Posted on December 20, 2018
The Minnehaha Creek Watershed District is beginning dredging work on two stormwater ponds that clean polluted stormwater that runs off city streets in Minneapolis and Edina.
The Southwest Bde Maka Ska Pond in Minneapolis filters runoff before it enters Bde Maka Ska – formerly known as Lake Calhoun – while the Pamela Park Pond Cell 1 in Edina filters runoff before it enters Minnehaha Creek.
Stormwater ponds capture dirty stormwater runoff from nearby streets and allow sediment and pollution to settle to the bottom before the water flows to a lake or stream. They also prevent flooding by providing temporary storage during large rainfalls. Over time, the sediment and pollutants accumulate and need to be removed for the ponds to remain functional. Dredging involves excavating the sediment out of the ponds and hauling it away. Any disturbed vegetation will be restored in the spring.
About 2,000 cubic yards of sediment will be removed from Southwest Bde Maka Ska Pond, which was last dredged in 2012. At that time, the dredged sediment that was removed was near contamination, but current tests indicate the sediment is not contaminated this time around. This reduction in contamination could be due to a 2014 state law that bans the use of coal tar driveway sealants which contain cancer-causing chemicals called PAH’s. Uncontaminated sediment will save money on disposal costs because the contractor can reuse the sediment.
“The MCWD was among the agencies that successfully lobbied for the passage of the statewide ban on coal tar driveway sealants and it appears we are seeing tangible results of that effort,” said Tiffany Schaufler, watershed district project and land manager. “By keeping PAH’s out of the runoff that ends up in our stormwater ponds, we have healthier water and we save money on maintenance costs.”
About 1,900 cubic yards of sediment will be removed from the Pamela Park Pond Cell 1; it will be the first dredging of this pond. The project is being conducted in partnership with the city of Edina.
“The pond is among three ponds that were built on the northern end of Pamela Park to improve the water quality in Minnehaha Creek and Pamela Lake,” said Ross Bintner, city of Edina engineering services manager. “These ponds are part of a multi-pronged strategy to reduce the impact of polluted stormwater on amenities that make Edina such a great place to live, work and play.”
Dredging is done during the cold weather months when the ground is frozen. The ponds will be “dewatered,” meaning the water will be pumped out of them and stored in an adjacent pond. The stormwater ponds will then be excavated using heavy machinery. The sediment from the ponds will be hauled off site.
There will be heavy equipment in the area and trucks hauling sediment from the site. People are urged to use caution around the machinery and potential thin ice for the duration of the project. The work is expected to last through February.
Source: Sun Current
