By Lydia von Schwanenfluegel, Williams College student
Every two weeks on an early sunny Thursday morning, Thom Gentle and I set out to collect 100ml water samples from 9 sites along the Hoosic and Green Rivers and their tributaries. These samples will contribute to a data sheet that will help HooRWA to compare bacteria levels in the water supply over time. First, however, they must be collected. From 8:30 -11:00am, we drive from site to site. Some sites are astonishingly picturesque, full of birdsong and lush flora. At one site on the Green River, I was even witness to a bear crossing the stream.
Other sites (mostly the tributaries) are less magical, including a muddy stream draining from a wetland near the North Adams Walmart that requires some acrobatics to access a good sampling site, and a trickle running into the Green River from a rusty drain pipe at Linear Park.
However, despite their less-than gorgeous appearance, these sites are arguably the most important sites to sample to make sure there aren’t any harmful chemicals or other toxins trickling into the main branches.
The samples have a maximum shelf life of 6 hours, so the cooler full of ice and samples must be quickly driven to Pittsfield, where professor Bruce Winn processes them. The only test currently done on these water samples is for E. coli count. To determine this, the bacteria in the samples are fed a substance containing a molecule that is partially nutritive and incubated for 24 hours. The bacteria only consume one part of the molecule. Once detached from its tastier half, the smaller part exhibits inflorescent properties. Any inflorescence lets the tester know which samples contain E. coli, as they would have consumed the molecule and caused it to glow.
For a more detailed explanation, watch THIS VIDEO.
There are a number of quality assurance measures to make sure bacterial counts are as accurate as possible. We perform “field splits” which involve collecting a larger sample and splitting it into two jars to make sure the counts match up as closely as possible. To make sure the lab is being accurate, we also collect a “blank” sample, by pouring distilled water into a sample. This bacterial count should come out as zero. This also allows us to test the cold chain from field to lab. If one of the blank samples comes out as containing E. coli, we know something has gone wrong.
According to Bruce Winn, water bodies are safe to swim in below 250 E.coli per 100ml, and safe for boating below 500. The reason why E. coli tests are important is not necessarily because the bacteria themselves are pathogenic. Only a select few strains of all E. coli bacteria are responsible for the outbreaks in supermarket lettuce, ice cream, and strawberries. Instead, E.coli are a flag or indicator for animal feces in the water, which invite other harmful coliform bacteria into the water.
These results are shared with the Housatonic Valley Association (HVA) and Berkshire Environmental Action Team (BEAT), and together with the results from their samples and other testing we are conducting, we will be able to create a health map of our region’s waterways.
