An Ecological and Human Health Risk Assessment of the Upper Santa Cruz River Using Environmental Management Tools

Abstract

Many cities are bolstering their groundwater and surface water supplies by directly discharging treated wastewater effluent into the environment; the treated water may permeate through the vadose zone and into the aquifer, thereby recharging groundwater, and the surficial flow of the discharge allows otherwise ephemeral rivers to flow perennially. The Nogales International Wastewater Treatment Plant (NIWTP) releases effluent wastewater directly into the Santa Cruz River. The Santa Cruz River flows between the United States and Mexico through several metropolitan areas. An issue of critical concern is the long-term impact of the discharge of treated effluent from the NIWTP to surface water and groundwater quality in the region. Several factors including failing infrastructure, operational limitations, and continued rapid population growth impart complexity to this issue. The affected community is generally low- to middle-income, so the costs for obtaining and maintaining new and advanced treatment options necessary for the removal of contaminants of emerging concern is economically burdensome. A recent study has shown that the discharge point of the NIWTP is in an area of high aquifer vulnerability, and there is evidence of environmental contamination from the presence of cadmium, chromium, copper, nickel, nitrates, and zinc, among other compounds. The objective of this study is to identify and assess areas of potential soil and groundwater pollution and associated risk to environmental and human health using modeling and environmental management tool analyses.