ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01808.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractStable isotopes,15N and18O, have been used as tracers to differentiate a contaminant nitrate plume emanating from a single domestic septic system, in a ground‐water system characterized by high and similar nitrate content outside and inside of the contaminant plume. A good delineation of the nitrate plume of septic origin was obtained using15N analysis in nitrate. The15N content ofthe nonplunie nitrate is in agreement with the sources of nitrate: solid cattle manure, synthetic fertilizer (NH4‐NO3), and soil organic nitrogen, at the study site.18O analysis in nitrate did not provide enough isotopic contrast to permit separation of nitrate derived from the septic system and that in the surrounding ground water, derived from agricultural fertilizer sources.18O data indicated that nitrification of ammonium is the main process responsible for formation of nitrate at the study site.18O in ground water clearly delineated the ground‐water plume associated with the septic system and suggest that this tracer should be considered in studies related with contaminant plumes of different o

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01809.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractStochastic analysis of flow and transport in soils usually assumes that the soil permeability is a stationary, homogeneous stochastic process. Some field data suggest, however, that permeability distributions may have a fractal character with long‐range correlations. One such set of data is analyzed in this paper. We also investigate the relationship between the fractal character of hydraulic conductivity distribution and the statistics of unsaturated flow. This was studied by means of Monte Carlo simulations of steady‐state infiltration in soils with generated fractal permeability distribution. The results of these simulations were compared to theoretical results obtained from spectral analysis of unsaturated f

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01810.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe use of steady‐state models can sometimes reduce the computational resources and input data required for solution of transient transport problems. A large column experiment was performed to test whether solute transport parameters determined from a steady flow experiment may be used in transient, unsaturated flow and transport model predictions. Tritiated water and bromide were applied at a steady rate to the top of a 0.95 m diameter by 6 m deep soil column containing unsaturated soil. After 10 days, tracers were eliminated from the irrigation water. When the soil moisture content within the column ceased to change, another 10‐day pulse of tritiated water and bromide was applied, followed by water without tracers. Transport model parameters were determined through optimization, using breakthrough curves observed at various depths. The tritiated water and bromide pulses lagged behind the wetting front during infiltration into the relatively dry soil. The bromide pulse moved 17–20% faster than the tritiated water pulse, because of anion exclusion. Breakthrough curves for the transient and steady‐state experiments were similar. Because the solute fronts lagged significantly behind the moisture fronts, steady‐state transport parameters, when used in a fully transient numerical model, fairly described the transport under transient c

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01811.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractBecause a water sample collected from a well is an integration of water from different depths along the well screen, measured concentrations can be biased if analyte concentrations are not uniform along the length of the well screen. The resulting concentration in the sample, therefore, is a function of variations in well‐screen inflow rate and analyte concentration with depth. A multiport sampler with seven short screened intervals was designed and used to investigate small‐scale vertical variations in water chemistry and aquifer hydraulic conductivity in ground water contaminated by leaded gasoline at Galloway Township, Atlantic County, New Jersey. The multiport samplers were used to collect independent samples from seven intervals within the screened zone that were flow‐rate weighted and integrated to simulate a 5‐foot‐long, 2.375‐inch‐outside‐diameter conventional wire‐wound screen. The integrations of the results of analyses of samples collected from two multiport samplers showed that a conventional 5‐foot‐long well screen would integrate contaminant concentrations over its length and resulted in an apparent contaminant concentration that was as little as 28 percent of the maximum concentration observed in

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01812.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractOne of the most difficult tasks in hydrogeology is to develop sustainable supplies of potable ground water from small atoll islands. Fresh ground‐water systems within atolls, if they exist at all, are extremely fragile and sensitive to development stresses. In this study, the mathematical model SUTRA was used to examine development alternatives for a two‐phase miscible ground‐water system in a cross section through the Laura area of Majuro Atoll, Marshall Islands. The geological framework modeled for Laura is a multilayered aquifer system in which the primary members are a sequence of moderately permeable Holocene carbonate sediments overlying highly permeable Pleistocene sediments and reef materials. Ground water in this system consists of a thin layer of fresh water separated from underlying sea water by a relatively thick, transitional layer of mixed saline and fresh water. Sensitivity analysis indicates that the modeled depth to the 50% salinity contour is most sensitive to permeability, and the transition‐zone thickness is most sensitive to transverse dispersivity. Results from the development analysis verify that shallow, linear skimming wells, or galleries, are the most efficient means of extracting fresh groun

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01813.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring the time over which the data for a regional hydrogeocheimical survey are collected, the physical and chemical attributes of the ground‐water flow regime may exhibit appreciable temporal variation. A case study is presented in which the temporal variance of many physical and chemical attributes of ground water at single locations was close to or even exceeded the spatial variance of concentrations measured over the region at a single point in time. Thus, the results of a multivariate analysis of the spatial variability could have led to incorrect inferences had the regional sampling not been done within a period of time that was short enough so that no appreciable temporal variation occurred. A methodology using both spectral and multi variate analyses was used in determining: (a) the window of time allowable in collecting the water samples so that the temporal variability of the attributes did not affect the spatial analyses, and (b) the dominant factors that explain the spatial variability of physical and chemical attributes at that particular period in tim

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01814.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractUntil now no objective classification of transmissivity has been introduced, in spite of the quantitative nature of transmissivity values and their obvious importance for quantitative appraisals of aquifers or major ground‐water systems. The usual subjective expression of transmissivity, for example as “high” or “low”, prevents the objective comparison of transmissivity values characterizing different areas and hydrogeological environments. A combined classification of magnitude and variation of transmissivity is proposed, with the intention to standardize the expression, comparison, and representation of transmissivity. This classification also enables its compact and unambiguous depiction in tables

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01815.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractIt is becoming widely recognized that field‐scale ground‐water contaminant plumes are irregular and difficult to predict. Factors which complicate the characterization of such plumes include geological variability, data limitations, and uncertainties about the source of contamination. This paper describes a new approach to site characterization which accounts for variability and uncertainty in a systematic way. The site characterization procedure extracts more information from limited data by combining field measurements with predictions from a stochastic ground‐water model. The model provides prior estimates of the mean and standard deviation of solute concentration throughout a contaminated site. These estimates are updated whenever new measurements of hydraulic conductivity, head, and/or concentration become available. The updated concentration standard deviation estimates may be used to guide the placement of sampling wells and to evaluate the accuracy of the site characterization. If updating and data collection are carried out sequentially, over a series of discrete sampling rounds, the sampling network can evolve in response to new information. A case study described in the paper illustrates how the characterization procedure can be applied to a typical field

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01816.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe long‐term safe withdrawal rate for a coastal aquifer in Mannar Island of Sri Lanka was assessed through the simulation of interface movement. A range of estimates of natural recharge sequence was first obtained from a water balance study considering the variations of factors affecting the soil moisture balance. The representative recharge sequence was then determined through the simulation of a field observed interface profile along a selected section. Following this, the sustainability of continuous water withdrawal in the future was assessed by limiting the extent of salt‐water upconing. An increase in the withdrawal rate in the future would be possible through proper monitoring of the system respo

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01817.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY