1972 Survey Results A total of 58 locations were soil sampled on Irene during the 1972 survey. At 37 locations, the samples were 0-15 cm cores, 6 locations were profile sampled from 0 to 35 em, 11 locations had 0-65 em profiles, and 4 locations had 0-185 em profiles. Many plant and several animal samples were also taken on Irene. The distribution of activity with depth in the soil samples was quite variable, and high subsurface activity of 239,240 py, 137cs and 99Sr was observed at several locations. The elevated activity was observed as deep as one meter, helping indicate the general locations of possible burials of contaminated soil and debris. In general, the depth distribution at a location was similar for 239,240 py, 13%cs and 90s, and the activity dropped steeply below one 1Cs, meter even in locations with elevated subsurface activity. The results for 0-15 em data for 90s and 239,240 py are summarized in Tables 7-1, 7-2 and 7-3, respectively. The soil data indicated not galy inhomogeneity in the depth distribution of activity, but also the existence of more than one 239:240py to 241 4m isotope ratio. The ratio is usually assumed to be constant for all contamination originating from a single event. This implies that any differences observed in the 239249py to 24lam ratio would be due to contamination from more than one source. The relative locations on Irene of the various ratios tended to confirm that hypothesis, so that boundaries bet ween ratio populations might be based on geographical location. In addition to the soil, plant and animal samples, several sampling wells were drilled for the groundwater studies in the 1972 survey. Two coconut trees were selected to be a part of the long-term study of radionuclide uptake in food plants. Efforts were made to preserve the wells and study trees during the cleanup. Surface Characterization The initial IMP measurements of Irene were made on a 50 m grid beginning 28 October and ending 7 November 1977. Measurements on the Helen spit were also made at 50 m intervals along the spit at the center of the area above the high tide line. These points did not fall on the nodes of the island grid, so the location was established by measuring the angles between adjacent sampling points. As shown in Figure 7-50, 19 points were taken on the Helen spit, starting at the main body of the island and extending as far out as was practicable. shown in Figure 7-49. The sampling points on the main section of Irene are Soil samples to determine the ratio of TRU to 24!am were taken initially at five locations in October 1977 (see Section 4.2.1). The results confirmed the variation in ratio of TRU to 24!Am seen in the 1972 data. In general, the ratio decreased with increasing distance from the Seminole GZ. This information was used to draw tentative boundaries between populations of ratios, and five more locations were sampled to confirm and better define the boundaries. Figure 7-49 shows the locations for both sets of samples and the boundaries between ratio populations that were used for initial characterization. The ratio of TRU to 24! Am used were 4.12 + 0.53 for the eastern end, 6.50 + 1.20 for the central area, and 11.13 + 1.7 for the western end and Helen spit (see Tech Notes 2.1 and 2.1-A). Along with the surface soil samples and measurements, samples were taken from two of the bunkers on Irene, Ivy stations 200 and 600. The samples were taken to help characterize the amount and type of activity on the concrete surface, because the bunkers were to be left in place. Tech Note 13 contains a description of the sampling, which took place on 7 July 1978, and the results of the laboratory analysis. Under worst-case assumptions, the contamination on the conerete was found to be nearly a factor of two below the release limit, so no further cleanup of the bunkers was done. The initial surface characterization of Irene is shown in Figure 7-51. The 0.5 s upper bounds on the average TRU estimates exceeded 40 pCi/g on only 1.5 ha, where s is the standard deviation of the kriging error, and nowhere did TRU estimates exceed 80 pCi/g based on original data. (See Tech Note 23 for discussion of original versus final data.) Although no surface cleanup was required to meet the cleanup criteria, later subsurface excavations altered the surface activity in some areas of Irene. For the Helen spit, the highest TRU value estimated from any IMP 24l'am value was less than 30 pCi/g. 264