Predicting Water Resource Impacts of Unconventional Gas Using Simple Analytical Equations

The rapid expansion in unconventional gas development over the past two decades has led to concerns over the potential impacts on groundwater resources. Although numerical models are invaluable for assessing likelihood of impacts at particular sites, simpler analytical models are also useful because they help develop hydrological understanding. Analytical approaches are also valuable for preliminary assessments and to determine where more complex models are warranted. In this article, we present simple analytical solutions that can be used to predict: (1) the spatial extent of drawdown from horizontal wells drilled into the gas‐bearing formation, and rate of recovery after gas production ceases; (2) the potential for upward transport of contaminants from the gas‐bearing formation to shallow aquifers during hydraulic fracturing operations when pressures in the gas‐bearing formation are greatly increased; and (3) the potential downward leakage of water from shallow aquifers during depressurization of gas‐bearing formations. In particular, we show that the recovery of pressure after production ceases from gas‐bearing shale formations may take several hundred years, and we present critical hydraulic conductivity values for intervening aquitards, below which the impact on shallow aquifers will be negligible. The simplifying assumptions inherent in these solutions will limit their predictive accuracy for site‐specific assessments, compared to numerical models that incorporate knowledge of spatial variations in formation properties and which may include processes not considered in the simpler solutions.     

Spectral modification and geographic redistribution of the semi-diurnal internal tide

A realistic-geometry global baroclinic tidal model forced with a single tidal constituent $(M_2)$ is used to investigate the generation of the internal tide and the associated radiated baroclinic energy flux. The model internal wave spectrum is populated at discrete frequency multiples $(1/2\text{,}1\text{,}3/2\text{,}2\text{,}5/2\text{,}\dots )$ of $M_2$. The $1/2M_2$ subharmonic is particularly energetic at its turning latitude of $\pm 28.8°$. Poleward only integer superharmonics of $M_2$ are significantly excited. The subharmonic turning latitude (SHTL) disturbance has high vertical wavenumber and shear, provided that internal tide energy level exceeds a threshold value. Under these circumstances, Richardson numbers smaller than 1/4 occur in the upper few hundred meters in both the realistic-geometry model and in a complimentary idealized geometry two-dimensional (2D) model. In the 2D model, the disturbance enables Richardson number dependent diapycnal entrainment to effect a modification of the stratification of the upper 400 m of the ocean, and poleward cross-SHTL energy flux falls to 10% of its pre-instability value due to energy transfer to the non-propagating (i.e., inertial) subharmonic. Realistic-geometry simulations suggest a more modest 40% decrease in net flux, although the strongest beams are almost entirely shut down. The predicted energy flux-convergence implies a thermocline dissipation rate in the 28.5–30.0°N latitude band of $5\times {10}^{-9}\text{W}{\text{kg}}^{-1}$, with an associated diapycnal diffusivity of ${10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. North of Hawaii the implied regional dissipation rate reaches $4\times {10}^{-8}\text{W}{\text{kg}}^{-1}$ with an associated thermocline diffusivity of $8\times {10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. Investigations of subgridscale parameterization and resolution sensitivity suggest that the basic character and magnitude of the predictions are robust to details of the numerical solutions. The present results are taken as further evidence that an increase in shear-driven turbulent mixing in the upper ocean is predicted at special latitudes. It is suggested that the search should be directed to regions where intense low-mode internal tide beams cross their subharmonic turning latitude.     

Progress in NTHMP Hazard Assessment

The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers.     

Situating local experience of risk: Peripherality, marginality and place identity in the UK foot and mouth disease crisis

Research into exposure to, and experience of, environmental risk that has an explicitly spatial focus can be broadly differentiated into two strands. The first strand focuses on the responses of communities of exposure (or the threat of exposure) to some form of environmental hazard and to the policies put in place by institutional actors to manage the hazard. The second strand addresses social inequalities in exposure to environmental hazards and seeks to correlate uneven spatial distributions of risk across different social groups. It is argued that both strands are limited by their respective understandings of space - and that the way in which vulnerable communities experience environmental risk and its management will be shaped significantly by the complex interactions of different spatialisations or constructions of space. We explore this process by examining accounts of local experience of the UK’s 2001 foot and mouth disease crisis and its management in terms of the interplay of two different spatialisations: socio-cultural marginality and political-economic peripherality. We trace the relationship between these cultural and political-economic spatialisations through an analysis of the discursive mobilisation of contrasting place rhetorics. We conclude that focusing on these rhetorics can enhance our understanding of the spatial processes which are constitutive of place identity and in turn mediate the experience of environmental risk and its management.     

Climatological observations and predicted sublimation rates at Lake Hoare, Antarctica

In December 1985, an automated meteorological station was established at Lake Hoare in the dry valley region of Antarctica. Here, we report on the first year-round observations available for any site in Taylor Valley. This dataset augments the year-round data obtained at Lake Vanda (Wright Valley) by winter-over crews during the late 1960s and early 1970s. The mean annual solar flux at Lake Hoare was 92 W m-2 during 1986, the mean air temperature -17.3 degrees C, and the mean 3-m wind speed 3.3 m s-1. The local climate is controlled by the wind regime during the 4-month sunless winter and by seasonal and diurnal variations in the incident solar flux during the remainder of the year. Temperature increases of 20 degrees-30 degrees C are frequently observed during the winter due to strong f?hn winds descending from the Polar Plateau. A model incorporating nonsteady molecular diffusion into Kolmogorov-scale eddies in the interfacial layer and similarity-theory flux-profiles in the surface sublayer, is used to determine the rate of ice sublimation from the acquired meteorological data. Despite the frequent occurrence of strong winter f?hns, the bulk of the annual ablation occurs during the summer due to elevated temperatures and persistent moderate winds. The annual ablation from Lake Hoare is estimated to have been 35.0 +/- 6.3 cm for 1986.     

Lunar Ice: Adsorbed Water on Subsurface Polar Dust

Differential scanning calorimetry indicates that adsorbed water and goethite, a product of hydrated ilmenite, are thermally stable over geologic time in the lunar polar regions. Adsorbed water can undergo burial as a result of several mechanisms, thereby achieving protection from sputtering or Lyman α radiation losses. Adsorbed, subsurface water layers on lunar dust, and any hydrated minerals present, could account for a majority of the hydrogen at the north lunar pole as well as account for a portion of that found at the south pole, particularly in small (<10 km) craters. Lunar ice, if it forms by condensation of water vapor in polar cold traps, will initially be in the form of amorphous solid water, and its rate of crystallization will depend on trap temperature and the composition of the surfaces upon which it has condensed. Between 95 and 110 K, diurnal temperature fluctuations cause surface ice deposits to migrate through the lunar regolith. Via such migration, stable and immobile layers of adsorbed water will be formed. In this temperature range, which can be expected at the margins of large craters and in smaller craters, any water resource would be a mixture of relatively unstable bulk ice and stable adsorbed water on subsurface dust and fines.     

Jurassic planktonic foraminifera from the United Kingdom

Unequivocal planktonic foraminifera have been discovered in Oxfordian strata from Dorset and Scotland. These assemblages are, in part, coeval with previously reported occurrences of planktonic taxa in the Oxfordian of Normandy and Seine Maritime (France). Three species are now reported from the United Kingdom for the first time: Globuligerina oxfordiana ( Grigelis, 1958 ), Haeuslerina helvetojurassica ( Haeusler, 1881 ) and Compactogerina sp. cf. C. stellapolaris ( Grigelis, 1977 ). There appears to be a close relationship between the distribution of these planktonic taxa in the UK and a marked sea-level highstand.