ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe computer program, RORA, allows automated analysis of streamflow hydrographs to estimate ground‐water recharge. Output from the program, which is based on the recession‐curve‐displacement method (often referred to as the Rorabaugh method, for whom the program is named), was compared to estimates of recharge obtained from a manual analysis of 156 years of streamflow record from 15 streamflow‐gaging stations in the eastern United States. Statistical tests showed that there was no significant difference between paired estimates of annual recharge by the two methods. Tests of the slopes of best‐fit lines through paired estimates showed that the slopes were not significantly different from unity. Tests of results produced by the four workers who performed the manual method showed that results can differ significantly between workers. Twenty‐two percent of the variation between manual and automated estimates could be attributed to having different workers perform the manual method. The program RORA will produce estimates of recharge equivalent to estimates produced manually, greatly increase the speed of analysis, and reduce the subjectivity inherent in manu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00632.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTraditional environmental investigations at tidally influenced hazardous waste sites such as marine fuel storage terminals have generally failed to characterize ground‐water flow and chemical transport because they have been based on only a cursory knowledge of plume geometry, chemicals encountered, and hydrogeologic setting and synoptic ground‐water‐ level measurements. Single‐time observations cannot be used to accurately determine flow direction and gradient in tidally fluctuating aquifers since these measurements delineate hydraulic head at only one point in time during a tidal cycle, not the net effect of the fluctuations. In this study, a more rigorous approach was used to characterize flow and chemical transport in a tidally influenced aquifer at a marine fuel storage terminal using: (1) ground‐water‐level monitoring over three tidal cycles (72 hours), (2) geostatistical filtering of ground‐water‐level data using 25‐hour and 71‐hour filtering methods, and (3) hydrocarbon fingerprinting analysis.The results from the study indicate that naphtha released from one of the on‐site naphtha tanks has been the predominant contributor to the hydrocarbon plume both on‐site and downgradient off‐site and that net ground‐water and hydrocarbon movement has been to the southeast away from the tank since 1989. These conclusions are supported by: (1) the elongate configuration of the hydrocarbon plume parallel to the mean ground‐water flow directions determined using the 25‐hour and 71‐hour filtering methods; and (2) the occurrence of free‐naphtha‐product and elevated levels of BTXE and TPH in the naphtha range (C7to C14) downgradient, but not upgradient, of the naphtha tank. The results also indicate that ground water containing 2.1 to 3.6 ppm TPH in the motor oil range (C22to C32) is migrating onto the site from an upgradient source area to the north and/or northwest. Therefore, the background concentration or cleanup level of TPH for the facility is 2.1 ppm or greater. This study provides a more quantitative approach than traditional approaches for characterizing flow, assessing chemical transport and upgradient impacts, determining site‐specific ground‐water cleanup levels, and optimally locating ground‐water monitor wells and extraction wells or trenches

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00633.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe most extensive data base for fractured bedrock aquifers consists of drilling reports maintained by various state agencies. We investigated the accuracy and reliability of such reports by comparing a representative set of reports for nine wells drilled by conventional air percussion methods in granite with a suite of geophysical logs for the same wells designed to identify the depths of fractures intersecting the well bore which may have produced water during aquifer tests. Production estimates reported by the driller ranged from less than 1 to almost 10 gallons per minute. The moderate drawdowns maintained during subsequent production tests were associated with approximately the same flows as those measured when boreholes were dewatered during air percussion drilling. We believe the estimates of production during drilling and drawdown tests were similar because partial fracture zone dewatering during drilling prevented larger inflows otherwise expected from the steeper drawdowns during drilling. The fractures and fracture zones indicated on the drilling report and the amounts of water produced by these fractures during drilling generally agree with those identified from the geophysical log analysis. Most water production occurred from two fractured and weathered zones which are separated by an interval of unweathered granite. The fractures identified in the drilling reports show various depth discrepancies in comparison to the geophysical logs, which are subject to much better depth control. However, the depths of the fractures associated with water production on the drilling report are comparable to the depths of the fractures shown to be the source of water inflow in the geophysical log analysis. Other differences in the relative contribution of flow from fracture zones may by attributed to the differences between the hydraulic conditions during drilling, which represent large, prolonged drawdowns, and pumping tests, which consisted of smaller drawdowns maintained over shorter periods. We conclude that drilling reports filed by experienced well drillers contain useful information about the depth, thickness, degree of weathering, and production capacity of fracture zones supplying typical domestic water wells. The accuracy of this information could be improved if relatively simple and inexpensive geophysical well logs such as gamma, caliper, and normal resistivity logs were routinely run in conjunction with bedrock drilling projects.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00634.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMultiport ground‐water sampling systems in five deep core holes near DOE's Y‐12 facility at Oak Ridge, Tennessee provide data on the three‐dimensional distribution of ground‐water types and chemical evolution processes. Interpretation of ground‐water chemistry, coupled with data on the primary and authigenic mineralogy from drill core, indicates the ground water evolves chemically by three main processes: (1) open system dissolution of calcite and dolomite at shallow depths to produce Ca‐Mg‐HCO3waters; (2) irreversible dissolution of gypsum, which causes dedolomitization and leads to the formation of Ca‐Mg‐SO4waters at deeper levels; and (3) mixing with deep brines to form saline Na‐Ca‐Cl waters. Evidence for dedolomitization included the precipitation of authigenic calcite in gypsum dissolution cavities, decrease in ground‐water pH, and increases in dissolved Ca, Mg, and SO4. In this study, we document the dedolomitization process along a relatively short (<2000 ft) flow path in low permeability Paleozoic carbonates. Mixing of the shallower ground water with an Na‐Ca‐Cl brine thought to be present at depth can account for the progressive increase in salinity of ground water with depth and the precipitation of authigenic barite and celestite. The mixing process could be a combination of diffusion from below, diffusion from older matrix water into fra

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00635.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSubsurface unsaturated soils and ground water directly beneath a manufacturing site have been shown to contain benzene. The vadose zone appears to be the current source for benzene to the aquifer. Although the ground water contains several mg/1 of contamination in the area immediately beneath the source, benzene was not detected in monitoring wells approximately 400 feet downgradient. Based upon the length of time benzene has been present in the ground water, as well as the permeability of the aquifer, physical processes alone such as adsorption and advection/dispersion are unlikely to account for the observed attenuation. Results from this investigation indicated the attenuation was primarily due to the natural biological processes occurring within the aquifer.Evidence for the natural bioremediation of benzene from the ground water included: (1) analysis of ground‐water chemistry, (2) laboratory studies demonstrating benzene biodegradation in aquifer samples, and (3) computer simulations examining contaminant transport. Laboratory studies indicated that under conditions similar to those encountered in the ground water, benzene was degraded to carbon dioxide by the naturally occurring microorganisms. The aerobic degradation of benzene in aquifer samples was quite rapid, with the time for 50% disappearance of the parent compound ranging from 4 to 14 days. In situ analyses of the ground water indicated significant levels of dissolved oxygen throughout the aquifer. Thus, the availability of oxygen should not limit the aerobic biodegradation of benzene. However, benzene was also shown to degrade under anaerobic conditions in microcosms prepared with aquifer material. Computer model simulations were also conducted to examine the processes influencing the transport of benzene in the aquifer. Results from the model simulations indicated biodegradation was the dominant process influencing attenuation of the contaminan

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00636.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the dolomite aquifer of Milwaukee County, Wisconsin, stratigraphic units deposited as mudstones have little or no visible macroporosity and, based on injection‐pressure tests, have average horizontal hydraulic conductivities of approximately 10−6cm/sec, controlled by jointing. Coarse‐grained units (packstones and grainstones), however, have horizontal hydraulic conductivities of 10−4cm/sec and greater, argued to be controlled by granularity, not jointing. Using this relationship between texture and hydraulic conductivity in Milwaukee County and a sedimentary facies analysis, trends in hydraulic conductivity values are predicted for five stratigraphic units over an area of approximately 3500 km2. The predictions are tested qualitatively with sets of specific capacity values within the various stratigraphic units, and quantitatively with injection‐pressure test values from five additional locations. Seven of eight qualitative and four of six quantitative predictions are judged to be successful. Therefore, trends in hydraulic conductivity, and to some extent local values, in this carbonate aquifer are predictable over areas of thousands of square kilometers without any site‐specific data on jointing.The success rate could not have been this high if hydraulic conductivity were not controlled by the granularity of the lithologic units. It is argued, therefore, that the local bulk hydraulic conductivity of this carbonate aquifer is controlled by the granular porosity, and the aquifer will generally behave as a porous medium, even at the small scale of a typical p

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00637.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSoil parameters controlling vapor flow in the subsurface are necessary to design soil vapor extraction (SVE) cleanup systems. Previous work assumes a confined flow model, with concrete and asphalt surface covers providing the confining layer and preventing air leakage into the zone of vapor transmission. SVE field tests conducted as part of this investigation, however, exhibited responses that are inconsistent with a confined flow model; it appears that the real world leaks. This paper develops a transient soil vapor extraction (SVE) testing method that considers the effects of vertical leakage. Analytic methodologies are developed that allow use of commonly available ground‐water flow type curves to evaluate SVE test data. The key implications of leaky compared to confined flow are (1) smaller values of derived vapor permeability, and (2) decreased radial cleanup efficacy, both with time and distanc

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00638.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis communication describes novel methods to measure site‐specific sorption data, and to determine if biodegradation of pentachlorophenol (PCP) in complex technical‐grade formulations occurs at industrial facilities. Ground‐water slurry samples containing between 0.012 and 230 mg/l PCP were collected from a former wood treating site, the liquid and solid fractions separated, and both fractions analyzed for PCP using selective ion monitoring to determine sorption coefficients (Kd(PCP)). Although field sorption coefficients could not be represented by simple Freundlich and Langmuir isotherms, an empirical hyperbolic function (Kd(PCP)) = 0.054 + 0.086/Caq) fit the isotherm (r>0.99), demonstrating that for PCP>10 mg/l, no measurable retardation occurred in the aquifer. Biodegradation of PCP in ground water was apparent when PCP concentrations were<20 mg/1, while at higher concentrations, PCP in the technical‐grade formulation appeared to break down less readily. The results imply that, at the plume periphery, PCP in the subsurface will be attenuated and degrade, while at higher concentrations (i.e., at the source), PCP is mobile, and more recalcitrant to degr

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00639.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMeasurements of air‐permeability in outcrops provide a means of obtaining numerous spatially distributed measurements for statistical analysis and subsequent parameterization of ground‐water flow and transport modeling. The air‐minipermeameters previously used for such studies generally consist of a compressed air source, rotameters, and diaphragm gauges. We present a lightweight syringe‐based air‐minipermeameter (LSAMP) design that is significantly more portable than previous instruments. The prototype model is contained in a 12.7 × 15.2 × 23 centimeter (5 × 6 × 9 inch) electrical box and weighs approximately 2 kilograms. The prototype LSAMP has a sampling range of 0.5 to 200 darcys. Individual measurements in this range require less than one minute. Permeability measured with the LSAMP closely correspond to permeability measured with a traditional minipermeameter and those measured on cores. Measurement error caused by soil moisture is less than 5 percent for volumetric water contents less than 5 percent. An analysis of variance on 38 triplicate measurements indicates that the variability associated with measurement error is much less than the range of measured values. Repeated permeability measurements under field conditions on two standard cores indicate that while the measurement error is greater under field conditions, the prototype device field performance is consistent with laboratory calibr

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00640.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY