Town says teamwork cleans up the Souhegan

With no fanfare, downtown Wilton seems to have cleaned up its river, one person at a time.

“Everybody seems to be doing their part to keep (pollutants) out . . . not cleaning the cat’s litter pan into the river, that kind of stuff,” said George May, explaining the happy surprise of good bacteria counts on the Souhegan River through Wilton, as detected by ongoing sampling efforts by volunteers.

May reached this conclusion as the 13th year of volunteer sampling efforts in area rivers wound up last week.

The levels of E. coli bacteria were mostly good, continuing a years-long improvement in the cleanliness of the Souhegan, Merrimack and Nashua rivers because of improvements at wastewater treatment plants, industries and other large-scale polluters.

The only exceptions occurred after some of the summer’s very heavy rains, which wash surface pollutants into the river and stir up sediment that contains bacteria. One measurement in early June was taken directly after a huge downpour and found bacteria levels so high that they couldn’t even be measured.

“The biggest difference between this year and past years has been the high flows all summer long, with the rains we had,” May said. “The saturated ground means any rain brought up the tributaries, producing more flow in both of those rivers.”

The biggest surprise was downtown Wilton, which has traditionally had bacteria counts higher than the 88 colonies per 100 milliliters recommended for safe swimming.

The problem is that the Souhegan travels relatively slowly through downtown because of two dams there, and passes next to – or, in the case of Label Art, underneath – many commercial and residential buildings.

Last year, the town upgraded its main sewer line as part of a reworking of Main Street, but May said DNA testing of bacteria in the Souhegan found that the problem wasn’t coming from the town sewer.

Instead, it appears the problem lem was a little pollution entering from each of the riverbank neighbors. This is known in the environmental industry as “non-point-source” pollution because it doesn’t come from a single place such as a treatment facility, and as a result, is considered difficult to tackle.

May said his guess is that Wilton has become cleaner because people there got tired of reading about the volunteer measurements saying their portion of the river was dirty.

“It may be partly because of the publicity,” May said. “I hear about it all the time. . . . I see people in the supermarket and they’ll say, ‘How are the rivers doing?’ ”

The biweekly testing at about three dozen locations runs from June to September and is organized by the Souhegan Watershed Association and the Merrimack River Local Advisory Committee. It also measures dissolved oxygen, which is important for fish and other aquatic life, and phosphorus.

If the program can get more funding from environmental grants, May said he’d like to expand it to include other toxins, such as heavy metals.

“We’re always looking for volunteers,” he added.