PLUTONIUM IN A GRASSLAND ECOSYSTEM 421 



grassland, this chapter will dwell primarily on data from environmental sampling at 

 Rocky Flats. 



The Rocky Flats installation uses nearly 30 km^ as a buffer zone to separate the 

 pubhc from plutonium-handUng operations. The climate at the installation is typified by 

 occasional strong WNW winds exceeding 40 m/sec and moderate precipitation, i.e., 40 

 cm/yr average (Rocky Flats 1975 annual weather summary, unpublished). The Rocky 

 Flats grassland has been modified by the activities of humans and includes plant species 

 typical of short-grass plains (Buuteloua gracilis and Biichloe dactyloides) as well as 

 tall-grass prairie (Agropyron spp. and Andropogon spp.) and ponderosa pine (Pimts 

 ponderosa) woodland (Web'er. Kunkel, and Shultz, 1974). Mule deer {Odocoileus 

 hemionus) are found on the site along with grassland species of reptiles, rodents, and 

 birds (Whicker, 1974). 



Source of the Contamination 



Investigations by Krey and Hardy (1970) of DOE's Environmental Measurements 

 Laboratory (EML, formerly Health and Safety Laboratory) suggested that the most likely 

 contamination source was a storage area of stacked 55 -gal barrels that leaked 

 plutonium-poUuted oil. Data supporting the conclusion of Krey and Hardy and a 

 description of the nature of the stored oil— plutonium mixture are delineated. 



Air-sampling data from Rocky Flats link the barrel storage area to the east -southeast 

 contamination pattern discovered by Krey and Hardy (1970). Air-samphng station S-8, 

 one of many such stations maintained and sampled regularly by Rocky Flats personnel, is 

 located about 75 m east and slightly south of the barrel storage area. Except for a brief 

 period during 1961, montlily averages of daily airborne contamination values have been 

 kept since at least 1960 to the present (Fig. 1). 



The S-8 air-sampling data indicated that contamination peaks in the air were 

 associated with dates of perturbation of the contaminated surface (Table 1 and Fig. 1). 

 Except for periods of disturbance, the gross alpha concentrations in ambient air were near 

 0.01 pCi/m^ . However, during excavation and paving of the barrel storage area, the alpha 

 concentration in air markedly increased (Table 1). 



The plutonium-contaminated cutting oil, about as viscous as lightweight motor oil but 

 thinned by carbon tetrachloride, was stored in the 55-gal barrels for periods of up to 7 yr. 

 The interactions between the oil, air, CCU , and plutonium within the barrels were 

 probably quite important in determining the eventual fate of the element. 



The oil was filtered through 2- to 3-jum filters before being placed in the barrels. The 

 discard Umit at the time of storing was 1 x 10~^ g of plutonium per liter of oil. If the 

 limit and the filtering had been observed and performed faithfully, each of the 

 approximately 3570 plutonium-containing barrels would have had no more than 2.1 g of 

 plutonium (0.13 Ci) (M. A. Thompson, Environmental Sciences, Rocky Flats Plant, and 

 F. J. Miner, Chemical Resources, Rocky Flats Plant, personal communications). 



It is difficult to assess what occurred once the oil was inside the barrels. The presence 

 of carbon tetrachloride in the drums allows the possibility that hydrochloric acid was 

 formed, which, in turn, may have reacted with the plutonium metal to form very low 

 concentrations of plutonium chloride, a more-soluble form of the element (J.M. 

 Cleveland, Environmental Studies, Rocky Flats Plant, personal communication). This 

 possibility is given credibility by the work of J. Navratil of Rocky Flats Chemical 

 Research Division, who has studied contaminated cutting oil in recent years. 



