Significant contamination of ground water requires, in combination, a source of pollutants, an aquifer which is susceptible to pollution, and geologic pathways capable of conveying contaminants to the aquifer. In New Mexico, major sources include pumping-induced saline intrusion, mill wastewater, septic-tank effluent, and (historically) brine disposal. Leaks, spills, municipal wastewater, animal confinement facilities, mine drainage, and industrial wastewater are locally important. Valley fill alluvium and fractured limestones represent the most vulnerable aquifers. Significant pathways reflect a highly permeable and/or thin vadose zone, or the presence of improperly constructed and abandoned wells which bypass vadose-zone protection. Northwestern and southeastern New Mex co contain most of the areas where sources, vulnerable aquifers, and pathways coexist. Because ground-water flow rates in vulnerable aquifers are generally 70 to 700 ft (21 to 213 m) per year, potential zones of pollution will be small and difficult to monitor. A surprising amount of ground-water monitoring occurs in the state, pursuant to regulatory programs, project evaluations, and scientific research. Monitoring can be improved through: (1) coordination of monitoring activity (especially among government agencies); (2) more focus on characterizing the pollutant sources; (3) measurements which define the hydrogeologic flow system in the immediate vicinity of the source; (4) reliance on indicator parameters rather than on comprehensive testing of water quality; and (5) much better qual ty control of the field sampling and laboratory analysis of ground water.

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