Monitoring of nitrate contents in the Puebla Valley Aquifer

During one year nitrate concentrations were measured monthly in eight zones in the Puebla Valley Aquifer, and the influence of rainfall and altitude was analyzed in relation with the nitrate contents. The average concentration of nitrate was 10.75 mg per liter of nitrate of nitrogen (N-NO ₃ ^-/ L) in the wells studied, and the highest concentration was 48 mg N-NO ₃ ^-/L, with 44 % of wells exceeding the thresholds for drinking water. The nitrate concentration in 56 % of the wells, increased with mean annual precipitation. The wells located at higher altitudes have concentrations, on average, below 3 mg N- NO ₃ ^-/L. In the regional mean the nitrate concentration in the aquifer does not exceed the maximum permissible limits. However, there are 8 wells of 16 in which nitrate concentrations exceed the thresholds set by the regulations, especially in areas of low to medium altitude.