Bacteria Monitoring Results 2022

Our 2022 Bacteria monitoring highlighted the same sites of concern as previous years. The Ashland, Lowell, and Maynard sites all had seasonal geometric means above the swimming threshold of 126 CFU/100 ml. The Hudson site was close to this limit, but this site has a history of low bacteria levels in dry weather and high bacteria levels in wet weather, indicating a dominance of pollution due to stormwater. This year was very dry, so Hudson was consistent with the historical pattern, though it is not clear what caused the spike on July 18th. The fact that Ashland, Lowell, and Maynard are all showing consistently high bacteria levels in dry weather indicates a high probability of sanitary sewer contamination.

This year we moved two sites in order to expand our monitoring scope. The Concord River site at Rt. 225 was always very clean (geo-mean between 27 and 40 CFU/100 ml), so we moved it downriver to Rt. 4. The new site has turned out to be even cleaner, with a 2022 geo-mean of only 9 CFU/100 ml. Two sampling events at this site during the middle of the drought returned results at the lowest possible detection level. The Sudbury River site at Rt. 20 was also almost always clean (geo-mean between 33 and 113), so we moved it upriver to Little Farms Rd. This new site has also had consistently low bacteria levels, with a 2022 geo-mean of 102 CFU/100 ml.

The following table summarizes the 2022 results for E.coli bacteria at our six core monitoring sites in the Sudbury, Assabet, and Concord Rivers.

Results (May 16, 2022 - September 12, 2022):

Cells are shaded pink if they exceeded the single-sample threshold more than 25% of the time or if they exceeded the geo-mean threshold for the year.

The following graphs show the full set of weekly results by river.

Please see our full reports for more details and analysis: