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~, ~~ Addendum to CDH Soil Plutoniumzsv«zao Sttrveys 1970-1991, Love, Jttne, ]994 2. Air and Sediment Record Monthly averages of daily airborne values from Air Sampler S-8 located just east of the Drum ' storage Area (903 Pad) from 1960 to 1971 support the conclusion that releases were due to increased activity in the 903 Pad area (Seed et al). The period from the end of 1966 to 1970 shows significant increases in airborne contamination. These releases go from less than 0.05 pCUm' to 1.54 pCUm' at the end of 1968 and into 1969 (CDHc). This peak at station S8 corresponds to the peak activity of drum removal, excavation and capping of the 903 Pad. The peak plutonium79z°0 levels in sediment of Standley lake also occur in 1969 (Hardy, 1978). Furthermore, the core sediment levels in Standley Lake steadily decline to pre-1966 levels in 1975(Hardy, 1978). The pattern of air releases at station S-8 peaking in 1969 matches the work at the 903 Pad. The Standley lake sediment record also shows increasing plutonium27v.ze° up to 1969 and then a steady decline until ]975(Hardy,1978). The pattern of plutonium7J+2`0 sediment deposition in Standley Lake and air results at S8 strongly match the chronology of events at the 903 Pad. Wind is the significant transport mechanism. While major drum deterioration and leakage started in 1964, plutonium resuspension did not really pic4: up until drum removal was initiated in 1967. Once the 903 Pad was capped in 1969 the sourca: was terminated and the S8 results declined dramatically. Redistribution of plutonium continued until 1975. The Standley Lake sediment record shows a slower steady decline to pre- 19661evels from 1969 to 1975. ' 3. Other Transport Mechanisms The role of other plutonium transport mechanisms, mainly runoff and infiltration, have been studied b}~ EG&G-Lataor and appear to be insignificant at this time (USDOE b). Therefore, using 1975 as a cutoff date for soil redistribution seems plausible. The plutonium levels have been maintained since then. The descriptive statistics in the preceding report of CDH soil survey data would appear to be a good measure of the variability of soil plutonium73'240vithin each sector. This information would support the contention that there is no trend of soil plutoniumz"'zao reduction over time in areas sampled since 1975. Prior to 1975, from 1969 through 1974 plutonium z;v.zao was being redistributed in the environment around Rocky Flats. The last published record at station S8 in March of 1994 is 0.000093 pCi/m', a mean of 11 samples (1:JSDOEe). This information and examination of historical air monitoring results provide a basis for collaborating the temporal distribution pattern of plutonium73'340 east of the plant. 4 J