This animation illustrates how a standard Polychem chain and flight scraper system is assembled and installed.
The town of Narragansett has continuously fought a battle against sewage and wastewater for over a decade. Currently the town is implementing a system that uses a pond's natural ecosystem in an effort to eliminate toxic pollutants caused by runoff rainwater.
"For years, this was unregulated," said Town Engineer Jeff Ceasrine. "We've shifted emphasis away from wastewater to what happened to road runoff. In a lot of ways, it can be more difficult because of the variety of things that can find their way into the river."
Raindrops collect pollutants as they steadily roll along the ground, from oil on the roads to dog feces to lawn pesticides, each drop becoming a toxic ball of waste. Until finally, it reaches the nearest body of water, which then absorbs the toxins.
Some of this waste-laden water, which until recently poured out of the storm drains at Montauk Road and Circuit Drive and directly into Narrow River, is now being routed through a series of eight man-made ponds.
Instead of using chemical or mechanical filtration systems, the town will let nature do the work.
Trapping the water, the ponds allow the pollutants to sink as the water moves from one pond to the next and finally into the river. Plant life, carefully selected by experts, absorbs the excess nutrients found in storm water.
"The goal of the ponds is to take this storm drainage and apply a certain level of treatment to it, but in a natural way," said Ceasrine, who heads the project. "It basically constructs a natural wetland in a series of ponds. Wetlands in and of themselves provide a great deal of natural treatment."
The ponds appear natural, even scenic, with green grass and healthy plant life. They leave no clues of the consummed toxins.
"It is designed to just look like a nice water feature and it's secretly doing its filtration work in the neighborhood," said Alicia Lehrer, district manager of the Southern Rhode Island Conservation District, which helped organize the project.
Though landscaping work continues, the pond filtration system is already operational and the project is 85 to 90 percent complete, said Ceasrine.
Water-monitoring tests to determine the effectiveness of the system will begin shortly, he added.
In 2002, the Environmental Protection Agency, which had largely limited its battles over clean water to large scale and industrial waste dumping, focused on the consistent, if unspectacular, pollution flowing from roads and storm drains into lakes and rivers.
A joint study of storm water in Narragansett, South Kingstown, and North Kingstown evaluated the 12 major drainage points into the river.
"The spot was one of the most polluted spots on the Narrow River," said Lehrer.
A similar construction effort is in the planning stages, this one just off Mettatuxet Beach. Plans for the site have already been submitted and the town is awaiting permits.
Even then, 9 of the 12 major entry points for polluted storm water will continue to empty runoff, untreated save for a sump and a metal grate, directly into the river. "These were identified as the worst," said Ceasrine. Addressing "the remaining ones will be a function of time and money."