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Smithtown project cleans storm water at its source

A basin near Accompset Middle School in Smithtown

A basin near Accompset Middle School in Smithtown is lined with gravel and filled with soil and plants to filter rainwater. Photo Credit: James Carbone

Smithtown’s second major green infrastructure — a channel and basin system along Meadow Road intended to prevent polluted storm water from running into the Nissequogue River — is nearly finished, the town’s principal planner said. 

Traditional stormwater infrastructure pipes stormwater away from developed areas and into nearby waters. The $225,000 town project is intended to clean the stormwater at its source. 

Built on Smithtown School district property near the Accompsett Middle School access road and topped with more than 20 species of native trees and shrubs, it looks more like an example of landscaping than civil engineering. It is both.

After a typical storm, thousands of gallons of snowmelt or rainwater course down Meadow Road toward Phillips Millpond, carrying sand, road salt, bacteria and other pollutants, town officials wrote in a project feasibility study. 

A series of basins dug alongside the road divert the water before it gets there. Dirt and other materials settle in one of the basins, known as a sediment forebay. From there, stormwater flows into a bioretention basin: roughly 200 feet long and 50 feet wide, lined with gravel and topped with soil and plantings, it acts as a giant filter, breaking down contaminants and returning clean water to the ground below. If this basin fills, stormwater spills over into the swale, a 500-foot groove carved from the roadside and lined with gravel and grass. The swale, sometimes known as a bioswale, absorbs contaminants and sends clean water along its original course to the Phillips Millpond, where it flows into the Nissequogue and from there into Smithtown Bay. 

“The purpose of green infrastructure is to clean the water,” principal planner Allyson Murray said in an interview. “If you just use traditional stormwater management — catch basins — the water’s not getting filtered. It gets captured and it gets piped to someplace, but it’s not getting cleaned.”

During the 1960s and '70s, a time of rapid growth for the town accompanied by the spread of impervious surfaces such as roads, sidewalks and driveways, workers for the town and developers built thousands of recharge basins and catch basins designed to hold and dissipate stormwater.

Green infrastructure is not new, and bioswales are working well in Florida and North Carolina, said Xinwei Mao, an assistant professor in Stony Brook University’s department of civil engineering. Cost and scale requirements make them a more attractive strategy for cities, rather than small communities, but parts of Long Island could benefit, she said. 

“Think about it as a very small-scale wastewater treatment plant” to filter contaminants, she said. Among those contaminants: nitrogen, found in many of the fertilizers that treat Long Island lawns and fields. “We see nitrification every year in the Great South Bay,” and when she and her colleagues analyzed stormwater they “saw a high concentration” of nitrogen, she said.

Murray said it was unlikely that bioswales would soon appear in Smithtown in great numbers. But as the town, like the rest of the region, faces more frequent and more intense storms capable of overwhelming the stormwater management system, officials are likely to encourage similar projects in key locations on the town’s waterfront. 

Suffolk County and the New York State Environmental Facilities Corporation funded most of construction with $200,000 in combined grants.

The project's funding source was incorrect in an earlier version. Also, it is Smithtown's second major green infrastructure project.

Reducing pollutants

The town's first major green infrastructure is intended to reduce the flow of nitrogen, phosphorous, sediment and bacteria into the Nissequogue River and Smithtown Bay.

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