Radionuclide Concentrations in Soils and Vegetation at Low-Level Radioactive Waste Disposal Area G during the 1997 Growing Season

Abstract

DISCLAIMERPortions of this document may be illegible electronic image products. Images are produced from the best available original document. LA-13495-PRProgress Report uc-2000 Issued: August 1998 ABSTRACT Soil and overstory and understory vegetation (washed and unwashed) collected at eight locations within and around Area G-a low-level radioactive solid-waste disposal facility at Los AIamos National Laboratory-were analyzed for 3H, ='Pu, 239Pu, 137Cs, 234Uy 2'4Pb, and 208Ti. In general, most radionuclide concentrations, with the exception of 3H and ='PU, in soils and overstory and understory vegetation collected from within and around Area G were within upper (95%) level background concentrations. Although 3H concentrations in vegetation from most sites were significantly higher than background (>2 pCi mL-l), concentrations decreased markedly in comparison to last year's results. The highest 3H concentration in vegetation was detected from a juniper tree that was growing over tritium shaft #150; it contained 530,000 pCi 3H mL-1. Also, as in the past, the transuranic waste pad area contained the highest levels of 239Pu in soils and in understory vegetation as compared to other areas at Area G. Radionuclide Concentrations in Soils and235U, "*U, "'U (calculated), 228Ac, 7Be, 2'4Bi, 6oCo, 40K, s4M.n, 22 The location of Area G at Los Alamos National Laboratory. @SP 1997), water (Mullen et al. 1996), soils/sediment (Conrad et al. 1995(Conrad et al. , 1996 Fresquez et al. 1996% 1997a, vegetation (Fresquez et al. 1995, 1996b, 1997a), small mammals (l3iggs et al. 1995, Bennett et al. 1996, Biggs et al. 1997, and bees and honey (Fresquez et al. 199%) are collected fiom within and around radioactive waste disposal site Area G on an annual basis to help monitor and assess the site's impact on the surrounding environment. Two important components of this program are the assessments of soil and vegetation within and around Area G for radiological contamination.A soil sampling program, for example, is the most direct means of determining the types, concentration, and distribution of radionuclides in the environment within and around nuclear facilities (Fresquez et al. 1998). Soil provides an integrating medium (reservoir) that can account for contaminants released to the atmosphere, either directly fiom gaseous effluents (air stack emissions) or indirectly fiom the resuspension of on-site contamination (fugitive dust) (Healy 1977). Subsequently, the knowledge gained fiom a soil radiological surveillance program is critical for providing information about potential pathways (e.g., soil ingestion, food crops, resuspension into the air, and contamination of groundwater) that may result in a radiation dose to humans (Hakonson et al. 1981). The uptake of isotopes by vegetation may also give some insight into surface (Hanson et al. 1980) and subsurface (Wenzel et al. 1987) contaminant pathways to humans fiom waste disposal areas. Trees, in particular, have been shown to be excellent indicators of subterranean tritium migr...