When 35W Construction Swallowed Powderhorn Lake

The harm that the construction of Highway 35W inflicted on South Minneapolis is well known. It destroyed hundreds of homes and did lasting damage to the historic southside African American community in the Central, Bryant and Kingfield neighborhoods. I have also long heard neighborhood lore that the construction of 35W destroyed an underground spring which fed Powderhorn Lake, contributing to the lake's poor water quality. I spent time researching this story to better understand what may have happened. 

To understand the ongoing water quality issues faced by Powderhorn Lake it can be helpful to understand the lake's natural history as well as the environmental impacts of the city that grew up around the lake. 

The glacial drift left behind by the last ice age covers an older underground topography of more ancient valleys and rivers. Powderhorn lake is home to an ancient Mississippi river tributary valley that flows south to Lake Hiawatha.  Powderhorn Lake is naturally shallow and marshy. In 1895 the lake was dredged which reduced the lake's size, deepened the lake, and create the island. In 1924/5 the swampy northern arm of the lake was filled in to create the current ball/soccer fields. The depth of Powderhorn Lake varies from four to twenty four feet deep. During hot and dry  years, lake levels fluctuate. Shallow lakes warm more than deeper lakes, and pollutants and nutrients are more concentrated. As Minneapolis grew around the park, the lake was degraded by storm sewer runoff and lawn and garden chemicals. In the late 1990's Powderhorn residents organized the Save Our Lake campaign to address the poor lake quality. Victories included the installation of five grit chambers to filter storm run off, and lakeshore stabilization plantings.

In the summer of 1963, neighborhood residents began to notice that the lake levels were noticeably dropping. In June of 1963 the Minneapolis Park Board reported that the lake level was dropping by one inch a day. By of July 1963, Park Board engineers warned that the lake would virtually disappear in about eight months if no action was taken. The Park Board spent thousands of dollars pumping millions gallons of city water into the lake in 1963 in an attempt to stabilize the lake, but water levels dropped again as soon as pumping stopped. The need to pump in city water to stabilize the lake level continued through 1963 and 1964. 

Park Board engineer Edward Braddock blamed the dramatic lake level drop on the nearby construction of 35W and the storm tunnel work being done on Stevens Ave between 36th and 37th Streets. At the construction site, water was being pumped out of the ground so that crews could build the 125 foot deep storm tunnel. The pumping lowered the surrounding water table, forcing lake water from Powderhorn Lake to seep from its muddy bottom into the ground. State Highway Commissioner James Marshall dismissed the concerns of the park board and neighborhood residents, stating, "it's the park board's problem, not ours." Their was discussion of suing the state to stop the construction based lowering of the water table and to recoup the costs of adding water to the lake. However, it was determined that the cost of a lawsuit would outweigh the financial return. 

The storm tunnel project was completed in February of 1965. The Park Board commented in its weekly news bulletin, "After the completion of the storm tunnel project, the ground water table in the area will begin to rise back to normal levels, which should have a considerable effect on the elevation of Powderhorn Lake."

Reviewing photos, newspaper articles, and letters to the editor it is clear that peril faced by Powderhorn Lake weighed heavily on neighborhood residents at the time. Considering that the  construction of 35W destroyed so much in South Minneapolis, i is not too surprising that as the years have passed, the legend around the draining of the lake grew; and a narrative that the construction of 35W had forever blocked a natural spring that fed the lake took root. Instead, what happened to Powderhorn Lake in the early 1960s was just a harbinger of the destructive environmental and cultural effects the highway would contribute towards in the decades to come.