Leachate from ground wood stockpiled at recycling facilities may be detrimental to water quality. Although mathematical modeling of water movement through stockpiles may help estimate leachate quantity, information on water retention and unsaturated hydraulic conductivity of wood particles needed to run the models are unavailable. Our objectives were to (a) estimate the hydraulic properties of field stockpiled wood material, (b) assess performance of three models of pore structure in simulating water flow, and (c) determine relationships between optimized hydraulic parameters and particle size. The particle size distributions (PSDs) of thirty samples collected from stockpiles of coarsely and finely ground wood were measured, and their geometric mean diameters (dg) and distribution spreads (So) were used to establish two groups (I and II), with Group I samples having greater dg values for any given So than Group II samples. Six samples with PSDs representative of both groups were selected for hydraulic characterization. Material was packed in acrylic flow cells and outflow was induced by applying successive pressure potentials of -2, -10 and -40 cm to the bottom of the cells. Water retention data from outflow tests and from steady state measurements carried out in pressure extractors at potentials of -200, -500, -2000 and -10000 cm were fitted to unimodal and bimodal water retention functions. Inverse modeling of outflow data was performed using the software HYDRUS-1D and assuming (1) a unimodal pore-size distribution-SPM, (2) a bimodal pore-size distribution –DPM, (3) two distinct and interacting pore domains each with their own water retention and hydraulic conductivity functions-DPeM. Wood material released almost 50% of their total water at -2 cm with Group I samples releasing significantly higher volumes than Group II. All models of pore structure captured outflow dynamics. Statistical tests indicated that the DPeM followed by the SPM were the best models for conductivity and the DPM for water retention. Parameters of hydraulic models could be estimated from PSD data. Predictions by all models indicate that hydraulic conductivity of the unsaturated material is very low (around 0.09 cm/hr at -10 cm), suggesting that water would move slowly through stockpiles except during intense rainfalls.
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Environmental Sciences
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Rutgers University Electronic Theses and Dissertations
Rutgers University. Graduate School - New Brunswick
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