Pollution Studies of the Regional Ogallala Aquifer at Portales, New Mexico

PROJECT OBJECTIVES:

To examine the regional Ogallala Aquifer at Portales, New Mexico for pollution during a one year period. The study examined both bacterial and chemical parameters. The analyses over a year period permitted elucidation of seasonal variations.

DEGREE OF ACHIEVEMENT OF PROJECT OBJECTIVES:

Chemical analyses included nitrate, pH, and phosphate. Bacterial analyses were performed using membrane filter techniques. Bacterial analyses included both total coliform and fecal coliform analyses. Sampling area consisted of a series of two mile radii, extending a distance of ten miles from the town of Portales, Twenty-two rural wells were sampled.

Both bacterial and nitrate contamination was found in varying amounts in most wells sampled and a correlation between the two was established. Seasonal fluctuations of nitrate concentrations were observed. Nitrate concentrations were at their highest observed values during the peak irrigation season in those wells surrounded by typical agricultural crops for which nitrogenous fertilizers were locally applied. A relationship was found to exist between nitrate concentration and rainfall during sampling interval. No phosphate contamination was found. Periods of high recharge potential appeared to parallel pH variation. An in vitro study was performed to determine the extent of possible nitrate conversion to other nitrogenous compounds by the coliform contamination observed. It was found that 47% available nitrate was converted to other nitrogenous compounds (including the insidious nitrite) by coliforms in soil columns.

Throughout the year except for the summer months, little variation in nitrate concentration, coliform density, or pH was observed.

PROJECT NUMBER: 3109-45 A-034-New Mexico