A leak survey of a major metropolitan area aqueduct was carried out using a combination of infrared thermography, ground penetrating radar (GPR), and ultrasonic techniques. The objective of the infrared survey was to investigate the entire length of the aqueduct in order to reveal possible leak conditions which would not be observable by other means. The objective of the GPR survey was to focus attention more locally on key areas such as known leak locations, proposed test pit locations, and areas which were identified from the infrared survey. The ultrasonic tests were carried out on the concrete wall of the aqueduct when it was exposed for detailed evaluation. The infrared survey was carried out from a helicopter, and covered the entire 16 mile length of the aqueduct. The GPR survey was carried longitudinally on 20665 linear feet of the aqueduct (26% of the total near surface length), and transversely at 89 different stations. The ultrasonic tests were carried out in 8 excavated test pits. The analysis of the infrared and GPR survey results revealed that: (1) of the 25 documented leaks surveyed, 13 were confirmed, 9 show no evidence of leakage, and 3 could not be evaluated; (2) 35 additional sites have indications of possible leakage; (3) the soil cover in one area far exceeds the anticipated design conditions; (4) the soil conductivity is high (i.e., corrosion is likely) in 9 areas, 6 of which surround or are close to documented leak sites; and (5) there is a major leakage channel along the side of the pipe caused by one of the leaks. The results of the ultrasonic testing revealed occasional delamination between the structural wall of the aqueduct and the inner steel lining.