Construction is underway at two boat launches on Scargo Lake in Dennis as part of a larger project to keep pollution from stormwater out of local waters.
Last week, at the lakefront on Doctor Lord’s Road South, which is also a popular spot for swimming, a construction crew from J.W. Dubis & Sons in Chatham was spreading stone in a new trench between the parking lot and the water.
The trench will catch stormwater running off the parking lot during heavy rains. At the same time, less water should run off than in the past, because the parking lot has been rebuilt with porous pavement, so water can drain into the soil.
The site will also have a bioretention facility, similar to a rain garden, which helps treat stormwater naturally.
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Together, those elements — known as green stormwater infrastructure — will trap oil, bacteria, nitrogen, and one of the biggest problems in the lake: phosphorus, said Tom Andrade, the Dennis town engineer.
“The technologies that we're looking at here, with porous pavement and the rain gardens, are two of the best management processes that remove the nutrients, especially in this kind of a situation where we're very close to groundwater,” he said. “We can't put in formal drainage structures, so we're using the best available technology to give us the best water quality treatment.”
The town of Dennis is working with the Association to Preserve Cape Cod, which has identified 20 boat ramps around the Cape as high priorities for reducing runoff. Some are small launch areas for canoes and kayaks.
The group is working to secure funding for similar projects in multiple towns.
Sites nearly ready for construction include boat ramps at Mashpee-Wakeby Pond in Mashpee, Follins Pond in Yarmouth, and the Herring River in Harwich.
In the past at Scargo Lake, stormwater runoff would pick up contaminants as it moved toward the lake.
“Stormwater runoff was running … from these surfaces and discharging directly into Scargo Lake without any treatment,” said Gemma Kite, an engineer working on the project for the Horsely Witten Group.
April Wobst, restoration program manager for the Association to Preserve Cape Cod, said contaminated stormwater runoff can lead to problems such as algal blooms, low dissolved oxygen, and overall impaired habitat. And at Scargo Lake, any problems would affect spawning habitat for river herring.
