Implementing Effective Monitoring Sites for Emerging Contaminants from the Assessment of Their Critical Areas: Comparative Studies of Multiple Watersheds in the United States.

Emerging contaminants traditionally have not been measured in the environment, but they recently have been detected in various water systems as a result of advancements in analytical methods. These contaminants pose potential threats to ecosystems and public health, but are generally not regulated, nor are they required to be routinely monitored. This paper presents the implementation of watershed-scale monitoring-site selection as an effective monitoring design for emerging contaminants. The study aimed to identify critical areas of emerging contaminants for both point and nonpoint sources in five selected watersheds in the United States with different land-use compositions and climate conditions. Spatial association analysis using the Getis-Ord's Gi statistic was employed to identify clusters of point and nonpoint emerging contaminants considering the impact of neighboring subwatersheds. This analysis identified subbasins containing major wastewater treatment systems as point-source hotspots and those containing and surrounded by concentrated agricultural activities or urban residential areas as nonpoint-source hotspots The results, supported by the measurement data, indicated that the outlets of these identified hotspots should be monitored during both dry- and wet-weather periods in order to understand their impacts on receiving waters. The significance of monitoring point- and/or nonpoint-source pollution was dictated by the pollution source distribution, watershed characteristics, and climate settings. The approach in this study provides a quantitative basis for selecting monitoring locations and managing emerging contaminants that can be applied to other watersheds. [ABSTRACT FROM AUTHOR]