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Compromising Coldwater?
Published January 2003 Southside Pride
by Susu Jeffrey
MnDOT is seeking permission from local watershed districts to alter its Highway 55/62 interchange redesign. Engineers have discovered that the light rail transit bridge footing is in the way of the proposed waterproof underground roadway liner. The interchange design, as it stands, is the centerpiece of a significant compromise between MnDOT engineers and activists working to preserve Camp Coldwater Springs, which flows beneath the future roadway. MnDOT’s proposed changes could significantly impact the spring, and activists are worried.
At issue in the design of the roadway is how it will affect the water table beneath it. The spring emerges from below ground at a well in nearby Camp Coldwater. Activists monitoring the spring have noticed that its outflow dropped precipitously when construction began.
In order to mitigate the impact of the roadway on the spring, MnDOT agreed to install a liner to separate the two for the length of their overlap. However, MnDOT engineers will discuss shortening the 350-meter liner under the road by 30-meters (about 100 feet) at a meeting scheduled for Thursday (1/23/03) to accommodate ongoing LRT bridge construction. The question is: How much would the water table be permanently lowered to avoid leakage of groundwater into the liner?
The lowest part of the interchange construction is designed to rest 4 to 8-feet into the water table and about 35 feet below the former land surface. The geo-textile liner would theoretically isolate the road from the surrounding underground water; however, small holes and tears in the liner during construction are expected.
In the fall of 2001, MnDOT cancelled construction on the interchange project when a 30-percent decrease in flow to historic Coldwater Springs was documented. Last September the Minnehaha Creek Watershed District, which has lobbied on behalf of the spring, gave approval to a “conceptual plan” for the redesign of the interchange. Coldwater supporters were told that if the interchange were built according to the concept, the loss of flow to the spring would not be noticeable.
Future loss was estimated at 2-3 gallons per minute, or 2,880 to 4,320 gallons per day—but not every day, since groundwater levels change over the seasons. Supporters are now asking that construction dewatering, which is considered temporary, be measured as well as the flow at Coldwater Springs. Early January 2003 readings averaged 100,000 to 107,000 gallons a day.
Another thing that has Coldwater supporters worried is that MnDOT is seeking step-by-step approval for their plan. The protracted approval process could conceal accumulating flow loss as each construction problem is encountered in isolation. MnDOT will be meeting with Minnehaha Creek Watershed District and Lower Minnesota River Watershed District administrators, engineers and hydrogeologic consultants. Watershed managers will then vote on construction changes based on staff comments and a rumor of being “tired of this issue” of the 10,000-year-old spring called Mniowe Sni (Spring Cold) on a Shakopee Dakota archival map.
Coldwater Springs, flowing at a preconstruction rate of 100,000-144,000 gallons per day, is located halfway between Minnehaha Falls and the confluence of the Mississippi and Minnesota rivers. Considered the birthplace of Minnesota, Camp Coldwater is where the soldiers who built Fort Snelling lived (1820-23). The spring furnished water to the fort for 100 years.
Previous to European settlement this bluff top area was a cultural and spiritual gathering center for many Indian nations. In the 1840s, Fort Snelling artist Seth Eastman painted Dakota burials and daily life near the fort. Aerial photographs show where Native American pow wows were held, between Minnehaha Park and Coldwater Springs, into the 1930s.
© Southside Pride |
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