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AYER — Some fancy-sounding things are in the works that will remove nasty stuff from rainwater and slow down the amount of pollution ending up in the ponds.

Residents will see new bioretention cells. Improved sumps and a hydrodynamic separator will be out of sight, installed under the road at catch basins.

They are simple things, designed to improve water in the town’s ponds by trapping objects, chemicals and fluids before they hit the open waters.

Bioretention cells, strategically placed and structured gardens, filter pollutants through plant roots, gravel and a pipe. The remaining, cleaner water goes into the ponds.

A Girl Scout Troop will plant one of these cells, often called rain gardens, at the Department of Public Works.

“They’re learning a lot,” said Town Engineer Dan Van Schalkwyk. “Those are not too difficult to install.” The DPW prepared the site for planting.

The project will earn the three eighth-grade members of Ayer-Shirley Troop 81319 a Silver Award, the highest award a cadette can get.

Van Schalkwyk just applied for a grant that requires an educational component. The rain garden was not only a learning opportunity for the Girl Scouts, it will allow the community to learn.

The troop members, Alison and Cailidh Houde and Natalie Kalgaren, worked with Pinard Florist and Landscape Supply to get plants at cost for the garden, said Heather House, the troop leader. Pinard will donate mulch.

Planting day was June 10. The DPW did the site work so it would be ready for the troop.

The girls called Dig Safe, Houde said.

If the town gets the grant from the state Department of Environmental Protection, it will get $60 for every $40 spent on improving storm water improvements. A 2016 pond study also provides a learning opportunity for the DPW and a guideline for changes.

The town is working to improve the best management practices, Van Schalkwyk said.

A larger bioretention cell is planned for Pirone Park, to treat runoff from the parking lot. The garden will not reduce the levels of pollutants in Grove Pond but it will be a good showcase, he said.

The study identified phosphorus, a nutrient caused by fertilizer and organic decomposition, as a major problem in the ponds. The gardens filter this pollutant.

The first municipal hydrodynamic separator is planned for Oak Ridge Drive, Van Schalkwyk said.

The equipment is not as complex as it sounds. Rainwater enters an underground container beneath a storm drain. The flow swirls the water around, isolating solid debris.

Sediment sinks to the bottom and floatable pollutants like oil get filtered before the water is piped to the outfall at the pond.

If a heavy storm hits that is beyond the capacity, the separator will still make a difference, Van Schalkwyk said. The first flush, which contains the highest levels of filth, will get treated before the overflow is diverted.

Improvements to existing sumps will remove more solid pollutants. Some older sections of the system have a two-foot sump under the catch basins.

The current standard is four feet, Van Schalkwyk said.

Storm water treatment is ongoing. The systems require maintenance and the best practices include ongoing monitoring of the water quality in the ponds.

Follow Anne O’Connor on Twitter @a1oconnor.

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