Design of Sand-Based Landfill Liners as Waste Containment Barriers in Coastal Areas

Two compaction energies, the Reduced British Standard Light (RBSL) and British Standard Heavy (BSH) covering a wide range of compactive efforts were used to investigate the variations in the hydraulic conductivity with compactive effort and bentonite content for sand-bentonite mixes. In this study the Patani sand from South-South Niger Delta, Nigeria was mixed with bentonite at varying percentages of 0%, 2.5%, 5.0%, 7.5%, and 10% by weight of sand. The index properties of the Patani sand are: specific gravity - 2.65, fines content (<0.075mm) - 4.65%, and SiO₂ content – 97.01%. The bentonite has fines content (<0.075mm) of 83.5%, liquid limit of 176.4%, and plasticity index of 115.3%. Test results indicate that hydraulic conductivity (k) of mixtures decreased by three orders of magnitude from 3.919×10^–7 m/s to 3.792×10^-10 m/s with increasing of bentonite content from 0% to 10% under the RBSL compaction, and from 3.704×10^–7 m/s to 2.700×10^-10 m/s with increasing of bentonite content from 0% to 10% under the BSH compaction. The hydraulic conductivity values at 5% bentonite content of 7.518×10^–9 m/s and 5.673×10^-9 m/s for RBSL and BSH compaction satisfied the specification of hydraulic conductivity, k ≤ 1×10^-9 m/sec for landfill liners by the United States Environmental Protection Agency. Mixing sand with appropriate bentonite contents and adequate compaction yielded a sand-bentonite mixture having low hydraulic conductivity that could be useful as a hydraulic barrier/waste containment liner for the Niger Delta coastal areas.