Monday, March 12, 2007

Update on Newly-Discovered Four Mile Run Pollution Issues

Here's the update I got from Aileen at Arlington County's Department of Environmental Services ...
I will try to check it out, although it does sound like the iron oxidizing bacteria that we see occasionally in the County streams. I was able to click on the pictures and see them up close. The iron is dissolved in the groundwater, and it oxidizes as it enters the stream along the edge of the stream. You can see that in the picture. Although there is also a large puddle of up on the bank too. The “oily” sheen is from the bacteria that oxidize the iron. They look very much like oil, but one way to differentiate them from an oil slick is to stir them up with a stick. The bacteria will break up into clumps, and oil would just swirl around on the surface of the water.

There is some information about the iron bacteria at the bottom of each of these pages:

Stream pollution information

Stream photos

I will check with the Fire Dept. and will stop by and check it out as well. I’ll let you know what I find out!

Here's the relevant paragraph from the stream pollution information page on "red-orange" discolorations ...

Filmy deposits on the surface or banks of a stream are often associated with greasy "rainbow" appearance of iron bacteria. This is a naturally occuring phenomenon where there is iron in the groundwater. However, a sudden or unusual occurrence may indicate a petroleum product release from an underground fuel storage tank. One way to differentiate iron-oxidizing bacteria from oil releases is to trail a small stick or leaf through the film. If the film breaks up into small islands or clusters, it is most likely bacteria. If the film swirls together, it is most likely a petroleum discharge.

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