scale fluid distribution within the medium. This LABORATORY INVESTIGATIONS AND Abstracts research suggests that the non-unique relation- ANALYTICAL AND NUMERICAL MOD- ship between moisture content and matric ELING OF THE TRANSPORT OF DIS- potential is less appealing than the relationship SOLVED SOLUTES THROUGH SATURAT- between electrical resistivity and moisture con- ED FRACTURED ROCK, by Timothy James New Mexico Geology recognizes the important tent for monitoring changes in moisture content Callahan, 2001, Ph.D. dissertation, Depart- research of students working in post-graduate over intermittent periods of wetting/draining ment of Earth and Environmental Science, M.S. and Ph.D. programs. The following conditions. New Mexico Institute of Mining and Technol- abstracts are from recently completed M.S. the- Both the parameter estimation models evalu- ogy, Socorro, NM 87801, 153 pp. ses and Ph.D. dissertations that pertain to the ated in this study appeared to produce estimates geology of New Mexico and neighboring states. The objective of this research was to determine of moisture retention properties comparable to the applicability of reactive tracer data obtained results obtained using direct laboratory meth- from laboratory tests to larger-scale field set- ods; however, both models require individual tings. Laboratory tracer tests were used to quan- New Mexico Institute of Mining and calibration for narrow distributions of particle tify transport properties in fractured volcanic Technology sizes and porosities. Although the separate cali- ash flow tuff from southern Nevada. In a series brations may be cumbersome, this research sug- of experiments, a pulse containing several ionic INVESTIGATION OF DIRECT AND INDI- gests that property estimation models can be tracers was injected into four tuff cores, each RECT HYDRAULIC PROPERTY LABORA- used to reduce the time intensity of direct labo- containing one induced fracture oriented along TORY CHARACTERIZATION METHODS ratory measurements, thus increasing the num- the main axis. Multiple tests were also conduct- FOR HETEROGENEOUS ALLUVIAL ber of samples analyzed for site characteriza- ed at different flow velocities. Transport data DEPOSITS: APPLICATION TO THE SAN- tion. Model predictions could be improved by from nonreactive tracers of different diffusivity DIA-TECH VADOSE ZONE (STVZ) INFIL- reducing sample disturbance during collection allowed the separation of the effects of hydro- TRATION TEST SITE, by Kristine E. Baker, and analysis and increasing sample sizes for lab- dynamic dispersion within the fracture and 2001, M.S. thesis, Department of Earth and oratory analysis. Direct measurements of air molecular diffusion between flowing and non- Environmental Science, New Mexico Institute entry pressure, porosity, and residual moisture flowing water within the systems, which was of Mining and Technology, Socorro, NM content would also improve the model predic- presumed to be in the fracture and bulk porous 87801, 475 pp. tions. matrix, respectively. Reactive tracers were also The need to predict water flow and solute trans- included to estimate the sorption capacity of the port at contaminated waste storage facilities has tuffs. shifted the focus of unsaturated flow research The experiments verified the importance of from near surface soils to deep vadose zone allu- OCCURRENCE AND SOURCES OF fracture/matrix and solute/solid interactions in vium deposits. The primary objective of this ARSENIC IN GROUND WATER OF THE the fractured tuffs. Using artificial tracers of dif- research was to characterize the hydraulic prop- MIDDLE RIO GRANDE BASIN, CENTRAL ferent physical and chemical properties in the erties of deep vadose zone deposits collected NEW MEXICO, by Laura M. Bexfield, 2001, same test provided unique interpretations of the from a vadose zone research facility in Socorro, M.S. thesis, Department of Earth and Environ- tests and minimized uncertainty in transport New Mexico, using both direct and indirect lab- mental Science, New Mexico Institute of Min- parameter estimates. Compared to separate oratory methods. Samples collected from the ing and Technology, Socorro, NM 87801, 191 field tests in the rock types, the laboratory site were analyzed for moisture retention, elec- pp. experiments tended to over estimate the degree trical resistivity, hydraulic conductivity, porosi- of diffusive mass transfer and under estimate ty, and particle-size distributions. The measured An understanding of the occurrence and sources sorption capacity due to the small scale and high results were then compared to properties report- of arsenic in ground water of the middle Rio tracer concentrations, respectively. The first ed for similar sandy soils and alluvial sands to Grande basin (MRGB), central New Mexico, is result suggests that geometry differences determine the need to characterize heteroge- essential to the establishment of drinking-water between lab apparatuses and field systems pre- neous vadose zones independently. Correlations supplies that will consistently meet the new cluded the direct extension of laboratory- µ between measured parameters were examined standard of 10 g/l established by the U.S. Envi- derived transport parameters to field scales. For to minimize the number of measurements ronmental Protection Agency for arsenic in example, smaller-scale processes such as diffu- required in site characterization. The Haver- drinking water. New chemical data from 288 sion within the stagnant water in the fractures kamp and Parlange (1986) parameter estimation ground-water sites, supplemented by historical (free-water diffusion), caused by fracture aper- model and a similar estimation model devel- data from the U.S. Geological Survey and the ture variability, were more important at small oped as part of this research (to predict the van city of Albuquerque, show that arsenic concen- time scales. Because free water diffusion coeffi- µ Genuchten parameters) were used to estimate trations in ground water exceed 10 g/l across cients are larger than matrix diffusion coeffi- moisture retention parameters for samples col- broad areas of the basin. The data indicate that cients, this led to an over estimation of the lected at the site. arsenic concentrations in the MRGB are deter- amount of diffusive mass transfer. Furthermore, Direct laboratory measurements of moisture mined primarily by the source and geochemical laboratory diffusion cell tests provided inde- retention for the site deposits showed curve fit- origin of ground water rather than by chemical pendent estimates of matrix diffusion coeffi- ting parameters that vary from values reported processes within the basin. One primary source cients for the tracers, and these values were sim- for sandy soils of similar texture; however, they of arsenic to the basin is related to volcanic ilar to those estimated for the same tracers in the appeared to be similar to values reported for activity in the Jemez Mountains to the north, field tests. Thus, the value of the diffusion coef- sandy alluvial deposits. This suggests that val- where dilute recharge water likely flows ficients in the larger-scale field tests appeared to ues reported for soils in many soil databases through rocks that have been altered by contact approach their asymptotic "true" values because should not be used to predict flow and transport with geothermal fluids. The other primary of the larger volume of porous rock accessed in deep, alluvial vadose zone environments. In source is mineralized water of deep origin that during tracer testing. addition, the STVZ deposits all exhibited a non- mixes with shallower ground water in several The sorption capacity of the solid material unique relationship between moisture content locations around the MRGB, particularly along was under estimated in both the laboratory and and matric potential (known as hysteresis), major structural features. Values of pH that field tracer experiments. A fraction of the ion- whereas the relationship between measure- exceed 8.5, where present, appear to cause de- exchanging tracer (lithium) moved through the ments of electrical conductivity and moisture sorption of arsenic from metal oxides. Analysis system unretarded because the ion exchange content did not appear to be hysteretic. It is pos- of normative salt assemblages calculated using sites on the solid phase were overwhelmed by sible that a porous medium may not exhibit hys- the computer program SNORM (Bodine and the tracer. This happened more so in the labora- teresis in electrical resistivity measurements Jones, 1986) indicates that MRGB ground waters tory tests due to the smaller amount of dilution even if hysteresis is observed in moisture reten- associated with carbonate-rock dissolution and in the system. These results clearly indicate that tion measurements because the potential energy weathering of calcic lithologies tend to have by injecting high-concentration tracers during state of a porous medium is determined by con- smaller arsenic concentrations than ground cross-well tests, the tracer data can indicate ditions at the air-water-solid interfaces, and the waters associated with hydrothermal systems or sorption parameters smaller than those deter- nature of surface films rather than by the quan- with the weathering of sodium-dominated mined under lower-concentration conditions. tity of water present in pores. On the other hand, siliceous rocks. These results indicate that one should be cau- electrical conductivity is a function of