PLUTONIUM IN A GRASSLAND ECOSYSTEM 429 



10^ 



10^ 



10-^ 



IC* 



DISTANCE SOUTH OF ASPHALT PAD (S), m 



Fig. 4 Plutonium concentration in 0- to 3-cm-deep Rocky Flats macroplot 1 soil as a 

 function of distance south of the asphalt oil-barrel storage pad. 



represented by each sieve size organized by depths did not produce any obvious patterns 

 with either depth or particle size range. Consequently regressions of the soil mass fraction 

 per sample as a function of depth were not significant for most sieve fractions. However, 

 these last results would not preclude a surface-attachment mechanism. 



The data on plutonium in soil at Rocky Flats can be summarized by several 

 statements. First, the variance in the plutonium concentrations of the soil samples was 

 large; CV's within groups of like samples (same depth and particle size) ranged to over 

 2.0. Frequency distributions for soil samples were positively skewed. Spatial variation was 

 also large; in one instance the plutonium concentrations of aliquots taken less than 15 cm 

 apart varied by nearly three orders of magnitude. 



Second, in spite of the large degree of variance in the data, the plutonium 

 concentrations in soil were significantly correlated with the location and soil particle 



