An Evaluation of Some Systems for Sampling Gas-Charged Ground Water for Volatile Organic Analysis

Loss of volatile organics during sampling is a well-recognized source of bias in ground water monitoring; sampling protocols attempt to minimize such loss. Such bias could be enhanced for ground water highly charged with dissolved gases such as methane. Such ground water was the object of this study. A positive-displacement bladder pump, a momentum-lift pump and a suction-lift, peristaltic pump were employed in sampling both methane-charged ground water for volatile aromatic hydrocarbons and a CO₂-charged reservoir water for volatile chlorinated hydrocarbons. In both cases, the suction-lift pump produced samples with a significant negative bias (9 to 33 percent) relative to the other methods. Little difference between samples produced by the other pump Systems was noted at the field site, but in sampling the reservoir, the bladder pump produced samples that were 13 to 19 percent lower in halocarbon concentration than were samples from the momentum-lift pump.
These negative biases are tentatively interpreted as losses due to volatilization during sampling. Slightly greater negative biases occur for compounds of higher volatility as estimated from their Henry's law constants. Additional studies appear to be warranted in order to adequately establish the scientific basis for recommending protocols for sampling ground water in which degassing could enhance the loss of volatile organics during sampling.     

Venus: On the phase variation of CO2 line profiles

The shapes of Venus' CO₂ profiles are found to vary with solar phase angle. High-resolution spectra of the P16 and P14 lines in the 8689- and 7820-Å bands, respectively, are presented for phase angles ranging from 6 to 158°. The scattering mean free path at 80 mbar, approximately the effective pressure, is 1.7 km. Use of the van de Hulst similarity relations with simple, parametric scattering models is inadequare to separate effects due to the scattering phase function from those due to inhomogeneities in depth when one attempts to determine the atmospheric structure by fitting a family of such models over a wide range of phase angles.     

Diagenesis of Upper Carboniferous rocks in the Ouachita foreland shelf in mid-continent USA: an overview of widespread effects of a Variscan-equivalent orogeny

Diagenesis of Upper Carboniferous foreland shelf rocks in southeastern Kansas took place at temperatures as high as 100–150° C at a depth of less than 2 km. High temperatures are the result of the long distance (hundreds of kilometers) advection of groundwater related to collisional orogeny in the Ouachita tectonic belt to the south. Orogenic activity in the Ouachita area was broadly Late Carboniferous, equivalent to the Variscan activity of Europe. Mississippi Valley-type Pb-Zn deposits and oil and gas fields in the US midcontinent and elsewhere are commonly attributed to regional groundwater flow resulting from such collisional events. This paper describes the diagenesis and thermal effects in sandstone and limestone of Upper Carboniferous siliciclastic and limestone-shale cyclothems, the purported confining layer of a supposed regional aquifer. Diagenesis took place in early, intermediate, and late stages. Many intermediate and late stage events in the sandstones have equivalents in the limestones, suggesting that the causes were regional. The sandstone paragenesis includes siderite cement (early stage), quartz overgrowths (intermediate stage), dissolution of feldspar and carbonates, followed by minor Fe calcite, pore-filling kaolinite and sub-poikilotopic Ca ankerite (late stage). The limestone paragenesis includes calcite cement (early stage); megaquartz, chalcedony, and Fe calcite spar (intermediate stage); and dissolution, Ca-Fe dolomite and kaolinite (late stage). The R _m value of vitrinite shows a regional average of 0.6–0.7%; Rock-Eval T _maX suggests a comparable degree of organic maturity. The T _h of aqueous fluid inclusions in late stage Ca-Fe-Mg carbonates ranges from 90 to 160° and T _mice indicates very saline water (>200000 ppm NaCl equivalent); ¹⁸O suggests that the water is of basinal origin. Local warm spots have higher R _m, T _max, and T _h. The results constrain numerical models of regional fluid migration, which is widely viewed as an artesian flow from recharge areas in the Ouachita belt across the foreland basin onto the foreland shelf area. Such models must account for heating effects that extend at least 500 km from the orogenic front and affect both supposed aquifer beds and the overlying supposed confining layer. Warm spots indicate either more rapid or more prolonged flow locally. T _h and T _mice data show the highest temperatures coincided with high salinity fluids.     

Spectrophotometry of Pluto from 3500 to 7350 Å

We have obtained spectra of Pluto on six nights during February 1979 using the Cassegrain Digicon spectrograph on the 2.1-m Struve reflector and the IDS spectrograph on the 2.7-m reflector of McDonald Observatory. These spectra, with nominal resolution of 6–7 Å, have been reduced to relative fluxes. Relative albedos were then calculated using the solar irradiances of Arvesen et al. (1969). The spectra taken in the blue show no indication of the upturn in albedo at $\text{λ < 3800}\text{A}\text{?}$ previously reported by Fix et al. (1970). The lack of a uv upturn cannot be interpreted in terms of a Rayleigh scattering atmosphere unless the albedo of the underlying surface is known. From the lack of methane absorption at the wavelength of the 6190- or 7270-Å methane bands we derive an upper limit of 1–3 m-am of gaseous CH₄. The albedo curve has a constant slope between 3500 and 7300 Å. The only other solar system body which has this feature is an S-type asteroid.     

The Holocene history of West Basin Lake,Victoria, Australia; chemical changes based on fossil biota and sediment mineralogy

Analyses of diatoms, ostracods, pollen and sediment mineralogy from a 524 cm core from a stratified, hypersaline crater lake, West Basin, Victoria, has revealed clear shifts in the lake's water balance and chemistry and the region's climate over the last 10 000 years. Diatom and ostracod analyses reveal lake water salinity changes which are consistent with the conditions suitable for the precipitation of the carbonate and other minerals identified using x-ray diffraction analysis. The fluctuations in lake water balance deduced from diatom and ostracod inferred lake salinity suggest that the lake began to fill at the beginning of the Holocene and was saline and shallow. Toward the mid-Holocene the water levels rose and yet the lake remained largely saline. The late Holocene is marked by a return to more shallow but fluctuating, water conditions. Through the whole period, the regional dryland vegetation was dominated by open sclerophyll woodland. Both the lacustrine and regional environments interpreted here are consistent with those from Holocene records elsewhere in the region.This is the fourth in a series of papers published in this issue on the paleolimnology of arid regions. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers.     

Longitudinal distributions of river flood power: the combined automated flood,elevation and stream power (CAFES) methodology

Stream power can be an extremely useful index of fluvial sediment transport, channel pattern, river channel erosion and riparian habitat development. However, most previous studies of downstream changes in stream power have relied on field measurements at selected cross‐sections, which are time consuming, and typically based on limited data, which cannot fully represent important spatial variations in stream power. We present here, therefore, a novel methodology we call CAFES (combined automated flood, elevation and stream power), to quantify downstream change in river flood power, based on integrating in a GIS framework Flood Estimation Handbook systems with the 5 m grid NEXTMap Britain digital elevation model derived from IFSAR (interferometric synthetic aperture radar). This provides a useful modelling platform to quantify at unprecedented resolution longitudinal distributions of flood discharge, elevation, floodplain slope and flood power at reach and basin scales. Values can be resolved to a 50 m grid. CAFES approaches have distinct advantages over current methodologies for reach‐ and basin‐scale stream power assessments and therefore for the interpretation and prediction of fluvial processes. The methodology has significant international applicability for understanding basin‐scale hydraulics, sediment transport, erosion and sedimentation processes and river basin management. Copyright © 2008 John Wiley & Sons, Ltd.     

Sediment dynamics in an upland temperate catchment: changing sediment sources,rates and deposition

We examine sediment dynamics in an upland, temperate lake system, Lake Bassenthwaite (NW England), in the context of changing climate and land use, using magnetic and physical core properties. Dating and analysis of the sedimentary records of nine recovered cores identify spatially variable sedimentation rates across the deep lake basin. Mineral magnetic techniques, supported by independent geochemical analyses, identify significant variations both in sediment source and flux over the last ∼2100 years. Between ∼100 years BC and ∼1700 AD, sediment fluxes to the lake were low and dominated by material sourced from within the River Derwent sub-catchment (providing 80% of the hydraulic load at the present day). Post-1700 AD, the lake sediments became dominantly sourced from Newlands Beck (presently providing ∼10% of the lake’s hydraulic load). Three successive, major pulses of erosion and increased sediment flux appear linked to specific activities within the catchment, specifically: mining activities and associated deforestation in the mid-late nineteenth century; agricultural intensification in the mid-twentieth century and, within the last decade, the additional possible impact of climate change. These results are important for all upland areas as modifications in climate become progressively superimposed upon the effects of previous and/or ongoing anthropogenic catchment disturbance.     

Controlled source strength variation by changing the firing pressure ‐ a sensitivity study for 4D calibration

For a 4D seismic operation to be successful, it is important to know what kind of 4D signal we expect to observe, as well as its magnitude. Normally, in a 4D feasibility study, we use rock physics models to quantify the effect of fluid or pressure changes within the reservoir and calculate the corresponding effects to the seismogram. However, to find if the predicted changes are actually observable at a given field, a dedicated calibration procedure might give valuable insight. One such procedure for marine seismics is to gradually change the source strength by varying the firing pressure in order to detect the sensitivity threshold for a given subsurface reflection. This procedure would be practical and feasible if the change of the source signature changes linearly with the source pressure. However, non‐linear effects will lead to minor changes in the later arrivals of the source signature, the so‐called bubble. By investigating these introduced errors for a reasonable air‐gun array we conclude that the method is still feasible since we find it possible to control and diminish the impact of the introduced errors.     

An Investigation of the Pressure Pulsing Reagent Delivery Approach

Pressure pulsing technology is an innovative method that has been developed with the aim of overcoming preferred flow paths associated with remediation techniques that rely on the injection of reagents. Numerical and field experiments were conducted to assess how pressure pulsing affects groundwater flow and solute transport during reagent injection. A series of field experiments were performed at two field sites where a monitoring network designed to capture the breakthrough of solutes delivered from an injection well was installed. Pressure pulsing and conventional injection methods were used at each site. One site was comprised of fine sand with low heterogeneity, while the other was moderately heterogeneous with discrete layers varying from fine sand to silt. The data suggest that breakthrough was more uniform for the pressure pulsing injections; however, this difference was minor and complicated by sorption of some of the tracers employed. The groundwater flow and solute transport modeling exercise simulated the rapid boundary pressure modulation that occurs in association with pressure pulsing. Two‐dimensional (2D) simulations revealed that repeated sudden onset of injection cessation produces brief periods of gradient reversal and the development of a mixing zone near the injection well. The spatial extents of this mixing zone were found to be highly dependent upon the hydraulic diffusivity of the medium, with medium heterogeneity and pulsing frequency playing secondary roles. Three‐dimensional (3D) numerical simulations were used to benchmark the observations from one of the field sites. The results from the modeling effort showed that solute breakthrough from a pressure pulsing injection is more dispersed relative to a conventional injection as a result of the mixing zone phenomenon; however, we were unable to directly observe this mixing zone using the instrumentation deployed at the two field sites.