For several years now, Mason has been participating in a toxins-monitoring system created by EPA to test the water in the Chesapeake Bay. In the sample provided by USGS, they found indication of agricultural pesticides, but not much evidence of automobile-related pollution . Huff stresses, however, that one sample does not produce reliable data. They will have to test samples from many different places in the river before they can have reliable results. For the moment, however, USGS is waiting for a storm before it takes mo re samples.
Pollutants enter rivers and streams as run-off during and after a rain.
Agricultural run-off contains residue of pesticides and other chemicals applied to crops. Urban run-off, from streets and parking lots, contains oil and other chemicals used in automobiles. Because run-off is strongest during and after a rainstorm, scientists believe they can learn more about what is getting into the water by taking samples right after a st orm occurs. The chemicals USGS is looking for are present in very trace amounts, so each sample it takes is quite large-35 liters. As the sample is prepared for analysis, it is reduced over several hours to about half a milliliter.