New Mexico Geological Society Annual Spring Meeting — Abstracts

Nitrate-contaminated ground water has existed in Tijeras Arroyo and Hells Canyon (TA/HC), between the mountain front and Rio Grande valley, about 40 years. The contamination persists in a narrowband underlying each channel, indicating on-going recharge and contamination. The plume contains high nitrate with unusually low chloride as shown below. Sewage cases include two septic- tank areas and a domestic sewage lagoon. Livestock cases include two dairies, a packing plant and a stock yard. Mountainview was probably caused by over-fertilization of a vegetable farm.

The high nitrate in TA/HC may be caused by evapotranspiration (ET) of infiltrating rain water in the shallow subsurface followed by ground-water recharge. These stream segments flow mostly during May through September after large precipitation events. Infiltration is so rapid that flows seldom reach the Rio Grande. After storm events, hot summer conditions return to enhance ET. Summer rainfall in northern New Mexico contains an average nitrate- N/chloride ratio of 3.2 by weight. An ET concentration line for rainfall, plotted below, is consistent with the data for TA/HC.