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

The funnel-and-gate system for in situ treatment of contaminant plumes consists of low hydraulic conductivity cutoff walls with gaps that contain in situ reactors, such as reactive porous media, that remove contaminants by abiotic or biological processes. Funnel-and-gate systems can be installed at the front of plumes to prevent further plume growth, or immediately downgradient of contaminant source zones to prevent contaminants from moving into plumes. Cutoff walls (the funnel) modify flow patterns so that ground water flows primarily through high conductivity gaps (the gates). This approach is largely passive in that after installation, in situ reactors are intended to function with little or no maintenance for long periods. This approach contrasts with the energy and maintenance-intensive character of pump-and-treat systems. This paper describes the funnel-and-gate concept, and uses two-dimensional computer simulations to illustrate the effects of cutoff wall and gate configuration on capture zone size and shape and on the residence time for reaction of contaminants in gates.

In Situ Remediation of Contaminated Ground Water: The Funnel-and-Gate System

In a new conceptual model for immiscible-phase organic liquids in fractured porous media that specifically includes the effect of molecular diffusion on the persistence of organic liquid in fractures, dissolved contaminant mass from the liquid in fractures is lost by diffusion from the fractures into the porous matrix between the fractures. Theoretical calculations for one-dimensional diffusive fluxes from single, parallel-plate fractures using parameter values typical of fractured porous geologic media establishes the concept of immiscible-phase disappearance time, which is the time required for a given volume of immiscible liquid in a specified aperture to disappear following its arrival in the fracture. Nonlithified surficial clayey deposits with matrix porosities ranging from 25 to 70% are extensive across many regions of North America and Europe, and at shallow depth, typically have fractures with apertures in the range of 1 to 100 microns. The common chlorinated solvents such as dichloromethane (DCM), trichloroethene (TCE), and tetrachloroethene (PCE) are expected to completely disappear in these deposits within a few days to weeks. For fractured sedimentary rocks with much lower matrix porosities (5–15%), disappearance times for these solvents are generally less than several years for fracture apertures ranging from 10 to 200 microns typical for shales, siltstones, sandstones, and carbonate rocks. This is sufficient time for the immiscible phase of chlorinated solvent contamination to have disappeared at many industrial sites. This conceptual model has important implications with respect to ground-water monitoring, diagnosis of the nature and degree of contamination, and expectations for ground-water remediation at many contaminated sites. Proposed methods for enhancing immiscible-phase mass removal using hydraulic manipulation, surfactants, or alcohols will be futile where the immiscible phase has disappeared into the clay or rock matrix, and reverse diffusion and desorption will control clean-up time frames. Therefore, prospects for permanent restoration of many DNAPL and LNAPL sites in fractured porous media are more limited than previously thought.

Diffusive Disappearance of Immiscible‐Phase Organic Liquids in Fractured Geologic Media

Vertical core samples were obtained from an impervious, unweathered, water-saturated clay deposit beneath a 5-year-old hazardous waste landfill at a site in southwestern Ontario. Sections of the cores were analyzed for chloride and volatile organic compounds. Waste-derived chloride was detected in the clay to a maximum depth of 83 cm below the bottom of the landfill. The most mobile organic compounds were found only to a depth of /approximately/ 15 cm. The downward transport of these chemical species into the clay was the result of simple Fickian diffusion. This study has implications for low-permeability clay liners used at waste disposal sites. For liners of typical thickness (/approximately/ 1 m), simple diffusion can cause breakthrough of mobile contaminants in approximately 5 years; the diffusive flux of contaminants out of such liners can be large.

Diffusive contaminant transport in natural clay: a field example and implications for clay-lined waste disposal sites

A field tracer experiment was conducted in a lateral flow field in the weathered and highly fractured upper 6 m of a 40-m-thick clay-rich till plain in southwestern Ontario. In the upper 3 m where fractures are closely spaced ( 5 m/d. Simulations with a discrete fracture/porous matrix flow and transport model, which used the cubic law for flow in fractures, showed that diffusion of the solutes, but not the much larger colloids, into the matrix pore water between fractures is sufficient to cause the observed difference in solute and colloid transport rates. Transport-derived and hydraulic conductivity-derived fracture aperture values were similar, within a factor of 3 and falling mainly within a range of 5–40 μm. In the upper 3 m the solute tracers were evenly distributed between pore water in the fractures and the matrix, and as a result, solute transport can be closely approximated with an equivalent porous medium (EPM) approach. Below this depth, fractures are more widely spaced (0.13 to >1 m) with concentration peaks tending to occur near visible fractures, and solute transport cannot be adequately described with an EPM approach.

https://works.bepress.com/larry_mckay/41/download/

Field Experiments in a Fractured Clay Till 2. Solute and Colloid Transport

http://www.geol.lsu.edu/blanford/NATORBF/12%20Organic%20Chemicals/Conant%20Jr%20et%20al_Contaminant%20Hydrology_2004.pdf

John A. Cherry

Papers

In Situ Remediation of Contaminated Ground Water: The Funnel-and-Gate System

Diffusive Disappearance of Immiscible‐Phase Organic Liquids in Fractured Geologic Media

Diffusive contaminant transport in natural clay: a field example and implications for clay-lined waste disposal sites

Field Experiments in a Fractured Clay Till 2. Solute and Colloid Transport

A PCE groundwater plume discharging to a river: influence of the streambed and near-river zone on contaminant distributions.