Waste containment facilities can experience elevated temperatures for a variety of reasons such as hydration of combustion ash, aerobic biodegradation, and smoldering combustion. Elevated temperatures can reduce service life or effectiveness of geomembranes by accelerating antioxidant depletion and polymer degradation. A case history is presented to illustrate the potential effects of elevated temperatures and time-temperature history on a high-density polyethylene geomembrane and the associated reduction in service life or effectiveness. The impact of peak temperature, e.g., 60-80°C, the duration of peak temperatures (time-temperature history), and the time to complete antioxidant depletion were found to significantly reduced by increasing temperatures investigated. The effect of tensile strains, thickness, and leachate characteristics on estimated service life is also discussed.