ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02243.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA Microprocessor‐controlled Resistivity Traversing (MRT) System using the Wenner configuration has been developed to measure the distribution of resistivity in the subsurface down to depths of 200 m. The data are presented as a contoured apparent resistivity cross section, a type of electrical image, from which useful information about the structure of the subsurface can be obtained. Quantitative interpretation consists of iterative computer modeling using a two‐dimensional finite‐difference method.Measurements conducted in Kwara State, Nigeria, in borehole siting surveys show that MRT surveys are an important aid in locating areas of deep weathering and fissure zones in structurally complex basement areas. The resistivity information obtained allows an appreciation of the subsurface structure which cannot be obtained easily with other geophysical techn

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02244.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractVertical communication between aquifers via open wells may cause migration of a chemical plume from a contaminated aquifer into a water‐supply aquifer. Hence, quantifying the rate of flow through such wells may aid either in identifying likely transport paths or in designing a migration monitoring system. In this study, a steady‐state solution was developed which allows quantification of the volumetric flow rate which will occur within an inactive well which fully penetrates two confined aquifers. The solution is an adaptation of the Thiem solution and includes a well‐loss term based on the square of the flow rate. The solution for flow between a confined aquifer and an unconfined aquifer is also presented. Based on three examples concerning hypothetical flow problems, it was shown that the well‐loss term is insignificant unless both aquifers have high transmissivities and the well‐loss coefficient is large. Limitations of the solution are also

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02245.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractUnder‐exploration of complex hydrogeologic settings may lead to the occurrence of short‐circuiting internal flows in monitoring wells. Susceptible settings include fractured formations with large thickness and monotonous lithology. The occurrence of internal flow may distort flow pattern and induce contaminant migration. Monitoring data from the affected wells may be misinterpreted if the flow is unaccounted for. In order to identify and measure well bore flow in several deep monitoring wells at a site, a technique of in‐well tracing was used. The vertical movement, dispersion, and dilution of an injected saline slug was tracked by periodic electrical conductivity logging.Combining internal flow measurements with baseline conductivity and temperature logs provided estimates of the quality and origin of water entering well bores from major transmissive fractures. Identified locations of these fractures coincided with locations of larger fractures seen on video logs; only a few fractures were significant for the flow. Relative distributions of heads and fracture permeabilities in a well with internal flow could be evaluated easily, but determination of their absolute values would require measurement of static heads. In data quality, cost, and feasibility, the in‐well slug tracking compares favorably with conventional fracture characterization methods, such as coring, packer permeability testing, flowmeter and other specialized geophysical

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02246.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractMathematical models are used to evaluate the potential for ground‐water contamination resulting from vapor transport of volatile organic solvents in the unsaturated zone. A two‐dimensional numerical model for density‐driven flow and transport of vapors shows that trichloroethylene (TCE) vapors can be expected to spread rapidly from a residual source above an unconfined aquifer in an unsaturated, sandy deposit. Sensitivity analyses show that the shape of the vapor plume is particularly sensitive to the ground surface boundary condition and the material permeability. The shape of the vapor plume is insensitive to the mass flux by diffusion through the capillary fringe, although the flux may be significant in terms of ground‐water quality because the drinking‐water standard is very low. The vapor plume simulations and a plug‐flow infiltration model are used to calculate a source function for a ground‐water transport model in order to estimate the potential for ground‐water contamination. Ground‐water simulations show that an impermeable surface cover could reduce the flux of contaminants to the aquifer by preventing infiltration through the vapor plume. However, for the conditions modeled, significant ground‐water contamination can be expected to occur regardless of whether the ground surface is covered or not. Contaminants can reach the saturated zone from a residual source either by liquid‐phase diffusion through the capillary fringe or by migrating as a vapor beyond the lateral limits of a cover and subsequently dissolving and being flushed to the saturated

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02247.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractAn integrated approach involving geohydrological, geochemical, and geophysical methods was used to determine the source of salinity contaminating a ground‐water supply in an area of Ohio where three possible sources existed: road salting, naturally saline ground waters at depth, and formation brines placed in surface pits during drilling of a gas well. Changes in chloride concentrations during pumping tests of contaminated wells indicated that the main source of salinity was derived from within the water‐table aquifer. Mixing curves of Br/Cl versus chloride concentration were used to determine which of each of the three salinity sources was the primary source affecting different well waters. The major source affecting the ground‐water supply was found to be the formation brines associated with the gas well drilling.Geophysical surveys using electromagnetic induction (Geonics EM–31) and dipole‐dipole electrical resistivity methods provided a three‐dimensional view of the brine contamination plume in the unsaturated and saturated zones in the area of the gas well. The plume location and orientation confirmed that the formation brine from the blow‐down pits used during drilling of a nearby gas well was the primary source polluting the ground‐water supply in

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02248.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe application of a numerical model to a coastal aquifer is presented including the simulation of single‐phase and two‐phase fluid flow. The single‐phase part of the model solves the diffusivity equation and helps to identify certain parameters of the aquifer and to simulate the flow field (fresh water) under different conditions. The two‐phase part of the model solves the partial differential equations describing the motion of salt water and fresh water separated by a sharp interface.The model was calibrated using the observed piezometry of the aquifer for the fresh‐water flow field. Simulations were made for both steady‐and unsteady‐state conditions to establish the position and movement of the interface under different schemes of pumping. Results show that the model reproduces very accurately the flow field of fresh water. It identifies the potential salt‐water intrusion (upconing) into some of the pumping wells, thus helping in the identification of optimal

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02249.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThree new software technologies were applied to develop an efficient and easy to use decision support system for ground‐water contaminant modeling. Graphical interfaces create a more intuitive and effective form of communication with the computer compared to text‐based interfaces. Concepts from the field of hypertext were applied to design the extensive electronic documentation and databases. Finally, object oriented programming permitted scientists with little programming experience to develop the system by manipulating preexisting software objects instead of writing computer code, greatly increasing the productivity of the project team.A decision support system is a class of software with different origins and characteristics than conventional programs or expert systems. Decision support systems are designed to help users with broad, semistructured problems, with the user directing the problem‐solving process. The decision support software described in this paper, the OASIS system, provides ground‐water modelers with a ground‐water biodegradation model, model documentation, background information, data from chemical and hydrogeologic databases, and data management tools. The system was developed using HyperCard software on a Macintosh personal computer. It currently has over 1700 different computer screens of information and occupies approximately 10 megabytes of hard disk storage.OASIS is a new type of modeling software where ground‐water models, data, and knowledge are integrated together using a graphical interface and an easily modified software architecture. Two groups of users can benefit from the system: current modelers who need more efficient interfaces and data management tools, and people who are not using models now because the modeling process is too involved and requires specialize

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02250.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractNonparametric upper prediction limits for ground‐water detection monitoring are developed. The limit is defined as the maximum of a previous background sample of size n (i.e., X(max, n)). The probability that at least one out of the next m measurements (i.e., Y(min, m)) will be less than X(max, n)at each of k monitoring wells is computed. In the context of ground‐water monitoring, m is equal to the initial new measurement in a particular monitoring well plus m –1 resamplings of that well. In this way, values of n and m can be selected to assure a desired confidence level (e.g., γ≥ .95). A series of typical examples are described, and a set of Tables that give these probabilities for values of n = 4 to 100, k = 1 to 100, and m = 1 to 3 are provided. Generalization to multiple variables (i.e., indicator parameters) is also d

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02251.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractHydrocarbon thickness measurements in monitoring wells are used to estimate the hydrocarbon volume in the subsurface and to evaluate the efficiency of hydrocarbon recovery. It is commonly assumed that the formation hydrocarbon thickness is linearly related to the measured one. However, field data quite frequently show hydrocarbon thickness fluctuations that are not related to either hydrocarbon recovery or its release.It is postulated that these fluctuations are related to hydrocarbon/ground‐water interface elevation changes, and can be explained by two mechanisms: (1) difference in the residual saturation of hydrocarbons entrapped below and above the “interface,” and (2) preferred flow of the liquids through the monitoring

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02252.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY