Local Impacts of Mercury Emissions from the Three Pennsylvania Coal Fired Power Plants.

Abstract

The Clean Air Interstate Rule (CAIR) and the Clean Air Mercury Rule (CAMR) as proposed by the U.S. Environmental Protection Agency (EPA) when fully implemented will lead to reduction in mercury emissions fiom coal-fired power plants by 70 percent to fifteen tons per year by 2018. The EPA estimates that mercury deposition would be reduced 8 percent on average in the Eastern United States.The CAMR permits cap-and-trade approach that requires the nationwide emissions to meet the prescribed level, but do not require controls on each individual power plant. This has led to concerns that there may be hot-spots of mercury contamination near power plants. Partially because of this concern, many states including Pennsylvania have implemented, or are considering, state regulations that are stricter on mercury emissions than those in the CAMR.This study examined the possibility that coal-fired power plants act as local sources leading to mercury "hot spots". Soil and oak leaf samples from around three large U.S. coal-fired power plants in Western Pennsylvania were collected and analyzed for evidence of "hot spots". These three plants (Conemaugh, Homer City, and Keystone) are separated by a total distance of approximately 30 miles. Each emits over 500 pounds of mercury per year which is well above average for mercury emissions from coal plants in the U.S.Soil and oak leaf sampling programs were performed around each power plant. Sampling rings one-mile apart were used with eight or nine locations on each ring. The prevailing winds in the region are from the west. For this reason, sampling was conducted out to 10 miles from the Conemaugh plant which is southeast of the others. The other plants were sampled to a distance of five miles. The objectives were to determine if local mercury hot spots exist, to determine if they could be attributed to deposition of coal-fired power plant emissions, and to determine if they correlated with wind patterns. The study found the following: 0 There was some correlation between the prevailing wind direction and measured soil and oak leaf concentrations. This correlation was not statistically significant, but higher soil concentrations were generally found in the east and southeast from the plants and lower soil concentrations were found west/southwest from the plants. The prevailing winds are to the east. The Conemaugh plant which was the most southeast of the three plants did have the highest average oak leaf and soil mercury concentrations. Based on emissions, the Keystone plant would be expected to see the highest concentrations as it emitted about 25% more mercury than the other two plants.The results of this study did not turn up strong evidence for large areas (several square miles) of elevated mercury concentrations around the three coal-fired power plants that were tested. This does not mean that there is no effect, there was some evidence of increasing mercury content to the east and south of these plants, however, the trends were not statistically significant suggesting that if the...

Spatial and Temporal Patterns of Bioindicator Mercury in Pennsylvania Oak Forest

“…Mean NRO litter Hg concentration exceeded that in NRO leaves by 41%, comparable to that reported for northern hardwood forests (Rea et al, 2002; Sheehan et al, 2006). Large increases in litter Hg compared with leaves are attributed to Hg accumulation from both wet/dry deposition and translocation from the underlying substrate (Demers et al, 2007; Grigal, 2003; Hall and St. Louis, 2004; Sullivan et al, 2008). Our studies of Hg levels in decomposing NRO leaf litter have also shown that Hg mass and concentration increased after 12 mo by 34 and 48%, respectively (McClenahen et al, unpublished observation).…”

“…Except for atmospheric deposition monitoring, we found no published studies that track long‐term temporal and spatial patterns of environmental Hg. Many studies report on the spatial status of Hg accumulation in plant foliage, lichens, mosses, and soils (among others) around emissions sources and the presence or absence of “hot spots,” nominally defined as localized areas of exceptional Hg deposition (Evers et al, 2007; Sullivan et al, 2008).…”

“…Soil Hg is greatest within the surface organic layer of the forest soil profile, is greater beneath forest than grassland, and may increase with elevation (Biester et al, 2002a; Grigal, 2003). Because Hg is retained mostly within the soil organic fraction, variation in mineral soil organic matter content may contribute spatial variability unrelated to Hg deposition (Biester et al, 2002b; Driscoll et al, 2007; Grigal, 2003; Sullivan et al, 2008).…”