Abstract: Dye tracing and electrical leak location testing were independently conducted to detect and locate leaks in the primary geomembrane liner of two cells in a municipal landfill. Despite extensive quality control and quality assurance programs, water in the leak detection zone after construction indicated that the primary liner had a leak. Fluorescein dye tests were conducted by placing a fluorescent yellow/green dye in water impounded on the liner and then sampling the water drained from the leak detection zone for periods of at least 40 days. The samples of water were visually inspected and tested with a spectrophotometer. No dye was ever detected. Anelectrical leak location survey of the same areas located two leaks. One leak was a 90 x 76 mm (7.5 x 3 in.) hole that was near a leak detection drainage pipe. The other leak was a 25-mm (1 -in.) diameter hole. The tests showed that dye testing was ineffective for detecting the presence of significant leaks in a liner system with sand above and below the leak. The electrical leak location method quickly and accurately located the leaks. KEY WORDS: Leak detection, geomembranes, construction quality assurance, landfills, performance evaluation!