2022-12-19_GENERAL DOCUMENTS - C1981010

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It is possible that the mercury concentrations measured in Colorado pikeminnow might result in a minor reduction of vigor through reduced mental and physical reaction times, which would impact their ability to escape predation from northern pike, smallmouth bass, or other piscivorous predators. Reduced swimming ability could also lead to a reduction in feeding success (i.e., capturing other fish to eat). However,the nonnative competitors and predators in the action area, such as northern pike and smallmouth bass, are experiencing the same water mercury concentrations and therefore may not have a significant competitive advantage or increased predation success over Colorado pikeminnow in the presence of elevated mercury. There is also evidence,however,that different predaceous fish species bioaccumulate mercury at different rates even within the same river segment due, in part,to differences in fish physiology and diet(CDPHE 2015, MacRury et al. 2002, EPA 2004). In fact, CDPHE (2015) found average mercury levels in Colorado pikeminnow adults were more than twice as high as northern pike adults in the Yampa River, although the sample size was small and different river segments were sampled for each species (CDPHE 2015). Despite the uncertainties outlined above,we can come to basic conclusions regarding the effect to endangered fish from the mining of coal and its eventual combustion. Given fish tissue mercury concentrations have been determined to be elevated in Colorado pikeminnow from both the Yampa and White Rivers,but in particular in the White River, and coal mining and local combustion adds mercury to the system,this additional mercury adds to any negative effects resulting from mercury exposure. Based on the best available science, we believe some Colorado pikeminnow individuals are experiencing low, chronic negative health effects from mercury already in the action area. The mercury added by this project will add to the effects of this chronic condition, although the relative contribution of project-related mercury is assumed to be a very small percentage of the total mercury that has been and will continue to be deposited in the action area, as explained above. Additionally, as stated in the Baseline section above,mercury concentration measurements have been higher in Colorado pikeminnow taken from the White River than from the Yampa River despite the fact that there are two coal-fired power plants (the Craig and Hayden Stations) located along the Yampa River and none within the White River watershed. This adds evidence to the assumption that local coal combustion from these power plants does not appear to constitute the primary source of mercury contamination in these watersheds. Despite the chronic, low-level harmful effects of mercury that Colorado pikeminnow are likely experiencing,we believe the population decline seen in Colorado pikeminnow populations within the Yampa and White Rivers over the past decade or more is primarily a result of increased nonnative species in these rivers, especially northern pike and smallmouth bass. As explained in the baseline section above,these nonnative fish populations have increased and have applied increasing pressure on the Colorado pikeminnow population. Coal emissions from the Craig and Hayden Stations have been largely constant since they became fully operational in the 1970s. The more recent decline of Colorado pikeminnow numbers in the action area coincides more closely with the expansion of nonnative fish, rather than any increase in mercury in the action area. 52