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

• We separate the roles of upward discharge and aquitards in flowing artesian zone. • Basinal flow are coupled with well hydraulics to examine hydraulics of flowing wells. • A low K aquitard causes a large flowing artesian zone but low stable discharge rate. • Baseflow reduction is the main source of groundwater derived in flowing wells. Causes and water sources of flowing artesian wells attracted the interest of many hydrogeologists throughout history, however, a quantitative model that satisfactorily considers the roles of topography, groundwater recharge/discharge and aquitards on hydraulics of flowing wells is still lacking. In this study, a three-layer river-valley basin with a recharge boundary is used to obtain the basinal flow field, spatial distribution and transient discharge rates of flowing wells. Even if there is an aquitard separating the unconfined and the confined aquifers, groundwater discharge to the river still plays a critical role in occurrence of flowing wells. An aquitard with lower permeability would enlarge the zone with flowing wells, implying that flowing wells are more likely to occur in basins with continuous aquitards. By comparing flowpaths and inter-aquifer leakages before and after numerically installing a flowing well in a three-layer basin, we find decreased upward leakage in the discharge limb plays a much larger role than increased downward leakage in the recharge limb in the stable discharge rate of a flowing well. This recognition is different from previous studies where the stable discharge rate is supported only by downward leakage from the overlying aquifer. By considering well hydraulics in a basinal background flow field, this study improves understanding of the mechanisms of flowing artesian wells and the interaction of surface water and deep groundwater, indicating that flowing wells are valuable for sampling deep groundwater representative of deep and old groundwater in the discharge area of a basin. 

Revisiting hydraulics of flowing artesian wells: a perspective from basinal groundwater hydraulics

Abiotic transformation of trichloroethene (TCE) in fractured porous rock such as sandstone is challenging to characterize and quantify. The objective of this study was to estimate the pseudo first-order abiotic reaction rate coefficients in diffusion-dominated intact core microcosms. The microcosms imitated clean flow through a fracture next to a contaminated rock matrix by exchanging uncontaminated groundwater, unamended or lactate-amended, in a chamber above a TCE-infused sandstone core. Rate coefficients were assessed using a numerical model of the microcosms that were calibrated to monitoring data. Average initial rate coefficients for complete dechlorination of TCE to acetylene, ethene, and ethane were estimated as 0.019 y-1 in unamended microcosms and 0.024 y-1 in lactate-amended microcosms. Moderately higher values (0.026 y-1 for unamended and 0.035 y-1 for lactate-amended) were obtained based on 13C enrichment data. Abiotic transformation rate coefficients based on gas formation were decreased in unamended microcosms after ∼25 days, to an average of 0.0008 y-1. This was presumably due to depletion of reductive capacity (average values of 0.12 ± 0.10 μeeq/g iron and 18 ± 15 μeeq/g extractable iron). Model-derived rate coefficients and reductive capacities for the intact core microcosms aligned well with results from a previous microcosm study using crushed sandstone from the same site.

Chlorinated Ethene Degradation Rate Coefficients Simulated with Intact Sandstone Core Microcosms

Region 15, St. Lawrence Lowland

This paper describes a field experiment involving a release of five litres of a mixture of chloroform, trichloroethylene and tetrachloroethylene below the watertable into a stratified sandy aquifer to create a heterogeneously distributed DNAPL source. The release was conducted in a steel sheet pile cell, where a controlled groundwater flow was introduced. Monitoring points were installed in a cross section downgradient of the source zone to allow very detailed monitoring of dissolved concentrations. The source depletion and total mass upgradient selected sampling points were estimated from observed changes in dissolved concentration ratios. The estimates seems to be reasonable, but will be confirmed later when the site is excavated and sampled to map the actual distribution of DNAPL in the aquifer. Preliminary results reveal that dissolution from a multi-component heterogeneously distributed source is a very complex process, which not only depends on the total DNAPL mass in the soil but probably also depends on the nature of the DNAPL zone.

Dissolution of Heterogeneously Distributed Solvent Residuals, a Field Experiment

Nuclear energy and shale gas development each began with the promise of cheap, abundant energy and prospects for national energy independence. Nuclear energy was touted as “too cheap to meter,” and shale gas promised jobs and other economic benefits during a recession.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014EO290005

John A. Cherry

Papers

Revisiting hydraulics of flowing artesian wells: a perspective from basinal groundwater hydraulics

Chlorinated Ethene Degradation Rate Coefficients Simulated with Intact Sandstone Core Microcosms

Region 15, St. Lawrence Lowland

Dissolution of Heterogeneously Distributed Solvent Residuals, a Field Experiment

Nuclear Waste Disposal: A Cautionary Tale for Shale Gas Development