摘要:

AbstractForty passive vapor samplers were placed in creek‐bottom sediment in an area where ground water contaminated with volatile organic compounds is discharging to surface water. The vapor samplers were composed of activated carbon fused to a ferromagnetic wire in a test tube. The samplers were analyzed in a laboratory using an extranuclear quadrupole mass spectrometer. Data from the samplers reveal distributions of chloroform, tetrachloroethylene, trichloroethylene, and benzene in the bottom sediment that closely correspond to the distribution of those compounds in the adjacent ground water. Moreover, concentrations of tetrachloroethylene in bottom sediment estimated from the samplers are similar to those measured in observation wells near the shoreline. Thus, the passive vapor samplers may be used to locate and map areas where contaminated ground water is being discharged to surface water and to determine the approximate concentrations of specific contaminants in the discharging ground wate

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00489.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA simple numerical two‐dimensional interpretation model for resistivity profiles and soundings, similar to the one presented by Mufti (1976, 1978, 1980), has been developed for a PC. With the aid of the computer program, a synthetic response of Wenner and Schlumberger soundings or profiles can be generated for two‐dimensional subsurface structures. The possibility of calculating a resistivity response in advance offers a tool to optimize electrode configurations and spacings, and hence greatly improves the value of the measurements. A better insight is also obtained into how geological structures may affect the size and shape of anomalies in resistivity profiles. With the aid of the model, the sensitivity of Schlumberger and Wenner arrays to the weathered layer thickness in a granitic environment is illustrated, and a case study of the quantitative interpretation for a resistivity profile from a schistose environment in Burkina Faso is presen

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00490.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFrom the analytical solution to the instantaneous injection model, two sets of equations are given for calculating the three important parameters V, D, and E (effective initial concentration) from two or three points on the tracer breakthrough curve. If two points are used, one must be the maximum concentration on the tracer breakthrough curve. The effective initial concentration (E) calculated from the tracer breakthrough must be less than the initial injection concentration (M/PS) (M is the tracer mass being injected, P is the porosity of the reservoir, and S is the cross‐sectional area of the flow for an injection). The difference between the initial injection concentration and the calculated effective initial concentration might be used to evaluate the degree of tracer loss resulting from a combined effect of multidirectional dispersion, adsorption, and/or decompositio

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00491.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractUnder freezing or near‐freezing conditions, temperature‐induced viscosity changes, solute immobilization, and solute exclusion can affect field‐scale solute transport in ground water. This can lead to concentration profiles significantly different from those predicted by models which do not account for these processes. A model (GWFREEZE) is presented which incorporates these processes into a two‐dimensional transport equation for saturated porous media subject to a hydraulic head field that does not vary with time.Ground‐water temperature can be expected to vary widely in some natural and artificial freezing and near‐freezing situations. Spatially varying temperature fields cause spatial variations in the fluid viscosity field, especially near 0° C, where viscosity varies faster with temperature than at higher temperatures. GWFREEZE models these phenomena with a viscosity‐dependent hydraulic conductivity that is a function of temperature. Solute exclusion is modeled by a variable exclusion coefficient (Ke) which represents the percentage of solute excluded at the freezing front. The freezing front is modeled as a planar no‐flow boundary behind which solutes are immobilized and at which solu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00492.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA tritium profile obtained from a core located on the Tipton Till Plain near West Lafayette, Indiana, showed a “tritium reversal” (corresponding to a low‐high‐low activity of tritium relative to depth) at 7 m, indicating the present position of recharge water derived from 1963/64 precipitation. The average recharge rate calculated using the tritium data is 3.5 cm/yr for the “mass‐balance” method and 4.7 cm/yr for the “transit‐time” method. The average of 4.1 cm/yr is in reasonable agreement with Arihood's (1982) estimate of 5.1 cm/yr for tills, based on numerical modeling of data from a water‐budget study in the White River basin of Indiana. Two other cores, located on a nearby topographically lower slope, showed no definite reversal in tritium activity, probably because of lateral flow components at these locations.To be applied, the tritium technique should assess the contribution of summer and winter precipitation to recharge because tritium activities tend to peak in spring and summer precipitation. Contrary to the usual assumptions that recharge to aquifers in temperate zones of the northern hemisphere occurs between October and April, stable isotopic data of well water in the study area indicate that an appreciable amount of annual recharge (about 34%) actually occurs betw

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00493.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThousands of leaking underground gasoline tanks have been found throughout California from which a tremendous amount of gasoline has leaked into ground water over the last half century. The most water‐soluble constituent of gasoline is benzene, and it typically contaminates ground water below leaking underground tanks. In a state‐mandated program 7,167 wells serving water‐supply systems throughout California were tested for a broad panel of organic contaminants. Of the wells tested, 812 (11.3%) had detectable concentrations of at least one of the contaminants tested for. Detectable concentrations of benzene were reported for only 10 wells. Similar findings were reported in surveys focused on San Gabriel and San Fernando Basins. While many processes influence the environmental fates of organic contaminants in ground water, the most likely explanation for the nonoccurrence of benzene is that it is destroyed near its source by biodegrad

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00494.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe equation to calculate the retardation factor of sorbing chemicals moving in aqueous solution through aquifers and vadose zones is derived using a linear sorption isotherm and a mass‐balance approach. The procedure is very simple and clearly illustrates the roles of porosity and water content, including those for saturated flow, unsaturated flow, and preferential flow or other systems with both mobile and immobile phases of the water. Applications of the equation to preferential flow in the vadose zone and macrodispersion in a layered aquifer are illustrated with numerical examples for hypothetical case

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00495.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe aqueous geochemistry of the sand‐and‐gravel aquifer in northwest Florida was characterized as part of the Florida Ground‐Water Quality Monitoring Network Program, a multiagency cooperative study delineating baseline and/or background water quality for the major aquifer systems throughout the State. The aquifer is the principal source of water in northwest Florida and consists predominantly of quartz sand with smaller amounts of andesine, chlorite, calcite, kaolinite, and illite. Water from 42 wells in the sand‐and‐gravel aquifer sampled during 1986 and 1987 was characteristically low in dissolved solids (median value of 72 milligrams per liter) and of nondistinct water type, although relative concentrations of magnesium and sulfate tended to be lower than those of other major ions. Nonparametric statistical tests of major‐ion concentration variations with depth and relative distance along flow paths indicate that the water chemistry does not change significantly (0.05 significance level) as the water moves vertically and laterally through the aquifer. Mass‐balance calculations indicate that dissolved solids from rainfall and saline‐water sources each account for 13 percent of the concentration of dissolved solids in ground water. Incongruent dissolution of andesine, chlorite, and muscovite to form kaolinite accounts for 94 percent of the neutralization of the total hydrogen ion input from rainfall and from carbonic acid weathering in the subsurface. The remaining neutralization is accounted for by the dissolu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00496.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractResults from analysis of models of heterogeneous porous media indicate that inverse plume analysis has potential for use in delineating zones of differing characteristics within porous media even when the zones are not penetrated by a borehole. By analyzing the concentrations at pairs of points in a contaminant plume, the spatial distributions of apparent transverse dispersivity and source size are determined. Since dispersivity is an intrinsic property of a porous medium, spatial distributions of the apparent dispersivities obtained from inverse analysis of plumes are an indication of transitions in the character of the porous medium.Dispersivity values obtained by inverse plume analysis in heterogeneous porous media are “apparent” because the equation on which the analysis is based was developed under the assumption that the porous media is isotropic and homogeneous. In the case of heterogeneous porous media, the dispersivity value obtained at a given location by inverse plume analysis is affected by the spreading of the plume through different materials. Therefore, variations in dispersivity should be interpreted qualitatively for delineation of heterogeneity and not quantitatively as for input to numerical transport mod

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00497.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractProtection of ground‐water resources from the effects of anthropogenic contamination requires definition of the source of water flowing in developed aquifers. Aquifer recharge areas for the confined Magothy and Lloyd aquifers of Long Island, New York, are estimated by using a three‐dimensional model of the Long Island ground‐water flow system and a particle‐tracking algorithm.Aquifer recharge areas under predevelopment conditions are consistent with an understanding of the ground‐water flow system operation. A budget comparison indicated that the recharge occurring in each area as calculated by particle tracking was within one percent of the flow entering that aquifer, according to the water budget computed from the flow model.Aquifer recharge areas for two stressed conditions, one at the present time and the other an estimate for the year 2020, are more difficult to define because of numerous pumped wells. Maximum and minimuitn recharge areas for each aquifer are presented for both present conditions and the year 2020 to bracket the actual aquifer recharge areas. These results also are consistent with the water budgets computed from the flow model.Results indicate that development causes large‐scale changes in flow patterns and the size and shape of aquifer recharge areas. The accuracy of defining recharge areas is limited by the model's representation of local‐scale characteristics of the flow system

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1991.tb00498.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY