Geohydrology of Bandelier Tuff

Abstract

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...

Runoff from a semiarid Ponderosa pine hillslope in New Mexico

“…: SEMIARID PINE HILLSLOPE RUNOFF It is difficult to pinpoint either the nature or the exact location of the barrier to vertical water movement on our hillslope. The R horizon (unweathered Bandelier Tuff) is an unlikely candidate, given its high hydraulic conductivity: reported measurements are in the range 360-3600 mm/h [Abeele et al, 1981], which is 3-4 orders of magnitude higher than those of the overlying soils. A more likely candidate is the zone of weathered tuff (CB horizon) found between the Bt and R horizons, which is prominent on the south hillslope (and may be present, as a much thinner layer, on the north side as well).…”

A new saturated/unsaturated model for stormwater infiltration systems

“…Infiltration and then drainage of a freely draining caisson containing Bandelier Tuff (Abeele et al, 1981;Abeele, 1984;) were simulated. This data was previously used to test variably saturated flow models including Hydrus (Kool and van Genuchten, 1991) and a model by Forsyth et al, (1995), as well as parameter estimation techniques (Abbaspour et al, 1997;Kool et al, 1987).…”

Performance evaluation of the technical capabilities of DOE sites for disposal of mixed low-level waste: Volume 3, Site evaluations

“…Christenson and Thomas (1962) observed increased gross alpha activity and moisture content that coincided with visual identification of a vertical fracture that intersected a number of their horizontal borings. They found that, in general, peak alpha activity was associated with fractures in the tuK Abeele et al (1981) found that fractures are commonly filled with fine-grained weathering products within 10 m (33 A) of the surface, but are open at greater depths and show no signs of weathering. Roots were observed to penetrate the filled fractures, because they were attracted by the higher moisture available in the fine-grained materials.…”