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

Glacial till in a 22-km/sup 2/ area of the Interior Plains Region of southern Alberta, Canada consists of an upper brown gypsiferous weathered zone (up to 20 m thick) and a lower discontinuous grey nonweathered zone (up to 25 m thick). Although the total sulfur content of the two till zones is the same (0.34%), the mean total sulfate content of the weathered till (4.0 mg g/sup -1/) exceeds that the nonweathered till (0.8 mg g/sup -1/). Similarities suggest that all SO/sub 4//sup 2 -/ in the nonweathered till and 20% of the sulfate in the weathered till was derived from sulfate-rich bedrock fragments incorporated in the till during deposition. Laboratory experiments and delta/sup 18/O and delta/sup 34/S analyses of total SO/sub 4//sup 2 -/ and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic S at some time after the till was deposited. Mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions. Groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier Altithermal period (11,000more » to 3000 years B.P.). The following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed. The oxidation of reduced S produced SO/sub 4//sup 2 -/ and H/sup +/. The H/sup +/ reacted with carbonate minerals under elevated p/sub CO2/, with Ca/sup 2 +/ loss by exchange for Na/sup +/ and gypsum precipitation. Volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity.« less

Origin and Distribution of Sulfate in a Fractured Till in Southern Alberta, Canada

Hydrogeology of two Saskatchewan tills, I. Fractures, bulk permeability, and spatial variability of downward flow

A uniform oxygen isotope value of –25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial Lake Agassiz basin. The lake occupied parts of North Dakota and southern Manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of Canada. Ground water from thick late Pleistocene-age clay deposits elsewhere, a till in southern Saskatchewan, and a glaciolacustrine deposit in northern Ontario show the same value at similar depths. These sites are at about 50°N latitude, span a distance of 2000 kilometers, and like the Lake Agassiz sites, have a ground-water velocity of less than a few millimeters per year. The value of –25 per mil is characteristic of meltwater impounded in the southern basin of Lake Agassiz. This value corresponds to an estimated air temperature of –16°C, compared with the modern temperature of 0°C for this area.

Isotopic Composition of Old Ground Water from Lake Agassiz: Implications for Late Pleistocene Climate

A new multilevel ground water monitoring system has been developed that uses custom-extruded flexible 1.6-inch (4.1 cm) outside-diameter (O.D.) multichannel HDPE tubing (referred to as Continuous Multichannel Tubing™ or CMT) to monitor as many as seven discrete zones within a single borehole in either unconsolidated sediments or bedrock. Prior to inserting the tubing in the borehole, ports are created that allow ground water to enter six outer pie-shaped channels (nominal diameter = 0.5 inch [1.3 cm]) and a central hexagonal center channel (nominal diameter = 0.4 inch [1 cm]) at different depths, facilitating the measurement of depth-discrete piezometric heads and the collection of depth-discrete ground water samples. Sand packs and annular seals between the various monitored zones can be installed using conventional tremie methods. Alternatively, bentonite packers and prepacked sand packs have been developed that are attached to the tubing at the ground surface, facilitating precise positioning of annular seals and sand packs. Inflatable rubber packers for permanent or temporary installations in bedrock aquifers are currently undergoing site trials. Hydraulic heads are measured with conventional water-level meters or electronic pressure transducers to generate vertical profiles of hydraulic head. Ground water samples are collected using peristaltic pumps, small-diameter bailers, inertial lift pumps, or small-diameter canister samplers. For monitoring hydrophobic organic compounds, the CMT tubing is susceptible to both positive and negative biases caused by sorption, desorption, and diffusion. These biases can be minimized by: (1) purging the channels prior to sampling, (2) collecting samples from separate 0.25-inch (0.64 cm) O.D. Teflon® sampling tubing inserted to the bottom of each sampling channel, or (3) collecting the samples downhole using sampling devices positioned next to the intake ports. More than 1000 CMT multilevel wells have been installed in North America and Europe to depths up to 260 feet (79 m) below ground surface. These wells have been installed in boreholes created in unconsolidated sediments and bedrock using a wide range of drilling equipment, including sonic, air rotary, diamond-bit coring, hollow-stem auger, and direct push. This paper presents a discussion of three field trials of the system, demonstrating its versatility and illustrating the type of depth-discrete data that can be collected with the system.

/pdf/a-new-multilevel-ground-water-monitoring-system-using-9ik1oiveti.pdf

John A. Cherry

Papers

Origin and Distribution of Sulfate in a Fractured Till in Southern Alberta, Canada

Hydrogeology of two Saskatchewan tills, I. Fractures, bulk permeability, and spatial variability of downward flow

Isotopic Composition of Old Ground Water from Lake Agassiz: Implications for Late Pleistocene Climate

A New Multilevel Ground Water Monitoring System Using Multichannel Tubing

Migration of contaminants in groundwater at a landfill: A case study: 2. Groundwater monitoring devices