Several sampling wells were drilled for groundwater studies in the 1972 survey in addition to the soil, plant and vegetation studies. Two pandanus trees were also a part of the long-term study of radionuclide uptake. Refer to Section 6.11 for more details on these studies. Characterization - Surface Sally was initially staked on a 50 m grid in the fall of 1977 except for Cape Mixan which was surveyed in the spring of 1978 on a 25 m grid. The 25 m grid was an extension of the 50 m grid but was staked later because of the confusion whether to consider that area Sally or Ruby. (The decision was made to call it a part of Sally.) The grid was tied in the Oscar coordinate system with the benchmark Dan, located in the northern part of the island (Figure 7-97). The benchmark Sally was also found after the surveyors began staking Sally. The grid on this island was erroneously laid 4 degrees west of true north. The initial TRU characterization of Sally did not inlude Cape Mixan, which will be discussed later in this section. The main part of Sally was measured by the IMP from November 1977 through January 1978, and nine surface soil samples were collected in December 1977 for the same area. locations and soil sample locations are shown in Figure 7-97. The IMP In order to calculate TRU values for Sally, the laboratory results from the soil samples were used to determine a TRU to 24lAm ratio. At each of the nine locations, soil samples were collected at 3 depths with 2 composites for a total of 54 samples (see Section 4.2.1). Because three of the 24lam concentrations were below minimum detectable activity, they were not used in the calculation of the ratio. It was clear from the range of values for the ratio that more than one population of ratios existed on Sally. Three ratios were finally calculated and used for the first TRU characterization of Sally with 3.86 + 2.72 for Yuma GZ, 6.16 + 1.73 for Kickapoo GZ and 3.37 + 1.08 for the rest of the island except Cape Mixan. (For more information on the computation of these ratios and data used, see Tech Note 2.5). The boundaries between the three ratio populations are shown in Figure 7-97. After the initial 50 m grid was measured with the IMP, the appropriate ratio was applied and TRU values calculated. Using these TRU data andthe kriging statistical technique (Section 5.1.1), 0.25 ha estimates were calculated based on original data. (See Tech Note 23 for discussion of original versus final data.) The variogram model estimated from the data was linear in mathematical form. An apparent anisotropy seen in the east and southeast directions was mainly caused by insuff icient data outside the PACE area in those directions. The PACE area was very low in 41am activity and homogeneous, therefore showing little change over distance in those directions. In the other directions, the wide range of TRU activity in the Kickapoo, Yuma and PACE area produced great change over distance in the raw variogram. estimate of the variogram. On the average, however, the linear model was a good Figure 7-98 shows the initial TRU characterization of the main part of Sally and indicates the areas with TRU activity exceeding 40 pCi/g with a 0.5 s upper bound, where s is the standard deviation of the kriging error. These areas were "cleaned up" during the project. Because these areas were frequently referred to, each area had a code name: the area on the north tip was called Kickapoo, the area along the beach on the lagoon side was Yuma, and the area near the northwestern beach was known as Hustead. The area known as Cape Mixan was surveyed on a 25 m grid and IMP measurements taken in March 1978. Initially, only three locations were soil sampled with two composites at three different depths for each site for a total of 18 samples. The results from these soil samples indicated that two distinct ratios were present as shown in Figure 7-97. The data from one location showed a ratio similar to the Yuma area while the other two locations indicated a new ratio entirely. It appeared that the new ratio was applicable to the region with higher 241m concentrations whereas the Yuma ratio seemed appropriate for the lower activity areas. Six more locations in the higher activity area were sampled in May 1978 with only one sample collected from each site. A ratio of 322