Characterizing hydrologic and contaminant transport attributes of scoriated lipillistone for emplacement of municipal solid waste

Unconsolidated, volcanic cinder (scoriated lipillistone) underlies the unlined City of Flagstaff - Cinder Lake Landfill in the eastern portion of the San Francisco Volcanic Field, north-central Arizona. Hydrologic transport through this material is primarily unsaturated. Experimental data derived from manipulating the moisture content of this material was used to establish a relationship between pressure head and volumetric water content, which was used to develop a moisture release curve. Numerical modeling based on previous work from van Genuchten (1980) was used to determine parameters that describe the shape of the moisture release curve. These parameters were used in a subsequent van Genuchten (1991) numerical model to estimate unsaturated hydraulic conductivity of the material over a narrow range of volumetric water contents.;Contaminant transport characteristics were evaluated using unsaturated column experiments. Synthetic landfill leachate, which was used in column experiments, was created by dissolving nine different molecular compounds in deionized water which contained thirteen different contaminant ionic species. These ionic species are commonly found in soil pore-water beneath Cinder Lake Landfill. This leachate was passed through unconsolidated, scoriated lipillistone and it was discovered that over 95% of metals in solution were retained by material in the column. At the beginning of each experiment, acetate (measured as total carbon) passed through the column and total carbon was being released at concentrations greater than the initial concentration. By the end of the experiments, acetate was retained. Metal ions may complex with acetate in solution and react with scoriated lipillistone in the column. Some cations displaced other cations on the scoriated lipillistone exchange substrate while others passed through. Most anions passed through unaffected. However, arsenic, present as As-2, did not. Arsenic exhibited the behavior of either a retained cation or metal ion suggesting that it may have oxidized and complexed with iron oxides in scoriated lipillistone. It is estimated that it will take over 1,300 years to saturate scoriated lipillistone with landfill leachate contaminants.;This study shows that scoriated lipillistone may be a good candidate for leachate drainage/filter material in the engineered design for the landfill liner in Cinder Lake Landfill expansion areas. Scoriated lipillistone reduces the concentration of certain contaminants in landfill leachate even at flux rates that are three orders of magnitude greater than what is predicted to occur from Cinder Lake Landfill. This study also shows that the hydrologic characteristics of scoriated lipillistone are not typical as compared to finer grained materials found in the literature. This is due to the minimization of capillary forces and dominance of gravity caused by large pore-spaces, along with a zero pressure head air entry value, both of which significantly contribute to the unique hydrologic characteristics of scoriated lipillistone. However, there is still adequate pore-space for storage of fluids to accommodate any landfill leachate that may be generated by Cinder Lake Landfill.