Models are tested by eliminating each 241am data value in turn, then using nearby data and the model being tested to estimate the missing value. The difference between the estimate and the measured value is called the "kriging error," and can be used to compare different models and check the statistical assumptions. For example, one assumption is that the kriging errors are normally distributed, and this was shown to be a valid assumption for both models. Because the model which ignored windrow effects gave fewer kriging errors on the 241 am activity in excess of 6 pCi/g, it was chosen for making the initial characterization estimates. The model for the 25 m data in the west area was also tested to confirm that it would yield acceptable estimates. In two areas of Janet, both of the 50 m model tests produced more large kriging errors than anywhere else on the island. One was a 450 x 250-m rectangle near the center of Janet, and the other a triangle on the northern edge of the island just west of the north baseline, near the old Test Grid. The fact that estimates using both models gave poor results in these areas indicated the activity itself was more variable, so that more measurements would be useful. Therefore both areas were staked on a 25 m grid and measured with the IMP at the finer spacing from 6-21 January 1978. The original characterization had resulted in an estimate of 21.25 ha with TRU activity in excess of 40 pCi/g with the additional 25 m data, this estimate dropped to 20.75 ha. 6.4.3 Grid Location Problems Because benchmark PORKY had not yet been uncovered in the dense vegetation when the surveyors began staking the 25m grid in the west area, benchmark LEE was used as a reference instead. Unfortunately, an error was made in the process of setting out the grid from LEE, which was discovered when the vegetation was cleared from PORKY. The error resulted in the 25 m grid being shifted 7.32 m (24 feet) west and 4.88m (16 feet) north of the intended location. In order to minimize further confusion, the area was not restaked at the time, but the 50 m grid with origin at PORKY was extended far,enough west to assure complete coverage of the island. The situation remained unchanged until the subsurface excision in December 1978. The excision site was in the area with the shifted grid, and had been sampled at locations referenced to the shifted grid. Therefore, the boundaries for the excision were transmitted to the Joint Task Group (JTG) in terms of the shifted grid. However, JTG was not informed of that fact until later and the first two lifts were made with the location based on PORKY coordinates. The misunderstanding was eventually cleared up, the excision completed as intended, and all locations thereafter were referenced to PORKY, even in the west area. For the Fission Product Data Base sampling, the 50 m grid was extended to cover all of Janet, so that all FPDB samples were taken at 50 m nodes of the PORKY grid. 6.4.4 Other Activities In April 1978, seven additional locations were chosen for soil sampling as part of an investigation of the variability of TRU in the soil and of an apparent discrepancy between soil and IMP data (see Tech Notes 22 and 23). To try to estimate the variance of soil TRU activity within an IMP view, four composites instead of the usual two (see section 4.2.1) were taken at each location. The samples also provided a check on the ratio of TRU to 24! Am eomputed from the original soil samples. The chemical analysis results for these samples confirmed that the soil TRU activity within a single IMP detector field of view is highly variable. Also, the variance of the sample TRU activities increased in proportion to the average TRU activity in the field of view. However, the ratio of TRU to 24lAm from these samples was not significantly different from the previously-estimated ratio, and the ratio variance was independent of TRU activity. The ratio of TRU to 24! Am for Janet was therefore not changed, and eventually soil sampling reverted to the usual two-composite method. 162