9.6 + 0.22 was computed for this area. (Refer to Tech Note 2.21 for more information on this ratio). The other ratio used for Cape Mixan, 5.3 + 0.2, was the ratio used for Yuma cleanup. (The cleanup ratio was different than the ratio used for characterization because more data were available for the later effort.) Using these ratios and the IMP data, TRU values were calculated. To get a 0.25 hectare estimate, the average of four IMP readings forming a square was calculated since the IMP field-of-view includes most of the surface. Using original data no 0.25 hectare average was estimated with TRU activity greater than 40 pCi/g but based on final data, one 0.25 hectare was estimated to have a TRU activity of 41 pCi/g. The final isopleths for the final TRU values for Cape Mixan are shown on Figure 7-107 on the map of Sally. Characterization - Subsurface Subsurface investigation, as described in Section 6.9, was conducted in five different parts of the island - Kickapoo, Yuma, Hustead, Yoke and Cape Mixan. The results will be discussed more fully later in this section. Figures 7-99 through 7-102 show the sampling locations for these five regions and also give the highest TRU value in each profile. Cleanup Activities The pilot soil removal for the cleanup project was done in the Kickapoo area (Section 6.6). The initial results from the characterization analysis showed three 0.25 hectare to have greater than 40 pCi/g average TRU activity. To better define the surface boundary exceeding 40 pCi/g, a 12.5 m grid was surveyed and additional IMP measuremets were taken in February 1978 for the area in Kickapoo that had TRU activity estimated to be greater than 40 pCi/g. Isopleths of TRU activity exceeding the 40 pCi/g level are shown in Figure 7-103 for both 12.5 m and 25 m grids, along with the boundary resulting from the kriged estimates done on the 50 m grid data. Because the isopleths shown for the 25 m grid and the 12.5 m grid were not significantly different, the isopleth for the 25 m grid was used to outline the area where soil removal was necessary. In addition to more IMP measurements, more surface soil samples were collected prior to any earth moving activities. This was done to verify that the ratio first calculated for Kickapoo was appropriate since the original number was based on one soi] sample location. The additional results did justify using the 6.16 TRU to 24lAm ratio, and therefore the fine grid TRU values were ealculated using this ratio. The subsurface data collected earlier indicated that more than one "6-inch" lift would be necessary in certain spots. Figure 7-103 also shows the outlines of subsurface contamination. Before any soil lifts were made, the vegetation in the cleanup area was removed in mid-March 1978. Surface soil samples were again collected and the TRU to 24lAm ratio verified. After this vegetation removal activity, different methods for soil removal were tried to compare their effectiveness. As a result of this experimentation, the soil was greatly disturbed. The area was then measured by the IMP to determine how this disturbance affected the surface TRU activity. The mean TRU concentrations before any soil disturbance was 146 pCi/g and after soil disturbance was 154 pCi/g; both ealeulations are based on data from the same sixteen locations. These results reflect no significant change in surface TRU activity due to soil disturbance. : After the first actual soil lift was complete, IMP measurements on a 25 m grid were taken and more surface and subsurface soil samples were collected during the first part of April 1978. The surface soil samples again verified the initial ratio and the subsurface soil results corroborated earlier results and also indicated another pocket of high activity along the northwest beach line. The IMP data showed that the majority of the area with TRU activity estimated above 40 pCi/g initially was still above 40 pCi/g. After the next soil lift, very little soil was left at Kickapoo so that the surface was mainly beach rock. Only IMP data were collected in June 1978, following this lift, and these results showed two areas still with high TRU activity, the same two areas that had shownhigh subsurfaceactivity. One 324