Non-U.S. Sources Contribute Most Mercury to San Juan River Watershed

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When EPRI combined atmospheric and watershed modeling to look at the fate of trace metal emissions across the San Juan River watershed, the research indicated that from 2020 to 2044, the coal-fired Navajo Generating Station will contribute less than 1% of mercury deposition, with 3% coming from all other North American sources (including local power plants), 16% from China, and 80% from the rest of the world.

The watershed includes portions of Arizona, Utah, New Mexico, and Colorado, and the research confirms results of a similar EPRI study of the Four Corners Power Plant in New Mexico—which revealed the growing dominance of non-U.S. sources as U.S. emissions drop.

Projections account for different plant operating scenarios along with projected emissions from China, the world’s largest source of man-made mercury emissions.

Other findings: Through 2074, the Navajo Generating Station will contribute a maximum of 0.035% of mercury in fish tissue in the watershed and a maximum of 0.44% of selenium in surface waters. The plant’s contribution to surface water arsenic concentration is less than the 0.01% discernible by the watershed model.

While this research is helpful in informing a potential decision to extend the plant’s site lease, it also points to the importance of fully understanding the multiple sources of a pollutant when permitting a specific power plant.