already missed by the 100-foot FIDLER grid which estimates 422 and 770 uCi/m? (Figure 8 for the two cells adjacent to GZ. Perhaps there should . m,,,m(v be a specific correction factor 10 /10 (v) : to account for a steep decline in Pu concentration within 100 feet or less of GZ. Perhaps the lognormal model itself is not quite adequate at very high levels. Only a custommade sampling experiment could help solve that question. The kriging estimates, approximately 400 feet south of GZ, are also somewhat lower than observed concentrations (Figure 4). However, some of these data were not used in the analysis (see Footnote 2), so that a certain amount of underestimation is expected. The correction (Formula 16) to the guess field is relatively small in areas of high activity near GZ and gets large only in areas of low activity (Figure 10). The relatively large correction south of GZ appears to be caused by the several Pu concentrations that were higher in that area than expected on the basis of prior FIDLER readings. The sparseness of data east of GZ may be related to the rather large correction in that area. In general, however, it may be said that most of the information about the geographical distribution of the Pu is already contained in the FIDLER data. The main role of Pu analysis is to cali-~ brate the regression (Equation 2). In general, the confidence interval factors in Figure 15 suggest we are able to estimate arithmetic mean Pu concentrations over 100- x 100-foot cells within, roughly, a factor of 2 with approximate 95 percent confidence. INVENTORY In Table 3, Part A, we compare estimates of Pu inventory (total amounts in the top 5 cm of soil) reported by Gilbert (1977) for Area 13 with those obtained using the kriging results given here in Figure 12. We recall that Gilbert (1977) used stratified random sampling, where the inventory estimate for a given stratum was obtained by multiplying the average Pu concentration (uCi/m*) for that stratum by the size (m*) of the stratum. The kriging estimate of Pu inventory for a given stratum was obtained by estimating the inventory for each 100- x 100-foot cell and summing these for all cells within the stratum, The estimated inventory for a given cell was computed by multiplying the average (kriging) Pu concentration (uCi/m*) by the size of the cell (929 m2). For cells that over lapped into adjoining strata, the area of the cell lying within the stratum of interest was approximated by "eyeball." 398