Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “tuff”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7

Origins of Small Volcanic Cones on Mars

Studies of volcanic cones identified in the MGS data indicate a range of possible origins, from primary vent constructs (cinder cones, tuff cones) to rootless cones formed by lava-ice interaction. Additional information is contained in the original extended abstract.

Fagents, S. A.↗

Constraints on Martian Surface Material from a Study of Volcanic Alteration in Iceland and Hawaii

Subaerial volcanic activity on Hawaii and subglacial volcanic activity on Iceland has led to the formation of a variety of silicate and iron oxiderich alteration products that may serve as models for chemical alteration on Mars. Multiple samples have been collected from palagonitic tuffs, altered pillow lavas, altered tephra, and S-rich vents for study in the lab. Variations in the kinds of alteration products have been observed depending on the alteration environment of the sample. We are working on building associations between the alteration products and formation conditions that can be used to provide information about environmental conditions on Mars.

J L Bishop↗

Classifying Terrestrial Volcanic Alteration Processes and Defining Alteration Processes they Represent on Mars

Characterizing alteration of the rocks on Mars is difficult, but some guidelines can be made through comparison with terrestrial volcanic alteration. Subaerial volcanic activity on the Hawaiian islands and subglacial volcanic activity on Iceland have led to the formation of a variety of silicate and iron oxide-rich alteration products that may serve as models for chemical alteration on Mars. Multiple samples have been collected from palagonitized tuffs, altered pillow lavas, altered tephra, and S-rich vents for study in the lab. Variations in the kinds of alteration products have been observed depending on the sample environment. We are defining associations between the alteration products and formation conditions that can be used to provide information about environmental conditions on Mars. In particular, we are providing definitions for palagonitic, pedogenic and solfataric alteration that can be used to characterize these alteration processes.

Bishop, J. L.↗

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.

NASA Discipline Exobiology↗

Workshop on Radar Investigations of Planetary and Terrestrial Environments

Contents include the following: Salt Kinematics and InSAR. SAR Interferometry as a Tool for Monitoring Coastal Changes in the Nile River Delta of Egypt. Modem Radar Techniques for Geophysical Applications: Two Examples. WISDOM Experiment on the EXOMARS ESA Mission. An Ice Thickness Study Utilizing Ground Penetrating Radar on the Lower Jamapa. Probing the Martian Subsurface with Synthetic Aperture Radar. Planetary Surface Properties from Radar Polarimetric Observations. Imaging the Sub-surface Reflectors : Results From the RANETA/NETLANDER Field Test on the Antarctic Ice Shelf. Strategy for Selection of Mars Geophysical Analogue Sites. Observations of Low Frequency Low Altitude Plasma Oscillations at Mars and Implications for Electromagnetic Sounding of the Subsurface. Ionospheric Transmission Losses Associated with Mars-orbiting Radar. A Polarimetric Scattering Model for the 2-Layer Problem. Radars for Imaging and Sounding of Polar Ice Sheets. Strata: Ground Penetrating Radar for Mars Rovers. Scattering Limits to Depth of Radar Investigation: Lessons from the Bishop Tuff.

Source record↗

Visible-Near Infrared Imaging Spectrometer Data of Explosion Craters

In a continuing study to capture a realistic terrain applicable to studies of cratering processes and landing hazards on Mars, we have obtained new high resolution visible-near infrared images of several explosion craters at the Nevada Test Site. We used the Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) to obtain images in 224 spectral bands from 0.4-2.5 microns [1]. The main craters that were imaged were Sedan, Scooter, Schooner, Buggy, and Danny Boy [2]. The 390 m diameter Sedan crater, located on Yucca Flat, is the largest and freshest explosion crater on Earth that was formed under conditions similar to hypervelocity impact cratering. As such, it is effectively pristine, having been formed in 1962 as a result of the detonation of a 104 kiloton thermonuclear device, buried at the appropriate equivalent depth of burst required to make a "simple" crater [2]. Sedan was formed in alluvium of mixed lithology [3] and subsequently studied using a variety of field-based methods. Nearby secondary craters were also formed at the time and were also imaged by AVIRIS. Adjacent to Sedan and also in alluvium is Scooter, about 90 m in diameter and formed by a high-explosive event. Schooner (240 m) and Danny Boy (80 m, Fig. 1) craters were also important targets for AVIRIS as they were excavated in hard welded tuff and basaltic andesite, respectively [3, 4]. This variation in targets will allow the study of ejecta patterns, compositional modifications due to the explosions, and the role of craters as subsurface probes.

Farr, T. G.↗

Formation of Nanophase Iron in Lunar Soil Simulant for Use in ISRU Studies

For the prospective return of humans to the Moon and the extensive amount of premonitory studies necessary, large quantities of lunar soil simulants are required, for a myriad of purposes from construction/engineering purposes all the way to medical testing of its effects from ingestion by humans. And there is only a limited and precious quantity of lunar soil available on Earth (i.e., Apollo soils) - therefore, the immediate need for lunar soil simulants. Since the Apollo era, there have been several simulants; of these JSC-1 (Johnson Space Center) and MLS-1 (Minnesota Lunar Simulant) have been the most widely used. JSC-1 was produced from glassy volcanic tuff in order to approximate lunar soil geotechnical properties; whereas, MLS-1 approximates the chemistry of Apollo 11 high-Ti soil, 10084. Stocks of both simulants are depleted, but JSC-1 has recently gone back into production. The lunar soil simulant workshop, held at Marshall Space Flight Center in January 2005, identified the need to make new simulants for the special properties of lunar soil, such as nanophase iron (np-Fe(sup 0). Hill et al. (2005, this volume) showed the important role of microscale Fe(sup 0) in microwave processing of the lunar soil simulants JSC-1 and MLS-1. Lunar soil is formed by space weathering of lunar rocks (e.g., micrometeorite impact, cosmic particle bombardment). Glass generated during micrometeorite impact cements rock and mineral fragments together to form aggregates called agglutinates, and also produces vapor that is deposited and coats soil grains. Taylor et al. (2001) showed that the relative amount of impact glass in lunar soil increases with decreasing grain size and is the most abundant component in lunar dust (less than 20 micrometer fraction). Notably, the magnetic susceptibility of lunar soil also increases with the decreasing grain size, as a function of the amount of nanophase-sized Fe(sup 0) in impact-melt generated glass. Keller et al. (1997, 1999) also discovered the presence of abundant np-Fe(sup 0) particles in the glass patinas coating most soil particles. Therefore, the correlation of glass content and magnetic susceptibility can be explained by the presence of the np-Feo particles in glass: small particles contain relatively more np-Fe(sup 0) as glass coatings because the surface area versus mass ratio of the grain size is so increased. The magnetic properties of lunar soil are important in dust mitigation on the Moon (Taylor et al. 2005). Thus material simulating this property is important for testing mitigation methods using electromagnetic field. This np- Fe(sup 0) also produces a unique energy coupling to normal microwaves, such as present in kitchen microwave ovens. Effectively, a portion of lunar soil placed in a normal 2.45 GHz oven will melt at greater than 1200 C before your tea will boil at 100 C, a startling and new discovery reported by Taylor and Meek (2004, 2005). Several methods have been investigated in attempts to make nanophase-sized Feo dispersed within silicate glass; like in the lunar glass. We have been successful in synthesizing such a product and continue to improve on our recipe. We have performed extensive experimentation on this subject to date. Ultimately it will probably be necessary to add this np-Fe(sup 0) bearing silicate glass to lunar soil stimulant, like JSC-1, to actually produce the desired magnetic and microwave coupling properties for use in appropriate ISRU experimentation.

Liu, Yang↗

JSC-1: Lunar Simulant of Choice for Geotechnical Applications and Oxygen Production

Lunar simulant JSC-1 was produced as the result of a workshop held in 1991 to evaluate the status of simulated lunar material and to make recommendations on future requirements and production of such material (McKay et al., 1991). JSC-1 was prepared from a welded tuff that was mined, crushed, and sized from the Pleistocene San Francisco volcanic field, northern Arizona. As the initial production of approxiamtely 12,300kgs is nearly depleted, new production has commenced. The mineralogy and chemical properties of JSC-1 are described in McKay et al. (1994) and Hill et al. (this volume); description of its geotechnical properties appears in Klosky et al. (1996). Although other lunar-soil simulants have been produced (e.g., MLS-1: Weiblen et al., 1990; Desai et al., 1992; Chua et al., 1994), they have not been as well standardized as JSC-I; this makes it difficult to standardize results from tests performed on these simulants. Here, we provide an overview of the composition, mineralogy, strength and deformation properties, and potential uses of JSC-1 and outline why it is presently the 'lunar simulant of choice' for geotechnical applications and as a proxy for lunar-oxygen production.

Taylor, Lawrence A.↗

Comparison of Morphologies of Apollo 17 Dust Particles with Lunar Simulant, JSC-1

Lunar dust (< 20 microns) makes up approx.20 wt.% of the lunar soil. Because of the abrasive and adhering nature of lunar soil, a detailed knowledge of the morphology (size, shape and abundance) of lunar dust is important for dust mitigation on the Moon. This represents a critical step towards the establishment of long-term human presence on the Moon (Taylor et al. 2005). Machinery design for in-situ resource utilization (ISRU) on the Moon also requires detailed information on dust morphology and general physical/chemical characteristics. Here, we report a morphological study of Apollo 17 dust sample 70051 and compare it to lunar soil stimulant, JSC-1. W e have obtained SEM images of dust grains from sample 70051 soil (Fig. 1). The dust grains imaged are composed of fragments of minerals, rocks, agglutinates and glass. Most particles consist largely of agglutinitic impact glass with their typical vesicular textures (fine bubbles). All grains show sub-angular to angular shapes, commonly with sharp edges, common for crushed glass fragments. There are mainly four textures: (1) ropey-textured pieces (typical for agglutinates), (2) angular shards, (3) blocky bits, and (4) Swiss-cheese grains. This last type with its high concentration of submicron bubbles, occurs on all scales. Submicron cracks are also present in most grains. Dust-sized grains of lunar soil simulant, JSC-1, were also studied. JSC-1 is a basaltic tuff with relatively high glass content (approx.50%; McKay et al. 1994). It was initially chosen in the early 90s to approximate the geotechnical properties of the average lunar soil (Klosky et al. 1996). JSC-1 dust grains also show angular blocky and shard textures (Fig. 2), similar to those of lunar dust. However, the JSC-1 grains lack the Swiss-cheese textured particles, as well as submicron cracks and bubbles in most grains.

Liu, Yang↗

P32Tools: reduction of ISOPHOT P32 oversampled maps

During the IS0 mission, the ISOPHOT instrument has collected more than 1100 observations in oversampled mapping mode (AOT PHT32) in the wavelength range of45 to 240 microns. The observations comprise mapping of small and large extended regions, but also faint point sources. PHT32 observations are affected by strong signal transients due to flux changes generated by the relatively fast chopper movement. A program described by Tuffs & Gabriel (2002), was developed to correct for these effects. It was integrated in the ISOPHOT Interactive Analysis (PIA) via a graphical user interface (GUI), so that most aspects of the processing can be addressed in a coherent and user friendly environment. The resulting package 'P32Tools' was introduced to the user community at three hands-on workshops on PHT32 processing held in spring 2001. The hands-on experience from these workshops lead to further improvements. Here we present an overview of the functionalities of the final release of this new software.

ISOPHOT oversampled mapping ISOPHOT Interactive An↗

Spectral Variability among Rocks in Visible and Near Infrared Multispectral Pancam Data Collected at Gusev Crater: Examinations using Spectral Mixture Analysis and Related Techniques

Visible and Near Infrared (VNIR) multispectral observations of rocks made by the Mars Exploration Rover Spirit s Panoramic camera (Pancam) have been analysed using a spectral mixture analysis (SMA) methodology. Scenes have been examined from the Gusev crater plains into the Columbia Hills. Most scenes on the plains and in the Columbia Hills could be modeled as three endmember mixtures of a bright material, rock, and shade. Scenes of rocks disturbed by the rover s Rock Abrasion Tool (RAT) required additional endmembers. In the Columbia Hills there were a number of scenes in which additional rock endmembers were required. The SMA methodology identified relatively dust-free areas on undisturbed rock surfaces, as well as spectrally unique areas on RAT abraded rocks. Spectral parameters from these areas were examined and six spectral classes were identified. These classes are named after a type rock or area and are: Adirondack, Lower West Spur, Clovis, Wishstone, Peace, and Watchtower. These classes are discriminable based, primarily, on near-infrared (NIR) spectral parameters. Clovis and Watchtower class rocks appear more oxidized than Wishstone class rocks and Adirondack basalts based on their having higher 535 nm band depths. Comparison of the spectral parameters of these Gusev crater rocks to parameters of glass-dominated basaltic tuffs indicates correspondence between measurements of Clovis and Watchtower classes, but divergence for the Wishstone class rocks which appear to have a higher fraction of crystalline ferrous iron bearing phases. Despite a high sulfur content, the rock Peace has NIR properties resembling plains basalts.

Farrand, W. H.↗

Evidence for Basinwide Mud Volcanism in Acidalia Planitia, Mars

High-albedo mounds in Acidalia Planitia occur in enormous numbers. They have been variously interpreted as pseudocraters, cinder cones, tuff cones, pingos, ice disintegration features, or mud volcanoes. Our work uses regional mapping, basin analysis, and new data from the Context Camera (CTX), High Resolution Imaging Science Experiment (HiRISE), and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to re-assess the origin and significance of these structures.

Oehler, Dorothy Z.↗

Common Ion Effects In Zeoponic Substrates: Dissolution And Cation Exchange Variations Due to Additions of Calcite, Dolomite and Wollastonite

c1inoptilolite-rich tuff-hydroxyapatite mixture (zeoponic substrate) has the potential to serve as a synthetic soil-additive for plant growth. Essential plant macro-nutrients such as calcium, phosphorous, magnesium, ammonium and potassium are released into solution via dissolution of the hydroxyapatite and cation exchange on zeolite charged sites. Plant growth experiments resulting in low yield for wheat have been attributed to a Ca deficiency caused by a high degree of cation exchange by the zeolite. Batch-equilibration experiments were performed in order to determine if the Ca deficiency can be remedied by the addition of a second Ca-bearing, soluble, mineral such as calcite, dolomite or wollastonite. Variations in the amount of calcite, dolomite or wollastonite resulted in systematic changes in the concentrations of Ca and P. The addition of calcite, dolomite or wollastonite to the zeoponic substrate resulted in an exponential decrease in the phosphorous concentration in solution. The exponential rate of decay was greatest for calcite (5.60 wt. % -I), intermediate for wollastonite (2.85 wt.% -I) and least for dolomite (1.58 wt.% -I). Additions of the three minerals resulted in linear increases in the calcium concentration in solution. The rate of increase was greatest for calcite (3.64), intermediate for wollastonite (2.41) and least for dolomite (0.61). The observed changes in P and Ca concentration are consistent with the solubilities of calcite, dolomite and wollastonite and with changes expected from a common ion effect with Ca. Keywords: zeolite, zeoponics, common-ion effect, clinoptilolite, hydroxyapatite

Beiersdorfer, R. E.↗

Chapter 3: Petrologic Evolution of Martian Volcanism and Clues from Meteorites

The formation and evolution of the Martian surface, and ultimately the fate of its various volcanic regions, are revealed in the chemistry of Martian meteorites, and the mineralogy of the crust. The interpretation of the chemistry from remote sensing instrumentation from orbiters and landers/rovers has been strongly influenced by our knowledge of geochemical processes on Earth, the Moon, and other asteroidal, rocky bodies [1]. The composition, and thus evolution, of the Martian crust has been resultant from SNC (shergottite –nakhlite –chassignite) meteorites, which are the igneous counterpart of rocks of Martian origin [2, 3, 4]. These meteorites are chemically similar to terrestrial basalts and cumulates, with the exception of higher concentrations of iron and other volatile elements (i.e., phosphorous, chlorine, chalcophile) [5]. From Tuff et al. [2], most Martian meteorites have relatively young crystallization ages ranging from 1.4 billion years to 180 million years ago [6]. These are considered to be derived from young, usually lightly-cratered volcanic regions, such as the Tharsis volcanic region [6, 7]. Though mainly basaltic in composition, surface rocks are richer in nickel and sulfur with lower manganese/iron ratios than Martian meteorites [2], which can be explained by the differences in oxygen fugacity during melting of the sulfur-rich mantle [2, 8]. From this difference, Martian meteorites are tied to surface rocks through an early (3.7 billion years ago) oxidation of the uppermost mantle, producing the more recent volcanic rocks [2]. The variety of compositions from basaltic, olivine volcanic rocks through pyroxene-cumulate nakhlites and peridotite chassignites, enable the hypothetical reconstructions of the silicic evolution of Mars similar to techniques used on Earth [2, 5, 9]. In this chapter, we will explore the basic Martian composition of the crust and mantle in regards to volcanic regions, the crustal components of the North-South dichotomy, and more detail of the SNC meteorites in relation to the evolution of the mantle for volcanism.

C Ahrens↗

Insights Into Reconstructing REE Compositions of Melt From Zircon-Melt Partition Coefficients Using Zircon-Hosted Melt Inclusions From the Yellowstone Volcanic Province

Establishing the major and trace element composition of the Earth’s melts (Hadean to recent) is essential for understanding crustal evolution. Due to its physical-chemical resilience, zircon spans the complete age spectra of Earth’s history, and thus provides the only physical record from the early Earth. However, the petrological context i.e., the melt from which zircon crystallised, is often lost, except for inclusions of melt preserved within zircon. Melt inclusions in zircon (MI) provide a valuable tool to constrain zircon-melt REE partition coefficients (D REE ), which are used with the zircon REE chemistry to reconstruct melt compositions. Such reconstruction requires accurate partition coefficients, which are particularly sensitive to temperature, but also to pressure and melt composition. We determined the major and trace element compositions of 60 co-existing zircon-MI pairs from two ~ 2 Ma age rhyolites (the caldera-forming Huckleberry Ridge Tuff; HRT-C and the post-caldera Blue Creek Flow; BC-1) of the Yellowstone Plateau volcanic field by EPMA and SIMS, and calculated a set of 60 zircon-MI partition coefficients. The MI from both units are glassy with average silica contents of 78.30 ± 0.74 and 77.19 ± 1.11 wt %, and Ti-in-zircon crystallisation temperatures are 839 ± 36 and 835 ± 35 oC. Measured D REE patterns for each population (n = 30) are tightly constrained and exhibit a smooth pattern spanning ~ six orders of magnitude from La to Lu, (with exceptions at Ce and Eu), and for the HRT exhibit greater curvature (i.e., flatter) between the MREE to HREE compared to the BC-1. D REE patterns for the HRT have small to moderate Ce anomalies (Ce/Ce* Di 50 ± 40), whereas those in the BC-1 are larger (98 ± 45), and both units exhibit negligible to positive Eu anomalies (Eu/Eu* Di 1.07 ± 0.89 and 1.80 ± 2.01, respectively). We compare the trace element compositions of the MI to bulk-glass compositions from Yellowstone to assess any differences, which are small, then compare the measured MI compositions to those reconstructed using published partition coefficients (natural, empirical and experimental). The choice of D REE for reconstruction of the melt REE pattern results in differing petrogenetic interpretations.

Laura J. Crisp↗

Geology and Hydrothermal Alteration of the Raft River Geothermal System, Idaho

The Raft River geothermal system is located in southern Idaho, near the Utah-Idaho state boarder in the Raft River Valley. The field, which is owned and operated by U.S. Geothermal, has been selected as an EGS demonstration site by the U. S. Department of Energy. This paper summarizes ongoing geologic and petrologic investigations being conducted in support of this project. The reservoir is developed in fractured Proterozoic schist and quartzite, and Archean quartz monzonite cut by younger diabase intrusions. The basement complex was deformed during the mid Tertiary and covered by approximately 5000 ft of late Tertiary sedimentary and volcanic deposits. Listric normal faults of Cenozoic age disrupt the Tertiary deposits but do not offset the basement rocks. RRG-9, the target well, was drilled southwest of the main well field to a measured depth (MD) of 6089 ft. The well is deviated to the west and cased to a depth of 2316 ft MD. It penetrated the Proterozoic reservoir rocks at a depth of 5286 ft MD and encountered a maximum temperature of 139 degrees C. Bottomhole temperatures in other deep wells range from 133 to 149 degrees C. X-ray diffraction and thin section analyses are being conducted on samples from 5 deep wells, RRG- 1, 2, 3, 7 and 9, to determine the characteristics of the rock types and hydrothermal alteration within the geothermal system. Thin section analyses of samples from RRG-9 document the presence of strong alteration and brecciation at the contact between the Tertiary and basement complex. The Tertiary rocks consist of ash-flow tuffs, lava flows, tuffaceous siltstone, greywacke, and sandstone. No core is available from RRG-9 but core was obtained from RRG-3C. The sample is a brecciated and altered siltstone from the base of the Tertiary sequence and is similar to rocks at the base of the Tertiary deposits in RRG-9. Here, the results of thermal and quasi-static mechanical property measurements that were conducted on the core sample are presented.

Jones, Clay↗

Analysis of Hydrology and Interim Measure Performance in the Chromium Plume at Los Alamos National Laboratory - 20498

Hexavalent chromium, Cr(VI), is present in the regional aquifer beneath Los Alamos National Laboratory (LANL) at concentrations greater than the New Mexico groundwater standard (50 ppb). The source of the Cr is blowdown from a power plant where potassium dichromate was used as a corrosion inhibitor from 1956 to 1972. Blowdown comingled with effluent from another source and migrated approximately 3 miles down a canyon, primarily as surface flow, until reaching an alluvial infiltration zone. The infiltrating water moved vertically through a thick (approximately 900 ft), complex stratigraphic sequence of unsaturated tuffs, basalt, and unconsolidated alluvial deposits. Horizontal transport also took place within spatially limited perched groundwater horizons in the vadose zone (VZ). Breakthrough at the regional aquifer water table is thought to have occurred in multiple hydraulic windows or 'drip points' located approximately 3 miles from the initial release site at the power plant. The regional aquifer is highly heterogeneous and anisotropic, and displays unconfined behavior in an upper zone and confined behavior at depth. The Cr(VI) contamination has so far remained confined to the upper approximately 25 m of the aquifer. The ambient hydraulic gradient in the regional aquifer is toward the east/southeast, but the water table is extremely flat in the Cr plume area compared to surrounding areas. There is some local variability in flow direction, potentially related to effects of seasonal pumping from nearby Los Alamos county water-supply wells, which draw from the regional aquifer several hundred feet below the water table. An interim measure (IM) is currently operating at the site to achieve hydraulic control of plume migration using a series of extraction wells, ion-exchange treatment, and injection along the downgradient portion of the plume. The migration of Cr contamination in the aquifer has been previously evaluated using a calibrated probabilistic numerical model, which has also been used to design the spatial configuration of extraction and injection wells for the IM, and to identify locations for monitoring wells. The model is built using the Finite Element Heat and Mass (FEHM) transfer code, and the Model Analysis and Decision Support (MADS) software is used for analyses. To date, the portion of the IM system that has operated in a continuous manner has been very effective at hydraulic control. Modifications to the flow field associated with the influence of IM pumping and injection are evaluated here, with modeling constraints to be provided by recent observations of tracers injected into both monitoring wells and IM injection wells, as well as opportunistic observations of geochemical signatures of treated ion-exchange effluent injected into IM injection wells. The tracer and geochemical data provide insights into modified flow directions within the Cr plume area that cannot be otherwise obtained. Results of the modeling work are being used to inform adaptive management of IM operations and will be a valuable tool for development and refinement of long-term remediation strategies. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Modeling the distribution of the endangered Jemez Mountains salamander (Plethodon neomexicanus) in relation to geology, topography, and climate

The Jemez Mountains salamander (Plethodon neomexicanus; hereafter JMS) is an endangered salamander restricted to the Jemez Mountains in north-central New Mexico, United States. This strictly terrestrial and lungless species requires moist surface conditions for activities such as mating and foraging. Threats to its current habitat include fire suppression and ensuing severe fires, changes in forest composition, habitat fragmentation, and climate change. Forest composition changes resulting from reduced fire frequency and increased tree density suggest that its current aboveground habitat does not mirror its historically successful habitat regime. However, because of its limited habitat area and underground behavior, we hypothesized that geology and topography might play a significant role in the current distribution of the salamander. We modeled the distribution of the JMS using a machine learning algorithm to assess how geology, topography, and climate variables influence its distribution. The best habitat suitability model indicates that geology type and maximum winter temperature (November to March) were most important in predicting the distribution of the salamander (23.5% and 50.3% permutation importance, respectively). Minimum winter temperature was also an important variable (21.4%), suggesting this also plays a role in salamander habitat. Our habitat suitability map reveals low uncertainty in model predictions, and we found slight discrepancies between the designated critical habitat and the most suitable areas for the JMS. Because geological features are important to its distribution, we recommend that geological and topographical data are considered, both during survey design and in the description of localities of JMS records once detected.

59 BASIC BIOLOGICAL SCIENCES↗