The Macroinvertebrate Multimetric Index, Chris Bellucci explained, is difficult to explain.
It’s sort of like the Dow Jones Index, which tracks a select group of stocks to gauge the health of the overall stock market.
In this case, the MMI assesses the health of insects including dragonflies, caddis flies and stoneflies to determine the water quality of the Naugatuck River.
To Bellucci, a supervising environmental analyst for the state Department of Energy and Environmental Protection, the MMI is a better indicator than testing for the presence of chemicals and heavy metals.
“They’re exposed to everything that’s in the river, so we look to see if the critters are OK,” he said.
Under that formula, the Naugatuck River is getting better, but not yet totally OK. Bellucci pointed to two of the 10 testing sites on the river, Frost Bridge at the Thomaston-Watertown line and Beacon Falls, where the DEEP has MMI data back to the early 1980s.
In 1983, the Frost Bridge site had an MMI score of 16 (out of 100) and the Beacon Falls site had a score of 14. Thirty years later, Frost Bridge most recently tested at 45 and Beacon Falls at 30.
Those scores, along with other testing, keep the Naugatuck on the state’s list of impaired rivers, but Bellucci is hopeful that status could change for the upper section of the river after water samples obtained this fall are analyzed.
“It needs to be at least 48 to show attainment of good water quality,” Bellucci said. “Frost Bridge is getting close to that. It will be interesting to see if it improves enough.”
A biological sample is obtained by disturbing the bottom of the river and scooping up the contents in a kick net. DEEP workers also obtain a fish sample using electrofishing and a diatom sample by scraping the algae off rocks in the bed.
“A lot of the chemical monitoring no longer turns up as many things,” said Bellucci. “It’s expensive to do, so we’ve scaled back on our chemical monitoring.”
There are still some permitted industrial discharges into the river by remaining factories as well as historic toxins lingering after decades of dumping.
Those aren’t considered the greatest threats to the Naugatuck’s health, though.
“The No. 1 overreaching problem is nonpoint source pollution in storm water runoff,” Bellucci said.
The runoff contains a cocktail of lawn fertilizer, motor oil and antifreeze leaks, the zinc dust rubbed off when drivers hit their brakes and other contaminants. Washed off parking lots and streets by the rain, it eventually ends up in the river.
“It’s tough to manage. We are trying to address that,” Bellucci noted. “The problem in the old days was the Uniroyals, but you knew where it was coming from. Today, it’s the nonpoint source pollution and it’s much harder to deal with.”