East Lyme - Five saplings newly planted in a specially permeable soil and gravel mix and surrounded by concrete frames will be helping keep pollution from finding its way into the Niantic River.
The five tree filters were constructed over the last few days along Colony Drive, a neighborhood of raised ranch homes and neat lawns that sends its runoff into Latimer Brook, a main tributary of the Niantic River. As part of the project, openings are being cut in curbs in front of each filter, so that storm runoff will flow down the road and into the filters.
"The idea is to catch the first inch of rainfall and get it treated before it goes into the brook," Judith Rondeau, natural resource specialist and Niantic River watershed coordinator with the Eastern Connecticut Conservation District, said Monday.
An $84,000 federal grant paid for the five tree filters, which have been around for about 10 years but are new to this area, she said.
"It's a method of bio-remediation and bio-retention that you can retrofit into an existing neighborhood or developed area," she said, noting that the units are relatively small - about 4 feet by 6 feet or 5 feet by 7 feet.
Next year, two more tree filters are slated to be built in the Niantic River watershed - one in downtown Niantic and the other on Mago Point in Waterford. In 2014, Rondeau said, there are plans for another tree filter on Baker Cove in Groton.
To construct the filters, construction crews excavated and removed 6 feet of soils around each filter, then replaced it with layers of different types of crushed stone, sand, compost and other permeable materials. Serviceberry trees were planted at the center of three of the filters and Eastern Rosebud trees in the other two. The filters are designed so that the roots of the trees can spread out in all directions. The entire area is surrounded by a concrete frame with a metal grid across the top to keep people, animals and debris out.
Rondeau said that when rain falls and flows into the filters, the compost, gravel and sand will trap bacteria and other pollutants, and the trees will take up water and nutrients.
Volunteers from the watershed committee and staff of the state Department of Energy and Environmental Protection regularly test Latimer Brook, she said, so it will be possible to see very soon how effective the filters are by comparing before-and-after water quality results.