FYI, "small" June tropical storms are a common event in the GoM. Small in terms of area not strength.
I think we are looking at bridging material (BM), my best guess is that BP is trying phase two of Top Kill, pumping BM with mud. Some of the BM is escaping the BOP which is to be expected. Movement is due to currents (up, but mostly down) created the high velocity BM particles.