masodo mashup - Background image is crop of a photo posted by whatthecaptcha on Reddit - WTF entitled "this_was_coming_out_of_the_citgo_plant_here_today" - Blinky image "lasso"ed from simpsons.wikia.com
IIOTIIMBT™ (if it's on the internet it must be true)
A likely explaination was offered by firstresponder1492
So here is what this really is:
The chemical used is most likely Fluorescein which is a synthetic organic compound and has been in use for industrial applications for many years. It is a completely inert substance and dissipates in the environment (think large amounts of food coloring). In fact, one of the common names for it is D&C Yellow #7.
In this case this is coming from a storm and rainwater treatment system. This is part of the bi-annual inspections required by the EPA. One if the things they look for is where runoff actually goes to make sure there are not pollutants in those locations. That way if anything had been spilled on-site they know where the runoff would go. They then test water and soil samples wherever they see the green to ensure full compliance with the vast array of rules, laws and regulations. Bottom line, when you see this you know someone is doing their job.
As for locations, although I am not certain, I would bet 100 Karma points this is at one of the facilities in Louisiana. And just in case anyone is still worried about the environmental impact, note this is the same dye that is used to dye the Chicago River green on St. Patrick's day.
Source: I am an industrial engineer at a chemical plant