Bacteria Monitoring and Combined Sewer Overflows: Water Quality Data and Public Understanding in Hampden County

The Connecticut River Conservancy has been collecting weekly water samples to test for E. coli bacteria in the Connecticut River and its tributaries. Some of the Hampden County sites in Massachusetts are heavily impacted by combined sewer overflows (CSOs), particularly from the more densely populated communities of Holyoke, Chicopee, and Springfield. Starting in 2022, CSO discharge reports have been made available to the public, so email subscribers are notified when there are CSO releases so that they can use this information when making recreation decisions.  

In a poster session at the Northeast Aquatic Biologists’ Conference in February 2025, CRC staff Ryan O’Donnell and Melissa Langley presented on what insights volunteer monitoring provides for the impacts of CSOs on water quality, limitations in the data collected by volunteers as well as in the CSO discharge reports, and the broader impact of public notification of CSO discharges on public understanding of water quality in the Connecticut River. 

Bacteria Monitoring 

CRC staff and volunteers collect and process water samples from dozens of sites throughout Vermont, Massachusetts, and Connecticut, measuring total coliform and E. coli. The E. coli levels are compared to EPA recommendations for safe primary and secondary contact. Sampling results are uploaded to CRC's Is It Clean?/¿Está Limpio? website to provide the public with data they can use to make informed recreation decisions. 

Background on CSOs  

CSOs are permitted releases of untreated or partially treated wastewater and stormwater into rivers or other water bodies from combined sanitary and storm sewer systems. Releases usually occur in wet weather due to the increase in stormwater and are used to prevent overwhelming the treatment system. CSO releases release contaminants that may be harmful to people and the environment.  

In addition to the locations in Hampden County, St Johnsbury, VT, Montague, MA, and Hartford, CT also have CSOs. Some information on VT and CT releases is publicly available. 

This diagram shows the impact of wet weather on CSO releases.

Challenges 

Bacteria levels in rivers are inherently complicated by many factors that are difficult to account for. CRC sampling occurs on a set schedule and is not conducted directly to measure impacts of CSOs, and the approximately 50 individual discharge points in the region make understanding the water quality impact of any one community alone impossible. Additionally, differences in the detection methods make the data difficult to analyze. At this time, Chicopee does not have automated detection for CSOs and depends on manually checking for evidence of CSOs and running a computer model to estimate the volume. The model may not always be able to estimate a volume of water released even when there is evidence of a discharge found during a manual check. Regulated flows on the Connecticut River and tributaries from dams may affect how long bacteria stay in different areas of the river. Overall, limitations on data collection, detection systems, and human impacted river flows complicate the question of how CSOs affect water quality. 

Results and Discussion 

During this study period, sampling events were designated as wet weather if there was significant rainfall in the previous 24-96 hours. Chart 1 below shows the total volume of CSO discharges in the ~48 hours prior to each sampling event. The biggest takeaway that we can see is that in 2023, a flood year, large volumes of CSO discharges due to heavy rainfall seemed to have a minimal impact on water quality; in 2024, a drought year, even small CSO discharges during smaller rain events appear to have a larger effect on bacteria levels.   

Chart 1

Within the context of the full stretch of the river that CRC volunteers monitor regularly, the segment through Holyoke, Chicopee, and Springfield tends to have the highest E. coli levels (see chart 2). Even with this stretch of poorer water quality, bacteria levels in the Connecticut River, on average, meet the threshold for primary contact recreation (swimming) during dry weather and at most locations during wet weather. There are a few sites that exceed this threshold during wet weather but they still, on average, meet the threshold for secondary contact recreation (boating). Individual results, especially in this stretch of poorer water quality, regularly exceed these thresholds (see chart 3).

Chart 2

Chart 3

 Public Impacts of Notifications 

The public notification of CSO discharges in Massachusetts began on July 1, 2022, and residents in Holyoke and Chicopee receive notifications automatically. They started receiving them when the notification law went into effect but without any context for what had changed for the notifications to start. Anyone can sign up to receive Springfield’s automated alerts by e-mail. At least two e-mails are triggered by each discharge location during a storm event resulting in numerous emails for each rain event.  

News outlets report on the alerts which have raised concerns about the ongoing water quality in the Connecticut River. The public sees millions of gallons of sewage discharged and is understandably concerned without the full context of the scale of the river. There is mixed public understanding with what has changed is the notification of discharges, not that discharges began in 2022. 

Conclusion 

CRC will continue to collect bacteria data this summer, and the water quality monitoring staff hope to look further into the impacts and community perceptions of CSOs.