Distribution and Probable Source of Nitrate in Ground Water of Paradise Valley, Arizona

Field investigations in Paradise Valley, Arizona, conducted during 1974 and 1977, delineated areas of ground water with up to 132 mg/1 nitrate. Two alternative interpretations are developed as to possible sources of the excess nitrate. The first is a conventional interpretation identifying the use of nitrogenous fertilizers as the primary source and disposal of treated waste‐water effluent as a secondary source. An alternative interpretation identifies the source as a sand and gravel unit that is interpreted as a braided‐stream deposit, located about 152 m (500 ft) below the land surface. The source of the nitrate may have been NH 4 Cl leached from tuffs in the adjacent Superstition Mountains, subsequently oxidized to nitrate and deposited in abandoned channels of the braided‐stream complex. At present, it is not possible to make a definitive choice among the possible nitrate sources.