Bacteria Monitoring Results 2023

Our 2023 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 also exceeded this threshold in 2023. The year 2023 was a wet-weather year, and Hudson has a history of low bacteria levels in dry weather and high bacteria levels in wet weather, which indicates a dominance of storm-water surface pollution.

The two new sites, Carter Ave. in Billerica and Little Farms Rd. in Framingham, continued to have low levels of bacteria. Carter Ave. is very similar to the Bedford Rt. 225 site that we previously monitored. Both Carter Ave and Rt. 225 have perfect records with no exceedances of the BAV threshold. Both sites are within the Wild & Scenic segment of the Concord River. Little Farms Rd. is very similar to the Wayland Rt. 20 site that we previously monitored. These two sites have very rare BAV exceedances, limited to significant precipitation events. Both of these sites are within the Wild & Scenic segment of the Sudbury River.

The following table summarizes the 2023 results for E.coli bacteria at our six core monitoring sites in the Sudbury, Assabet, and Concord Rivers.

Results (May 15, 2023 - September 11, 2023):

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: