Bacteria Testing—Summer 2015

Bacteria Testing

Professor Tami Imbierowicz of Harford Community College oversees her daughter Stephanie as she takes a water sample at Kilgore Falls in Harford County, Maryland.

Tom Zolper.

Are the fresh water streams and rivers of Maryland safe for swimming and other recreational uses after storms? How much does polluted runoff affect water quality in those streams?

These are questions we hope to answer this summer. The Chesapeake Bay Foundation, Hood College, Howard Community College and Harford Community College are partnering on a project to test water samples for bacteria. Samples will be taken throughout the summer in Frederick, Howard and Harford counties.

Stormwater runoff is water that runs off the land during and after a storm. Sometimes the water picks up contaminants—manure from farms, dog waste, weed killer, and other impurities. The runoff can go directly into local streams and rivers. The Maryland Department of the Environment recommends Marylanders avoid contact with water in creeks and rivers for 48 hours after a significant storm because of polluted runoff.

In this project we are looking only for the presence of a certain type of bacteria in the water—enterococci. The presence of enterococci in streams and rivers indicates recent contamination from fecal waste.

We picked sites indicated in the map below that are known to be used for swimming or recreation during the summer. They may be swimming holes on fresh water streams, community lakes, or other sites. We took samples on dry days, but in Howard and Frederick counties we also sampled within 24 hours of a rain storm of at least .50 inches. In Howard County we also sampled 48 hours and 72 hours after a rain storm. In Harford County we sampled regularly once a week.

County health departments in these counties sample and test for bacteria at a few "public beaches" determined by the government. Those tests don't include more informal recreational areas such as swimming holes. Also, those tests are mostly in dry weather, and are often infrequent. With our protocol—testing informal recreation areas specifically after rain storms or at least frequently—we hope to provide a fuller picture of the impact of polluted runoff on local streams and rivers.


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