650 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Small mammals {Microtus pennsylvanicus modestus and Peromyscus msutus) were 

 kill-trapped throughout the study period. Mule deer {Odocoileus hemionus) samples were 

 collected from road kills. 



Results 



Sediment 



Figure 3 shows the average 2 3 9,2 4opjj concentrations in water and surface sediments over 

 the entire study period. The accidental release in March 1971 resulted when process waste 

 solutions low in 2 39,24 0pu content, due to be pumped to solar evaporation ponds for 

 concentration, were accidentally released to the sanitary waste system. The resultant 

 elevation over ambient conditions is readily apparent in Figs. 3 and 4. Reconstruction of 

 the pond area had a marked effect on the mean sediment concentrations. Concentration 

 levels increased significantly during construction and remained high during the rest of the 

 study period for most ponds (Table 1). Plutonium concentrations also increased in the 

 sediment sampled at Walnut Creek at Indiana Avenue (baseline reservoir), wliich indicated 

 that considerable activity escaped the holding-pond system during the period of 

 reconstruction (Fig. 4). 



Pond Bi showed the higliest surface concentrations throughout the study period. A 

 slight decrease in mean sediment concentrations was noted in ponds B2 and B4 following 

 peak levels. However, pond B3, which was the first pond to undergo reconstruction and 

 underwent the most extensive remodeling, showed a marked decrease in sediment activity 

 after the period of maximum values. This can be attributed to the deposition of 

 appreciable soil that contained lower concentrations of plutonium during and after the 

 dam and pond remodeling. 



Subsurface sediments were probably mixed when the ponds were refilled. Core 

 samples contained highest plutonium concentrations at 20- to 30-cm depths. Some minor 

 construction modifications were made in the effluent bypass system which could have 

 caused redistribution of high-level plutonium sediments from this area. Sewage-treatment 

 modifications in May 1972, before reconstruction, could also have resulted in 

 high-activity flocculate being released to the holding ponds. 



Plutonium-239,240 concentrations in pond B3 sediment peaked in late June 1972; 

 those in pond B2 peaked in July, and those in ponds B, and B4 peaked in August. This 

 suggests that pond reconstruction played a major role in tlie redistribution of plutonium 

 since this is the order in which remodeling occurred. In any case it is readily apparent that 

 mean-surface -sediment values increased markedly during tlie period of pond reconstruc- 

 tion and remained at liigher levels except in pond B3 . 



The clay sediments showed an extremely high affinity for plutonium, and, if left 

 undisturbed, they appear to be an excellent reservoir for plutonium in an aquatic system. 



Water 



The mean concentrations of plutonium in unfiltered water samples during the course of 

 this study (Fig. 3) showed that construction played a major role in the redistribution of 

 plutonium from pond to pond. The increase in plutonium concentrations was also 

 detected downstream at the Walnut Creek at Indiana Avenue sampling station (Fig. 4). 



The majority of the plutonium in the water component was usually associated with 

 the filterable fraction (> 0.45 pm) (Table 2). However, ponds Aj and Ci , the monitoring 



