[mad_as_he$$]

You think they were recirculating mud for core sample drilling? Interesting. When we core drill for gold we just use water and some drilling fluid. Mud just adds another thing to deal with in the outback. It has to be trucked in and then stored and agitated when mixed.

[EarthResearcher333]

Look at the sediment at the base of the metal catch basin in the prior drill rig photo. Whatever material they are using, the color of the material is consistent with a grey to whitish residue. Below is a photo where there is whitish grey residue on the ground, on the rig, and on the guide chute for the drill there looks to be a grey clumpy residue. This was at a core sample drill location in front of the emergency spillway.

They may be using a low viscosity mix as I've seen metal catch basins blend in color to the drill area location - especially when the top layer is the reddish soil. It turns the basin fluid to a light orange color. In any case, the voiding and the "lift" of the perforated drains under the slabs would allow a volume of this drill mix material to accumulate without entering into the underslab drains. Only under pressurized "wash" conditions, when the spillway is in operation, will this residual volume of material be flushed out. The revelation of the whitish grey residue in the emergency spillway photo infers a link to the mystery of the "milky white" coloring that entered into the Feather River.