ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02129.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTGround‐water recharge by injection of reclaimed water is a feasible method of improving ground‐water quality in the shallow aquifer system in the Palo Alto Baylands along the San Francisco Bay. Ground water was initially more saline than sea water. Reclaimed water was injected at a rate of 10 gallons per minute from June 5, 1980, to July 1, 1980. At the completion of injection, water from an observation well 31 feet from the injection well was 98 percent injected water‐in essence, fresh water.An abrupt rise in the water level in the injection well of about 1.5 feet during the initial injection test was the result of a 3.5 percent density difference between injected fresh water and saline ground water. The arrival of injected water at observation wells showed the same effect, allowing monitoring of chemical and hydraulic changes entirely through water‐level data.The initially sodic clays in the confining layer were expected to swell as the saline ground water (sodium source) was diluted by recharge water. The sodium ion causes excessive coordination with the hydronium ion (H3O+) in the clay lattice, resulting in expansion as the saline water is diluted. X‐ray diffraction analysis of clay samples soaked first in native and then in injected water showed this effect. Calcium replaces sodium and limits expansion.Prior to injection the saline ground water was supersaturated with calcite. Dilution, as injection proceeded, eventually produced an undersaturation of calcite. An increase in well specific capacity indicates that calcite dissolved from the aquifer matrix, improving hydraulic con

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02130.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe distribution coefficient of trichloroethylene (TCE) was obtained from field and theoretical methods. The field method was based on measuring TCE concentrations in the soil samples and in the adjacent ground water. The theoretical method was based on using the organic carbon content of the soil and the octanol/water partition coefficient for TCE. The average distribution coefficient for 19 field samples and four methods of calculation was 0.18 ml/g which is in agreement with literature data and octanol/water partition coefficients results. For soils containing greater than 0.1 percent organic carbon, the theoretical methods of calculating the distribution coefficient appear to be valid. For soils low in organic carbon content, laboratory determinations of the distribution coefficient can provide reasonable estimates for predicting actual migration rates. Field determinations of distribution coefficients are, however, preferred because they integrate the effect of various factors on partitioning of TCE.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02131.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTA simple to understand and easy to implement numerical technique, based on reverse calculation of ground ‐water flow paths, is applied to delineation of time‐related capture zones around water‐supply wells. The areal extent of a t‐year capture zone in a two‐dimensional regional flow domain is approximated by a large set of reverse pathlines all with t‐year travel times. The numerical approach is suitable for calculation of time‐related capture zones in steady, nonuniform flow with inhomogeneous, anisotropic aquifer conditions. The example applications show the sensitivity of this technique to the influence of multiple wells in a block inhomogeneou

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02132.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTAquifer diffusivity (transmissivity divided by storage coefficient) was calculated for three sites in a glacial‐autwash valley aquifer near Cortland, New York from water‐level fluctuations induced by rises in stream stage. The observed response data were analyzed through use of a one‐dimensional floodwave‐response model to calculate the theoretical head response in the aquifer generated by a floodwave in the stream, and then matched to the observed head response. Diffusivity values computed from sharply peaked flood rises ranged from 6.08 to 8.68 ft2. The closest match between observed and calculated heads was obtained from a site where the aquifer is confined and the saturated thickness (and thus the diffusivity) remains constant with the passage of a floodwave. Arrival time of the observed flood‐peak seems to be the most useful criterion for curve matching, especially under unconfined conditions, where a match to the rising limb and floodpeak is difficult because of changes in the saturated thickness.A transmissivity value of 14,700 ft2/d for the glacial‐outwash aquifer, calculated from specific capacity data from a nearby industrial well, combined with diffusivity calculated by the floodwave‐response method, indicates a storage coefficient between the normal ranges for unconfined and confined aquifers. Calculated storage coefficients were 0.015, 0.027, and 0.034 at the three sites.The floodwave‐response method of calculating aquifer diffusivity is relatively inexpensive compared to standard aquifer tests and is effective in glacial‐valley fill aquifers that are hydraulically connected to a majo

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02133.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTCommonly employed techniques for the installation, purging, and sampling of monitoring wells are examined. The degree to which hollow‐stem augering disturbs the near‐borehole environment, and how this may result in the movement of contaminated solids or fluids from one stratum to another is discussed. The desirability of driving temporary casing to shield one stratum from another, and to improve the general quality of the monitoring well installation (especially the effectiveness of the filter pack emplaced), is argued. A call for further testing of sampling devices, based on limited field comparisons and a lack of reports of conclusive tests elsewhere, is gi

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02134.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTA classical dimensional analysis of the Theis non‐equilibrium radial flow problem in a confined aquifer indicates that three dimensionless parameters are required for its representation. A new set of type curves based on three dimensionless parameters sT/Q, Qt/sr2, and S, is developed that can be employed to analyze aquifer test data by a curve‐matching procedure similar to the procedure used at present with two dimensionless variables.The possible advantages of the proposed new type curves are as follows: (1) The concave shape of the type curves along the x‐axis and particularly their point of vertical tangency permits curve matching with a minimum of ambiguity. Furthermore, the possibility of gross errors in the curve‐matching procedure is reduced because both type curves and the plot of field data use the same dimensionless parameter on the horizontal axis (x‐axis) so that the process of curve matching permits movement of the field curve only parallel to the vertical axis (y‐axis). (2) The shape of the proposed type curves provides a focus for aquifer‐test design‐that is, given very approximate estimates for the field parameters (T and S), the investigator can target a specific range for the field‐measured parameters for which curve matching will give best

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02135.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTIn situestimates of advective and dispersive properties of ground‐water flow systems are essential for the adequate prediction of solute flow. Field tracer tests provide the best estimates of these properties; however, this approach is often precluded by the expense and time involved. Various laboratory techniques have been developed to circumvent these problems and provide convenient estimates of hydraulic conductivity and dispersivity. Although these techniques are used extensively in hydrogeological investigations, very few attempts have been made to compare their estimates with field values.A detailed investigation was performed on an unconfined sand aquifer using a combination of routine laboratory techniques and an innovative field tracer test. The extensive data set provided a unique opportunity to compare field results with those obtained by a variety of laboratory techniques.The hydraulic conductivity results from two different methods of grain‐size analysis (Hazen, 1893; and Masch and Denny, 1966) were observed to be quite well correlated, although their absolute values did not correspond with the hydraulic conductivities determined from the tracer test. However, contrary to previous studies, the results from grain‐size analysis were the same order of magnitude as thein situvalues. In addition, the two grain‐size methods appear to provide upper and lower boundaries within which lie the hydraulic conductivity estimates determined from the tracer test. Thus, grain‐size analysis of moderately to well sorted sands may provide reasonable and convenient approximations of hydraulic conductivities of the aquifer.No correlation was observed between field tracer test longitudinal dispersivity values and those determined from laboratory column tracer tests. The latter, however, differed by only an order of magnitude from thein situpoint measurements, a difference which is considerably smaller than has been previously reported. This is largely attributed to the accuracy of the sampling methods used in the tra

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02136.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTNumerical analysis based on the finite‐difference and boundary element methods is used to investigate the impact of the Dupuit‐Forchheimer approximation on results of salt‐water intrusion simulation. It is found that for sinks or sources (drain, ditch) that are small compared to the freshwater‐zone thickness, the use of the Dupuit‐Forchheimer approximation may cause substantial errors. For such cases, a correction method is proposed and

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02137.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe scale‐dependence of dispersivity values used in contaminant transport models to estimate the spreading of contaminant plumes by hydrodynamic dispersion processes was investigated and found to be an artifact of conventional modeling approaches (especially, vertically averaged parameters in two‐dimensional plume simulations). The work reported here shows that variations in hydraulic conductivity with depth result in significant variations in ground‐water flow and contaminant transport velocities; it is the resulting velocity variations that, if vertically averaged, give rise toapparentscale‐dependency of dispersion (e.g., increased dispersion with increasing travel distance). Special depth‐selective observation well designs are recommended by the authors for use in tracer tests, so that detailed estimates of the variations in hydraulic conductivity, and flow and transport velocities can be obtained. Innovative modeling techniques that take advantage of the detailed information obtainable from such tests (by emphasizing advective transport, as opposed to dispersive transport), have been developed by the authors. These modeling techniques are shown to have an element of true predictive ability, being able to closely simulate actual results with little or no ca

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02138.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY