The studies involved in this investigation are based upon data and materials secured in the sandy areas of Washington and Iron Counties in southern Utah. The regions in which Yucca angustissima is found have a scant vegetation, are dry, sandy to sandy loam, well-drained, and with an elevation of from 2500 to 5000 feet. Watkins (1937) worked out a very extensive report of the megagametophyte development of Yucca rupicola. He begins with the four megaspore stage, and shows next the disintegration of the three micropylar megaspores. He reported that the chalazal megaspore forms eight free nuclei, by three successive divisions, to form the mature megagametophyte. His report "conforms in general to that of Folsom and included certain additional intermediate developmental stages.'' This investigation, with a few variations, corroborates the findings of both Folsom and Watkins.

12 pp. / plant disease bulletins; July 2006 original publishing date, rev. 10/08 / Cacti, agaves and yuccas are classified as succulents, plants that have highly specialized anatomical features such as thick waxy cuticles, fleshy or minimal leaves, modified leaves (spines), and roots with extra storage capabilities for food and water. These modifications allow them to survive and thrive in harsh desert environments. They survive long periods of drought in areas of sparse rainfall and intense heat. During stressful periods, many succulents cease to grow, drop unnecessary leaves, dehydrate and become dormant until conditions for growth return. Despite their adaptations, succulents suffer from diseases, insect pests and cultural problems. Some of the more common problems that occur in cacti, agave and yuccas in Arizona are discussed in this bulletin.

Studies are currently underway to determine the suitability of Yucca Mountain in Nevada as the nation's first high-level nuclear waste repository. Values of net infiltration are required to determine pre-waste emplacement groundwater travel times and the performance of the repository as a waste containment system. The objective of this study was to develop a numerical model to perform water balance calculations and predict rates of net infiltration for the site. The model included processes of precipitation, runoff, evapotranspiration, infiltration, and redistribution of water within a soil profile. The watershed was divided into 477 grid cells 75.7 x 75.7 m. The elevation, slope, aspect, and hydrologic properties were assumed to be constant within a grid cell but varied from one cell to the next Water balance calculations were performed for each cell using a one-dimensional form of Richards equation. The solution was obtained using the finite difference method with Newton-Raphson iteration. The model was calibrated using water content data obtained from neutron-moisture meter measurements in boreholes located in Pagany Wash Watershed Measurements were made in channel and terrace alluvium and in tuffs. Computer simulations reproduced water content data for a major precipitation event that occurred in 1984. Simulations verified the importance of antecedent soil water content in controlling the occurrence of runoff. Sensitivity analysis indicated that the soil and alluvium grain-size distributions, which are used to calculate unsaturated hydraulic conductivity, can greatly affect predicted rates of water movement / Graduation date: 1991

The United States plans to bury high level radioactive waste from commercial power reactors and from nuclear weapons manufacturing in Yucca Mountain, Nevada. Yucca Mountain, located about 80 miles northwest of Las Vegas, consists of horizontally bedded tuff deposits. Although the region is very arid, enough water exists in the tuffs to create a vapor dominated geothermal system as the pore water evaporates, circulates and recondenses. This study examines how silica leaching might occur as a result of water-tuff interactions in Yucca Mountain after the emplacement of heat-producing nuclear waste canisters. A vertical thermal gradient experiment (VTGE) was designed and built in order to simulate the water cycling scenario where water in the tuff is vaporized by the heat from the canisters, moves to cooler regions along fractures and condenses as a liquid which flows downward toward the hot canisters. This experiment was used to measure the rate of silica leaching from Yucca Mountain tuff at various heat fluxes. The results show that under the experimental conditions silica is leached from the tuff sample very effectively (about 1.85 x 10 -8 g per Joule of heat transferred). With such a rate, significant amount of amorphous silica (135 kg per canister for the first 1,000 years after emplacement) could be leached, transported and deposited above the repository horizon; the resulting low permeability zone might change the geological and hydrological properties of the host rock. A significant amount of colloidal silica was formed in the solution soon after the water recycling began. Such colloidal silica could adsorb and transport radionuclides released from breached waste canisters more efficiently than that when radionuclides act alone. The results indicate that silica leaching is a potential problem for the current designs of the Yucca Mountain repository. / Master of Science

Perched water zones have been identified in the fractured, welded tuff in the semiarid to arid environments of Yucca Mountain, Nevada and near Superior, Arizona. An understanding of the formation of such zones is necessary in order to predict where future perched water might form at Yucca Mountain, the proposed site of a high-level nuclear waste repository. The formation or growth of a perched zone above a repository is one factor of the factors to be considered in the risk assessment of the Yucca Mountain site. The Apache Leap Research Site (ALRS) near Superior, Arizona is a natural analog to the Yucca Mountain site in terms of geology, hydrology, and climate. Perched water has been identified over an area of at least 16 km² in the Apache Leap Tuff, a mid- Miocene fractured, welded ash-flow tuff. A primary goal of this investigation was to characterize the physical and hydrologic properties of the tuff in the region above and including the perched zone, and to evaluate those characteristics to develop a model for a perching mechanism in the tuff. A second goal was to determine what fraction of water entering a watershed reaches the subsurface, to potentially recharge the perched zone. The Apache Leap Tuff has been subject to considerable devitrification and vapor phase crystallization, which dominate the character of the rock. With depth to the perched zone, pumice fragments become increasingly flattened and segregated; the pumice fragments are the primary locations of porosity in the rock, therefore porosity also becomes greatly reduced with depth, to the extent that the rock matrix is virtually impermeable at the perched water zone. Fractures are the primary pathways by which water moves through the rock; fracture hydraulic conductivity values were determined to be nine orders of magnitude greater than measured matrix hydraulic conductivity at the perched zone. An increase in fracture filling by silica mineralization beneath the perched zone reduces the secondary permeability, enhancing the formation of perched water. Thus, the primary mechanisms for the formation of the perched zone include fracture flow bringing water into the subsurface, combined with extremely low matrix hydraulic conductivity at depth, and reduced secondary permeability by filled fractures and lower fracture density. Water budgets were calculated for two years in a 51.4-ha watershed. Direct measurements were made of precipitation and runoff', evapotranspiration was both directly measured, and modeled based on measurement of a number of weather parameters. Infiltration was calculated as the residual of precipitation after runoff and evapotranspiration were removed. Infiltration was determined to be less than 10% of the annual water budget; evapotranspiration removes on the order of 90% of precipitation on an annual basis.

Yucca Mountain, Nevada is the proposed site for the underground storage of high-level civilian nuclear waste in the United States. The repository must be isolated from the general environment for at least 10,000 years. Ground water and gases are potential carriers of radioactive materials. Fractures and connected pores in the host rock are the major pathways for ground water and gases. Therefore, the mechanical and flow properties of the host rock should be understood and utilized in the design of the underground repository. Samples of Topopah Spring tuff from Yucca Mountain were used in this study. Cylindrical specimens were prepared to perform uniaxial and triaxial "damage" tests where specimens are loaded to a particular stress level to induce damage and fracturing and then unloaded. Mechanisms of microcracking at different fracturing levels have been studied by using both an optical microscope and a Scanning Electron Microscope (SEM). The original rock sample without loading was also observed under the microscopes. Many kinds of defects including pores, preexisting fractures, and soft inclusions were found in the undamaged Apache Leap tuff samples. Pores were determined to be the main microstructures in Topopah Spring tuff that could influence the mechanical and hydrologic properties. Under compressive stresses, microcracking initiates from some of the pores. These microcracks will interact and coalescence to form large microcracks or macroscopic cracks as the load is increased. Crack propagation phenomena, such as pore cracking, pore linking, pore collapse and the formation of en echelon arrays were all found in specimens unloaded prior to complete failure. The failure of tuff specimens is often through a process of shear localization. In summary, the deformation and failure of both tuffs occurred by progressive fracturing, starting from microcracking on the small scale, and ending as fractures coalesced to form macroscopic fractures and shear localization. On the basis of the experimental studies, micromechanical models such as the pore collapse model and the pore linking model have been developed based on fracture mechanics theory. These models are used to predict the constitutive behavior for tuff and the predicted stress-strain curves match well with the experimental curves.

This report integrates and summarizes findings from the 1987 and 1988 Native American cultural resource studies related to the Yucca Mountain high level radioactive waste isolation facility. The purposes of the report are to describe the traditional cultural values associated with the Cultural Studies Area, describe the methods used in the research, and provide a theoretical discussion of the role of cultural resources in American Indian groups' past and contemporary society (DOE 1988:3 -9). Findings from these Native American cultural resource studies are presented in what are termed "interim reports." Each of these were submitted for concurrent review by the sixteen involved American Indian tribes, Science Applications International Corporation, and the Department of Energy. This report is based on five reports, including three interim reports.

This report presents Native American interpretations of and concerns for plant resources on or near Yucca Mountain, Nevada. This is one of three research reports regarding Native American cultural resources that may be affected by site characterization activities related to the Yucca Mountain high -level radioactive waste disposal facility. Representatives of the sixteen involved American Indian tribes identified and interpreted plant resources as part of a consultation relationship between themselves and the U.S. Department of Energy (DOE). This report integrates data from the ethnobotanical fieldwork and visits conducted over a three -week period. The bulk of this report divides plants into their logical components: plant parts used; places where used; purposes of uses; and persons who used, do use, and will use the plants. The remainder of this Introduction is devoted to conveying an American Indian holistic perspective on plants as a part of the world.

This report presents a review of the literature concerning Native American occupancy and use of the Yucca Mountain area and vicinity. It draws on a wide range of material, including early traveler reports, government documents, ethnographic and historical works, and local newspapers. The report complements two other concurrent studies, one focused on the cultural resources of Native American people in the study area and the other an ethnobotanical study of plant resources used by Native American people in the study area. Both concurrent studies are based on interviews with Native American people. The literature review was designed to contribute to the understanding of the presence of Native American people in the Yucca Mountain area. A review of the existing literature about the Yucca Mountain area and southern Nye County, supplemented by the broader literature about the Great Basin, has verified three aspects of the study design. First, the review has aided in assessing the completeness of the list of Native American ethnic groups that have traditional or historical ties to the site. Second, it has aided in the production of a chronology of Native American activities that occurred on or near the site during the late nineteenth and early twentieth centuries. Third, it has helped to identify the location of cultural resources, including burials and other archaeological sites, in the study area and vicinity.

The Yucca Mountain region was used by Owens Valley Paiute, Western Shoshone, and Southern Paiute people for thousands of years. The area contains numerous plants, animals, and sacred resources traditionally used by these people. This report presents the location and interpretation of Native American cultural resources on or near Yucca Mountain, Nevada. This work built upon the archaeological reconnaissance and identifications of cultural resources by the Desert Research Institute. Interpretations provided by Native American Indian people are not intended to refute other scientific studies, such as botanical, wildlife, and archaeological studies. Rather, they provide additional hypotheses for future studies, and they provide a more complete cultural understanding of the Yucca Mountain area. Representatives of sixteen American Indian tribes identified the cultural value of these resources as part of a consultation relationship with the U.S. Department of Energy (DOE). This interim report is to be used to review research procedures and findings regarding (1) initial consultation with the sixteen tribes, (2) in -depth interviews with tribal elders, and (3) findings from the first on -site visit with representatives of the sixteen tribes.