Bacteria Monitoring Results 2021

Bacteria levels in 2021 have generally confirmed the patterns we have been seeing over the past two years. Maynard, Ashland, and Lowell continue to have concerning levels of bacteria, hovering near or above the EPA swimming threshold. Hudson has slight lower bacteria levels than Maynard in dry weather, but tends to have equivalent or higher levels in wet weather (download the wet-weather analysis). This indicates a dominance of surface runoff or storm-water contamination sources in Hudson. In Maynard, on the other hand, there is little difference between wet and dry weather, which indicates a high probability of sanitary sewer contamination.

The July 19 data were interesting because levels were extremely low at all sites. July 19 was the third week in several weeks of very heavy rain and flooding, so the samples were heavily diluted and reflect the fact that most contaminants had already been washed out of the system. Data and graphs excluding July 19 are included below.

The following tables summarize the 2021 results for E.coli bacteria at our six core monitoring sites in the Sudbury, Assabet, and Concord Rivers.
Results (June 7, 2021 - September 13, 2021):

Results without July 19:

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.