Question: How can you tell if a sheen on water is bacterial or petroleum (oil)?

stevie is asking a question about water-quality
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by stevie | January 24, 2020 18:42 | #22396

Bacterial sheens on water can often look like oil. However, they are completely harmless and natural. I'm interested in simple tests that can help people identify the difference between these two things. Petroleum (oil or gas) sheens and spills need to be reported, the bacteria ones do not.


There's a simple test people can do sometimes referred to as "the stick test." In this method, you would use a stick or a rock to poke a hole in the sheen. In a bacterial sheen, "the sheen will typically break into small platelets. In contrast, a petroleum sheen will quickly try to reform after any disturbance."

Another test you can do is smell the sheen. If it has no smell it's likely bacterial, if it smells like oil or gas, it's likely a petroleum product.

Here is a post form the Minnesota Pollution Control Agency on this:

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