ALBERT

Notes: The affinity of soil organic matter for water influences resistance to microbial degradation, the rate of wetting and adsorption processes. Such properties play key roles in organic matter and microbial biomass dynamics, aggregate stability, water infiltration, leaching of organic and inorganic pollutants, chemical composition and the dynamics of dissolved organic matter (DOM). The hydrophobicity of the organic matter as a function of management have been studied in two soils with contrasting textures using diffuse reflectance infrared fourier transform spectroscopy (DRIFT). The results show that agricultural management clearly influences the amount of aliphatic C-H units and implicitly the hydrophobicity of the soil organic matter. A decrease of organic C due to management is accompanied by a decrease of hydrophobicity as well as of soil microbial activity and aggregate stability. The hydrophobicity index is a sensitive quantity to characterize the‘quality’ of soil organic matter. DRIFT spectroscopy proves to be a rapid and reliable technique to determine quantitatively the hydrophobicity of soil organic matter.

Notes: There is confusion about the effects of acidification on soil P because its impact on sorption and on P dissolution have not been separated. We investigated these effects with two soils treated with H2SO4 by both percolation and batch titration methods. Repeated percolation with dilute acid removed less P than repeated percolation with water. In contrast, the more acid was added in the batch method the more P was released. The conflicting outcome was attributable to the differences in the closed and open systems; the solutions used to remove P differed in their ionic strength and composition. The Q/I plots and the fractionation analyses revealed that the P release and the changes in the dynamic relation between solid-and solution-phase P are a net effect of two coincident, but opposing reactions on oxide surfaces. As a result of acidification the sorption sites available on the Fe and Al oxide surfaces will diminish through the resorption of P dissolved by acid from the Ca-bound fraction. This increase in the P saturation enhances the desorption tendency, which is counteracted by the protonation of the oxide surfaces enhancing the sorption affinity.

Notes: Investigating the biogeochemistry of plant material decomposition in soil has been restricted by difficulties extracting and identifying organic compounds. In this study the decomposition of 13C- and 15N-labelled Lolium perenne leaves mixed with mineral soil has been investigated over 224 days of incubation under laboratory conditions. Decomposition was followed using short-term rates of CO2 evolution, the amounts of 13C and 15N remaining were determined by mass spectrometry, and 13C and 15N solid-state nuclear magnetic resonance (NMR) spectroscopy was used to characterize chemically the plant material as it decomposed. After 224 days 48% of the added 13C had been lost with a rapid period of C02 evolution over the first 56 days. The fraction of cross-polarization magic angle spinning (CP MAS) 13C NMR spectra represented by O-alkyl-C signal probably in carbohydrates (chemical shift, 60–90 p.p.m.) declined from 60 to 20% of the spectrum (chemical shift, 0–200 p.p.m.) over 224 days. The rate of decline of the total 13C exceeded that of the 60–90 p.p.m. signal during the first 56 days and was similar thereafter. The fraction of the CP MAS 13C NMR spectra represented by the alkyl- and methyl-C (chemical shift, 10–45 p.p.m.) signal increased from 5 to 14% over the first 14 days and was 19% after 224 days. CP MAS 13C NMR of 13C- and 15N-L. perenne contained in 100-μm aperture mesh bags incubated in the soil for 56 days indicated that the remaining material was mainly carbohydrate but there was an increase in the alkyl- and methyl-C associated with the bag's contents. After 224 days incubation of the labelled 13C- and 15N-L. perenne mixed with the soil, 40% of the added N had been lost. Throughout the incubation there was only one signal centred around 100 p.p.m. detectable in the CP MAS 15N NMR spectra. This signal corresponded to amide 15N in peptides and may have been of plant or microbial origin or both. Although there had been substantial interaction between the added 15N and the soil microorganisms, the associated redistribution of 15N from plant to microbial tissues occurred within the amide region. The feasibility of following some of the component processes of plant material decomposition in soil using NMR has been demonstrated in this study and evidence that microbial synthesis contributes to the increase in alkyl- and methyl-C content of soil during decomposition has been represented.

Notes: Radiocaesium is more available to biological systems in organic soils than in mineral soils. Part of the reason is that the adsorption of caesium on minerals, particularly illites, is very specific, whereas its adsorption on organic matter is non-specific. However, increasing evidence shows that even organic upland soils contain enough illitic material to immobilize caesium effectively. The presence of organic matter may reduce the affinity of soil minerals for caesium.We have studied adsorption of radiocaesium on the clay fractions of a mineral soil obtained from a surface, and the corresponding C, horizon. The soil clay fractions were treated to remove organic matter and Fe oxides progressively.Adsorption isotherms of caesium were obtained in dilute suspension using trace amounts of 137Cs and stable caesium. In general, adsorption was greater when the organic matter content was less, namely on the soil from the C horizon rather than the surface horizon, or when organic matter had been removed. However, adsorption is not a simple function of organic matter content: Cs adsorption was greater on the topsoil fraction after organic matter removal than on the subsoil fraction. X-ray diffraction analysis indicated that the surface soil clay contained more weathered minerals and less illite than the subsoil clay. The effect of organic matter removal was more marked at large Cs concentrations than when only radiocaesium was added, suggesting that very selective Cs adsorption sites are less sensitive to the presence of organic macromolecules. Iron oxides do not play a role in the affinity of soil clays for Cs. The form of the Freundlich isotherm was unchanged by any of the chemical treatments.

Notes: The critical-state theory can be applied profitably to analyse the mechanical behaviour of agricultural soil. Critical-state parameters and other soil properties are affected by the microstructure and unsaturated nature of agricultural soils. We determined the critical-state boundaries of an agricultural soil in both saturated and unsaturated triaxial tests and examined the effects of matric suction and initial structure on critical-state boundaries. On the compression plane, the presence of air and matric suction in the pores of unsaturated soil significantly affected critical-state boundaries by increasing compressibility, λ On the deviatoric stress-mean net stress plane, the strength increased with matric suction. On this plane, the critical-state lines for the unsaturated tests had non-zero intercepts. For a given soil structure, the frictional parameter M remained fairly constant with matric suction change. However, a change in the initial microstructure resulted in a change in M, causing the position of the critical-state line to ‘pivot’ in state space.

Notes: The geometry of pore space in soil is considered to be the key in understanding transport of water, gas and solute. However, a quantitative and explicit characterization, by means of a physical interpretation, is difficult because of the geometric complexity of soil structure.Pores larger than 40 μm within two soil horizons have been analysed morphologically on 3-dimensional digital representations of the pore space obtained by serial sections through impregnated specimens. The Euler-Poincaré characteristic has been determined as an index of connectivity in three dimensions. The pore connectivity is quantified as a function of the minimum pore diameter considered leading to a connectivity function of the pore space. Different pore size classes were distinguished using 3-dimensional erosion and dilation. The connectivity function turned out to differentiate between two soil materials. The pore space in an upper Ah horizon is intensely connected through pores between 40 and 100 μm, in contrast to the pore space in the AhBv beneath it. The morphological pore-size distributions were compared to the pore-size distribution obtained by water retention measurements. The discrepancy between these different methods corresponds to the expectation due to pore connectivity.

Notes: Sorption isotherms of heavy metals in soil often vary strongly from place to place in the field. Scaling might be useful to quantify the variability of such functional relations. Application of scaling to sorption isotherms requires a rule. In this paper the derivation of a scaling rule for sorption isotherms, based on a hypothesis of 'sorption similarity’, and its application to cadmium sorption isotherms measured in 25 fields on sandy soils are reported. Scale factors are calculated by least squares procedures. Scaling reduced the variation of the Cd isotherms, expressed as sum of squares about an average, by about 86%, preserving the variation through the calculated scale factors. Scaling of sorption isotherms requires no specific equation to fit the sorption data. The aforementioned average should be calculated as scale mean because of the theoretical stringency of this approach.

Notes: In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl2 and Ca(NO3)2 of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h−1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg2+ and Ca2+ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha−1 of native potassium was leached from the alluvial soil, but only about 10 kg ha−1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.

Notes: This study focuses on the processes occurring during incorporation of inorganic nitrogen into humic substances. Therefore rye grass, wheat straw, beech saw dust, sulphonated lignin and organosolve lignin were incubated together with highly 15N-enriched ammonium sulphate in the laboratory for 600 days. Samples from the incubates were periodically analysed for weight loss, and carbon and nitrogen contents. The samples were also analysed by solid-state 13C- and 15N-CPMAS-NMR-spectroscopy to follow the turnover of the materials during incubation. Most of the detectable N-signals was assigned to amide - peptide structures. The remaining intensities could be ascribed to free and alkylated amino groups, and those on the low field side of the broad amide-peptide signal to indole, pyrrole and nucleotide derivatives. Abiotic reactions of ammonia with suitable precursors and the formation of pyridine, pyrazine or phenyloxazone derivatives were not observed. Signals from ammonia and nitrate occurred only at the end of the incubation.

Notes: Citrate forms strong complexes with A1 ions and may thus influence the stability and formation of Clay-A1 hydroxide polymer systems (CAIHO). We studied the adsorption of citrate to CAIHO and the influence of citrate on the stability and formation of CAIHO at different A1:clay and A1:citrate ratios and pH values and at a total salt concentration of 0·01 M monovalent anions. The amount of citrate sorbed to the aged CAIHO was independent of the A1 fixed to the clay as A1 hydroxide polymers (AIHO) at 5 〈 pH 〈 6·6. The added citrate seemed not to sorb to the AIHO but only to the edges of the clay. As the citrate: Al ratio increased from 15–1:l at pH 6, more of the AIHO of the aged CAMO systems dissolved. The change in the CEC of the clay indicated that the nature of the remaining AIHO is independent of the amount of A1 dissolved. Citrate influenced the formation of CAIHO systems as measured at pH 6·6, to an extent which depended on the citrate: Al ratio. At a small ratio (1:5), AIHO formed and all citrate was incorporated in the AIHO, probably leading to a coprecipitate. The amount of citrate incorporated depended linearly on the amount of AIHO present. Co-precipitation of AIHO and citrate probably led to the formation of a separate phase, which was only weakly bound to the clay particles. At a large citrate: Al ratio (1:1) soluble Al-citrate complexes became dominant, and only a small part of the added A1 was present as AIHO.

Notes: Surface complexation of SO2−4 and H+ exchange were compared between goethite, gibbsite and a soil material from a podzol B horizon. Intrinsic equilibrium constants were determined for the surface complexation of SO2−4 and H+ using the diffuse layer model (DLM). Three surface group configurations for the SO2−4 adsorption were tested. A model with only one SO2−4 surface species and no H+ explicitly taking part in the reaction gave the overall best prediction of adsorption. The concomitant H+ exchange occurring during SO2−4 adsorption was attributed to decreased surface potential caused by charge neutralization in the inner layer. The H+/SO2−4 stoichiometric ratios (η) were determined by back-titration under different pH, ionic strength (I) and SO2−4 concentrations. The experimentally determined η was close to 1 for all materials at I= 0·1 M but 1·5, 1·0 and 1·7 in I = 1 mM for goethite, gibbsite and the soil suspension, respectively. The DLM gave a quantitatively correct description of SO2−4 and H+exchange at small I, but predictions were less accurate at large I. The surface complexation model give insight in the role of SO2−4 adsorption for the reversibility of soil acidification but remain to be evaluated in experiments more closely related to field conditions.

Notes: The Ca concentration of the soil solution influences K plant nutrition by its influence on K concentration of the soil solution and on soil buffer power through ion exchange and K release or fixation. The effects of the imposed solution Ca concentration on the estimates of these parameters and on these two phenomena were studied on a loamy soil. Potassium sorption and desorption experiments were conducted for 16 h at five initial Ca concentrations (from 0 to 10−1 M) and followed by the measurement of soil exchangeable K (ammonium acetate extraction). Soil K-Ca exchange properties and the contributions of exchangeable K and non-exchangeable K to K dynamics of the soil-solution system were estimated. The‘Ratio Law’ applied for the medium range of Ca concentrations, i.e. 10−1 M to 10−3 M. But, it failed for some experiments at small initial Ca concentrations (0 M and 10−4 M). This failure went with a decrease of the number of sites of great affinity for K in K-Ca ion exchange and/or a decrease of the amount of K not in exchange equilibrium with Ca but extracted by M ammonium acetate. Release of K increased and fixation of K decreased when Ca concentration increased. The relation between the change in the amount of non-exchangeable K during the experiment and the initial constraint (ø) was curvilinear on the large range of ø investigated. But, this relation was independent of Ca concentration. The K concentration of the solution for which neither sorption of K by the soil nor desorption of K from the soil occurred decreased and the slope of the sorption-desorption curve at this K concentration increased when the solution Ca concentration decreased. These two parameters can be considered the K concentration of the soil solution of the soil and the buffer power of the soil, respectively, only if the initial Ca concentration imposed during the sorption-desorption experiments is close to the Ca concentration of the soil solution of the soil. A predictive model of the soil buffer power based on ion exchange and release-fixation properties is proposed. Despite some discrepancies at very low Ca concentrations (〈0·5 mM Ca) when‘Ratio Law’did not apply the agreement between calculated and observed values was good. The model permits the correction of the experimentally obtained buffer power for the bias related to the great solution volume: soil weight ratio commonly used during the sorption-desorption experiments.

Notes: Calculation of [Al3+] is necessary to understand geochemical processes involving aluminium. Quickly reacting aluminium is a quantity from which [Al3+] can be calculated. We have modified the method used to determine quickly reacting aluminium in soil leachates. The modifications consist of changing the reaction pH from 5·0 to 4·5 and increasing the reagent concentration from 4 to 12 mmol 1−1. The range of concentrations for which Beer's law applies has been increased up to 40 mg Al l−1 using a 20 μl injection volume. The sample throughput is 69–88 injections per hour, depending on concentration. A slight improvement in the buffering capacity has been obtained. The fractionation obtained is similar to that of the original method, except that a clearer separation is obtained for the complex AlHPO4+, enabling easier calculation of [Al3+].

Notes: Books reviewed in this article.Schinner, R., Öhlinger, R., Kandeler, E. & Margesin, R. (eds) Methods in Soil Biology.Coleman, D.C. & Crossley, J.R. Jr. Fundamentals of Soil Ecology.Hall, G.S. (ed.) Methods for the Examination of Organismal Diversity in Soils and Sediments.Boutton, T.W. and Yamasaki, S. (eds) Mass Spectrometry of Soils.Yaron, B., Calvet, R. & Prost, R. Soil Pollution. Processes and Dynamics.Buurman, P., van Lagen, B. and Velthorst, E.J. (eds) Manual for Soil and Water Analysis.Legros, J.-P. Cartographie des sols - De l'analyse spatiale b la gestion des territoires.

Notes: The fine earth (〈2 mm) and rock fragments (〉2 mm) fractions of two soils derived from Oligocene sandstone have been examined to assess the origin of the discrepancies between cation exchange capacity (CEC) and effective CEC (ECEC). The soils differ in terms of acidity: soil A is more acid than soil B. When the A samples are treated with BaCl2, the solution became sufficiently acid (pH 〈 4·5) to dissolve and to maintain Al in solution. From these samples more Al is released than base cations. Aluminium was continuously replenished even after 192 h, so that the ECEC was always larger than the CEC. Samples from soil B contain less H and Al ions, and the BaCl2 solution could not lower the pH below 5·0. In these samples little Al is released, and the base cations dominate the exchangeable pool of ions. This Al can be considered to be exchangeable, and a good agreement exists between the ECEC and the CEC. The source of non-exchangeable Al in the A samples is the OH-Al polymers of the hydroxy-interlayered vermiculite (HIV) and hydroxy-interlayered smectite (HIS) that tend to dissolve during the BaCl2 treatments. In the less acid B samples the Al polymers are not affected by BaCl2 treatment. Different results were obtained when the clays, extracted from an Na-dispersed suspension, were treated with BaCl2 solution. Because the clays are no longer acid, no H+ is released, and the OH-Al polymers are not dissolved. Therefore, the saturating ions play an important role in the dissolution of the OH-Al polymers and cause differences between the CEC and ECEC. We discount organic matter and specifically Al-organo complexes as a source of non-exchangeable Al. Both A and B soils contain very similar pyrophosphate-extractable Al, but show substantial differences in the amount of exchangeable Al.

Notes: Sorption on the mineral matrix is an important process restricting the movement of dissolved organic matter (DOM) in soils. In this study, we aimed to identify the chemical structures responsible for the retention of DOM by sorption experiments with total DOM and acidic humic substances (AHS), containing humic and fulvic acids, on soil samples and minerals (goethite, ferrihydrite, and amorphous Al(OH)3). The AHS remaining in solution after sorption were studied by 13C nuclear magnetic resonance (NMR) analysis, and total DOM and AHS for bed on the surfaces of minerals by diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy. The soil samples were taken from strongly sorbing Bw horizons of two Inceptisols rich in pedogenetic Fe (29 and 35 g kg −1) and containing little C (7 and 22 g kg−1). The 13C-NMR spectra showed that sorption causes a preferential removal of aromatic and carboxyl C from the solution, whereas alkyl-C accumulates in the solution. No change was observed for O-alkyl C. The DRIFT spectra of sorbed total DOM and AHS showed a relative increase of the band intensity of carboxyl groups compared to DOM in the initial solution, confirming the importance of those groups for the sorption to mineral surfaces. The spectra also indicated reactions of carboxyl groups with metals at the mineral surfaces. The extent to which the carboxyl groups are bound depended on the surface coverage with DOM and the type of mineral.

Notes: The influence of atmospheric fluoride deposits on the soil microbial biomass and its enzyme activities was investigated near the aluminium smelter at Ranshofen, Upper Austria. Soil samples at various distances from the emission source were analyzed for water-extractable F and microbial activity. The water-extractable F contents at the sites examined reflected the gradient of F exposure (10 to 189 mg F kg−l dry soil). The microbial activities increased with distance from the emission source and were inversely correlated with the degree of F contamination. The linear correlation coefficients between the water-extractable F concentrations and the microbial biomass, dehydrogenase and arylsulphatase activity were r=−0·8, −0·86 and −0·84, respectively. In the most contaminated soil (up to 189 mg F kg−1), the microbial activities were only 5–20% of those in the unpolluted soil. The microbial biomass and dehydrogenase activity decreased substantially where the concentration of F exceeded 100mgkg−1, whereas arylsulphatase activity was already inhibited at 20 mg kg−1. The accumulation of organic matter near the smelter (123 mg F kg−1) also indicated severe inhibition of the microbial activity by F. Our investigations show that the ratio of arylsulphatase to microbial biomass can be used as a sensitive index for evaluating environmental stress such as F Contamination.

Notes: Time-domain reflectometry (TDR) evaluates the bulk dielectric constant, K, of the soil by measuring the travel time of an electromagnetic pulse through a sensor, and through it estimates the volumetric water content. We show that for saline soils the effects of conductivity and frequency on the travel time cannot be neglected and that, as a result, TDR systematically overestimates the water content in saline soils. Simultaneously the bulk electrical conductivity of soils can be estimated by TDR. The equivalent impedance after multiple reflections is related to the bulk electrical conductivity, σ This relation differs from sensor to sensor and requires calibration for each individual sensor.A method is proposed for correcting the volumetric water content in saline soils. First, the bulk electrical conductivity, o, is estimated from the equivalent impedance at a specific equivalent distance of cable, several times the actual length of the sensor. The zero-salinity dielectric constant, KO, of this soil is obtained by correcting the apparent K as a function of the measured bulk electrical conductivity. The volumetric water content is estimated from Ko. The correction of K is a function of the equivalent frequency of the electromagnetic pulse. The imaginary part of the dielectric constant is primarily due to ohmic losses. The model, which calculates the velocity of propagation of the electromagnetic pulse and which takes into consideration the imaginary part, performs reasonably well. An empirical approach based on calibration gave slightly better results.

Notes: A method for mapping soil properties at a regional scale with acceptable precision and cost was investigated. It combines soil classification and interpolation, and uses sample information from a reference area and simple soil observations over the region. The method consists of two stages. First is the prediction of soil properties at a set of sites covering the region by classifying each site according to the soil classification of the reference area, and then by assigning to each site the values of soil properties measured at the representative profile of its soil class. The second is by interpolating the predictions of the properties from the classes at the observation sites. Three methods were considered: kriging, inverse squared distance and nearest neighbour. The performance of classification combined with interpolation was evaluated for mapping water content at wilting point in an area of 1736 ha in a physiographic region of Southern France. The method was compared with conventional methods, namely kriging with actual data and prediction from a soil map at a scale of 1:100000. Estimates from classification combined with kriging were more precise than those from the 1:1OOOOO soil map in all instances, and close to those of ordinary kriging with actual data when prediction points were near the observation points. Classification combined with inverse squared distance or with nearest neighbour interpolation was always less precise than classification with kriging. However, it was more precise than classification at the 1:100 000 scale except when prediction points were far from the observation points.

Notes: A critical-state finite element model was used to simulate compaction under single and dual tyres and tracks. The compaction involved deformations at three different scales, from small tyres with a contact area of about 70 cm2 (single tyre) supporting a load of about 50 kg, to large tyres of about 1.2 m2 (dual tyres) supporting a load of about 4500 kg. The predictions were compared with measured values for several different quantities. These included: rut depths; vertical displacement and shear strain: vertical stresses; and, void ratios and precompression stress measured on sampled soil cores. In general, the predictions and measurements agreed reasonably well. However, the agreement between prediction and measurement depended on the precision of measurements, soil disturbance, and the volume of soil involved in a measurement relative to the volume of soil influenced by the tyre or track. This study shows that the critical-state finite element model is useful, offering insight into the compaction process, the dependence of compaction on soil strength and compressibility, and practical implications for soil management.

Notes: We prepared five samples of pure goethite and three samples of aluminous goethite with mole fractions of aluminium ranging from 0·05 to 0·20. One of the samples of pure goethite was repeatedly heated in an autoclave at 150°C. We studied the samples using transmission electron microscopy and XRD and we measured the surface area (BET), rate of dissolution of the samples in acid, the surface charge in four concentrations of sodium nitrate from pH 4–10, and the sorption of calcium and chloride from a dilute solution of calcium chloride. Surface areas ranged from 18 to 132 m2 g−1. The BET adsorption-desorption isotherms had hysteresis loops which increased as the surface area increased. These showed that there were pores present with diameters smaller than 2 nm and that the number of pores increased as the surface area increased. All samples of goethite showed typical X-ray diffraction patterns but with peak heights decreasing, and width increasing, as surface area increased. Mean coherence lengths, as determined by XRD line broadening, were smaller than those determined by transmission electron microscopy. This was because each crystal was composed of several domains, and the XRD data reflect the size of the domains. Heating one of the goethite samples in an autoclave caused most of the domains to coalesce and slightly decreased the surface area. As the surface area of the eight goethite samples increased, the mean coherence length in the direction of the a, b and c axes decreased. The better crystallized samples dissolved more slowly in acid and the dissolution curves were sigmoid because the acid was able to penetrate between the domains allowing access to a larger surface area and consequently accelerated dissolution. The points of zero charge increased with increasing surface area of the goethite. The charge carried by the goethite at pH values distant from the point of zero charge increased as the surface area increased. This may indicate movement of protons or hydroxyl ions into pores or other defects in the crystal. The effects of pH and of salt concentration on surface charge were closely described by the variable-charge/variable-potential model. This model also closely described adsorption of Ca2+ and Cl− from calcium chloride solutions requiring only the allocation of constants for these ions. The substitution of aluminium for iron did not affect the charge properties of goethite.

Notes: The determination of the structure of humic substances from peat soils and natural waters is a major problem in soil science. Humic substances are chemically heterogeneous and consist of molecules covering a wide distribution of molecular size. A quantity related to both molecular size and structure in the hydrated state is the volume of the humic molecules per unit mass or partial specific volume (ν2). The partial specific volumes of humic substances have been estimated from atom and chemical group volume contributions for 17 proposed structures of fulvic and humic acids taken from the literature. The results show that the partial specific volume reflects the composition of humic substances, decreasing with increase in the carbon: hydrogen (C:H) molar ratio. The more oxidized the humic material the smaller is its partial specific volume. These trends agree with our experimental measurements of partial specific volumes for a range of humic materials (aquatic fulvics, aquatic and peat humics). The predicted values of partial specific volumes for the proposed structures, however, are overestimated by approximately 15% compared to the experimental values. There is little difference between values of ν2 calculated from the detailed humic structures and those calculated from their empirical formulae; calculations of partial specific volumes using a random modelling approach leads to overestimation by approximately 37%. It seems that the estimates based on additivity of atom and chemical group volumes do not take into account an overall contraction of the structures because of hydrophobic interactions. In general terms the values of the partial specific volumes of humic substances suggest they are more compact molecules than globular proteins, and intrinsic viscometry studies suggest that aqueous salt solutions approach θ-solvent conditions for humic substances.

Notes: Stable isotopes of hydrogen and oxygen were used to trace the sources of recharge from sinking streams to wells and springs several kilometers downgradient in the karst Madison aquifer near Rapid City, South Dakota. Temporal sampling of streamflow above the swallets identified a distinct isotopic signature that was used to define the spatial dimensions of recharge to the aquifer. When more than one sinking stream was determined to be recharging a well or spring, the proportions were approximated using a two-component mixing model. From the isotopic analysis, it is possible to link sinking stream recharge to individual wells or springs in the Rapid City area and illustrate there is significant lateral movement of ground water across surface drainage basins. These results emphasize that well-head protection strategies developed for carbonate aquifers that provide industrial and municipal water supplies need to consider lateral movement of ground-water flow from adjacent surface drainage basins.

Notes: Predictive ground-water flow modeling may be simplified by application of superposition when the governing equations are linear. The simplification allows evaluation of impacts of individual aquifer stresses and minimized model input, output, and interpretation. Modeling is performed by using (1) boundary conditions and aquifer properties provided by previous calibrations or analytical techniques, (2) setting the initial potentiometric surface and prescribed-head boundaries to an arbitrary horizontal datum, and (3) simulating a specific recharge or discharge stress.Superposition was applied to an existing, calibrated model of the Snake River Plain aquifer to simplify prediction of changes in interaction with the Snake River. Simulations predict the temporal relationships between ground-water use at multiple locations within the Snake River Plain and surface-water depletion in four hydraulically connected reaches of the Snake River. Simulated aquifer water use at a location approximately five miles from a hydraulically connected river reach results in river depletions greater than 80% of the pumping rate after 10 years. Water use further than 50 miles from hydraulically connected river reaches results in depletions from 10 to 30% of the annual average pumping rate after 100 years. Results present spatial and temporal impacts of water uses on the Plain that are conceptually and quantitatively beneficial to water resources planners and water users.

Notes: The incorporation of auxiliary data into ground-water flow parameter estimation is a challenging task which can ultimately result in a better site characterization. In this study a maximum likelihood estimation procedure has been applied to the joint identification of the parameters of the aquifer transmissivity random field, and the parameters of the linear regression between the logarithm of transmissivity and the logarithm of the electrical transverse formation factor (TF), determined from surface geoelectrical methods (Vertical Electrical Sounding or V.E.S.). This approach is basically a co-kriging technique applied to the transmissivity and transverse formation factor random fields, but it avoids the independent estimation of the cross-covariances and the secondary variable covariance. The procedure needs some direct well data for transmissivity and a (usually larger) number of V.E.S. measurements which have to be in part at a distance from the well locations in order to provide useful information. The algorithm determines the characteristics of the local (site dependent) transmissivity-transverse formation factor relationship and utilizes this auxiliary information for a geostatistical transmissivity field estimation. The methodology is tested on a real field scenario: a fractured aquifer impacted by landfill leachate contamination. The use of the formation factor in place of the raw resistivity of the subsoil layers accounts for possible effects of clay and contaminant concentration on pore-water resistivity. The information provided by the V.E.S. can add, to some extent, to the understanding of the aquifer characteristics and vulnerability. However, the specificity of each site has to be fully understood for an effective application of the present procedure. It seems unlikely that geoelectric data can differentiate between transmissivity values differing by less than two or three orders of magnitude.

Notes: The prevalent and straightforward routine of impulsively collecting masses of new data for studies relating to ground-water contamination can be inefficient and costly as it does not provide optimal value from existing hydrogeologic and other information. A preliminary guidance framework is outlined, for early stage monetary risk assessments prior to any new measurements, considering both the probability and the economical consequences of contamination. The framework is aimed at providing a basis for cost-effective decision-making regarding ground-water protection and management actions. It centers on improved conceptual hydrogeological site descriptions based on existing information and professional judgments prior to any new measurements. A key aspect of the framework is to derive maximum possible quantitative understanding of risks from limited prior available qualitative information. The framework has a dual-site approach, assuming a situation of a contaminant source site and a receptor site. A two-step procedure leads to the monetary risk assessment with respect to existing compliance levels: (1) conceptual model development, and (2) quantitative model realization, addressing the probability of contaminant release at the contamination source, the hydraulic connection between the source and the receptor, and the contaminant transport conditions. The purpose of the framework is twofold: (1) to provide a risk assessment framework which optimizes use of professional judgment for studies where data are limited, and (2) to give synergistic interpretive values that complement field measurements and that can be used as prior estimates in more detailed studies.

Notes: An analytical model for evaluating mass leaching from contaminated soil or soil stabilized waste is presented. The model is based on mass transport due to advection, dispersion, and retardation and can be used to evaluate the suitability and/or efficiency of soil washing solutions based on the results of column leaching studies. The model differs from more traditional models for column leaching studies in that the analysis is based on the cumulative mass of leachate instead of leachate concentration. A cumulative mass basis for leaching eliminates the requirement for determination of “instantaneous” effluent concentrations in the more traditional column leaching approach thereby allowing for the collection of relatively large effluent volumes. The cumulative masses of three heavy metals—Cd, Pb, and Zn—leached from two specimens of soil mixed with fly ash are analyzed with the mass leaching model to illustrate application and limitation of the model.

Notes: Inverse models using, for example, nonlinear least-squares regression, provide capabilities that help modelers take full advantage of the insight available from ground-water models. However, lack of information about the requirements and benefits of inverse models is an obstacle to their widespread use. This paper presents a simple ground-water flow problem to illustrate the requirements and benefits of the nonlinear least-squares regression method of inverse modeling and discusses how these attributes apply to field problems. The benefits of inverse modeling include: (1) expedited determination of best fit parameter values; (2) quantification of the (a) quality of calibration, (b) data shortcomings and needs, and (c) confidence limits on parameter estimates and predictions; and (3) identification of issues that are easily overlooked during nonautomated calibration.

Notes: The ability to predict the transport of dissolved gases in the presence of small amounts of trapped gas in an otherwise water-saturated porous medium is needed for a variety of applications. However, an existing model based on equilibrium partitioning of dissolved gas between aqueous and trapped gas phases does not accurately predict the shape of experimentally observed breakthrough and elution curves in column experiments. The objective of this study was to develop and test a kinetic model for dissolved gas transport that combines the advection-dispersion equation with diffusion controlled mass transfer of dissolved gas between the aqueous and trapped gas phases. The model assumes one-dimensional, steady-state ground-water flow, a single dissolved gas component, and a stationary trapped gas phase with constant volume. The model contains three independent parameters: the Peclet number, P, retardation factor, R, and dimensionless mass transfer parameter, ω. The model accurately described the shape of breakthrough and elution curves for dissolved oxygen in column experiments performed with a poorly graded sand and varying amount and composition of trapped gas. Estimated values of P for the bromide tracer increased from 5.92 to 174, corresponding to a decrease in dispersivity from 5.02 to 0.17 cm, as the trapped gas volume increased from 0 to 30% of the pore space. It is speculated that this effect is due to a narrower pore size distribution (and hence more uniform pore scale velocity distribution) caused by trapped gas bubbles selectively occupying the largest pores. Estimated values of R increased from 1 to 13.6 as the trapped gas volume increased and confirmed earlier observations that even small amounts of trapped gas can significantly reduce rates of dissolved oxygen transport. Estimated values of ω ranged from 0.3 to 12.1. Although it was not possible to independently measure mass transfer coefficients or interfacial areas, values computed from flow rates and estimated w values are consistent with values computed by assuming (1) that interfacial area is proportional to trapped gas volume, (2) that trapped gas bubbles are spheres with diameters the same size as soil particles, and (3) that mass transfer is limited by diffusion of dissolved oxygen through water films surrounding trapped gas bubbles.

Notes: Contamination of soil and ground water due to spills of light nonaqueous phase liquids (LNAPL or simply oil) is a widespread environmental problem. This paper describes the development and testing of a semianalytical model that may be used to design LNAPL containment and recovery systems at spill sites. The objective of this study was to derive an enhanced semianalytical algorithm for calculating recovery and trapping of free phase oil. The enhancements were derived and evaluated by comparison with an established numerical model that describes transient flow of oil and water. The semianalytical model employs an analytical solution for steady-state drawdown in an unconfined aquifer due to water pumping. When pumping rates are sufficient to contain the separate phase plume, the model calculates recoverable and residual oil volumes based on the initial free oil distribution. Refinements were implemented to calculate the water-table drawdown and the maximum unsaturated zone residual saturation (Sog) as functions of soil type. Also the influence of hysteresis on the oil-water capillary fringe was incorporated into the calculation of oil trapping below a rising oil-water interface. A method was derived to reduce saturated zone trapping to account for oil recovery that occurs while pumping proceeds. The above enhancements yielded close agreement between the semianalytical model and the transient model predictions of recoverable oil and residual oil in the unsaturated and saturated zones. The models were compared for hypothetical gasoline spills in a sandy and a silt loam soil, using a range of pumping rates and regional water-table fluctuations. Field data from a pipeline leak were evaluated by the semianalytical model for hypothetical scenarios involving oil recovery from three wells and a falling regional water table. Results suggest that the semianalytical model captures many of the trends of transient oil recovery. Recovery is less accurately predicted when irregular water-table fluctuations occur.

Notes: Bedding-plane partings, particularly those enlarged by stress relief, tend to provide principal ground-water flow pathways which are often overlooked. In order to identify them, the use of a proper conceptual model of the bedrock aquifer system and appropriate methods of hydrogeologic characterization are necessary. Several pervasive bedding partings were identified at a study site located within a dipping sequence of mudstone and shales, typical of the Passaic Formation in the Newark Basin of New Jersey. These bedding fractures constitute the discrete aquifer units of a multiunit, leaky bedrock aquifer system. One such unit of exceptional transmissivity (the “Raritan unit”) was identified and selected for a detailed characterization. Results of three short-duration pumping tests verified the continuity and relatively uniform transmissivity of the Raritan unit over distances exceeding 1,500 feet. Significant hydrochemical differences between the various aquifer units at this 100-acre site were found to be consistent with the multiunit structure of the bedrock aquifer system. A similar pattern can be observed in regional hydrochemical data recently published by others. The principal finding, that a few bedding fractures dominate ground-water flow at many sites in the region, has a major implication on hydrogeologic characterization requirements for the water supply, well-head protection, and aquifer remediation projects in the Newark Basin and similar areas of sedimentary bedrock.

Notes: It has generally been recognized that molecular diffusion can be a significant process affecting the transport of carbon-14 in the subsurface when occurring either from a permeable aquifer into a confining layer or from a fracture into a rock matrix. An analytical solution that is valid for steady-state radionuclide transport through fractured rock is shown to be applicable to many multilayered aquifer systems. By plotting the ratio of the rate of diffusion to the rate of decay of carbon-14 over the length scales representative of several common hydrogeologic settings, it is demonstrated that diffusion of carbon-14 should often be not only a significant process, but a dominant one relative to decay. An age-correction formula is developed and applied to the Bangkok Basin of Thailand, where a mean carbon-14-based age of 21,000 years was adjusted to 11,000 years to account for diffusion. This formula and its graphical representation should prove useful for many studies, for they can be used first to estimate the potential role of diffusion and then to make a simple first-order age correction if necessary.

Notes: The concepts of two-way coordinates and one-way coordinates are used to describe the different characteristics of two key aquifer parameters, transmissivity and storativity, under constant-rate pumping conditions. A two-way coordinate is such that the conditions at a given location are influenced by changes in conditions on either side of that location; a one-way coordinate is such that the conditions at a given location are influenced by changes in conditions on only one side of that location. Results from sensitivity analysis indicate that storativity has the characteristics of two-way coordinates, but transmissivity has the characteristics of one-way coordinates, i.e., its information can be transferred mainly from upstream to downstream. An upstream observation well can produce information on storativity both upstream and downstream, but it can produce little information on transmissivity downstream.These characteristics of the aquifer parameters have important implications on pumping-test designs and interpretation. For example, to estimate the parameters of an anomalous zone in an aquifer, an observation well should be located downstream but near the zone. It should not be placed upstream if the parameters downstream are to be estimated. An observation well which can provide adequate information for estimating storativity may not provide adequate information for estimating transmissivity, and vice versa. The aquifer area represented by estimated storativity may be different from that represented by estimated transmissivity.

Notes: Subsurface brines in the Sichuan Basin occur within sedimentary rocks ranging in age from Sinian to Cretaceous, especially within rocks of Triassic age. The chemical and isotopic compositions of the brines and general geological considerations suggest that the Sichuan Basin brines are derived from waters of different origin. Water in brines from Upper Cretaceous clastic reservoirs in Anren, and from basin margin aquifers of Lower Jurassic, Triassic, and Cambrian age are modern meteoric in origin. Salinity in these brines is from dissolution of salt-bearing formations. Lower Jurassic and Upper Triassic clastic aquifers contain a mixture of meteoric water and brines from older rocks based on isotopic data. Brines in Middle and Lower Triassic carbonate aquifers originated from sea water and are residual brines left after evaporite precipitation. Brines from the Upper Sinian carbonate aquifer in Weiyuan originated from sea water mixed with magmatic waters.

Notes: Many piezometers/wells produce at such low rates and frequency that their impact on local hydraulics is negligible, e.g. monitoring piezometers or homeowner wells installed in highly permeable soils. Defining a deterministic capture zone for such wells is often of limited utility as the capture zone is effectively a single flow line directed upgradient. In order to provide more insight into the capture zone of such wells, a statistically based capture zone, termed a “percentile capture contour” (PCC), is introduced and analyzed. The capture zone is defined by quantifying, for a given travel time, the variation of the length and orientation of the flow line emanating upgradient from the well. Capture zone variation herein depends on second-order stationary random hydraulic conductivity fields and is calculated using Monte Carlo analysis.Monte Carlo analysis yielded increases in mean travel distances as the variance and/or integral scale in log K increased, but decreases as the angle between the principal direction of the correlation structure and the regional flow increased. The average travel distance exceeded the travel distance estimated by a homogeneous solution using the geometric mean hydraulic conductivity. Transverse variation depended both on the variance and integral scale of log K, but was insensitive to the orientation of the principal correlation direction. The mean orientation of the flow path varied with the principal direction of the correlation structure, deviating up to 20° from the orientation of the hydraulic gradient. These observations are consistent with flow following preferential pathways and indicate that significant uncertainty exists for source prediction of water feeding passive wells.

Notes: A case study of a leaky fluvioglacial aquifer concentrates on methods of estimating the zonated log10-transmissivities of a regional-scale ground-water model covering 450 km2. Mainly three estimation methods are discussed: (a) kriging based on local measurements and predictions, (b) hydrologic inversion (i.e., nonlinear regression) based on head data, and (c) hydrologic inversion based on head data and on prior estimates from kriging. (a) Due to the shortage of data which is usual in heterogeneous aquifers, the present study questions the practical value of forming zonal kriging estimates from local data whenever estimates are to be used as an input to ground-water models. In some parts of the homogeneous aquifers local data are sufficient to make such estimates, (b) In this study zonal hydrogeological parameters can be estimated by inversion based on head data. However, inaccuracies in head data may seriously damage the reliability of estimated parameters and, as a consequence, the ground-water model, (c) Using zonal kriging estimates as prior information in the regression reduces the width of the confidence intervals of the parameters with prior information by up to 75%. The study indicates, however, that using prior information in the estimation of the hydrologic model parameters only minimally reduces the uncertainty of the predicted hydraulic heads.For this specific case, the results suggest that in order to parameterize and identify the parameters of the ground-water model one should concentrate on qualitative mapping of the hydrogeology, on sampling accurate head data and on subsequent estimation of the zonal parameters by inversion (or manual calibration).

Notes: Nonaqueous phase liquid (NAPL) is a long-term source of ground water contamination as the pollutant slowly partitions into the air and water phases. The objective of this work was to study the efficacy of aqueous surfactant solution to enhance the dissolution of a residual NAPL below the capillary fringe, hence reducing the time needed for aquifer restoration. An analytical technique was developed to measure the concentration of NAPL in a nonionic surfactant. Soil column experiments simulated conditions in the saturated soil where a NAPL may become trapped as a discontinuous immobile phase. Experimental results indicate that dissolution was a rate-limited process, approaching equilibrium concentrations after 24 hours. The relative permeability of the aqueous phase initially decreased as surfactant was injected, but increased over time as the saturation of residual NAPL was reduced through mass transfer into the surfactant-enhanced aqueous phase. These findings suggest that enhancing the aqueous phase with a nonionic surfactant may significantly enhance the in situ recovery or residual NAPL.

Notes: The leaching of chromium-copper-arsenic salts from old wood preservation sites is a threat to ground water at many places in Sweden. The installation of in situ reactive barriers is an attractive “passive’ technique to prevent the further spreading of contaminants. The use of peat as a reactive barrier material has been suggested for heavy metals, but this material was expected to be unsatisfactory for arsenic (As). Therefore, the feasibility of using spodic B horizon material for the retention of arsenic was tested in laboratory column experiments. Contaminated soil was taken from an old preservation site and leached under conditions designed to imitate the field conditions. The arsenic load during the three-month duration of the test corresponded to a load at the field site during three years. The B horizon material proved to be efficient for retention of arsenic, despite the observation that As(III) dominated the As speciation. The As(III) concentration was reduced from 1 to 3 mg dm−3 to 〈 0.02 mg dm−3. Pure peat was, as expected, not suited as a reactive barrier for As, and a mixed B horizon/peat reactive barrier also proved unsatisfactory for the removal of As. It is therefore important to separate the B horizon material from any peat that is used to sorb heavy metals. Before applying the B horizon reactive barrier technique in the field, the effect of the naturally occurring variability of the reactive compounds should be tested. The inclusion of oxidizing agents in the barrier could possibly improve the lifetime considerably. Furthermore, the influence of the flow rate should be evaluated since the kinetics of the arsenic adsorption is relatively slow.

Notes: As landfill specifications become more stringent in the United Kingdom, the development of increasingly sophisticated monitoring methods is necessary to meet environmental protection goals. This case history describes the development of a 2-million-cubic-meter-capacity landfill located in a sandstone quarry and 1 km from a public water supply borehole, where the sensitivity of the site to ground water contamination and the proximity to a public water supply borehole are particular issues.The landfill design incorporated a more sensitive environmental monitoring system, using a geophysical technique. The monitoring system comprises a permanent grid of electrodes installed beneath the landfill, connected by multicore cable to a computer-controlled earth resistance meter and switching unit in the site weighbridge. It was designed to detect holes in the landfill liner prior to and after covering with waste and to monitor the migration of contaminants beneath the landfill before they reach the perimeter observation boreholes, should leakage occur.Such monitoring can enable the integrity of the landfill to be routinely reviewed; holes can be repaired if they are readily accessible and, if not, monitoring provides an early warning to enable the implementation of any additional monitoring or corrective action, based on the environmental risk posed by the site.The system was first used as a quality assurance test once the landfill liner, which covered an area of 3 hectares, was installed. The system proved sensitive, detecting a hole consisting of two narrow knife cuts. Such sensitivity allows a high degree of confidence to be placed upon the integrity of the liner resulting in a significant contribution to public reassurance. The landfill is now operational, and monitoring using the geophysical system will be undertaken on a monthly basis for the first year, with the frequency of monitoring reviewed thereafter.

Notes: Arrays of unpumped wells can be used as discontinuous permeable walls in which each well serves both as a means to focus ground water flow into the well for treatment and as a container either for permeable reactive media which directly destroy dissolved ground water contaminants or for devices or materials which release amendments that support in situ degradation of contaminants within the aquifer downgradient of the wells. This paper addresses the use of wells for amendment delivery, recognizing the potential utility of amendments such as electron acceptors (e.g., oxygen nitrate), electron donors (primary substrates), and microbial nutrients for stimulating bioremediation, and the potential utility of oxidizers, reducers, etc., for controlled abiotic degradation. Depending on its rate and constraints, the remedial reaction may occur within the well and/or downgradient. For complete remediation of ground water passing through the well array, the total flux of amendment released must meet or exceed the total flux demand imposed by the plume. When there are constraints on the released concentration of amendment (relative to the demand), close spacing of the wells may be required. If the flux balance allows wider spacing, it is likely that limited downgradient spreading of the released amendment will then be the primary constraint on interwell spacing. Divergent flow from the wells, roughly two times the well diameter, provides the bulk of downgradient spreading and constrains maximum well spacing in the absence of significant lateral dispersion. Stronger lateral dispersion enhances the spreading of amendment, thereby increasing the lateral impact of each well, which allows for wider well spacing.

Notes: For this statewide assessment, 1808 wells were; sampled and a data base compiled that included water-quality data (NO3-N, pesticides, coliform bacteria) and site-specific data collected at each location. Domestic, rural Water quality in Nebraska varies substantially from one ground water region to another and is a function of well characteristics, distances to potential contamination sources, and hydrogeologic and site characteristics. The percentage of wells exceeding the 10 ppm MCL for NO3-N ranged from 3 to 39 percent, depending on the ground water region. This large range of values indicates the inadequacy of stating that an average of 19 percent of domestic wells in Nebraska are contaminated by nitrates. This statistic does not describe the nature, extent, and variability of the contamination problem. Depending on the ground Water region, the degree of nitrate contamination in rural domestic drinking water wells has remained generally unchanged or has only slightly increased since the last statewide assessment conducted from 1985 to 1989. Bacterial contamination has either remained the same or has decreased. The percentage of wells affected by bacteria ranged from 8 to 26 percent, depending on the ground water region. Statewide, about 70 wells, or 4 percent of the wells sampled, had detectable pesticide levels, of which atrazine was the most common. Eighty-two percent of the detections were in the Platte River Valley of in the South Central Plains, both of which are characterized by heavily irrigated corn and a statistical association between nitrate and atrazine contamination. To improve the quality of domestic drinking water will require a combination of activities, including the application of best management practices specific to a ground water region and individual action at rural households, such as conducting sanitary surveys of existing wells before installing new wells.

Notes: An algorithm is presented that allows estimation of the saturation and composition of a single of multi-component NAPL within a core sample. These estimates are possible because, in addition to distributing the organic chemicals between aqueous, sorbed, air, and NAPL phases according to traditionalpartitioning equations, the algorithm incorporates equations for the conservation of mass and volume. A unique solution is obtained by solvihg the set of nonlinear equations implicitly. The algorithm is built into a code called NAPLANAL, which is tested and applied to actual core samples collected in the field.

Notes: Current site assessment techniques do not always generate adequate information regarding the presence, type, or distribution of nonaqueous phase liquids (NAPLs) at sites with ground water contamination. Without this information, however, the design of remediation methods is uncertain, often resulting in costly and/or failed attempts to minimize risks associated with the contamination. In this work, it is proposed that a thorough multivariate analysis of data from ground water sampling efforts could improve our overall understanding of these sites. Multivariate analyses can provide considerable insight into the contaminant source characteristics by elucidating correlations in ground water concentrations that identify recurring chemical patterns or “signatures.” These correlations are related to the type of NAPL and proximity to the contaminant source.Multivariate plots and a principal components analysis (PCA) are used to interpret ground water data from a manufactured gas plant site in Iowa contaminated with both gasoline and coal tar. Conclusions from these analyses regarding the distribution of NAPL contaminants were generally consistent with those derived from direct physical evidence of the NAPL sources. The multivariate analyses, however, provide an additional level of interpretation regarding the distribution of coal tar in the subsurface that was not possible with the standard evaluation techniques used during the remedial investigation (RI). Comparison of chemical signatures of ground water samples among wells identified two distinct regions of coal tar contamination, and suggests which wells are impacted by each source providing greater confidence in the location of the DNAPL sources.

Notes: A laboratory study was conducted to determine the effectiveness ol vertical and horizontal well configurations for ground water remediation using in situ air sparging. A lexan lank was designed and constructed to allow both the visualization of air flow and quantitative measurement of the distribution of air flow. Two media, sand and glass beads. were tested with both Vertical and horizontal air sources. In each case, most of the air traveled through preferential channels as continuous flow rather than as discrete bubbles as reported in other studies. Liven though glass beads were selected to have the same grain-size distribution as the sand, air flow was quite different through the two media. Results show that glass beads are not a suitable material for modeling air flow through natural sediments. In this study, the horizontal well proved to be more effective than the vertical well by impacting more of the media with a uniform distribution of air throughout the media. The vertical well resulted in a nonuniform distribution of air flow with most of the air concentrated directly above the well.

Notes: Trichloroethene (TCE) was reduced with zero-valence iron and palladized iron in zero-head-space extractors. Progress of the reaction in these batch studies was monitored with purge-and-trap gas chromatography and a flame ionization detector. When a 5 ppm initial concentration of TCF. reacts with zero-valence iron, approximately 140 ppb of vinyl chloride persists for as long as 73 days. The concentration of vinyl chloride (approximately If) ppb) remaining with palladized iron is approximately an order of magnitude less than when zero-valence iron is the reductant. These data suggest that volatile byproducts may be under-represented in oilier published data regarding reduction with zero-valence metals. These results also demonstrate that the reduction of TCE with palladized iron (0.05 percent palladium) is more than an order of magnitude faster than with zero-valence iron. Wilh a 5:1 solution-to-solid ratio the TCE half-life with zero-valence iron is 7.41 hours. but is only 0.59 hours with the palladized iron.

Notes: Sea foam and sea-surface films are pelagic habitats of common origin. This suggests a possible similarity between their microplanktonic assemblages and an a priori possibility to use foam samples in qualitative sea-surface film studies. The composition and abundance of microheterotrophs (nanoflagellates 〈5 μm and bacteria) in the Dalnezelenetskaya Inlet, Kola Peninsula, Barents Sea, in August 1987, was nearly identical in the foam and sea-surface film samples. In contrast, the enrichment of foam with autotrophs (nano- and microphytoplankton) exceeded by an order of magnitude that of sea-surface films, whereas their taxonomic compositions were virtually identical in both habitats. Elevated growth rates of phytoplankton in sea foam appear to be an ecological mechanism responsible for the enrichment.

Notes: An 8 m long carcass of a bowhead whale (Balaena mysticetus) melted out from remnant glacier ice in the lateral moraine of the Jemelianovbreen glacier in August 1996. Folded and sheared sediment bands in the ice suggest that the whale was incorporated during an advance of the glacier. The whale's longitudinal axis was oriented parallel to the direction of the ice-flow, with the thinnest posterior part dipping upflow. The posterior section was best preserved with muscles and blubber, although the entire skin surface was strongly decomposed and only a thick fibrous surface was left of the blubber. The abdominal wall was holed, most likely by marine organisms, and partly filled with a compacted mixture of well-sorted gravelly beach sediments and fat. the whale seems to have been incorporated into the glacier together with glaciomarine sediments and carried by the flowing ice to an altitude of ca. 15 m. Jemelianovbreen is a tidewater glacier with two known surge-episodes. The first and most extensive of these occurred ca. 1900 AD and reached ca. 7 km outside the present coast-line. Radiocarbon dating of a fragment of a caudal vertebra yielded 345 ± 40 14C years BP (1535-1660 cal. AD), suggesting that the whale lived some time during the last part of the cold period known as the Little Ice Age.

Notes: The effect of egg volume on body mass, body composition and growth rate in arctic tern Sterna paradisaea chicks was studied at Ny-Ålesund, on Svalbard (78°55'N, 12°00'E), in order to investigate whether differences in egg size influence the physiological characteristics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large eggs had larger body masses than hatchlings from small eggs, with 71% of the overall variation in body mass accounted for egg volume. In newly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in proportion to egg volume. Hatchlings from large eggs, however, had disproportionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, indicating that the leg muscles of small hatchlings were functionally more mature. There was a weak, but significant, correlation between egg volume and growth rate. However, a residual analysis made to eliminate the effect of egg volume showed no correlation between hatchling body mass and growth rate. The results of the present study show that Arctic tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During embryonic growth in small eggs, however, there seems to be a greater relative usage of yolk, resulting in a more developed leg musculature. This may partly compensate for the higher mass-specific heat loss in small hatchlings.

Notes: Morphological structures and the occurrence of sea-ice sediments and ice-related algae at the ice floe-water column interface were studied by video observations in summer 1995. Recordings at twelve stations in the northern Laptev Sea and the adjacent Arctic Ocean showed large variations. On a medium-scale (metres), level ice and deformed floes as well as whole rafted and stacked floes were found. At the underside of floes, small-scale structures (centimetres such as bulges, depressions and holes were observed. The surface and sides of rafted floes sometimes had downward running grooves. Sediment inclusions occurred in diffuse or concentrated forms as well as in parallel streaks. Ice-related algae were visible as green areas at the underside of floes or as threads haniging into the water column. The distribution of sediments and algae was patchy. Some processes which might lead to the observed structures are suggested.

Notes: The existence of a large subglacial lake beneath the antarctic Ice Sheet at Terre Adélie indicates the presence of basal ice at its pressure-melting temperature. A numerical model of the ice-sheet thermal regime is employed using the balance velocity of the ice sheet as an initial model input in order to calculate ice-sheet basal temperatures. However, the results from this model show the Terre Adélie area to be characterised by basal freezing. Heat in addition to that accounted for in the model is thus required at the ice-sheet base in order for pressure melting temperatures to be attained. The sources for such heat are (1) an enhanced geothermal heat flux and (2) an increase in frictional heating caused by the flow of ice. In this paper the latter possibility is expanded by hypothesising that subglacial topography induces convergent ice flow around Terre Adélie, causing enhanced basal ice velocities. Model experiments indicate that an increase in ice velocity (from 7 to at least 42 m yr−1) is required to raise the temperature of the basal ice to the pressure melting value. Increased ice velocity, and consequent frictional heat production due to convergent ice flow, may therefore be important in explaining the location of the subglacial lake in this region. These results allow the process of convergent ice flow within a contemporary ice sheet to be quantified. A verification (or otherwise) of the model results may be possible if ice surface velocity measurements from modem GPS methods are made.

Notes: Argand (1924) and later Holmes (1965) proposed that the Himalayan orogeny and Tibet uplift were the result of large underthrusting of the Indian continental crust beneath Tibet. Since then, plate motion studies have yielded new constraints on the relative displacements of India and Asia and a large number of geological and geophysical investigations have helped to determine the structure of the Himalayas and Tibet, the best natural laboratory for understanding mountain belts. The aim of this paper is to review briefly the various models of Himalayan mountain building in light of recent geological and geophysical data and to estimate the role of continental subductions.

Notes: Ion-microprobe U-Pb zircon ages of detrital zircons from a metasediment of the Loch Maree Group, Lewisian Complex, NW Scotland show striking similarities to those in coeval Palaeoproterozoic belts of Laurentia and Fennoscandia, and confirm previous suggestions of a connection between them. Late-Archaean zircons (3.06–2.48 Gyr old) represent derivation from Lewisian quartzofeldspathic gneisses, andlor a contemporaneous terrane. Palaeoproterozoic zircons (2.2–2.0 Gyrold) place a maximum age constraint upon deposition. An appropriate quartzofeldspathic source for these latter zircons is not presently known, either in the Lewisian or the wider Laurentia-Fennoscandia region, although its requirement would be consistent with a development of the Loch Maree Group, together with juvenile magmatic arc rocks, at an active margin which was probably removed by lateral tectonics. Comparisons are made with contemporaneous supracrustal sequences throughout the Laurentia–Fennoscandia region, which exhibit marked similarities in source region age characteristics, lithologies, and inferred depositional environment.

Notes: Geological observation in the eastern end of the Himalaya shows that the Asia/India Suture is folded. Metamorphic rocks derived from India occur structurally below the suture, in the core of a regional antiform. Isotopic and fission track dating establish cooling-exhumation of rocks from c.30 km depth within the last 4 Myr. We argue that exhumation is caused by ∼ 10 mm yr-1 erosion coeval with crustal scale folding.

Notes: The Early Cretaceous carbonate carbon isotope stratigraphy established in pelagic limestones is marked by several pronounced excursions towards positive δ13C values. We investigated a biostratigraphically and palaeomagnetically calibrated Aptian section to see whether C isotope stratigraphy could be recognized in shallow-water carbonates. The chosen carbonate platform sections are located in southern Italy and have been dated by biostratigraphy. Bulk samples, chosen from the Barremian-Albian part of the sequence, were analysed for their O and C isotope compositions. The C isotope curve established shows two major positive excursions which can be correlated with the synchronous and globally recognized Aptian C isotope events. The data provide evidence that C isotope stratigraphy can be used as a powerful correlation tool between pelagic and shallow-water limestone sequences.

Notes: The frequently observed parallelism between rifts and the preexisting orogenic fabric of continents suggests that the inherited tectonic fabric of the lithosphere influences the rupture of continents. We propose that the existence of a pervasive fabric in the lithospheric mantle induces an anisotropic strength in the lithosphere, that guides the propagation of continental rifts. Subcrustal mantle mechanical anisotropy is supported by (i) the anisotropic strength of olivine, (ii) an ubiquitous tectonic fabric in exposed mantle rocks, and (iii) measurements of seismic and electrical anisotropy. During major episodes of continent assembly, a pervasive deformation of the lithosphere induces a lattice-preferred orientation of olivine in mantle rocks. Later on, this crystallographic fabric is ‘frozen-in’ and represents the main source of shear wave splitting. This olivine fabric may entail a mechanical anisotropy in the lithospheric mantle. During subsequent tectonic events, especially during rifting, mechanical anisotropy may control the tectonic behaviour of the lithosphere

Notes: Modern terrestrial speleothem-like calcareous deposits in streams draining a disused lime quarry on Black Mountain, South Wales have anomalously negative δ18O and δ13C compositions compared with other similar European deposits. Black Mountain water chemistry is unusual only in its locally very high pH (〉 11.5) and carbonate ion concentrations. The high pH is caused by dissolution of lime spoil, resulting in high OH– concentrations. This high alkalinity causes uptake of atmospheric CO2 and strong fractionation of both carbon and oxygen stable isotopes, resulting in calcite precipitates with unusually negative isotopic compositions. Since shifts in δ18O of 〈 1° are highly significant for Holocene palaeoclimate reconstructions, depletions caused by hyperalkaline waters must be avoided. While extreme lime spoil contamination should be obvious, less heavily affected sites will record smaller fractionation effects and might escape detection. Even small depletions from low-level contamination will have large effects on palaeotemperatures based on carbonate crust δ18O values.

Notes: Structural mapping in the Southern half of the Oman ophiolite has revealed a palaeoridge organization with similarities to an EPR microplate, forming in superfast spreading conditions. A NW-trending propagator was rapidly opening in a lithosphere no more than 1 Myr older and itself created in a NE-SW ridge system. The NW-trending propagator, underlined by small mantle diapirs, was active or dying when detached as part of a future ophiolite. Local thrusting of the future ophiolite was also initiated very early, between 1 and 5 Myr after ridge accretion; it was accompanied by a 40° rotation within this time lapse. Such an activity supports the comparison of the Oman palaeoridge system with an oceanic microplate, and provides evidence to suggest the existence of thrusts at active microplates.

Notes: Large variations in clinopyroxene-garnet (cpx-grt) temperatures are recorded in thin peraluminous eclogite layers from Beni Bousera ultramafic massif (Morocco): cpx-grt temperatures in the core of layers 〈 20 cm thick are higher by up to 300°C than in the margins. The cpx-grt temperatures are correlated to both Al-concentration in cpx and Ca-concentration in grt, the two latter parameters being themselves closely intercorrelated. It is demonstrated that the regular interaction parameter ΔwgrtCa calculated from the Beni Bousera natural data is very close to ΔwgrtCa calculated from experimental data analysis for Ca-rich garnet. It is concluded that: (i) Al-concentration in cpx has no significant effect on the distribution of Fe and Mg between cpx and grt; and (ii) cpx-grt temperature variations observed across Beni Bousera peraluminous eclogite layers do not correspond to real thermal gradients, but merely result from the inadequacy of the thermometric equations in Ca-rich systems (XgrtCa 〉 0.15).

Notes: The Kostomuksha greenstone belt consists of two lithotectonic terranes, one mafic igneous and the other sedimentary, separated by a major shear zone. The former contains submarine 2.8 Gyr old komatiite-basalt lavas and volcaniclastic lithologies with trace element and isotopic compositions resembling those of recent oceanic flood basalts [ɛNd(T) =+ 2,8, μ.1= 8.73 (Nb/Th)N= 1.5–2.1 (Nb/La)N= 1.0–1.5]. We suggest that the mafic terrane is a remnant of the upper crustal part of an Archaean oceanic plateau derived from partial melting of a mantle plume head. When the plateau reached the continental margin, it collided with the sedimentary terrane but was too buoyant to subduct. As a result, the volcanic section of the plateau was imbricated and obducted thus becoming a new piece of continental crust. The deeper zones were subducted and disappeared from the geological record.

Notes: General Circulation Models (GCMs) are currently used to predict future global change. However, the robustness of GCMs can, and should, be evaluated by their ability to simulate past climate regimes. Their success in ‘retrodiction’ can then be assessed by reference to the testimony of the geological record. Geological evidence provides a database which can be used in the estimation of sea surface temperatures and other proxy data useful in palaeoclimatic studies. These data can then be used to refine the prescribed boundary conditions for running GCMs themselves. Results of modelling experiments confirm a generally warmer Mesozoic earth with arid tropics and convective rainfall higher over the oceans than at present. Circum-polar wetlands are also indicated. Modelled cloudiness is also higher in the Mesozoic, contributing to greenhouse conditions and possibly influencing terrestrial biomes and marine ecosystems.

Notes: The sealing efficiency of shale layers is studied through the hydraulic parameters which are required for sustaining overpressure during geologically significant periods. Assuming a 1D sedimentary complex composed of a sealing layer overlying a permeable one, we give approximate solutions for the dissipation of a given initial overpressure. The time constant for relaxation involves the thickness, hydraulic conductivity and specific storage of the seal and also those of the permeable layer. The values of the various hydraulic parameters are discussed. It is argued first that the specific storage corresponding to plastic deformation during burial compaction is larger than the one which would correspond to elastic deformation. When taking into account (i) plausible values for specific storage of the upper shale layer and (ii) the storage effect of the lower permeable layer, it is found that a shale layer of several tens of m with an hydraulic conductivity of the order of 10-15 ms-1 maintains overpressure for 1 Myr. For such hydraulic parameter values, in the absence of on-going pressuring forces, initial overpressures would decay with a time constant (corresponding to a decrease by a factor e ∼, 2.7) of 1 Myr. This is interpreted as supporting a dynamic origin for observed abnormal pressures.

Notes: An integrated interpretation of seismicity, fault plane solutions and deep seismic reflection data suggests that the NE–SW to NW–SE trending Rhone–Simplon fault zone and the gently S-dipping basal Penninic thrust separate fundamentally different stress regimes in the western Swiss Alps. North of the Rhone-Simplon fault zone, strike-slip earthquakes on steep-dipping faults within the Helvetic nappes are a consequence of regional NW–SE compression and NE–SW extension. To the south, vertical maximum stress and N–S extension are responsible for normal mechanism earthquakes that occur entirely within the Penninic nappes above the basal Penninic thrust. Such normal faulting likely results from extension associated with southward movements (collapse) of the Penninic nappes and/or continued uplift and relative northward displacements of the underlying Alpine massifs. Geological mapping and fission-track dating suggest that the two distinct stress regimes have controlled tectonism in the western Swiss Alps since at least the Neogene.

Notes: The distribution of barium and other elements related to biological productivity has been studied in two Palaeocene sections from the Middle East. In the bathyal Ben Gurion section, Israel, Ba* (= Ba/Al2O3× 15%) concentrations are low, in the range 0.04% to 0.3% in the lower Palaeocene, and very high, 1% to 2%, throughout most of the upper Palaeocene. In the neritic Gebel Aweina section in Egypt Ba* values are low, 〈 0.1%, throughout the entire Palaeocene. The Ba* enrichments at Ben Gurion and their correlations with increases in P2O5 and opaline silica, and local and global δ13C maxima, indicate that upwelling and high productivity were important in this region during the late Palaeocene. The absence of Ba* enrichments in the shallower Gebel Aweina section probably reflects the strong depth dependence of biobarium deposition.In the uppermost Palaeocene, at the level where the global benthic extinction event is registered, Ba* concentrations in the Ben Gurion section increase to anomalous 6%. which suggests that upwelling and possibly wind strengths intensified during this event. The results speak against deep-water formation in this region since downwelling and not upwelling is required.

Notes: Many ductile shear zones are interpreted to operate by simple shear flow but some form under other flow regimes. Lineations and foliations in such shear zones can lie obliquely to those in simple shear zones, which can lead to erroneous tectonic interpretations on the assumption of simple shear flow. This paper describes a gently dipping shear zone system from the N-central segment of the Palaeoproterozoic Nagssugtoqidian orogen of W. Greenland, which operated with a lateral constriction component. This resulted in the development of upright folds with axes parallel to the transport direction where the constriction component is weak. Where it is strong, a linear fabric and even a subvertical foliation normal to the rotation axis of bulk flow developed. This steep foliation is interpreted as the origin of the Nordre Strømfjord steep belt, previously interpreted as a crustal-scale sinistral transcurrent shear zone. Shear zones of this type may occur elsewhere and shear zone fabrics should therefore be carefully analysed before the direction of tectonic transpost can be determined

Notes: In a series of papers, Lohmann and Lohmann (1991, 1994a, 1994b, 1996) provide evidence for remarkable sensitivity of sea-turtles to the earth's magnetic field and suggest that it is used by these animals to determine global position and to navigate. In this paper, we emphasize that a consequence of these observations taken together is that sea-turtles should be able to accurately detect the full (vector) magnetic-field, and perhaps spatial gradients. In order to interpret these observations, we propose a simple model in which the turtle is considered as a small permanent magnet, on which the geomagnetic field exerts a torque. This torque varies as a function of turtle azimuth and field parameters which depend mainly on latitude. Although this simple model accounts for some of the observational evidence, discrepancies might be due to a number of other factors, such as speed of magnetic field changes during experiments or lack of field homogeneity. Also, the earth's field has varied significantly over the last few centuries and some of the magnetic features observed today and suggested by the Lohmanns for use in sea-turtle navigation were very different or even not present two or three centuries ago. This would place constraints on the rate at which genetically inherited magnetic behavioural preferences can change with time. Alternately, it may imply that the experimental results need to be re-evaluated and complemented.

Notes: Three-dimensional patterns of soft-sediment deformation, affecting middle Pleistocene fluvial deposits in the Lower Manzanares Valley (SW Madrid City), are reported. They promote a small-scale hummocky topography, defined by different-sized domes, mud volcanoes, wavy ridges and fissures on an ancient flood plain surface. Related channel fill deposits are pervasively dewatered, indicating liquefaction. The sedimentological context reveals that the deformation of both floodplain surface and channel-fill deposits, were contemporaneous (singular deformed level) and generated at, or near, the ground surface; this rules out the possibility of sediment-loading and indicates a possible earthquake-induced origin.

Notes: The late Neoproterozoic (750–545 Ma) was a time of revolutionary environmental change, recurrent glaciation and tectonic upheaval, which culminated in the evolution of metazoans and animal biomineralization. Geochemical data are presented for a post glacial (∼ 700 Ma) limestone succession from W. Mongolia. 87Sr/86Sr is used to constrain the timing of early diagenetic exchange. Stratigraphic trends to high δ13C(carb)) and δ13C(org) mirror sea-level fluctuations, which, we argue, is consistent with the hypothesis that late Precambrian ocean chemistry, was controlled by vertical stratification. Repeated establishment of stratification 700–545 Ma would have led to greater oxygen availability in the surface environment. A causal link between this oxygenation and the further evolution of animals is proposed.

Notes: Unroofing of the western Tauern window involved both low-angle detachment faulting (Brenner Fault) and enhanced footwall erosion, contemporaneous with upright antiformal folding. This combination reflects orogen-parallel (˜E–W) extension during continued ˜N–S Alpine convergence. New fission-track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface. During exhumation, some units migrated from the footwall to the hanging wall of the main detachment fault, due to the interplay between folding and faulting. The region can effectively be divided into 3 distinct domains. (1) The Penninic units of the western Tauern Window were always in the footwall to the fault, with maximum exhumation in the core of the dome, due to folding and erosion. (2) The Lower Austroalpine unit north of the Tauern Window was first part of the hanging wall to the Brenner Fault. At a later stage this unit was exhumed by a further 4–5 km as part of the footwall to a more discrete, through-going fault (the Silltal Fault). (3) The Middle and Upper Austroalpine units west of the Tauern Window were always within the hanging wall.Exhumation of the footwall from an initial depth of ∼ 25 km led to a transition in mechanical behaviour. The curviplanar (folded) ductile shear zone marking the boundary to the Tauern window was eventually transected by a more planar discrete brittle fault (Silltal Fault, with unit 2 now in the footwall), along which the pre-existing mylonites were passively exhumed to the surface.

Notes: The Sierra Nevada core, located in the Betic hinterland, features a N-S large-scale open antiform with a central relatively uplifted highly extended domain placed between two less extended domains (in the east and in the west) dipping eastwards and westwards, respectively. The core-bounding detachment system formed during the Serravallian (15–11 Ma) in an episode of ENE-WSW extension. The ESCI-Beticas 2 deep seismic reflection profile, a transect through the core, shows a highly reflective deep crust overlying a subhorizontal Moho, and a fairly transparent upper crust and upper mantle. The lack of Moho relief beneath this area, with differential values for supra-crustal thinning, suggests a mechanism of intracrustal isostatic compensation. Surface geology data together with seismic imaging indicate intracrustal flow and upward doming as a response to footwall unloading accompanying the middle Miocene supracrustal extension. A prominent mid-crustal reflector (MCR) is deemed to represent a decoupling zone between the upper and the deep crust. Subsequent N-S shortening and associated folding occurred in the late Miocene. The interference pattern of this folding over the middle Miocene core produced the current E–W dome-shaped tectonic windows where the deepest complex of the Betic hinterland crops out.

Notes: Sedimentological evidence indicates metre-scale, cyclic changes in global sea-level during Mesozoic greenhouse climates; the cyclicity is thought to be due to Milankovitch forcing. The absence of continental ice-caps requires other mechanisms than glacier build-up to explain these variations. We propose that thermal expansion of the entire oceanic water column may partly explain the observed sea-level variations on Milankovitch timescales. Using existing climate model results, we show that an increase in deep water temperature of ∼ 2°C and a corresponding sea-level rise of 1.7 m by thermal expansion can be induced by Milankovitch forcing via increased formation of warm deep waters in low latitudes.

Notes: Cliff-front dunes are a common coastal feature, but this is the first time that the structures indicative of their formation are documented. A late Pleistocene cliff-front dune in southern Mallorca has been studied. Owing to early lithification of the calcarenite, its morphology is well preserved. The dune occurs in front of a curved, near-vertical coastal cliff, but the bedform cannot be classified as a fixed echo dune. The dune grew with time and its brinkline gradually moved closer to the cliff front. In the final stage of evolution the top of the dune reached a height of at least 23 m. The dune is composed of wind-ripple strata. These strata are arranged in critical to supercritical climbing-dune cross-stratification recording its growth stages. The angle of climb of the dune increases toward the cliff and reaches 50°. The morphological features of cliff-front dunes result from both cliff slope and whether the cliff front is curved or straight.

Notes: Compositions and distributions of mafic dykes in the Antarctic Peninsula continental arc show that tapping of several mantle sources was tectonically controlled. In the Cretaceous to Tertiary, between 135 Ma and 55 Ma, calc-alkaline dykes intruded the arc. In the late Cretaceous, however, between 95 Ma and 65 Ma, there was a pulse of compositionally diverse magmatism. This change resulted from collision of an ocean spreading centre with the trench. As a consequence, non-partitioned dextral transtensional shear in the overriding plate became partitioned into strike-slip and extensional domains. Calc-alkaline magmatism was, therefore, replaced by strike-slip-related shoshonitic magmatism towards the rear-arc and extensionrelated tholeiitic magmatism towards the fore-arc. OIB-like dykes were emplaced because of the break in otherwise continuous subduction. During the early Tertiary subduction continued but ceased after a late Tertiary ridge-trench collision.

Notes: The effect of parameter uncertainty and overly conservative measures on risk assessment has been addressed in numerous researches. Most of the work conducted to date is based on the use of the classic Monte Carlo simulation method (MCS) as a probabilistic modeling tool. Although the MCS is robust and asymptotically convergent, it lacks computational efficiency when the simulated probability is small. Furthermore, the sensitivity information can only be obtained with additional computational effort. First- and second-order reliability methods (FORM and SORM) have been developed in the structural analysis field and have been recently applied to ground-water contaminant transport and remediation problems. In this work, we extend the application of the reliability methods to the probabilistic assessment of cancer risk due to ground-water contamination. Results of the reliability methods compared well with a published case study of PCE contamination of a ground-water supply in California. The target risk level is extended over a larger range, and the sensitivity of the probability of failure to the relevant random variables is analyzed. The application of the methods to another case study, cancer risk due to the ingestion of benzene contaminated water, further illustrates a systematic way of directly accounting for the intrinsic uncertainty of the transport and fate model parameters involved in the risk assessment procedure. The probability of exceeding the target risk level in this case was found to be most sensitive to the uncertainty in the parameters describing the ground-water transport process.

Notes: Type curves derived from Theis’ exact nonequilibrium well function solution are proposed for graphical estimation of aquifer hydraulic properties, transmissivity (T), and storage coefficient (S), from water-level recovery data after cessation of a constant-rate discharge test. Drawdown (on log scale) is plotted versus the ratio of time since pumping stopped to duration of pumping, a normalized time. Under Theis conditions, individual type curves depend on only the dimensionless pumping duration, which depends in turn on S and radial distance from the pumping well. Type curve matching, in contrast to the Theis procedure for pumping data, is performed by shifting only the drawdown axis; the time axis is fixed because it is a relative or normalized time. The match-point for the drawdown axis is used to compute T, and S is determined from matching the curve shape, which depends on early dimensionless-time data. Multiple well data can be plotted and matched simultaneously (a composite plot), with drawdown at different radial distances matching different curves. The ratio of dimensionless pumping durations for any two matched curves is equal to one over the squared ratio of radial distances. Application to two recovery datasets from the literature confirm the utility of these type curves in normalized time for composite estimation of T and S.

Notes: Herbicide compounds were prevalent in ground water across Iowa, being detected in 70% of the 106 municipal wells sampled during the summer of 1995. Herbicide degradation products were three of the four most frequently detected compounds for this study. The degradation product alachlor ethanesulfonic acid was the most frequently detected compound (65.1%), followed by atrazine (40.6%), and the degradation products deethylatrazine (34.9%), and cyanazine amide (19.8%). The corn herbicide acetochlor, first registered for widespread use in the United States in March 1994, was detected in a single water sample. No reported herbicide compound concentrations for this study exceeded currem U.S. Environmental Protection Agency's maximum contaminant levels or health advisory levels for drinking water, although the herbicide degradation products examined have yet to have such levels established.The occurrence of herbicide compounds had a significant, inverse relation to well depth and a significant, positive relation to dissolved-oxygen concentration. It is felt that both well depth and dissolved oxygen are acting as rough surrogates to ground-water age, with younger ground water being more likely to contain herbicide compounds. The occurrence of herbicide compounds was substantially different among the major aquifer types across Iowa, being detected in 82.5% of the alluvial, 81.8% of the bedrock/ karst region, 40.0% of the glacial-drift, and 25.0% of the bedrock/nonkarst region aquifers. The observed distribution was partially attributed to variations in general ground-water age among these aquifer types. A significant, inverse relation was determined between total herbicide compound concentrations in ground water and the average soil slope within a 2-km radius of sampled wells. Steeper soil slopes may increase the likelihood of surface runoff occurring rather than ground-water infiltration–decreasing the transport of herbicide compounds to ground water. As expected, a significant positive relation was determined between intensity of herbicide use and herbicide concentrations in ground water.

Notes: A finite-element package has been developed for the U.S. Geological Survey Modular Ground-Water Flow Model, MODFLOW (McDonald and Harbaugh, 1988). The package, entitled the Node Centered Flow (NCF) Package, offers alternatives for constructing and solving ground-water flow problems. As with MODFLOW's Block Centered Flow (BCF) package, NCF uses a finite-difference solution for vertical flow, but unlike BCF it uses a 2d Galerkin finite-element solution for flow within a layer. The algorithm used in NCF is described in Neuman et al. (1982). This technique permits simulation within a layer of off-diagonal elements in the (2 × 2) transmissivity or hydraulic conductivity tensor. The most advantageous feature of the NCF Package is the capability for designing a nonrectangular grid. User specification of the horizontal (x, y) coordinates of individual nodes allows model features such as meandering stream channels, faults, and wells to be more precisely represented. NCF uses the same input style as BCF and will be immediately familiar to MODFLOW users; BCF input files are also easily converted to NCF input files. NCF parameters are input by layer, row, and column, allowing NCF and BCF to work with all of the same MODFLOW packages with the exception of matrix solving packages.

Notes: A sand and gravel quarry was simultaneously operated as a landfill. The underlying contaminated aquifer is unconfined at the landfill and becomes confined as it dips to the north. A ground-water model based on the MODFLOW program was developed to evaluate remediation alternatives and provide a basis for modifying the Record of Decision for the site. Hydraulic conductivities were contoured and continuously varied across the modeled area instead of defining zones of constant hydraulic conductivities. The model was calibrated by matching monthly water levels and travel times for nonadsorbing contaminants to migrate from the landfill to the extent of the contaminant plume. Drawdown data from a 72-hour pump test were used to confirm the model's ability to predict an accurate response to pumping stresses and to reduce the uncertainty of the model.Modeling indicated that ground-water recharge was required to prevent soil desaturation, minimize recontamination of ground water due to rebounding water levels, and to provide continuous flushing of the soils. The ground-water extraction system designed for the site, consisting of eight extraction wells and one recharge trench, was predicted to reverse the natural ground-water gradients observed at the edge of the contaminant plume, minimize travel distance for contaminants, and reduce contaminated ground-water flow through clean aquifer soils. Recharged water was predicted to flow through the most heavily contaminated soils and be captured primarily by two extraction wells closest to the landfill. Model results were used to successfully modify the existing Record of Decision design.

Notes: The case study presented in this paper illustrates how statistical methods can help to understand the relationships between ground-water wells and pollutant sources in alluvial systems. The observation of a time series of chloride concentrations in a specific well in Strasbourg, France, influenced by the infiltration of chlorinated water from the Rhine river, made it possible to derive a two-predictor model of the water quality in the well. This model combines a linear dependence upon a time-lagged chloride concentration in the river, reflecting the steady-state water balance in the well, and a nonlinear dependence upon average lagged water output pumped from the well. This simple model explains 86% of the variance in well chloride concentration measured weekly over a two year period.

Notes: In many situations, inadequate design or performance of ground-water remediation systems is the result of underestimation of aquifer hydraulic heterogeneity, and in particular, the vertical variation of hydraulic conductivity which plays an important role in contaminant migration. Described herein are applications of the electromagnetic (EM) borehole flowmeter to fluvial sediments in Louisiana and South Carolina. The direction of natural vertical flow in the test aquifers was defined easily, and short pumping tests enabled the calculation of hydraulic conductivity profiles for each test well. The results correlated well with other information obtained independently, including natural gamma logs, driller's logs and a hydraulic conductivity profile based on grain size analysis. Large variations in hydraulic conductivity over short vertical and horizontal distances were documented. Tests in gravel-packed wells suggested that flowmeters produce misleading data for a variety of reasons in such situations. Among other things, an annulus of high permeability around a well screen allows flow to bypass the meter, and the phenomenon is amplified by high pumping rates. The resulting error is displayed as an erroneous high permeability zone at the top of the well screen. This observation deserves further study. In its present form the EM flowmeter is awkward to handle on a routine basis. However, none of the present design flaws preclude its effective use.

Notes: Definition of the hydrologic framework in layered sediments of fluvial and deltaic origin is a difficult challenge for environmental characterization and remediation programs due to the lithologic and stratigraphic heterogeneities inherent in these settings. We set out to use complementary geophysical surveys to determine the nature and extent of a deep confining unit at the Savannah River Site, South Carolina. Time Domain Electromagnetic (TDEM) soundings were used to define the electrical conductance of the clayey confining unit (aquitard), and shear-wave reflection seismic was used to define the stratigraphic framework. Based on correlations with borehole geophysical logs and sieve data, the shear-wave seismic proved capable of defining relatively fine layering in the coastal plain sediments, the upper and lower surfaces of a critical confining unit, and erosional features on the surface of the confining unit. The TDEM surveys defined the presence or absence of the clay facies of the confining unit. Moreover, by constraining the interpretation of the TDEM data with the thickness of the confining unit derived from the seismic data, we mapped the extent of the unit, showing where the clay is thicker, where it probably was never deposited, and where it was eroded by downcutting channels. These results have significant implications on the design and optimization of remedial systems.

Notes: The theory of ground-water flow in fractured rocks has been used to interpret aquifer tests and stream flow data for the Oak Ridge Reservation of U.S. Department of Energy. This interpretation has resulted in a better understanding of the data needed for ground-water models. The hydraulic conductivity values calculated from most aquifer tests are meaningless. Slug tests and early data from pumping tests measure the total transmissivity of all fractures within the area of influence; this value can be used to calculate rates of ground-water flow and transport near the well. Larger transmissivity values are calculated from late aquifer-test data and from an analysis of stream flow hydrographs because most ground-water flow occurs in a thin layer at the water table. This layer supplies most ground-water discharge to streams and apparently is a late-time water source for pump age from deeper wells.The calibration of distributed flow and transport models will be difficult, if not impossible, because about 90% of the ground-water flow occurs in only 10% of the area, and the locations of these flow paths are unknown. Also, large changes in transmissivity occur with recharge and discharge cycles that change the saturated thickness of the permeable layer near the water table.