levels. 



Information about the ecological transport of plutonium from any of these systems 

 would be of special interest since they represent the results of actual contamination 

 events as they exist today. The distribution and fate of plutonium in a waste pond at 

 Hanford, specifically called U-Pond (Fig. 1), have been studied since 1973 (Emery, 

 BClopfer, and Weimer, 1974; Emery et al., 1976). The results appear to provide a good 

 example of the behavior of plutonium in a freshwater environment. U-Pond has an 

 estabUshed ecosystem and has been exposed to plutonium longer than any other aquatic 

 environment. Since 1944 plutonium has reached this 14-acre pond via waste ditches, 

 which have received occasional pulses of transuranic elements from the clean-up of minor 

 accidental spills of low-level contaminants within the reprocessing laboratories. 



One of the major goals of the study at U-Pond has been to obtain sufficient 

 information about the pond's ecosystem and the distribution of plutonium within it so 

 that plutonium export routes can be assessed quantitatively. Although it is often difficult 

 to measure with reasonable certainty the parameters necessary for describing these export 

 routes, the purpose of this wark is to formulate the best expressions of export given the 

 conditions that Umit this process. The objectives are to determine ranges of quantities of 

 plutonium in the pond's ecosystem and assess the amount of plutonium being exported in 

 relation to this inventory. To accompUsh this task, we estimated the pond's plutonium 

 inventory quantities on a basis of minimum, mean, and maximum values for each 

 ecosystem compartment to postulate the amount of these inventories that is exported 

 yearly. 



Methods and Materials 



To examine the pond's inventory and export conditions, we separated the ecosystem into 

 two categories, the aquatic system and the contacting terrestrial system. The entire 

 inventory and export scenario is shown in Fig. 2. The aquatic system is divided into 10 

 compartments: 



1. Nonfilamentous algae (including sestonic diatoms). 



2. Filamentous algae. 



3. Submerged macrophytes. 



4. Emergent macrophytes. 



5. Lower invertebrates (excluding insects and gastropods). 



6. Resident insects (those with aquatic adult stages). 



