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

Field Evidence of Denitrification in Shallow Groundwater Flow Systems

The extensive lacustrine Chalco Plain in the southeastern part of Mexico City is underlain by an aquitard up to 300 m thick composed of a layered sequence of very porous (80-90%) fine-grained, organic-rich Quaternary deposits, with thin horizontal interbeds of volcanic sand (“Capas Duras”) The aquitard overlies a thick sequence of alluvial-pyroclastic sediments which form a highly productive regional aquifer The Chalco Plain was a shallow lake until the 1940s when it was drained for agricultural use and human habitation Historic information indicates that the Chalco Plain was an area of ground-water discharge prior to the onset of heavy ground-water extraction from the semiconfined aquifer Due to aquifer pumping, however, the hydraulic gradient has reversed throughout the full thickness of the aquitard in areas where the aquitard is thin (< 100m), and recharging conditions now prevail Where the aquitard is thick, the hydraulic head data show a progressive decline with time even though the hydraulic gradient still indicates upward flow in at least the upper part of the lacustrine sequence Between the early 1960s, when major ground-water extraction began beyond the periphery of the aquitard, and the onset in 1982 of heavy pumping from aquifers beneath the aquitard, the land surface subsided approximately 3 m An additional subsidence of 2 m occurred between 1984 and 1989, causing a shallow lake to form and gradually expand If the present rate of ground-water withdrawal from the Chalco Basin continues, total land subsidence in the middle of the plain will probably continue to a rate of about 04 m per year for many years, and could eventually reach a total subsidence of tens of meters in the thickest part of the Chalco Plain Pore water in much of the aquitard is saline; however, release of salts and other chemical constituents to the underlying aquifer has not yet significantly impaired the aquifer water quality A better understanding of the behavior of the aquitard under the influence of aquifer pumping is needed to assist in long-term management of ground water and land use in the Chalco Plain

Large-Scale Aquitard Consolidation Near Mexico City

Although the potential for KMnO4 to destroy chlorinated ethenes in situ was first recognized more than a decade ago, the geochemical processes that accompany the oxidation have not previously been examined. In this study, aqueous KMnO4 solutions (10−30 g/L) were injected into an unconfined sand aquifer contaminated by the dense non-aqueous-phase liquid (DNAPL) tetrachloroethylene (PCE). The effects of the injections were monitored using depth-specific, multi-level groundwater samplers, and continuous cores. Two distinct geochemical zones evolved within several days after injection. In one zone where DNAPL is present, reactions between KMnO4 and dissolved PCE resulted in the release of abundant chloride and hydrogen ions to the water. Calcite and dolomite dissolved, buffering the pH in the range of 5.8−6.5, releasing Ca, Mg, and CO2 to the pore water. In this zone, the aqueous Ca/Cl concentration ratio is close to 5:12, consistent with the following reaction for the oxidation of PCE in a carbonate-rich aqu...

Geochemical reactions resulting from in situ oxidation of PCE-DNAPL by KMnO4 in a sandy aquifer.

Enhanced detection of hydraulically active fractures by temperature profiling in lined heated bedrock boreholes

An evaluation of contaminant migration patterns at two waste disposal sites on fractured porous media in terms of the equivalent porous medium (EPM) model

John A. Cherry

Papers

Field Evidence of Denitrification in Shallow Groundwater Flow Systems

Large-Scale Aquitard Consolidation Near Mexico City

Geochemical reactions resulting from in situ oxidation of PCE-DNAPL by KMnO4 in a sandy aquifer.

Enhanced detection of hydraulically active fractures by temperature profiling in lined heated bedrock boreholes

An evaluation of contaminant migration patterns at two waste disposal sites on fractured porous media in terms of the equivalent porous medium (EPM) model