The 2024 MRWC water quality assessment revealed measurable levels of bacteria in the Merrimack River.
Lawrence, Massachusetts – The Merrimack River Watershed Council (MRWC) released its analysis of 2024 water quality data, raising questions about dangerous fecal bacteria levels in specific segments of the Merrimack River.
In 2024, MRWC conducted baseline water quality monitoring throughout the year and also tested for three days after significant combined sewer overflows (CSOs). MRWC tested for basic ecological parameters (pH, salinity, total dissolved solids, conductivity and temperature) as well as fecal bacteria.
The test results for the basic parameters were within recommended limits for human use and/or were supportive of aquatic ecosystems. However, while the fecal bacteria levels in the Merrimack were safe most of the time at most of the test sites, high bacteria levels frequently occurred at some test sites and warrant additional research.
Most notably, results from test sites in Newburyport/Salisbury Harbor indicated frequent high bacteria levels from an unidentified source. Given multiple factors (including but not limited to distance from the nearest CSO outfall, dilution and die-off rate), it is unlikely that CSOs are measurably impacting these bacteria levels. Multiple harbor test sites had frequent high bacteria readings – sometimes exponentially higher – during both wet and dry weather, indicating an unknown source of bacterial contamination. At Newburyport Harbormaster Peir, 41% of regular Friday tests were unsafe, 100% of heavy rain events tested had at least one unsafe reading in the following three days, and 54% of tests were unsafe in a two-week daily test period during a dry period in October.
Another test site of concern was the Essex Dam impoundment, including the Lawrence Boathouse. However, there are multiple factors making this site challenging to analyze. This site is a mile upstream of the Essex Dam and it is at a significant bend of the river, both of which contribute to hydraulic complexities at this site and could lead to a pooling-effect that could impact bacteria levels. Large flocks of Canada geese also frequented this site in 2024 and could contribute to the bacteria level. There are also two stormwater outfalls right at the Boathouse. Given the level of youth recreation at the Lawrence Boathouse and the concerning frequency of high bacteria readings in this area, timely further study is needed to determine the source(s) of the bacteria and initiate mitigation.
While CSOs are widely assumed to impact the bacteria level for the full length of the river downstream of CSO outfalls, engineering studies and MRWC’s 2024 data suggest that the range of impact from any given CSO outfall site is limited to only a portion of the downstream river. When considering the causes of dangerous bacteria levels throughout the river in all weather conditions, CSOs are likely dwarfed by the impacts of stormwater runoff, illicit discharges, broken storm drain/sewer pipes and other causes. CSOs are a significant identifiable contributor to dangerous bacteria levels but are only one part of the bacteria problem.
However, while CSOs are an easy to identify source of bacteria, its impact is hard to measure. During CSO event testing, results from test sites varied greatly. Some sites had a minimal number of unsafe tests and we are re-evaluating whether they are within the geographic range of impact from their upstream CSO outfall(s). Other sites recorded unsafe conditions after some but not all of their upstream CSO events (Haverhill recorded unsafe conditions after 50% of their upstream CSO events). One site (Dracut) recorded unsafe conditions after 100% of their upstream CSO events. This variation between sites and between CSO events reinforces the inability to predict the bacterial impact of CSO events due to the complexity of factors impacting results, including but not limited to the rainfall within the specific sewershed (amount, duration, intensity), the CSO outfall discharge (volume, duration), the coinciding stormwater runoff, the streamflow, and the water temperature. Additionally, each test site is a unique distance from differing municipalities’ CSO outfall(s), with significantly different hydrology (patterns of water movement/currents) in the intervening river segments. The bottom line is that each CSO event is categorically different in its impact on the safety of the river.
The primary takeaway from MRWC’s 2024 analysis is the pressing need for more data. Although MRWC significantly increased testing in 2024, the results raised more questions than were answered. To understand how bacteria is originating and functioning in the river, a full season of more robust testing is required – significantly more test days and tests during varying conditions.
The full report can be accessed on MRWC’s homepage merrimack.org
Tewksbury PR Partner
These posts are from the great organizations around Tewksbury that provide updates to the Carnation.
I wonder if this is because of Lowell emptying thousands of gallons into it. Seems to be almost once a month.