Students and staff returning next week won’t be able to tell that a significant change for the good of the local environment was made to the grounds this month. Four rain gardens were built along both sides of the interior road leading past the ball field. Without the plants, as mentioned, they don’t look like much. But all the magic happens underground.
Rain gardens are a relatively new revolution in dealing with stormwater runoff pollution, a major issue on the school property. Between the two schools and the parking area quite a bit of stormwater flows off the property through catch basins and pipes straight to the Westport River. The stormwater runs unfiltered through the drainage system, taking with it nitrogen, phosphorous and any gas, oil, and metals washed up from the ground along the way.
The project that started in August will catch stormwater in several strategic spots and hold it there, where sand and stone will filter nutrients and pollutants and then slowly release it all into the soil. Plants in the rain gardens will absorb much of the nutrients, feeding themselves while removing problem nutrients like nitrogen and fecal matter that cause algal blooms.
“The sand allows it to drain and holds the stormwater, the loam provides organic material for the plants, and the plants take up nitrogen,” said John McAllister of Norfolk Ram Group, the engineering firm that designed the system. “It’s designed to capture, infiltrate and treat stormwater.”
Other than catch basins to handle road flooding, there were no other drainage control measures on the property and none that prevented pollution from washing off the land.
How it works
What makes these gardens work are layers of stone and an engineered soil mix.
The rain gardens are dug down 5 feet, are about 6 feet across and vary in length. Each is filled with with 1 foot of assorted-size stone and 3 feet of soil mix — two parts coarse sand, two parts loam, and one part hardwood bark mulch. Think of it as a very sandy potting soil; it has that same rich look as high-quality soil.
Each material plays a part — the sand and stone slowly draining the water down into the ground and the rest pulling out pollutants along the way. The mulch is especially effective, soaking up nitrogen, phosphorous, metals, oil and grease from the stormwater.
“Wood chips are a crazy cheap way to take care of nitrogen,” says Roberta Carvalho of the Westport River Watershed Alliance (WRWA).
Ten years of WRWA water-quality testing had shown that the Head was “one of the most polluted spots in the river,” Ms. Carvalho said. Fecal matter counts were so high, she says, that the spot was unsuitable for swimming a decade ago.
Steps have already been taken to improve the health of the river there. Four years ago the Town of Westport built a constructed wetland at the Head (behind the Sea Osprey Kayak shop) that handles stormwater runoff from the west side of Old County Road. It works much the same as a rain garden, capturing and filtering pollutants.
The pollution-control project at the middle school will build upon that work. With the school property less than half a mile from the river, the system will treat the major stormwater-runoff issue flowing from the east side.
Already, WRWA has recorded much lower fecal-matter levels at the Head — a 90 percent reduction from counts 10 years ago, Ms. Carvalho said. Some of that is due to the constructed wetland, and also that there are now fewer livestock farms near the river, better land management practices and more frequent cleaning of the town’s catch basins, she said.
As of this year the same spot has been testing suitable for swimming, Ms. Carvalho said.
Without a joint effort these projects wouldn’t have happened.
WRWA built a case history of the detrimental effect of stormwater runoff on the river, then wrote all the grant paperwork. Massachusetts Department of Environmental Protection grants funded both stormwater projects, and Buzzard’s Bay National Estuaries Program issued the request for proposals for both projects. The Town of Westport has assisted throughout the process, most significantly contributing the labor through the Highway Department of the constructed wetlands and new drainage systems at the middle school.
Ms. Carvalho singled out the highway department laborers’ efforts. “They are the boots on the ground. We wouldn’t be able to complete the project at all without them.”
With four rain gardens built, the middle school project is about 30 percent complete. Even without the plants the rain gardens will still work to capture stormwater runoff, Mr. McAllister says, they just won’t pull out nutrients from the captured runoff — that’s the job of the plants.
In the fall the finishing touches will be put on the gardens with plantings of hydrangea, iris, azaleas, rose bushes, ornamental grasses and other flowers.
That’s when the gardens will become most effective at removing nutrients from the stormwater runoff. All native plantings, the gardens are designed to bloom at different times throughout the year and with a variety of color.
“Rain gardens are effective and visually pleasing at the same time,” said Wayne Perry of Norfolk Ram Group.
Work will pick up again when school is not in session, over spring break or next summer. Closer to the school, more rain gardens will be built along with vegetated swales and a recharge area. Vegetated swales act similar to rain gardens but are planted with just grass.
The recharge area is “like a septic system for stormwater drainage,” Mr. McAllister explained. It will be a bowl-shaped area dug out underground and connected by pipes to the drainage system. It takes the overflow of the system and allows it to sit underground and slowly dissipate through the sandy material already there.
Once the new drainage system is complete it’s expected to prevent 90 percent of runoff from average storms from getting into the river, Mr. McAllister said. To break that down, it should remove 90 percent of nitrogen, 65 percent of phosphorous and most suspended solids (sand and grit — not a pollutant but pollutants bind to it) from the stormwater runoff.
And another great feature of this project is that students will learn about the design and how it helps keep pollutants from getting into the river and wetlands. WRWA will teach sixth-graders at the middle school about about the project that is right on their doorstep.
Got a green thumb?
Volunteers are needed to help plant the rain gardens in the fall. If you’d like to volunteer contact Roberta Carvalho at [email protected] or 508-636-3016.