6.9 SUBSURFACE SAMPLING AND EXCISION (by Bert Friesen, H&N) The Enewetak Radiological Survey (See Section 2.1.4) provided guidance with respect to possible locations where subsurface contamination might be found. In general, these locations were limited to islands used for nuclear tests. Also in general, the more tests conducted on an island, and the larger the yield of nearby tests, the more complex was the distribution of radioactive elements in the subsurface soil At GZ locations like Item on Janet, Inca on Pearl, and Kickapoo on Sally, where only one test was conducted, post-test construction and cleanup actions were minimal Consequently, contaminants remained relatively near the surface and relatively close to the test site; apparent anomalies will be discussed later. At GZ locations like Seminole on Irene, Easy/X-ray on Janet, and Yoke/Yuma onSally, the cleanup following one test, and the construction preceding the next, created a heterogeneous mix of soil and contaminants which could be located anywhere relative to the test GZ. Because of the many nuclear tests conducted on Yvonne, this island is a special case to be separately discussed in Section 6.10. Subsurface sampling and excision progressed through a series of phases as described below. 6.9.1 Early Programs As lane clearing progressed from oneisland to the next, with priority given to GZ islands, effort was directed toward finding a satisfactory method of sampling for subsurface contamination. Many possible techniques were discussed at length and discarded for some reason; usually the reason related to time and effort requirements, machinery and logistics problems, or to undeveloped detection equipment. The soil profile sampling methods described in NVO-140 (pages 93-94) were not readily adaptable to the present situation because of differences in the number of profiles required and the number of people available to do the work. For example, during the 1972-73 survey, there were approximately 18 people involved in the soil survey; during their mission, 21 profile holes were hand-dug and sampled on Irene. The hole depths and number of holes to that depth were: 0-35 em, six; 0-65 em, 11; 0-185 em, four. The initial sampling effort outline for Irene in November 1977 included 27 profiles each to a depth of 120 em, the water table or bedrock, whichever occurred first. Work was to be done by a crew of five in as short a time as possible due to constraints imposed by boat availability, favorable tide conditions, the tight schedule of soil sampling on other islands and sample preparation requirements at the laboratory complex. Profile sampling at selected 50-meter grid points on Irene was conducted from mid-November through December 1977. Holes were hand-augered with soil recovery attempted in 20-em increments, Recovered soil was placed in a copper- and lead-lined tub and seanned for alpha, beta, and gamma with portable instruments. An attempt was made to establish correlations between laboratory counting results, portable field instruments, and the IiViP's gamma detector system. None of the experiments gave acceptable quantitative results, although there was a general agreement as to the presence or absence of radionuclides. An evaluation of the augering system concluded that soil conditions were generally not amenable to this technique. When the soil was very loose and sandy, the sidewalls would cave in as the auger was pulled from the hole. On the other hand, the auger eould not penetrate rocky soil and the sample could not be recovered when the hole reached the water table. Since the primary objective of the sampling was to isolate zones of high radionuclide activity, there was also the concern that contamination between zones would occur and destroy the credibility of the sampling results. Hand augering was abandoned early in the program following limited use on islands Irene, Janet, Pearl, Sally, and Yvonne. A plan for additional subsurface sampling on Irene was prepared in late January 1978, and conducted in mid-February. Profile holes were dug by backhoe at 19 selected locations, and discrete 5 em samples were taken from 0-5 em, then every 20 em centered on multiples of 20. Results of this sampling effort indicated several areas where subsurface transuranic concentrations might exceed the cleanup criteria. Another sampling mission was laid out in late February and executed during early March, this time to obtain additional samples from around grid points 13-N-1l, 12-N-2, and between 10-BL-0 and 10-N-1, found earlier to have elevated levels of transuranics. 184