July 21: Bacteria surge in Merrimack River near state line

E. coli counts on the Merrimack and Souhegan Rivers were at generally acceptable levels when tested on Tuesday morning by the all-volunteer water quality monitoring program sponsored by the Souhegan Watershed Association and the Merrimack River Local Advisory Committee. But there were a couple of unexpected exceptions.

Notably, testing on the Merrimack River produced very high readings around the Massachusetts state line – near the Sagamore Bridge and again near the Tyngsborough Bridge. This was unexpected because the Merrimack River almost always tests very clean as far as the E. coli bacteria counts go.

The counts do rise dramatically to the numbers seen here after very heavy rainstorms that cause the Nashua Wastewater Treatment Facility to be overwhelmed. When that happens, the water from the combined street stormdrains and the sewers is released directly into the river at up to eight different sites in Nashua.

This could be the cause of the unexpected counts. But the weather was completely clear for the three days prior to the tests and for the normal lifespan of the bacteria. There was a thunderstorm four days prior to the testing but the treatment plant should have been able to handle that event without a CSO discharge.

The flow on both rivers was high for this time of year as a result of all the recent rain. Flow on the Merrimack was double what it should be at this time of year. Flow was 4190 cubic feet per second. This is higher than the historic average of 1780 but still low enough that all of the flow can be used by the generators at Amoskeag in Manchester to produce electricity. The generators there can use up to 4500CFS before spilling the excess over the dam.

But in spite of the higher flow, the Merrimack River looks lower to anyone passing over the bridges in Nashua and downstream. This is because the dam in Lowell has lowered the water to work on the dam. This has been a problem for several years now according to a spokesman for the Merrimack River Local Advisory Committee. “They keep lowering the water in the pond that extends back upstream of Nashua way too often,” according the LAC. “This causes problems with boaters having to dodge rocks and causes serious erosion along the banks.” The LAC has been monitoring erosion that could endanger buildings at Thoreau’s Landing at the end of Lock Street in Nashua.

E. coli counts on the Souhegan River were generally good. Although a number exceeded the 88 count level that is the standard for public swimming areas and the gold standard the testing program looks for, they all fell within the acceptable level for this program. Here also there was an unexpected test. The Horseshoe in Wilton usually tests better than other sites on the river – almost always below the 88 threshold for public swimming. But this time the count came in at 135 and was the highest count on the entire river. The Horseshoe is a popular swimming hole on the Souhegan. At this level swimmers could experience ear and eye infections and gastrointestinal problems.

There were very few tests done on the upper section of the Merrimack River because of a lack of volunteers. Anyone interested in helping with the biweekly testing can contact georgemay@comcast.net or karenmattor@gmail.com for more information.

The tests take about a half hour every other Tuesday morning. The next tests will be done on August 4.