Equitable Management of Mexican Effluent in Ambos Nogales (Wastewater Management in Nogales, Arizona and Nogales, Sonora, Mexico‪)‬

The cities of Nogales, Arizona, and Nogales, Sonora (together known as Ambos Nogales) have many cultural and historic bonds that tie them together. The communities also share surface and groundwater resources, which have been the source of both cooperation and conflict. Population pressures have placed added demand on the shared resources (see table 1) and have caused the communities to search for more water sources to supplement traditional supplies. In addition, wastewater from both cities is treated nine miles north of the border in Rio Rico, Arizona, at the Nogales International Wastewater Treatment Plant (NIWTP). Ambos Nogales is located in a semiarid region with high climate variability characterized by frequent drought and occasional serious flooding. The prominent water resource in the area, supplying both Nogales, Arizona, and Nogales, Sonora, is the Santa Cruz River (see map 1). With its headwaters in the San Rafael Valley, the river flows southward through Sonora, Mexico, for twenty-five miles and returns to Arizona about five miles east of Nogales, Arizona (ADWR 1999). River flows are ephemeral or intermittent with some perennial reaches. A perennial reach of the river exists downstream of the NIWTP, caused by effluent discharge into the river from the plant. On both sides of the border, the Santa Cruz River aquifer system is generally shallow with limited storage capacity and extreme sensitivity to drought. The aquifers also recharge quickly when rain is present. The Mexican effluent is an important water resource in times of drought because of the low storage capacity of the river aquifers.