摘要:

AbstractNumerical simulations were carried out to investigate the capillary barrier effect and the wicking ability of multilayer earth liner systems. Two specific cases were studied: a two‐layer liner composed of a fine‐ over a coarse‐textured material, and a three‐layer liner composed of a medium‐textured material in between a fine‐ and a coarse‐textured material. Results of the simulations show that a quadratic relationship exists between the thickness of the fine‐textured material and the arrival time of the wetting front to the interface. At the time the wetting front reaches the interface, the width of the lateral spreading within the fine material is smaller than the thickness of this material. The lateral spreading and thickness are linearly related. The wicking ability of the different materials is more significant under relatively smaller infiltration rates and is controlled by the magnitude of the hydraulic diffusivity. For the two‐layer liner the criteria of minimizing the vertical movement and maximizing the wicking effect within the fine‐textured material conflict. A three‐layer liner satisfies both of these criteria. The results for the three‐layer system show that the medium‐textured material has more superior wicking properties th

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00604.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractRecent research has confirmed that low flow rate purging (i.e., ∼11/min) is a valid technique for 2 (5 cm) diameter monitoring wells with short screened intervals. The use of low flow, dedicated pumping devices for purging and sampling minimizes both the disturbance of stagnant water in the well casing and the potential for mobilization of particulate or colloidal matter which could lead to sampling artifacts. In addition, these techniques allow the use of purging indicator parameters (e.g., dissolved oxygen and specific conductance) to determine when to collect a sample for volatile organic compound (VOC) determinations. Detailed results from a monitoring network in a sand and gravel aquifer contaminated by organochlorine solvents support these findings. Recent publications on monitoring well hydraulic behavior and considerations of mass averaging effects due to pumping also support the use of low flow rate, minimal drawdown purging procedures to achieve reproducible sampling results. The suggested procedure includes documenting purging indicator parameters while purging with dedicated devices at low flow rates with minimal drawdown. This sampling method is less time‐consuming and reduces the need to handle large volumes of purge water since VOC concentrations, 02, and specific conductance values stabilized consistently in less than one bore vol

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00605.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe life and career of Henry Darcy are intimately connected with the city of Dijon. He was born there; he died there; and it was there that he carried out the experiments that have brought him lasting fame. Darcy was not an obscure scientist; he was a well‐known and respected public figure. His efforts as an engineer and advocate put Dijon on the main line of the Paris‐Lyon railway, and brought a modern water‐distribution system to Dijon some 25 years before such a system was put in place in Paris. During his life he received great honors, suffered political persecution, and carried out his most productive research in his later years despite ill health. He died at the relatively young age of 55. The main square in the city of Dijon is named Place Darcy in his

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00606.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBecause it considers basic hydrogeologic variables believed to influence contaminant transport from surface sources to ground water, the DRASTIC method can be a valuable tool for identifying ground‐water supplies that are vulnerable to contamination. Theoretically, areas with high DRASTIC scores should have more frequent occurrences of ground‐water contamination events than areas with low scores given similar land use, well construction, and well densities. Relationships between DRASTIC scores and incidents of contamination, however, have not been extensively documented. In Nebraska, significant positive correlation appears to exist between incidents of VOC contamination of ground‐water supplied community water systems and the relative hydrogeologic vulnerability of surficial aquifers as quantified with the DRASTIC method. These results provide a means of verifying the usefulness of planning tools such as DRASTIC for identifying areas where water supplies are most vulnerable to contamination from surface so

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00607.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract“No Migration” Petitions must be submitted by operators of Class I hazardous disposal wells to apply for an exemption from the federal land ban restrictions on the disposal of hazardous waste. In many Class I disposal well operations, the injectate density can vary daily and usually has a different density than the native formation brine. The influence of the density contrast on the fluid potential must be included in a “No Migration” Petition modeling demonstration. After the model wells (s) is shut‐in, the density contrast results in a net updip (lower density injectate) or downdip (higher density injectate) component of flow near the center of mass of the calculated plume (neglecting regional flow). In many cases, two model runs are required: one using the lowest anticipated injectate density and one using the highest anticipated injectate density for the entire modeled operational period. This was intended to provide adequate plume delineation over the injectate density range and implies that buoyancy effects on the plume position are not related to the average density. Three separate cases of a two‐dimensional generic numerical model were used to examine buoyancy effects using constant and variable injectate density input values. Case 1 used a random selection of the daily variation about the mean density, and case 2 used correlated daily injectate densities over a five day period. The model calculated concentrations from cases 1 and 2 were compared to the results from a third case that used the mean density input value for the entire operational period. The calculated plume extent for all three cases is virtually identical for simulation times up to 10,000 years. The modeling results demonstrate that using a long‐term average injectate density in “No Migration” Petition modeling rather than the range of extreme values may be justifiable by operators of Class I injectio

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00608.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe quantification of permeability and geostatistical scaling from laboratory to well field to regional systems requires large spatial data sets for which field and laboratory minipermeameters have proven to be effective tools. We developed an electronic gas minipermeameter for use in either the field or the laboratory. This design alleviates several problems common to minipermeameters. In particular, errors in measurement of gas flow rate, calibration of flow rate meters, and countering pressure and temperature effects were reduced by using electronic mass‐flow transducers. Problems of sealing the injector (probe) tips and of measuring the permeability of weathering rinds and fracture “skins” were remedied with a sample chamber capable of handling thin wafers or rock cores of arbitrary dimensions. Calibrations with samples of known permeability were excellent. It is now possible to measure permeability very accurately on weathering rinds, fracture surfaces, utcrops, and large hand sa

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00609.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAn approximation of the drawdown function developed by Hantush (1964) for late times was used to estimate the aquifer diffusivity directly from measured data from a constant‐head pumping test. This method of evaluation is especially useful in cases where early time data are absent or are obscured by other phenomena The use of the constant‐head time type curves allows ambiguity in the choice of the time match point because of the shallow slopes of the type curves for later times.Using the described approximation, constant‐head time type curves specific to the dimensionless distance from the pumping well may be compared with the measured data to find anomalies and bias in the measured data. A case study is presented to compare the results of the analyses with the constant‐head time type curves and with the approximation of the drawdown function. The results show that the approximation is valid after the first 100 minutes of meas

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00610.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBased on analysis of over 300 injection‐pressure tests and their assignment to logged stratigraphic intervals, it is argued that the Silurian dolomite aquifer in Milwaukee County, Wisconsin, behaves as both a fractured and porous medium. This paradox is resolved by examining the aquifer's individual stratigraphic units and their respective sedimentologic characteristics. Like many carbonates, the aquifer contains shoaling upward sequences and cycling through a variety of depositional environments and textures. Most of the stratigraphic units are fine‐grained mudstones, but interbeds with porous coarsegrained packstones and grainstones are also present.The packstone and grainstone units have unimodal distributions of hydraulic conductivity with geometric means between 104and 103cm/sec. The high matrix porosity masks any effects of jointing in these deposits, and they behave as porous high conductivity media. In contrast, hydraulic conductivities within the mudstones are bimodal, with one mode of very low matrix conductivities and a second higher mode controlled by jointing. Mudstone conductivities increase logarithmically with joint frequency, but never attain the magnitude of the values for the coarse‐grained units. Because the geometric mean hydraulic conductivities of the porous units are up to 1000 times greater than the thicker mudstones, the aquifer's bulk hydraulic conductivity is controlled by the thinner porous zones. Therefore, as a whole, the aquifer behaves as a porous medium even though most of the section is fracture‐dominated.Only the large number of hydraulic conductivity measurements isolated within specific stratigraphic units has allowed recognition of the importance of porous medium conditions in this aquifer. Because upward shoaling sequences are common within carbonates, a similar combination of porous and fractured medium conditions may be present, but unnoticed, in other carbonate aquifers. Investigators working in dolomites with minimal tectonic deformation should be particularly alert for porous medium

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00611.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe salinity in the Breede River in the Robertson area (S. W. Cape, South Africa) has increased at an alarming rate over the past two decades. Water analyses have shown that a few tributary streams which drain Bokkeveld Shale catchments are responsible for the high salinity in this agriculturally important river. Research carried out to investigate the sources of salinity in one such catchment, the Poesjesnels River Valley, found that heavy salt loads were contributed by return flow seepages after irrigation of deeply ripped, thin soils which overlie decomposed shale. A smaller contribution was coming from ground water which had leached out some salt from these shales while moving through bedrock fractures under pressure from the head in the encircling mountains, and eventually seeped into the river; evidence for this was provided by comparison of the oxygen isotope ratios of the various water bodies in the valley with that of the river water. A salt balance model drawn up to differentiate between the sources of salinity gave an indication of the systems which need management in future hydrological and agricultural development in this and similar valleys.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00612.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractGround water at many sites is contaminated by chlorinated solvents which are of relatively low solubility and denser than water, as well as other contaminants of similar properties. The presence of a dense nonaqueous phase liquid (DNAPL) in an aquifer can provide continued flux to the dissolved phase long after the initial discharge. The flux may be significant even when the nonaqueous phase has dispersed to a state of residual saturation, in which little or no free product can be detected or recovered. At an industrial site we required an estimate of the magnitude of a DNAPL source without undertaking invasive exploration. In theory, the presence and magnitude of a residual DNAPL source can be inferred from observations of downgradient concentrations by (1) developing an inverse modeling solution to estimate flux, and (2) matching estimated flux to a conceptual model of NAPL dissolution, which yields an estimate of residual mass. Such a method can provide a qualitative indication of the presence of a residual DNAPL source. However, the sensitivity of the solution to assumptions regarding physical characteristics of the source medium are such that a useful quantitative estimate cannot be made without observations over long periods of time.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00613.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY