March 5 , 2008
Shedding light on Big Stone Lake levels and mercury emissions
During the past few weeks, several people have told me they are getting conflicting information about how Big Stone II will impact the level of Big Stone Lake and the amount of mercury emissions coming from the Big Stone site once the new plant is built. Because everyone in the Minnesota River watershed is concerned about the lake and river environments, I want to shed some light on those two issues.
Since 1975, the Big Stone Plant has had a permit to use up to 8,000 acre-feet of Big Stone Lake water each year. In 2006, the South Dakota Water Management Board awarded us another permit allowing us an additional 10,000 acre-feet annually for both plants. In 2007, the Board awarded us a permit to use up to 10,000 acre-feet of groundwater per year. The groundwater permit will supplement the plant's water supply when our pumping from the lake is limited by permit restrictions.
Our surface water permit assumes a normal lake elevation of 967 feet. If the lake drops below that level, only limited pumping can occur. Our water-use model showed there would be occasions where lake level would drop by six inches or more. But, those occasions would last less than one week after which the lake level would rebound. Again, regardless of the drop in lake level, we can only have limited pumping when lake elevation falls below 967 feet.
The second issue is mercury. In August 2007, we announced that we would meet the terms of the 2006 Minnesota Mercury Emissions Reduction Act , which requires large Minnesota power plants to use technology most likely to remove at least 90 percent of the mercury emitted. The Act is one of the nation's most stringent mercury statutes.
The Big Stone site currently emits 189 pounds of mercury annually. In meeting the Minnesota mercury standard, site emissions will be reduced to 70-90 pounds annually, depending on the mercury content of our coal supply. Thus, we will more than double the amount of power coming from the site while realizing a drastic reduction in mercury emissions.
I hope this short explanation helps assure your readers of our commitment to provide area consumers with economical power while respecting the integrity of our water resources.
Sincerely,
Mark Rolfes,
Manager
Big Stone II Project
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