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Volunteer testing finds Merrimack River bacteria spike in Franklin

  • The Merrimack River. Monitor file



Monitor Staff
Saturday, August 26, 2017

A monitoring program on the Merrimack River saw an unexpected – and still unexplained – spike in bacteria counts this week, as the summer-long volunteer Upper Merrimack River Monitoring Program finished up.

A high count of E. coli bacteria was found Thursday where the Pemigewasset and Merrimack rivers come together below the Central Street Bridge in Franklin, the most northern of the group’s 11 sample sites.

The test found 1,299 colonies per 100 milliliters of river sample water at the site, three times the state limit of 406 for what are known as Class B waters, which covers all the test sites. (The bacteria limit for public beaches is much lower, at 88.)

Michele Tremblay, program manager for the long-running river health monitoring program, wrote in the group’s report that it was unclear why the bacteria count was so high in Franklin, as the count was low two weeks earlier.

“One of our working theories for why we had bacteria spikes is that algal growth, which has been common this summer, has created a medium for bacteria to breed. There may have been transient animal (including humans) activity in the area just before the samples were taken,” she wrote.

Tremblay wrote that a similar spike in bacteria counts in Franklin led to the discovery of some illicit pipes more than a decade ago, through which buildings were sending waste directly into the river. Nothing of that kind has been found, she said.

Otherwise, bacteria counts at the 11 test sites, which extend south to Garvins Falls in Concord, were well below the 406 limit, as all but one of the sites have been all summer.

The monitoring program gathers samples every two weeks from mid-June to mid-August and has them tested for E. coli bacteria, whose presence can be a sign of various types of organic waste.

For more information, including bacteria level from all 11 sites throughout summer, see MerrimackRiver.org.

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com.)