E. W. Peterson

Bio: E. W. Peterson is an academic researcher. The author has contributed to research in topics: Fracture (geology) & Waste Isolation Pilot Plant. The author has an hindex of 2, co-authored 4 publications receiving 154 citations.

Atmospheric pumping: A mechanism causing vertical transport of contaminated gases through fractured permeable media

Abstract: As the barometer falls, gases are drawn upward out of the permeable Earth into the atmosphere. Conversely, a rising barometer pushes air downward. In a homogeneous permeable medium, these cyclical gas motions are piston-like and nearly reversible, so they contribute only modestly to the net transport of contaminant gases. In a fractured permeable medium, however, the fractures will generally serve as breathing passages for all of the gas-filled porosity, greatly increasing the amplitude and nonuniformity of vertical motions. The resulting transport process may be orders of magnitude more significant than molecular diffusion, according to the theoretical analysis presented here. Analytical solutions are first derived for the sinusoidal pressure response of a medium containing identical vertical fractures equally spaced by slabs of permeable matrix material. These solutions are then used to constrain the relationship between fracture aperture and fracture spacing, based on field comparisons between surface and subsurface pressure variations. The final phase of the analysis addresses the diffusive and advective transport of an inert trace gas which is carried by an oscillatory flow along a fracture having permeable walls. A maximum rate of transport is predicted to occur for an intermediate fracture spacing which is typically a few meters.

Barometric Pumping of Contaminated Gases Through Fractured Permeable Media

Abstract: Contaminated gases may be transported vertically through a fractured permeable medium by the breathing process which is associated with cyclical changes in the barometric pressure. A review of results from analytical and numerical modelling indicates that the contaminant transport induced by barometric pumping may be orders of magnitude greater than the rate of transport by molecular diffusion.

Containment analysis for LLNL: 1988

Abstract: A double-porosity model which recognizes fracture permeability as well as matrix permeability is used to investigate some aspects of gas flow from the cavity produced by an underground nuclear explosion. In its simplest form, the double-porosity model treats a family of identical, equally-spaced, vertical fracture planes separated by a permeable matrix material. The matrix properties are known from core sample data and the flow characteristics of the fracture system are constrained by field-scale measurements of the pneumatic diffusivity. Three different issues are investigated: estimation of fracture aperture vs. fracture spacing relationships based on pneumatic diffusivity data, transport of radioactive gases from a nuclear chimney to the earth's surface as a result of cyclical gas motions which are induced by barometric pressure variations, and seepage losses from a hydrofracture which is driven by high pressure cavity gas into a double-porosity overburden. The containment of cavity gases is generally favored by a large number of closely spaced fractures rather than a few more widely spaced fractures, both configurations having the same pneumatic diffusivity. The sensitivity of containment measures to unknown fracture configurations is explored, subject to the constraint of a known large-scale pneumatic diffusivity. 13 refs., 30 figs.

Finding deeply buried deposits using geochemistry

Abstract: It has become increasingly common for geologists to drill through 100 m or more of cover in search for buried mineral deposits. Geochemistry is one tool applied to this search, using a variety of approaches, including selective leaching of soils to extract the mobile component of elements, and the measurement of inorganic and organic gases. This paper provides an overview of some of the work carried out by the project Deep-Penetrating Geochemistry, sponsored by the Canadian Mining Industry Research Organization (CAMIRO), and supported by 26 Canadian and international companies and by the Ontario Geological Survey and the Canadian Geological Survey. The objective was to provide the mining industry with information relating to processes that may form anomalies at surface over buried deposits and to provide comparative data on methods used to detect these anomalies. Phase I of the project considered the theoretical and experimental framework for the movement of material from deeply buried deposits to the surface; much of this information has come from research on the containment of buried nuclear waste. In arid or semi-arid terrain, with a thick vadose zone, advective transport, which is the mass transfer of groundwater or air along with their dissolved or gaseous constituents, is the only known viable means of moving elements to the surface; diffusion of ions in water or gases in air is orders of magnitude slower. Examples of advective transport are pumping of mineralized groundwater to the surface during seismic activity and the extraction of air plus gas by barometric pumping. Both mechanisms require fractured rock and the interpretation of the derived anomalies requires consideration of neotectonic structures. In wetter climates, where water lies close to the surface, a variety of mechanisms have been proposed for creating anomalies at the surface. Diffusion-based models again suffer from slow rates of migration. Electrochemical models show a cathodic zone at the top of a buried sulphide conductor. Cations are attracted to the cathode, rather than to the surface, yet metals that most commonly migrate as cations are found to form anomalies at the surface. Phase II of the CAMIRO study involved field studies at ten test sites. The test sites included buried porphyry deposits in northern Chile, a gold–copper deposit in the Carlin district of Nevada, and volcanogenic massive sulphide bodies covered by glacial sediments in the Abitibi greenstone belt of Ontario. In all cases anomalies were found in soils above buried mineralization. It is suggested that anomaly formation is an episodic and cyclic process, in which batches of metal in water-soluble form are introduced and the metal is then progressively incorporated with time into the secondary minerals of soil. Selective leaches have been developed to dissolve specific phases in the soil to detect these anomalies. We have compared the results for five selective leaches that are available from commercial laboratories: deionized water, ammonium acetate, hydroxylamine hydrochloride, Enzyme Leach and Mobile Metal Ion (MMI) plus one non-selective decomposition, aqua regia. In addition, the Institute of Geophysical and Geochemical Exploration laboratory in China has supplied data for four sequential selective leaches: water-extractable, adsorbed, organic-bound and iron- and manganese-bound. The weakest leaches dissolve mainly the most recently introduced metals that remain in water-soluble form. Other leaches dissolve specific secondary minerals, such as carbonates, or iron and manganese oxides, which contain the introduced metals. The usefulness of leaches that dissolve secondary minerals depends on the ratio of introduced (exogenic) metal that the minerals contain relative to that of endogenic origin derived from the primary minerals of soils. Our results indicate that this ratio is variable from site to site, so that there is no universal ‘best’ leach for dissolving secondary minerals in exploration surveys. For the test sites in Chile and Nevada, anomalies may have formed incrementally over a period of a million years or more, which permitted metals of exogenic origin to become incorporated into many secondary minerals. For these sites, some anomalies can be detected by aqua regia, although the anomaly/background contrast is less than for selective leaches. For the test sites in Ontario, only a few thousand years have elapsed since glacial sediments were deposited to conceal mineralization. Over this short period, metal of exogenic origin has been incorporated into only the most labile of secondary minerals and it is the leaches that dissolve these labile minerals that can successfully identify anomalies. At the two sites where the most detailed studies have been carried out, the Spence deposit in Chile and Cross Lake near Timmins, we have found that the optimum sampling depth in soils is critical to detecting anomalies.

Trace gas emissions on geological faults as indicators of underground nuclear testing

Abstract: UNDERGROUND nuclear explosions produce trace amounts of distinctive but ephemeral radionuclide gases. In the context of monitoring a comprehensive test ban treaty, the detection of these gases within the territory of a signatory, during a challenge inspection1–5, may indicate the occurrence of a clandestine nuclear event. Here we report the results of an experiment simulating a well-contained underground nuclear explosion, undertaken to test the ability of natural gas-transport processes to move highly dilute and rapidly decaying radionuclides to the surface. We find that trace gases are transported to the surface within periods of weeks to a year, by flow along faults and fractures driven by barometric pressure variations. Both our observations and related simulations exhibit a chromatographic behaviour, with gases of higher atomic mass and lower diffusivity reaching the surface more rapidly. For a 1-kilotonne nuclear test under conditions identical to those of our experiment, we predict that short-lived 133Xe and 37Ar would be detectable, respectively, about 50 and 80 days after the detonation. Our results indicate that radionuclide sampling along natural faults and fractures, as a forensic tool, can be an extremely sensitive way to detect nearby underground nuclear explosions that do not fracture the surface.

Atmospheric pumping: A mechanism causing vertical transport of contaminated gases through fractured permeable media

Abstract: As the barometer falls, gases are drawn upward out of the permeable Earth into the atmosphere. Conversely, a rising barometer pushes air downward. In a homogeneous permeable medium, these cyclical gas motions are piston-like and nearly reversible, so they contribute only modestly to the net transport of contaminant gases. In a fractured permeable medium, however, the fractures will generally serve as breathing passages for all of the gas-filled porosity, greatly increasing the amplitude and nonuniformity of vertical motions. The resulting transport process may be orders of magnitude more significant than molecular diffusion, according to the theoretical analysis presented here. Analytical solutions are first derived for the sinusoidal pressure response of a medium containing identical vertical fractures equally spaced by slabs of permeable matrix material. These solutions are then used to constrain the relationship between fracture aperture and fracture spacing, based on field comparisons between surface and subsurface pressure variations. The final phase of the analysis addresses the diffusive and advective transport of an inert trace gas which is carried by an oscillatory flow along a fracture having permeable walls. A maximum rate of transport is predicted to occur for an intermediate fracture spacing which is typically a few meters.