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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Surface application offers an inexpensive, noninvasive alternative to injection wells and infiltration galleries for in situ ground-water bioreniediation applications. The technology employs artificial recharge to create favorable hydraulic conditions for mixing and vertical transport of supplemental electron acceptor and nutrients. A test plot infdtration test and a conservative tracer test at Eglin Air Force Base, FL confirmed the potential for transporting solutes to the subsurface via recharging water. These experiments demonstrated both the mounding hydraulics and vertical solute transport that occurs in response to surface application. Modeling provided quantitative estimates of site-specific hydrogeologic and transport parameters. Experimental results also indicated that dilution may be a dominant attenuation mechanism associated with high surface application rates. The tests also served as the basis for the design of a pilot scale surface application system for delivery of nitrate to bioremediate a JP-4 contaminated aquifer at the Eglin site. Models calibrated to data from the infiltration experiment were scaled up for design of the pilot scale surface application system. Preliminary tracer results from the pilot scale experiment confirm that surface application can adequately deliver chemicals to the subsurface.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 16 (1980), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : A circulation and salinity model was used to predict the effects of wind, fresh water inflow, and the construction of a navigation channel on Vermilion Bay, Louisiana. The model numerically solved continuity and motion equations and provided a time history and spatial distribution of tidal depths, flows, velocities, and salinity in two lateral dimensions. The model predicted that high south winds or high fresh water inflow would reduce average bay salinities, as would the construction of a channel through Vermilion Bay. The results suggested the main reason for this behavior is the presence of two bay outlets to the Gulf of Mexico.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 16 (1980), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The effect of urbanization on alternative flood control strategies was investigated for a large developing watershed in Texas. Urban and rural areas were modeled separately using a geographically-referenced data base and the U.S. Corps of Engineers HEC-1 and HEC-2 programs, and results yielded a double-peaked hydrograph. Hydrograph input parameters were modified to predict the effects of a wide range of management alternatives including on-site storage, reservoirs, channelization, and development controls. Results indicated a combination of alternatives is required to protect existing and future developments.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 17 (1997), S. 0 
    ISSN: 1539-6924
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: A central part of probabilistic public health risk assessment is the selection of probability distributions for the uncertain input variables. In this paper, we apply the first-order reliability method (FORM)(1–3) as a probabilistic tool to assess the effect of probability distributions of the input random variables on the probability that risk exceeds a threshold level (termed the probability of failure) and on the relevant probabilistic sensitivities. The analysis was applied to a case study given by Thompson et al.(4) on cancer risk caused by the ingestion of benzene contaminated soil. Normal, lognormal, and uniform distributions were used in the analysis. The results show that the selection of a probability distribution function for the uncertain variables in this case study had a moderate impact on the probability that values would fall above a given threshold risk when the threshold risk is at the 50th percentile of the original distribution given by Thompson et al.(4) The impact was much greater when the threshold risk level was at the 95th percentile. The impact on uncertainty sensitivity, however, showed a reversed trend, where the impact was more appreciable for the 50th percentile of the original distribution of risk given by Thompson et al.4 than for the 95th percentile. Nevertheless, the choice of distribution shape did not alter the order of probabilistic sensitivity of the basic uncertain variables.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 28 (1990), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A new hydrogeologic database, the HGDB, was developed from a national survey of National Water Well Association (NWWA) members. The database contains general hydrogeologic information from 400 field site investigations across the country and detailed statistical summaries of five ground-water parameters: hydraulic conductivity, seepage velocity, hydraulic gradient, saturated thickness, and depth to top of aquifer. The HGDB was developed to verify and expand statistical distributions used in a Monte Carlo ground-water model developed by EPA for land disposal regulation (Federal Register, 1986,1988).The database structure is a unique application of the aquifer classification method used in the NWWA's DRASTIC system (Aller et al., 1987). Respondents were asked to classify their aquifers as one of 111 different DRASTIC hydrogeologic settings, and 12 groupings of settings were analyzed to produce statistical distributions of hydrogeologic data based on site geology and geomorphology. Three examples of the hydrogeologic groupings are coastal beaches; alluvial basins, valleys and fans; and outwash settings.The HGDB can be used for several purposes. First, the HGDB results indicate that the EPA's distributions of seepage velocity and hydraulic conductivity used in the land disposal model are sound. These are the most important hydrogeologic parameters in the model. The HGDB goes a step further, and provides a set of statistical distributions that can be used to make the land disposal regulations more site-specific than the national approach now being used. Finally, the HGDB data can be used for general site characterization and for educational purposes. The database is available as a detailed written report and spreadsheet file from the American Petroleum Institute, and is contained in a graphical computerized decision support system for ground-water modeling called OASIS. The HGDB serves as a framework for organizing hydrogeologic information from different site investigations and can be expanded easily beyond the 400 sites now in the database.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 35 (1997), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The effect of parameter uncertainty and overly conservative measures on risk assessment has been addressed in numerous researches. Most of the work conducted to date is based on the use of the classic Monte Carlo simulation method (MCS) as a probabilistic modeling tool. Although the MCS is robust and asymptotically convergent, it lacks computational efficiency when the simulated probability is small. Furthermore, the sensitivity information can only be obtained with additional computational effort. First- and second-order reliability methods (FORM and SORM) have been developed in the structural analysis field and have been recently applied to ground-water contaminant transport and remediation problems. In this work, we extend the application of the reliability methods to the probabilistic assessment of cancer risk due to ground-water contamination. Results of the reliability methods compared well with a published case study of PCE contamination of a ground-water supply in California. The target risk level is extended over a larger range, and the sensitivity of the probability of failure to the relevant random variables is analyzed. The application of the methods to another case study, cancer risk due to the ingestion of benzene contaminated water, further illustrates a systematic way of directly accounting for the intrinsic uncertainty of the transport and fate model parameters involved in the risk assessment procedure. The probability of exceeding the target risk level in this case was found to be most sensitive to the uncertainty in the parameters describing the ground-water transport process.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 26 (1988), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The USGS MOC Model is a useful tool for evaluating different well patterns in an aquifer restoration scheme under variable hydrogeologic conditions. The best well pattern for a ground-water cleanup is highly site-specific and depends upon the objectives and constraints for each problem. In this study, seven different well patterns were investigated to determine the one(s) most efficient in achieving a range of desired levels of contaminant reduction. The well patterns were evaluated on the basis of cleanup time, volume of water circulated, and volume of water requiring treatment. Eight generic hydrogeologic conditions were modeled using different combinations of drawdown, hydraulic gradient, and dispersivity. The key hydrogeologic variables which control the rate of cleanup are well locations, pumping rates, transmissivity, dispersivity, and hydraulic gradient. For a given set of well locations, by varying transmissivity and maintaining drawdown, dispersivity, and hydraulic gradient constant, the cleanup time was found to be inversely related to the pumping rate.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 30 (1992), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Chromatographic analysis of published laboratory data suggests that the observed tailing behavior of aromatics (benzene, toluene, ethylbenzene, and xylene) being leached from a residual-petroleum phase into a flushing-water phase is explicable using nonlinear (specifically favorable) partitioning relations in the absence of kinetic limitations. This result raises questions regarding the legitimacy of deducing kinetic limitations of interphase transfer based upon the assumption of linear partitioning.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 28 (1990), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Three new software technologies were applied to develop an efficient and easy to use decision support system for ground-water contaminant modeling. Graphical interfaces create a more intuitive and effective form of communication with the computer compared to text-based interfaces. Concepts from the field of hypertext were applied to design the extensive electronic documentation and databases. Finally, object oriented programming permitted scientists with little programming experience to develop the system by manipulating preexisting software objects instead of writing computer code, greatly increasing the productivity of the project team.A decision support system is a class of software with different origins and characteristics than conventional programs or expert systems. Decision support systems are designed to help users with broad, semistructured problems, with the user directing the problem-solving process. The decision support software described in this paper, the OASIS system, provides ground-water modelers with a ground-water biodegradation model, model documentation, background information, data from chemical and hydrogeologic databases, and data management tools. The system was developed using HyperCard software on a Macintosh personal computer. It currently has over 1700 different computer screens of information and occupies approximately 10 megabytes of hard disk storage.OASIS is a new type of modeling software where ground-water models, data, and knowledge are integrated together using a graphical interface and an easily modified software architecture. Two groups of users can benefit from the system: current modelers who need more efficient interfaces and data management tools, and people who are not using models now because the modeling process is too involved and requires specialized knowledge.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 11 (1975), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : An environmental simulation model of the Upper St. Johns River Basin, Florida, has been developed in order to predict hydrologic responses under proposed management plans. Land use projections for each of 19 hydrologic planning units are provided by a linear programming analysis of agricultural activities. Inputs to the model include rainfall, runoff, evapotranspiration (ET), aquifer properties, topography, soil types, and vegetative patterns. A water balance is developed in the uplands based on infiltration, ET, surface runoff, and groundwater flow. Valley continuity is based on stage-volume relationship for inflows and outflows and a variable roughness coefficient dependent on vegetative patterns. Land use changes form the basis for predicting hydroperiod variation under alternative management schemes. Plans are ranked according to two criteria, deviation from a natural hydroperiod and flood or drought control provided. Results indicate that (1) a single reservoir without irrigation and (2) floodplain preservation plans are superior to (3) multiple reservoir with irrigation and (4) uncontrolled floodplain plans with regard to both criteria.
    Type of Medium: Electronic Resource
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