The U.S. Geological Survey reported the size of the spill to be more than 3 million gallons, compared with the initial EPA estimate of 1 million gallons
Not that I don't share the animosity toward the EPA but I'd bet that most of the orange hue is due to iron-hydroxide particles/floc and thus the low pHs in the river now.
I wouldn't be shocked if they eventually spin the iron as 'fertilizer'. ;^)