CEDAR RAPIDS — Alliant Energy has begun capping four coal ash ponds tied to a former power plant near Interstate 380 and Cedar Lake in Cedar Rapids.

Sealing the ash ponds is one of the last components of closing the book on the Sixth Street NE power plant, which was torn down in 2014 after being destroyed during the 2008 flood. Ash ponds are used to capture fly ash generated as a byproduct of coal burning.

The company estimates capping the ponds is going to cost $3.5 million.

“That entails clearing off the brush, bringing in some fill, putting a cap over it and, in the end, it will look like a big grassy field,” said Jill Stevens, manager of decommissioning for Alliant Energy.

The ash has been dredged over the years and little remains, Stevens said. What’s left will not be removed but rather covered over and capped.

“There’s a pretty low level of contaminants, but yet something we want to go above and beyond to cover up,” she said.

The capping process includes emptying the ponds of water, sediment, rubble and old pipes, compacting a base layer of clay to a precise density, adding clean fill dirt and topping it with a layer of topsoil.

Approximately 70,000 cubic yards of fill dirt are needed, Alliant officials said. Grass and native prairie is to be planted on the topsoil, leaving it as green space.

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On Thursday, large hoses and pumps were used to drain three of the Cedar Rapids ash ponds into a fourth, while excavators pushed around dirt and rubble in preparing to fill the ponds, which are about 15 feet deep in some places. Alliant is permitted to dump the excess water into Cedar Rapids’s sanitary sewer system.

The project is slated to wrap up in October.

Project Hurdles

Justin Foss, a spokesman for Alliant, said it’s unusual to conduct such work so close to a downtown area and it creates additional hurdles. He pointed out that the power plant was the largest generating station west of the Mississippi when built more than 100 years ago, and the ponds were in place well before I-380 came through and the city filled in.

Alliant has fastened sensors on interstate bridge piers to measure vibration and ensure the roadway is stable during the capping work. Another sensor is measuring the stability of berms surrounding the ponds.

The biggest hurdle is a “no fill zone” in an area that includes 12 of the I-380 piers. Alliant still must cap this section, but can’t use the typical dirt and clay, per requirements of the Iowa Department of Transportation. Instead, a geosynthetic clay liner is to seal the ground, said Wendy Greene, the project manager.

Another complication, although not related to the interstate, is geese nesting in the area. Alliant plans to work around the geese until they relocate, Stevens said.

The pond area is likely to remain fenced off and closed to the public for the foreseeable future, Stevens said. The ground is not to be disturbed and Alliant is required to perform annual inspection to insure the cap remains intact, which is why deep-rooted native grasses can’t be used and the area can’t be opened to the public for recreation, she said.

‘headed in the right direction’

Alliant cleared its closure plans with the Iowa Department of Natural Resources, although it wasn’t technically required, Stevens said. The closure of the plant occurred before new federal rules for ash ponds.

According to the Environmental Protection Agency, coal ash is among the most common industrial waste generated in the United States. Poor storage conditions in some locations across the country have sparked concerns of mercury, cadmium, arsenic and other toxins leaching into water sources. A 2016 Duke University study of coal ash ponds near 21 power plants in the southeastern United States found evidence of unlined ash ponds leaking into nearby surface waters and groundwater.

Dale Todd, president of Friends of Cedar Lake, which is pushing for restoration of the lake and surrounding area, said he has been reviewing Alliant’s plans for the ash ponds and noted a heightened sensitivity exists for the aesthetics in that area for users of the lake, as well as those passing by on I-380.

“At this stage in the game, anything is an improvement, but we would like it to be something everyone can be proud of,” said Todd. “I believe they are headed in the right direction.”

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