Properties of geosynthetics exhumed from a final cover at a solid waste landfill

Samples of geocomposite drain (GCD), geomembrane (GM), and geosynthetic clay liner (GCL) were exhumed from a final cover at a solid waste landfill to assess their condition after 4.7–5.8 yr of service. Permittivity of the GCD diminished by a factor of 3.9, but the transmissivity was higher than published by the manufacturer. Ply adhesion of the GCD diminished by a factor of 2.0. Geonet ribs in the geocomposite drain (GCD) contained a light coating of fines and plant roots, but there was no evidence of significant clogging. The geotextile on the upper surface of the GCD met the commonly used criterion for filtration (AOS < 0.6 mm for adjacent soil with <50% fines), indicating that this filtration criterion was satisfactory. Tensile yield strength of the GM diminished by a factor of 1.2, but the melt flow index was unchanged and the oxidation induction time exceeded the manufacturer's specification. GCD-geomembrane interface strength appeared unchanged. Four GCL samples had hydraulic conductivities 1000–10,000 times higher than the hydraulic conductivity measured during construction, whereas hydraulic conductivity of the other seven samples was practically unchanged. Based on these observations, the following reduction factors are suggested for installation damage and near-term service conditions (<6 yr) for the geosynthetics used at this site: GCD permittivity or transmissivity – 4.0, GCD ply adhesion – 2.0, geomembrane tensile strength – 1.5, and GCD-geomembrane interface friction – 1.0. No recommendation is made regarding a factor for the hydraulic conductivity of GCLs.