E. Brush Attenuation. Is there a bias in the brush attenuation factor used? F. Soil Moisture. The soil sample results are given in activity in dry soil. What is the influence of soil moisture on the IMP readings? ll. Experiment Objective The abovelist is not intended to be complete or comprehensive. It is apparent, however, that there are many factors that influence the comparison of IMP readings to soil sample results. When this list was prepared (3 May 1978), it was the intention of the ERSP to investigate these items, as time permitted. Some could be investigated by experiment and some by computations. The intention of this experiment was to investigate items C and D.2 in Section II. A relatively undisturbed area on the island of Tilda was chosen for the experiment (Figure B-8-2). The 241Am concentrations were about 5 pCi/g. The location had little or no brush. Thearea was roped off and designated a DOE test area to be undisturbed until the end of the cleanup project. IV. Description of Field Experiment The location was divided into two areas, one for detailed measurements and one for a control area. A sketch of these two areas is shown in Figure B-8-3. Access lanes were chosen for minimum disturbanceof the soil. IMPs I and III were used for measurement at both areas with the detector at 740 em and 460 em heights. Two 15-minute measurements were made at each point at each height. For the control area, normal soil samples were taken for the A and B composites. The "cookie cutter" was used for these samples. From the weight of the soil collected and the depth of the instrument, it is estimated that the depth of sampling was from the surface to about 2.5 em. For the experimental area, 12 different spots were chosen for soil samples, corresponding to the normal A and B locations. The soil from each location and depth was kept separate. For 6 of the locations, 2 samples were taken (0 to 2.5 em and 2.5 to 5 em). For the other six locations, 6 samples were taken (0 to 1.5, 1.5 to 3, 3 to 4.5, 4.5 to 6, 6 to 8, 8 to 10 em). The locationscircled in Figure B-8-4 correspond to the latter 6 locations. For the 6 locations where only 2 samples were taken, the cookie cutter was used. For the other locations (circled in Figure B-8-4), a different method was used. Two pieces of tin, about 20 x 30 em in size, were taped (yellow) with 1.5 em strips for reference. The two pieces of tin were then "sawed" into the soil to a depth of 10 em forming a 90° angle with each other. Soil was then removed from the perimeter of the sample area and placed into a plastic bag. With a third piece of tin a 1.5 em layer was "cut" off the top and removed. Successive layers were then removedin like manner. After sampling was completed, the soil from the bag was placed back into the hole. All sampling locations were in undisturbed soil. At only one location was it necessary to stop short of 10 em depth due to a ledge of old beach rock. Vv. Results The IMP results are tabulated in Table B~8-2 and summarized in Table B-8-3. The control area appears to contain a little higher 241 Am activity than the experimental area. The decrease in values with increase in height is as expected (approximately 10%) for the control area, but is not consistent for the experimental area. Little significance should be placed on this, however, because activity within the area is not likely to be uniform and brush is not uniform within the area. It is noted that IMP I, detector No. 496, requires a correction of 1.1 because of detector size. It is also noted, after applying the detector correction factor, that the results of IMP III appear to be slightly greater in value than those of IMP I The averages are within countingstatistics. B-8-3