GEOCHEMICAL AND ISOTOPIC CONSTRAINTS ON RECHARGE; PUEBLA, VALLEY, MEXICO

Puebla Valley, Mexico, located in the east-central portion of the Trans-Mexican Volcanic Belt (TMVB), has a temperate, sub-humid climate with an average annual precipitation of 830 mm. It contains a complex aquifer system that includes two productive units: a deep, confined, sulfur-rich aquifer and an unconfined unit composed mainly of Quaternary alluvial and volcanic deposits. The two aquifer units are separated by Tertiary lacustrine sediments. Water resource management is one of the most urgent environmental issues in Mexico; and the unconfined Puebla Valley system is one of the 100 overexploited aquifers that occur within the populous and economically active area of central Mexico. Puebla City, the largest urban area within the Valley with a population of 1.5 million people, has a water deficit of about 700 l/s.

In this study, oxygen and hydrogen isotopes as well as major and trace elements have been used to identify recharge and to provide geochemical constraints useful in modeling the aquifer system. Recharge elevations have been estimated for a total of 38 sites (52 samples) based on oxygen and hydrogen isotopic measurements. Three predominant recharge elevations have been identified. These correlate with three distinctive geochemical groups: (1) cool springs (13.2 -22.7 degrees C) located on or near the flank of a major active volcano (Mt Popocatepetl) with an average recharge elevation of 4015 masl, (2) artesian springs and wells characterized by the presence of sulfide (22.9 – 36.3 degrees C) with an average estimated recharge elevation of 3508 masl and (3) pumping wells drilled within the unconfined aquifer (18.8 – 28.8 degrees C) with estimated average recharge elevation of 3177 masl.