Estudio hidrogeológico-hidroquímico del complejo sistema multicapa del Anillo Verde de Vitoria-Gasteiz

Résumé

The city of Vitoria-Gasteiz is mainly settled on quaternary deposits (fluvial, alluvial) that comprise the Hydrogeological Unit of the same name. These deposits give origin to an aquifer of high permeability and reduced saturated thickness (4-5 m). Underneath there is a thick marly formation of very low permeability, but with fractured levels that enable local ascending flows. This multilayer scheme characterizes the system of periurban parks in transition between the city and its agricultural environment (Green Belt). Current research is focused on the southern sector of the city, where the future Larragorri Park would close the Belt. In this sector there are several potential sources of pollution (Gardelegi municipal landfill, uncontro- lled deposits in gravel pits, agricultural activities...). There is an important network of shallow (6-8 m) and deep (30-40 m) piezometers, and frequent chemical analyses, as well as isotopic determinations in different molecules (H2O, 3H, SO42-, NO3-, NH4+). Complex processes are evident. The waters associated with the marls, with a higher pollutant load (EC up to 18000 μS/cm) and very slow flows, are clearly distinguished from those of the surface deposits, in direct relation to the streams. However, there are piezometers which, although shallow, are indicative of ascending flows, whose interpretation is fundamental for the correct design of the future park and its management as green and blue infrastructure.