Groundwater salinization in the harbour area graben in Mar del Plata, Argentina. Hydrochemical perspective.

MARTÍNEZ D:E:, MASSONE H.E., BOCANEGRA E.M.

Groundwater and saline intrusion

Ibergraphi

Lugar: Madrid; Año: 2005; p. 585 - 596

Mar del Plata lies on the Atlantic Coast of Argentina and has a population of 700,000 inhabitants. Water supply for all use is from groundwater, exploited from a phreatic multilayer aquifer. Seawater intrusion takes place mainly in the downtown area, up to a distance of 2,500 m from the coastline. In the harbor area a salinization process affecting a short number of wells has been also observed. This area is a structural graben, isolated from the seaside by a quartzitic horst. The chemistry of the salinization process is different from that observed in the downtown area. Here TDS reach values of 7,000 mg/L while the maximum value in the harbor area is 2,700 mg/L. These observations and the fact that the quarzitic horst does not allow marine intrusion into the graben, makes it necessary to consider other hypothesis. The considered hypotheses have been the rising salinization from Miocene sediments and salinization as a result of the exploitation in a closed underground basin. The second one could be supported by the increase in the nitrate content, but the geochemical model includes the dissolution of about 3 moles per liter of halite, which is considered improbable. The rise of waters coming from Miocene formations is evidenced by the presence of green clays and sands well profiles. The concomitance of both processes appears as a reasonable hypothesis.