Browsing by Author "Rifai, Hanadi Said"

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    Numerical techniques for modeling in situ biorestoration and biodegradation of organic contaminants in groundwater
    (1989) Rifai, Hanadi Said; Bedient, Philip B.
    Biodegradation, the transformation of organic matter using microorganisms, is a promising technology for ground water cleanup. The research presented in this dissertation is aimed at developing numerical techniques for simulating biodegradation coupled with physical transport processes in ground water. The focus is mainly on aerobic biodegradation. A two-dimensional biodegradation model, BIOPLUME II, was developed that incorporates two different conceptual approaches for simulating aerobic biodegradation. The first approach assumes that the transport of oxygen into a contaminant plume is limiting and that biodegradation could be approximated with an instantaneous reaction between the contaminants and oxygen. The second approach argues that the biodegradation of organic contaminants is kinetically limited by microbial utilization rates and that the process could be represented with a dual Monod kinetic relationship between oxygen and the contaminants. Comparisons between the instantaneous model and the kinetic model suggest that oxygen transport is limiting in aquifers with seepage velocities less than 0.03 ft/d. The rate of oxygen utilization takes on more importance in aquifers with high velocities and for organic contaminants which are slowly degrading. The instantaneous reaction model is applied to a pilot scale bioremediation demonstration project at the Traverse City field site. A nutrient mix containing phosphate, ammonia and an oxygen source is injected into a portion of the contaminated aquifer. The BIOPLUME II model was used to select the design parameters for the test, mainly: the injection flow rate, the number of injection wells and the time required for renovation. Dissolved oxygen and contamination data from the monitoring wells in the demonstration area for the last ten months of operation were analyzed to assess the degree of cleanup. The field data indicate that benzene, toluene, ethyl benzene, and xylenes have been selectively removed from the soils and water in the demonstration area. The field data were compared to the predictions from the BIOPLUME II model. The model results imply that modeling is a useful tool for predicting the biodegradation of organic contaminants in ground water.
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    On-line hydrologic simulation of Lake Conroe Reservoir releases for downstream flood control
    (1985) Rifai, Hanadi Said; Bedient, Philip B.; Andrews, John F.; Rowe, Peter G.
    Lake Conroe was designed for water supply and not for flood control. As a result, a flood control release policy was not established for the reservoir. This study seeks to establish the effect of Lake Conroe releases on downstream flooding and to develop operational policies to release the excess stormwater from the reservoir. A computer model was programmed on a microcomputer (Apple IIe) to simulate the response of the Lake Conroe watershed to a storm event and to provide the operators at Lake Conroe with a viable method of on-line simulation. The model was calibrated with data from four historical events and verified against simulations from HEC-1, a flood hydrograph model. Recommended operational policies on four design storms were developed with the objective of minimizing peak releases from the dam. Guidelines for developing a release scheme for any design storm event were established based on the results of the HEC-1 analysis.