Effects of Aggressive Leachates on Modified Geosynthetic Clay Liners (GCLs)

Investigator: Florida State University

Start Date:
October 2017

Award Amount:
$152,105

Municipal solid waste incinerator (MSW-I) residues are being co-landfilled in MSW landfills or mono-filled in several states in the U.S. When MSW is incinerated, the organic matter in the waste is combusted and converted into CO2, leaving the inorganic material in the MSW-ash. Leachates from these types of waste contain cations at concentrations of a few orders of magnitude higher than typical MSW leachate and can significantly affect the performance of geosynthetic clay liners (GCLs). GCLs are hydraulic barrier systems that have a very low hydraulic conductivity to prevent contamination of the surrounding ground water. The aggressive characteristics (e.g. high total dissolved solids, such as K+, Na+, Mg2+ Ca2+ and NH4+ of the MSW-I landfill leachates may alter the bentonite fabric and lead to unacceptable increase in hydraulic conductivity. To resist these high ionic strength leachates, polymer-modified bentonites (PMBs) GCLs containing a blend of Na-B and various polymers have been introduced in recent years; these GCLs are referred to as second generation GCLs. The performance data and design criteria from the first generation GCLs cannot be directly applied to the second generation of GCLs, as the first generation of GCLs cannot manage the increased contaminants in the leachate. To date, only a limited number of studies have been performed on polymer modified GCLs, and the effects of the aggressive leachates on the performance and design of the second generation GCLs have not been well understood.

The first objective of this study is to develop new alternative index tests, or criteria to predict the long-term hydraulic performance of the second generation GCLs. The second objective is to mechanistically understand how aggressive leachates like the MSW-I ash landfill leachate affect the performance of the second generation GCLs. The proposed study will also add more data to the literature on polymer modified GCLs.