This church possesses famous Romanesque wall paintings in a crypt situated underground close to a river. Research on the causes of deterioration started in 1978 focused on climatic phenomena in the crypt. It has been necessary to complement the findings with a thorough hydrogeological environmental study, which is presented in this text accompanied by diagrams, one showing a longitudinal section of the church, another the geology and hydrogeology of the subsoil of the painted crypt (a lower crypt is not painted), another illustrates water transfer in the non-saturated section of the subsoil affecting the painted crypt, and a last one exemplifies the heat regulation effect of the building at certain times of the year. Additional studies were needed before intervention because of the reappearance in 1983 of a white veil over the murals. The result of these additional analyses are presented and tabulated, the conclusions on the treatments to undertake presented.