SPECIAL STUDIES Several extensions of the original mission of the Soils Element as previously described relate to in-depth studies of problems which became evident as the program developed. These studies include soil radionuclide profile evaluations, quality assurance, determination of isotopes of uranium by means other than mass spectrometry, and study site selection. Soil Radionuclide Profiles Profile samples were obtained initially as a part of the sampling program for inventory. As profile data accumulated, it became evident that a considerable fund of information was available which might be used to indicate possible mechanisms of soil-radionuclide interactions. Essington et al. (1976) have reported on profile data as related to soil structure and soil anomalies. Figure 2 indicates one type of concentration profile found and the soil structure associated with plutonium concentrations. The points of interest are the two peaks in radioactivity at the 10 and 17 cm depths. Those peaks are at the depths where the profile changes from the A to the B horizon and the B changes to the C horizon. Apparently, the physical nature and/or the chemical changes occurring at the horizon interfaces act upon plutonium, thus causing deposition. All soil profiles from the safety shot sites have been taken to a depth of 25 em. No information is available to indicate the maximum depth of penetration of plutonium. In fact, several of the profiles indicate that plutonium may have migrated to depths greater than 25 cm as shown in Fig. 3. Relatively high and constant concentrations of plutonium were found between 7 and 25 cm and there is no indication of a substantial decrease in plutonium between the two depths. Presumably, similar levels of plutonium could be found to greater depths. Quality Assurance The quality assurance program was established to provide needed data for comparison of results from different laboratories which used different analytical methods for the estimation of plutonium. The Soils Element has prepared and submitted for analysis "standard" samples of soil, meat, and vegetation to participating laboratories. Where available, results have been reviewed and used to indicate problem areas which might exist. Results of analyses performed on dosed meat samples are presented in Tables 2 and 3; three isotopes and two levels of radioactivity were investigated. With respect to the high activity samples on Table 2 and the low activity samples on Table 3, results are considered generally satisfactory, although there are anomalies. Variations observed do indicate the need for extreme care to avoid cross contamination when low activity samples are processed. Such quality control comparisons can be used to alert those involved to potential problems which might not be recognized otherwise. 24