Brad F. Lyles

Bio: Brad F. Lyles is an academic researcher from Desert Research Institute. The author has contributed to research in topics: Geothermal gradient & Groundwater flow. The author has an hindex of 6, co-authored 18 publications receiving 199 citations. Previous affiliations of Brad F. Lyles include University of Nevada, Reno & Nevada System of Higher Education.

Testing and parameterizing a conceptual model for solute transport in a fractured granite using multiple tracers in a forced-gradient test

Abstract: [1] A cross-hole tracer test involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients (bromide and pentafluorobenzoate) and a weakly sorbing solute tracer (lithium ion) was conducted in a fractured granite near an underground nuclear test cavity in central Nevada. The test was conducted to (1) test a conceptual radionuclide transport model for the site and (2) obtain transport parameter estimates for predictive modeling. The differences between the responses of the two nonsorbing tracers (when normalized to injection masses) are consistent with a dual-porosity transport system in which matrix diffusion is occurring. The large concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggests that diffusion occurs primarily into matrix pores, not simply into stagnant water within the fractures. The relative responses of the tracers at late times suggest that the diffusion-accessible matrix pore volume is possibly limited to only half the total volume of the flow system, implying that the effective retardation factor due to matrix diffusion may be as small as 1.5 for nonsorbing solutes in the system. The lower end of the range of possible sorption Kd values deduced from the lithium response is greater than the upper 95% confidence bound of Kd values measured in laboratory sorption tests using crushed granite from the site. This result suggests that the practice of using laboratory sorption data in field-scale transport predictions of cation-exchanging radionuclides, such as 137Cs+ and 90Sr++, should be conservative for the SHOAL site.

Threshold Precipitation Events and Potential Ground-Water Recharge

Abstract: In this paper, the frequency of threshold precipitation events is discussed from the perspective of ground-water recharge in arid and semiarid environments of the Nevada Test Site (NTS). The terminology threshold precipitation refers to precipitation events resulting in the penetration of moisture approximately 1 m into the unsaturated zone at study sites on NTS. While it is not proved that this type of moisture penetration results in ground-water recharge, it is suggested that deep penetration does remove moisture from the atmospheric and surface components of the hydrologic cycle. Estimates of the frequency of episodic recharge events are important from the viewpoint of regional contaminant transport models and provide perspective on the length of precipitation record required to estimate recharge.

Chemical and isotopic data for water from wells, springs, and streams in carbonate-rock terrane of southern and eastern Nevada and southeastern California, 1985-88

Abstract: Chemical and isotopic data for water collected from wells, springs, and streams in southern and eastern Nevada and southeastern California in 1985-88 as part of the Nevada Carbonate Aquifers Program are presented. These data include temperature, specific conductance, pH, dissolved oxygen, dissolved organic carbon, major ions, trace constituents, stable isotopes, and radioactive isotopes. A total of 247 samples were collected at 209 sites. Methods used in sample collection are described and the laboratories used to analyze the samples are identified.

Groundwater chemistry at the Nevada Test Site: Data and preliminary interpretations

Abstract: The interpretation of chemical analyses of groundwater collected at and near the Nevada Test Site (NTS) has been vital in developing conceptual models of groundwater flow in the area. These conceptual models are tested using recent chemical data generated by the Desert Research Institute, as well as historic analyses from the US Geological Survey. A total of 81 wells are represented by analyses from 1957 to 1990, with generally excellent agreement between repeat samples from the same location. As identified by previous workers, three hydrochemical facies are represented by the samples: Ca-Mg-HCO{sub 3} water in carbonate rocks or alluvium derived from carbonates, Na-K-HCO{sub 3} water in volcanic rocks and alluvium derived from volcanic rocks, and a mixed fades found in many carbonate and alluvium water samples, and some volcanic waters. There is a general lack of lateral continuity in chemical characteristics along presumed flowpaths within each hydrologic unit (alluvium, carbonate, and volcanic). Though a lack of continuity between basins on the east side of the NTS was expected for water in alluvial and volcanic units due to the absence of interbasin flow, chemical differences observed within individual basins suggest a dominance of vertical over lateral flow. Groundwater in volcanic materials on the east side of Yucca and Frenchman Flats and on the west side of Pahute Mesa and Yucca Mountain has a nearly pure Na-K-HCO{sub 3} signature that reflects contact with primarily volcanic material. Groundwater in volcanic units in the middle of the NTS and on the east side of Pahute Mesa contains a higher proportion of Ca, Mg, Cl, and SO{sub 4} than the other volcanic waters and indicates the contribution of water from the upper carbonate aquifer and/or hydrothermally altered regions.

Assessing Near Surface Hydrologic Processes and Plant Response over a 1600 m Mountain Valley Gradient in the Great Basin, NV, U.S.A.

Abstract: This study investigated near surface hydrologic processes and plant response over a 1600 m mountain-valley gradient located in the Great Basin of North America (Nevada, U.S.A.) as part of a long-term climate assessment study. The goal was to assess shifts in precipitation, soil water status and associated drainage with elevation and how this influenced evapotranspiration and plant cover/health estimated by a satellite-derived Normalized Difference Vegetation Index (NDVI), all to better understand how water is partitioned in a mountain valley system. Data were acquired during a three-year period from meteorological stations located in five plant communities ranging in elevation from 1756 m (salt desert shrubland zone) to 3355 m (subalpine zone). The analysis also included groundwater depths measured at the Salt Desert Shrub West site, mine water flow near the Pinyon-Juniper West site and drainage estimates using drainage flux meters at the four higher elevation sites. Annual precipitation increased with elevation in a linear fashion (R2 = 0.93, p < 0.001) with an average increase of 2.9 cm for every 100 m in elevation. Reference evapotranspiration (ETref) declined in a highly linear fashion with elevation (R2 = 0.95, p < 0.001) with an average 4.0 cm decline for every 100 m rise in elevation. Drainage occurred only at the Montane West and Subalpine West sites and not at the lower elevations. No drainage occurred after Julian day 160. Growing degree days were found to be negatively associated with the time of peak drainage (R2 = 0.97, p < 0.001), the date drainage first occurred (R2 = 0.90, p < 0.001), drainage duration (R2 = 0.79, p < 0.001) and total drainage volume (R2 = 0.59, p < 0.001). It was estimated that 27% of precipitation at the Montane West site (years 1, 2 and 3) and 66 % at the Subalpine West site (40% without year 1) contributed to drainage at the local site level, indicating possible strong recharge contribution from the higher elevation plant communities. Percent vegetation cover and ETref accounted for 94% of the variation in NDVI and 90% of the variation in ET totals when data from all sites were combined. Such data will be extremely valuable to collect and compare over time to assess shifts associated with potential climate warming and/or basin water diversion.

Trends, prospects and challenges in quantifying flow and transport through fractured rocks

Abstract: Among the current problems that hydrogeologists face, perhaps there is none as challenging as the characterization of fractured rock (Faybishenko and Benson 2000). This paper discusses issues associated with the quantification of flow and transport through fractured rocks on scales not exceeding those typically associated with single- and multi-well pressure (or flow) and tracer tests. As much of the corresponding literature has focused on fractured crystalline rocks and hard sedimentary rocks such as sandstones, limestones (karst is excluded) and chalk, so by default does this paper. Direct quantification of flow and transport in such rocks is commonly done on the basis of fracture geometric data coupled with pressure (or flow) and tracer tests, which therefore form the main focus. Geological, geophysical and geochemical (including isotope) data are critical for the qualitative conceptualization of flow and transport in fractured rocks, and are being gradually incorporated in quantitative flow and transport models, in ways that this paper unfortunately cannot describe but in passing. The hydrogeology of fractured aquifers and other earth science aspects of fractured rock hydrology merit separate treatments. All evidence suggests that rarely can one model flow and transport in a fractured rock consistently by treating it as a uniform or mildly nonuniform isotropic continuum. Instead, one must generally account for the highly erratic heterogeneity, directional dependence, dual or multicomponent nature and multiscale behavior of fractured rocks. One way is to depict the rock as a network of discrete fractures (with permeable or impermeable matrix blocks) and another as a nonuniform (single, dual or multiple) continuum. A third way is to combine these into a hybrid model of a nonuniform continuum containing a relatively small number of discrete dominant features. In either case the description can be deterministic or stochastic. The paper contains a brief assessment of these trends in light of recent experimental and theoretical findings, ending with a short list of prospects and challenges for the future.

Hydraulic tomography in fractured granite: Mizunami Underground Research site, Japan

Abstract: [1] Two large-scale cross-hole pumping tests were conducted at depths of 191–226 m and 662–706 m in deep boreholes at the Mizunami Underground Research Laboratory (MIU) construction site in central Japan During these two tests, induced groundwater responses were monitored at many observation intervals at various depths in different boreholes at the site We analyze the two cross-hole pumping tests using transient hydraulic tomography (THT) based on an efficient sequential successive linear estimator to compute the hydraulic conductivity (K) and specific storage (Ss) tomograms, as well as their uncertainties in three dimensions The equivalent K and Ss estimates obtained using asymptotic analysis treating the medium to be homogeneous served as the mean parameter estimates for the 3-D stochastic inverse modeling effort Results show several, distinct, high K and low Ss zones that are continuous over hundreds of meters, which appear to delineate fault zones and their connectivity The THT analysis of the tests also identified a low K zone which corresponds with a known fault zone trending NNW and has been found to compartmentalize groundwater flow at the site These results corroborate well with observed water level records, available fault information, and coseismic groundwater level responses during several large earthquakes The successful application of THT to cross-hole pumping tests conducted in fractured granite at this site suggests that THT is a promising approach to delineate large-scale K and Ss heterogeneities, fracture connectivity, and to quantify uncertainty of the estimated fields

The relative contributions of summer and cool-season precipitation to groundwater recharge, Spring Mountains, Nevada, USA

Abstract: A comparison of the stable-isotope signatures of spring waters, snow, snowmelt, summer (July thru September) rain, and cool season (October thru June) rain indicates that the high-intensity, short-duration summer convective storms, which contribute approximately a third of the annual precipitation to the Spring Mountains, provide only a small fraction (perhaps 10%) of the recharge to this major upland in southern Nevada, USA. Late spring snowmelt is the principal means of recharging the fractured Paleozoic-age carbonate rocks comprising the central and highest portion of the Spring Mountains. Daily discharge measurements at Peak Spring Canyon Creek during the period 1978–94 show that snowpacks were greatly enhanced during El Nino events.