http://netedu.xauat.edu.cn/jpkc/netedu/jpkc2009/szylyybh/content/wlzy/1/Review%20of%20Arsenic%20in%20natural%20water%20-%20Smedly.pdf

A review of the source, behaviour and distribution of arsenic in natural waters

Solid phase microextraction with thermal desorption using fused silica optical fibers

The science of the total environment

The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role alon...

Mechanisms of Slow Sorption of Organic Chemicals to Natural Particles

found that field-scale dispersivities are several orders of.magnitude greater than lab-scale values for the same material; it is generally agreed that this difference is a reflection of the influence of natural heterogeneities which produce irregular flow patterns at the field scale. Consequently, laboratory measurements of dispersivity cannot be used to predict field values of dispersivity. Instead field-scale tracer tests are sometimes conducted to estimate dispersivity at a particular site. Early efforts to document the scale dependence of dispersivity [Lallemand-Barres and Peaudecerf, 1978; Anderson, 1979; Pickens and Grisak, 1981; Beims, 1983; Neretnieks, 1985] were based on field values of dispersivity reported in the literature and the test scales associated with those values. These studies were useful in that they indeed documented field evidence of the scale effect, but they were lacking in that they did not assess the reliability of the data presented. Because we felt that the data would be more

A Critical Review of Data on Field-Scale Dispersion in Aquifers

At most CERCLA and RCRA sites and numerous other sites, plumes of groundwater contamination emanate from subsurface source zones, commonly DNAPL or LNAPL source zones, where considerable volumes of immiscible organic liquids persist below the water table. Pump-and-treat can provide an effective means of containing hydraulically the dissolved contaminants emanating from these sources; however, at many sites pump-and-treat will have to continue for many decades or longer because the source zones dissipate slowly. Projected long term costs of operation, maintenance, and water disposal or reinjection are therefore large. A new approach for source zone containment or plume control that is more passive than pump-and-treat and that offers considerable potential for long term cost savings has been developed at the University of Waterloo (UW) and is referred to as the fuel-and-gate system (patent pending). In this system low permeability vertical barriers are placed across plumes. Gaps in the barrier allow passage of the plume through the barrier. In the gaps, referred to as gates, a reactive medium is positioned or released so that the plume water is treated while passing through the gates. The reactive medium can be solid phase particles and/or liquid from a controlled release system. The goal ismore » to cause the plume to meet water quality standards on the down gradient side of the funnel-and-gate system and to avoid pumping plume water to surface for treatment.« less

Funnel-and-gate for in situ groundwater plume containment

'This research project addresses the nature and and distribution of DNAPL sources (typically chlorinated solvents) in fractured clays or shales and the potential for natural attenuation of plumes derived from these sources. Specific goals include: (1) determining whether typical DNAPLs can penetrate fractures and the fine-grained matrix pore structure for head values within the range expected for a typical DNAPL spill; (2) investigate methods of measuring or estimating fracture or matrix entry pressure and pressure-saturation curves for these materials; (3) experimentally determine whether DNAPL residuals in fractures can be significantly depleted by dissolution and diffusion into the fine-grained matrix over the time-frame relevant to many contaminant investigation and remediation programs; and (4) assess potential for natural attenuation of common DNAPLs (TCE and its degradation products) in these deposits. Preliminary investigations indicate that DNAPL source removal will be a much more difficult and slower process for fractured clay-rich deposits than for granular deposits. These basic research investigations are needed to build the scientific framework for assessment of remediation options or for determining whether remediation, at least for the source zone, should be considered Technically Impractible (TI). This report summarizes progress made during the first 1.7 years of a 3-year project. Themore » project investigates the behavior of DNAPLs in two fractured clay-rich materials: weathered shales at Oak Ridge National Lab. in east Tennessee; and weathered glacial till in southern Ontario. The materials, although very different in origin, are similar in terms of fracturing, porosity and hydraulic conductivity and DNAPLs are expected to behave in similar fashions in the two materials. This allows the researchers to share their expertise, as well as helping to determine whether the findings of these studies are applicable to a broader spectrum of fractured clay-rich materials. Results to date for the major sub-projects are briefly described.'« less

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Behavior of dense, immiscible solvents in fractured clay-rich soils. 1998 annual progress report

Natural unfractured clays and clayliners without structural defects are commonly thought to provide adequate barriers for contaminant transport if the hydraulic conductivity of the clay is low. However, even when advection is minimal, contaminants can migrate through clay by simple Fickian diffusion at rates that can be significant.

Diffusion of Trichloroethylene in a Natural Clay: A Field Experiment

Quantifying Water Flow And Contaminant Flux In Boreholes

Hydrochemical data from proposed surface mining sites in North Dakota, Montana, Wyoming, and Alberta indicate much regional similarity in chemical characteristics of shallow groundwater. SO/sub 4//sup 2 -/ and HCO/sub 3//sup -/ are commonly dominant anions. Na/sup +/ and Ca/sup 2 +/ are generally the dominant cations. The pH of the groundwater normally ranges form 7 to 9. The electrical conductance of the shallow groundwater typically ranges from 500 to 4500 ..mu..S. Groundwater at depth is generally of the Na-HCO/sup 3/ type. A hydrogeochemical model based upon mineralogical data and unsaturated and saturated-zone hydrochemical characteristics has been developed for this region. Critical hydrogeochemical processes include: oxidation of organic matter, pyrite oxidation, carbonate-mineral dissolution (mainly calcite), gypsum precipitation and dissolution, cation exchange, and sulfate reduction. The hydrogeochemical model suggests that the potention for chemical degradation of groundwater is severe in certain mine settings in the Northern Great Plains. The potential for generation of highly mineralized groundwater in postmining landscapes is particularly great in areas where unoxidized pyritic and sodium montmorillonitic overburden is emplaced in the near-surface weathering zone.

John A. Cherry

Papers

Funnel-and-gate for in situ groundwater plume containment

Behavior of dense, immiscible solvents in fractured clay-rich soils. 1998 annual progress report

Diffusion of Trichloroethylene in a Natural Clay: A Field Experiment

Quantifying Water Flow And Contaminant Flux In Boreholes

Potential hydrogeochemical impacts of surface mining in the Northern Great Plains