An Assessment of an Alternative Cap Cover for the King Road Landfill

It is difficult to design Evapotranspiration (ET) covers that satisfy performance requirements for solid waste landfills in humid regions that are also economical because of the excess precipitation relative to ET. The Ohio EPA is allowing a remedial option wherein native plants can be included in the vegetative configuration for creating an ET cover for the former King Road Landfill, located in Lucas County, Ohio, to restore more than 100 acres of local Oak Openings ecosystem. The objective of this research is to utilize numerical models to predict the effectiveness of an ET cover that incorporates native plants and soil that is derived from waste materials. The alternative cover material that is being considered is NU-Soil, a locally mixed soil of dredged material and biosolids stabilized with waste lime from a water treatment plant. Trial 730-day simulations of lysimeters were conducted with Virginia wild rye as the vegetative cover using HYDRUS 2D. Several 730-day simulations were conducted on a section of the landfill cover. The neural network option in HYDRUS 2D based on the textural percentages and the bulk density of the NU-Soil was utilized to predict soil retention functions as well as the hydraulic conductivity function. The results of several HYDRUS 2D lysimeter simulations gave cumulative bottom flux results below the EPA maximum allowable annual leachate criteria of for Subtitle D covers of 32 cm.

Groundwater Modeling System (GMS) was also utilized to model existing steady state groundwater elevations and to model the effects of the placement of an alternative cap. The results of the GMS simulations show that placement of an alternative cap lowered the existing groundwater elevations by 40 feet. Hydraulic Evaluation of Landfill Performance (HELP) is a computer simulation program and is considered the industry standard. HELP was utilized to validate the HYDRUS 2D models. The HELP simulation results which included historical climate data for Toledo, Ohio also showed the alternative cap meeting the EPA criteria for subtitle D covers.