ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00650.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSoil solution samples are often collected and analyzed without consideration for either the drainage period or changes in solution or solute flux. A sampling method to assess the vertical flux of solution and solute in the unsaturated zone was evaluated. Potassium bromide (KBr) solution and distilled water were applied to the surface of a soil. Estimated and measured solution and solute discharge through the soil column were compared. The column consisted of Plainfield sand (mixed, mesic, Typic Udipsamments) packed in a 208‐liter cylinder. Following solution application, discrete samples were collected at one‐ to two‐hour intervals with a ceramic soil solution sampler centrally located in the column. In each test, the Br concentrations of discrete samples were measured, and the Br concentration of a time‐integrated composite sample was calculated. Solution flux was estimated by monitoring vertical soil‐water tension and content gradients with tensiometers and time domain reflectometry probes, respectively, and applying the unsaturated form of Darcy's equation. In three of four tests, differences between measured and estimated solution discharge were 20%. Differences in measured and estimated Br mass discharge ranged from 1 to 37%. Correlation coefficients between estimated and measured Br mass discharge based on discrete and composite sample concentrations were 0.905 (p = 0.095) and 0.70 (p = 0.30), res

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00651.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA more general solution to the step‐drawdown test, called the General Well Function, GWF, is proposed to replace the classic Jacob's step‐drawdown equation for situations when the time that wells are continuously pumped varies greatly. Jacob's equation requires a preselected discharge duration and does not incorporate time as an independent variable. Jacob's equation has been criticized for that shortcoming since drawdown is obviously dependent on time as well as discharge. The General Well Function, GWF, not only corrects for this weakness but appears to better predict drawdowns that extend beyond the test data than, for example, the FASTEP code based on Jacob's equation. The GWF assumes that both formation and well losses increase over t

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00652.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents two analytical methods for estimating longitudinal and transversal dispersivities for a two‐dimensional plume generated by a slug tracer injection in a uniform ground‐water flow field. The first method requires the mapped plume area measurements at a given time after the tracer sources are injected. The second method requires concentration versus time data from one sampling well through which the plume passes. Detailed example calculations and comparisons with other procedures show that the methods presented herein represent improvements in both accuracy and ease of use over previous meth

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00653.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA permeable wall injection system is capable of introducing dissolved substances into an aquifer in a manner which minimizes the displacement of naturally present ground water, and maximizes the potential for dispersive mixing. The system operates predominantly in a passive mode, and should require relatively little power and small amounts of chemicals. The injection wall is a permeable cutoff wall installed across the path of a contaminant plume. The ground water can be amended with the desired nutrient solution using pumping and injecting wells within the wall. The high permeability of the wall ensures that the injection‐withdrawal operation causes flow which is primarily confined to the wall itself. Thus, only a minimal disruption of the ambient flow need result from a nutrient injection. After the nutrients have been introduced to the wall, the pulse is permitted to drift into the aquifer under natural gradient conditions, spreading longitudinally as it goes. Theoretical calculations and preliminary results of a field trial indicate that if this pulsing cycle is repeated at intervals of weeks to months (site‐specific), a stable microbial population can be supported at some distance downgradient from the wall.The advantages of this system include the predominantly passive nature of its operation, the effective use of longitudinal dispersion to maximize the mixing of added substances with contaminated ground water, and the flexibility of the system with regard to the types of biodegradation reactions which it can prom

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00654.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMacropores play an important role in many soils in relation to ground‐water contamination by providing preferential pathways from the root zone to the water table. Surface‐applied agrochemicals may hereby be carried quickly to the shallow ground water. The reduced retention combined with a small contact area between the flowing water and the soil implies that little removal from physical, chemical, and microbiological processes may take place, thus increasing the risk of ground‐water contamination.A laboratory procedure for evaluating the effect of macropores in a given soil is proposed and tested. The procedure involves the following sequence of experiments on two undisturbed soil monoliths: (1) measurements of the distribution of outflow, (2) measurements of breakthrough curves, (3) dye application for visual observation of macropores; and (4) horizontal slicing of the monoliths to measure macropore distribution and continuity of macropores. The experimental procedure is based on well‐documented techniques that combined will provide evidence on the significance of macropores in relation to ground‐water contamination and guidance for selecting the appropriate model for simulating flow and transport at the field in question.The laboratory procedure was tested on two large, undisturbed soil monoliths (30 cm in diameter) removed from the unsaturated zone at a clayey moraine agricultural field in Denmark. This soil was known to have many macropores. The investigations documented the strong influence of these structures on flow and transport suggesting that a traditional flow and transport model would be inadequate for simulating the processes occurring in

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00655.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA leachate plume emanating from the Shelby County Landfill located at Memphis, Tennessee is defined using selected major and trace inorganic constituents. High specific conductance values and elevated concentrations of ammonia, barium, boron, calcium, chloride, dissolved solids, potassium, sodium, and strontium were measured in water samples from wells screened in the alluvial and Memphis aquifers downgradient from or proximal to the landfill. Of these constituents, barium, boron, chloride, and strontium were used in the geochemical model code PHREEQE to estimate the percent leachate component in selected Memphis aquifer samples. Estimates of the leachate component in samples from affected Memphis aquifer wells range from 5 to 37 percent for barium and strontium, the most reliable tracers found during this study.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00656.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSteady‐state two‐ and three‐dimensional ground‐water‐flow models coupled with particle tracking (fluid‐particle pathline analysis) have been evaluated to determine their relative effectiveness in delineating contributing areas and particle traveltimes to public‐supply wells in two contrasting stratified‐drift aquifers of Cape Cod, Massachusetts. Several contributing areas delineated by the three‐dimensional pathline analysis do not conform to simple ellipsoidal shapes that are typically delineated by use of two‐dimensional analytical and numerical modeling techniques. They also include discontinuous areas of the water table and do not surround the supply wells. Because two‐dimensional area! models do not account for vertical flow, they cannot adequately represent many of the hydrogeologic and well‐design variables that complicate the delineation of contributing areas in three‐dimensional flow systems on Cape Cod, including the presence and continuity of discrete zones of low hydraulic conductivity, large anisotropic ratios of horizontal to vertical hydraulic conductivity, partially penetrating supply wells, shallow streams and lakes, and low (less than about 0.1 million gallons per day) pumping rates.Particle traveltimes calculated by the two‐dimensional models are longer than those calculated by the three‐dimensional models, and time‐related capture zones determined by the two‐dimensional models underpredict the size of the land area contributing water to simulated wells. It appears that the two‐dimensional models do not accurately represent shallow, partially penetrating wells, or heterogeneous and anisotropic sediments for the purposes of simulating contributing areas and travelti

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00657.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe magnitude of water‐table drawdown achievable by a fully penetrating pumping well in an unconfined aquifer commonly is limited to a small fraction of the initial aquifer thickness. The maximum potential water‐table drawdown can be estimated based on the aquifer thickness, the pumping well effective radius, and the estimated radius of influence in the aquifer during maximum steady‐state pumping (Kozeny, 1953). The maximum steady‐state flow rate into a well can be predicted if the aquifer hydraulic conductivity is known based on observed water‐table drawdown during a pumping period.To achieve the maximum potential pumping rate from a fully penetrating well in an unconfined aquifer, the water level inside the well must be maintained at the bottom (Kozeny, 1953; this paper). This condition creates a seepage face along the inside of the well screen. The hydraulics of the seepage face control the removal of water from the aquifer and the size of the resulting cone of depression. The area of the seepage face, which is a direct function of the effective radius of the pumping well, strongly influences the maximum potential water‐table drawdown and the maximum steady‐state pumping rate.The vertical component of the hydraulic gradient in the formation is downward and increases toward the pumping well. The hydraulic potential, therefore, decreases with increasing depth below the water table. Only shallow observation wells that are screened across the uppermost fraction of the saturated zone are adequate for delineating the actual water‐table position during pumping. Observation wells screened across deeper portions of the aquifer, including fully penetrating, fully screened observation wells, exhibit potentiometric drawdown in excess of true water

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00658.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractLinear sorption coefficients and first‐order biotransformation rates for para‐dichlorobenzene (pDCB) and naphthalene are fit to data from a three‐well forced‐gradient (injection‐production) field test performed at the site of an abandoned creosoting facility in Conroe, Texas. The breakthrough curve of an injected inert tracer, chloride, is used to describe the hydraulics of the field test. Along each streamline, the movement of a reactive solute is described by a one‐dimensional transport equation. The hydraulic and streamline transport models are coupled through a combination integral, the evaluation of which yields the effluent concentration (at the production well) of that reactive solute as a function of time. Transport parameters for the field site, sorption coefficients and biotransformation rates for pDCB and naphthalene, are obtained through inverse analysis of effluent data obtained at one of the production wells. The method is formulated such that no formal treatment of dispersion

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00659.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY