The results show the distribution of fecal coliforms at 22 locations within the Severn River watershed. Coliform counts have varied bases on the weather. In general, we see a clear pattern of high numbers of bacteria in the river when we have at least one-half inch of rainfall within 48 hours of sampling. Dry weather is associated with lower bacteria counts.
Samples of beach or marina water are collected on Wednesday mornings by Dr. Hornor's assistant. Water samples are held on ice and returned to the laboratory at the Environmental Center at AACC by noon. At the lab, they filter several volumes of river water through filters which retain bacteria. These filters are then incubated with growth medium appropriate for culturing the bacteria know as "fecal Coliforms". After 24 hours incubation, Dr. Hornor counts the bacteria and calculates the number present in 100 ml of river water.
Fecal Coliforms are bacteria which are abundant in the feces of warm-blooded animals. These bacteria are not considered a hazard to human health if they are present in bathing water, but they are used as indicators of contamination. Thus a higher number of fecal coliforms indicates the presence of fecal matter and possibly other bacteria, viruses or protozoans which are hazardous to our health. However Dr. Hornor has added a note of caution to the interpretation of high fecal coliform counts. It cannot be said categorically that water with a high (>240/100 ml) count is not fit for swimming. Starting in 2001Operation Clearwater started testing for enterocicci instead of fecal coliform bacteria. Both organisms are found in the intestines of warm blooded animals, but recent studies have shown that enterocicci bacteria is a more accurate indicator of water quality. The EPA recommends against swimming when when enterocicci counts exceed the accepted levels of 35 per 100 ml of water. It does say that at the time the sample was taken, there was recent contamination of the water by animal waste, be it human or not. Although bathing beaches are not closed by the Health Department when the fecal coliform count exceeds this number, they are re-opened when the count drops below this number following documented correction of contamination by sewage spills of septic tank overflows.
High counts are often recorded after rainstorms delivering more than one inch of rain. It has been well documented in the scientific literature that overland flow from summer rainstorms contributes significantly to elevated coliform counts in streams and rivers. These higher counts are probably due to septic tank failures as well as wash in of animal waste from storm drains. It is likely that these bacteria die within 24 hours, resulting in lowered counts within that time. During relatively dry periods, fecal coliforms are primarily derived from septic tank failures, boat heads, and wild and domestic animals, including ducks and geese.
Our community results have been fairly consistent over the past years. Generally we have some of the cleanest water on the river. Our counts are high after heavy rains and it is generally a good idea to stay our of the water for 24 hours after a hard rain. This will allow for the river to "clean" it self out.
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