People who work and live to the north and south of the plant report much - though not complete - relief from the smells.
That's what was predicted when City Council and Mayor John Bell ended years of debate with a commitment to capture the malodorous gases in a biofilter system.
Summer is when the smells - primarily from hydrogen sulfide, the aroma of rotten eggs - have been most intense, owing to prevailing southerly breezes that pushed the gases from open tanks past businesses and homes.
With windows open and neighbors trying to spend time outdoors, the invisible gases, rolled past more human noses in July.
It was a lot of gas. The plant, which was built in the 1980s with six open tanks and two open channels, processes about 5 million gallons of untreated sewage a day.
Responding to years of pleas from long-suffering neighbors who complained they were forced to close the windows and retreat inside, the city authorized the project in 2003. The bulk of the work was completed last fall.
But until this month, it was impossible to draw conclusions.
Now, complaints - which peaked in past Julys - are almost nonexistent, and the owner of the business closest to the plant, Tony's Mobil Mart (perhaps 50 yards away on the other side of Essex Avenue), believes the work was successful.
"It's a little bit better, not 100 percent, but they achieved what they were after," Jim Taliadoros said yesterday.
Taliadoros' name comes up most often in In the files of complaints kept as the as the project went forward, .
"His nickname," said city environmental engineer Christine Millhouse, is "the odor ambassador."
Gaspar Lafata, a former city councilor who lives about a quarter mile northwest of the plant on Birch Grove Heights, said the improvement is dramatic.
"No smell. It's great, whatever they did, they cleaned a lot of it up," Lafata said.
George Grammas, who lives on Western Avenue across from the Little League field just past Hough Avenue, the Stage Fort Park cut-through, about 100 yards from the plant, gave the odor control project mixed reviews.
"I'm still getting the odors. When it smells, it's more potent," he said yesterday. "But the frequency hasn't been as much."
Shawna Sanborn, who lives on Western Avenue not far from Grammas, said she has perceived an improvement, though she noted she did get the bad smell one day last week while at Taliadoros' mini-mart.
The work is not quite done, and even when it is, Millhouse said, the odors will not be eliminated.
In council hearings during 2002, SEA, an environmental consulting firm employed by the city, wrote that eliminating all odors "is both a costly and unattainable goal."
Millhouse said aluminum covers have been fitted over the five open tanks and the channel through which the sewage flows.
A fan was installed to pull the contained gases to the back of the plant and into a biofilter system, a large field at the back of the plant.
There, the gas are released below 6 inches of mulch and 36 inches of wood chips that are kept moist. By the time gas reaches the surface, noxious compounds have been filtered out. On the field yesterday, the only odor was of mulch.
But Millhouse noted that one open channel is still to be covered, and the city has not yet attacked the odors released when trucks deliver septage to the plant from septic systems and tight tanks. This form of waste contains a higher concentration of organic solids and hydrogen sulfide.
"Odors still come from septic delivery," she said.
To these she attributed two of the three complaints received so far this year.
Two of them were solicited from Taliadoros, Millhouse said, when she went to get coffee at the mini-mart.
In the years since 2003, when the council authorized the loan orders making the project certain, she said, the number of complaints dropped as people no longer felt the need to maintain the political pressure.
Last year, with the project nearing its end, no complaints were recorded.
But while the council and Bell's administration were wrestling with the problem, documenting the odors - which neighbors said suppressed real estate values near the plant - became a neighborhood crusade.
Just before hearings began, 18 complaints were filed in the summer of 2002, which happened to be extra hot and humid, with incessant winds from the south. Millhouse said most of these complaints represented weeks and months of agony.
"You don't know - you really don't know - what we go through," Gaspar Lafata told the council in November 2002.
In 2003 and 2004, the number of written complaints was down, but Millhouse said it was likely "there was not complete documentation."
At the time, the city was in the process of replacing the plant manager - the environmental management firm of Woodard and Curran - with EarthTech, which continues to operate the plant under Millhouse's supervision.
She said the odors experienced before the seals and filtering system were added were especially harsh.
When the plant was built more than 20 years ago, she said, it was not unusual to design with open tanks and channels, but it was rare to do so for a plant located in a residential and commercial neighborhood on a state highway.
Moreover, the plant was never required to upgrade from primary treatment, which uses chemicals to separate solids from liquids, to secondary treatment which also employs biological agents to breakdown the organics.
No other major plant in New England has been exempted from the upgrade.
The lesser form of treatment "produces more offensive odors," engineer-consultant Steve Geribo explained at the November 2002 hearing.
Today, with the plant spewing fewer odors, a new problem has arisen.
A number of residents along Essex Avenue have reported, and Millhouse has confirmed, that similar odors are emanating from the sewer line installed earlier this decade into the town of Essex.
Millhouse said city engineers are aware of the widespread odors which are thought to result from a lesser flow along the Essex Avenue line than the main was designed for.
Movement is slower with lesser flow, she said.