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A semianalytical model to predict recovery of light, nonaqueous phase liquids from unconfined aquifers
Contamination of soil and ground water due to spills of light nonaqueous phase liquids (LNAPL or simply oil) is a widespread environmental problem. This paper describes the development and testing of a semianalytical model that may be used to design LNAPL containment and recovery systems at spill si...
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Published in: | Ground water 1997-03, Vol.35 (2), p.280-290 |
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Main Authors: | , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Contamination of soil and ground water due to spills of light nonaqueous phase liquids (LNAPL or simply oil) is a widespread environmental problem. This paper describes the development and testing of a semianalytical model that may be used to design LNAPL containment and recovery systems at spill sites. The objective of this study was to derive an enhanced semianalytical algorithm for calculating recovery and trapping of free phase oil. The enhancements were derived and evaluated by comparison with an established numerical model that describes transient flow of oil and water. The semianalytical model employs an analytical solution for steady-state drawdown in an unconfined aquifer due to water pumping. When pumping rates are sufficient to contain the separate phase plume, the model calculates recoverable and residual oil volumes based on the initial free oil distribution. Refinements were implemented to calculate the water-table drawdown and the maximum unsaturated zone residual saturation (Sog) as functions of soil type. Also the influence of hysteresis on the oil-water capillary fringe was incorporated into the calculation of oil trapping below a rising oil-water interface. A method was derived to reduce saturated zone trapping to account for oil recovery that occurs while pumping proceeds. The above enhancements yielded close agreement between the semianalytical model and the transient model predictions of recoverable oil and residual oil in the unsaturated and saturated zones. The models were compared for hypothetical gasoline spills in a sandy and a silt loam soil, using a range of pumping rates and regional water-table fluctuations. Field data from a pipeline leak were evaluated by the semianalytical model for hypothetical scenarios involving oil recovery from three wells and a falling regional water table. Results suggest that the semianalytical model captures many of the trends of transient oil recovery |
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ISSN: | 0017-467X 1745-6584 |
DOI: | 10.1111/j.1745-6584.1997.tb00085.x |