ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02109.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02110.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe El‐Shawak area in eastern Sudan lies within a large synclinal basin known as the Gedaref Basin, composed principally of elastic sediments of the Nubian Sandstone Formation which are overlain by sheets of basalt and dolerite and underlain by a metamorphic Basement Complex.As a part of a hydrogeological research project in the area, gravity and seismic refraction techniques were combined to locate the extent of the basaltic flow and to determine the thicknesses of the sedimentary formations.The results of these studies show that the topography of the Basement Complex is undulating and characterized by two troughs separated by subsurface ridges. The thicknesses of the Nubian Formation sediments range from 50 m (164 ft) to greater than 250 m (820 ft). Although the thicknesses of the Nubian Formation are favorable for ground‐water occurrence, the yield is very limited because the sediment succession is composed largely of compact mudstone.The application of the gravity method in the El‐Shawak area has shown that a polynomial trend‐surface fit can be used to separate the regional and the residual components to reflect local geological f

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02111.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTShallow soil gas (<2 meters deep) was collected and analyzed for trichloroethylene (TCE) to determine the relationship with ground‐water contamination directly below. The gaseous TCE plume was mapped with 46 probes and spanned three orders of magnitude in concentration (<0.001 to 2 μg/1). TCE concentrations in water from five monitoring wells around the study site ranged from 4 to 2800 ppb and had a correlation coefficient (r) of 0.90 with TCE concentrations in shallow soil gas. Vertical borings were completed to the water table at four locations in order to obtain profiles of soil gas contamination, air porosity, and water saturation. Gaseous diffusion and air/water partitioning are probably the dominant mechanisms involved in transporting TCE from the ground water to the shallow soil g

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02112.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe distribution of fracture permeability in granitic rocks was investigated by measuring the distribution of vertical flow in boreholes during periods of steady pumping. Pumping tests were conducted at two sites chosen to provide examples of moderately fractured rocks near Mirror Lake, New Hampshire and intensely fractured rocks near Oracle, Arizona. A sensitive heat‐pulse flowmeter was used for accurate measurements of vertical flow as low as 0.2 liter per minute. Although boreholes were spaced at intervals ranging from 10 to 50 meters, acoustic televiewer logs showed little direct continuity of individual fractures from borehole to borehole in either the moderately fractured rocks or intensely fractured rocks. Results indicated that nearly all inflow and outflow to boreholes occurred by means of one or two discrete fractures in both cases. These fractures did not appear very different from other prominent fractures indicated on televiewer and resistivity logs for these boreholes. Hydraulic connections between boreholes apparently were composed of conduits formed by the most permeable portions of intersecting fractures. Most flow in the moderately fractured rocks occurred at isolated fractures at a depth of about 45 meters indicating a nearly horizontal zone of fracture permeability composed of orthogonal, steeply dipping fractures. Previous studies have identified a zone of horizontal permeability in the lower part of the boreholes in the intensely fractured rocks, but flowmeter tests indicated that flow also entered and exited individual boreholes by means of one or two steeply dipping fractures. These results indicate zones of fracture permeability in crystalline rocks are composed of irregular conduits that cannot be approximated by planar fractures of uniform aperture, and that the orientation of permeability zones may be unrelated to the orientation of individual fractures within those zone

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02113.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTGeophysical methods have been used for many years to assist in hydrogeological exploration for ground water. For the direct detection of water‐bearing formations, the electrical resistivity method has been effective but relatively slow and costly.More recently, surveys have been conducted successfully with electromagnetic prospecting apparatus developed primarily for the mineral industry. Such equipment has the advantages of greater speed and portability, improved subsurface resolution, and better potential discrimination of conductive aquifers.Electromagnetic methods also can be applied from moving platforms, including fixed‐wing aircraft and helicopters. Detailed and regional surveys conducted in recent years for geological mapping and mineral exploration in Africa and elsewhere have revealed important information on the location and nature of water‐bearing formations and structures. Simultaneous measurements of the magnetic field have been used also to map faults and dikes of potential ground‐water significance.New, wide‐band, digital airborne equipment and processing systems are capable of carrying out rapid, inexpensive studies of subsurface formations to depths of at least 200 meters. Computerized interpretation techniques can produce maps of depth and electrical conductance of a variety of buried aquifers. This information can be of direct assistance to the hydrogeologist or hydrologist in the identification and development of underground‐wat

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02114.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTDiscrete‐state compartment (DSC) models and their associated age distribution functions permit the quantitative interpretation of environmental radioisotope data such as carbon‐14 ground‐water decay ages. These mixing‐cell models offer a means for constructing ground‐water flow models that can be used to relate decay ages to ground‐water mean ages. In addition, DSC models can also generate the entire distribution of ages in various subregions of a ground‐water reservoir. A preexisting DSC model of a portion of the Tucson Basin alluvial aquifer is used as an example. Ground‐water mean ages in this aquifer range from 100 to almost 15,000 years old, with the oldest waters about 40,000 years old. Since the ground‐water ages are not normally distributed, means and medians are not equivalent. The results indicate that care must be used in interpreting both ground‐water radioisotope decay ages as well as mean ground‐water ages and that knowledge of the entire age distribution is preferable. Age distributions are especially useful in hydrogeologic studies in which mixing is important and may find use in paleohydroge

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02115.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTSubsurface air is a refuge for radon gas escaping from rock and soil surfaces, as well as from subsurface water. Where the subsurface air is confined in a zone by overlying poorly permeable material or by downward‐moving water, the radon can accrete and become mobile. The crystalline rocks of eastern United States contain granites and associated rocks that have moderate to low amounts of uranium source material; the amounts are sufficient for radon to emanate significantly from both the soil‐saprolite zone and the part of the underlying fractured rock above the water table.Both the soil‐saprolite confined air system and the fracture air system are nondescript and are erratic in size and shape from place to place and from time to time. They tend to have a gross horizontality because of blanket infiltration of precipitation and in some cases by crude layering of soil horizons or tension fracturing of bedrock.The pressure increases in the air systems chiefly as infiltrated water moves downward and as the water table rises. The radon‐laden air moves toward two types of low‐pressure chambers. One type of chamber is a house on sloping topography niched into the soil‐saprolite zone and perhaps into bedrock fractures. The other type is the unwatered fracture zone of a pumping cone of depression where overlying clays are less permeable. These two types of low‐pressure chambers have characteristics of vacuum cleaners, sucking in radon‐laden air.Conditions leading to high indoor radon concentrations are: (1) granites and associated rocks with normal or above normal amounts of uranium, (2) normal interconnecting fracture pattern, (3) a thin mantle of relatively impermeable clay soil, (4) repeated cycles of recharge and of a fluctuating water table in the fracture zone or in the overlying regolith, (5) indentation of buildings into soil and rock materials, and (6) building construction allowing relatively easy inflow of air from the s

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02116.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

ABSTRACTThe U.S. Geological Survey (USGS) Solute Transport Model is a widely used, well‐documented computer code which simulates contaminant transport in ground water using a finite‐difference grid and the method of characteristics. In this study, the model was applied to an industrial site where trichloroethylene (TCE) and other industrial solvents had contaminated a shallow sand aquifer. At the study site, the geology was well‐characterized and the migration of the contaminant plume was monitored by a network of 15 wells.Although the rate of release of the industrial solvents to the aquifer was unknown, the model gave a good prediction of the movement of the plume when the release of contaminants was modeled as a point source injection. The model was also successful in simulating the behavior of the plume under the influence of a recovery system. During simulation of a four‐well withdrawal system, model predictions of TCE concentrations and hydraulic head in the aquifer matched actual data collected at two points in time after start‐up of the recovery system. The model predicted that the same configuration of withdrawal wells would reduce concentrations of TCE in the ground water from approximately 1000 μg/1 to 6 μg/1 after two years

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02117.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.A method of analyzing the pumping and recovery phases of large diameter wells based on a Kernel function method is presented. Consideration is given to the effect of the seepage face, which is the difference between the well‐water level and the aquifer level on the well face. A computer program for the Kernel function method written in BASIC, is provided. In the analysis of a representative field test, the importance of including the seepage face is demonstrated; if the seepage face is ignored, both the transmissivity and storage coefficient are underestimate

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1987.tb02118.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY