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River testing reveals big difference in bacteria levels after rainfall

It was a cold and windy day in mid-October. Bundled in winter coats, a dozen people gathered at Wharton Brook State Park. Swimming wasn’t on the agenda, but it was in mind, as they had come to hear the results of the River Advocates recent tests for bacteria levels in the local rivers and streams, indicating how fit they are for recreation.

State Rep. Mary Mushinsky, executive director of River Advocates, shared their findings. High levels of bacteria impaired water quality at nearly all 20 testing sites following rainfall. However, during dry conditions, the results were dramatically different, with bacteria levels at many of the sites low enough to make the water suitable for public use, including swimming. 

Testing was conducted at multiple locations along the Mill, West and Quinnipiac Rivers on two different days in September: one dry day without previous rainfall, and one wet day, following more than an inch of rainfall. Testing sites spanned Wallingford, Cheshire, North Haven, Hamden and New Haven.

Volunteers collected samples and then delivered them to two labs to analyze for the bacteria that indicates sewage or animal waste contamination: e-Coli in freshwater and Enterococcus in brackish water (the mixture of saltwater and freshwater).

On the dry day, the results proved surprisingly good. Although the four brackish water sites in New Haven had unacceptably high bacteria levels, the remainder had levels low enough for recreational activity, with eleven of them even meeting the standard for designated swimming areas.

In contrast, on the wet day, 19 of the 20 testing areas failed to meet any recreational standards “in a big way,” emphasized Mushinsky, most of them with bacteria counts so high they exceeded the mathematical limits of the test.

So why such extreme differences in the wet vs. dry results, and what can be done to reduce the dangerously high bacteria loads on rainy days?

E-coli and enterococcus indicate the presence of human and animal waste. In developed areas, with lots of pavement, parking lots and pipes, rainfall easily carries this waste into the rivers, from dog poop to lawn fertilizer. 

In older cities like New Haven the problem is exasperated by combined sewer systems where industrial wastewater, domestic sewage and stormwater all share the same pipes. Under normal conditions, the pipes transport the wastewater to a sewage treatment plant, where it is treated and then discharged into the nearest waterbody. However, in heavy rainfall, the water volume can exceed the capacity of the pipes or treatment plant, resulting in overflows of untreated waste flowing directly into the watershed.

Such overflows are a priority water pollution concern in municipalities across the U.S.In New Haven, the work has begun, but the expense of the project makes the timelines slow.  In the meantime, other efforts are required to reduce the bacteria load. “Towns and cities must clean up runoff, both for their own residents and for downstream populations,” read the River Advocates statement, which also provided the following recommendations. Towns can create natural buffers to hold and purify water and promote the use of natural landscaping with plants, trees and soil, rather than paved surfaces. Residents can pick up after their dogs, create rain gardens to capture water, and ensure septic systems are properly maintained.

The testing project was made possible by the Quinnipiac River Fund and the Greater New Haven Green Fund. Looking ahead, the River Advocates hope that further testing will be able to pinpoint sources of contamination in order to improve segments of the rivers and tributaries. With the hope that someday, whether rain or shine, the waters in south central Connecticut will run clean and be all clear for swimming and summer fun.