s which could be Numerous attempts have been made to develop a set of equation used to define the distribution of Pu in soil in the off-NTS area. No attempt 0.34. tested thus far has resulted in a correlation coefficient larger than ng Concern for the assumptions made in defining soil bulk density when converti field concentration values to deposition values prompted the EPA to perform a et Church by reported as d collecte were study in which two sets of samples al., 1974, and another set collected where the actual volume was measured. Some soil collectors presume a sample volume by using a collection tool of known size and use an average soil bulk density to define the sample weight. This procedure is subject to errors in collection technique as well as the In this study, the third collection included variability in soil bulk density. refilling each sampled hole with a standard sand. The measured weight of sand was used to define the sample volume and bulk density. Each of the first two sample collectors sampled four profiles to 20 cm deep in 5-cm increments, The i.e., collected 16 samples, while the third collected four samples. 1.62 g/cm? and rs 1.70 were collecto two first the for average densities computed ent measurem volume actual the By 0.05. and with standard deviations of 0.08 used in the third collection set, the computed density was 1.53 + 0.05. It was noted that the former two collectors had errors in collection depths of +2.8 and +1.9 cm. Correcting for this excess volume revises their bulk density measurements to 1.49 and 1.48, both within the one-sigma error of the method in which actual sampling volume was measured. It may be concluded, then, that careful sampling with a known volume tool is sufficiently accurate to calculate bulk density for the objectives of the NAEG survey. Plutonium in Air Results from the analysis of air filters from the eight western U.S. locations previously reported (Bliss and Jakubowski, 1975) show ambient levels of 2399 240py to be remaining within the range of data collected for the period 1966 through 1973. An ongoing study which should be concluded by early 1977 will allow reporting the uncertainty of the air data. Laboratory analytical and counting errors can be determined but sampling errors have not been fully evaluated. Duplicate sampling has begun for the purpose of estimating the total error associated with the sampling and analyzing of air samples. Three sampling locations near NTS have been selected for routine plutonium analysis in addition to the eight above. These locations are Las Vegas, Lathrop Wells, and Diablo. No analyses have been completed for these locations. All locations routinely analyzed for plutonium are now using filters of polysty- rene fiber mat which are easily dissolved in organic solvents. Related Projects 1. Basin Studies--Sampling has been completed in three drainage basins to assess the concentrating effects of hydraulic movement. These areas are Fortymile Canyon, a basin southeast of Frenchman Flat, and a basin 160 km 228