Big Stone II and water use
Minimizing water impact while meeting energy needs
Pumping restrictions the same as the past 30 years.
When the existing Big Stone Plant was being planned in the early 1970s, the owners sized the water intake infrastructure for a future second generating station. Big Stone Plant uses water from nearby Big Stone Lake in accordance with a South Dakota Department of Environment and Natural Resources permit. Big Stone Plant is allowed to take up to 8,000 acre-feet per year from Big Stone Lake. The water is stored in holding ponds on the plant site.
On July 12, 2006, the South Dakota Water Management Board issued a surface water permit to Big Stone II, allowing the existing plant and the new plant to take up to an additional 10,000 acre-feet of water from the lake annually if necessary and if the surface elevation of Big Stone Lake doesn’t fall below 967 feet. Then only limited pumping can occur. This is the same restriction that has applied to the Big Stone Plant for more than 30 years. While modeling shows instances where the lake level could be reduced by 10 inches, those instances would last less than one week. That is, the lake level should recover in one week.
Flexible water usage plan will protect Big Stone Lake.
Initially, plans called for an additional water storage pond on the Big Stone site. The South Dakota Public Utilities Commission instructed us to conduct an evaluation of alternative water supply options that could provide water to the plant in the event that withdrawals from Big Stone Lake are curtailed for an extended period of time. After a detailed hydrological study, the participants found they could avoid constructing the pond by using groundwater during times when withdrawal from Big Stone Lake is curtailed and that the Veblen Aquifer can supplement water without impacting existing water rights.
On July 11, 2007, South Dakota issued Big Stone II a groundwater permit, allowing the site to use up to 10,000 acre-feet of water from the Veblen Aquifer. The Big Stone site would likely use only Big Stone Lake water during years of greater snowmelt or higher than average rainfall. Lesser amounts of surface water and greater amounts of groundwater would be used during periods of extended drought when Big Stone Lake water is unavailable.
Answers to other frequently asked questions about:
The volume of water to be withdrawn from the lake. Water is a renewable resource. Hydrological studies show area water resources are adequate to support our needs while not adversely impacting the needs of others.
The groundwater-testing model used. In modeling our use of groundwater, we used the description of the Veblen Aquifer as approved by the South Dakota Department of Environment and Natural Resources.
The adequacy of testing to determine long-term supply. Our modeling purposefully used a very conservative groundwater recharge rate — about one-eight to one-fourth of the rate normally used in other regional groundwater studies.
Consideration of fish kills on the lake. Periodic fish kills are common to virtually all Minnesota lakes. The cause can be natural and/or manmade. Big Stone Lake is sufficiently deep that the modeled impacts to lake levels are not expected to increase fish kills.
The impact of pumping on downstream waters. Most withdrawals from Big Stone Lake will occur when Minnesota River flows are relatively high. Our modeling shows that pumping would reduce Minnesota low flow levels only 1.5% of the weeks modeled.
The effect of increased pumping on algae blooms. Because only limited pumping can occur below 967 feet elevation, Big Stone I and Big Stone II should have limited impact on algae blooms. In addition, Big Stone I and II will not introduce water into Big Stone Lake.
For more information, contact:
Dan Sharp, Manager, Communications . 701-426-3650
Steve Schultz, Manager, External Affairs . 218-770-9111
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