The paper discusses an RCC dam project where an exposed geomembrane system was installed in 2002 and has been successfully performing for now 13 years. The RCC dam, Miel I, is located in Colombia with 188 m high, and the dam is used for power production. The RCC mix has a cement content of 85 to 160 kg/m3. To meet contractual schedule, the original design of an upstream face made of slip formed reinforced concrete was changed to a Carpi drained exposed PVC geocomposite system, placed on a 0.4 m thick zone of RCC material enriched with cement grout and vibrated. Placement of the geocomposite system in horizontal stages allowed starting dam impoundment while RCC placement was still ongoing at higher elevation. The geocomposite system was completed in 2002, before complementary concrete works were finished. ISAGEN, the owner of the dam, constantly monitors the dam and the geocomposite system. The measured leakage has never surpassed the historical values, or overcome the maximum allowed drainage design values. After 11 years of good performance, in 2013 ISAGEN decided to have a comprehensive monitoring of the general conditions and weathering behaviour of the geocomposite system. Objectives of the investigation were to assess the reason of small cuts that had been detected and repaired (in total 15 in 11 years on a 31,000 square meters surface), to assess the conditions of the PVC geocomposite, ascertaining at which extent its characteristics had changed over service, and to evaluate if the weathering behaviour was in accordance with the expected durability. Inspection at the upstream face and in the drainage galleries was followed by sampling and testing of the exposed geocomposites in the laboratory, to compare the physical and chemical properties of the aged geocomposite sample collected at the dam with those of the same geocomposite as manufactured. Evaluation of test results, based also on most recent research on geomembrane weathering mechanisms, completed the investigation. Results confirmed that the behaviour of the PVC geocomposite is extremely good and fully in line with expectations. The performance of the dam in 2015, after 13 years of service, keeps being extremely satisfactory. The paper will describe the geocomposite system installed at the dam, and then discuss all steps of the investigation, and detail the test results and the conclusions drawn.