Reducing the false alarm rate of vehicular and hand-held mine detection systems has been a goal of most countermine detection programs. No thorough investigation into the causes of false alarms has been conducted to date. We present here an investigation into the sources of persistent ground-penetrating radar (GPR) false alarms that occurred during testing of a vehicular mine detection system. Data collected with this system was used to identify false alarms that persisted over several tests conducted over a two-year period over the same simulated roadway. A dig list was generated and several sites were excavated. Soil samples were collected at the sites and analyzed in the lab. The results of the excavation will be presented.