ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThis article describes a computer automated, hydrologic analysis system designed to allow the collection of high quality, long‐term pumping test data. The instrument solves two of the major problems encountered in the field during aquifer tests: insufficient data, particularly during the early part of a test when drawdown is rapid; and high labor costs associated with long‐term monitoring.To illustrate the system's application, results are presented from the test of a highly transmissive aquifer. The aquifer's drawdown response was rapid; thus the time‐drawdown curve was essentially flat after the first two minutes of the test, and correspondingly rapid data acquisition was essential for a unique solution of the aquifer's three‐dimensional hydraulic conduct

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01214.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractTraditional monitoring methods using chemical analysis of ground water samples to detect pollutant migration are being superseded or used in conjunction with innovative approaches. A need to detect pollutants before they reach the water table has drawn interest to vadose (unsaturated) zone monitoring and brought together hydrogeologists, soil scientists and agricultural engineers who have been working on this subject for years.Recent studies have identified over 50 different types of vadose zone monitoring devices and methods that have optimum utility in varying hydrogeologic settings. In general, measurements made in the vadose zone are trying to define storage, transmission of liquid waste in terms of flux and velocity, and pollutant mobility.Criteria for the selection of alternative vadose zone monitoring methods are important for the development of site‐specific systems. These criteria include: type of site; applicability to new, active, and abandoned sites; power requirements; depth limitations; multiple use capability; type of data collection system; reliability and life expectancy; degree of operational complexity; direct versus indirect methods; applicability to alternate media; effect on flow regime; and effect of hazardous waste on sampling or measurements. Application of the selection criteria is discussed in Everett et al. (1982a

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThere are many electronic tools available for ground water field studies including a wide variety of computer equipment. Consideration should be given to the use of computers when planning field studies. A foundation for determining the appropriate use of computers in field studies is presented in two parts. Part One includes a brief description of the components that comprise a computer and is intended to clarify terminology and illustrate the general characteristics of these machines. Related and frequently‐used computer equipment is described in detail. Topics of special concern will be presented in Part Two, which will appear in the Spring 1984 issue, to alert the reader to common misconceptions and problems. This is illustrated by the description of two field studie

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01216.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA composite tape has been developed which can be the link to various sensing devices for measuring ground water parameters. The tape consists of a standard steel engineering tape with two conductors at the edges of the tape, similar to a TV antenna wire. The tape coating is clear Tefzel®, which has outstanding chemical and physical resistance. At the bottom end of the tape is a probe which can sense either water level by conductivity, a layer of organic liquid by an optical device, temperature by advanced semiconductor temperature transducers, pH, dissolved oxygen, absolute conductivity, or any other measurement that can be made with a small in situ probe.The steel tape itself provides one of three conductors and, because of its thin, flat shape, provides an excellent ground plane for electronic noise reduction. A multiplexing circuit commonly used in the electronics industry is placed inside the probe tip housing and routinely allows up to 16 signals to be transmitted to the hub at ground level. Most probes can be powered with a common 9V rechargeable battery. Signals are given either by low power‐consuming light‐emitting diodes (LEDs) ∼ 5 milliamperes (mA), piezo‐audible alarms ∼ 3mA, or liquid crystal displays ∼ l‐2mAThis configuration allows for extremely accurate depth profiles of the desi

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01217.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIn recent years we have seen major advances in the variety and quality of ground water sampling instrumentation, in almost every case involving increases in sensitivity of one or more orders of magnitude. Software number‐crunching ability brings us the capability of running sophisticated mathematical and statistical programs, while modern analytical chemistry routinely makes determinations of metals, organics and radioactive elements accurate in the parts per billion range.The construction of sample points rarely supports these levels of precision. The well is the basic sampling machine for the ground water industry and its ability to produce a truly representative sample underpins all data and conclusions. Regardless of the type of instrumentation employed, a sample point that cannot be shown to be truly representative and that fails to provide a series of reliable samples over the long term–let us say 25 years minimum–is a negative investment.In the authors’professional sampling work, it has been observed that, wherever it is possible to improve the quality of the ground water sample point, a reduction in the measured level of pollutant elements in the sample is found and the confidence level improves. Volatile organic values are the sole exception to this observed reduction in concentration, the reason being that sample point and method improvements capture the fully representative water sample, thus reducing volatile losses.It is not possible to address all hydrogeologic environments and sampling methods in this review. Instead, features were selected that had been found to be important in commercial, high‐precision, water quality sampling in Western U.S. environments. In this area, water movement is slow and little or no exchange of water occurs between wells and the surrounding aquifer without artificial stimulation. Water quality stabilization requires multiple casing volume evacuations in wells ranging to 1,000 feet deep. High‐volume pumping or mechanized bailing is an economic requirement. Dedicated installations cannot supply the volume of water required for comprehensive analytical programs.It is the nature of these sources, as well as practical recommendations for corrective action, that will be addressed in this article.Any attempted improvement in utilization of data by mathematical processing or statistical treatment will be inadequate because:• Samplings are infrequent and often accumulate at rates of only two or four sample suites per year. Seasonal variations may obscure evidence of passage of a low‐intensity pollution front and some years may elapse before the true situation becomes apparent from statistical analyses. By such time, the problem pollutant may have escaped from the treatment area.• Powerful biases occur due to the failure of the sample point to eliminate false contributions to the sample from sources other than the natural environment or a pollution source, most frequently originating in casing materials and

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01218.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01219.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractTwo electrical methods were used and compared in the Investigation of a solid waste landfill site in the central Coast Ranges of California Terrain conductivity measurements and dipole‐dipole resistivity surveys were used in support of an investigation of the hydrology and geochemistry of the site with main concerns being: 1) establishment of baseline conditions, 2) determination of possible contamination and 3) design of a sampling/ monitoring system. Geophysical data were obtained prior to the start of the drilling program and later integrated with reconnaissance geologic data for the purpose of selecting sites for monitoring wells. Two electrical methods were used: 1) dipole‐dipole resistivity; best suited for determining changes in electrical properties with depth and 2) terrain conductivity; best suited for determining lateral changes in electrical properties at a particular depth. Interpretations of the surveys were used in making inferences about the geometry of the saturated zone, ground water gradients, and relative depths to the saturated zone in areas with highly variable conditions. The data were useful in checking for possible ground water contamination and for extrapolating well data across the site.Electrical properties of rock at low frequencies are dominated by effects due to the presence of pore fluids. Differences in conductivity between saturated and unsaturated rock depend primarily on inherent electrical properties of the rock, porosity and conductivity of the fluid. Electrical detection of subsurface zones of contamination, sometimes referred to as “plumes”, in either the saturated or unsaturated zones, requires the existence of a zone of contrasting electrical behavior produced by the contamination. Such contrasts, or anomalies, can be caused by the presence of increased (higher conductivity) or decreased (lower conductivity) concentration of ions. In areas where materials with contrasting electrical properties (such as sandstone and claystone) are present in the subsurface with irregular geometry, anomalies can be difficult to interpret and additional information about geology and ground water conditions must be relied upon.The geophysical survey for this study began with dipole‐dipole resistivity measurements carried out along orthogonal lines in the landfill area. Subsequently, terrain conductivity measurements were carried out and compared with this data. A brief explanation and comparison of the methods used and the results of the surveys are discussed. Following completion of the surveys, the dipole‐dipole data were modeled with the use of a finite‐element computer algorithm. The models are compared with geological and hydrological data obtained during the drilling phase o

ISSN:1069-3629    

DOI:10.1111/j.1745-6592.1984.tb01220.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY