The size, shape, and arrangement of structured voids 1-10 mm in size play an important role in the transport of water and solutes through soil. However, these characteristics are complex and difficult to quantify. Improved methods are needed to quantify the characteristics of these voids to better understand and predict the behavior of water and solutes passing through them. This study applied fractal analysis to soil bulk density data measured by X ray computed tomography (CT), a relatively new tool for nondestructively measuring macropore-scale density in soil cores. Studies were conducted using undisturbed soil cores (7.6 cm ID) from forested and cultivated sites in the A horizon of a Menfro silt loam soil containing macropores and using two groups of soil cores which were uniformly packed with Menfro aggregates from 1-2 mm in diameter for one group and <1 mm in diameter for the other group. Samples were probed using CT to produce a 512 by 512 digital matrix of CT pixel values corresponding to bulk density. Pixels above a specified CT "cutofF' value were designated as occupied. A box-counting method was used to find the fractal dimension of the perimeters between occupied and unoccupied pixels and of the areas formed by the unoccupied pixels. For length scales from ! to 10 mm, perimeters and areas of these regions appeared to be fractal systems. Single degree of freedom orthogonal contrast tests determined from analysis of variance showed significant differences between the fractal dimension for (1) forest and cultivated cores versus uniformly packed cores, (2) two groups of uniformly packed cores made of different aggregate sizes, and (3) forest versus cultivated cores. IntroductionThe presence of fractal geometry in many diverse geophysical systems was illustrated by Mandelbrot [1977, 1983]. Applications of fractal geometry in soil science have been made by Burrough [1981, 1983], who examined variations in properties such as sand, silt, and clay content; sodium content; soil moisture; thickness of soil deposits; electrical resistivity; pH; and bulk density at sampling intervals ranging from 0.2 to 125 m and over transects ranging from 20 to 3!25 m. Tyler and Wheatcraft [!989] applied fractal geometry to the estimation of soil water retention curves. Young and Crateford [1991] found that soil aggregates from three fields out of four fields were fractal and that the fractal dimension of the aggregates was significantly altered by rotary cultivation. Bartoli et al. [199!] described soil structure using the fractal dimension applied to mercury porosimetry data, soil thin sections, soil surface charges, and soil disaggregation kinetics. Others have applied oeractal geometry to various aspects of pore size distribution and transport in porous media [Avnir et al., 1985; Katz. and Thomps•m, 1985; Lenormand and Zarcone, 1985; Krohn and Thompson,

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Waste sorts were conducted during each of the four quarters (or seasons) of 1996 at the City of Columbia Sanitary Landfill. A detailed physical sampling protocol was outlined. Weight fractions of 32 waste components were quantified from all geographic areas that contribute to the Columbia Sanitary Landfill using a two-way stratification method, which accounted for variations in geographical regions and seasons. Comparisons of solid waste generated between locations and seasons were conducted at the 80% confidence level. The composition of the entire waste stream was 41% paper, 21% organic, 16% plastic, 6% metal, 3% glass and 13% other waste. Paper was the largest composition and glass was the smallest composition for all geographical regions. The result of this study was also compared with a 1987 Columbia, Missouri study conducted by EIERA (1987), with studies conducted in other states such as Minnesota, Wisconsin, Oregon and with national study conducted by the USEPA (USEPA 530-R-96-001, PB96-152 160. US Environmental Protection Agency, Office of Solid Waste, Washington, DC). The results of studies from other states are different from this study due to different local conditions, different methodologies and a different scope. There was a small (5%) increase in per capita weight from 1987 to 1996. The total per capita weight in the present study was 60% greater than the national per capita weight reported by the USEPA (1996) due to that the USEPA report excluded industrial, construction and certain commercial waste. The total per capita weight agrees with the national per capita weight for municipal waste reported by Tchobanoglous (1993), which included industrial, construction and commercial sources. The geographical and seasonal effects on the waste composition are evaluated and discussed. Statistical analysis indicates that waste characteristics are different among geographical regions and seasons. The potential for waste recovery and reduction is also discussed.

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Heterogeneities are common in natural porous media and are present on different scales. Use of X-ray computed tomography (CT) may provide a tool for quantifying smallscale heterogeneities in porosity and hydraulic conductivity in porous media. Porosity and saturated hydraulic conductivity distributions were estimated using CT for a series of undisturbed soil core samples taken from a field site. CT measurements were collected during breakthrough experiments using an iodide tracer. Techniques were developed to estimate porosity and hydraulic conductivity from solute breakthrough data. Results were compared with bulk sample measurements. CT-measured porosity compared well with laboratory-measured porosity. Hydraulic conductivity estimated from CT methods slightly overestimated laboratory-measured values. These techniques provide a method to quantify the spatially variable porosity and hydraulic conductivity on a millimetre scale rather than on a core-averaged scale. Chemical transport through the soil was predicted using a finite element method for each core using the CT-measured soil properties. Comparisons between measured and predicted chemical transport suggest that small-scale heterogeneities cause departures between measured and simulated solute breakthrough curves, and that a smaller grid size may be needed to improve the simulation.

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