Landfill Cap Soil and Vegetation Responses to Municipal Solid Waste Leachate Applications.
Neil MacDonald1, Richard R. Rediske2, and Brian T. Scull2. (1) 1 Campus Dr., Grand Valley State Univ., Grand Valley State University, Department of Biology, Allendale, MI 49401-9403, (2) Grand Valley State Univ, Annis Water Resources Institute, Muskegon, MI 49441
The Michigan Department of Environmental Quality completed the capping of the Fenske landfill near Grand Rapids, Michigan in 2002, and spray irrigated the municipal solid waste leachate on the landfill cap between 2003 and 2005. We studied the effects of these leachate applications on soil chemistry, solute leaching, and plant growth on six 20-m diameter plots: three that were spray irrigated at operational levels and three that remained as untreated controls. The landfill leachate was high in conductivity, ammonium-N, and total organic carbon, but low in metals and volatile organic compounds. In 2003, initial high rates of leachate application produced elevated soil solution concentrations of nitrate-N (>135 mg/L) and soil solution conductivities exceeding 0.4 S/m. To reduce leachate constituent deposition rates and potential for elevated leaching losses, leachate applications in 2004 and 2005 were timed to match periods of greatest evapotranspirational demand (May-September), and each spray head on the landfill cap was sequentially rotated among three non-overlapping spray areas. While soil electrical conductivities and soil solution nitrate-N concentrations remained elevated on irrigated plots as compared to controls, they declined on irrigated plots through time. Leachate applications had no significant effects on soil metal or volatile organic compound concentrations during the study. Plant biomass on irrigated plots was significantly greater than on control plots in all years, while plant metal concentrations on irrigated plots remained within normal ranges. The sequential rotation of spray areas instituted in 2004 was effective in reducing the localized impacts of leachate irrigation observed in 2003, while still permitting the efficient disposal of leachate on site. While elevated leaching of nitrate-N remains of concern, the potential for adverse impacts of leachate application on soil properties and plant growth has been greatly reduced.