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., ROCKY FLATS SOII. PLUTONIiJM""Z'0 SURVEYS FROM 1970 TO 1991 Temporal Analysis of the Data ' Graphs 7, 8, 9, and 10 show the yearly data for Sectors 1, 2, 6 and 7. The relationship to the state plutonium standard and any discernable relationships among the ' Sectors h,as been adequately discussed above. Examination of the trend over time is not apparent except pre-1975 data versus post-1975 data. Data since 1975 shows no clearly visible relationship, either increasing or decreasing for the four Sectors examined. The other 9 Sectors are significantly below (a magnitude) that of these four. Pre-1975 data as a rule is definitely higher. The differences between the descriptive statistics for the 1970-1991 and 1975-1991 data sets shown in table II are significant. Questions about consistency in the sampling depth could be explained by the sampling procedure for pre-1975 period and the resulting reduced levels over the post period. Another possible explanation is that essentially the release form the 903 Pad was a sinl;le event; once capped no new material was released. Residuals in the nearby surrounding area would have been re-distributed for a time, until all significant particles became entrapped. Available reports on the chronology of events and environmental data at Rocky Flats support the separation into pre-1970 period as the release period and the 1970 to 1974 years a period of significant re-distribution of plutonium"~'2°0. Essentially after 1975 little or no substantial plutonium792°0 may have been redistributed. '' The descriptive statistics for each sector indicate the median or geometric mean is a good measure of central tendency for the data. Trends in plutonium""=d0 within each sector are not readily apparent after 1974. The standard deviation, variance and 95% confidence interval are good measures of the variability inherent in the data within a sector. The variability of the plutonium measurements is reduced when only post-1974 data is used. Maps 4 and 5 show results of the ] 98 ] and the 199] survey. 1981 data for Sector 10 has a reading of 0.52 pCUgram. As discussed previously this is considered an outlier. The value exceeds the 95% confidence value for Sector 10 by one to three multiples depending on the data set: O.1f~22, 1970-1991; 0.2510, 1975-1991. Sector 10 is the only sector with a larger mean and confidence interval with the 1975-1991 data set. The 1981 data value is an outlier and is ' excluded in map 4. The median value for the rest of the record is used for map 4. Use of descriptive statistics based on the complete record for each sector from 1970 to 1991 are conservative measures of soil plutonium79~2°0 in and around the Rocky Flats Plant. Map 1 is a conservative representation of soil plutonium792°0in the environment surrounding Rocky Flats. 24 1 m .:..:..........:. ..:..:...::.:... ..:.......:.::........:.....:...:...................:.:..:........ ~~