ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00432.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00433.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTSmall oceanic limestone islands represent a unique hydrogeological environment. High transmissivities and small land areas cause the average water‐table relief to be of the order of cm, while permitting larger diurnal and barometric sea‐level changes to penetrate the aquifer. Extremely accurate surveying and monitoring at observation wells and tedious data reduction are necessary to obtain representative water levels.Numerical modeling of island aquifers, while largely in its infancy, can be an excellent focus for research, and ultimately a useful management tool. Essential inputs to an island model are barometric changes in oceanic base level and a thorough assessment of recharge.In Bermuda, the main ground‐water lens provides 4500 m3/d of ground water for public supply. Because of the importance of this resource, the Bermuda Public Works Department has invested in a ground‐water monitoring and research program. As part of this, a well‐evaluated example of an island aquifer model has been developed.Bermuda is generally typical of this hydrogeological environment, but differs from other small islands in two ways: (1) internal marshes, major discharge areas elsewhere, act as barriers to ground‐water flow; and (2) development of a high density of housing (typical of only a few small oceanic islands) has significantly increased Bermuda's recharge, because of domestic waste water and road drainage contributions.A number of aquifer management options were tested by the Bermuda model. Steady‐state modeling results suggest that an increase in abstraction to 8500 m3/d without serious derogation is possible. Such a policy would increase the vulnerability of the lens to point‐source pollution, and should therefore be gradual, monitored, and combined with stronger measures for pollu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00434.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTAn analytical transport model is presented for evaluating vertically averaged concentration data derived from purged and partially penetrating monitoring wells. The model is applicable to continuous contaminant emission from a finite source with longitudinal advection, and three‐dimensional dispersion. The model is used to investigate how screened length may influence contaminant detection, mapping, and modeling. Sensitivity analyses suggest that contaminant concentrations determined from monitoring wells may underestimate the level of aquifer contamination, depending on screened depth, location of the well relative to the contaminant source, the vertical source dimension, and degree of vertical plume spreading. The magnitude of this effect may be comparable to, and in excess of, concentration biases related to construction materials and sampling procedures. Additional screened interval influences may include: underestimates of contamination extent and migration rate; apparent indications of attenuation processes and steady‐state conditions; over‐ estimates of vertical contaminant spreading; increased time of contaminant detection; and poor transport model predictions, owing to well‐biased concentration distri

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00435.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTEnhanced aerobic biodegradation of hydrocarbons in the subsurface requires large quantities of oxygen to be distributed throughout the contaminated zone. Although hydrogen peroxide is a commonly used source of oxygen, its uncontrolled decomposition can result in wasteful off‐ gassing. Our results indicate that bacterial catalase is responsible for rapid decomposition of hydrogen peroxide at a jet fuel spill site undergoing enhanced biodegradation. Catalase positive bacteria found in infiltration galleries have dramatically decreased the useful oxygen supplied to the subsurfac

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00436.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe unconsolidatcd sediments which border the Missouri River constitute an important ground‐water aquifer that has been developed for municipal and industrial water supplies. The hydraulic efficiency of wells in these sediments decreases with time because of well screen encrustation caused by the oxidation of dissolved ferrous iron to insoluble ferric oxyhydroxides. The kinetics of ferrous iron oxidation are strongly dependent upon the solution pH and to a lesser extent the dissolved oxygen content. Chemical analyses of the well water including pH, Eh, dissolved oxygen, and dissolved iron indicate that at least one‐half time for ferrous iron oxidation occurs prior to ground water entering the wells. As ground‐water velocity increases near a pumping well, shallow, oxygen‐bearing ground water may mix with deeper, reduced water by mechanical dispersion and turbulent flow and facilitate the oxidation of dissolved ferrous iron. Although little can be done to prevent well screen encrustation, the rate of encrustation may be slowed by regulated pumping and avoidance of sh

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00437.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTDrawdown and recovery data obtained for stepped‐ rate pumping tests can be used to calculate the drawdowns that would occur if the test were carried out a constant rate without stopping. The recovery phase of constant‐rate pumping tests can be analyzed by the same method because cessation of pumping can be treated as a step change of pumping rate. The calculation assumes only that pumping during each step is at a constant rate, and that the principle of superposition is applicable, i.e., that the ground‐water system is linear and time‐invariant. It does not depend on the availability of theoretical expressions for the drawdown due to pumping. The calculation can be carried out for as long as water‐level measurements are continued; however, possible errors in the values of calculated drawdown increase with increasing time, thus limiting the practical length of time for which the calculated values are reliable.The constant‐rate drawdown curves characterize the response of the linear time‐invariant ground‐water system to pumping. They can be used for the determination of formation parameters if an appropriate theoretical model is available. They can also be used directly to predict drawdowns, and the scope of this application can be broadened by use of the reciprocity principle. In either case the use of recovery data can significantly extend the effective duration o

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe recent advances in space science have now made it possible to construct models of the existence. volume, and hydrologic cycle of the ground water of the planet Mars.Outgassing models of water vapor indicate that the surface of Mars should be covered with water to a depth of 10 to 100 meters (1·4 × 1015 to 1·4 × 1016m3). Geomorphic evidence suggests a depth of at least 500 meters (7 × 1016 m3) of water should occur over much of the planet, yet no surface water, other than glacial ice at the poles (2·3 × 1015 to 9 × 1015 m3), exists today. Martian gravity, though only 40 percent of Earth's, would keep water from escaping the planet. A survey of surface and atmospheric water volumes indicates that the majority of water, 1·2 × 1016 to 6 × 1016 m3, is hidden as ground water.Hydrologic cycle models indicate that Mars has an active but near static hydrologic cycle, dominated by water discharge in desert lowlands and water recharge at the ice‐ covered poles. Ground‐water flow plays a major role

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTHydrogeological mapping and numerical simulation techniques have been used to characterize the flow of ground water in Ross Creek Basin, Alberta, Canada. Forty percent of the basin's ground water is recharged in the Cypress Hills and discharged through local, intermediate, and regional flow systems at lower topographic elevations north of the hills. The remaining 60 percent is recharged through randomly distributed areas of restricted sizes. The similarity between the flow patterns mapped in the field and simulated numerically is an indication that the mapping technique is useful in determining ground‐water flow patterns throughout the various climatic regions in the Alberta prairies. Ground‐water discharge was found not to be restricted to the thalwegs of the main drainage ways, Ross and Gros Ventre Creeks, and their tributaries. Consequently, measurable base flow cannot represent the total discharge of ground water, which is estimated to be 2·0 × 10−4m3/s or 22 percent of the total precipitation in the basin. There is evidence that soil development has been influenced by ground water in th

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTSeptic tanks are the most frequently reported causes of contamination in ground‐water disease outbreaks associated with the consumption of untreated ground water in the United States. The placement of septic tanks is generally controlled by county‐wide or state‐wide regulations, with little consideration given to the local hydrogeologic, climatic, and land‐use conditions. Using the travel time necessary to achieve a seven‐order‐of‐magnitude reduction in virus number as the criterion, a wide range of septic tank setback distances (from less than 15 m to greater than 300 m) were calculated for a part of the Tucson Basin. This study makes use of disjunctive kriging to calculate the conditional probabilities associated with the setback distance estimates. The results are presented in two different ways: first, given a setback distance (e.g., prescribed by law) the probabilities that the level of viruses will be within acceptable limits are calculated; and second, the desired probability level is specified (e.g., 90%) and the setback distances required to achieve that level of confidence that the water will be free of virus contamination are calculated. The methods have potential for use by local government officials for land‐use pl

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1989.tb00441.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY