ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb03726.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents an optimization analysis of the remedial pumping design for a contaminated aquifer located in Elmira, Ontario, Canada. The remediation task presented in the paper is to remove two ground‐water contaminant species, NDMA (N‐nitrosodimethylamine) and chlorobenzene, to such extent that the specified ground‐water quality standards are met. The contaminants, NDMA and chlorobenzene, have different initial plume configurations and retardation characteristics. The required quality standard for NDMA is five orders of magnitude smaller than the initial peak concentration. The objective is to minimize total pumping, and the constraints incorporate ground‐water quality requirements on the maximum and the spatially averaged residual concentrations, with contaminant source control being considered. On the combination of simulation and optimization, the results of this study indicate that the performance of an optimization algorithm based on gradient search is controlled by the specified cleanup levels, and that contaminant concentrations can be nonconvex and nonsmooth for some pumping

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01858.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractUse of the specific capacity of a pumping well to predict aquifer transmissivity is desirable due to the cost of pumping tests and the availability of specific capacity measurements. The geostatistical technique of cokriging is a method of incorporating the spatial variability of a correlated variable (e.g., specific capacity) in estimating a related undersampled variable (e.g., transmissivity). This study examines the reliability of cokriging transmissivity estimates using a data set of 215 pairs of transmissivity and specific capacity. Subsets of pairs of transmissivity and specific capacity were selected and cokriged to estimate transmissivity at the remaining well locations. The estimates of transmissivity were then compared to actual measurements of transmissivity. The same subsets of pairs were used to estimate transmissivity with loglinear regression of transmissivity on specific capacity and ordinary kriging of transmissivity alone. Comparison of these three methods indicates the number of wells with both transmissivity and specific capacity data necessary to obtain improvement in transmissivity estimates with cokriging over the simpler regression and kriging methods. The results show that significant improvement in the transmissivity estimate is obtained by cokriging with 50 or more pairs of transmissivity and specific capacity, and that loglinear regression is superior when less than 30 pairs are available. With between 30 and 50 pairs of available data measurements, cokriging does not reliably improve the estimate over loglinear regression.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01859.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe purpose of this work was to briefly outline and evaluate simple methods used for estimating the volume of water and the time required to remove contaminants from the subsurface by flushing (e.g., “pump‐and‐treat,”“soil washing”). The methods are based on three general approaches to treating flow and transport: perfectly mixed flow, hydraulic, and advective‐dispersive. Data obtained from a small field experiment designed to evaluate aquifer flushing was used to illustrate the performance of the estimation methods. The methods based on the hydraulic and ideal advective‐dispersive transport approaches will generally provide estimates that underpredict the actual time. The magnitude of the underprediction will depend, in part, on the degree of nonideal behavior influencing contaminant removal (e.g., heterogeneity, rate‐limited mass transfer) and on the ratio of target to initial contaminant concentration. The perfectly mixed flow reactor approach, because of its asymptotic removal curve, may be useful in providing rough approximations of required pore volumes and times. However, it cannot be overemphasized that all estimation techniques are prone to failure as long as the conceptual models upon which they are based do not accurately represent field‐scale co

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01860.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWater quality at many karst springs undergoes very high amplitude but relatively brief degradation following influxes of runoff. Accurately recording transient variations requires more rigorous sampling strategies than traditional methods. A pilot study to determine the usefulness of high‐frequency, flow‐dependent sampling strategies, combined with coincidental quantitative dye tracer tests, was implemented in the Big Spring Ground‐Water Basin in Mammoth Cave National Park, Kentucky.Data recorded following two separate runoff events showed that the concentrations of two nonpoint source pollutants, fecal coliform bacteria and suspended sediment, greatly exceeded prerunoff event values for very short periods of time. A phreatic conduit segment, calculated at 17 million liters in volume, instantaneously propagated head changes, caused by direct runoff entering the aquifer, from the ground‐water inputs to Big Spring. A significant delay between the initial increases in discharge and the arrival of direct runoff, as indicated by a steady decrease in specific conductance, represented the time required to displace this volume of phreatic water. The delay showed that sampling a karst spring only during peak discharge would be an unreliable sampling method.Runoff from two different subcatchments was tagged with tracer dye and the timing of the passage of the resultant dye clouds through Big Spring were compared to water quality variations. Distinct lag times between the arrival of direct runoff at Big Spring and the bacteria and suspended sediment waveforms were shown through the concurrent quantitative tracer tests to be related to the areal distribution of land‐cover type within

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01861.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractHydrocarbon concentrations in soil water and vapor are generally used to evaluate the progress of biodegradation and vapor extraction of petroleum contamination in the unsaturated zone. This study shows that changes in the inorganic composition of vadose zone water samples can be used to evaluate the reactions that occur in the unsaturated zone during such a remediation effort. Chemical analyses were completed on water samples collected from alluvial sediments contaminated with diesel fuel and gasoline at the Gallatin Farmers Cenex, Belgrade, Montana. The samples were collected from 7 suction lysimeters for 3 months after fertilization, but before vapor extraction, and then for 6 months following the start of vapor extraction. The geochemical reaction progress code SOLMINEQ.88 is used to calculate the aqueous equilibria in the samples and to simulate possible reaction pathways.Reduction in TPH and BTEX concentrations indicated that biodegradation of the petroleum began after fertilization, prior to vapor extraction, and continued after the start of vapor extraction. SO4=, HCO3‐, pH, and PCO2show large systematic variations with both time and depth. These variations are independent of evaporation, mixing, sample extraction time, and soil moisture content and thus appear to be a direct consequence of bioremediation and vapor extraction. PCO2is found to be a measure of the effectiveness of vapor extraction. The chemical mass transfer calculations also show that if vapor extraction occurs alone removing CO2from solution without coupling of a process to buffer the solution pH, large amounts of carbonate minerals could precipitate, significantly reducing sediment permeability. These data suggest that analyses of inorganic compounds in lysimeter samples can be used to evaluate geochemical changes during vadose zone remediation and can be used to improve remediation desig

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01862.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMathematica, a symbolic computer mathematics program, is used to construct a tool package for ground‐water flow and contaminant transport simulations. High level, mnemonic functions are designed that allow users to plot type curves, to animate ground‐water flow fields, to perform parameter determination, and to visualize the movement of contaminant cl

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01863.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractLaboratory column experiments were performed to evaluate the fate of a series of chlorinated and nonchlorinated organic contaminants in Rhine sediment and in sediment from the infiltration area of the Municipal Water Works of Amsterdam, near Zandvoort, The Netherlands. Columns were operated under aerobic, denitrifying, and methanogenic conditions. All nonchlorinated and few chlorinated compounds were aerobically transformed. Of the compounds tested under denitrifying conditions, only 1,2‐dichloro‐4‐nitrobenzene was partially transformed. Methanogenic conditions favored the transformation of chlorinated substances by reductive dechlorination. Toluene was the only nonhalogenated compound that was transformed under methanogenic conditions. Steady‐state effluent concentrations after biotransformation were at least 10 times lower than the drinking water limit of 1 μg/l except in the case of 1,2,4‐trichlorobenzene which had a steady‐state effluent concentration of 2.6 μg/l. Steady‐state effluent concentrations did not depend on the influent concentration applied. Most transformations proceeded at the same steady‐state rates at a temperature of 4° C, although the process of reductive dechlorination was slower at 4° C than at 20° C. Hydrological calculations revealed that the combined action of hydrology and sorption to organic matter in the infiltration system can reduce the concentrations of 2 week pulses of polar and nonpolar contaminants by at least 80 and 95%, respectively. There was a good qualitative agreement between removals observed in column experiments and in the du

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01864.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA method for monitoring water flow and solute transport through the unsaturated zone is of crucial necessity for early detection of threats to ground water. A method developed by Ukrainian hydrogeologists in the 1970s involves a borehole of a large enough diameter for a person to enter, that provides the possibility of installing monitoring equipment, and enables collecting undisturbed sediment blocks and samples of pore water and gas. Practically, tensiometers and vacuum lysimeters are installed at various levels in the borehole walls. They provide high quality sampling and measurements, and enable determining parameters of unsaturated water flow and solute transport and their temporal and spatial variability.The method was tested at several locations. Selected results from two sites, showing the temporal and spatial distributions of capillary pressure and solute concentrations, are presented. The results exhibit the difference between lateral variation in water flow and solute transport characteristics. The accuracy and representativeness of the measurements were tested against the mutual interaction between the various instruments installed in the borehole walls. Monitoring using the large‐diameter boreholes provides the possibility of early detection of threats to ground water under areal contamination inputs, and of quantitative prediction of its future trend

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01865.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractSlug interference responses within unconfined aquifers are characterized by an initial wave or “hump,” which is followed by a flat transitional plateau region and then by a declining, recessional limb segment. The shape and amplitude of the initial wave are primarily controlled by the elastic characteristics (i.e., S) and degree of anisotropy within the aquifer, while transmissivity is the principal parameter affecting the transmission (i.e., arrival time) of the slug interference response. Wellbore storage and delayed‐yield effects tend to attenuate the test response. The transitional and late‐time recessional segments are significantly influenced by the aquifer's specific yield. In addition, test well/aquifer relationships, e.g., observation well distance, aquifer thickness, and well depth/aquifer penetration, also strongly affect slug interference characteristics. The sensitivity of the propagated response to test well/aquifer relationships indicates that slug interference tests can be designed to maximize the expected response for aquifer property character

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01866.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY