The city is working to keep pollutants out of Wright's Pond and better manage flood events by constructing an environmentally friendly rain garden.

Wright’s Pond is about to get an ecological makeover.

The city of Medford is constructing a rain garden at the Middlesex Fells pond that will help filter out pollutants, including phosphorous, nitrogen, suspended solids and bacteria. It will also be designed to conserve water.

Staff from the Department of Public Works, under the guidance of consultants from the Horsley Whitten group, will be installing the rain garden in the coming weeks.

“They’ll be putting in soils that are conducive to plants that thrive well both in really wet conditions and in dry conditions,” Alicia Hunt, director of energy and environment for the city, explained. “You don’t want to be watering this stuff during a drought – you want to let it be natural.”

The rain garden will contain plants that soak up phosphorous and nitrogen from rainwater before it flows into Wright’s Pond. Phosphorous and nitrogen are common water pollutants that cause excessive growth of aquatic plant life, which depletes water of oxygen necessary to support fish and other organisms.

Residents have grown increasingly concerned about pollutants in the pond, Hunt said, because the city stores plowed piles of snow near the pond in the winter, which runs into the pond when it melts.

“This is a way for that runoff to get cleaned, treated and filtered naturally before it goes into the pond,” Hunt said. “We haven’t tested what is there, but there’s a perception that there’s bad stuff running off in there.”

In addition to filtering the water, the rain garden will divert less contaminated water into the pond during a heavy downpour to prevent flooding.

“Usually the first half inch to inch of rain has the most contaminant in it,” Hunt said. “So if there’s less rain, it flows into the rain garden first, but if there’s more than that, it has a controlled overflow into the pond.”

The rain garden project, which will cost the city a total of $50,000, is a match project for a $125,000 grant that Medford received from the Massachusetts Office of Coastal Zone Management. That grant will fund various infrastructure projects at multiple locations in the city to reduce the volume of pollutants that enter the Mystic River.

Since alewife and blueback herring swim up the Mystic River to spawn, the city was able to obtain the grant even though the river is not technically coastal water.

Hunt explained that Wright’s Pond, which ultimately drains into the Mystic River as well, was selected because it is on city-owned land, unlike many of the areas adjacent to the Mystic. The scale of this project was also more practical for the city to do on its own.

“There are other kinds of bioretention areas, but this was the best place for a demonstration project that the city could build without hiring a contractor,” she said.