Hydrochemical implications of an overexploited aquifer in a semi-arid environment of Northern Mexico

The Guadalupe aquifer represents the central section of the Guadalupe River Basin in Baja California, and has been a water supply for Ensenada for more than 25 years. Water overexploitation caused a drastic decrease in the water level as well as modifications in groundwater chemistry. Bore and dug wells were monitored from January 2004 to April 2005 and showed a great variation in water quality with TDS ranging from 300 mg/L to over 2500 mg/L. Wells nearest to the recharge areas showed TDS < 1000 mg/L and little fluctuation in chemical composition. The water types vary from HCO3-Ca to Cl-Na composition. The chemical data imply hydrogeochemical deterioration in the areas furthest to the natural recharge areas. This deterioration can be attributed to over-exploitation of the aquifer sections close to the recharge areas limiting the flow of low TDS groundwater to these parts of the aquifer as well as and local the evaporation.