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

Shale gas development has led to concerns regarding fugitive CH4 migration in the subsurface and emissions to the atmosphere. However, few studies have characterized CH4 migration mechanisms and fate related to fugitive gas releases from oil or gas wells. This paper presents results from vadose zone gas and surface efflux monitoring during a natural gas release experiment at Canadian Forces Base Borden, Alliston, Ontario, Canada. Over 72 d, 51 m3 of natural gas (>93% CH4) was injected into a shallow, unconfined sand aquifer at depths of 4.5 and 9 m. Methane and CO2 effluxes in combination with soil gas concentrations and stable C isotopic signatures were used to quantify the spatiotemporal migration and fate of injected gas. Preferential gas migration pathways led to vadose zone hot spots, with CH4 concentrations exceeding the lower explosive limit (5% v/v). From these hot spots, episodic surface CH4 effluxes (temporally exceeding 2500 mmol m−2 s−1 [3465 g m−2 d−1]) occurred during active injection. Higher injection rates led to increased average CH4 effluxes and greater lateral migration, as evidenced by a growing emission area approaching 25 m2 for the highest injection rate. Reactive transport modeling showed that high CH4 fluxes resulted in advection-dominated migration and limited CH4 oxidation, whereas lower CH4 effluxes were diffusion dominated with substantial CH4 oxidation. These results and our interpretations allowed us to develop a conceptual model of fugitive CH4 migration from the vadose zone to the ground surface.

https://acsess.onlinelibrary.wiley.com/doi/pdf/10.2136/vzj2018.02.0033

Vadose Zone Gas Migration and Surface Effluxes after a Controlled Natural Gas Release into an Unconfined Shallow Aquifer

Combined use of straddle packer testing and FLUTe profiling for hydraulic testing in fractured rock boreholes

A contaminant plume more than 7,700 meters long and a few hundred meters wide has been delineated using a network of bundle piezometers. The location, concentration, and starting time of the source are well-defined. The plume occurs in a stratified, highly permeable, sand and gravel aquifer in which the ground-water flow is unusually steady in direction and magnitude. A ground-water velocity of 380 meters per annum and a longitudinal dispersivity of 60 to 120 meters are obtained by simulating chloride breakthrough data at 7,700 meters from the source. Simulation of the cross-sectional distribution of chloride concentrations at 5,500 meters shows the horizontal transverse dispersivity to be at most 0.10 meters. This very small maximum value for horizontal transverse dispersivity is two to four orders of magnitude smaller than values reported in the literature for plumes of similar lengths. It is postulated that the very weak lateral dispersion is due primarily to the steadiness of the ground-water flow.

An ICP-MS, equipped with an ultrasonic nebulizer and active-film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram-per-liter (part-per-billion = ppb) range. Most of the other elements are present at nanogram-per-liter (part-per-trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.

Field Study of a Long and Very Narrow Contaminant Plume

A new downhole groundwater sampler reduces bias and error due to sample handling and exposure while introducing minimal disturbance to natural flow conditions in the formation and well. This "In Situ Sealed", "ISS", or "Snap" sampling device includes removable/lab-ready sample bottles, a sampler device to hold double end-opening sample bottles in an open position, and a line for lowering the sampler system and triggering closure of the bottles downhole. Before deployment, each bottle is set open at both ends to allow flow-through during installation and equilibration downhole. Bottles are triggered to close downhole without well purging; the method is therefore "passive" or "nonpurge". The sample is retrieved in a sealed condition and remains unexposed until analysis. Data from six field studies comparing ISS sampling with traditional methods indicate ISS samples typically yield higher volatile organic compound (VOC) concentrations; in one case, significant chemical-specific differentials between sampling methods were discernible. For arsenic, filtered and unfiltered purge results were negatively and positively biased, respectively, compared to ISS results. Inorganic constituents showed parity with traditional methods. Overall, the ISS is versatile, avoids low VOC recovery bias, and enhances reproducibility while avoiding sampling complexity and purge water disposal.

John A. Cherry

Papers

Vadose Zone Gas Migration and Surface Effluxes after a Controlled Natural Gas Release into an Unconfined Shallow Aquifer

Combined use of straddle packer testing and FLUTe profiling for hydraulic testing in fractured rock boreholes

Field Study of a Long and Very Narrow Contaminant Plume

A downhole passive sampling system to avoid bias and error from groundwater sample handling.

Uranium Tailings Acidification and Subsurface Contaminant Migration in a Sand Aquifer