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[1998]. They designed a compartmental liquid sampler, which was inserted into a horizontal borehole, to collect infiltrating solution at multiple locations. They estimated the amount of water flowing through the fractures and imbibing into the matrix across the fracture walls and determined that under variable moisture content conditions the fracture aperture, roughness, and flow channels varied with time. They also noted that under field conditions the effective fracture aperture was more than 1 order of magnitude smaller than that expected based on laboratory conditions. Or and Ghezzehei [2000] studied water dripping into subterranean cavities in a fractured porous medium in order to improve estimates of dripping rates onto waste disposal canisters placed in caverns. These results suggest that conventional approaches and concepts, such as Darcy flow through a constant fracture aperture, may not be valid for characterizing unsaturated fractured rocks.Several laboratory-scale investigations were conducted using natural fracture cores and fracture replicas to investigate factors and processes affecting flow and transport under con- In 1996, three groups of 16 wells were drilled to install monitoring instrumentation, including vertical wells of series T (depths of 3-6.7 m), and inclined wells (270-45 ø from vertical) of series E and R (lengths of 18.3-22.9 m). In 1997, after interpretation of the results of the 1996 infiltration test, which showed a zone of preferential flow between wells R1 and R2, two additional inclined wells (R5 and R6) were drilled between existing R wells. Note that inclined boreholes were mostly drilled from the outside of the pond to reduce the disturbance to the pond surface and to intersect more vertical columnbounding fractures to better characterize the three-dimensional geometry of flow below the pond.The types of instrumentation used during the infiltration tests are summarized in Table 1. A more detailed description of the instrumentation is given by Faybishenko et al. [1998b]. All the instruments were installed in boreholes using the following method of borehole completion [Faybishenko et al., 1998d]. The instruments were attached to the outer faces of polyethylene packers mounted onto sections of 3.5-crn OD PVC manchette pipe, and the sections were glued together to form a continuous string of instruments placed at preselected depths. After the string with the probes was lowered into a borehole, the packers and the space between the packers were infilled with impermeable polyurethane resin, thus pressing the instruments against the borehole walls. This completion method ensured that no water flow occurred through the bore- small trench (15 cm high by 15 cm wide) was cut into the basalt at the location of the previous berm and a permanent concrete wall was constructed that practically eliminated water leakage beneath and through the berm. The experimental data and fitting curves are shown in Figure 6, and the fitting parameters for each test, which were determined using a lea...

To increase the operating lifetime of landfills and to lower leachate treatment costs, an increasing number of municipal solid waste (MSW) landfills are being managed as either aerobic or anaerobic bioreactors. Landfill gas composition, respiration rates, and subsidence were measured for 400 days in 200-L tanks filled with fresh waste materials to compare the relative effectiveness of the two treatments. Tanks were prepared to provide the following conditions: (1) air injection and leachate recirculation (aerobic), (2) leachate recirculation (anaerobic), and (3) no treatment (anaerobic). Respiration tests on the aerobic wet tank showed a steady decrease in oxygen consumption rates from 1.3 mol/day at 20 days to 0.1 mol/day at 400 days. Aerobic wet tanks produced, on average, 6 mol of carbon dioxide (CO 2 )/kg of MSW as compared with anaerobic wet tanks, which produced 2.2 mol methane/kg of MSW and 2.0 mol CO 2 /kg methane. Over the test period, the aerobic tanks settled on average 35%, anaerobic tanks settled 21.7%, and the no-treatment tank settled 7.5%, equivalent to overall mass loss in the corresponding reactors. Aerobic tanks reduced stabilization time and produced negligible odor compared with anaerobic tanks, possibly because of the 2 orders of magnitude lower leachate ammonia levels in the aerobic tank. Both treatment regimes provide the opportunity for disposal and remediation of liquid waste. INTRODUCTIONThe United States produces ϳ200 million t of municipal solid waste (MSW) annually, 1 of which 57% is disposed of in municipal landfills. With increasing costs and difficulties in permitting new landfill sites, existing landfill space is becoming a valuable commodity. Current regulations require capping of landfills to isolate waste from incoming rainwater and collection of leachate for treatment before release to the environment. In addition, landfill air emissions are required to be monitored to limit the release of methane (CH 4 ) and other volatile organic compounds. While this reduces the potential for contaminating surrounding air, soil, and groundwater, this design was intended to restrict exposure of air and water to the MSW. This slows or stops biodegradation rates, therefore, and increases the time required for landfill stabilization and contamination monitoring. A landfill is stabilized when leachate is no longer a pollution hazard, gas production is negligible, and the majority of settlement has occurred. 2 In an effort to increase the biodegradation rates in landfills, there has been increasing interest in managing municipal landfills either as anaerobic or aerobic bioreactors. Bioreactors optimize the conditions for microbial decomposition and accelerate stabilization and settling, thus allowing for additional MSW disposal or faster land re-use. In both aerobic and anaerobic bioreactors, leachate produced by the MSW is recirculated, redistributing nutrients and bacteria through the MSW mass. In anaerobic bioreactors, the increased water content increases the rate of CH 4 production...