Tracing groundwater flow in the Borden aquifer using krypton-85

Krypton-85 was measured in air, soil gas, and ground water at the Borden aquifer in Ontario in October 1989. The measured specific activities in air and soil gas were 52.0 ± 2.0 and 53.6 ± 1.8 disintegrations per min (dpm) cm⁻³ krypton. These measurements are in excellent agreement with the global atmospheric trend and demonstrate that krypton-85 enters the water table at the Borden site without a lag in the soil gas reservoir. The krypton-85 specific activity in five groundwater samples ranged from 44.9 to 9.5 dpm cm⁻³ corresponding to groundwater ages of 2–17 years with a monotonic decrease in specific activity (increase in age) along the groundwater flow path. Travel times calculated from a two-dimensional steady-state model of groundwater flow agree well with the krypton-85 ages in the main recharge region of the aquifer where flow is predominantly vertical, but were 30–40% older than the krypton-85 age downstream of the main recharge area where the flow is mainly horizontal. The effect of dispersion on the distribution of krypton-85 was determined by modelling the transport of krypton-85 in the Borden aquifer with a two-dimensional time-dependent advection dispersion model using the steady-state flow field. Agreement between model specific activity and observed specific activity was excellent for samples in the main recharge region, but the model specific activities were 30–50% lower than observed specific activities in the region of horizontal flow. The differences in travel times and krypton-85 ages and in model krypton-85 and observed krypton-85 specific activities are considered to be small given the heterogeneities that exist in the hydraulic conductivity and aquifer geometry and hence in the groundwater flow field. The model simulated krypton-85 distribution was not sensitive to changes in longitudinal dispersivity and was only weakly sensitive to changes in transverse dispersivity. The geochemical inertness, well-defined source function, and insensitivity to dispersion of krypton-85 allow estimates of groundwater age to be made in a straightforward manner and measurement of krypton-85 can significantly enhance the characterization of groundwater flow in many shallow subsurface systems.     

Elementary properties of internal Rossby waves in a two-layer ocean with a uniform current

The elementary properties of internal Rossby waves in a horizontally infinite two-layer ocean with a uniform east-west current, apparently not previously reported in the literature, are documented.     

Interannual Variability of Antarctic Hydrographic Structure and Frontal Zones along Meridional Sections between Syowa Station and Southern Africa

Six years of quasi-meridional crossings of the Antarctic Ocean from Antarctica to southern Africa between 4°W and 16°E longitude are analyzed, with emphasis on temperature and salinity distributions. Data are sparse, but (particularly in the southern part of the sections) adequate to show significant variations in the latitude/depth distributions and T-S characteristics of the principal water masses. In particular, the cross-sectional area occupied by Warm Deep Water (Weddell Deep Water) dropped by about one third in 1968. Positions of major features associated with the Antarctic Divergence varied by up to 5 degrees of latitude. The surface temperature gradient often observed at the Antarctic Divergence appears to be the surface expression of a shallow (possibly seasonal) thermocline which sometimes slopes upward to intersect the sea surface. There is a clear need for more closely spaced and consistently planned data from Antarctic cruises, particularly those on which physical oceanography is an ancillary activity. As a bare minimum, much more closely spaced surface temperature (and if possible also salinity) measurements would be useful.     

Effects of vertical irregularity and thickness of unreinforced masonry infill on the robustness of RC framed buildings

Presence of irregularities in reinforced concrete (RC) buildings increases seismic vulnerability. During severe seismic shaking, such buildings may suffer disproportionate damage or even collapse that can be minimized by increasing robustness. Robustness is a desirable property of structural systems that can mitigate susceptible buildings to disproportionate collapse. In this paper, the effects of vertical irregularity and thickness of unreinforced masonry infill on the robustness of a six‐story three‐bay RC frame are quantified. Nonlinear static analysis of the frame is performed, and parametric study is undertaken by considering two parameters: absence of masonry infill at different floors (i.e., vertical irregularities) and infill thickness. Robustness has been quantified in terms of stiffness, base shear, ductility, and energy dissipation capacity of the frame. It was observed that the infill thickness and vertical irregularity have significant influence on the response of RC frame. The response surface method is used to develop a predictive equation for robustness as a function of the two parameters. The predictive equation is validated further using 12 randomly selected computer simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

Life cycle greenhouse gas footprint of shale gas: a probabilistic approach

With the increase in natural gas (NG) production in recent years, primarily from shale gas, some sources, including the US Environmental Protection Agency (EPA), have suggested that upstream methane emissions are increasing. Much of the recent controversy has centered on emissions during well drilling, testing, and completion even though emissions downstream of the wellhead are also of concern. The study critically assessed the current state of knowledge about the life cycle GHG footprint of NG, analyzed the assumptions, data and analysis methodologies used in the existing literature. This study comprehensively analyzed the emission of methane from different stage of the life of well for conventional and unconventional NG using the EPA’s revised 2011 estimates as well as other existing literature and publicly available government data. The study proposed a probabilistic model to estimate the range of total GHG footprint of NG with varying probabilities. Through the bottom up approach starting from the well construction to the delivery of NG to the small user and using Monte Carlo simulation, the study identified the critical sources of fugitive emissions from the NG. As expected, emissions from well completion and periodic emissions (e.g. liquid unloading in the case of onshore conventional wells and workovers in the case of unconventional wells) are significant contributors to the overall GHG footprint of NG, and possess large opportunity for reduction. Finally the application of probabilistic model is demonstrated through a case study using the data from the Montney and Horn River shale gas basins in the Northern British Columbia to estimate the range of total GHG footprint of shale gas with varying probabilities. The study found that the GHG footprint of Montney and Horn River wells are much smaller than that of Barnett shale (which is representative of US shale gas) due to strict flaring regulations followed in BC. The study also undercuts the outcome of Howarth et al. (Clim Chang Lett 106:679–690, 2011), which states that the GHG footprint of shale gas is at least 20 % greater than coal.     

Gas-partitioning tracer test to quantify trapped gas during recharge

Dissolved helium and bromide tracers were used to evaluate trapped gas during an infiltration pond experiment. Dissolved helium preferentially partitioned into trapped gas bubbles, or other pore air, because of its low solubility in water. This produced observed helium retardation factors of as much as 12 relative to bromide. Numerical simulations of helium breakthrough with both equilibrium and kinetically limited advection/dispersion/retardation did not match observed helium concentrations. However, better fits were obtained by including a decay term representing the diffusive loss of helium through interconnected, gas-filled pores. Calculations indicate that 7% to more than 26% of the porosity beneath the pond was filled with gas. Measurements of laboratory hydraulic properties indicate that a 10% decrease in saturation would reduce the hydraulic conductivity by at least one order of magnitude in the well-sorted sandstone, but less in the overlying soils. This is consistent with in situ measurements during the experiment, which show steeper hydraulic gradients in sandstone than in soil. Intrinsic permeability of the soil doubled during the first six months of the experiment, likely caused by a combination of dissolution and thermal contraction of trapped gas. Managers of artificial recharge basins may consider minimizing the amount of trapped gas by using wet, rather than dry, tilling to optimize infiltration rates, particularly in well-sorted porous media in which reintroduced trapped gas may cause substantial reductions in permeability. Trapped gas may also inhibit the amount of focused infiltration that occurs naturally during ephemeral flood events along washes and playas.     

Thermal evolution of the moon

The thermal history and current state of the lunar interior are investigated using constraints imposed by recent geological and physical data. Theoretical temperature models are computed taking into account different initial conditions, heat sources, differentiation and simulated convection. To account for the early formation of the lunar highlands, the time duration of magmatism and presentday temperatures estimated from lunar electrical conductivity profiles, it is necessary to restrict initial temperatures and abundances of radioactivie elements. Successful models require that the outer half of the Moon initially heated to melting temperatures, probably due to rapid accretion. Differentiation of radioactive heat sources toward the lunar surface occurred during the first 1.6 billion years. Temperatures in the outer 500 km are currently low, while the deep interior (radius less than 700 to 1000 km) is warmer than 1000°C, and is of primordial material. In some models there is a partially melted core. The calculated surface heat flux is between 25 and 30 erg/cm² s.Presently at the Research Triangle Institute, Research Triangle, North Carolina 27709, U.S.A.     

Group Method of Data Handling (GMDH) Neural Network for Estimating Total Organic Carbon (TOC) and Hydrocarbon Potential Distribution (S1, S2) Using Well Logs

Natural Resources Research - Recent advancement in computing capabilities has brought to light the application of machine learning methods in estimating geochemical data from well logs. The widely...     

Radioactive waste management policies in seven industrialized democracies*

This paper provides an inventory of radioactive waste management policies in seven industrialized democracies: the U.S., France, Japan, West Germany, Canada, the U.K. and Sweden. Collectively, these countries account for almost 75% of the world's installed nuclear power capacity and over 61% of its spentfuel production. Special emphasis is given to siting procedures for both high- and low-/intermediate-level waste repositories. Although several low-level repositories are operating or under construction, only West Germany has selected a site for high-level waste disposal, at Gorleben. It is expected that siting decisions will be highly conflict-laden in each country except for pro-nuclear France. The procedures for resolving potential siting conflicts are briefly reviewed. Sweden's strategy of siting its low-level repository near Forsmark offshore beneath the Baltic seabed minimizes conflict and may become attractive to other nations. Also, transnational agreements may eventually be sought as radioactive waste disposal is an international problem. This paper concludes with a comparative discussion of siting policies and their potential impacts.