ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02223.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTA 72‐hour aquifer test was conducted at the Sweet‐water Recharge site in Tucson, Arizona for the purpose of estimating aquifer parameters using the graphical curve‐matching technique of Neuman (1974). These parameter estimates will be used to estimate the movement of ground water under seasonal recharge and recovery operations at the site. The lithology of the saturated sediments at the site appears to be relatively uniform and homogeneous from the water table at about 100 feet below land surface to about 600 feet below land surface. The aquifer base is a finegrained unit which extends from 600 feet to an unknown depth below the site. Poorly sorted sandy gravels and gravelly sands are predominant above 600 feet. A well was pumped at an average rate of 2,020 gallons per minute for 72 hours. Drawdown and recovery measurements of water levels were made in five shallow monitoring wells and one deep monitoring well.The log‐log drawdown versus time plots indicated delayed gravity response. The method of Neuman (1974) was used to estimate aquifer parameters from the test results. Because the pumped and monitoring wells were characterized by varying degrees of partial penetration, the computer program code developed by Neuman (1974) called DELAY2 was used to generate type curves for the unique arrangement of wells at t

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02224.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTGround water in a shallow glacial till aquifer and a deeper weathered shale aquifer at a site near Rock Creek, Ohio has been contaminated with trichloroethylene (TCE). Evaluation of remedial alternatives indicated that a system of subsurface drains would be most effective for decontaminating the shallow ground water. The performance of the proposed subsurface drainage system for the shallow aquifer was simulated using finite‐element flow and transport models. Model results indicate that the drains should reduce TCE concentration in the shallow aquifer to about 8 ppb in approximately 24 years.A single extraction well was the selected alternative to remediate trichloroethylene concentrations in the deeper weathered shale aquifer. The performance of the proposed well was analyzed by an analytical method. Results of the analysis indicated that the extraction well should reduce contamination in less time than required for the shallow glacial till aquifer. Validation of the predicted performance of the remedial system will be assessed following installation of the system and collection of field dat

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02225.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTMixing of fluids at fracture intersections was examined using both a series of plexiglass models and a two‐dimensional, finite‐element, discrete fracture model. The physical laboratory models included 12 models having two continuous, fully intersecting fractures with different intersection angles and apertures, a single model consisting of a single continuous fracture offsetting a second fracture, and a fracture system model consisting of parallel fractures in two intersecting sets. The plexiglass model results indicated essentially no mixing occurred in the fully intersecting fracture models when the apertures were equal. Mixing was found to be dependent only upon the relative size of the inlet and outlet fractures even with multiple intersections.For transport of a conservative solute in a discontinuous, random, discrete fracture system, the numerical model used the mixing algorithm for fracture intersections, developed from the physical model study. At each four‐way intersection, a novel approach was used to uncouple and recouple the nodal points to ensure the proper assignment of concentrations to each fracture element. Using the laboratory‐determined mixing algorithm, the numerical model demonstrated that more longitudinal and less lateral dispersion takes place than when complete mixing at fracture intersections is assumed. In addition, more longitudinal transport takes place in discontinuous than in continuous fracture systems. These findings indicate that contaminants migrating through fractured media, where the fracture walls are not in contact, will not be dispersed and diluted to the extent that previous numerical models have predicted; hence, the contaminant will be discharged to the biosphere in much greater concentration than e

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02226.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe City of Columbus, Ohio, obtains nearly 15 percent of its municipal water supply from four radial‐collector wells located along the Scioto River and Big Walnut Creek. Upstream from the three wells located adjacent to the Scioto River are five uncontrolled landfills and two aggregate mines that operate quarry‐dewatering systems. Flow paths along which leachate could migrate from the landfills, under existing conditions and under various hypothetical conditions related to the cessation of quarry dewatering, were simulated with a two‐layer, steady‐state, ground‐water flow model incorporating spatially variable recharge, transmissivity, and hydraulic conductivity. The model was calibrated with two sets of water‐level data and with the results of a seepage study along the Scioto River and Scioto Big Run. Results of simulations indicate that water levels near the quarries and landfills will rise to an altitude sufficient to saturate some of the landfill wastes. Predicted flow directions associated with all the hypothetical conditions indicate that leachate migrating from the landfills will not discharge directly into the capture zones of the collector wells; rather, the leachate will be diverted into one or the other quarry‐dewatering systems and/or into the Scioto River. The model simulations also indicate that approximately 60 percent of the ground water discharged within the study area is by quarry dewatering, and about 13 percent of the yield of the collector wells under normal pumping rates is from induced stream

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02227.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTAn analytic method is described for estimating the volume of mobile Light Nonaqueous Phase Liquids (LNAPL) in porous media from observed LNAPL thicknesses in monitoring wells. Static (mechanical) equilibrium of fluids in a homogeneous porous medium is the key condition on which the method is based. Both the Brooks‐Corey and van Genuchten equations, with parameters derived from laboratory column experiments reported in the literature, are used to relate fluid contents to capillary pressures. The calculations show that LNAPL in the vadose zone does not distribute itself as a distinct layer floating on the top of a capillary fringe. Rather, the traditional concept of a capillary fringe is not applicable when LNAPL is present. Further, neither the LNAPL level nor the water level in monitoring wells is equal to the water‐table elevation. The water table, being the surface on which the water pressure is zero gage, is located above the LNAPL‐water interface in the well, and LNAPL in the porous media will reside below the water table.It is shown that finite volumes of LNAPL theoretically can exist in materials with positive entry pressures (e.g., Brooks‐Corey porous media) without revealing their presence in the form of an LNAPL layer in monitoring wells. However, LNAPL in porous media with zero entry pressure will always appear in monitoring wells, regardless of the volume of LNAPL in the porous medium. In addition, the theory shows that the ratio of the volume of LNAPL per unit area in the vadose zone to the thickness of LNAPL in monitoring wells is strongly dependent upon the capillary properties of the porous medium. Only in porous media with very uniform pore sizes is the volume of LNAPL in the vadose zone approximately proportional to the thickness of LNAPL in monitorin

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02228.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTUnder the assumption of local vertical equilibrium, fluid pressure distributions specified from well fluid levels in monitoring wells may be used to predict water and hydrocarbon saturation profiles given expressions for air‐water‐hydrocarbon saturation‐pressure relations. Vertical integration of the oil‐saturation profile yields the actual oil volume in porous media per unit area adjacent to the well. Three‐phase fluid distributions are predicted using a scaling procedure which requires knowledge of two‐phase air‐water saturation‐pressure relations, hydrocarbon density, and hydrocarbon surface tension. Air‐water saturation‐pressure relations are parameterized by either the Brooks‐Corey or van Genuchten expressions. Parameters in the models are estimated from grain‐size distribution data for two hypothetical soils.Results reveal that whereas the distance above an oil‐water table at which oil saturations become zero may be independent of soil type, estimated light nonaqueous phase liquid (LNAPL) volumes per unit area may differ substantially. Hence, estimates of LNAPL volume cannot be inferred directly from soil LNAPL thickness or well LNAPL thickness data without consideration of effects of soil properties. Furthermore, it is demonstrated that no simple linear conversion scheme can be employed to relate the height of LNAPL in a monitoring well to the LNAPL volume in porous media. Effects of grain‐size distribution and well LNAPL thickness on the ratio of actual LNAPL thickness in the aquifer to wel

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02229.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTGround‐water‐sampling protocols generally recommend that a well be purged prior to sampling. This recommendation is based on the assumption that the water quality of the water standing in the casing is not the same as that in the aquifer. Three criteria that have been used to determine when a well has been purged sufficiently to yield “representative” water‐quality samples are (1) flushing an arbitrary number of casing volumes, usually a minimum of three, (2) flushing the well until field water‐quality characteristics‐temperature, pH, specific conductance, and dissolved oxygen‐in the purge water are stable, and (3) flushing until hydraulic equilibrium between casing water and aquifer water is achieved. The primary purpose of this study was to evaluate the effectiveness of these criteria in sampling for purgeable organic compounds.Wells, screened in unconsolidated sand and gravel aquifers at six sites, were sampled during a total of 10 purgings. The discharge from each well and the field characteristics were monitored as a function of time and number of casing volumes flushed. Grab samples for purge‐able organic compounds, chloride, and ultraviolet absorbance at 254 nanometers wavelength‐a gross indicator of the presence of aromatic organic compounds‐were taken each time a set of field measurements was taken. The variation of field characteristics, purgeable organic compounds, chloride, and ultraviolet absorbance at 254 nanometers was compared with time and number of casing volumes flushed.The results indicate that (1) purgeable organic compound concentrations sbailized when three casing volumes were purged in only 55 percent of the cases evaluated in this study, (2) purgeable organic compounds concentrations did not consistently follow the temporal variation of, nor stabilize at the same time as, the measured field characteristics, and (3) purging to achieve hydraulic equilibrium between casing and aquifer water consistently underestimated the time and casing volumes needed to achieve stable values of water‐quality measurements in highly transmissive aquifers. The conclusion from these data is that none of the previously recommended criteria for purging a well can be applied reliably to collecting a “representative” sample of purgeable organic compounds. These results indicate that the criteria for purging a well prior to sampling for purgeable organic compounds must take into account other factors, such as the unique hydrogeologic characteristics of a site, the nature and extent of purgeable organic compounds present, the areal extent of the contamination, the well construction, and the sampling obje

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02230.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA numerical model (NEWVAR) to simulate the transient movement of a discrete interface between salt water and fresh water has been developed. NEWVAR is designed to allow the analysis of a regional two‐dimensional ground‐water flow in coastal aquifers. The numerical solution permits the prediction of both regional fresh‐water levels and two‐dimensional fresh‐water/salt‐water interface by using nested square meshes.The numerical solution is based on the finite‐difference method; the Gauss‐Jordan direct method is used for solving steady‐ and unsteady‐state linear equations. Different procedures are used to avoid numerical difficulties in the transient position of the interface toe for two‐dimensional areal flow.The numerical solution was tested against the analytical ones for the cases of an advancing interface and of a floating fresh‐water lens over sea water. These tests showed good agreement, thus verifying the finite‐difference approximation. The results of an application of this model to a real aquifer are discussed in a companion paper entitled: “A Compatible Single‐Phase/Two‐Phase Numerical Model 2. Application

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02231.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTSix borehole methods for determining the vertical distribution of hydraulic conductivity in unconsolidated geologic formations are evaluated. Straddle packer tests are inappropriate if there is a hydraulic path around the packer on the outside of the well screen. Methods based on grain‐size analysis fail to incorporate the influence of small‐scale structure and packing. Methods based on relationships between electrical and hydraulic conductivity require special conditions and are site‐ and formation‐specific. Borehole effects invalidate methods based on the natural flow of fluid through a well bore. Stoneley wave attenuation methods are not effective in unconsolidated formations. A single‐well electrical tracer test is effective, but requires the injection of significant volumes

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1990.tb02232.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY