Wed Dec 27, 2006 03:27

(cont'd.) part 3

concentrations were from samples that were taken in the first few years of the survey." (Introduction and overview, pg. 2).
"The postulated decrease in concentration over time was suggested to have been due to any number of removal mechanisms, including erosion and migration to greater depth from the surface." (Introduction and overview, pg. 2).
"The Jones and Zhang study, however, indicates that in fact the concentrations have not decreased over time, but rather that the measured concentrations have decreased in successive surveys because the contamination that had fallen on the surface was being diluted in samples that were collected to greater depth as the survey technique evolved." (Introduction and overview, pg. 2).
Deposition contours of 239Pu deposits ranged from 20 dpm/gm on the southeasterly side of RFETS to .02 in outlying areas.
Close in sectors (1.5 mi.) exhibited a decrease of plutonium concentrations over time; e.g. sector 2: 66.84 dpm/gm (66,840 dpm/kg) gradually declining to 6.57 dpm/gm.
The CDPHE web site contains links to a whole series of reports on the Rocky Flats site, the most important of which will be reviewed and added to this section of RADNET during 1997.
Krey, P.W. and Hardy, E.P. (August 1970). Plutonium in soil around the Rocky Flats Plant. Report of the U.S. Atomic Energy Commission. Report No. HASL-235. Health and Safety Laboratory: New York, New York.
Feb 14, 1970 Rocky Flats, CO On site soil 239Pu 171,000 d.p.m./kg dry soil (2,850 Bq/kg)
Soil Samples were collected to a depth of 20 cm at 33 sites extending as far as 40 miles from the plant site.
Deposition concentrations of 239Pu as high as 2,000 mCi/km2 were found off the plant site: concentrations decreased rapidly with distance (pg. 1). (weapons testing fallout baseline is 1.5 mCi/km2 )
This report contains a graphic contour map; "the contamination pattern extends eastward from the plant in the direction of the resultant wind vector and has virtually no westward component. The pattern is incompatible with the wind direction on the day of the May 11, 1969 fire. Leaking barrels of plutonium laden cutting oil stored in the southeast corner of the plant are the likely source of the contaminant." (pg. 1).
The May 11, 1969 fire as well as several others (Sept. 11, 1957; 1967) also released substantial quantities of plutonium in the resulting smoke plume; while this report does not comment on the smoke plume's source term, it is likely this component of the Rocky Flat's release plume was dispersed to far field locations in quantities too small to significantly impact the deposition patterns documented in the contour map in this report which resulted from the leaking drums. The same observation may be made about the stack releases.
"Three mCi/km2 of 239Pu is the lowest contour readily discernible in the contamination pattern and extends about 8 miles E and SE of the plant." (pg. 1).
Krey, P. W. (1976). Remote plutonium contamination and total inventories from Rocky Flats. Health Phys. 30, 209-214.
Krey, P.W., Hardy, E.P. and Toonkey, L.E. (1976). The distribution of plutonium and americium with depth in soil at Rocky Flats. USERDA Environmental Quarterly Report. HASL-318. U. S. Atomic Energy Commission, Health and Safety Lab. New York.
Krey, P.W., et. al. (1976). Plutonium and Americium contamination in Rocky Flats soils - 1973. HASL-304. U.S. Atomic Energy Commission, New York.
Litaor, M. I., Thompson, M.L., Barth, G.R. and Molzer, P.C. (1994). Plutonium-239+240 and Americium-241 in soils east of Rocky Flats, Colorado. J. Environ. Qual. 23(6), 1231-1239.
"Plutonium 239 + 240 and Am-241 activities in the soils ranged from 164 280 Bq/kg to 0.0037 Bq/kg, decreasing with distance from the source." (pg. 1231, abstract).
"More than 90% of the Pu-239 + 240 and Am-241 activities were confined to the upper 12 cm of the soil, regardless of the soil characteristics, or distance and direction from the source." (pg. 1231, abstract).
"Earthworm activity is probably important in the redistribution of actinides in the upper 40 cm of many of the soils investigated." (pg. 1231, abstract).
"Past cleanup operations have been limited to the upper 10 to 15 cm of the soil (Baker, 1982). Earthworms and other soil fauna, however, may bring Pu-239 + 240 activity that will exceed the 33.3 Bq/kg guideline from depths > 15 cm. Hence, future cleanups to greater soil depth may be cost prohibitive because of the greater volume of contaminated soil." (Pg. 1238).
Litaor, M.I., et al. (1995). Comprehensive appraisal of 239+240Pu in soils around Rocky Flats, Colorado. Health Physics, 69, 6, 923-935.
"Plutonium activity reported in the exhaustive data set ranged from 0.03 Bq kg-1 to 407,000 Bq/kg-1 with a mean of 1,443 Bq kg-1..." (p. 923).
Litaor cites several other studies of global fallout plutonium in Colorado which suggest a large range of plutonium activities "probably due to weather patterns, surficial soil processes, and land-use practices in the last 30 years, as well as error associated with the various soil sampling techniques and laboratory methods employed." (pg. 933).
"In the present study, we selected a threshold of 2.96 Bq kg-1 as the uppermost representation of global-fallout plutonium and 1.29 Bq kg-1 as its mean." (p. 933).
The use of the reporting unit of Bq/kg for denoting plutonium deposition is extremely misleading; plutonium deposition is usually reported in Bq/m2, as the depth used for the kg soil samples can vary from researcher to researcher, and the kg soil samples are taken over a smaller area thereby allowing more impact from wind erosion processes. Multiple bioregional plutonium source points further complicate the attempt to pin down the specific contribution of weapons testing derived plutonium fallout.
It is obvious in this series of reports by Litaor and others that wind dispersion mechanisms are spreading the RFETS derived plutonium over wide areas of the eastern slope of the Rocky Mountains with the result that some of the deposition levels documented by the contour maps in theses reports are declining. One may then incorrectly conclude that earlier reports of higher levels of plutonium deposition may have been incorrect when in fact these erosion mechanisms are rapidly and efficiently spreading this plutonium over wide areas in quantities which cannot be differentiated from either weapons test derived plutonium or other plume source points such as Los Alamos National Laboratory. In this desiccated environment, the efficiency of wind dispersion mechanisms cannot be underestimated.
"A PPRG of 126 Bq kg-1 of 239+240Pu in soil was computed to meet the stringent requirements of a residential scenario." (p. 933).
Litaor, M. I. (1995). Reply to comments on "Spatial analysis of plutonium-239+240 and americium-241 in soils around Rocky Flats, Colorado," by M. I. Litaor. J. Environ. Qual. 24:506-516. J. Environ. Qual. 24(6), 1229-1231.
Litaor, M. I. (1995). Spatial analysis of plutonium-239+240 and americium-241 in soils around Rocky Flats, Colorado. J. Environ. Qual. 24, 506-516.
"Soils were sampled from 118 plots ... by compositing 25 evenly spaced samples..." (pg. 506, abstract).
"Plutonium-239+240 activity ranged from 1.85 to 53 560 Bq/kg with a mean of 1924 Bq/kg and a standard deviation of 6327 Bq/kg. Americium-241 activity ranged from 0.18 to 9990 Bq/kg with a mean of 321 Bq/kg and a standard deviation of 1143 Bq/kg." (pg. 506, abstract).
"The isopleth configuration was consistent with the hypothesis that the dominant dispersal mechanism of Pu-239+240 was wind dispersion from west to east." (pg. 506, abstract).
"In general, Am-241 is more difficult to measure than Pu-239+240 due to the elaborate extraction procedure required to separate Am-241 from lanthanides and Cm. The increase in analytical error resulted in anomaly of the Am-241/Pu-239+240 ratio." (pg. 515).
"These findings clearly demonstrated that the level of contamination in surface soils near the eastern boundary of Rocky Flats and the exposure risk to Pu-239+240 and Am-241 are negligible." (pg. 515).
See Hardy and Krey: comments on this conclusion and their response to this paper cited above.
Litaor, M.I. (1995). Uranium isotopes distribution in soils at the Rocky Flats Plant, Colorado. J. Environ. Qual. 24, 1-5.
"Uranium-234 activity ranged from 25.9 to 92.8 Bq kg-1, U-235 activity ranged from 0.1 to 25.1 Bq kg-1, whereas U-238 activity ranged from 30.7 kg-1 to 286 Bq kg-1." (pg. 1, abstract).
"Most of the observed activities of U-234 and U-235 were well within the natural range of U isotopes in soils." (pg. 1, abstract).
"The two soil plots with the highest U-235 activity (Fig. 3) were probably resulted from surface flow and interflow from the east spray field (see Fig. 1). The east spray field received large amount of irrigation water from a series of holding ponds that between 1952 and 1979 received laundry waste water containing actinides." (pg. 3).
"These results suggest that the impact of RFP on U distribution in surficial soil is limited. Hence, future remedial activities of U-isotopes in soils should focus on the directly impacted areas such as the East Trenches, the former storage site, and the few plots with elevated U activities." (pg. 4).
Litaor, M.I., Ellerbroek, D., Allen, L., and Dovala, E. (1995). A comprehensive appraisal of plutonium-239+240 in soils of Colorado. Health Phys. 69. 923-935.
Litaor, M.I., Barth, G.R. and Zika, E.M. (July-August, 1996). Fate and transport of Plutonium-239+240 and Americium-241 in the soil of Rocky Flats, Colorado. J. Environ. Qual. 25.
"Approximately 90% of the Pu-239+240 and Am-241 activity in the soils under study was observed in the upper 12 cm, below which a rapid decrease of actinide activity occurred (Fig. 3). However, appreciable Pu-239_240 activities were observed at depths of 24 and 36 cm in Pit 5 (1032 and 895 Bq/kg, respectively), and increases in Pu and Am activities were also observed at 48 and 96 cm in Pit 4 (Fig. 3). These actinide activities are significantly higher than previously reported for soils at the Site. ... This apparent discrepancy can be explained by the edaphic factors observed in the study area. Pit 5 is located on a steep slope (12%) and its upper 48 cm exhibited a very coarse texture (Table 2). Pits 1 through 5 exhibited high hydraulic conductivities in the A horizon, and occasionally, in the B horizons (Table 2)." (pg. 4).
"Plutonium-239+240 and Am-241 activities in the soil interstitial water collected by the ZTS [Zero-Tension Sampler] showed a clear distribution with depth (Fig. 4). Actinide activities were significantly higher in the upper 20 cm than in the deeper sampling depths (Table 3)." (pg. 4).
"... Am-241/Pu-239+240 ratios did not increase significantly with depth ... The results indicated that Am-241 does not move faster than Pu-239+240 in the soils of the Site." (pg. 4).
"The actinide activities in the soil interstitial water were completely uncorrelated with the magnitude of volume flux (r2 = 0.006). This profound lack of correlation was consistent under all rain simulations." (pg. 5).
"This study has also demonstrated that our current understanding of the edaphic [soil related] factors that control the fate and transport of actinides in the soil environs is limited." (pg. 6).
Litaor, M.I. and Allen, L. (September, 1996). A comprehensive appraisal of 241Am in soils around Rocky Flats, Colorado. Health Physics. 71(3). 347-357.
"Weapons grade plutonium processed at RFETS was reported to have isotopic composition of 0.04% 238Pu, 93.3% 239Pu, 6% 240Pu, 0.58% 241Pu, and 0.04% 242Pu (Krey and Krajewski 1972; Martell 1975). The initial 241Am activity in the weapons grade plutonium processed at RFETS did not exceed 10-4% (Krey et al. 1976). Consequently, nearly all the 241Am activity in the soil around RFETS resulted from radioactive decay of 241Pu (t1/2 = 14.4 y) to 241Am." (pg. 347).
"The physicochemical characteristics of 241Am in the environment are markedly different than those of 239+240Pu. Fowler and Essington (1974) ascertained that americium is more soluble than plutonium and may become the radionuclide of prime concern because it has a faster migration rate in soils. Romney et al. (1985) showed that root uptake of 241Am by various plants was consistently greater than that of plutonium. 241Am exhibited a higher solubility than did 238Pu and 239+240Pu, as observed in rumen contents of cattle grazing on actinide-contaminated desert vegetation (Barth et al. 1985)." (pg. 347).
"The major finding of this work was that the spatial distribution and dispersal mechanisms of 241Am were similar to those of 239+240Pu. The area adjacent to the former storage site is the most significantly contaminated with 241Am in spite of several soil removal operations (Barker 1982)." (pg. 356).
This report includes interesting contour maps of 241Am distribution which illustrate a more easterly rather than southeasterly pattern of RFETS effluent distribution as suggested by Krey and Hardy (1970).
Litaor, M.I. and Ibrahim, S.A. (September-October, 1996). Plutonium association with selected solid phases in soils of Rocky Flats, Colorado, using sequential extraction technique. J. Environ. Qual. 25.
"Prediction of Pu transport in the soil and vadose zone will be significantly improved if the Pu distribution and association with the various solid phases of the soil are well defined." (pg. 1).
"A sequential extraction experiment was conducted to assess the geochemical association of Pu with selected mineralogical and chemical phases of the soil. In the surface horizons, Pu-239+240 was primarily associated with the organic C (45-65%), sesquioxides (20-40%), and the residual fraction (10-15%). A small portion of Pu-239+240 was associated with soluble (0.09-0.22%), exchangeable (0.04-0.08%), and carbonates (0.57-07.0%) phases. These results suggest that under the observed pH and oxic conditions, relatively little Pu-239+240 is available for geochemically induced transport processes." (abstract).
"Uncommon hydrogeochemical conditions were observed during the spring of 1995, which may have facilitated a partial dissolution of sesquioxides followed by desorption of Pu resulting in increased Pu mobility." (abstract).
"... under ... anoxic conditions, certain bacteria may even dissolve the insoluble Pu-oxides (Rusin et al., 1994), and may further enhance its mobility and bioavailability. This hydrogeochemically induced transport mechanism was not envisioned under any environmental condition or hyudrogeochemical modeling scenarios (USDOE, 1991)." (pg. 4).
"Plutonium-239+240 activity in the top soil horizons ranged from 3920 to 18 200 Bq kg-1, with mean activity of 8480 Bq kg-1. The distribution of Pu-239+240 activity in the samples collected from the five pits showed that >90% of the Pu isotopes is residing in the upper 18 cm of the soil (Table 2). The activity of Pu-239+240 at all locations decreased with depth to near background levels (i.e., global fallout ~ 1.5 Bq kg-1) in the deepest horizons (>1 m)." (pg. 2-3).
Liator, M.I., Barth, G., Zika, E.M., Litus, G., Moffitt, J. and Daniels, H. (1998). The behavior of radionuclides in the soils of Rocky Flats, Colorado. Journal of Environmental Radioactivity. 38(1). pg. 17-46.
"The distribution of radionuclides during the monitoring period from 1993 to 1995 suggested that Pu-239 + 240 and Am-241 are largely immobile in semi-arid soils." (pg. 17).
Little, C. A. and Whicker, F. W. (1978). Plutonium distribution in Rocky Flats soil. Health Phys. 34, 451-457.
Little, C. A., Whicker, F. W. and Winsor, T.F. (1980). Plutonium in a grassland ecosystem at Rocky Flats. J. Environ. Qual. 9, 350-354.
Love, J. (1994). Rocky Flats soil plutonium survey from 1970 to 1991, technical status report. Colorado Department of Health.
Poet, S.E. and Martell, E.A. (1972). Plutonium-239 and americium-241 contamination in the Denver area. Health Physics, 23, 537-548.
"...the 239Pu

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