A variety of geomembranes is widely used in hydraulic applications. Some of the additives included in the manufacturing process will be extracted from the geomembrane after contact with water or a soil. Depending on their chemical nature, additives or their degradation products represent a possible source of impact on natural ecosystems. The paper present the objectives of the research program IMAGES (IMpact of ADditives in GEomembraneS) aiming at quantifying the potential impact of additives extracted from geomembranes installed in hydraulic applications. The methodology consists in identifying the additives contained in HDPE and PP Geomembranes, the additives that can be extracted following various environmental conditions, the additives degradation products, developing a model for additives extraction/diffusion from/through geomembranes and evaluating the potential toxicity of the additives extracted through ecotoxicity tests. Details on the selected protocol are given. The UV spectrometry analyses of the immersion solutions at 82°C evidence an acceleration of hindered phenol AO type degradation products extraction with the acidity of the medium. The small decrease in the OIT value after 96 days at 82°C of the HDPE GM shows that, depending on the ecotoxicity threshold determined, the alert value of AO nocivity will have to be determined with an accurate technique like UV spectrometry.