The distribution of Pu, 241Am, and water in Bandelier Tuff beneath a former liquid waste disposal site at Los Alamos was investigated. The waste use history of the site was described, as well as the previous field and laboratory studies of radionuclide migration performed at this site. One of the absorption beds studied had 20.5 m of water added to it in 1961 in an aggressive attempt to change the distribution of radionuclides in the tuff beneath the bed. Plutonium and 241Am were detected to sampling depths of 30 m in this bed, but only found to depths of 6.5 to 13.41 m in an adjacent absorption bed (bed 2) not receiving additional water in 1961. After 17 yr of migration of the slug of water added to bed 1, 0.3 to 5.1% of the Pu inventory and 3.0 to 49.6% of the 241Am inventory was mobilized within the 30‐m sampling depth, as less than one column volume of water moved through the tuff profile under the bed. The results of similar lab and field studies performed since 1953 were compared with our 1978 data and site hydrologic data was used as a time marker to estimate how fast radionuclide migration occurred in the tuff beneath absorption bed 1. Most of the radionuclide migration appeared to have occurred within 1 yr of the 20.5‐m water leaching in 1961. The implications of our research results to nuclear waste management were also discussed.

The Los Alamos National Laboratory has been disposing of radioactive wastes since 1944. Environmental studies and monitoring for radioactive contamination started concurrently. In this report, only two mechanisms and rates by which the radionuclides can enter the environment are studied in detail: subsurface transport of radionuclides by migrating water, and diffusion of tritiated water (HTO) in the vapor phase. The report also includes a section concerning the influence of moisture on shear strength and possible resulting subsidences occurring in the pit overburdens. Because subsurface transport of radionuclides is influenced by the hydraulic conductivity and this in turn is regulated by the moisture content of any given material, a study was also undertaken involving precipitation, the most important climatic element influencing the geohydrology of any given area. Further work is in progress to correlate HTO emanation to atmospheric and pedological properties, especially including thermal characteristics of the tuff. 3000-1 , Si«rra do los Vdlles Bandolier tuff Basaltic rocks cf Chino Mesa Tschicomo formation Puye conglomerate Tssuque formotion Precombnon crystalline rocks 'i&m'''''>''Z''''"7!m&*B ondtlier tuff PajOfilo Ploteou East-2400 West Seal* East i k 8 kilometers Fig. 2. Geologic stratigraphic relationships of Los Alamos County from Sierra de los Valles to the Rio Grande. The oldest rock unit in the Los Alamos area is the Tesuque Formation, consisting of fossiliferous siltstones and sandstones with lenses of clay that were deposited as basin fill in the Rio Grande structural trough. Near Los Alamos these sediments are light pinkish-tan and include some interbedded basalts. The Tesuque underlies the Pajarito Plateau and is exposed at lower levels along the Puye Escarpment and in White Rock Canyon. The main water supply for Laboratory and domestic use is derived from the Tesuque. The age of the Tesuque is Miocene. The Tschicoma Formation forms the major part of the interior mass of the central Jemez Mountains; thus, exposures are limited to the western and northern parts of the Los Alamos area. Rock types are porphyritic dacite, rhyodacite, and quartz latite containing phenocrysts of pyroxene, hornblende, biotite, plagioclase, and quartz (Bailey et al., 1969; Smith et a!., 1970). Some units of latite and quartz latite in the Los Alamos area contain xenocrystic plagioclase that has been partially remelted, embayed, and resorbed, as well as subrounded and embayed quartz (Griggs, 1964). The maximum thickness of the 6.7 to 3.7 million-year-old (Myr) Tschicoma Formation exceeds 900 m (Bailey et al., 1969; Smith et al., 1970). The Puye Formation, named for exposures in cliffs along the Puye Escarpment, is divided into two informal members, the lower Totavi Lentil, overlain by a fanglomerate. The basal Totavi Lentil (0 to 25 m thick) consists of well-rounded pebbles, cobbles, and small boulders of Precambrian quartzite and granite in a matrix of coarse arkosic sandstone. The upper unit is a poorly consolidated, s...

mlnnpt ptroub «"In this report an analysis is made of a numbe* of nalural phenomena which could result in the relense of plutonium front radioactive wastes buried at the Loo Alamoa Scientific Laboratory (LASL). Background information concerning the history and practice of radioactive waste disposal at LASL is provided. The potential impact of buried radioactive wastes on the environment is addressed through the mechanisms and rates by which the radionudldes can enter the environment. Only mechanisms independent of human activity are considered. They are divided into two classes, acute and chronic. The acute release mechanisms considered are earthquakes, meteorite impacts, and tornadoes. These have been typified by low occurrence probabilities (10 * -10 Vyr). The chronic mechanisms that have been considered are release through uptake by plant roots, exposure by soil erosion, and transport by soil water. The ratos of these processes are low, but may result in radionuclide release over long time periods. The analysis of uptake by plant roots was made using an environmental model currently under development; the model is discussed in some detail. the environment as a result of migration, or the environment may encroach upon the waste pita through erosion or other mechanisms that breach the burial containment. All processes that result in contact between the wastes and the environment are time dependent, either in a rate or probabilistic sense. The first task in evaluating the potential impact of buried wastes is to identify the mechanisms specific to a given burial site that would result in radionuclide releases to the environment. Second, the ratea or frequency of these processes must be determined. Finally, the movement of the released radionuclides through the biosphere must be described in order to arrive at some estimate o»" the resultant consequences of the release.Such an evaluation has been performed, on a preliminary baais, for the waste burial grounds at LASL. A review of potential release processes indicates that the frequencies of probabilistic processes are very low (10" f -lOVyr). These low occurrence frequencies, combined with the small effects these mechanisms exert on buried wastes, indicate that they can be considered insignificant for radionuclide release. Movement of emplaced radionuclides into the environs by soil moisture involves transport times greatly in excess of the halflife of even "*Pu. Chronic release after soil erosion to the depth of the buried wastes could be expected to occur on a time scale of 50-150 thousand yean. The most evident chronic release mechanism on a time scale of a few thousand yean has been found to be plutonium uptake by plant roots, with subsequent dispersal to the environs. An analysis has been made of e release scenario assuming revegetation of waste burial grounds with the natural specie* of the Los Alamos area. This analysis is based on a preliminary version of an environmental model, and employs estimated input parameters obtained from current literature. Within

Solid radioactive wastes are disposed of by burial in pits excavated in rhyolite tuff at the Los Alamos Scientific Laboratory (LASL). Contaminant* in the waste include fission products, uranium, and tranturanic elements. In 1976, horizontal core holes were drilled beneath a waste disposal pit that was used from 1963 to 1966. Samples of the core were analyzed for gross alpha, gross beta, total uranium, "Sr, 1J7Cs, 2M Pu, "••»°Pu, and H1 Am. The measured gross alpha, gross beta, and uranium concentrations were above minimum detection limits; concentrations of the remaining radionuclides, all of which are man-made isotopes, were below the minimum detection limits. Statistical comparisons were made of the gross alpha, gross beta, and uranium data to identify any significant variations from natural concentrations in the tuff. The comparisons demonstrated that none of the radioactivity detected in the samples can be attributed to migration from the disposal pit.

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