Radioactive hydrogeochemical processes in the Chihuahua-Sacramento Basin, Mexico

Abstract

The Chihuahua Basin is divided by its morphology into three main subbasins: Chihuahua-Sacramento subbasin, Chihuahua Dam subbasin and Chuviscar River subbasin. In the aquifers at the Sacramento subbasin, specific concentrations of uranium in groundwater range from 460 to 1260 Bq / m$^{3}$. The presence of strata and sandy clay lenses with radiometric anomalies in the NW of Chihuahua Valley was confirmed by a litostatigraphic study and gamma spectrometry measurements of drill cuttings. High uranium activity values found in the water of some deep wells may correspond to the presence of fine material bodies of carbonaceous material, possible forming paleo-sediment of flooding or paleo-soils. It is suggested that these clay horizons are uranyl ion collectors. Uranyl may suffer a reduction process by organic material. Furthermore the groundwater, depending on its pH and Eh, oxidizes and re-dissolves uranium. The hydrogeochemical behavior of San Marcos dam and the NW Valley area is the subject of studies that should help to clarify the origin of the radioactive elements and their relationships with other pollutants in the watershed.