Showing papers by "Karim C. Abbaspour published in 2004"

Estimating Uncertain Flow and Transport Parameters Using a Sequential Uncertainty Fitting Procedure

Abstract: Inversely obtained hydrologic parameters are always uncertain (nonunique) because of errors associated with the measurements and the invoked conceptual model, among other factors. Quantification of this uncertainty in multidimensional parameter space is often difficult because of complexities in the structure of the objective function. In this study we describe parameter uncertainties using uniform distributions and fit these distributions iteratively within larger absolute intervals such that two criteria are met: (i) bracketing most of the measured data (>90%) within the 95% prediction uncertainty (95PPU) and (ii) obtaining a small ratio (<1) of the average difference between the upper and lower 95PPU and the standard deviation of the measured data. We define a model as calibrated if, upon reaching these two criteria, a significant R 2 exists between the observed and simulated results. A program, SUFI-2, was developed and tested for the calibration of two bottom ash landfills. SUFI-2 performs a combined optimization and uncertainty analysis using a global search procedure and can deal with a large number of parameters through Latin hypercube sampling. We explain the above concepts using an example in which two municipal solid waste incinerator bottom ash monofills were successfully calibrated and tested for flow, and one monofill also for transport. Because of high levels of heavy metals in the leachate, monitoring and modeling of such landfills is critical from environmental points of view.

Research Note: Estimation of Field Capacity and Wilting Point from Basic Soil Physical and Chemical Properties

Abstract: In recent years, using pedotransfer functions to estimate hard-to-measure soil properties has become an attractive alternative to direct measurements due to savings in time and experimental costs. The purpose of this study was to investigate the use of pedotransfer functions in estimating field capacity and wilting point from soil texture, organic matter, and cation exchange capacity (CEC). Soil samples collected from the arid region of Isfahan, Iran, were used for this study. The results indicated a strong linear correlation between the field capacity and sand and CEC, and between wilting point and silt and CEC. We found that CEC was a more important factor for estimating field capacity and wilting point than clay and organic matter content, as the former incorporates the effects of both clay and organic matter content.

Hydrological and geochemical factors controlling leachate composition in incinerator ash landfills

Abstract: Abstract The hydrological and geochemical processes that control leachate composition are discussed for two examples, the first being a landfill containing municipal solid waste incinerator (MSWI) bottom ash, Landfill Lostorf, and the second a lysimeter containing blocks of cement-stabilized MSWI air pollution control (APC) residues. In both examples the leachate consists of a component that takes months to years to pass through the landfill and rainwater that passes through the landfilled material via preferential flow paths. The composition of the leachate is relatively constant and is only diluted with rainwater during rain events. The concentration of major leachate components (Na+, K+, Cl− and OH−) is controlled by diffusion processes and by the precipitation of solubility-controlling phases (Ca(II), Al(III), SO42− and Si(IV)). The observed concentrations of some relatively insoluble heavy metal and metalloid species may be explained by the precipitation of secondary phases. More soluble species may be adsorbed on surfaces of or incorporated in minerals, but the mechanisms remain to be elucidated.