ahaa
FIGURE 6-24. SOIL REMOVAL AREAS ON ISLAND IRENE. Subsurface soil was removed from what appears as four
cleared areasin this aerial photograph. The 14-N-1 area is near the lower left; three other locations toward
the top of the picture had soil removed following the FPDB survey. The Seminole Crater is at picture center.
{July 1979}
Sample Scanning by IMP. In the early months of 1978, a large numberof soil profile samples were
collected in GZ subsurface investigations. As analyses came out of the laboratory, it became
evident that a large percentage of the samples contained less than the minimum detectable activity
system to sean samples for 24lAm. Samples with very low activity would not be submitted to the
RADLAB. With only minor experimentation, a system was developed, tested and implemented.
(Details of the system appear in Appendix B, Tech Notes 6.0 and 6.1, and examples of field use
appear in Tech Notes 9.0 and 18.0, and in Section 6.8, Aomon Crypt Exploration and Excision.) A
general rule evolved to determine the level of 24am activity above which all samples would be
a
of 24lam or 239:240py, Discussions were held to search for an acceptable means of reducing the
number of samples submitted to the RADLAB without impairing the thoroughness of GZ
investigations. The EG&G scientist on duty at the time suggested using the IMP gamma detector
submitted to the RADLAB: Using the appropriate TRU/24!Am ratio, any sample with indicated TRU
greater than about one-half the applicable guideline would be laboratory processed; in addition, 10
percent of the samples below the cutoff would be laboratory. processed for quality control purposes.
For example, Aomon Crypt soil with TRU-activity greater than 400 pCi/g was to be excised, and the
For eonvenience, the 241m cutoff was set at 25 pCi/g
(400/6.17 = 64.8; 64.8/2 = 32.4; 32.4 - 25 = 7.4, which allowed for about a 30 percent error).
Core
sampling at the Aomon Crypt produced in excess of 1,000 samples, of which fewer than 200 required
RADLABprocessing. Significant savings of time and effort were realized by using the IMP detector
to sort, or screen, soil samples collected in the plowing experiment, the Aomon Crypt excavation,
and the subsurface explorations following the FPDB sampling program.
193
wr a
applicable TRU/24lAm ratio was 6.17.